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Evaluation of the Variable Rate Fertilization in winter crops for shallow soils using soil depth maps and crop simulation models in southeastern Pampas, Argentina

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  131620904,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: http://dx.doi.org/10.13031/aim.20131620904) @2013
Authors:   Gabriel G Vazquez-Amabile, Martin Gonzalo, Martin Pella, Sebastian Galbusera, Gustavo B. Cueto
Keywords:   Site specific management Crop simulation models Variable Nitrogen Fertilization Greenhouse gas emissions Shallow soils Argentina

Abstract. Variable fertilization rate is often difficult to prescribe under rainfed agriculture, since it depends on soil limiting factors and year-to-year weather variations. Soil spatial variability is not easy to map when differences are due to textural changes or chemical properties that affects plant growing and, therefore, its potential yield. In southern Buenos Aires province, Argentina, the main limiting factor for cropping is soil depth, limited by a limestone layer. In that region, soil depth variation is very significant and may vary into the field, from 40 cm up to 1.2 m depth in short distances. Since soil depth determines the soil water storage capacity, most of the years, this factor explains the crop yield spatial variation within the field. However, crop yield spatial variability change from year to year depending on the rainfall amount and frequency. Crop simulation models, such as CERES-wheat are valuable tools to analyze year-to-year- yield variability for different soils and fertilization rates. In the last years, GPS technology made possible to map soil depth at relative low cost, providing valuable information at field scale, to decide crop rotation and crop management practices according to the average soil depth and its variability. This kind of maps allows identifying areas of high and low potential yields, which might require higher and lower amounts of nutrients. In this study, the combination of soil-depth maps with crop simulation models is evaluated as a tool to be used by farmers and advisors to design site specific management strategies. On-farm experiment based on field scale strip-trials were carried out during two years, at two locations, to evaluate crop yields under both uniform and variable fertilization rate of Nitrogen for winter crops. Yield maps records were used to evaluate the differences between variable and uniform fertilization rate, at different soil depths. Nitrogen Fertilization rates were established for 4 soil depth ranges (30 cm; 50 cm ; 80 cm and more than 1 m) according to the demand of nutrients to reach the average maximum yield. Economical benefits of this practice were analyzed, as well as its environmental impact due to available N for leaching and the greenhouse gas (GHG) emissions of both strategies.

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