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 deficie nt in the spring. Early season N applications to grass-clover pasture, can help overcome this deficiency. Our objective was to test the effects of ear ly season N application and harvest height on total dry matter (DM) yield a nd 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 Resea rch 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 Hapludal f, 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 glomer ata L. cv. Pennlate)white clover (Trifolium repens L. cv. Will) sward harve sted at three sward heights (15, 22.5, and 30 cm). Increasing N fertilizati on and target sward harvest height (TSHH) generally increased the early sea son total DM yield and reduced the clover fraction in the sward. However, b y the end of the growing season, the clover fraction from the fertilized tr eatments 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 4 5 kg N ha(-1) would maximize the clover fraction in the sward.