SOIL DRAINAGE INFLUENCE ON BIOMASS AND NITROGEN ACCUMULATION BY RYEGRASS

Grasslands are the basis for a stable agriculture in the Northeast USA . However, knowledge of interactive effects of soil drainage and N fer tilization on grassland production in this region remains scant. Our o bjective was to quantify the effect of soil drainage on grassland biom ass production and N accumulation. The study was conducted for 2 yr on a floodplain site iii central Pennsylvania on two soils selected for extreme drainage conditions. Perennial ryegrass (Lolium perenne L. cv. Bastion) was treated with a split application (50% in mid-April, 50% in mid-July) of 0, 84, 168 and 252 kg, N ha-1 of N-15 depleted NH4NO3. Biweekly biomass samples were taken starting mid-May of each year and continuing until the grass headed and all herbage was removed from th e plots. Plots were re-fertilized and monthly biomass sampling commenc ed at the end of August and continued until the end of October 31. Fer tilizer nitrogen recovery was greatest in the first harvest after fert ilization, irrespective of soil type or season. Peak fertilizer N reco very for spring growth was 50% on the well-drained soil and 32% on the poorly drained soil. In the summer-fall growth period, peak fertilize r N recovery was 26% on the well-drained and 18% on the poorly drained soil. Biomass on the poorly drained soil was 26% less in the spring a nd 8% less in the summer-fall periods compared with that of the well-d rained soil. Overall, poor soil drainage conditions resulted in a 39% reduction in fertilizer N recovery and a 21% reduction in yield of per ennial ryegrass.