towett soil plant spectroscopy for evidence-based agronomy

Soil-Plant Spectroscopy for Evidence-Based Agronomy

Erick Towett and Keith Shepherd

Land Health Decisions

World Agroforestry Centre (ICRAF), Nairobi, Kenya

SCALING PRECISION NUTRIENT MANAGEMENT (PNM) PRACTICES IN SOUTH ASIAN CEREAL SYSTEM, MUSSOORIE, INDIA, APRIL 27 – 29TH, 2016

Getting the best out of light

Context

• Currently, predicting a response to fertilizer addition usually involves performing a soil test (usually chemical extraction), and interpreting the test results based on critical limits developed from agronomic trials and pot studies.

• The relationship between soil tests and relative yield (RY) response to fertilizer is subject to the influence of environment (e.g. water, temperature, soil type & chemistry) and management (e.g. cultivation, sowing date).

• Variability in response and risk are ignored when making recommendations.

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Calibrating relative yield response to soil tests

| PNM South Asia, Mussoorie | India | 27-29 April 2016|

• Degree of precision is often low when the soil test calibration is based

on a wide range of experiments conducted on many soil types, over

many years, by many different scientists.

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Figure 1: Example of a derived critical soil test value in Australia.



• Conventional soils tests are cumbersome and of variable accuracy when predicting relative yield response to nutrient inputs. Huge problems with reproducibility across labs.

• Soil tests based on soil extracts do not characterize all the nutrient pools that determine a soil’s ability to re-supply the soil solution, e.g. readily mineralizable organic P, sorbed P, and slowly extractable K.

• The conventional tests do not produce any absolute measure of nutrient availability, but always have to be calibrated using extensive agronomic field trials on different soil types to be able to predict crop response to applied nutrients.

• Calibration trials not done in many regions. Uncertainty ignored.

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• New direct soil spectral methods using only light (infrared & X-ray) hold promise for providing rapid, low cost & reproducible soil characterization.

Provides a fingerprint or spectrum that relates to organic and mineral composition and therefore soil functional properties

Simplicity of measuring light reflected off soils/plants at different wavelengths.

Highly reproducible technology used by pharmaceutical industry

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Simplicity of light for measurement of soil health


Mid-infrared spectrometer Portable XRF analyser

• Light-based technology moving rapidly towards portable and miniature instruments that could be used in the field.

• New spectral metrics emerging that may replace conventional soil guidelines.

• Portable X-ray fluorescence (pXRF) can directly measure what the plant is doing – total element concentrations of macro and micro nutrients.

Simplicity of light for measurement of soil health

5 | PNM South Asia, Mussoorie | India | 27-29 April 2016|

Spectral Shape Relates to Basic Soil Properties

• Mineral composition • Iron oxides • Organic matter • Water (hydration, hygroscopic,

free) • Carbonates • Soluble salts • Particle size distribution

Functional properties

| PNM South Asia, Mussoorie | India | 27-29 April 2016| 6

• Conventional soil tests (Mehlich P&K) consistently predict poorly from spectral tests.

– Serious reservations whether the test is telling us anything useful – it

does not relate to any fundament soil properties.

– Soil P test does not give you organic P, which is so critical in soils, nor P sorption, which is also critical for the rate at which P can be supplied to the soil solution.

– The soil test K does not tell you about the intermediate K pools, which are also important for maintaining K supply, but which MIR detects through the mineralogy.

Spectral prediction performance


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Spectral tests better predict soil nutrient supply capacity, as determined by crop nutrient uptake potential, than conventional soil P, K, micronutrient tests

Soil MIR–TXRF Complementarity?

• Spectral methods could predict plant nutrient uptake potential and crop yield responses to applied nutrients as well or better than soil tests based on soil extracts, or at least complement existing soil tests.


• Robust - basically counting atoms!

• Enables pairing of soil and plant testing at multiple georeferenced locations – towards an evidenced based approach.

• Can also sample natural variation in crop growth in landscapes to develop norms.

pXRF for plant analysis


• pXRF spectroscopy is a breakthrough technology as it allows us to quickly and cheaply determine plant nutrient status which we can use to test traditional soils tests and develop new soils tests using spectroscopy.

• Ten universal calibrations and standard operating procedures developed by ICRAF for macro-and micro nutrient analyses in soil, plant and fertilizer samples.

pXRF calibration

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Light elements (Mg-S) analyzed performed well under 3 data

acquisition parameters for the pXRF.

