nutrient budgeting of primary nutrients and their use

_____________________________________________________________________________________________________ *Corresponding author: E-mail: [email protected], [email protected];

International Research Journal of Pure & Applied Chemistry 21(11): 92-114, 2020; Article no.IRJPAC.59589 ISSN: 2231-3443, NLM ID: 101647669

Nutrient Budgeting of Primary Nutrients and Their Use Efficiency in India

Gayatri Sahu1*, Shreya Das2 and Samanyita Mohanty2

1Department of Soil Sciences, Institute of Agricultural Sciences, Siksha ‘O’ Anusandhan Deemed to

be University, Bhubaneswar, 751030, India. 2Department of Agricultural Chemistry and Soil Science, Bidhan Chandra Krishi Viswavidyalaya,

Mohanpur, Nadia, 741252, India.

Authors’ contributions

This work was done in collaboration among all the three authors. Author GS designed the study and wrote the first draft of the manuscript. Authors SD and SM supervised the study and analyzed the

data. All the authors managed the literature search and wrote the final manuscript. All authors read and approved the final manuscript.

Article Information

DOI: 10.9734/IRJPAC/2020/v21i1130227

Editor(s): (1) Dr. Hao-Yang Wang, Shanghai Institute of Organic Chemistry, China.

Reviewers: (1) Olajide Ayodele Sadiku, University of Ibadan, Nigeria.

(2) Moses M. Ngeiywa, University of Eldoret, Kenya. Complete Peer review History: http://www.sdiarticle4.com/review-history/59589

Received 25 May 2020 Accepted 01 August 2020 Published 08 August 2020

ABSTRACT

The imbalanced use of fertilizers in India is evident from the fact that the current ratio of nitrogen, phosphorus and potassium in agricultural soil in several states is skewed towards nitrogen. This imbalance causes problems, right from stagnating or declining productivity to soil sickness, widespread deficiency of macro nutrients and micronutrients, and soil alkalinity and salinity. Eventually, it results in reduced efficiency of fertilisers, low yields and low profitability for farmers. Also, nitrogen pollution of surface and groundwater due to excessive fertiliser use has reached alarming levels in several states. Chemical fertilizers are currently the major emitters of nitrous oxide gas, a potent greenhouse gas and ozone depleting substance. Nutrient budget is an important tool to provide an early indication of potential problems arising from nutrient surplus and nutrient deficit. Balanced use of all types of fertilizers, including traditional organic manures and biofertilizers are needed to bring about a change in the prevailing regime that encourages excessive use of chemical fertilizers. However, meeting future food security targets in an over-populated developing country like India, needs to increase the nutrient use efficiency. This

Review Article

Sahu et al.; IRJPAC, 21(11): 92-114, 2020; Article no.IRJPAC.59589

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ultimately leads to site-specific need-based nutrient application and minimizing nutrient losses from fields. This leads to the 4R Nutrient Stewardship concept, applying the Right Source of nutrients, at the Right Rate, at the Right Time and in the Right Place. This paper provides a historical overview of the nutrient budgeting efforts and systematically reviews major challenges, opportunities, in defining, quantifying, and applying nutrient budgets and improving nutrient use efficiency.

Keywords: Nutrient budgeting; chemical fertilizers; primary nutrients; nutrient use efficiency; 4R

nutrient stewardship.

1. INTRODUCTION The global population is estimated to cross 9 billion by the year 2050, and the increase in population will occur mostly in developing countries that are already under stress to meet their food requirements. An additional 1.1 billion tons of cereal and 470 million tons (Mt) of meat per year will be required for the growing population. According to [1], this increase in the population will also lead to increase in NPK-fertilizer demand. With increasing urbanization in developing countries, such as India, demand for quantity and quality of food will increase further. India is predominantly an agricultural country with 65% of its people depending on agriculture. Agriculture in India, until the middle of the twentieth century, relied mostly on organic manure. With the advent of Green Revolution era in the mid-1960s, improved seeds of high yielding varieties and developed irrigation facilities led to increased consumption of high analysis chemical fertilizers. In 1950–1951, consumption of N fertilizer in the country was only 0.06 Mt, which increased to 10.8 Mt in 2000–2001, an increase of about 190-fold in the last 50 years (FAI 2000–2007). Consumption of P fertilizer has also risen sharply with less than 0.01 Mt in 1950–1951 to 1.8 Mt in 2000–2001. However, use of K fertilizer has been very low with almost nil in 1950–1951 to only 0.81 Mt in 2000–2001. Though along with increase in the consumption of fertilizer, agricultural production has increased considerably initially, later it became stagnant and started to decline. Annual per capita food availability increased from 141 kg during 1950– 1951 to 208 kg during 1990–1991 but declined to 192 kg during 2000–2001. This is a serious concern and more efforts need to be explored to plug the demand-supply mismatch and increase the per capita food availability.

Recent analysis of a large number of long-term soil fertility experiments reported that the plateauing in productivity of this system appeared possibly due to fatigued exploitation of natural resource base. Non-judicious use of

nutrient in relation to amount, timing, and balance has been identified as a possible reason of such yield stagnation and/or, decline [2]. In many areas, yields started declining because of a decrease in factor productivity and farmers have resorted to using higher than the recommended doses of mineral fertilizers to maintain previously attained yield levels. Meeting future food security targets requires the responsible use of fertilizer nutrients. Therefore, one of the most promising means for increasing yield in the rice-wheat system is to develop alternative nutrient management practices, which may increase factor productivity and crop yields. In this direction, integrated management of organic manures and mineral fertilisers can be a useful practice to increase crop yields along with soil fertility. Hence, research should be conducted to recognize the yield trends and to assess the N, P, K budget as influenced by application of organic manures in combination with or without mineral fertilisers over the years. Nutrient budgets are becoming increasingly common as a tool to describe nutrient flows within farming systems and to assist in the planning of the complex spatial and temporal management within rotational cropping and mixed farming systems. Budgets are the outcome of a nutrient accounting process, ranging from simple to complex, which details all the inputs and outputs to a given system over a fixed period of time. Earlier, Union Budget 2019-20 the Government of India (G.O.I.) emphasised on ‘zero-budget farming’ that reduces dependency on chemical fertilizers. While presenting the Union budget 2020-2021, G.O.I. has emphasized on balanced use of all types of fertilisers, including traditional organic and other innovative varieties (e.g., biofertilizers, city compost etc.) to bring about a change in the prevailing regime that encourages excessive use of chemical fertilizers. But its implementation is a huge challenge due to policies that favour excessive and imbalanced use of chemical fertilizers and lack of any serious attempt to promote organic fertilisers and city


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compost on a large scale. Large amount of information distilled in this review should prove useful in formulating strategies not only for sustaining high yield levels of crop in developing countries like India but also for using and recycling the plant nutrients from organic and inorganic sources in a rational and efficient way.

