Perda de nitrogênio pela Brachiaria decumbens após a antese: relação com a umidade do solo / Nitrogen loss through Brachiaria decumbens after anthesis stage: relation with soil moisture
The objective of this researchwork was to evaluate the N loss through Brachiaria decumbens in the stage of post-anthesis related to the soil moisture. The experiment was carried out in green-house condition and the experimental design was a completely randomized, with three treatments and six replications. Plants of grass-Brachiaria were cultivated in pots filled out with sandy soil. The soil of each pot was fertilized with ammonium sulfate-15N (800mg vaso-1 of N). The treatments consisted of harvest of plants in the stages and soil moisture conditions, as following (a) A60 stage of anthesis and with soil moisture maintained to 60 percent of the maximum water retention capacity; (b) PA60 post-anthesis stage or maturity with soil moisture maintained to 60 percent of the maximum retention capacity, and (c) PA20 post-anthesis stage with soil moisture of 20 percent of the maximum water retention capacity established after the anthesis stage. The plants of the treatments post-anthesis (PA60 and PA20) were harvested after 17 days beginning of the flowering stage. The balance of N from ammonium sulfate (15N) in the soil-plant system indicated losses of N, presumably from the aerial part of grass-Brachiariaplants in the post-anthesis stage (treatment PA60). These values were of the order of 25 percent in relation to the anthesis treatment (A60). The N loss in the post-anthesis stage as evaluated in the treatment with water deficits (PA20), it was minimized comparatively to the PA60 and it was of the order of 11 percent in relation to the treatment A60.