Prospects of Micro Irrigation and Fertigation

In China’s agriculture

H. Magen (1)

(1) ICL Fertilizers

Paper presented at the Funding and investing in China’s agricultural projects and trade. IBC

conference, 1-2 Dec. 98, Beijing, PRC

Abstract

Irrigation is considered as one of the major factors for increasing productivity. Increased water efficiency and improved technology, as well as introduction of new cultivation systems such as no-till or low-till, offer the prospect of significant water savings. Micro-Irrigation systems are the latest innovation of irrigation. Modern Micro-Irrigation Systems (MIS) are much more efficient in terms of Water Use Efficiency (WUE) thus more land may be irrigated for a given quantity of water. Fertigation is the application of solid or liquid mineral fertilizers via pressurized irrigation systems, creating nutrient-containing irrigation water. Water use efficiency in Chinese irrigation is rather low compared with developed countries. One of the more promising areas to utilize more water for irrigation, is to increase the water use efficiency through the implementation of MIS. The development of agriculture in Israel is strongly dependent upon the efficient use of irrigation water. Efficient use has led to a constant decrease in water consumption from an average of 8700 m3/ha in 1951 to 5600 m3/ha in 1990. In 1996, the Israeli farmer applies approximately 50% of the N and P2O5, and 65% of the K2O through fertigation. The Israeli experience is also applicable in China. The need for sophisticated irrigation and fertigation devices as well as training is described. One of the major obstacles for the penetration of MIS is the investment involved, which makes them attractive only for cash crops with high rate of return, such as vegetables, orchards, green house and plantations. The net return for the investment can be as high as double of the yield. This is achieved by saving 50% of the water requirement. MIS enables irrigation of large plots under water shortage, reduces problems of over humidity in greenhouses, enables growing under salinity conditions and enables fertilization at high water table conditions. Urea and KCl are available in the Chinese market, and are adequate under certain limitations for use with fertigation. Their cost is attractive. The use of by-pass tank and field made stock solution is an example of an efficient, simple and cheap management for advanced fertigation systems in China. The preparation of field prepared stock solutions is described.

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Introduction

It is widely recognized that many countries are entering an era of severe water shortages. The International Water Management found that the growth in world requirements for the development of additional water supplies varies between 59 percent in the first scenario to 25 percent in the second scenario (1). Irrigation is considered as one of the major factors for increasing productivity (2). Increased water efficiency and improved technology, as well as introduction of new cultivation systems such as no-till or low-till, offer the prospect of significant water savings. Micro-Irrigation systems are the latest innovation of irrigation. The use of pressure requires energy at the field level and relatively high investment in equipment. Modern Micro-Irrigation Systems (MIS) are much more efficient in terms of Water Use Efficiency (WUE) thus more land may be irrigated for a given quantity of water. This relatively new management is also highly responsive for fertigation. Fertigation is the application of solid or liquid mineral fertilizers via pressurized irrigation systems, creating nutrient-containing irrigation water. Solid fertilizers can be applied as a single nutrient (e.g. urea), or as multi-nutrient composite of a fertilizer mixture. Liquid fertilizers are of single or multi-nutrient, but due to solubility, the total nutrient concentration is much lower. Water use in China China's total annual water resources totaled 2.8 trillion M3, approximately 1/4 of the per-capita world average in 1979 (3). When divided by the amount of cultivated land, each hectare's share is 26,535 M3, which is only 3/4 of the world average. From 1950-1988, on average 26 percent of cultivated land suffered from floods or drought annually, and 10 percent of cultivated land underwent a loss in production of more than 30 percent. Periodic droughts are particularly acute in north China, while the lower reaches of all major rivers are susceptible to flooding (3). China's early civilizations developed agriculture dependent on water conservancy and irrigation. The Dujiang Weir in Sichuan Province, dating from the 3rd century BC still supplies water to 202,000 hectares. During the Ming and Qing dynasties, extensive irrigation works were also developed in the north and central China plains (3). The greatest expansion of (surface) irrigation facilities took place from 1949-1990, when the irrigated area tripled from 16 million to 48 million ha, thus approximately 50% of the cultivated area is being irrigated. Nearly 3/4 of grains as well as most of the cotton and other cash crops are produced on irrigated land. Many Chinese rivers are tapped for irrigation, with the Yangtze and the Yellow rivers supplying much of the country's irrigation water through a system of dams and reservoirs that also function as flood control units. According to official figures for 1997, the irrigated land is approximately 50.4 million ha (4). The ministry of Water Resources estimates that irrigated areas can be increased to approximately 53 million ha by the year 2000, but further expansion would be difficult due to water shortage (5). China depends on irrigated land to produce 70 percent of the grain for its huge population of 1.2 billion people, but it is drawing more and more of that water to

