Release of Nitrogen From a Leguminous Cover Crop and the
Subsequent Utilization by Bell Pepper
Richard Smith, Louise Jackson, and Phil Foster
Leguminous cover crops begin to release nitrogen to the soil once they are incorporated into the soil and adequate water is available for microbial decomposition of the plant tissue. The amount of nitrogen that is released from a productive cover crop can clearly be substantial, however the rate of release of nitrogen and the duration of the release is not well understood. This study attempted to investigate the rate of release of nitrogen from lana vetch and its subsequent utilization by bell pepper - a long-season, high-nitrogen demanding vegetable. We also treated some plots with superimposed applications of a slow-release fertilizer (feather meal) to determine if the additional nitrogen, supplemental to the cover crop, provided season-long nitrogen to the crop. In 1992, we observed that there was a steady increase in the nitrate-nitrogen levels of the soil solution up to 74 days following incorporation of vetch residue into moist soil. This release of nitrogen from the vetch followed an earlier trend observed in 1991 in a sweet corn field. The release curve of nitrogen by vetch fit the growth patterns nicely for some vegetables such as sweet corn and melons; these crops have their peak demand for nitrogen at the time when the cover crop is releasing maximum amounts of nitrogen. However, for a crop such as bell pepper which is in the ground for 200-250 days and which has a high demand for nitrogen, is the nitrogen provided by a cover crop sufficient to produce good yields? This is the question that we set out to answer in this study.
The 1992 data indicates that the nitrogen supplied
by the cover crop alone did not keep the petiole nitrate-N levels as high
as plots that were amended with slow release fertilizer that supplied late
season nitrogen to the pepper crop. However, we did not see a significant
improvement in yield from any of the fertilizer treatments, possibly because
of a late-season disease outbreak. In 1993 we again saw an increase in
the petiole nitrate-N levels later in the growing season in the fertilized
plots and this year the yield in this plot fertilized with 160 pounds of
nitrogen as feather meal had a significantly higher yield (P>0.10).
These results indicate that the nitrogen released from a leguminous cover
crop such as vetch can provide significant amounts of nitrogen for subsequent
vegetable crop production, however long-season, high-nitrogen demanding
crops such as bell peppers may need supplemental applications of late season
fertilizer for optimal growth.
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