Dependência espacial em levantamentos do estoque de carbono em áreas de pastagens de Brachiaria brizantha cv. Marandu

Abstract

RESUMOFoi conduzido um estudo utilizando análise de semivariogramas para quantificar a autocorrelação espacial dos estoques de carbono (EC) no solo, biomassa da gramínea e das plantas daninhas em três parcelas experimentais de pastagens de Brachiaria brizantha cv. Marandu com níveis baixo, médio e alto de degradação, cultivadas em Neossolo Quartzarênico Órtico. As coletas das plantas e do solo foram realizadas em malha de amostragem regular com distâncias de 5 x 5 m em área de 900 m². Os EC das pastagens foram submetidos às analises de estatística descritiva, ao teste não-paramétrico de Kruskal-Wallis ao nível de 5% de significância, ao estudo geoestatístico e interpolação por krigagem ordinária. A variabilidade espacial do EC foi observada dentro e entre as pastagens de capim-Marandu com níveis baixo, médio e alto de degradação. A pastagem de capim-Marandu com nível baixo de degradação teve menor continuidade espacial, por apresentar menores alcances no EC, na biomassa da gramínea e na biomassa total (gramínea + plantas daninhas), no solo e no sistema solo x pastagem (solo + biomassa total). A grade de 5 x 5 m foi adequada para caracterizar a variabilidade espacial de pastagens de capim-Marandu com níveis de degradação baixo e alto. Área de pastagem de capim-Marandu com grau médio de degradação apresenta coeficientes de variação altos entre os valores EC; o que comprometeu a modelagem espacial que também pode ter ocorrido devido ao baixo número de amostras realizadas (n=36). Assim, pontos de amostragem menores que 5 m podem melhorar a precisão dos ajustes dos semivariogramas. PALAVRAS-CHAVE: CO 2 , degradação de pastagem, geoestatística, inventário do carbono, sequestro de carbono. Spatial dependence in surveys of carbon storage in grassland areas of Brachiaria brizantha, Marandu grass.ABSTRACT A study was carried using semivariogram analysis to quantify spatial autocorrelation of carbon stock (CS) in soil, grass and weed species biomass in pastures of Brachiaria brizantha, Marandu grass with low, medium and high degradation, and grown an entisol. The sampling of plants and soil were carried out in regular grid with distances of 5x5 m in an area of 900 m². Grassland CS was assessed through descriptive statistics, comparison of averages through the test Kruskal-Wallis at 5% level of significance, geostatistics and ordinary kriging analysis. The spatial variability of CS was observed within and between pastures with low, medium and high degradation. Pastures with low levels of degradation had less spatial continuity due to smaller ranges in CS in grass biomass and total biomass (grass + weed species), in soil carbon and soil versus grass (total biomass + soil). The grid of 5x5 m was adequate to characterize the spatial variability of pasture with low and high levels of degradation. Areas of Marandu grass with average degree of degradation has high coefficients of variation (CV) between the CS values, which negative by affected the spatial modeling. High CV may also be due to the low number of samples taken (n = 3...

Implementation of Silvopastoral Systems under Nutrient Cycling in Secondary Vegetation in the Amazon

“…These readings were taken at 50 georeferenced points within the SPS, in an equidistant and representative mesh (8 × 8 m), which was also used for the sampling of leaf litter deposition and nutrient cycling (Figures 1A and 1B). Both light reading and management in each area were performed according to Silva Neto (2012). Figure 1.…”

“…An adaptation of Wedderburn and Carter's (1999) method, by Silva Neto (2012), was used to quantify the leaf litter production in SPS and native-forest areas, using 0.25-m 2 surface collectors. These collectors had a wooden frame with a nylon screen (1-mm 2 mesh) and were installed systematically at 50 georeferenced and equidistant points throughout the areas of SPS and native forest, so the biomass detached from plants could be collected randomly.…”

“…For leaf litter decomposition, the methods described by Mancilla-Leyton et al (2013), and Silva Neto (2012) were used, placing 30-g leaf litter into 1-mm 2 mesh-size litterbags (nylon bags). The decomposition rate was estimated using senescent grass shoot material (above 20 cm), according to Bahamond et al (2012).…”

“…The rates of remaining material and decomposition per period (bimester) were calculated according to Cunha Neto et al (2013) and Silva Neto (2012).…”

“…According to Silva Neto (2012), the most striking feature in systems with arboreal components and in monocultures is leaf litter deposition. Moreover, K, Ca, and Mg are the main elements of leaf litter, and K, Mg, and N are the most released in decomposition since they are soluble or compose easily degradable molecules susceptible to leaching and soil washing (Luizão, 2007).…”