Indicadores da qualidade estrutural de um latossolo cultivado com oleaginosas em sistema de sucessão com soja e milho

Abstract

The physical quality of the soil is one of the sustainable agricultural factors and it could be altered by use and management systems. On the other hand, the search for cultivation alternatives of oleaginous crops, for rotation between cultures in notillage system, can be implemented in the Central-West region of Brazil and these soil structural alterations can affect these cultivations, especially in projects involving succession crops with soybean and maize can become of utmost importance. Thus, it was the objective of this research to evaluate the use of the least limiting water range as an indicator the structural quality of a Latosol cultivated in no-tillage system with different successions of oleaginous crops. Moreover, develop these successions models of load bearing capacity between preconsolidation pressure and volumetric water content. The experiment was carried out in field conditions, in Dourados, Mato Grosso do Sul state, Brazil, in a clayed Red Latosol (Rhodic Acrustox), during the years of 2009/10 and 2010/11. A randomized complete block design was used, containing 11 treatments, with four replicates. In the first year of the study (2009/10), the treatments consisted of oleaginous crops cultivated in no-tillage system in the autumn-winter seasons: sunflower (Helianthus annuus L.), rapeseed (Brassica napus L. e Brassica rapa L.), safflower (Carthamus tinctorius L.), crambe (Crambe abyssinica Hochst.) and to níger (Guizotia abyssinica Cass.), sown in succession to the soybean and maize crops in the summer, and the succession of soybean/maize (summer/autumn-winter), most farmed in the region. In the flowering of the cultures of autumn-winter, undisturbed soil samples were collected, in depths of 0-5 and 5-10 cm. In the second year of study (2010/11), the treatments were the cultivation of the soybean and maize during the summer, sown in succession to the oleaginous crops of autumn-winter: sunflower (Helianthus annuus L.), rapeseed (Brassica napus L. e Brassica rapa L.), safflower (Carthamus tinctorius L.), crambe (Crambe abyssinica Hochst.) and to níger (Guizotia abyssinica Cass.), and the succession soybean/maize (summer/autumn-winter). After the harvest of the soybean and maize crops in the summer, undisturbed soil samples were collected, in depths of 0-5 and 5-10 cm. There was an increase in the macroporosity and total porosity of the soil, and a reduction of the soil density when was used the culture of níger in succession of cultures in no-tillage system. The culture of níger implanted before or after the crops of soybeans and maize resulted in a smaller load bearing capacity and increased least limiting water range at the depths of 0-5 and 5-10 cm, therefore improving soil structure. The least limiting water range is an indicator of physical quality of the soil, can be used to identify the main physical limitations and how to adopt improved soil management techniques. After attainment the models of load bearing capacity, it was verified that the optimum moment to soil management in terms of water content in the soil, is different for the diverse oilseeds grown in succession with soybean and maize, resulting in an increase in the load bearing capacity with a reduction of the water content and increase of the soil density.