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supply the needs of its fast-growing cities and industries (3). Most of the irrigated area is at the South and East China: Shandong province (4.7 million ha), Henan and Hebei (4 million ha each) and Jiangsu province (3.8 million ha) (6). Water use efficiency in Chinese irrigation is rather low compared with developed countries. The WUE for all China average is less than 50 percent: in areas employing canals it is 30-40%, while in areas using groundwater the WUE is higher (about 70%). By comparison, the WUE for U.S. are in the 60-70% and Israeli figures are even higher (90%). Naturally, this reflects the different irrigation methods. In China, the efficiency is dictated by the vast use of open canals and surface irrigation (which counts for 98% of the irrigation employed), while in Israel, all systems are in closed pipes and methods of irrigation include only center-pivot, sprinkling and the most effective one – the drip system (fig. 1). The shortage of water was the trigger for research work on water projects. It was found that water saving by high as 50% can be achieved in Southern Hebei and northwestern Shandong provinces, which suffer from acute water shortages and a falling water table (3). According to the Ministry of Water Resources figures, approximately 2.6 million ha (5% of total irrigated land) already employ various types of pipes, with PVC and PE being preferred over concrete. 0.8 million ha use sprinkler systems, especially Beijing suburbs, realizing a 50% saving over traditional irrigation methods. Drip or trickle irrigation is used in the South in citrus orchards subject to late summer and autumn drought. In the North, it is mostly used in greenhouses and for vegetables. At present, only a small percentage of China's 5.3 million ha of fruit orchards (3.3 million ha of which is found in the water-short north) employ this type of irrigation. It is therefore concluded that one of the more promising areas to utilize more water for irrigation is to increase the water use efficiency through the implementation of MIS. This change may be achieved through massive investments. Drip and other MIS systems present the best up-to-date option for water saving in horticulture, greenhouse and plantations crops.

50.4

2.60.8

0

10

20

30

40

50

60

Irrigated area

Pipes in the system

Sprinkle irrigation

Area

(mill

ion

ha)

010203040

5060708090

WUE

(%)

Area WUE

Figure 1: Irrigated area and water use efficiency in China

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Water use, fertilizers and fertigation in Israel (Or what can we adopt from the Israeli experience?)

The development of agriculture in Israel is strongly dependent upon the efficient use of irrigation water. Due to the country’s semi-arid climate, it is necessary to irrigate almost all crops. The high cost of water encourages the use of pressurized irrigation systems as the sole method of irrigation since it allows full control of quantities, timing of application and fertilization through fertigation. Efficient use has led to a constant decrease in water consumption from an average of 8700 m3/ha in 1951 to 5600 m3/ha in 1990 (7) (fig. 1, 2). Higher yields can be obtained in spite of lower water inputs, mainly by the adoption of advanced irrigation systems and better water management. Yields of most crops grown have increased significantly since 1965 (table 1). The main reasons for this growth are the increase in irrigation and fertilization efficiency, the introduction of pressurized and partial wetting irrigation systems and fertigation, the detailed study of crop water and nutrient consumption, precise monitoring and control of irrigation and extension work. The main reasons for increased fertilization efficiency are the introduction of fertigation, detailed studies of crop fertilizer consumption and uptake curves, the development of new fertilizers for fertigation, the intensification and calibration of plant & soil analysis and extension work. Israel is an unmatched example of the use of fertilizers by fertigation. In 1996, the Israeli farmer used an average of 115, 46 and 57.5 kg of N, P2O5 and K2O per hectare, respectively (figure 6). Over 50% of the N and P2O5, and 65% of the K2O is applied by fertigation. For K2O, clear liquid N-P-K, N-K or P-K solutions or soluble complex or binary fertilizers are the common formulations.