• Our work using the simplicity of light or spectral tests can speed up soil testing and reduce costs.

• An ideal system for soil and plant analysis would include accuracy, replicability, portability, and minimal sample preparation.


Context

• The huge missing link is testing and validation of plant nutrient uptake and crop response to fertilizers in relation to soil tests.

• Plant tissue analysis can be used to directly identify nutrient-related problems; rule out nutrition as the source of a problem; monitor nutrient status as a basis for managing a crop fertility program; and/or evaluate the effectiveness of a fertility program.

• pXRF will enable greater emphasis on plant tissue analysis – tell us what is limiting now and what will be limiting next. IR for plant N.

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Crop response to spectral test


To speed up the process of developing calibrations of crop response to spectral test (and conventional soil tests) for soil fertility recommendations, we have developed a rapid screening approach using plant growth chambers in the lab.

Plant growth bioassays in test tubes for high throughput diagnosis of soil macro and micronutrient deficiencies.

• Plant growth potential and response to nutrients can quickly be measured this way and related to IR spectra of the soils as well as to convectional soil tests.

Crop response to spectral test

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• Around 119 million farmers in India depend on agricultural production for their livelihoods. Information on soil health and nutrient status is of high value to farmers to help them apply the right types and amounts of nutrient inputs and management practices to their soils to maximize their profitability.

• Current annual capacity of existing soil laboratories in India is ≈ 1.3 million soil

samples per year, against a projected demand of about 40 million samples per year as planned by the Government.

• ICRAF working closely with the Indian Institute of Soil Science (IISS) of the Indian

Council of Agricultural Research (ICAR) on an initiative to transfer to India its light-based technology for rapid and cost effective analysis of soil health and nutrient status.

• ICRAF has established a fully functional MIR and pXRF laboratory at IISS and trained 12 Indian scientists to use the technology.

• Scanning soil archives including from fertilizer response trials.

India technology transfer and capacity building


• IAMM, Mozambique

•AfSIS, Sotuba, Mali

•AfSIS, Salien, Tanzania

•AfSIS, Chitedze, Malawi

•CNLS, Nairobi, Kenya

•SoilCares, Kenya (mobile)

•IISS, Bhopal, India

•YPC, Kunming, China

•ATA, Addis Ababa, Ethiopia (6)

•CNRA, Abidjan, Cote D’Ivoire

•KARI, Nairobi, Kenya

• ICRAF, Yaounde, Cameroon

• IAR&T, Obafemi Awolowo

University, Ibadan, Nigeria

• IAR, Zaria, Nigeria

•FMARD, Nigeria

• IITA, Ibadan, Nigeria

• IITA, Yaounde, Cameroon

•SARI, Salien, Tanzania

Soil-Plant Spectroscopy

Support Group

PhD and MSc studentships and training/exchange between ICRAF and Universities across the globe.

Over 500 visitors/year to ICRAF Spectral Diagnostics Lab

Training for agricultural officers in 47 counties in Kenya through ChromAfrica LLC Support to other projects: -Optimizing Fertilizer Recommendations in Africa (OFRA) - World Bank Living Standards Management Study -Transformation of agronomic research and delivery services for smallholder farmers in maize-based systems of Sub-Saharan Africa (TAMASA)

Spectral Lab Network/Outreach

• ICRAF supports a network

of 30 MIR spectrometers

for soil fertility evaluation &

digital mapping of soil

properties at national and

sub-national levels.


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• Digital mapping of soil properties to identify soil fertility constraints, target fertilizer supply/recommendations and soil management interventions, and map soil carbon stocks

• Soil health baselines and monitoring in sustainable land management projects for impact

• Soil testing services for smallholder farmers

• Soil characterization in long-term soil monitoring initiatives (e.g. VitalSigns, World Bank Living Standards Management Study)

• Evidence-based (predictive) agronomy through low cost soil and plant nutrient analysis in multi-location field trials, and plant bioassays in growth chambers

• Fertilizer, compost and organic resources quality testing

• Characterization of mine reclamation sites, including heavy metal detection in soils and plants

• Nutritional and product quality testing and quality control in harvested products (e.g. selenium in grains)

Spectral applications


Thank you

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towett soil plant spectroscopy for evidence-based agronomy

Technology