1.1 Effect of Green Revolution on Crop Production and Fertilizer Consumption

Soils of the arid and semi-arid subtropical regions of South Asia developed under harsh climate are inherently poor in soil organic matter, fertility and water-holding capacity. Securing the first position in the world in terms of net cropped area, India is in limelight among the South Asian countries where the agricultural sector plays a significant role in the overall socio-economic fabric. India occupies an area of 329 million hectares (mha) and ranks 7th in the world. While it has only 2.5% of the world area, it is home to 17% of the world population. Prior to 1950, India had a history of declining per capita food production, food shortages, and even famines. Until the early 1960s, the focus was to bring more area under cultivation to augment food-grain production for ensuring national food security. In 1950/51, the food-grain production was merely 51 Mt, which increased to 72 Mt by 1965/66 (Fig. 1). During this period, the area of cultivation of food crops also increased by 18.6% but the productivity was very low (522-710 kg ha

-

1). The reasons might be attributed to lack of irrigation infrastructure, negligible fertilizer use, and growing of low-yielding non-nutrient-responsive crop varieties etc. Hence, the pre-green revolution period was characterized by low productivity, lack of inorganic fertilizer use, and dependence on animal manure and biological nitrogen fixation (BNF) as sources of nitrogen [3]. With the advent of Green Revolution, the high-yielding technologies developed in Mexico helped to revolutionize cereal production during the 1960s and 1970s. The food-grain production in India, which was only 82 Mt during 1960/61, more than doubled (170 Mt) in 1988/89 (Fig. 2) and further increased to 264 Mt in 2013/14. Though net sown area of 141 mha remained nearly constant in India, large increase in food-grain production resulted from an increase in productivity with enhanced use of high yielding varieties, high analysis fertilizers, development of irrigation through bore wells, adoption of new technologies with mechanization of farm

operations, and greater intensity of cropping [4]. Productivity of food grains increased threefold, from 710 kg ha

-1 in 1961/62 to 2100 kg ha

-1 in

2012/13. Area under irrigation coverage increased from 32 to 89 mha. The fertilizer consumption (N, P and K), which was only 0.34 Mt in 1961/62, increased by several orders of magnitude in 1976/77, and to more than 80-fold (28 Mt) in 2010/11. Now India stands second in the world in terms of gross fertilizer consumption with average rate of nutrient application at 141 kg NPK ha-1 year-1 with N alone accounting for 88 kg ha

-1. The current fertilizer consumption ratio,

however, is highly skewed toward N with N:P:K ratio of 6.7:2.4:1 [1].

Despite achieving self-sufficiency in food-grain production, there is little scope for complacency as India’s population is currently growing at 1.2% and the food-grain production has to keep pace with this burgeoning population. Slower growth in yields is alarming because adoption of modern crop varieties is virtually complete, fertilizer use on crop is now close to optimal in many regions, and application of additional fertilizer is often not profitable. Even though farmers are increasing the levels of nutrient inputs, productivity returns to fertilizer use on crops appear to be declining or, stagnant by following the law of diminishing return. Actually, nutrient extraction by crop plants is not always matched by nutrient inputs via fertilizers, manures, crop residues. Continuing cereal-based crop rotations such as rice-wheat, soil physical problems caused by puddling, intensive cultivation, complete removal of post-harvest crop residue for animal consumption and fuel purpose or, its burning, salinity and sodicity problems of irrigated land due to declining water tables and pumping water from greater depths etc. added another feather to low factor productivity.

To bridge the gap between blanket recommendation of NPK fertilizers in the field and the nutrient supplying capacity of soil, nutrient use efficiency should be improved by means of balanced use of nitrogen, phosphorus, and potassium fertilizers and rational use of organic manures along with biofertilizers. South Asian agriculture can be described as progressing through three phases of technical change: a “Green Revolution phase,” an “input intensification phase,” and an “input efficiency phase” [5]. At the last of these three phases, system-oriented research is required to develop the sophisticated, site-specific management information needed to improve input use efficiency.


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Fig. 1. Fertilizer N, P and K consumption and food grain production in India since 1950 [3]

Fig. 2. Population and food grain production and food availability in India over the years

[3]

1.2 Soil Nutrient Balance Sheet In the early 1990s, when the country’s foreign exchange reserves were depleted to alarmingly low levels, major economic reforms act as a fresh air to the panting Indian economy. The benefits of triggering off the negative monetary balances were witnessed not only by India but also the world over. The state of depletion of soil nutrient reserves reflected in negative nutrient balances is very similar to the macro-economic crisis of the early 1990s. The only difference being that while the economic reforms were put into place rapidly, the concern for deteriorating negative soil nutrient balances is largely limited to the scientific community and have not yet rung the alarm bell in the corridors of planning and policy-making. According to [6], Negative nutrient balances in most Indian soils not only mirror poor soil health, they also represent severe on-going depletion of the soil’s nutrient capital, degradation of the environment and vulnerability of the crop production system in terms of its ability to sustain high yields. In the prevailing regime of widespread negative nutrient balances, it is difficult to foresee positive nutrient balances in most parts of India, even when all available sources of plant nutrients are deployed, unless their quantity and efficiency is raised substantially. Depleted soils cannot be expected to support bumper crops or high growth rates. The key factor in enabling the country to achieve future agricultural production targets will be how

well and fast the depletion of soils is reduced and the nutrient balance sheet is moved from red towards green. A Balance sheet deals with the balance of income and expenditure over the preceding period. Likewise, soil nutrient balance sheet shows the difference between the nutrient inputs entering soil system and the nutrient outputs leaving the system. It is a book-keeping exercise for assessing the nutrient additions, removals, and balances in the agricultural production system which generates useful, practical information on whether the nutrient status of a soil (or area) is being maintained, built up, or depleted. A simplified schematic diagram of different nutrient inputs and outputs of agricultural soil is depicted in Fig. 3. Many approaches have been used to estimate nutrient balances, depending on the intended use. For example, the technique for developing national, regional, or global estimates of efficiency may be much different from a field-scale or micro-plot approach. Additionally, a nutrient deficit or surplus over a short term is not immediately indicative of undesirable consequences, but in fact may be beneficial and desirable for building overall soil fertility. There are mainly three types of estimating nutrient balances, viz. Soil surface Balance, Farm gate Balance and Soil system Balance; benefits and limitation of which are summarized in Table 1.


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Fig. 3. Schematic diagram of nutrient additions and removals in agricultural soils [7] Nutrient balance sheets in most soils of India have been deficient and continue to be so as nutrient removals by crops far exceed the nutrient additions through manures and fertilizers. In many cases, even the need-based application of nutrients to individual fields results in negative balances as nutrient uptake exceeded nutrient input. In an experiment conducted in ten different locations across India in 2006, [8] reported that N and P balances were positive at five sites, negative at another five sites whereas, K balances were negative at al ten sites. Interestingly, crops had received recommended rates of nutrients through fertilisers as per the site-specific nutrient management plan in all ten experimental sites. [9] reported negative nutrient balance in rice-wheat system in Indo-Gangetic plains (Fig. 4). According to [6], on a gross basis the balance is positive for N and P, but is negative for K whereas, on a net basis, which is more realistic and useful for planning nutrient management, the balance is negative for N, P and K.

In 2010, [3] reported some hotspots of excess nutrient loads as well as soil nutrient mining threatening the sustainability of Indian agriculture which further helped in reorienting fertilizer policies for different states. They had also presented the inputs of N, P and K from different sources (inorganic fertilizer, animal manure, compost, green manure, leguminous fixation, non-leguminous fixation, crop residues, rain and irrigation water), outputs (crop uptake and losses through leaching, volatilization and denitrification) and balance in agricultural soils of different states in India for the agricultural year of 2000–2001 (Fig. 5). Inorganic fertilizer was the dominant source contributing 64% of N and 78% of P inputs in Indian agriculture, whereas K input through inorganic fertilizer was 26%. Removals of N, P and K by major agricultural crops in the country were 7.7, 1.3 and 7.5 Mt, respectively.

There were positive balances of N (1.4 Mt) and P (1.0 Mt) and a negative balance of K (3.3 Mt).

