Effects of silage crops between crop seasons on soybean grain yield and soil fertility in tropical sandy soils

Soybean production in sandy soils under the recovery process presents risks that can be mitigated by growing crops between crop seasons, focused on silage production, which can assist in environmental improvement, accelerating soil recovery, in addition to improvement in soybean grain yield. The objective of this study was to evaluate soybean grain yield, silage yield and soil fertility in an area converted from degraded pasture to soybean production. The study was conducted a sandy soil, in Presidente Bernardes, Sa tilde o Paulo, Brazil, from 2015 to 2018. The treatments consisted of six silage crops (maize, sorghum, sunflower, palisade grass, millet, and pigeon pea) and a control with fallow (March-July) between soybean crop seasons (October-March). The mean soybean grain yield in the soybean-millet system (4400 kg ha-1) was, on average, 42% higher than that in the soybean-fallow (3100 Mg ha-1). The mean soybean grain yield (three crop seasons) in the systems with maize, sorghum, and sunflower was similar to that in the soybean-fallow system. The mean palisade grass silage yield was higher in two of the three crop seasons (16.8 Mg ha-1); maize also presented a good performance in the second crop seasons (10200 kg ha-1). The higher palisade grass silage production resulted in higher mean (three crop sea-sons) extraction of macronutrients (136, 129, 65, 54, 13.2 9.6 kg ha-1, for K, N, Ca, Mg, P, and S, respectively). The growth of millet and palisade grass crops between soybean crop seasons improved the soil fertility, but the effect of millet was faster (first harvest). The main soil fertility attributes affected were: phosphorus, potassium, organic matter, cation exchange capacity, and base saturation. The best crop option to be grown between soy-bean crop seasons are millet and palisade grass for silage when focused on improvements in soil fertility and grain yield of the following soybean crop, and the choice between these two species depends on the farmer's priority.