SOIL CHEMICAL ATTRIBUTES AND CORN PRODUCTIVITY GROWN ON LEGUME STUBBLE IN AGROFORESTRY SYSTEMS

ABSTRACT Leguminous species can improve nutrient cycling and chemical quality of Oxisols, resulting in higher productivity of intercropped crops. Thus, this research aimed to evaluate the decomposition rate and nutrient accumulation in legume stubble, as well as its contribution to soil chemical attributes, the growth of baru trees (Dipteryx alata Vogel), and yield of intercropped maize in an agroforestry system. The experiment was developed during the crop years of 2010-2011 and 2011-2012, in Goiás State, Brazil. The experimental design was a randomized block with five replicates. Leguminous species consisted of sunn hemp (Crotalaria juncea), jack bean (Canavalia ensiformis), pigeon pea (Cajanus cajan), Stylosanthes (Stylosanthes macrocephala - 20% and Stylosanthes capitata - 80%), and spontaneous vegetation (control treatment). The decomposition rates of legume and spontaneous vegetation residues remained unchanged in the agroforestry system. Sunn hemp, jack bean, and Stylosanthes plants are advantageous options for total accumulation of nutrients. However, sunn hemp grown as straw cover for next crop seasons increases the available phosphorus levels in the soil and productivity of maize cobs. With this coverage, maize productivity values were up to 24% higher than were those with maize growing on spontaneous vegetation, besides having no effect on the growth of baru trees.摘要 豆科植物可改善氧化土的养分循环与化学性状，进而提升间作作物的生产性能。为此，本研究旨在评估豆科残茬的分解速率与养分积累情况，及其对土壤化学属性、巴里阿豆树（Dipteryx alata Vogel）生长以及农林业系统中玉米间作产量的贡献。试验于2010-2011及2011-2012作物季在巴西戈亚斯州开展，采用随机区组设计，设置5次重复。供试豆科植物包括太阳麻（Crotalaria juncea）、刀豆（Canavalia ensiformis）、木豆（Cajanus cajan）、柱花草（其中大头柱花草Stylosanthes macrocephala占比20%、头状柱花草Stylosanthes capitata占比80%）以及自然植被（对照处理）。在该农林业系统中，豆科与自然植被残体的分解速率无显著差异。太阳麻、刀豆与柱花草均为养分总积累量较优的备选方案。不过，将太阳麻作为秸秆覆盖物用于后续作物季，可提升土壤有效磷含量与玉米果穗产量。相较于自然植被覆盖处理，该覆盖模式下的玉米产量最高可提升24%，且对巴里阿豆树的生长无不良影响。