Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1998
Publication Date: N/A
Interpretive Summary: Nitrogen is required for optimal crop growth and yield. Nitrogen is present in soil organic matter and in the residues (leaves, stems, etc.) of previous crops. However, much of this nitrogen is not in a form available to plants. This nitrogen must first be transformed into chemical forms that plants can take up. This study examined the possibility of predicting the plant- availability of nitrogen from soil organic matter and crop residues. Laboratory studies used to predict nitrogen availability were compared with field studies that measured nitrogen availability. It was found that field nitrogen levels could be predicted from laboratory studies by accounting for the influence of soil temperature and time on nitrogen availability. This is important because scientists have yet to adequately predict this information in the field. Now that this prediction appears feasible, it should allow us to fine-tune our nitrogen fertilizer applications, thereby requiring less nitrogen fertilizer while maintaining yield. This means the grower will not need to spend as much money on nitrogen fertilizer, and the environment is at less risk of harm from over-fertilization.
Technical Abstract: Accurate prediction of N mineralization under field conditions would promote optimal N use efficiency from both organic and inorganic sources. Soil thermal units have been proposed for transferring laboratory predictions of N mineralization to the field. This study was conducted to compare laboratory predictions with field measurements of N mineralization, to assess the utility of microplot cylinders with mixed bed exchange resins for monitoring field N mineralization, and to determine the impact of using ground (1 mm) crop residues in the laboratory to predict N mineralization of unground residues in the field. In two out of three years, N mineralization from soil organic matter and hairy vetch (Vicia villosa Roth) residues were adequately monitored with microplot cylinders and exchange resins in the field. In those same two years, N mineralization from soil organic matter under field conditions was overestimated by laboratory predictions, possibly owing to the drier field soils. However, field measurements of N mineralization from both ground and unground vetch residues fell within the 95% confidence bands of laboratory predictions for much to all of these two growing seasons. It appears that residue N mineralization in the field can be predicted from laboratory studies using ground residues and thermal units.