0

5000

10000

15000

20000

25000

30000

M3

/ ha

China (1979)

Israel (1951)

Israel (1990)

Figure 2: Water consumption per area unit in China and Israel

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Table 1: Average crop yields of selected crops 1965-1992 (tons per hectare, unless otherwise specified)

Crop 1965 1977 1988 1992 Tomatoes 33 33 49 65 Cucumbers 13 23 24 38 Carrots 28 55 52 59 Dry onions 13 22 22 33 Potatoes 25 33 37 33 Apples 18 35 30 35 Pears 19 27 27 25 Plums 10 22 22 25 Table grapes 10 13 15 25 Wine grapes 8 14 19 21 Bananas 21 37 34 34 Avocados 5 9 4 11 Citrus: Shamouti Lates Grapefruit Lemons

28 27 37 22

32 46 55 36

32 29 45 28

30 29 49 35

Cotton lints (irrigated) 1.32 1.35 1.25 2.0 Wheat, (unirrigated) 1.53 2.45 2.29 2.50 Roses (thousand units/hectare) 1300 Carnations (thousand units/hectare) 1000 950 1400

Year

0

50

100

150

200

250

51-55 56-60 61-65 66-70 71-75 76-80 81-85 86-900

2000

4000

6000

8000

10000

Average consumption, M3 /haIrrigated area, ‘000 ha

Fig 3: Irrigated land & average water consumption in Israel (1951-1990)

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The most common sources of potassium for K fertigation in Israel are Potassium Chloride (KCl, Muriate of Potash - MOP), Potassium Nitrate (KNO3), Mono-Potassium Phosphate (KH2PO4) and Potassium Sulfate (K2SO4, Sulfate of Potash - SOP). The K fertilizer is chosen according to its price, solubility, anion type and ease of use. Approximately 30% of K2O consumed are applied as soluble potassium chloride either in by-pass tanks (fig. 4), as small volume stock solutions prepared by farmers and in factory- prepared liquid fertilizers (fig. 5). The other two thirds, ~35% each, are 1) non-chloride K fertilizers in solid or liquid form, mainly as potassium nitrate and mono-potassium phosphate, and 2) as solid straight muriate of potash (MOP) broadcasted with mechanical spreaders (figure 6). The application of fertilizers is executed by various methods, including the technique of stock solution preparation. In this technique, farmers are using solid fertilizers as ammonium sulphate, urea, potassium chloride and nitrate, and liquid phosphoric acid to prepare a “tailor made” stock solution. The stock solution is then injected into the irrigation system, at rates of 2-10 liters per 1 M3 of water, depending on the desired concentrations of N, P and K (8).

Figure 4: By-pass tank facility for application of soluble – solid fertilizers

Figure 5: Stock solution tank with installed fertilizer displacement pump

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as soluble KCl

57.5

46

115

Kg / ha

as MOP mechanically

spread

as non-chloridesource of K2O

K2O

K2OP2O5

N

Figure 6: Nutrient consumption per area unit & K2O use in Israel The use of advanced fertigation systems allow the farmer to follow precisely crop’s requirements for nutrients. Recommendations are than given on a daily basis (table 2).

Table 2: Typical fertilization recommendations for vegetables when using fertigation (7)

Crop Nutrient (gr/ha/day) N P2O5 K2O Tomato (greenhouse)

1500-6000 700-1500

1500-9000

Pepper 2400-4500 600-1150 2000-3600 Cucumber (greenhouse)

1000-4000

1000

1000-5000

Watermelon 750-4000 100-400 700-3000 Onion 2100-7000 250-400 1500-3500 Muskmelon 750-4000 100-500 700-3000 Eggplant 2000-4500 200-350 1500-3750

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We believe that the Israeli experience in efficient use of water and fertilizers is also applicable in China. The need for sophisticated irrigation and fertigation devices can be met via import or local production. The Chinese academic institutes which are very familiar with these systems must meet the need for advanced extension work. Future prospects for MIS and fertigation in China

MIS

One of the major obstacles for the penetration of MIS is the investment involved. The amount needed varies greatly between different suppliers and specifications. Nevertheless, we can adopt the figure of ~$USD 1000-1500 as the required investment for the installation of 1 hectare of drip, jet or mini-sprinkler system. This figure brings in account that at the farm gate there is a water source with about 20-40 m head. The conclusion is that such systems are possible only for cash crops with high rate of return, such as vegetables, orchards, green house and plantations. Some of the items are particularly expensive when installing small plots. The price of the components in the control head (filter, water meter, fertigation system etc.) are getting cheaper (in terms of price / area) when the size of the plot increases. The net return for the investment can also vary significantly. When the limiting factor is the quantity of water available on an annual basis, we can assume even doubling the crop achieved, when converting from flood to MIS. This is of course very attractive from the economic point of view. Another obstacle, especially in rural areas, is the lack of water source with operational pressure (20-40 m head). An Israeli company introduced an interesting solution for this problem in China a few years ago. The solution is based on a 200-l barrel located at the field and special drippers / emitters operating at a very low discharge rate, which distribute the water evenly in the field. This system is more attractive in terms of the initial investment required (fig. 7 & 8).

