Delayed-Release Nitrogen Fertilizer Effects on In-Season Soil Nitrogen for Michigan Sugarbeet Production.

Delayed-release N fertilizers have received attention for Michigan sugarbeet production as producers seek to improve the timing of N availability to better match plant demand and to maximize plant N use efficiency.  The N release characteristics of these products are particularly important in sugarbeet production, where excessive N availability late in the season can have adverse impacts on crop quality.

The objective of this research was to evaluate delayed-release N fertilizer sources, alone and in combinations with conventional N fertilizers, on sugar beet yield and quality. Fertilizer sources included two conventional fertilizers, urea and urea ammonium nitrate solution, and two delayed-release fertilizers, polymer-coated urea and liquid polymer N. Treatments at two locations were arranged in a RCBD with 4 replications and included a no-N control and seven source/combinations at two N rates (90 and 124 kg N ha^-1). Soil samples (0-15 cm) were collected on 10-14 day intervals throughout the growing season for evaluation of soil N status. Sugar beets were harvested for determination of root yield and subsamples were analyzed for quality components including recoverable sucrose, clear juice purity, and amino N. 

Results from 2007 showed that delayed-release N products often resulted in similar root yield and quality as conventional N fertilizers.  Soil N concentrations did not generally differ between 90 and 124 kg N ha^-1 rates throughout the season.  Differences in soil N concentrations were observed between N sources at in-season timings, but differences were not consistent across time.   No relationships were found between in-season soil N and root yield or quality characteristics at harvest.