Soil fertility and nutrient budget after 23-years of different soil tillage systems and winter cover crops in a subtropical Oxisol

Growing cover crops to recycle soil nutrients in no-tillage systems provide nutrients accumulation in more labile forms in the soil surface reducing the demand for fertilizers. This study aimed to evaluate the long-term (23-yrs) effect of soil tillage systems and winter cover crops on (i) soil acidity, (ii) nutrient availability, and (iii) P and K budget in a subtropical Oxisol from Southern Brazil. The experiment was established in 1986 with six winter treatments (blue lupine, hairy vetch, oat, radish, wheat, and fallow) and two tillage systems (conventional tillage-CT and no-tillage-NT) in a very clayey Rhodic Hapludox in Southern Brazil. Nutrient availability (P, K, Ca, and Mg) and soil acidity (pH, potential acidity, base and Al saturation) were evaluated in five soil depths (0-5, 5-10, 10-20, 20-30, and 30-40 cm). Nutrient budget was calculated considering the inputs (amount of P and K applied via fertilizer) and outputs of P and K from the system (exported by the grains), and the soil available P and K before and after 23-years of experiment. Continuous NT system for 23-years resulted in higher soil fertility in the topsoil (0-10 cm) compared to CT, but with some limitations of nutrient availability and soil acidity below 10 cm depth. Long-term NT builds up a strong gradient of nutrient availability, with higher concentration of nutrients on the soil surface layers that abruptly decrease with soil depth, unlike CT. Surface application of lime in NT reduced soil acidity up to 20 cm compared to CT. The budget of P was negative for all treatments, highlighting the P-sink behavior of this strongly weathered subtropical Oxisol. However, NT system resulted in less negative budget compared to CT and, therefore, higher efficiency of use of P. Growing cover crops in the winter is effective to increase P and K availability through plant cycling, but the plants grown in winter did not affect soil acidity. Nutrient cycling by winter cover crops reduced P and K losses, especially when the soil is not plowed. Fallow in the winter decreases the use efficiency of P and K. Among the cover crops tested, black oat stood out by its greater production of biomass, resulting in higher P and K availability in the soil surface. Lupine resulted in a greater cycling of P possibly due to its ability to absorb P from less labile forms in the soil.