Intervalo hídrico ótimo (IHO) do solo em área sob sistema de plantio direto consolidado

Abstract

The physical quality of the soil in areas under no-tillage system is crucial for the longterm success and viability of the system. Despite all the benefits already proven, physical problems have been observed in several areas that are managed under NTS, causing concerns regarding the physical quality of these areas and possible structural degradation, mainly in clayey soils. The main physical soil attributes that directly affect plant growth are: water availability, aeration and soil mechanical resistance to root penetration. The Least Limiting Water Range (LLWR) of the soil is an indicator of soil physical quality that integrates the main physical parameters that affect plant development, it corresponds to the range of available soil water in which there are no restrictions by aeration (AP) and nor by soil resistance to root penetration (RP), with minimal limitations imposed on plant growth. The objective of this work was to determine the soil LLWR in an area with an Oxisol under NTS for over 20 years. Ninety samples of soil with preserved structure were collected to obtain the soil density (Ds), volumetric soil moisture, soil penetration resistance and determine the LLWR. The samples were divided into 5 groups with 18 rings, 9 for the depth of 0-10 and 9 for the depth of 10-20. The 5 groups were distributed in the area in order to generate variability of Ds. This variability was obtained by sampling locations from where there is greater machine traffic to locations with better structural quality and higher crop productivity. In the laboratory, water retention and RP curves were determined, in addition to Ds. To determine the LLWR, the RP critical limits of 2 and 3 MPa were considered. The DC was determined by the ratio between the Ds obtained in the samples and the Dsmax used for soils with the characteristics of the studied area. Using the value of 2 MPa as the RP limit, the moment when the LLWR was null and the Dsc was obtained was at the Ds of 1.31 Mg m-3, presenting a GC of 86%, a value considered low to impose limitations on the plants. At the limit of 2 MPa, 26.4% of the samples presented Ds>Dsc, in these places the plants can find limitations more frequently. For the limit of 3 MPa, the Dsc obtained was 1.49 Mg m-3 with GC of 97%, under these conditions only 5.74% of the samples presented Ds>Dsc. The 3 MPa limit was more adequate to determine restrictions for these soil conditions. The RP was the main limiting factor of the LLWR in the two limits considered, being highly sensitive to the increase in Ds. TheLLWR proved to be a more sensitive tool than the AD to determine the limitations suffered by the plants, being more adequate to evaluate the physical quality of the soil.