Soybean yield, seed protein and oil concentration, and soil fertility affected by off-season crops

The main cropping system in Brazil is soybean-maize off-season, particularly in tropical climate regions. How-ever, there is a lack of information about the effects of alternative off-season crops on soybean performance and soil chemical fertility. The objective of this study was to evaluate, in a long-term experiment, the effects of off-season crops on soybean yield, seed protein and oil concentration, and soil chemical fertility under a no-tillage system. A seven-year experiment was conducted in Londrina, Paran ' a, Brazil. Treatments comprised six crop systems in the soybean off-season: (i) maize with nitrogen (N) fertilizer topdressing (80 kg N ha-1, (ii) maize without N fertilizer topdressing, (iii) wheat without N fertilizer topdressing, (iv) ruzigrass (Urochloa ruziziensis) without fertilizers, (v) showy rattlebox (Crotalaria spectabilis) without fertilizers, and (vi) unplanted fallow. Maize and wheat were used as cash crops and ruzigrass and showy rattlebox as cover crops. Ruzigrass had the highest straw production (average of 6.8 Mg ha-1 year-1) and improved soil fertility, especially organic carbon and potassium concentrations in the superficial soil layer. Ruzigrass and wheat off-season provided the highest soybean yields in succession (4311 and 4228 kg ha-1, respectively), whereas maize without N and fallow resulted in the lowest soybean yields (3841 and 3825 kg ha-1, respectively). Ruzigrass off-season provided the greatest yield stability of soybean and the fallow the lowest yield stability (coefficients of variation of 14.70 % and 23.78 %, respectively). The highest soybean seed protein concentration was observed with ruzigrass (368 g kg-1) and the lowest with fallow (353 g kg-1). The highest seed oil concentration was observed in maize with N and showy rattlebox (224 g kg -1 for both off-season crops) and the lowest with wheat (216 g kg -1). The ruzigrass provided the highest soybean seed protein and oil yields (1586 and 945 kg ha-1) and fallow the lowest (1352 and 845 kg ha-1). The ruzigrass used as soybean off-season cover crop improved the soil chemical fertility and soybean grain yield.