QUALIDADE FÍSICA DO SOLO E LIMITES CRÍTICOS DE ATRIBUTOS FÍSICOS DE LATOSSOLO BRUNO DISTRÓFICO EM FUNÇÃO DA PRODUTIVIDADE DAS CULTURAS DE MILHO E AVEIA

Abstract

With the upgrading of the agriculture and production of seeds and fodder, mostly under no tillage system, the use of agricultural machines and implements of great size has become more common, many times under not appropriated soil conditions, all on behalf of operating income. On that way, the excessive traffic, allied to a high soil humidity, have been upgrading the levels of soil compaction. The process of soil compaction, is related to the modification of the soil physical quality, presenting increases in soil density, decreases of macroporosity, decreases of water infiltration tax in the soil and increases the soil penetration resistance. The modification of the soil physical quality affects the root development and the crops productivities. To have technical subsidy at the decision-making to realise the mechanical intervention or the management practice change aiming decompress the soil, is necessary to know the critical levels of the soil physical attributes that are employed to determine the soil physical quality. Therefore, the objective of this work was to submit the soil to various intensities of tractor traffic to achieve different levels of soil compaction aiming to identify the critical limits of physical attributes to the maize and oat crop on a Xanthic Hapludox. The study was conducted at the experimental area of the agronomy department from Unicentro, at Guarapuava, PR. The trial design was a completely randomized blocks with six repetitions. The treatments were: The witness (without compaction), two, five and twenty passes with the agricultural tractor. The physical attributes were determined before the maize sowing and before the black oat sowing. Both crops were cultivated under no tillage system and measured their productivities. The critical limits for soil density, relative density, macroporosity and capacity of total aeration were determined for the maize and oat crops. The soil compaction caused by the tractor traffic caused change of the soil density, relative density, macroporosity, microporosity, field capacity, capacity of total aeration, water infiltration tax in the soil and soil resistance of penetration. Among the parameters associated to the crops, fodder and seed productivities of maize and dry matter of oat held higher effect of compaction, entailing on lower productivities on both crops. The depth sampled that best represented adjusted to determine the critical limits of the physical attributes from the soil was at 0,07 to 0,12 m. At this depth, for the maize crop, the ideal range of soil density was at the range from 0,93 to 1,07 Mg m-3 , for relative density the ideal range was from 76,9 to 90,4%, for macroporosity the ideal range was from 0,12 to 0,21 m3 m-3 and for the attribute capacity of total aeration the ideal values are on the range from 0,14 to 0,24 m3 m-3. The oat crop showed productivity limitation when the values of soil density were lower than 1,03 Mg m-3 , relative density lower than 85,7%, macroporosity lower than 0,13 m3 m-3 and capacity of total aeration lower than 0,15 m3 m-3 for the 0,07 to 0,12 m depth.