Alfalfa yield response to nitrogen applied after each cutting

Although alfalfa (Medicago sativa L.) usually obtains a high percentage of its required N via symbiotic N fixation, additional fertilizer N applied on ce in the spring can increase forage yields, However, little is known about alfalfa yield response to low N rates (<50 lig N ha(-1)) immediately follo wing each cutting. Low N rates (immediately following each rutting) were ev aluated for total alfalfa dry matter production on a Grant silt loam (fine- silty, mixed, thermic, Udic Argiustoll). This nonirrigated experiment was i nitiated on a 2-yr-old alfalfa stand where sufficient P and K had been appl ied. 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 contin uous N application, no differences in soil NH4N or NO3N were found at depth s >15 cm (0- to 240-cm sampling depth). In 1994, total alfalfa drg matter y ield (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). Tot al forage N decreased from the second to the fifth harvest in most Sears. B y-harvest dry matter yield increases due to applied N were only found in la te-season harvests, consistent with late-season decreased N-2-fixing capaci ty in alfalfa documented by others.