Sustainable intensification of agriculture improves soil nitrogen in the argentinean humid pampas

Abstract

In the Argentinean Humid Pampas, intensification practices like crop rotation, cover crops (CC) and fertilization can improve soil nitrogen (N) balance. This study aimed to assess how intensification practices affect soil organic N (Norg), Norg in the particulate fraction (PF-Norg), and N mineralized during a short-term (7 days) anaerobic incubation (aN) in a 4-yr experiment with soybean [Glycine max (L.) Merr.]-based crop sequences. At two sites differing in initial soil organic matter (SOM), five crop sequences were evaluated: continuous soybean (Sb); continuous soybean fertilized with phosphorus (P) and sulphur (S) (Sbf); CC/ PS-fertilized soybean (Sbf/CC); nitrogen (N)-fertilized CC/ PS-fertilized soybean (Sbf/CCf); NPS-fertilized crop rotation (Rot). In addition, at one site we evaluated the carbon (C) and N accumulation in CC dry matter, CC inclusion effect on soil inorganic N dynamics, and C and N content in soybean grain and shoots. At site 1 (low SOM), Norg and PF-Norg increased in intensified sequences as compared with Sb and Sbf, whereas no differences among treatments were detected at Site 2 (high SOM). Also, an increase in aN was observed in intensified treatments at both sites. At site 2, soil sampling took place at soybean sowing and harvest during two growing seasons. At soybean sowing, Sb and Sbf presented ∼30 kg NO3--N ha-1 more than intensified sequences, whereas at soybean harvest this trend was the opposite. In the fallow, CC captured N, minimizing N leaching, without affecting N accumulation in soybean. Our results indicate that intensification in soybean-based sequences improves soil N balances.