Residual da adubação fosfatada e plantas de cobertura: impacto na produtividade de soja após oito anos sem aplicação de fósforo

Abstract

Phosphorus is one of the main elements required by plant species, playing a direct role in key processes such as respiration and photosynthesis. Its demand has increased in recent years due to the higher yield potential of modern cultivars and the growing need for food production. However, in Brazilian tropical soils rich in iron and aluminum oxides there is a high phosphorus adsorption capacity, which reduces its availability to plants and compromises its use efficiency. This study aimed to evaluate the residual effect of phosphate sources and their interaction with winter cover crops on soybean productivity. The experiment was established in 2009 at the Federal University of Technology Paraná (UTFPR), Dois Vizinhos campus, and the evaluated crop season was 2023/2024. A randomized block design was used in a 3 × 8 factorial scheme, with three phosphorus sources (No P, Single Superphosphate, and Natural Phosphate) and eight cover crop treatments: black oat, ryegrass, common vetch, forage radish, blue lupin, rye, a mix (black oat, radish, and rye), and fallow. Phosphorus sources were applied from 2009 to 2015 at a rate of 100 kg ha⁻¹ of P₂O₅, with no reapplication since then. Dry matter production of the cover crops and subsequent soybean yield were evaluated. Images obtained by RPA (Remotely Piloted Aircraft System) were used to generate spectral indices, such as the Green Leaf Index (GLI), assisting in the comparison among treatments. The results showed that the use of cover crops significantly influenced soybean productivity, especially in treatments with the mix, rye, and lupin, which presented the highest average yields. Among the phosphorus sources, Natural Phosphate showed better residual performance compared to Single Superphosphate, particularly when associated with cover crops that produced more biomass and had greater nutrient cycling capacity. In the no-P treatment, the best performances were observed in plots with vegetative cover, highlighting the role of these species in mobilizing non-labile phosphorus and maintaining soil fertility. It is concluded that, even after eight years without phosphorus application, it is possible to maintain soybean productivity through the residual effect of phosphate sources, especially when combined with the strategic use of cover crops. This interaction strengthens sustainable agricultural practices, reduces dependency on fertilizers, and promotes greater nutrient use efficiency.