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Title: RESIDUAL FERTILIZER N USE BY WARM-SEASON FORAGES

Author
item Mackown, Charles
item Williams, Robert
item ESQUIVEL, R - USDA-NRCS
item LEMUNYON, J - USDA-NRCS

Submitted to: American Society of Agronomy
Publication Type: Abstract Only
Publication Acceptance Date: 10/26/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Perennial non-legume forages require N to sustain productivity. Earlier, we evaluated N use efficiency and fertilizer N recovery by six grasses and one forb grown in 1995 with 180 kg N/ha of 15N-depleted fertilizer. Plots established in 1991 received yearly applications of broadcast fertilizers, were periodically clipped or left uncut until dormant, and surface residues burned before the onset of spring growth. Effects of clipping on the continued recovery of the N fertilizer applied in 1995 was determined in 1996. For nearly all species most of the previous year N fertilizer was recovered in the first of three clippings. Fertilizer N in each successive harvest of 1996 tended to decline to less than 0.9 kg N/ha in the dormant harvest. In contrast, yields for the second clipping of four species exceeded the first by 200%, were nearly equal for two species, and was 75% less for Maximilian sunflower (Helianthus maximilianii Schrad., cv. Aztec). Recovery of N in 1996 ranged from 1.7 to 8.3% of the N applied in 1995. Overall, N recovery from the clipped plants (9.1 kg/ha) exceeded that of unclipped plants (4.1 kg/ha). This difference appears primarily associated with 1.8-fold less dry matter collected from plots of unclipped plants. For the 2 yr period, 13 to 58% of N applied in 1995 was accumulated by the forages. Lower N recoveries were associated with plants left unclipped. Among species the difference in total fertilizer N accumulated was only about 20 kg N/ha, indicating that in most cases accumulation of fertilizer N was similar, even though up to a 2-fold difference in total yield for the 2 yr was observed among the forages.