Abstract
The system of no-till sowing stands out as being a technology that suits the objectives of more rational use of the soil and greater protection against the erosion. However, through till, any of it, occurs modifications of the soil's structure. This current work aims to study the influence of the energy state of the water and of the organic matter on the mechanism of compaction of Red Oxisol under no-till management system. Humid and non-deformed sample were collected in horizon AP of two agricultural areas under no-till, with and without rotation of cultures. In the laboratory, these samples were broken into fragments and sifted to obtain aggregates of 4 to 5 mm sized, which were placed in equilibrium under four matrix potentials. Thereafter, they were exposed to uni-dimensional compression with pressures varying from 32 to 1,000 kPa. The results in such a way show that the highest compressibility of aggregates both for the tilling with rotation of cultures as for the tilling without rotation of cultures, occurred for matrix potential -32 kPa (humidity of 0.29-0.32 kg kg-1, respectively), while the minor occurred for the potentials of -1 and -1,000 kPa (humidity of 0.35 and 0.27 kg kg-1, respectively), indicating that this soil should not be worked with humidity ranging around 0.29 to 0.32 kg kg-1 and the highest reduction of volume of aggregates was obtained for the mechanical pressures lower than 600 inferior kPa, indicating that these soils showed to be very influenced by compression, when exposed to mechanical work. Also, the aggregates of soil under no-till and rotation of crops presented higher sensitivity to the compression than the aggregates of soil under no-till and without rotation of crops, possibly for having better structural conditions given to a higher content of organic matter.
Highlights
Another point to be observed is related to the air index (a), which presented a well differentiated behavior between the two types of aggregates studied, as for the soil sample under the no-till without crop rotation (NT) system, the air index is low and this index curve has two distinct phases, or in other words, between the potentials of -1000 and -32 kPa there is no variation in the air index, between -32 and -3.2 kPa occurs a sharp reduction in this index, and between – 3.2 and 1 kPa the air index is null, Figure 2
Another point to be observed from the water index curve (θ) (Figure 2) is that moisture is systematically more elevated in the soil aggregates under RNT, mainly for the matrix potentials higher than -32 kPa, in which the humidity relies on pores distribution and as a consequence, suffer influence of the soil structure (Mathieu & Pieltain, 1998), indicating that the pores volume higher than 5 μm is more important in the RNT soil, where probably the soil is better structured due a higher organic mater content than in the NT soil
The higher compressibility of the aggregates of an Oxisol under no-till, both for the management with crop rotation and to management without crop rotation, occurred to the matrix potential -32 kPa, and the lowest to potentials of -1 and -1,000 kPa, indicating that the soil should not be worked with humidity around 0.29 to 0.32 kg kg-1
Summary
The process of occupation of agricultural lands in the Northern tropical zone of the State, from the 30’s until the late 60’s, was mainly made by coffee culture in an extensive mode, with low use of mechanization, and subsistence crops; and with the destruction of plantations by a severe frost in 1975 the process of modernization of agriculture occurred rapidly, especially in the lands of high fertility and where the topography was more favorable to mechanization, those soils became occupied by business orientated production systems, principally with the expansion of soybean and wheat cultures, with intensive management of soil, based on the use of disc ploughs and moldboards ploughs and burning of the wheat after the harvest As a result, these soils suffered a process of depletion, with fast decomposition of organic matter, fertility reduction, occurrence of soil compaction, resulting in the worsening of erosion and reduction of crop yields, requiring, attitudes and strategies as to increase soil cover, the water infiltration and the surface overflow (Vieira, 1989; Casão Jr.et al, 2000; Muzilli, 2008). It is believed that the systems called conventional cause more structural modification in the soils, while the systems called conservationists, as the no-till, cause less impaction as they do not move the soil; this lack of soil evolvement, associated to a intensive use of the soil exposes it, to Collares et al (2006), to a heavy machine traffic in inadequate conditions of moisture and helps to change the structural quality of the same, which leads to an increase in compression with the disappearance of some of the soil pores, leading to a change in the infiltration properties and water availability, aeration and root penetration in the soil, affecting crop yields, and creating problems of erosion (Tavares Filho & Tessier, 1998; Silva et al, 2000; Tavares Filho et al, 2001; Goedert et al, 2002; Tavares Filho et al, 2005; Collares et al, 2006)
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