Alfalfa yield response to nitrogen applied after each cutting
1999
Raun, W.R. | Johnson, G.V. | Phillips, S.B. | Thomason, W.E. | Dennis, J.L. | Cossey, D.A.
Although alfalfa (Medicago sativa L.) usually obtains a high percentage of its required N via symbiotic N fixation, additional fertilizer N applied once in the spring can increase forage yields. However, little is known about alfalfa yield response to low N rates (< 50 kg N ha(-1)) immediately following each cutting. Low N rates (immediately following each cutting) were evaluated for total alfalfa dry matter production on a Grant silt loam (fine-silty, mixed, thermic, Udic Argiustoll). This nonirrigated experiment was initiated on a 2-yr-old alfalfa stand where sufficient P and K had been applied. Nitrogen rates of 11, 22, and 44 kg N ha(-1) were applied immediately following each cutting for 5 yr (4-5 cuttings yr(-1)). After 5 yr of continuous N application, no differences in soil NH(4)-N or NO(3)-N were found at depths > 15 cm (0- to 240-cm sampling depth). In 1994, total alfalfa dry matter yield (sum of five harvests) increased 1.29 Mg ha(-1) from a total annual N application of 110 kg N ha(-1) (22 kg N ha(-1) following each cutting). Total forage N decreased from the second to the fifth harvest in most years. By-harvest dry matter yield increases due to applied N were only found in late-season harvests, consistent with late-season decreased N(2)-fixing capacity in alfalfa documented by others.
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