Contribuição de leguminosas arbóreas em consórcio com palma forrageira fertilizada com diferentes estercos

Abstract

The consortium of forage plants adapted to the soil and climatic conditions of the Brazilian Northeastern semi-arid region and the use of appropriate management practices can contribute to improve soil fertility, increase crop productivity and the sustainability of livestock production systems in the northeastern semi-arid region. The objective of this project was to evaluate the productive potential and mineral composition of forage cactus cv. (Leucaena leucocephala [Lam.] De Wit) or gliricidia (Gliricidia sepium [Jacq.] Steud.), and fertilized with different sources of manure, as well as deposition of litter and nutrients in these systems and their effects on the soil. The experiment was conducted at the Caruaru Experimental Station belonging to the Agronomic Institute of Pernambuco, IPA. Treatments were allocated in a splitplot arrangem ent in a randomized complete block design, with four replications. Main plots consisted of cropping systems (cactus in monoculture, intercropped with leucaena or gliricidia), measuring 480 m2. Split-plots consisted of manure sources (bovine, ovine, goat, and broiler litter), measuring 120 m2. The experimental period strated in March 2014, with the staging cut for the cactus. The harvest occurred after two years of growth at 1, 2, 3 and 4 m away from the double rows of legumes in the intercropping systems. In the monocrop system (cactus only), four plants were harvested per subplot. The dry matter production and the concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were determined in the cactus. The litter deposition of the tree legumes was quantified monthly, from November 2014 to October 2016, through the collection of the litter deposited in collecting boxes (0.25 m2) arranged between the double rows of legumes. Response variables in this trial included litter DM deposition, litter N, P, and K concentrations, and litter C: N ratio. Plant components were separated into leaves, branches, reproductive structures (flowers, fruits and seeds), and miscellaneous after the 7th evaluation date. Soil samples (0-0.20 m) were collected between legume rows, and 2.5 and 4.5 m away from the rows, and analyzed for soil chemical characteristics. No significant differences were observed for cactus production between the three cropping systems, reaching values of 20.5, 21.3, and 24.5 Mg DM ha-1 2 years-1, in the cactus intercropped with gliricidia, cactus intercropped with leucaena, and cactus in monoculture, respectively. In the intercropping systems, the greater proximity to the legumes increased cactus production, for the treatments fertilized with the bovine and ovine manure, and increased the concentrations of P, K, and Mg, but not the N concentration. The greatest concentrations of P and K were obtained in the cactus in monoculture and in a consortium with gliricidia, whereas for N, the concentration were greater when fertilized with broiler litter. Litter deposition was seasonal, with the greatest values occurring at the end of the rainy season, being the largest proportion of the leaf fraction, followed by reproductive structures and branches. The mean value of total deposition was 2.8 Mg DM ha-1 year-1 for leucaena and 4.3 Mg DM ha-1 year-1 for gliricidia. However, greater N concentration in the leucaena litter lead to greater deposition of this nutrient to the soil. The improvement in soil chemical characteristics occurred at 2.5 to 4.5 m away from the legume rows, with reduction of the soil acidity and elevation of base saturation, CEC, and SOM. The introduction of leucaena or gliricidia intercropped with IPA-Sertânia cactus, along with the application of manure, is a relevant alternative for production systems in the semi-arid region, in order to increase soil organic matter and soil nutrients because deposition of litter with low C: N ratio. Such improvements imply the maintenance of soil fertility, cactus productivity, and the sustainability of these systems.