Agregação em Latossolo amarelo submetido à adubação nitrogenada e potássica em plantio direto

Abstract

Soil aggregation stands out as one of the variable for assessing the state of soil physical quality. This is a very sensitive property to the land use and management practices, due to inadequate management, resulting in aggregate ruptures and soil structure decrease. The objective of this research was to evaluate the aggregation in a Oxisol under no - tillage system submitted to nitrogen and potassium fertilization. An experiment was carried outimplanted at five years (in the year of 2013, being renewed annually), cultivated corn in no-tillage system with application of the combination of different doses of nitrogen and potassium. The experiment was installed following a randomized block design with 11 treatments and 5 replicates. The treatments were arranged according to the Plan Puebla III matrix, resulting from the combination of five doses of Nitrogen (N) in the form of Urea (5, 30, 50, 70 and 95 kg ha-1) and five doses of potassium (K), as KCl (4; 24; 40; 56 and 76 kg ha-1), plus the control (without fertilization). The samples were collected after maize harvest (approximately 120 days after planting). Soil samples were collected in layers 0.0-0.10 and 0.10-0.20m deep, with soil samples being deformed and undeformed for physical and chemical determinations. The granulometric analysis of soil samples was performed by the distribution of primary particle diameter, according to the Densimeter (Bouyoucos Hydrometer) method. The separation and size classification of the weighted average diameter of dry and wet aggregates were determined by sieving. The best values of dry macroaggregates for the different treatments ranged from 90,1 to 90,8% and the worst value being 85% in the line, for interlining the best value was 92,5% and the worst 86,6%, this in the layer of 0-0.10 m, whereas in the layer 0.10-0.20 m to row were observed the best values between 91,6 to 92,1% and worse value 86,1%, in the interline values ranging from 88,1 to 92,6%, but there was no significant difference. The no-tillage system and a combination of nitrogen and potassium fertilization do not present changes in the stability of the aggregates. After five years of successive cultivation, a Latosol structure related to the Distribution of pore sizes and a soil density, remains unchanged. Field capacity and the constant point of view are not at stake between nitrogen and potassium fertilizer combinations, but with a significant effect on the water available in the soil.