Contribution of Urochloa as off-season crop to mitigate the water stress and soil compaction for soybean root growth

A third crop using cover plants may be a sustainable strategy to enhance diversification in no-tillage systems and mitigate soil compaction. This study aimed to evaluate the performance of Urochloa brizantha grown in compacted soil under different water deficit conditions and its potential to produce biomass in the short and medium term, as well as its effects on a subsequent soybean crop. A greenhouse pot experiment was conducted using a randomized block design in a 3×2×2 factorial arrangement, with three soil moisture levels: 80–90%, 60–70%, and 40–50% of field capacity (FC); two growth durations of U. brizantha cv. Marandu: 28 and 70 days after emergence; and two management practices: U. brizantha grown alone or prior to soybean. The 6–12 cm soil layer was artificially compacted to a bulk density of 1.65–1.70 Mg m⁻³. After cultivation, undisturbed samples from the compacted layer were collected to assess soil physical and hydraulic properties. Shoot and root biomass were quantified in both compacted and uncompacted layers. U. brizantha exhibited moderate water deficit tolerance, but shoot dry matter and soil air permeability declined under severe moisture limitation. Cultivation for 28 days was insufficient to improve soil physical-hydraulic conditions or support subsequent soybean biomass. However, 70 days of U. brizantha cultivation significantly reduced soil compaction and improved porosity, enabling adequate soybean development. Under greenhouse conditions, cultivating U. brizantha for 70 days is a viable third-crop strategy, enhancing plant diversity and mitigating compaction in no-tillage systems under moderate water stress.