|Stout W L,|
|Schnabel R R,|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 1993
Publication Date: N/A
Interpretive Summary: In the Northeast USA, many of the soils that are used to grow crops and forages are poorly-drained. This means that these soils tend to contain excess water during much of the year. This excess water can affect how well crops and forages grow and how efficiently they use fertilizers, especially nitrogen fertilizer. The purpose of our experiment was to determine exactly how much forage growth and nitrogen use were reduced on a poorly-drained floodplain soil. We found that forage growth was reduced by 21% and fertilizer nitrogen use by 47% on a poorly-drained floodplain soil. This was because the nitrogen fertilizer was converted to a gas by a microbial process called denitrification and returned to the atmosphere. Denitrification usually occurs where soils are poorly- drained. The results of the study can be used to better manage poorly-drained soils, and also to determine the extent to which poorly- drained floodplain soils can be used to intercept excess fertilizer N from upland fields, denitrify it, and return it harmlessly to the atmosphere, thereby preventing it from entering streams or groundwater.
Technical Abstract: Grasslands are the basis for a stable agriculture in the Northeast USA. However, knowledge of the interactive effects of soil drainage and N fertilization on grassland production in this region remains scant. Our objective was to quantify the effect of soil drainage on grassland biomass production and N accumulation. The study was conducted for two years on a floodplain site in central Pennsylvania on two soils selected for well and poor water drainage conditions. A tetraplodial forage type perennial ryegrass (Lolium perenne L., cv. Bastion) was treated with a split application (50%/50%) of 0, 84, 168 and 252 kg N ha-1 of 15N depleted ammonium nitrate. Bi-weekly biomass samples were taken starting May 15 (day 135) of each year and continuing until the grass reached heading stage (day 166). At heading, plots were cut at a 7.5 cm stubble height and all herbage removed from the plots. Plots were refertilized and monthly biomass sampling commenced on August 31 (day 227) and continued until October 31 (day 304). Fertilizer N recovery in ryegrass was highest in the first harvest following fertilizer application, irrespective of soil type or growth period. Peak fertilizer N recovery for the spring growth period was 50% on the well-drained soil and 32% on the poorly-drained soil. In the summer/fall growth period, peak fertilizer N recovery was 26% on the well-drained and 18% on the poorly- drained soil. Correspondingly, biomass on the poorly-drained soil was reduced by 26% in the spring and 8% in the summer/fall periods compared to that of the well-drained soil. Overall, poor soil drainage conditions resulted in a 47% reduction in fertilizer N recovery and a 21% reduction in yield of perennial ryegrass.