1.3 Nitrogen, Phosphorous and Potassium Budgets in Indian Agriculture

Nutrient budgets offer insight into the balance between crop inputs and outputs. It takes into account all the nutrient inputs on a farm and all those removed from the land. The origin of nutrient budgeting dates back to mid-nineteenth century, when European scientists started to quantify nitrogen in rain and drainage waters in field plots [10,11]. As N had just been identified as one of the critical nutrients for plant growth, nutrient budgeting started with a focus on soils and crops as a system, targeted at utilizing nitrogen for plant productivity. Since then, the budgeting approach, also called soil nutrient balance, has been developed with more input and output items [12] and has been applied to other important nutrients for crop growth, such as phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Nutrient budgeting is a useful tool in determining present and future productivity of agricultural land as well as undesirable effects of nutrient mining and environmental pollution [7]. Overall, it helps to ensure that agricultural practices are conducted in an efficient, economic and environmentally sustainable manner. It has been reported that most fertilizer management practices in intensive agriculture do not consider nutrient budget in relation to yield and there is lack of notion that application of N, P, K and other nutrients is highly unbalanced; resulting in stagnation or decline in yield. According to [13], use of nutrient audits and nutrient budgets to assess the changes in soil nutrient status and the prospects for future food production is becoming increasingly important in many agricultural systems.


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Table 1. Different types of estimating nutrient balances, their advantages and disadvantages Types Definition Advantages Disadvantages Soil Surface Balance

This approach measures the difference between the inputs (or the application of nutrients) and the output (or removal of nutrients) from the soil.

It provides the most detail for nutrient management planning.

Usually, uncertainty is associated with the data inputs and the partitioning of the components of the nutrient balance between air, soil, and water.

Farm Gate Balance

This type of balance simply measures the difference between the nutrient content of farm inputs and the nutrient content of farm outputs.

Easy to construct, requires relatively little data, quantifies nutrients supplied to and removed from the farm, used widely for policy analysis.

It ignores many of the complex on-farm transformations that N is subject to (e.g. NH3

volatilization, denitrification, volatile losses during crop senescence, etc.), and does not quantify the nutrients circulating within the farm enterprise.

Soil System Balance

This approach is commonly used where detailed information on inputs, outputs, and internal transformations is available for all the important components.

Use of relevant computer models can help with parameter estimates when field observations are not available.

It requires much larger data inputs than the other approaches.


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Table 2. Nutrient addition through fertilizers and nutrient removal by crops State N P2O5 K2O N+P2O5+K2O

Add Rem Bal Add Rem Bal Add Rem Bal Add Rem Bal A.P 1256 477 779 576 497 79 191 817 -626 2023 1791 232 Assam 38 257 -257 15 74 -59 18 294 -276 71 625 -554 Bihar 618 481 137 101 102 -1 54 492 -438 773 1075 -302 Chhattisgarh 67 156 -89 68 68 0 13 137 -124 148 361 -213 Gujarat 691 340 351 268 121 147 61 426 -365 1020 887 133 Haryana 597 362 235 201 145 56 5 490 -485 803 997 -194 H.P 29 43 -14 5 8 -3 4 25 -21 38 76 -38 Jharkhand 40 165 -125 15 60 -45 5 20 -15 60 245 -185 Karnataka 681 473 209 374 239 135 216 604 -388 1271 1316 -45 Kerala 87 149 -62 44 53 -9 87 176 -89 218 378 -160 M.P 519 696 -177 344 431 -87 24 849 -825 887 1976 -1089 Maharashtra 923 1559 -636 450 608 -158 197 2096 -1899 1570 4263 -2693 NE States 19 96 -77 5 17 -12 3 84 -81 27 197 -170 Odisha 196 227 -31 56 104 -48 40 282 -242 292 613 -321 Punjab 1081 589 492 275 279 -4 19 764 -745 1375 1632 -257 Rajasthan 547 835 -288 147 235 -88 7 1068 -1061 701 2138 -1437 Tamil Nadu 484 405 79 145 111 34 162 398 -236 791 914 -123 U.P 2387 1497 889 776 305 471 114 1777 -1663 3277 3579 -302 W.B 562 764 -202 297 241 56 226 801 -575 1085 1806 -721 All India 10923 9613 1310 4188 3702 486 1454 11657 -10203 16565 24972 -8407

(*Add- Addition, Rem- Removal, Bal- Balance)

Fig. 4. Negative nutrient balance in rice

Fig. 5. Input, output and balance

Table 3. Annual nutrient budget of India

Process N (000, ton)Addition 10923 Removal 9613 Balance 1310

Table 4. Consumption of NPK fertilizers for last 50 years in India

Year Fertilizer consumption (kg haN

1960-61 1.39 1970-71 8.92 1980-81 21.3 1990-91 43.1 2000-01 58.9 2010-2011 84.9 2015-16 89.1


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nutrient balance in rice-wheat system in Indo-gangetic plains [

output and balance of N, P and K in Indian agriculture during 2000

Table 3. Annual nutrient budget of India

N (000, ton) P2O5 (000, ton) K2O (000, ton)4188 1454 3702 11657 486 -10203

Consumption of NPK fertilizers for last 50 years in India

Fertilizer consumption (kg ha-1

) Ratio of N: P: KP2O5 K2O 0.35 0.19 7.3:1.8:1.03.26 1.43 6.3:2.2:1.07 3.6 5.9:1.9:1.017.3 7.2 6.0:2.4:1.022.8 8.5 7.0:2.7:1.041.3 18 4.7:23.:1.035.8 12.3 7.5:3.0:1.0

; Article no.IRJPAC.59589

gangetic plains [3]

during 2000-2001 [3]

O (000, ton)

Ratio of N: P: K

7.3:1.8:1.0 6.3:2.2:1.0 5.9:1.9:1.0 6.0:2.4:1.0 7.0:2.7:1.0 4.7:23.:1.0 7.5:3.0:1.0


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Tandon [9] reported state-level nutrient balance sheet which is summarized in Table 2. By adding up recent state-level nutrient balance sheets computed earlier [9], an illustrative balance sheet of NPK in Indian agriculture is summarized in Table 3. The present scenario is based mostly on nutrient input through fertilizers for which data are available. The net figures have been arrived at by adjusting fertilizer input for use efficiencies of 50% for N, 35% for P2O5 (including residual effects), and 70% for K. On the removals side, 80% of crop uptake for N and P was considered along with 60% of crop K uptake.

Ramamurthy [14] showed the fertilizer statistics from 1960 to 2015 in support of K depletion (Table 4). Recommended N: P: K fertilizer dose for cereals is 4:2:1, but in India now it is 7.5:3:1 which is the main cause of nutrient imbalance.

1.4 Nitrogen Budget

Nitrogen (N) is an important source of nutrition for plants. While N deficiency negatively affects plant growth, N surplus (NS) can negatively impact environmental quality and human welfare [15]. These impacts include negative effects on biodiversity, eutrophication, nitrate accumulation in waters, acidification, nitrous oxide emissions (with effects on global warming and the depletion of the stratospheric ozone layer), and risks to human health due to exposure to ozone and particulate matter [16,17]. The agricultural sector is an important source of the N that ends up in ground- and surface waters and the atmosphere [18]. N deficiency, NS and N use efficiency (NUE) in agricultural production are estimated on the basis of agricultural N budgets.

According to [3], during 2000–2001, 10.8 Mt of N fertilizer was used in Indian agriculture, whereas animal manure, biological N fixation (BNF), atmospheric deposition plus irrigation water, and crop residues contributed 1.4, 2.4, 2.3 and 0.1 Mt, respectively. Total N input was 17.0 Mt and fertilizer was the dominant source contributing 64% of it. They also reported that Manure N input is highest in Karnataka (0.219 Mt) followed by Punjab (0.212 Mt) and West Bengal (0.179 Mt). The shares of manure N input to total N input for these states are 17, 15, and 18%, respectively. Uttar Pradesh, with the highest cattle population of 108 million adds only 2% of total N input through manure, which is much less in comparison to above three states. With maximum area of 7.6 mha under leguminous crops (FAI 2000–2007), Madhya Pradesh tops in biological fixation of N. Removal of N by crop

uptake was 7.7 Mt and the uptake by rice was highest followed by wheat and oilseed crops. Losses of N included leaching (2.3 Mt), ammonia volatilization (2.3 Mt) and denitrification (3.1 Mt). Thus, crop removal and losses of N accounted for 15.4 Mt, resulting in an accumulation of 1.4 Mt N in soil system.

