Influence of Nitrogen Application Rate On the Extent of Nitrogen Leaching.

There is a lot known about nitrogen (N) leaching from turfgrass ecosystems, but little research has been done to determine what the maximum soluble N application rate should be from an N leaching prospective, an important best management practice. The objective of this study is to determine the maximum single soluble N application rate that does not result in an increase in N leaching over different growing seasons and soil types. The study was conducted in soil containers were filled with a quartzite sand and sandy loam soil then sodded with Kentucky bluegrass. After a 2 month establishment period, 15 fertilizer treatments were applied in July and again in Oct.  Application rates ranged from 4.9 to 73 kg N/ha (at 4.9 kg N/ha intervals, an un-fertilized control), using ammonium sulfate is the N source. Just prior to and one wk. after each application the containers were leached with water equivalent to 2 pore volumes to leach all soluble N from the containers. The drainage water was analyzed for NH4-N, NO3-N and total N. For the sand there was no N leached when N was applied up to 14.7 kg N/ha of soluble N when applied in July and a very small amount of leaching at 19.6 kg N/ha. At higher applications there were significant amount of leaching. For the sandy loam soil, apply no more than 34.3 kg N/ha of soluble N in July resulted in a little NO3-N leaching and up to 24.5 kg N/ha there was no leaching. At higher applications there were significant amounts of leaching. It was apparent that when more N was applied there was less efficient use of N, thus suspect to leaching.