Figure 7: The layout design of a low pressure drip system water source

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Figure 8: A 200 l barrel as water source with a very low head for drip irrigation Apart from increased WUE, additional agronomic benefits are presented. We can summarize the advantages of MIS in China as follows:

• Using MIS reduces problems of over humidity in green-houses. • MIS enables a much better control for growing growing under saline conditions. • When high water table prevents proper fertilization, MIS is the best irrigation system.

Soluble fertilizers - Fertigation

As demonstrated with the Israeli experience, fertigation must come along with the introduction of MIS. Our experience in many countries shows that farmers tend to overlook this issue. We also know, that decreased yields are shown only some time later, say after 2-3 years in tree crops but much earlier with vegetables. Fertigation provides the only solution for introducing the fertilizers to the wetted zone. The cost of fertilizers for fertigation varies greatly. The most expensive formulas (around $USD1000 pt) are those containing multi-nutrient solutions, whereas the cheapest are those single-nutrient fertilizers available in the market, such as urea and potassium chloride (market price). There is no scientific evidence for preferring solid or liquid fertilizer, thus, the only factors to be taken in account by the farmer are the quality, cost, ease of application and availability of fertilizers. All fertilizers for fertigation must be 100% water soluble, with no sediments or particles that may clog the emitters. The options available in the market are as follows:

• dry mixtures of NPK, • liquid fertilizers, • conventional fertilizers available in the market with modification in their application, to apply via by-pass

tank (solid) or for stock solutions preparation (at the farm level).

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In this paper, we give more emphasis on the most conventional and cheapest option. We believe that for new comers to MIS, the use of ‘regular’ fertilizers is safe, straightforward and will yield a good return. Under the term ‘regular’ we include Urea as the N source and KCl (MOP) as K source, provided it does contain iron oxides (red potash). The advantages are: 1) there is no problem of availability all over China, with no special dealership involved, 2) agronomicaly we can easily achieve balanced fertilization management, 3) the cost of these fertilizers is cheap and does not differ from the price the farmer paid before the installation of MIS. Nitrogen: Urea is a fully soluble fertilizer, clean and with no insolubles. Urea will dissolve fast and will leave no insoluble residues. Phosphorous: SSP, TSP or DAP can be applied as basal dress. If phosphoric acid (white) is available, it can be easily used in the fertigation system. Potassium: KCl (60% K2O): is the cheapest source of K. The use of red potash in fertigation systems is not recommended due to the red insoluble substance (iron oxide) which clog the emitters. Only white potash can be used. It’s solubility is high and time of dissolution is short. K2SO4 (50% K2O): is a non-chloride fertilizer used for Cl sensitive crops. SOP is more expensive than KCl, its solubility is very limited and the speed of dissolution is relatively low. The sulfate content in the fertilizer limits it’s application in ‘hard water’ due to precipitation of CaSO4. KNO3 (46% K2O): this binary fertilizer is an excellent solution for greenhouse production. Some limitations in its use arise when there is a need for K application at the last stages of growth. At these stages, the NO3 (nitrate) is not needed and may even cause adverse affects. The cost of each K2O unit is high: assuming that 1000 kg cost $USD 500 pt and the value of the nitrate is twice (!) the price of N from urea, 1 unit of K2O costs about 3 times more than that from KCl.

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Preparation of stock solutions: This application method is attractive for the use of urea, phosphoric acid (which can be omitted) and KCl. Table 3 shows the results of an experiment we conducted to create a whole set of multi nutrients solutions, as required by the crops. This approach can be adopted easily by the new users of MIS in China, especially those using the very low-pressure systems. For these users, the by-pass tank or any other pressurized systems for fertilizer injection, are not applicable.

Table 3: Composition, mixing order and solution characteristics of ‘grass root’ prepared stock solutions (8).

