Aggregation of an ultissol under guava orchard after application of organic guava-processing industry residues/Agregacao de um argissolo sob pomar de goiabeiras apos aplicacao de residuos da industria processadora de goiaba

The use of industrial residues from fruit processing in agriculture can provide improvements to soil quality. Thus, the aim of this study was to evaluate the effect of residues of guava seeds on soil aggregation and soil organic carbon stock (SOC). The experiment was inserted in an irrigated orchard of guava trees (cv. Paluma) seven years old on a Red-Yellow Ultissol. The experimental design was randomized block and split plot with five treatments (doses: 0, 9, 18, 27 and 36 Mg [ha.sub.-1] of residue) and two soil layers (0.00 to 0.10 and 0. 10 to 0.20 m). It was evaluated the same type of soil on a native forest adjacent to the experimental area. It was analyzed the size distribution of water stable aggregates, the average diameter, the geometric mean diameter, aggregates larger than 2 mm and SOC. Data were subjected to analysis of variance (F test) following a randomized complete block design with split-plot (5 x 2 layers). The treatment means were compared by Tukey test at 5% probability and the average of the layers were compared by F test at 5% probability. The data collected in the forest soil were used only as a reference soil in natural state and therefore were not considered as a factor of variation in the analysis of variance. The values of aggregation index with the soil organic carbon stock were subjected to Pearson correlation (p ≤ 0.05). The effect of residual doses of guava seeds on the soil organic carbon from 0.00 to 0.20 m of soil layer was evaluated by regression analysis. The treatments did not differ in relation to soil aggregation; however, SOC was directly related to the amount of residues applied to the soil. There was significant positive correlation between aggregation index and SOC. The application of residues from guava seeds provided an improvement of soil quality.