Using Heat Unit Models to Predict N Release from Controlled Release Fertilizers for Vegetable Production

Controlled release N fertilizers (CRN) perform poorly when N release rates are mismatched with crop demand.  Studies were conducted to develop a method to predict N release rates from CRN products and develop a tool to recommend specific products for specific crop planting and harvest windows.   Initial studies involved weighing CRN products into nylon mesh bags and burying the bags 7 to 8 cm into the soil within vegetable production fields.  Soil temperature measuring data loggers were installed in each site and the mesh bags were excavated approximately every 7 to 14 days after burial.   Replicate samples pulled at each recovery date were digested, and total N was determined in the laboratory.   Studies also involved correlating measured field release rates to laboratory release tests using alternative temperature summation models.  These data were used to match up predicted release rates with soil temperature summations for alternative crop planting and harvest windows based on long term data bases of weather and crop growing period.  We have compiled a list of recommended CRN products for various vegetable crops and planting dates in the arid southwestern US.