| Abstract/Contents: | Recovery of fertilizer N in plant tops is generally considered to be about 50% of that applied. With increasing cost of fertilizer N and concern for environmental contamination by N lost from soil-plant systems, it is important that absorption of fertilizer N be maximized. Introduced warm-season grasses have different morphological characteristics, and they may differentially absorb N. To investigate this possibility, a field study with enriched 15NH4 15NO3 was superimposed in March 1977 on a nontracer N experiment with three warm-season grasses-Ona stargrass (Cynodon nlemfuensis Vanderyst), Transvala digitgrass (Digitaria decumbens Stent), and Pensacola bahiagrass (Paspalum notatum Flugge)-on EauGallie fine sand (sandy, siliceous, hyperthermic Alfic Haplaquods) at the Agricultural Research Center, Ona, Florida. Two N rates (100 and 200 kg ha-1) were the subplots, and three times of 15N-labeled fertilizer N application were the sub-subplots. In 1977, quantities of total and 15N-labeled fertilizer N in forages did not differ among grass species, but they were largest in the Pensacola bahiagrass stolon-root mass. Recovery of fertilizer N in forage as averages of the two N rates and the three times of 15N-labeled fertilizer application was 35, 40, and 35% of that applied to Ona stargrass, Transvala digitgrass, and Pensacola bahiagrass, respectively; 13, 9, and 20% of that applied was in the stolon-root masses; and 22, 17, and 20% of that applied was in the soil presumably in organic form, since it was neither water-soluble nor exchangeable. Approximately 50% of the N in forages came from the 15N-labeled fertilizer and 50% from nonfertilizer sources. Recoveries of fertilizer N in soil-plant systems were 70, 66, and 75% of that applied to Ona stargrass, Transvala digitgrass, and Pensacola bahiagrass, respectively. The sums of fertilizer N in forages from 1977 and 1978, and in the stolon-root masses and soil at the end of 1978, did not differ significantly from amounts accounted for at the end of 1977. Results from the study indicated (1)essentially equal quantities of labeled N in the three soil-warm season grass systems, (2)relatively large retention of labeled N in these sandy soils, and (3)a large amount of nonfertilizer N in forages in 1977, the year of 15N-labeled fertilizer application. |
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