Effects of early season nitrogen on grass-clover swards in the northeastern USA

Grass-legume pastures that rely on biologically fixed N are often N deficient in the spring. Early season N applications to grass-clover pasture, can help overcome this deficiency. Our objective was to test the effects of early season N application and harvest height on total dry matter (DM) yield and clover fraction of a grass-clover sward in the northeast USA. The study was conducted for 3 yr (1996-1998) at the Russell Larson Agricultural Research Center in Rock Spring, PA (40 degrees 48'N, 77 degrees 52W; 330 m above sea level). The soil on the site is a Hagerstown silt loam (Typic Hapludalf, fine, mixed, mesic). The effect of early season N fertilization (0, 22.4, 44.8, and 89.6 kg ha(-1)) was measured on an orchardgrass (Dactyls glomerata L. cv. Pennlate)white clover (Trifolium repens L. cv. Will) sward harvested at three sward heights (15, 22.5, and 30 cm). Increasing N fertilization and target sward harvest height (TSHH) generally increased the early season total DM yield and reduced the clover fraction in the sward. However, by the end of the growing season, the clover fraction from the fertilized treatments was identical to that of the unfertilized treatments. Total early season DM yields on mixed grass-clover swards were increased by 20% with an application of 45 kg N ha(-1). Also, maintaining a 15-cm TSHH along with 45 kg N ha(-1) would maximize the clover fraction in the sward.