Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2000
Publication Date: N/A
Citation: Interpretive Summary: Nitrate-N contamination of ground water is a serious and ubiquitous concern because of its potential health hazard to humans and animals. In a three year study, we have examined the influence of various combinations of tillage, cover crops, and nitrogen fertilization. Three years of tomato production resulted in a considerable amount of N in the soil because of low N recovery. The accumulation and movement of residual nitrate-N in the soil profile was influenced by tillage, cover cropping, and nitrogen fertilization. It was observed that minimum tillage, such as chisel, can reduce NO3-N movement relative to no-till, maintain tomato N uptake, and avoid soil and water quality losses associated with moldboard. Compared with 180 kg N/ha, 90 kg N/ha can reduce NO3-N content, movement, and leaching and produce sustainable tomato yield because N uptake was similar but N recovery was higher with 90 than with 180 kg N/ha. Due to similar NO3-N content and movement from hairy vetch (HV) and N fertilizer, HV is not effective in reducing NO3-N accumulation and movement in the soil compared with N fertilization.
Technical Abstract: Management practices can influence NO3-N content and movement in the soil. We examined the influence of three years of tillage [no-till(NT), chisel(CH), and moldboard(MB)], cover crop [hairy vetch (Vicia villosa Roth)(HV) and no hairy vetch(NHV)], and N fertilization (0,90, and 180kg N/ha) on residual NO3-N content and movement on a Norfolk sandy loam (fine-loamy, siliceous, thermic, Typic Kandiudults) under tomato (Lycoperscion esculentum Mill) in central Georgia. Due to low N recovery by tomato, NO3-N content in the soil increased with depth, regardless of treatments, and ranged from 127 to 316 kg/ha at 0-to 120-cm depth in the fall (September 1997). The content increased with increasing rate of N addition from cover crop residue and N fertilizer. From fall to spring (March 1998), 22 to 58% (37 to 129 kg NO3-N/ha) of this content was lost, mostly due to leaching. Greater loss occurred in NT than in CH or MB, with HV than with NHV, and with 180 or 90 than with 0 kg N/ha. Similarly, greater loss occurred at 0-to 60-cm than at 60-to 120-cm depth. Significant correlation between soil NO3-N and clay concentration with depth indicates NO3-N moved from the surface layer to the underlying clay layer, where it moved slowly. Nitrate-N content and movement in the soil from cover crop residue and N fertilizer were similar. Minimum tillage reduced NO3-N movement compared with NT, yet avoided the negative effects on soil and water quality associated with MB. Although HV increased tomato N uptake and recovery, it was not effective in reducing NO3-N content and movement compared with N fertilizer.