Earlier in a study, [19] reported that about 35.4 Mt N input from different sources, with output from harvested crops of about 21.2 Mt N resulted in positive N balance, i.e. surplus of about 14.4 Mt N for agricultural lands in India. Though the N balance was negative in some states, all the agro-ecological regions of the country showed surplus N loads ranging from 19 to 110 kg N ha

-1

yr-1. The prime reason behind this may be heavy subsidies on urea; in the 1970s, urea subsidy used to be 10-20 per cent of the cost of production; it’s now at 75 per cent. This has led to excessive use of urea in agriculture over the other chemical fertilisers. In fact, the share of urea consumption among all nitrogenous fertilisers is the highest 80 per cent in India, compared with 23 per cent in the United States and Europe, 54 per cent in Brazil and 46 per cent in China. [20] and [21] also estimated net accumulation of N in soil (positive N balance) ranging from 1.9 to 14.4 Mt. The estimates, however, differed from that of Fertilizer Association of India (FAI 2000–2007), which estimated a negative balance of N. This is because addition of N through irrigation, rain and crop residues was not considered in the study of FAI.

Long-term fertilizer experiments conducted in India have indicated that the response to fertilisers could be increased significantly with balanced application of organic manures in addition to synthetic fertilizers. In a long-term experiment conducted in a rice-wheat cropping system under subtropical climatic condition, [22] found negative N balance, i.e. N deficit in control plot (–42.2 kg ha

-1 year

-1) and treatment plots

having sub-optimal (50% or 75% recommended fertilizer NPK) and optimal doses only through chemical fertilizer inputs to both rice and wheat; whereas, positive N balance was reported from the treatment plots having combined application of both chemical fertilizers and organic inputs (farm yard manure or, wheat straw or, green leaf manure).

1.5 Phosphorous Budget

Phosphorous (P) is one of the imperial factors in root development and enhancing crop output


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Table 5. Input, output, and balance of P in different states of India in 2000–2001

State Input Crop removal

Balance Fertilizer Manure Deposition

Andhra Pradesh 263.3 38.4 4.6 97.0 209.2 Assam 15.9 2.9 3.5 20.4 1.9 Bihar 92.4 17.0 4.8 64.9 49.4 Gujarat 85.4 7.0 4.2 68.2 28.4 Haryana 90.1 8.8 4.7 71.9 31.7 Himachal Pradesh 2.9 16.7 0.4 6.5 13.4 Jammu and Kashmir 7.8 2.1 0.3 6.1 4.1 Karnataka 167.5 58.4 8.8 77.0 157.7 Kerala 16.4 2.0 3.1 3.4 18.1 Madhya Pradesh 111.6 19.7 11.0 191.1 -48.9 Maharashtra 195.7 12.1 8.3 144.3 71.9 Odisha 31.1 24.0 4.8 24.7 35.2 Punjab 123.1 67.1 12.6 105.8 97.0 Rajasthan 71.7 26.7 3.9 92.2 10.2 Tamil Nadu 90.8 9.0 2.6 65.6 36.8 Tripura 0.8 0.3 0.3 2.0 -0.7 Uttar Pradesh 299.2 21.4 16.0 124.6 212.0 West Bengal 129.7 61.6 5.7 102.1 94.9 Others

* 1.7 1.9 1.4 7.6 -2.6

All India 1,797.0 397.2 101.2 1,275.6 1,019.8 (* Include Andaman and Nicobar Islands, Arunachal Pradesh, Chandigarh, Dadra and Nagar Haveli, Delhi, Goa,

Daman and Diu, Manipur, Meghalaya, Mizoram, Nagaland and Sikkim. The values are in ‘000 Mg yr-1

)

growth. Inorganic fertilizer was the dominant source contributing 78% of total P. According to [23], the application of phosphorus (P) fertilizer to agricultural soils increased by 3.2% annually from 2002 to 2010. In 2010, [3] gave a detailed state-wise P balance of the year 2000-2001 for India (Table 5). They also reported that annual removal of P through crop uptake was 1.27 Mt and there was an overall positive balance of 1.02 Mt P in agricultural soils of India. [24] also reported positive balance of P in the long-term experiments in rice-rice systems in the treatments with N and P application. Negative P balance was reported from the states like Arunachal Pradesh, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim and Madhya Pradesh which might be attributed to low fertilizer P application (3.7 kg P ha

-1) along with high P

removal by crops. It has been reported that balance of P per unit of area of land is highest in Himachal Pradesh and Punjab.

1.6 Potassium Budget

Balanced application of N, P and K also means replenishing the soil potassium reserves which are being continuously mined by following high intensity rice wheat cropping sequence and should also ensure transferring better soil to future generations of mankind. While nitrogen

remained heavily subsidized, reduction in subsidies of phosphate and potash in India adversely affected their consumption. This resulted in continued imbalanced fertilizer use. It has also been reported that rice-wheat farmers in the Indo-Gangetic plain seldom adopt recommended fertilizers doses and potassium fertilizers are rarely used. Fertilizer use pattern for rice-wheat system in the Indo-Gangetic plains varies greatly from one part to another. [24] showed that in two long term experiments of India Barrackpore and Pantnagar how potassium depletion occurs due to prolonged cultivation of rice and wheat with different doses of NPK fertilizer. [25] observed negative balance of K in the long-term experiments in rice-rice systems in Orissa, Andhra Pradesh, Uttarakhand and West Bengal even in the treatments with 35–50 kg ha

-1

K application. This suggested the need of adequate supply of K to crops for obtaining sustainable high yields. According to [3] unlike N and P major input of K came from irrigation water and rain (1.99 Mt) followed by manure (1.63 Mt). Fertilizer K (1.30 Mt) contributed 26% to total K input in India. Potassium consumption in India in year 2000 was about one- seventh of the country’s N consumption. In the entire history of fertilizer use in India, K has been approximately 10% of total NPK usage [8]. [3] estimated an overall negative balance of 3.29 Mt K was


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Table 6. Input, output, and balance of K in different states of India in 2000–2001

State Input Output Balance Fertilizer Manure Deposition Crop removal Loss

Andhra Pradesh 167.6 158.1 107.2 514.7 64.9 -146.7 Assam 25.6 16.0 59.6 116.1 15.2 -30.1 Bihar 54.8 80.0 115.1 355.1 37.5 -142.7 Gujarat 47.4 32.2 96.5 369.4 26.4 -219.7 Haryana 8.1 38.2 90.9 390.9 15.4 -269.0 Himachal Pradesh 3.8 62.5 11.7 33.0 11.7 33.3 Jammu and Kashmir 1.0 11.4 4.6 31.4 2.6 -16.9 Karnataka 194.1 214.0 168.7 442.3 86.5 48.0 Kerala 51.5 8.9 42.8 19.3 15.5 68.4 Madhya Pradesh 43.2 86.2 205.2 1,013.2 50.2 -728.8 Maharashtra 194.2 56.9 171.1 817.9 63.3 -459.0 Orissa 33.8 95.3 116.6 135.9 36.9 73.0 Punjab 18.6 254.1 187.7 556.3 51.5 -147.4 Rajasthan 4.5 112.3 66.5 504.3 27.5 -348.5 Tamil Nadu 173.2 45.2 48.8 369.6 40.1 -142.4 Tripura 0.5 1.6 5.8 11.2 1.2 -4.4 Uttar Pradesh 86.5 110.9 337.7 1,180.4 72.6 -717.8 West Bengal 188.5 236.1 129.6 602.0 83.1 -131.0 Others

* 1.2 8.4 22.8 41.1 4.9 -13.6

All India 1,298.1 1,628.3 1,989.1 7,504.0 706.8 -3,295.3 (* Include Andaman and Nicobar Islands, Arunachal Pradesh, Chandigarh, Dadra and Nagar Haveli, Delhi, Goa,

Daman and Diu, Manipur, Meghalaya, Mizoram, Nagaland and Sikkim. The values are in ‘000 Mg yr-1

)

estimated for the country. With exception of Karnataka, Orissa and Kerala which showed positive K balance, all other states showed negative balance of K. Uttar Pradesh, where removal of K due to crop production is highest (1.18 Mt), added only 0.53 Mt K through different sources, resulting in a negative balance of K, as high as 0.72 Mt (Table 6). Highest negative K balance was estimated for Haryana (76 kg ha-1 yr

-1) followed by Uttar Pradesh (41 kg ha

-1 yr

-1).

