Variabilidade espaço-temporal de nematoides e atributos físicos e químicos de solo cultivado com cana-de-açúcar

Abstract

In Southeastern, Midwest and Northeastern Brazil sugarcane cropping plays a highly important role in agricultural scenario due to the growing demand for renewable fuels. However, the continuous crop growing can deplete and erode soil, disturbing the food chain ecosystem. The continuous soil management may shift spatial variability of nematodes and soil physical and chemical properties as well relationships between them.Therefore, this study aimed to evaluate relationships and spatial distribution patterns of soil physical (soil gradation, soil moisture, bulk density and total porosity), soil chemical (pH, Ca2+, Mg2+, K+exchangeable, C-CO2 evolutionin soil and total organic carbon) and plant tissue chemical attributes (Ca2+, Mg2+, K+) with nematode community and the effects on sugarcane development (sprouting, stalk height and number, fresh and dry leaf mass) and nutrient absorption. The study was carried out in Juripiranga – PB, on an Ultisol cultivated with sugarcane, in 2013/2014 harvest. Samples were taken at 10-30-cm depth and were collected before planting, and at 3, 6, 9, 12 months after, following a 84-point grid with sampling points spaced 8-m apart, bring in 84 sampling points at each time. Descriptive analysis and Principal Components Analysis were performed. Pearson‟s correlation coefficients between nematode taxa and attributes of soil and plant were calculated. Geostatistics tools was used to characterize the spatial dependence for the nematodes, physical and chemical attributes of soil, besides chemical and growth attributes of plant, employing semivariogram models to create prediction surface maps with kriging. To evaluate the functions performed by nematodes in the ecosystem, analysis were carried out with the following nematode ecological indices: MI, MI (2-5), Sigma MI, PPI, BI, EI, SI and CI. Nematode metabolic footprints were calculated to assess the contribution of nematodes for services and ecosystem functions. Results indicated at the study period the soil food web was in the enrichment process, even at harvest, when the chain were in the structuring process. The three initial periods Sigma MI presented more sensible than MI index; in general, the ecological indices responded to the changes caused in the soil, specially by the addition of vinasse, along with the dry condition that strengthened Ba1 and H3 response. Plant-parasitic nematodes were dominant: Tylenchorhynchus, Pratylenchus, Helicotylenchusand the family Criconematidae. The area management before planting did not affect spatial distribution of physical and chemical soil attributes, except the random distribution of Mg2+ in this period.The effects on nematode community from soil and plant chemical variables proceeded interrelated, so that the plant-parasitic nematodes did not respond to one or few variables enough, but to sequence of events acting en bloc, enforcing the complexity and mutual influence among the variables studied.