ASSESSING NITROGEN MINERALIZATION TO REFINE NITROGEN RATES FOR CROPS TO MINIMIZE LOSSES

Larry Bundy [1]

Nitrate enrichment of groundwater and surface waters are important water quality issues.  The need remains to better predict N mineralization and availability in cropping systems so that fertilizer additions can be more efficiently used.  Previous work has shown that preplant (PPNT) and pre-sidedress (PSNT) soil nitrate tests do improve identification of sites where corn would not respond to N fertilization.  However, the use of these tests on soils with substantial organic N mineralization has been less promising, indicating a need to better understand and quantify N mineralization potential in these cropping systems.  For example, in 301 field studies, about 65% (range 29-78%) of the nitrogen that was mineralized over the summer was mineralized after taking the pre-sidedress nitrate test (V10 stage).

The purpose of the new study will be to develop and evaluate rapid tests for estimating soil N-mineralization capacity across a range of cropping systems.  The corn phase in the continuous corn system (CS1), the no-till corn-soybean system (CS2), the no-chemical corn-soybean-wheat/cover crop (CS3) and the alfalfa + manure and corn rotation (CS5) will be the test treatment.  Plots will be sampled and a battery of tests used to estimate nitrogen fertilizer needs and then the plots will be amended with fixed amounts of N-fertilizer.  The study will indicate which of the assays under study best predicts the need for additional N-fertilizer during corn production under a range of cropping systems.

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