Indicadores biológicos da qualidade do solo em sistemas agroflorestais de palma forrageira e leguminosas no Agreste de Pernambuco

Abstract

Botanical composition influence soil microbiology. Thus, it is necessary to study how different intercropping systems affect soil biological parameters to predict potential benefits of their implementation. The objective was to evaluate the intercropping effect of forage cactus with tree legumes on soil microbial biomass in Agreste Pernambucano. The treatments tested were the association of legumes and forage cactus, as described below: i) Gliricidia sepium (Jacq.) Steud and forage cactus IPA-Sertânia (Nopalea cochenillifera Salm Dyck); ii) Leucaena leucocephala [Lam.] de Wit. and forage cactus IPA-Sertânia; and iii) forage cactus IPA-Sertânia. The randomized complete block design was used in a split-plot scheme, with four replications. Soil sampling were made in the months of October/2018 April/2019 and July/2019. Samples were collected at depths of 0-10 cm and 10-20 cm at 0; 1.5; 3.0 and 4.5 m away from legume rows in intercropping plots. In the monoculture plots, samples were collected at just one point parallel to the legume trees at the same depths described above. Determinations of soil basal respiration (BSR), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), metabolic quotient (qCO2), microbial quotient (qMIC), ratio carbon and microbial nitrogen (C:Nmic), total organic carbon (TOC), total nitrogen (TN), ratio carbon and nitrogen (C:N), and natural abundance of soil 13C and δ15N (δ13C and δ15N) were performed. The BSR, MBN, qCO2 and qMIC were lower (P<0.05) for samples collected in Apr/2019 in the 0-10 and 10-20 cm layers, 8.74 and 11.45 μg CO2 g-1 day-1; 21.48 and 31.45 mg kg-1; 0.05 and 0.05 μg CO2 g-1 MBC day-1; 1.86 and 1.03%, respectively. The MBC and C / Nmic ratio were lower for samples collected in Oct/2018 in the 0-10 cm layer, and TOC in the 10-20 cm layer. The TN was higher for samples collected in the Oct/2018. The δ13C varied with distance from trees, indicating the contribution of the different groups of plants. The δ15N also varied with the distance from the trees, indicating greater contribution of fixed N under the tree legume canopy. Microbial activity was similar for samples collected in the Oct/2018 and Apr/2019 in the different cropping systems. Microbial biomass benefits by adding leguminous tree to forage cactus cultivation during the Jul/2019.