Biomassa microbiana e atividade enzimática na rizosfera de genótipos de capim-elefante (Pennisetum purpureum Schum.) sob manejo de irrigação na região do semiárido de Pernambuco

Abstract

Elephant grass (Pennisetum purpureum, Schum.) is one of the most widespread and important grasses in Brazil. It is used in various ways in animal feed because it has good digestibility and has high energy potential, mainly due to high biomass production. It has good adaptability to the semiarid climate, although it varies in production over the years. Irrigation provides stability in crop yield and provides better conditions for soil microbial activity. Soil microorganisms reflect as quality indicators, being associated with several biogeochemical processes, besides being sensitive to environmental changes. The present work aimed to evaluate the changes in biological attributes indicating soil quality in the Brazilian semiarid, due to the influence of irrigation management on different Pennisetum purpureum genotypes and seasonal variations. The study was carried out at the experimental farm of the University Federal Rural of Pernambuco, in Garanhuns-PE. The area was arranged in a randomized block design with factorial scheme. The treatments consisted of a combination of two elephant grass cultivars (Elephant B and Mott), two irrigation regimes (with and without irrigation) and two climatic periods (dry season and rainy), with three repetitions. Two collections were carried out in July and December 2017, corresponding to the rainy and dry season, respectively. Rhizospheric soil samples were collected at a depth of 0-10 cm. Key biological indicators such as microbial biomass carbon (CBM), soil basal respiration (RBS), metabolic quotient (respiration / biomass ratio), and soil enzymatic activity were evaluated. Microbial biomass carbon and basal respiration had higher values in the genotype Mott. Irrigation management presented lower RBS in the rainy season and CBM was significant only in the genotype Elephant B in both evaluated seasons. The metabolic quotient did not differ between treatments. The use of irrigation presented higher enzymatic activities in both evaluated periods, except for urease activity and FDA in the rainy season. The genotype Mott showed higher soil enzymatic activities, except for β-glucosidase and acid phosphatase in the rainy season. According to the results obtained, in the soils examined, the increase of soil water content by drip irrigation management in the dry period can improve the nutrient cycling potential, helping to maintain the biological and chemical fertility of soils in semiarid agroecosystems. Genotype Mott has better biological attributes in soil quality, providing better microbial activities regardless of the evaluated seasons and different irrigation managements. Seasonality may alter soil microbial community, considering structure and functionality. It is of fundamental importance that works like this continue to be developed, to understand if these communities can adapt to these environmental changes and if from this change the enzymatic activities will be kept in the soil.