EVALUATION OF THE CHARACTERISTICS OF 14 COVER CROPS USED IN A SOIL REHABILITATION TRIAL

Many of the soils in Santa Cruz Department, Bolivia, are degraded by serious weed infestation, subsoil compaction, and low organic matter and nitrogen contents. Fallow periods with cover crops are frequently used to recuperate the fertility of degraded soils, but little information exists on the desired characteristics of cover crops for this purpose. The aim of this study was to describe those characteristics, believed to be most relevant to the rehabilitation of degraded soils in Santa Cruz, of 14 cover crops, which included three grasses, nine legumes, and two winter cover crops sown after summer soybean (Glycine max). The cover crop characteristics, evaluated over two years, were ease of establishment, competitiveness against weeds, tolerance to drought, dry matter production and nutrient contents of the above-and below-ground residues, nodulation, rooting density and root diameters. The three grasses Tobiata (Panicum maximum var. Tobiata), Centenario (Panicum maximum var. Centenario) and Brizantha (Brachiaria brizantha) appeared to be the most promising for increasing soil organic matter contents, and the three grasses and groundnuts (Arachis hypogaea)/pigeon pea (Cajanus cajan) for the recuperation of subsoil structure. Mucuna deeringiana and Lablab (Dolichos lablab) were the most promising for increasing soil N status. All of these cover crops competed successfully with weeds.