Impact of incorporating a legume (Grona heterocarpa) into a Brachiaria (Urochloa brizantha) pasture on soil carbon stocks

To assess the impact of incorporating a legume (Grona heterocarpa) into a Brachiaria (Urochloa brizantha) pasture on soil carbon stocks. Treatments were three pastures types, namely: (1) Marandu palisadegrass and ovalifolium mixed pasture, without N fertilizer application (Mixed pasture); (2) Marandu palisadegrass monoculture fertilized with 150 kg N ha-1 year-1 (Fertilized pasture); and (3) Marandu palisadegrass monoculture without N fertilizer application (Unfertilized pasture). All pastures receive annual fertilization with P and K The whole experimental area is divided into three blocks. Each block was once again divided into three paddocks (experimental unit) where treatments were randomly allocated. The size of each paddock was adjusted based on previous studies. For the Fertilized and Mixed pastures, paddock size was 0.78 ha and the Unfertilized pasture paddock, 0.98 ha. Three replications Sampled depths: 0-10, 10-20, 20-30, 30-40 cm Soil samples were taken at random from each paddock to produce a composite sample per block. Soil analyses were carried out using mbrapa standard techniquesfor pH (H2O), exchangeable Al, Ca and Mg (KCl extracts and AA analysis), and available P and K (Mehlich I method). Soil samples were analized for total C and total N using a CHN analyzer (dry combustion) Undisturbed soil samples were collected from three trenches excavated in each paddock. Soil density was determined by calculating the ratio of dry soil mass to sampled volume; Aggregate stability was determined by wet sieving (WS), in which aggregates were slowly immersed in distilled water and mechanically raised and lowered. Aggregate stability was determined as the proportion of aggregates retained on the sieve after removing of coarse particles. Soil texture was determined in samples taken for the C and N stock analyses using sieve and pippete method. Soil mineralogy was not performed. Soil samples were subjected to the BioAS method.