L. K. Heng
FAO/IAEA Agriculture and Biotechnology Laboratory,
Soil Science Unit, Seibersdorf, Austria
l.k.heng@iaea.org

P. Moutonnet
Joint FAO/IAEA Division, Vienna, Austria
p.moutonnet@iaea.org

W. A. Baethgen
IFDC, Muscle Shoals, AL 35662, USA
baethgen@undp.org.uy

Introduction

    About 40% of wheat produced in developing countries is irrigated. However, efficient use of water and nutrients (especially nitrogen fertilizer) under irrigated conditions in these countries is low based on international standards. In 1997, developing countries used more than 50 million metric tons of nitrogen fertilizer, worth more than 16 billion US$ (FAO, 1997). However, studies conducted using ¹⁵N techniques showed that only 30-40% of the nitrogen fertilizer that is being applied is utilized by crops. The rest is lost to the atmosphere or leached to the groundwater. The joint Division of Nuclear Techniques in Food and Agriculture of the Food and Agriculture Organization (FAO)/International Atomic Energy Agency (IAEA) recognized the importance and implications of this problem. It implemented a Coordinated Research Project (CRP) entitled “The use of nuclear techniques for optimizing fertilizer application under irrigated wheat to increase the efficient use of nitrogen fertilizer and consequently reduce environmental pollution.” The goal of this CRP was to investigate fertilizer N uptake efficiency of a wheat crop, grown under irrigated conditions through an interregional research network that involved countries that grow large areas of irrigated wheat. One of the main objectives was to use ¹⁵N and soil-moisture neutron probes to determine the fate of applied nitrogen fertilizer, to trace water and nitrate movement in the soil, and to increase the nitrogen and water-use efficiency in wheat cropping systems, ultimately reducing environmental pollution. A second objective was to develop a database from the experimental data collected and to apply the CERES-wheat crop simulation model of the Decision Support System for Agrotechnology Transfer (DSSAT) to formulate specific management strategies and nitrogen fertilizer recommendation for the various production and climatic conditions.

    The project was conducted between 1994 and 1998 through the technical coordination of the Soil and Water Management and Crop Nutrition Section of the Joint Division of Nuclear Techniques in Food and Agriculture. Fourteen member states of the IAEA and FAO participated, including Austria, Bangladesh, Brazil, Chile, China, Egypt, France, India, Mexico, Morocco, Romania, Syria, Turkey and United States of America (Figure 1).

A brief overview of the participating institutions and the experimental design implemented at each site is presented in Table 1. The specific nitrogen fertilizer types, rates, application methods, and timing of N application are also shown in Table 1. A detailed description of each experimental setup and the specific objectives of each participating institution can be found in the final project report (IAEA-TECDOC-1164, 2000), which can be downloaded under “Coordinated Research Projects” at www.iaea.org/­programmes/­nafa/­d1/­index.html. In general, the selected nitrogen fertilizer rates represent 0%, 50%, 100% and 150% of the regionally recommended nitrogen fertilizer application rates.

General Observations

    In Table 2 the amount of rainfall received during the growing season, as well as irrigation and pre-season irrigation applied in each country are shown. In several countries a large quantity of water was used to produce wheat. As a result, large losses of irrigation water were observed, e.g., China and India and on the sandy soils in Egypt. It was also found that a well-scheduled sprinkler irrigation system helps to reduce potential irrigation water losses and increases nitrogen fertilizer recovery, e.g., Syria (results not shown). In general, the fertilizer recovery was relatively low, with most countries recovering less than 60% of total nitrogen fertilizer applied. It was also observed that the first split application of N fertilizer, applied at planting, was usually recovered less efficiently than the second split application, applied at the end of tillering, e.g., Bangladesh, Brazil, India, Morocco, Romania, Syria and Turkey.

DSSAT Simulations

    During the course of the experiments, the minimum data sets for soil, crop and weather were collected to be able to run the CERES-Wheat simulation model. A relatively good agreement between observed and simulated data was obtained for both grain yield (Figure 2a) and biomass (Figure 2b) The data shown in figure 2 include the data for all 14 participating countries collected over the four-year study period. The model also simulated other soil and crop parameters reasonably well for most of these countries. As a result, the CERES-Wheat received a rigorous evaluation for various production practices and across different climatic conditions.

Conclusion

    Improved management of soil water and fertilizer is needed to maximize resource use and to reduce potential losses. The CERES-Wheat model, which is part of the DSSAT suite of simulation models, was able to explain the differences in crop and soil information collected over a wide range of environments. The next step is to apply this information to refine various specific management strategies with respect to recommendations for fertilizer applications for the individual countries that participated in the study.

References

FAO, 1997. FAO Yearbook. Fertilizer, Vol.47.

IAEA-TECDOC-1164, Vienna, 2000. Optimizing nitrogen fertilizer application to irrigated wheat.

For more information visit

www.iaea.org/programmes/nafa/d1/index.html

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