Diagnóstico da compactação do solo em sistema plantio direto e monitoramento dos efeitos do preparo mecânico nas propriedades do solo e na produtividade de grãos

Abstract

The no-tillage system (NT) is proven to be sustainable in grain cultivation, however, studies indicate that the adoption of NT can cause soil compaction problems. In this context, an alternative recently presented in the literature for the mitigation of soil compaction under NT is occasional tillage (OT), which consists of mechanical soil tillage in order to break up the compacted layers. However, caution is needed in the adoption of the OT, since the soil disturbance violates this basic principle of the NT. In this way, so that the adoption of the OT does not undo the ecological services achieved by the NT, an accurate diagnosis of soil compaction is necessary, allowing mechanical interventions to be carried out at times when the level of compaction is compromising crop productivity. From an agronomic point of view, changes in physical properties do not always indicate soil compaction, as they often do not express a drop in crop productivity. Thus, studies on soil compaction in NT areas should relate diagnostic attributes to variations in agricultural productivity. There are no studies in the literature that monitored the long-term effects of OT on soil properties and its effects on crop productivity. The objectives of this study were (a) to evaluate the effect of OT and OT associated with liming on soil properties and its effects on grain yield in the long term; and (b) to evaluate the effects of the pre-established frequency of subsoiling (every two and every three years) on soil physical properties and grain yield. For this, a study was conducted in an experiment implemented in strips in the year 2015 at Fazenda Santa Helena, in the municipality of Nazareno - MG, where three implements were tested at different frequencies of OT in the mitigation of compaction as well as its reflexes on productivity. Thus, the treatments were: NT – continuous no-tillage system; NTS2 - NT subsoiled predominantly every 2 years; NTS3- NT subsoiled every 3 years; NTSSL – Subsoil NT in 2015 + surface limestone application; NTSDL - NT subsoiled in 2015 + application of limestone in depth; NTC – NT scarified to a depth of 26 cm in 2015. Occasional tillage in soil under consolidated NT promoted an improvement in the physical quality of the soil with an increase in grain yield of direct duration of 18 months, and some beneficial residual effect on total yield of the 5 years of experiment, being that all the mechanized treatments only once presented a productive average superior to the control treatment, however the adoption of pre-established frequency of preparation proved to be harmful to the productivity of the cultures, since it presented the worst productive performance in the accumulated from the 9 crops. At the time of greatest water restriction in the experiment, it was possible to show more clearly the differences between treatments. The equipment used in subsoiling differed only in the persistence of structural relief effects, but in the accumulated production at the end of the experiment, there was no difference between the implements.