Dinâmica da serapilheira e da matéria orgânica do solo em Urochloa decumbens Stapf. e Mimosa caesalpiniifolia Benth. sob monocultivo e sistema silvipastoril

Abstract

Silvopastoral systems are productive systems composed of trees, herbaceous forage swards, and livestock in an integrated way. The study aimed evaluate the dynamics of litter and soil organic matter in urochloa decumbens stapf. and mimosa caesalpiniifolia benth. under monoculture and silvopastoral system, during the trees establishment phase. Treatments were distributed in a randomized complete block design with three repetitions. Litter deposition was assessed in a two-year trial, and leaf decomposition was measured in both legume and grass, until 512 days, in monocropping and silvopastoral systems (between rows, at a 2-m distance). Moreover, the contents and stocks of C and N, also the microbial biomass, soil density and organic matter fractionation were evaluated in the silvopastoral system considering distances of 0, 2, 4, and 6 m from double-rows, and in the monocropping system too. Soil samplings were collected at the establishment of the silvopastoral system (16 months after tree planting = one year), one year later (two years), and two years later (three years), on soil layers of 0-10, 10-20, and 20-40 cm. The greatest total litter deposition (531.9; 347.9; 201.6 kg ha-1) and leaf deposition (425.3; 235.9; 130.5 kg ha-1) were observed in the monocropping system, between double-rows (0 m) and at a 2-m distance. Greater total deposition and those of leaves, stems, and miscellaneous, also litter contents of organic and mineral matter, calcium, potassium, and contributions of all nutrients, were verified in the dry season. Conversely, the greatest C content of litter was found in the rainy season. The Mg content of litter was greater at a 2-m distance from the tree double-row. Regarding litter decomposition, the remaining biomass from each species was not influenced by the cropping systems, but it decreased exponentially during the incubation period. The content of remaining N increased while the C/N ratio and C content reduced during the incubation period. Regarding the chemical composition of the remaining litter, greater remaining N was verified in palisade grass under the monocropping system (10.13 g kg-1 OM). In the silvopastoral system, contents of C (438.23) and lignin (225.68), and lignin/N ratio (39.77) of palisade grass were greater between tree double-rows while the C/N ratio was greater at 2 m from this double-row. Concerning the chemical composition of remaining litter from sabiá, the N content was greater between double-rows (22.06 g kg-1 OM) and at a 2-m distance (22.52 g kg-1 OM) compared to the legume’s monocropping. Conversely, the C/N ratio (21.79) was greater in the monocropping system. Fiber fractions like NDF, ADF, and lignin increased throughout incubation time. Sabiá monocropping displayed greater contents and stocks of N compared to palisade grass pasture, but without differences regarding the silvopastoral system. At the implantation of the silvopastoral system, there was a greater content of microbial carbon in the soil (419.09 mg kg-1). Soil density was greater in the the first year, while a reduction was verified in the second-year, mainly at the 40-cm soil layer. In the second year of implantation, there were increases in C contents (7.80, 7.57, and 7.22 g kg-1), and C stocks (9.18; 8.38; 14.18 Mg ha-1) compared to the first year, in all soil layers. Intercropping between Mimosa caesalpiniifolia Benth. and Urochloa decumbens Stapf., in silvopastoral systems, can produce more stable organic matter and constant return of soil nutrients because these species provide different compositions of litter. Furthermore, using sabiá in this system showed the potential to increase both contents and stocks of soil nitrogen, and after two years, to increase considerably carbon stocks.