Spatial variation and area definition of nutrient extraction by Marandu grass biomass

Resumo

The present study aimed to quantify, describe and identify areas of nutrient extraction by Brachiaria brizantha cv. Marandu biomass in integrated forest-pasture systems from a Cerrado-Amazon transition region with Typic Quartzipsamment soil by using geostatistical techniques, principal components analysis and non-hierarchical fuzzy k-means clustering. The evaluations were conducted in two integrated forest-pasture systems from an association with Brachiaria brizantha cv. Marandu and native vegetation thinned with 50% and 75% (integrated forest production-I (IFP-I) and IFP-II, respectively) shading and in Brachiaria brizantha cv. Marandu monoculture. For each treatment, an area of 4,000 m² (40 x 100 m) was demarcated containing 32 collection points arranged in a 4 x 25 m mesh. At each point, the rates of leaf elongation, senescence and stem elongation were estimated. At the end of each production cycle, the nutrient content (N, P, K, Ca and Mg) was determined in the leaf blades and stem. The nutrient uptake was calculated according to the rates of gross forage production, forage accumulation and leaf accumulation. The nutrient extraction zones of Brachiaria brizantha cv. Marandu biomass were defined using geostatistical techniques, principal components analysis and non-hierarchical fuzzy k-means clustering. Thus, the use of these procedures is feasible for the definition and delimitation of homogeneous zones within and between the pasture production systems studied.