WATER-USE EFFICIENCY OF PERENNIAL RYEGRASS AS AFFECTED KY SOIL DRAINAGE AND NITROGEN-FERTILIZATION ON 2 FLOODPLAIN SOILS

Quantitative knowledge of the interactive effects of soil drainage and N fertilization on water use efficiency (WUE) of grasses growing on f loodplains in the northeastern United States is scant. Our objective w as to quantify the effects of soil drainage and N fertilization on wat er use efficiency of perennial ryegrass. The study was conducted for t wo years on a floodplain in central Pennsylvania on two soils selected for soil drainage conditions. A tetraploid, forage-type, perennial ry egrass (Lolium perenne L., cv. Bastion) was treated with a split appli cation (50%/50%) of 0, 84, 168 and 252 kg N ha(-1) as ammonium nitrate . Overall, denitrification caused by poor soil drainage conditions dur ing the spring growth period resulted in a 26 percent reduction in WUE . During the summer growth period, the reduction of WUE was 20 percent . These reductions in biomass yield resulted mostly from lost N fertil izer value due to denitrification.