Soil aluminum saturation threshold for subtropical crops in no-tillage system

Context Neutralising native soil Al3+ is crucial in subtropical agriculture before implementing no-tillage (NT).Aims The aim of this study was to monitor variations in soil Al saturation and crop yields over 34 years in a field trial under NT, to define the best rate and frequency of lime reapplication for maximum productivity of grain and forage crops.Methods We measured the soil Al3+ saturation in 11 soil sampling seasons in three soil layers (0-5, 5-10, and 10-15 cm). From these 11 soil samplings, the Al saturation was extrapolated for the harvesting day of each crop by fitting a sigmoid model with five parameters. Then, Al saturation values of each year were plotted against the relative crop yields. From that, the critical Al saturation at which crop yield declined by more than 5% was estimated by a linear plateau model.Key results We observed that the yields of six of the 10 soybean crops, and all corn, millet, and black oat crops were not decreased even though the soil had been cultivated for 34 years without reapplying lime. The critical Al saturation values in the 10-15 cm soil layers for soybean, wheat, and cover crops were 44, 24 and 20%, respectively.Conclusions The soybean, corn, and wheat varieties available for Brazil's subtropical region are tolerant to high Al3+ saturation, but responsive to liming. It is possible to maintain high crop yields in the long term by reapplying limestone on the soil surface.Implications It is imperative to establish an agronomic soil profile without Al3+ when adopting NT for a diverse crop rotation system. The combination of NT, Al-tolerant varieties, and reapplication of surface limestone is a suitable strategy to optimise both grain and forage yields. Agricultural production models in subtropical regions should involve the use of Al-tolerant plant varieties that respond well to the application of lime. We have been monitoring soil reacidification and its impact on crop yields for more than 3 decades following the conversion from conventional to no-tillage cultivation. The tolerance of the varieties to Al3+ made it possible to obtain high and stable yields only with superficial reapplications of lime, because the natural potential acidity had been amended when adopting no-tillage.