| Abstrakt: |
The feasibility of increasing N rates on forage grasses, brought about by low cost commercial N fertilizer, has focused attention toward the effects of high N levels on grass development and production and the hazard of ground water pollution where the applied N is not completely utilized by the forage. A 3‐year study was initiated to investigate the effects of N fertilization and N carryover on dry matter yield and percent N in orchardgrass (Dactylis glomerataL.) and to determine the N rate that would give minimal pollution problems. The N treatments, 0, 84, 168, 336, 672, and 1344 kg/ha/year of N were applied for 2 years previous to the experiment. With the initiation of the study, plots were split, half receiving N treatment and half receiving no N fertilization. Dry matter yield was found to increase up to 336 kg/ha of applied N. At the higher N rates, yields leveled off or declined, apparently due to stand reduction. Nitrogen fertilization also increased total N content of orchardgrass. Response of orchardgrass to N carryover the first year of the residual study, as measured by dry matter yield, was found at residual N rates greater than 84 kg/ha. Nitrogen carryover during the second year was observed only at the 672 and 1344 kg/ha residual N rates, and only at the 1344 kg/ha residual N rate the third year of the study. Nitrogen carryover affected total N content only in the first year of the study and only at the two highest residual N rates. Over a 5‐year period, N application equaled N removal at 246 kg/ha/year of applied N. Above this rate, N carryover was observed. This study indicates that on Crosby silt loam soil, approximately 250 kg/ha of N should be applied per year on orchardgrass in central Indiana. |
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