The reason behind negative balance of K may be the removal of K by above ground plant parts and losses through leaching far exceeds the small additions through fertilizers and manures which should not be sustainable on a long-term basis. 2. NUTRIENT USE EFFICIENCY (NUE) In the last five decades, nutrient applications to farmlands have significantly improved crop yield and public awareness about nutrient use efficiency (NUE). The objective of nutrient use is to increase the overall performance of cropping systems by providing economically optimum nourishment to the crop while minimizing nutrient losses from the field. Nutrient use efficiency (NUE) may be defined as yield per unit input. In agriculture this is usually related to the input of fertilizer, whereas in scientific literature the NUE

is often expressed as fresh weight or product yield per content of nutrient. Mineral fertilizers have sustained world agriculture and thus global population for more than 100 years. Their contribution to increasing crop yields has spared millions of hectares of natural ecosystems that otherwise would have been converted to agriculture [26]. However, lacking, imbalanced, inappropriate or excessive use of nutrients in agricultural systems remains a concern. Additions of fertilizers and amendments are essential for a proper nutrient supply and maximum yields. Estimates of overall efficiency of applied fertilizer have been reported to be about or lower than 50% for N, less than 10% for P, and about 40% for K [27]. Plants that are efficient in absorption and utilization of nutrients greatly enhance the efficiency of applied fertilizers, reducing cost of inputs, and preventing losses of nutrients to ecosystems. Inter- and intra-specific variation for plant growth and mineral nutrient use efficiency (NUE) are known to be under genetic and physiological control and are modified by plant interactions with environmental variables. There is need for breeding programs to focus on developing cultivars with high NUE. Identification of traits such as nutrient absorption, transport, utilization, and mobilization in plant cultivars should greatly enhance fertilizer use efficiency. The

development of new cultivars with higher NUE, coupled with best management practices (BMPs) will contribute to sustainable agricultural systems that protect and promote soil, water and air quality.

3. CURRENT STATUS OF NUTRIENT USE EFFICIENCY

Nutrients demand is increasing in agriculture with the passage of time i.e. N, P, and K. However, in 2015, the world demand for NPK was 186.6 Mt, and it was expected to increase to 199 Mt in 2019 [28]. Therefore, it is need of the hour to make certain managements practices for the use of major (NPK) fertilizers in future. The increasing pattern of world demand for NPK is shown in Fig. 6. Nutrient mining is a major cause for low crop yields in parts of the developing world. According to [29] if the input of fertilizer is more than the crop requirement, it leads to a waste of fertilizer through runoff water and causes low NUE. The maximum NUE is always observed where nutrient supply is lowest. In other situations, nutrients such as nitrogen (N) and phosphorus (P) often move beyond the bounds of the agricultural field because the management practices used fail to achieve good congruence between nutrient supply and crop nutrient demand [30]. Hence, increasing nutrient use efficiency continues to be a major challenge for

Fig. 6. Increasing trends of global


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development of new cultivars with higher NUE, coupled with best management practices (BMPs) will contribute to sustainable agricultural systems that protect and promote soil, water and air

CURRENT STATUS OF NUTRIENT USE

Nutrients demand is increasing in agriculture with the passage of time i.e. N, P, and K. However, in 2015, the world demand for NPK was 186.6 Mt, and it was expected to increase to 199 Mt in

. Therefore, it is need of the hour to certain managements practices for the use

of major (NPK) fertilizers in future. The increasing pattern of world demand for NPK is

Nutrient mining is a major cause for low crop yields in parts of the developing world. According

the input of fertilizer is more than the crop requirement, it leads to a waste of fertilizer through runoff water and causes low NUE. The maximum NUE is always observed where nutrient supply is lowest. In other situations,

d phosphorus (P) often move beyond the bounds of the agricultural field because the management practices used fail to achieve good congruence between nutrient supply and crop nutrient

]. Hence, increasing nutrient use major challenge for

world agriculture. Low nutrient use efficiency causes low efficiency nitrogen 30immobilization, volatilization, denitrification, leaching. In case of Phosphorus it is 15fixation in soils Al–P, Fe–P, Ca–P and in case of Potassium 70-80% fixation in claycase of secondary nutrients like sulphur it is 810% due to immobilization, leaching with water and in case of micro nutrients (Zn, Fe, Cu, Mn, B) it is 1-2% by fixation in soils. According to [31], the cause for low NUE and declining response to fertilizers can be attributed to low status of soil organic carbon and soil degradation, susceptibility of N fertilizers to losses by various mechanisms, imbalanced use of fertilizers, poor management for secondary and micronutrients especially S, Zn, Mn, Fe and B, use of high analysis fertilizers like urea and Diammonium phosphate (DAP) and inadequate addition of organic manures, inappropriate rate, time and method of application etc. (Table 7).

Hence, management practices that improve NUE without reducing productivity or the potential for future productivity increases are likely to be most valuable. At the same time, as nutrient rates increase towards an optimum, productivity continues to increase but at a decreasingand NUE typically declines [32]. The extent of the decline will be determined by source, time, and place factors, other cultural practices, as well as soil and climatic conditions.

6. Increasing trends of global nutrients (N-P2O5-K2O) consumption [

; Article no.IRJPAC.59589

world agriculture. Low nutrient use efficiency causes low efficiency nitrogen 30-50% by immobilization, volatilization, denitrification, leaching. In case of Phosphorus it is 15-20% by

P and in case of 80% fixation in clay–lattices. In

case of secondary nutrients like sulphur it is 8-10% due to immobilization, leaching with water and in case of micro nutrients (Zn, Fe, Cu, Mn,

for low NUE and declining response to fertilizers can be attributed to low status of soil organic carbon and soil degradation, susceptibility of N fertilizers to losses by various mechanisms, imbalanced use of fertilizers, poor management for secondary

d micronutrients especially S, Zn, Mn, Fe and B, use of high analysis fertilizers like urea and Diammonium phosphate (DAP) and inadequate addition of organic manures, inappropriate rate, time and method of application etc. (Table 7).

ctices that improve NUE without reducing productivity or the potential for future productivity increases are likely to be most

At the same time, as nutrient rates increase towards an optimum, productivity continues to increase but at a decreasing rate,

]. The extent of the decline will be determined by source, time, and place factors, other cultural practices, as well as

[33]


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Table 7. Nutrient use efficiency of some nutrients and cause of low efficiency Nutrient Efficiency Cause of low efficiency Nitrogen 30-50% Immobilization, volatilization, denitrification,

leaching Phosphorus 15-20% Fixation in soils Al – P, Fe – P, Ca – P Potassium 70-80% Fixation in clay - lattices Sulphur 8-10% Immobilization, Leaching with water Micro nutrients (Zn, Fe, Cu, Mn, B) 1-2% Fixation in soils

4. MEASURING INDICES NUTRIENT USE

EFFICIENCY

It indicates that how the use efficiency of Nitrogen, Phosphorus and Potassium from mineral fertilizer is commonly defined and measured, what needs to be considered for interpreting such values, and how it can be improved through soil, crop and fertilizer management. It focuses on cereal systems because they consume the bulk of the world’s fertilizer, but the principles discussed are similar in all agricultural crops. Where possible, attempts are made to discuss differences between developed and developing countries. Two key messages emerge: (i) Nutrient use efficiencies measured under practical farming conditions are mostly lower than those reported from research experiments, but information on current levels of fertilizer use and nutrient use efficiency by different crops, cropping systems and world regions remains insufficient; (ii) Numerous technologies for increasing nutrient use efficiency exist. They have been evaluated thoroughly, but adoption by farmers is lagging behind.

