Soybean seed yield and protein response to crop rotation and fertilization strategies in previous seasons

Abstract

Annual crops dominate Argentinean landscapes with a majority of fields dedicated to soybean production. Consecutive years with full-season soybean crops are frequent and this practice is associated with organic carbon losses affecting soil chemical and physical properties. It is proposed that more intensive and diverse cropping sequences coupled with targeted fertilization may allow keeping near-neutral nutrient and carbon balances while improving successive crops performance. We conducted four on–farm experiments along six seasons in the Argentine Pampas where three crop rotations and two fertilization strategies (high and regular rates of N, P, and S) were evaluated. Crop rotations involved were i) soybean monoculture, ii) a typical wheat-soybean/maize/soybean rotation, and iii) a more intensified rotation consisting of wheat-soybean/field pea-maize/soybean. After five years, soil organic carbon was consistently lower under soybean monoculture compared to that under more intensive and diverse rotations. During the sixth and last season, identically managed soybean crops were grown in all treatments to determine the influence of previous management history on soil, plant nutrients, and on crop performance. Results indicate that crop rotation largely influenced soybean seed yield (range from 120 to 690 kg ha−1 yield increase) mainly through changes in water use affecting solar radiation interception and, by a lesser extent, the conversion efficiency of radiation into biomass and partition to seeds. Comparatively, increased fertilization rates in preceding seasons resulted in a lower seed yield response (range from nil to 180 kg ha−1), which indicates that fertilization strategies alone are ineffective to restore productivity levels after years of soybean monoculture. However, in most cases, the high fertilization strategy in previous seasons resulted in greater soybean protein concentration in seeds and in overall protein yield.