Spatial dependence in surveys of carbon storage in grassland areas of Brachiaria brizantha, Marandu grass

• Published in: Acta amazonica Vol. 42; no. 4; pp. 547 - 556
• Main Authors: da Silva Neto, SP, dos Santos, AC, de Lima Leite, RL, Dim, V P, das Neves Neto, DN, Da Cruz, RS
• Format: Journal Article
• Language: Portuguese
• Published: 01-12-2012
• Subjects: Biomass; Brachiaria brizantha; Carbon sequestration; Degradation; Grasses; Grasslands; Pasture; Soil; Spatial distribution; Weeds
• ISSN: 0044-5967

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 m super(2). 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 = 36). Sampling points in grid lower than 5 m can improve the accuracy of the adjustment of semivariograms.Original Abstract: Foi conduzido um estudo utilizando analise de semivariogramas para quantificar a autocorrelacao espacial dos estoques de carbono (EC) no solo, biomassa da graminea e das plantas daninhas em tres parcelas experimentais de pastagens de Brachiaria brizantha cv. Marandu com niveis baixo, medio e alto de degradacao, cultivadas em Neossolo Quartzarenico Ortico. As coletas das plantas e do solo foram realizadas em malha de amostragem regular com distancias de 5 x 5 m em area de 900 m super(2). Os EC das pastagens foram submetidos as analises de estatistica descritiva, ao teste nao-parametrico de Kruskal-Wallis ao nfvel de 5% de significancia, ao estudo geoestatistico e interpolacao por krigagem ordinaria. A variabilidade espacial do EC foi observada dentro e entre as pastagens de capim-Marandu com niveis baixo, medio e alto de degradacao. A pastagem de capim-Marandu com nivel baixo de degradacao teve menor continuidade espacial, por apresentar menores alcances no EC, na biomassa da gramfnea e na biomassa total (graminea + 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 niveis de degradacao baixo e alto. Area de pastagem de capim-Marandu com grau medio de degradacao apresenta coeficientes de variacao altos entre os valores EC; o que comprometeu a modelagem espacial que tambem pode ter ocorrido devido ao baixo mimero de amostras realizadas (n=36). Assim, pontos de amostragem menores que 5 m podem melhorar a precisao dos ajustes dos semivariogramas.