4.1 Agronomic Indices for Short-Term Assessment of Nutrient Use Efficiency

In Table 8, it summarizes a set of simple indices that are frequently used in agronomic research to assess the efficiency of applied fertilizer [34] mainly for assessing the short-term crop response to a nutrient. More detailed studies on the fate of nutrients in agro-ecosystems often involve isotopes, which are particularly useful for understanding loss, immobilization, fixation and release mechanisms. In field studies, nutrient use efficiencies are either calculated based on differences in crop yield and/or nutrient uptake between fertilized plots and an unfertilized control, or by using isotope-labeled fertilizers to estimate crop and soil recovery of applied nutrients. Time scale is usually one cropping season. Spatial scale for measurement is mostly a field or plot.

At low levels of nutrient supply, rates of increase in yield and nutrient uptake are large because the nutrient of interest is the primary factor limiting growth. As nutrient supply increases, incremental yield gains become smaller because yield determinants other than that nutrient become more limiting as the yield potential is approached. Because each of the indices in Table 8 has a different interpretation value, fertilizer research should include measurements of several indices to understand the factors governing nutrient uptake and fertilizer efficiency, to compare short-term nutrient use efficiency in different environments, and to evaluate different management strategies. The ‘difference method’ is simple and cost-efficient, which makes it particularly suitable for on-farm research. However, sampling and measurement must be done with great care. Agronomic indices only provide accurate assessment of nutrient use efficiency for systems that are at relatively steady-state with regard to soil nutrient content and where differences in root systems between unfertilized and fertilized crops are relatively small. For example, nitrogen in roots as well as any net accumulation of N from fertilizer in soil organic matter and its effect on the indigenous soil N supply for subsequently grown crops cannot be easily accounted for. This may lead to an underestimation of the overall system level efficiency of applied N inputs. In the example shown in Table 9, the average PFP of applied N suggested that the recommended management system was more N-efficient than the intensively managed system because it produced 70 kg grain/ kg N applied (or 0.88 kg grain N/kg N applied) as opposed to 50 kg grain/kg N (or 0.65 kg grain N/kg N applied) in the intensive system. However, when the net change in soil N was included, both systems had nearly the same system level N use efficiency (0.92- 1.01) because fertilizer-N contributed to build-up of soil organic matter in the intensive system. Over time, this will increase soil N supply, reduce the need for fertilizer, and increase PFPN. Nutrient budgeting and isotope


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Table 8. Different types of nutrient use efficiency Index Calculation Interpretation N in cereals RE = Apparent crop recovery efficiency of applied nutrient (kg increase in N uptake per kg N applied)

RE= (U – Uo)/F RE depends on the congruence between plant demand and nutrient release from fertilizer.

0.30–0.50 kg/kg; 0.50–0.80 kg/kg in well-managed systems, at low levels of N use, or at low soil N supply.

PE = Physiological efficiency of applied N (kg yield increase per kg increase in N uptake from fertilizer

PE= (Y– Yo)/(U-Uo)

Ability of a plant to transform nutrients acquired from fertilizer into economic yield (grain). • Depends on genotype, environment and management.

40–60 kg/kg; >50 kg/kg in well-managed systems, at low levels of N use, or at low soil N supply

IE = Internal utilization efficiency of a nutrient (kg yield per kg nutrient uptake)

IE=Y/U Transform nutrients acquired from all sources (soil, fertilizer) into economic yield (grain). • Depends on genotype, environment and management.

30–90 kg/kg; 55-65 kg/kg is the optimal range for balanced nutrition at high yield levels

AE = Agronomic efficiency of applied nutrient (kg yield increase per kg nutrient applied)

AE= (Y – Yo)/F or AE=RE x PE

Product of nutrient recovery from mineral or organic fertilizer (RE) and the efficiency with which the plant uses each additional unit of nutrient (PE). •AE depends on management practices that affect RE and PE.

10–30 kg/kg; >25 kg/kg in well managed systems, at low levels of N use, or at low soil N supply

PFP = Partial factor productivity of applied nutrient (kg harvested produce per kg nutrient applied)

PFP=Y/F or PFP=(Yo/F) + AE

Most important for farmers because it integrates the use efficiency of both indigenous and applied nutrients.

40–80 kg/kg; >60 kg/kg in well managed systems, at low levels of N use, or at low soil Nsupply

F – Amount of (fertilizer) nutrient applied (kg/ha) Y – Crop yield with applied nutrients (kg/ha)

Y0 – Crop yield (kg/ha) in a control treatment with no N U – Total nutrient uptake in aboveground biomass at maturity (kg/ha) in a plot that received fertilizer

U0 – Total nutrient uptake in aboveground biomass at maturity (kg/ha) in a plot that received no fertilizer


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methods should be used to assess the fate of nutrients in the entire soil-crop-atmosphere system over different time periods and at different scales.

4.2 Nutrient Budgets for Medium- to long-Term Assessment

Nutrient budgeting approaches are used to evaluate system-level nutrient use efficiency and to understand nutrient cycling by estimating input, storage and export processes by mass balance. A surplus or deficit is a measure of the net depletion (output > input) or enrichment (output < input) of the system, or simply of the ‘unaccounted for’ nutrient. This approach is used in studies on the fate of nutrients, for medium- to long-term assessment of FBMPs, nutrient flows and their respective impact on soil and the environment in managed or natural ecosystems, and for regulatory purposes in industrialized countries.

Nutrient budgets can be constructed for different time periods at any scale, ranging from small fields to whole countries or the globe. Budgets constructed for the purpose of guiding and regulating agricultural management or for policy decisions often consist of simple mass balances. Generally speaking, nutrient budgets for larger regions are often highly uncertain because of

imprecise available information on key processes such as fertilizer input by different crops and cropping systems, N input from atmospheric deposition and biological N fixation, and gaseous, leaching and runoff losses.

Most common are partial budgets that do not include all inputs or outputs or make assumptions about those that are difficult to quantify at the scale of interest. For a correct interpretation, nutrient budgets must be compared with the nutrient stock in the soil and its availability. A negative nutrient balance on a soil that has excessive levels of that nutrient is not necessarily bad. Likewise, a neutral nutrient balance indicates that the total stock in the soil does not change, but the ‘quality’ of the stock, and hence soil fertility, may still alter. Hence, a differentiation between ‘available’ and ‘not-immediately available’ nutrients is useful in nutrient balance studies, but has only been attempted occasionally [35]. Table 10 shows different K balances for an irrigated rice system in South Vietnam. Partial K budgets resulted in K balance estimates that were too negative because of neglected K inputs via rain, irrigation water and sediments. Irrespective of fertilizer-K input, large annual K input from sediments resulted in a positive balance of total K, but most of this was not plant-available.