Ratio (N-P2O5-K2O)

Composition (Weight/volume)

Raw materials (by adding order)

Turbidity (NTU)

Specific gravity

pH (1:1000)

Conductivity (1:1000, dS/m)

K 0-0-1 0-0-7.9 KCl 12.2 1.06 6.7 0.22

NK 1-0-1 4.9-0-4.9 Urea/KCl 16.0 1.07 6.2 0.16 1-0-2 3.1-0-6.3 Urea/KCl 7.5 1.07 5.4 0.19 1-0-3 2.7-0-8.1 Urea/KCl 8.8 1.09 5.1 0.24 2-0-1 6.1-0-3.1 Urea/KCl 7.5 1.05 4.8 0.09 3-0-1 7.8-0-2.6 Urea/KCl 15.3 1.08 5.1 0.07

PK 0-1-1 0-6.3-6.3 H3PO4/KCl 3.2 1.09 2.7 0.45 0-1-2 0-3.7-7.4 H3PO4/KCl 8.4 1.11 3.3 0.35 0-1-3 0-3.2-9.6 H3PO4/KCl 7.1 1.12 3.4 0.36 0-2-1 0-7.4-3.7 H3PO4/KCl 3.0 1.09 2.7 0.41

NPK 1-1-1 3.6-3.6-3.6 H3PO4/Urea/KCl 5.4 1.08 3.3 0.30 1-1-3 2.7-2.7-8.1 H3PO4/Urea/KCl 5.0 1.11 3.6 0.36 1-2-1 2.7-5.4-2.7 H3PO4/Urea/KCl 4.0 1.08 3.1 0.38 1-2-4 2.5-5.1-10.1 H3PO4/Urea/KCl 4.3 1.14 4.3 0.49 3-1-1 7.4-2.5-2.5 H3PO4/Urea/KCl 6.8 1.07 4.3 0.20 3-1-3 5.1-1.7-5.1 H3PO4/Urea/KCl 8.3 1.08 3.7 0.22

The results presented in this work (8) show that a variety of K, NK, PK and NPK clear stock solutions can be prepared from urea, phosphoric acid and white potassium chloride with total nutrients, as expressed in units of N, P2O5 and K2O, of at least 8-10%. The overall concentration of mixed fertilizer solutions is not dependent on the order of addition, but the kinetics of dissolution are affected, especially in the case of minimal mixing, because of the different heats of solution. The pH (1:1000) of K and NK solutions are in the range of 5-6, whilst solutions based on phosphoric acid are in the range of 3-4. The pH of the fertilizer solutions is only affected slightly by the pH of the water and remains in the ranges quoted above for water with pH between 6 to 8. Application of, for example, 2 liters of 1-1-1 (3.6-3.6-3.6) stock solution to 1M3 irrigation water, will give concentrations of 72 ppm of N, P2O5 and K2O .

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Figure 9: FERTI-K, soluble potassium chloride for fertigation

References

(1) Seckler, D., Amarasinghe, U., Molden, D., Rhadhika de Silva and Barker R. International Water Management Institute, Colombo, Sri Lanka.

(2) L. R. Brown. 1997. Facing the challenge of food scarcity: Can we raise grain yields fast enough? In: Plant nutrition – for sustainable food production and environment. T. Ando et al. (eds.) Worldwatch Institute, U.S.A.

(3) Irrigation In China Demands More Efficient Technologies. A report from the U.S. Embassy Beijing, Environment, Science and Technology Section, June 1996.

(4) China Statistical Yearbook No. 16, 1997. Compiled by the State Stat. Bureau, PRC.

(5) "China's Agenda 21" published in 1993 and "Utilization of China's water resources" published in 1989 cite 1980 data based on the most recent nationwide water resource study conducted in the late 1970s.

(6) E. B. Vermeer, 1997. In: Agricultural policies in China. OECD report, pp 141-163.

(7) Tarchitzky J. and H. Magen. 1997. Status of potassium in soils and crops in Israel, present K use indicating the need for further research and improved recommendations. A paper presented at the IPI regional workshop, Izmir, Turkey.

(8) Lupin, M., Magen, H. and Z. Gambash. 1996. Preparation of solid fertilizer based solution fertilizers under “grass roots” field conditions. Fertilizer News, 41, pp 69-72. New Delhi, India.