The fate of fertilizer nitrogen applied to three warm-season grasses on a spodosol in florida as indicated by nitrogen-15

Abstract

The field experiment with 15 N-enriched fertilizer (12.4687 atom % of 15 N) was superimposed in March 1977 on a nontracer N experiment with UF-4 (Cynodon nlemfuemsis Vanderyst), Transvala digitgrasss (Digitaria decumbens Stent), and Pensacola bahiagrass (Paspalum notatum Flugge), grasss sods previovsly established on EauGallie fine sand (sandy, siliceous, hyperthermic Alfic Haplaquod) at the Agricultural Research Center, Ona, Florida. The experiment was established to compare the effect of N rates, and seasonal N applications on forage yields, N uptake efficiency, residual fertilizer N, and distribution of fertilizer N in soil and components of the three warm-season grass species for two-year period. Treatments were arranged in a split-split-plot experimental design with two replications. The three warm-season grass species were the main plots, two N rates (100 and 200 kg/ha) were the subplots, and three seasonal N applications (1, 2 and 3) were the sub-subplots. Fertilizer N was observed in oven-dry forages, stolon-root masses, soils, and soil solutions. In 1977, total N in forage was not different among grass species, but total N in the stolon-root mass from Pensacola bahiagrass was the largest. Recovery of fertilizer N in forage was 35, 40 and 35% of that applied from UF-4, Transvala digitgrass, and Pensacola bahiagrass; 13, 9 and 20% of that applied in stolon-root mass; and 26, 19 and 21% of that applied to the soil. Recovery of fertilizer N in forage was not different among grass species. Approximately 50% of the forage N came from fertilizer and 50% from non-fertilizer sources. Recovery of fertilizer N in the stolen-root mass from Pensacola bahiagrass was lager than from UF-4 and Transvala digitgrass. Soil solution samples collected from depth of 60 cm showed no evidence of N leaching leaching. Recoveries of fertilizer N in soil-plant systems were 74, 68 and 76% of that applied from UF-4, Transvala digitgrass, and Pensacola bahiagrass, respectively. In 1978, fertilizer N storaged in stolon-root masses at the end of the 1977 were translocated into forage regrowth in 1978 and some were released into the soil. The sum of fertilizer N in forage from 1977 and 1978 plus fertilizer N in the stolon-root mass and soil at the end of 1978 were 72, 69 and 68% of that applied from UF-4, Transvala digitgrass, and Pensacola bahiagrass, respectively. Three important conclusions from this experiment were the large amount of non-fertilizer N in forage, the essentially equal accountability of applied N in the three soil-warm season grass systems, and the relatively large relention of fertilizer N in these sandy soils.