Nutritional composition of merremia aegyptia, calotropis procera, and senna uniflora for use as green manure in different types of soils

We assessed the nutritional composition of Merremia aegyptia, Calotropis procera, and Senna uniflora for use as green manure in different soil types. Soil and plant samples were collected at four sites in the municipality of Natal, Rio Grande do Norte, Brazil, from May to June 2014. The experimental design was a completely randomized factorial design (4 x 3) with four replications. Treatments consisted of four types of soils (I - Red Yellow Acrisol Eutrophic Latosol; II - Vertisol; III - Dystrophic Yellow Red Latosol with sandy texture; and IV - Cambisol) and three weed species (above mentioned). We assessed the following characteristics of soils: N; Organic Matter (OM); pH; P; K+; Na+; Ca2+ and Mg2+. The following attributes of weed species were evaluated: N; P; K+; Ca2+; Mg2+ and carbon/nitrogen ratio (C/N). We found significant interaction of soil types and weed species for phosphorus, calcium, and magnesium. Levels of nitrogen and potassium were statistically different among weeds, with M. aegyptia showing the highest mean values: N (23.8 g kg-1) and K+ (17.2 g kg-1); C. procera with the following averages: N (20.9 g kg-1) and K+ (15.2 g kg-1); and S. uniflora with following averages: N (21.3 g kg-1) and K+ (10.4 g kg-1). Soil types influenced the nutrient concentration of the weed species.