Table 9. Nitrogen use efficiency in a long-term experiment with irrigated continuous maize systems (CC) managed at recommended (-rec) and intensive (-int) levels of plant density and fertilizer inputs. Total amounts for a five-year period (2000-2005) at Lincoln, Nebraska, USA

2000-2005 CC-rec CC-int Average maize yield (t/ha/yr) 14.0 15.0 Fertilizer- N input (kg N/ha) 1005 1495 Nitrogen removal with grain (kg N/ha) 880 970 Measured change in total soil N (kg/ha) 139 404 N unaccounted (kg/ha) 14 121 NUE1: partial factor productivity (kg grain/kg N applied) 70 50 NUE2: kg grain N/kg N applied 0.88 0.65 NUE3: kg grain N+change in soil N/kg N applied 1.01 0.92

Table 10. Comparison of partial and complete K input-output budgets in two treatments of a long-term experiment with irrigated double-cropping of rice at Omon, Vietnam. NP: no K

fertilizer; NPK: 150 kg K/ha/yr [35]

K budget (kg/ha/yr) NP NPK Balance of soluble K (partial budget) -92 22 Balance of soluble K (complete budget) -69 44 Balance of labile K (Ammonium acetate K, complete budget) -66 47 Balance of non-labile K (NaTPB-K, complete budget) -58 55 Balance of total K (complete budget) 251 364 Partial budget: inputs- fertilizer; outputs- crop K removal with grain and straw Compete budget: inputs- fertilizer, rain water, irrigation water, sediments from annual flood; outputs- crop K removal with grain and straw, leaching, runoff, sediment removal


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Fig. 7. 4R concept for fertilizer application to increase use efficiency of nutrients (IPNI) [36]

5. MANAGEMENT STRATEGIES FOR

INCREASING NUTRIENT USE EFFICIENCY

5.1 4R Nutrient Stewardship for Improved

Nutrient Use Efficiency Fertilizers play a significant role in securing the production of food crops around the world. In fact, it is estimated that fertilizers currently support 40-60% of all crop production currently. Meeting future food security targets requires the responsible use of fertilizer nutrients. The 4R Nutrient Stewardship guidelines were developed by the fertilizer industry as a process to guide fertilizer Best Management Practices (BMP) in all regions of the world. This approach was required to address the growing concern that fertilizers are applied indiscriminately to the detriment of the environment. Given that farmers purchase fertilizers at world prices in most regions, and these prices have been steadily increasing over time, most users are very cautious about the rates of nutrients they apply. The 4R nutrient

stewardship concept defines the right source, rate, time, and place for fertilizer application as those producing the economic, social, and environmental outcomes desired by all stakeholders to the plant ecosystem (Fig. 7).

To avoid unnecessary policy intervention by governments, the fertilizer industry needs to be unified in their promotion of BMPs that support improved nutrient use efficiency and environmental sustainability, while supporting the farmer’s profitability. This ultimately comes down to developing appropriate recommendations that match crop nutrient requirements fertilizer additions and minimize nutrient losses from fields. This led to the 4R Nutrient Stewardship concept, applying the Right Source of nutrients, at the Right Rate, at the Right Time and in the Right Place. Right source means matching the fertilizer to the crop need and soil properties. A major part of source is balance between the various nutrients, a major challenge globally in improving nutrient use efficiency. Finally, some fertilizer products are preferred to others based on the soil properties, like pH. Right rate means


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matching the fertilizer applied to the crop need simplicity. Adding too much fertilizer leads to residual nutrients in the soil and losses to the environment. Ultimately, striking a balance between the crop needs, environmental conditions and the farmers’ economic situation is required. Right time means making fertilizer nutrients available to the crop when they are needed. Nutrient use efficiency can be increased significantly when their availability is synchronized with crop demand. Split time of application, slow and controlled release fertilizer technology, stabilizers and inhibitors are just a few examples of how fertilizer nutrients can be better timed for efficient crop uptake. Right place means making every effort to keep nutrients where crops can use them. This is an issue which poses the greatest challenge in small holder agricultural systems, where most fertilizer is broadcast applied, and in many cases without incorporation.

Research indicates that fertilizer placement can not only improve crop response, but also improve fertilizer use efficiency significantly by lowering nutrient application rates. Adaptation to non-mechanized agriculture has been made in certain regions which clearly support efforts to modify fertilizer placement as a BMP. Nitrogen use efficiency in rice through integrated nutrient management is given by [37] in Table 11.

5.2 Site Specific Nutrient Management

The Site-Specific Nutrient Management (SSNM) is need-based feeding of crops with nutrients while recognizing the inherent spatial variability which enhances crop productivity, profitability, NUE and avoids nutrient wastage. For efficient and effective SSNM, use of soil and plant nutrient status sensing devices, remote sensing, GIS, decision support systems, simulation models, and machines for variable application of nutrients play an important role. Nutrient use efficiency of NPK can be increase by giving fertilization based on site specific nutrient management. Table 12 shows that use efficiency of the nutrients increased by site specific nutrient management practice in rice [34].

5.3 Intercropping

Intercropping is a multiple cropping practice involving growing two or more crops in proximity. In other words, intercropping is the cultivation of two or more crops simultaneously on the same field. Intercropping with green manure increases nutrient use efficiency in cropping system.

Similar results can be found when cereals are intercropped with legume crops. Grain yields of rice and wheat were significantly greater in plots receiving green manuring than those without green manuring (Table 13). In general, advantages of green manuring were greater at low levels of N than at higher N levels. The residual effect of green manuring on succeeding wheat was very small. When averaged over N rates, rice yielded 12.84 kg grain kg-1 applied N with green manuring and 11.52 kg grain kg

-1

applied N without green manuring. Wheat, however, yielded 11.87 kg grain kg

-1 applied N

without green manuring and 11.52 kg grain kg-1 N without green manuring [38]. The benefits of legume crops to succeeding cereal crops are well documented, mainly by way of improving productivity, nutrient use efficiency, regenerating soil fertility through biological N fixation (BNF) and nutrient mining from relatively deeper soil profile [39]. Greater wheat yield responses to P over no P treatment in pigeon pea–wheat (16.3–36.1%) compared with those in rice–wheat system (10.5–17.3%) in different years (though significant in the terminal year only) are explicable in terms of relatively higher AEP and ARP values in wheat following pigeon pea. 5.4 Tillage and Residue Management Combined effects of tillage, residue retention, and nutrient management effects the crop yields and nutrient use efficiency. The tillage and residue management reduces the soil disturbance and increases the nutrient use efficiency. Use of tillage and residue management improves agronomic and recovery efficiency in rice and maize is given by [40] in Table 11.

6. CHALLENGES ASSOCIATED WITH NUTRIENT BUDGETING

The flourishing application of nutrient budgets has significantly advanced our understanding of nutrient cycles, especially for N and P, but has also been accompanied with confusion, even misunderstanding, over nutrient budgets (i.e., inputs and outputs of a system) and the assessment of the system efficiency, leading to major challenges in comparing nutrient budget results among studies. While defining the nutrient budget in soil-plant system for assessing the efficiency of crop nutrient management, we come across two major challenges, viz., (i) the


109

efficiency assessment is based on the assumption that the system has achieved a steady state but long‐term observations are often required to ensure the quasi steady state, especially for cropping systems with multiyear rotation practices, perennial crops, or large nutrient reserves in soil; (ii) whether to include crop residue as part of the productive output of the system can lead to significant difference in

NUE assessment, e.g., the N use efficiency for the soil-plant system can increase from 43% to over 58% (depending on the harvest index) if crop residue is included as one of the productive outputs. However, the consideration of crop residue should depend on whether the residue is harvested (i.e., removed from the site) and how it is used, for which information is often limited [41].

