Soil resistance to penetration in integrated crop-livestock with grazing intensities and fertilization

Abstract

Inadequate management of agricultural systems induces soil degradation. In livestock grazing, the low nitrogen supply associated with intensive grazing can lead to soil compaction, which directly affects crop productivity. Periodic monitoring of soil compaction through soil resistance to penetration (RP) is a rapid, easy and economic way to evaluate the effect of different management systems on soil physical attributes. The objective was to evaluate the effect of grazing intensities and nitrogen fertilization in two winter/summer seasons (black oat/maize/black oat/soybean) on soil RP in a crop-livestock system. The experimental design was a randomized complete block with four replicates in a factorial 2 × 3. The first factor consisted of residual heights of black oat pasture (15 and 7 cm), under rotational grazing, and the second factor were nitrogen rates applied in black oat topdressing (0, 75 and 150 kg N ha^-1). Soil RP was measured using an Eijkelkamp® electronic penetrograph to a depth of 80 cm. At the same time, samples were collected to determine gravimetric moisture. No interaction was observed between grazing intensities and N rates, and RP values ​​were below the levels considered critical to crop and pastures growth and establishment (i.e., < 2,5 MPa). In the first year, 75 kg N ha^-1 resulted in the highest depth compaction while intensive grazing (7 cm) resulted in the highest RP. In the second year, plots without N resulted in lower RP, mainly in the superficial layers (0-5 cm). However, the rate of 150 kg N ha^-1 presented greater compaction in the 15-20 cm layer after grazing. The high moisture levels in depth reduced RP in all evaluated periods, highlighting the close relationship between RP and soil moisture. The rotational grazing system with residual height monitoring was fundamental to minimize the effects of animal trampling on the soil.