Long-term cover-cropping systems: 15N-fertilizer recovery and soil organic matter quality affected by intercropping

Abstract

This research is a continuation of a long-term cover-cropping experiment initiated in the 2006/07 season at Experimental Lageado Farm of the College of Agricultural Science at UNESP, in Botucatu - SP. This is one of the longest cropping system experiments in São Paulo State, registered in the Global Long-Term Agricultural Experiment Network, organized by Rothamsted Research. Since its inception, nitrogen (N) recovery from fertilizer in the soil-plant system has never been evaluated. Given the importance of N to plant nutrition, we hypothesized that cropping systems with greater plant diversity through cover cropping inserted in the intercropped would lead to greater recovery of N-fertilizer, and potentially extracting less N from Soil Organic Matter (SOM). Therefore, the objective of this study is to evaluate the effect of different intercropped systems on chemical and physical attributes of soil, SOM quality, root growth, nutrition and productivity of corn and soybean in the rotation sequence, as well as recovery of N-fertilizer in soil to 1.0 m depth, in labile and stable fractions of SOM, and in plants. The treatments consist of four cropping systems (System I - Season-off-season + Fallow; System II - Season-off-season + Forage; System III - Season-off-season + Green manure; IV - Season-off-season + Forage + Green manure). All treatments will consist of soybean during the season and with corn in the off-season (I - monocropped; II - intercropped with Urochloa ruziziensis; III - intercropped with Crotalaria spectabilis; IV - intercropped with U. ruziziensis + C. spectabilis). Enriched ammonium sulfate (15NH4)2SO4 will be the source of N fertilizer with isotopic abundance of 7% as 15N. (AU)