Predicting inorganic nitrogen availability from control-release fertilizers (CRFs) is essential in designing precision management in forest nurseries that balances optimal plant nutrition with minimal environmental impact via nitrate leaching. Cumulative temperature-based quadratic equations have been used in field studies to predict nitrogen release. However, one factor quadratic equations exclude the influence of soil moisture content on nitrogen release from CRFs. We tested two hypotheses: 1) a nitrogen-release model based on a combination of degree-days and soil moisture content will better predict nitrogen availability relative to a model based on degree-days alone because temperature and soil moisture are equally important in controlling nutrient release from CRFs, and 2) the prediction of two-factor model will correlate to field measurements in a container-grown nursery operation regardless the locality of soil media. To test these hypotheses, we conducted a laboratory incubation experiment under four temperature regimes and three soil moisture conditions to establish a nitrogen release model for urea-based, multi-cote CRFs. The result of incubation study confirms the strong influence of temperature and soil moisture on nitrogen release from CRFs; the combination of higher temperature and soil moisture releases nitrogen faster than lower temperature and soil moisture content. Modeled results also show good agreement with field measurements in container-grown nurseries. Disagreements between modeled results and field measurements highlight the site-specific influence of soil climate on urea hydrolysis via soil microbial activities.
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