Effect of five forage legume covers on soil quality at the Eastern plains of Venezuela

Abstract

At the Eastern planes of Venezuela, large to tracts of pastureland are sustained by low fertility acid soils that often lead to overgrazing, decreased pasture production, invasion by weeds, and soil compaction and erosion. The objective of this study was to evaluate the behavior of local forage legume species and its influence on chemical and biochemical properties of soil with the ultimate goal of identifying which one of these species have the potential to be used as cover in the establishment of a “Ley farming” system. The study was conducted on an Oxisol and used five local species from the genus Centrosema (Centrosema brasilianum, Centrosema macrocarpum, Centrosema pascuorum, Centrosema rotundifolium and Centrosema molle) which were established as cover for a period of 3 years. Dry matter (DM) and soil samples were collected twice a year, during the dry season (April) and during the rainy season (October). The soil parameters evaluated were total nitrogen, organic matter, calcium, potassium, magnesium, pH, soil respiration, and enzymatic activities that include β-glucosidase, arylsulphatase, phosphatase, urease, protease, dehydrogenase and catalase. The annual average data were used to identify indicators of soil quality through principal component analysis (PCA) that led to calculate a soil quality index (SQI). The results indicated that DM production varied among the different legume covers, showing C. macrocarpum the greatest productivity (1340 kg h−1). The PCA identified seven of the tested soil variables as quality indicators: total nitrogen, pH, calcium, soil respiration and arylsulfatase and β-glucosidase activities. Total nitrogen, P and β-glucosidase activity were the indicators showing the largest changes over time being able to discriminate between treatments. After the 3 year period of the trial the SQI of the soil tested raised from 0.17 (very low quality) to 0.30 (low quality) where C. brasilianun, C. pascuorum and C. molle were established and to 0.40 (moderate quality) where C. macrocarpum and C. rotundifolium were established. Thus, the legume crop covers influenced positively the soil quality. C. macrocarpum was the legume cover that showed the greatest soil improvement, having the best potential to be used as forage cover to establish a “Ley farming” system at the Eastern planes of Venezuela.