Banca de DEFESA: JOAO GUEDES BORRE

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : JOAO GUEDES BORRE
DATE: 12/09/2023
TIME: 08:30
LOCAL: VIDEOCONFERÊNCIA
TITLE:

N cycling in tropical pastures mixed with forage legume or fertilized with N.

KEY WORDS:

Nutrient cycling, Nitrogen fertilization, Consortium, litter, animal excreta

PAGES: 72
BIG AREA: Ciências Agrárias
AREA: Agronomia
SUBÁREA: Ciência do Solo
SUMMARY:

The decline in pasture productivity is an increasingly recurrent process in tropical regions. The extensive nature of animal husbandry on pasture, combined with scarce N replacement, favors the process of pasture degradation. In the current scenario, this phenomenon corresponds to the main limiting factor of Brazilian livestock production. The integration of legumes in pastures is the most promising alternative for recovering degraded pastures (RPD). By fixing atmospheric N2, these plants increase the input of N into the pasture, inhibiting the degradation process. This study aimed to compare N cycling in pastures of Urochloa spp. intercropped with legumes or fertilized with N. The experiment was carried out during two years divided into two seasons, Águas and Seca. The design used was a case-by-case block design with three treatments and four replications. The treatments were: Urochloa brizantha cv Marandu fertilized with 138 kg of N ha-1 year-1 (N-fert); Urochloa brizantha cv Marandu with Macrotyloma axillare cv. Java (Consortium); Urochloa brizantha cv Marandu not fertilized with N (Control). The animals were kept under continuous stocking with a variable stocking rate and forage supply (FO) was adopted as a grazing management criterion. The presence of the legume favored the stock of total N in the forage mass (MF, kg N ha-1), and in the Consortium it became equivalent to the N stored in the biomass of the fertilized pasture. N management did not affect existing litter (LE,) and N stock in LE (kg N ha-1). In N-Fert, a higher rate of litter deposition was observed (LD, kg ha day-1; p = 0.0003), however the proportion of N cycled by LD was 33.5 and 45.8% higher in Consortium compared to to N-Fert and Control, respectively (p < .0001). Both LE and LD on the basis of MO showed higher values in the Dry, in view of the higher rate of senescence in the aerial part of the plant. The N applied in the system did not act as a determining factor in litter decomposition. Environmental factors such as temperature and precipitation favored the rate of decomposition in the rainy season (p = 0.009). The contribution of Biological Nitrogen Fixation (BNF) followed the same behavior pattern as the legume mass throughout the experiment, indicating higher values in the Waters compared to the Dry, respectively. Similar values referring to N intake and excretion, per animal, were found between treatments. The highest N excretion per area (kg ha-1 season-1) was observed in N-Fert (p = 0.010), probably due to the increase in animal stocking. In general, a positive N balance was observed in the soil-plant-animal system in the N-Fert and Consortium treatments, with 106 and 132 kg N ha-1 year-1, respectively. Conversely, pastures without nitrogen fertilization showed a negative N balance of -27 kg ha-1 yr-1. These results suggest that the input through nitrogen fertilization or intercropping with Macrotyloma in the pasture has a great influence on the maintenance of N reserves in the soil.

COMMITTEE MEMBERS:
Interno - 1104775 - ADELSON PAULO DE ARAUJO
Externo à Instituição - DANIEL RUME CASAGRANDE - UFLA
Presidente - ***.898.198-** - SEGUNDO SACRAMENTO URQUIAGA CABALLERO - EMBRAPA