Table 11. Nitrogen use-efficiency in rice through integrated nutrient management

Treatment Apparent N Recovary Agronomic efficiency

Physiological efficiency

1st rice 2nd rice 1st rice 1st rice

GM N40+ N0 24.8 28.0 18.0 72.7 N40 43.3 44.9 23.5 54.5 GM N40+ N40 35.6 35.7 15.5 43.5 N80 46.3 43.9 17.1 37.0 GM N40+ N80 44.3 45.6 14.4 32.5 N120 31.8 30.8 10.3 31.4 GM N40+ N120 34.4 38.8 9.7 28.2

Table 12. Effect of site-specific nutrient management NPK use efficiency

Crop NUEN NUEP NUEK

Rice (Farmer’spractice) 0.33 0.24 0.38 Rice (SSNM) 0.43 0.25 0.44 Wheat 0.58 0.27 0.51

Table 13. Grain yield kg ha

-1, agronomic efficiency (AE) and recovery efficiency (RE) of applied

N in rice and wheat as influenced by Sesbania green manuring in rice–wheat system

Treatment Grain yield (kg ha-1) AE (kg grain kg-1 N) RE %

Rice Wheat Rice Wheat Rice Wheat

Solo Rice-Wheat

N0 3458 3741 0 0 0 0 N60 4055 4395 9.95 10.9 10.00 25.00 N120 452 5218 6.64 12.3 11.66 13.33

Sesbania green manured Rice- Wheat

N0 3807 3030 0 0 0 0 N60 4615 4526 13.45 11.6 13.33 30.00 N120 5367 5329 12.07 12.49 10.83 14.16

Table 14. Use of tillage and residue management improves agronomic and recovery efficiency

in rice and maize

Source of variation Rice P value at 5 % level of significance

Wheat P value at 5 % level of significance

Agronomic efficiency

Recovery efficiency

Agronomic efficiency

Recovery efficiency

Tillage (T) 0.000 0.004 0.000 0.044 Residue Management (R) 0.000 0.005 0.000 0.001 T × R 0.036 0.009 0.000 0.045


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Several challenges are associated with while quantifying the nutrient budgets in soil-plant system. Synthetic fertilizers are the major N and P inputs for soil-plant system but accurately quantifying the nutrient inputs from synthetic fertilizer is critical for balancing the nutrient budget. Information on fertilizer inputs is often available at two spatial scales, namely farm and national scales. Farmers (or scientists conducting field experiments) usually have good knowledge of the amount of fertilizer applied in their fields, since it is one of the major costs for their production. On the national scale, countries have been requested to report their fertilizer use for agricultural production, for which they often aggregate their census data on fertilizer use or sales from subnational scales. These data have been compiled and made available by FAOSTAT since 1961 [42]. The International Fertilizer Industry Association (IFA) also reports fertilizer production and consumption data on a national scale based on surveys with fertilizer companies [43,44]. While most countries have reported total synthetic N fertilizer consumption from the two data sources in approximate agreement, a few countries (e.g., China) show up to 30% underestimation by the Food and Agriculture Organization of the United Nations (FAO) data source, leading to different global fertilizer consumption estimates from the two data sources in recent decades [41]. Only a few efforts have downscaled the fertilizer application rate considering the heterogeneity among regions and crop types [45]. It has been reported that some downscaling was carried out based on the assumption that fertilizers were applied in the state (or a subnational political unit) where they were sold or adjacent states [46], while others assume a constant fertilizer application rate for all crops [47] or all states [48,49]. Runoff and leaching are the major pathways that nutrients escape the agricultural land and contaminate water bodies. N and P in runoff and leaching can be measured directly in the field. Where direct measurements or models are not available, nutrient loss in leaching and runoff has been estimated with simple assumptions, e.g., P in leaching is sometimes assumed as a fixed fraction of P budget terms, such as 12.5% of P inputs [50] or 20% of P surplus [51]. These simple assumptions introduce large uncertainties into results. For example, global P leaching and runoff from cropland estimated by [52] is 20% lower than that by [50], whereas the estimates for pasture by [52] is 60% higher than [53]. Soil is one of the major nutrient stocks of a system that

can increase or become depleted. Part of the P applied to crops has been shown to be retained in agricultural soils during multiple years of P application [54,55]. This increased soil‐P stock can become a source of P for future years, which is called the P legacy. But some soils, particularly those in tropical areas with highly weathered soils, are P‐fixing because phosphate binds to iron and aluminium oxides [56]. In the areas with high proportions of P‐fixing soils, P recovery by crops can be low and P surpluses can be high, with most of the P surplus retained in the soil. The release of P fixed on iron and aluminium oxides may be slower than the release of P accumulating in less highly weathered soils in temperate regions. Therefore, the consideration of the P legacy effect is different when compared with soils that are “non‐P‐fixing.” P legacies can also play a role after agricultural activities cease, influencing P budgets in the post-agricultural ecosystems [57]. The legacy effect is probably less common for N than for P, but N can also accumulate in soils. When soil N is at or near steady state, mineralization and immobilization of soil N are roughly in equilibrium. However, where soil C sequestration is occurring (e.g., conservation tillage), part of the N surplus will be retained with the C sequestration, promoting the stabilization of soil N through microbial turnover [52].

7. CHALLENGES ASSOCIATED WITH ENHANCING NUTRIENT USE EFFICIENCY

The quantification of nutrient budgets has provided indispensable information for nutrient management, e.g., the NUE and nutrient surplus for a soil-plant system on a farm scale can help farmers to understand changes in soil nutrient stocks and estimate the fertilization needs for the next season. However, using nutrient budgets to inform sustainable nutrient management faces multiple major challenges, e.g., challenges to define and assess “sustainable” nutrient management with nutrient budgets, connect actions by stakeholders with their impacts on the environment, effectively communicate nutrient budgets to engage actions etc. [41]. NUE focuses on cereal systems because those consume the bulk of the world’s fertilizer, but the principles discussed are similar in all agricultural crops. Where possible, attempts are made to discuss differences between developed and developing countries. Two major limitations emerge in this aspect, viz., (i) Nutrient use efficiencies measured under practical farming


111

conditions are mostly lower than those reported from research experiments, but information on current levels of fertilizer use and nutrient use efficiency by different crops, cropping systems and world regions remains insufficient; (ii) Numerous technologies for increasing nutrient use efficiency exist. They have been evaluated thoroughly, but adoption by farmers is lagging behind.

8. CONCLUSION

Nutrient management is fundamental to sustainable development in this century and it requires good information about nutrient budgets. It draws attention especially in the agriculture-based overpopulated developing countries where resources are limited but demands are not limited and a majority of the farming community is poor and marginal farmers. Under such circumstances when poverty is knocking at the door of the “real-life Heroes” who grows food for the entire country, 4R nutrient stewardship as well as combined application of organic manure, biofertilizers and synthetic fertilizers are proved to be helpful in increasing nutrient use efficiency (NUE) markedly. The growing efforts in quantifying nutrient budgets for agricultural land system have enabled researchers to understand complex nutrient cycles and their interactions with plant and soil system. Those efforts have also provided useful information for many stakeholders, including farmers, retailers, consumers, and policy makers, to assist their decisions that affect nutrient management. However, the expanding application still requires consistent and structural definitions of systems and their budget terms to enable comparisons and inter-linkages among studies; large uncertainties in multiple nutrient budget terms need to be constrained; and the scientific findings need to be better communicated to engage positive changes. The current limitations in nutrient budgets and the need for their improvement should be better communicated not only among researchers but also stakeholders engaged in nutrient management. It will take decades, even centuries, for all nutrient budget terms to be accurately accounted for, but this should not prevent scientists from communicating the importance of nutrient budgets and the insights they provide for sustainable management.

COMPETING INTERESTS

Authors have declared that no competing interests exist.

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nutrient budgeting of primary nutrients and their use

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