Soybean Yield Gap Analysis and N Balances in Agricultural Systems of Argentina As Quantified By the Cropgro-Soybean Model.

Soybean dominates agricultural systems in Argentina, occupying ca. 19 million hectares in 2011 and producing ca. 40 million tons. This crop is cultivated in an ample area (ca 26° 18′ to 37° 59′ S and 58° 13′to 65° 24′), comprising soils with different effective depth (from 50 to 200 cm depth) and potential fertility (organic matter content between 5.5 to 38 g kg^-1). Also, climatic conditions in the soybean production area allow a wide choice of planting dates x genotypes combinations that may generate different seed yield potential (YP) and yield gaps (YG). Calculations of soil nitrogen (N) balances are a useful for estimating the magnitude of nitrogen loss/gain when using legume crops in agro ecosystems. The objectives of the present study were to: i) evaluate YP, water-limited yield potential (WLYP) and the YG between them as affected by planting date and genotype and ii) Build simple N balances for estimating N export with seed in the soybean production area of Argentina using crop modeling. Seed yield was simulated using CROPGRO-Soybean model. Six locations within the soybean production area representing the more important soils were chosen. In each location two typical planting dates and two widely used genotypes were selected for simulation. A seasonal analysis was performed using 33 years of climatic records.  The largest YG were observed in sites characterized by shallow sandy soils and great water deficit during the crop season. On the opposite the shortest YG were estimated in the main production area of Argentina, characterized by soils that can accumulate more than 300 mm at planting with a rainfall regime above 900 mm per year. Planting date showed larger YG than genotype choice. N balances were built and the need of a precise estimation of biological N fixation is discussed.