Effect of the organic matter from crop residues on the structuration of an Oxisol, at semi-arid region

Abstract

Crop residues can either be incorporated into the soil or left on the soil surface as a mulch producing soil organic matter in different quantities, having many potential benefits such as reducing soil compaction caused by passage of agricultural machines. The aim of this study is to evaluate the effect of crop residues such as maize and bean straw on the dynamic properties of a sandy soil incorporated in the laboratory condition. The experiment was carried out in laboratory. Air-dried maize (Zea mays L.) and cowpea (Vigna Unguiculata L. Walp) straw with an average size of 35 mm were incorporated into the soil in proportions of 2%, 4%, 6% and 8% in trays. Sample of each soil was collected to determine the organic matter after 120 days in wet conditions. An isolated design was carried out for each soil from maize and bean straw, consisting of two soil densities (1.2 and 1.4 g/cm3), 4 carbon contents and 4 water contents from tensions of 20, 40, 60 and 80 kPa (2x4x4) with 3 repetitions. The soil compression curves of the soil samples were determined adjusted in cylinders with 70 mm diameter and 24 mm in height using the oedometric test. The structural voids index as a function of applied pressure, as well as the soil compression index and pre-compression stresses as a function of water content and carbon content were evaluated using linear regression models with coefficient of determination at 95% confidence. The soil compression index showed a strong positive correlation with organic matter (carbon) derived from bean (r = 0.905) and maize straw (r = 0.787) at 95% confidence. The soil density was 1.2 g cm-3, which was explained by a simple linear regression model.