Structural soil quality and system fertilization efficiency in integrated crop-livestock system

Abstract

The nutrient use efficiency in integrated crop-livestock systems under system fertilization may be related to soil structural variations caused by grazing. These hypothetical cause-effect relationships are not known, which reflects a limited understanding of the underlying processes. This study evaluated the association between soil structural quality and system fertilization efficiency of phosphorus and potassium in an integrated crop-livestock system and a pure crop system. The treatments were two fertilization strategies (system fertilization and crop fertilization) in a factorial scheme with two production systems (an integrated crop-livestock system and a pure crop system) distributed in a randomized block design with four replicates. In the pure crop system, soybean was grown followed by Italian ryegrass as a non-grazed cover crop. In the integrated crop-livestock system, the ryegrass was grazed by sheep. In the crop fertilization strategy, phosphorus and potassium were applied at the soybean planting, and nitrogen in the ryegrass establishment. In the system fertilization strategy, nitrogen, phosphorus, and potassium were applied during the establishment of ryegrass. Soil physical quality indices were calculated for the beginning, middle, and end of the pasture phase (2020) and at the soybean harvest (2021). Forage and soybean production were also evaluated. Based on the soil physical quality index, the soil’s ability to perform its physical functions decreased from 94% under an integrated crop-livestock system to 89% under a pure crop system. The results indicated higher total forage production (36%) and soybean yield (13%) in the system fertilization strategy as compared to the crop fertilization strategy. Moreover, the integrated crop-livestock system produced more forage (31%) and soybean grains (15%) than the pure crop system. The study provides the first evidence that higher structural quality of soils in an integrated crop-livestock system favors crop yields at all stages of production. However, the nutrient use efficiency in system fertilization is only partially explained by the soil’s physical quality.