Relação entre a produtividade de trigo e a liberação de nutrientes de culturas de cobertura pré-trigo

Abstract

Cover crops promote nutrient cycling and increase the productivity of crops grown in succession. However, even under no-tillage, sustainable practices are not guaranteed: the lack of rotation and crop residue is common, leaving the soil exposed during the fallow autumn period in southern Brazil. Among producers, the perception prevails that cover crops do not generate income nor cover establishment costs. The objective of this study was to evaluate the relationship between the nutrients released from the dry matter of autumn cover crops and wheat yield. The experiment was established after soybean harvest on a private property in Vitorino, PR, with three treatments: fallow (soybean residue), forage radish, and Mix 440® (Millet BRS 1501, Buckwheat IPR 92, and Forage Radish IPR 116). A randomized block design with six replications was used, totaling 18 plots. At 54 days after sowing the cover crops, the residues of forage radish and Mix RX 440 were placed in litter bags (20 g each), then dried, weighed, and analyzed across nine periods: 0, 15, 30, 45, 65, 85, 105, 135, and 165 days after field deposition, assessing dry matter decomposition and nutrient release (N, P, K). Wheat cultivar TBIO Ponteiro, with a medium to late cycle, was then sown over the experiment, using a seeding rate of 170 kg ha¹ and base fertilization of 300 kg ha¹ of NPK (10-15-15). Subsequently, nitrogen fertilization was applied during wheat tillering, using 150 kg ha¹ of ammonium nitrate (NHNO) (33-00-00). To compare the total amount of nutrients released (N, P, and K) from the dry matter of soybean fallow, forage radish, and Mix RX 440, analysis of variance (ANOVA) followed by Duncan’s multiple range test ( = 5%) was used. The remaining dry matter at 0 and 165 days and the total N, P, and K released by cover crops from 0 to 165 days were correlated with wheat grain yield using Pearson correlation ( = 5%). The use of autumn cover crops increased biomass input, nutrient release, and wheat grain yield compared to soybean fallow, with forage radish showing the greatest effect. Wheat grain yield was more strongly associated with higher initial biomass accumulation and greater release of N, P, and K—especially N and K—than with the final amount of residue remaining on the soil. Therefore, the chemical quality and decomposition rate of cover crop residues are more important for wheat productivity than merely the volume of leftover straw.