Building the Foundation for the CropManage Nitrogen Fertilizer Decision Support Framework to Guide Hawai‘i's Vegetable Production Systems.
Building the Foundation for the CropManage Nitrogen Fertilizer Decision Support Framework to Guide Hawai‘i's Vegetable Production Systems.
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2018-05
Authors
Loo, Mitchell K.
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Tropical Plant & Soil Sciences
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There is a need for nitrogen (N) fertilizer management strategies that can improve synchrony between N fertilizer application and crop N uptake in Hawaii. The ability to diagnose soil mineral nitrogen (SMN) status in a timely fashion can facilitate farmer adoption of N fertilizer management strategies. Although soil N diagnostic technology has been available for about four decades, there are critical drawbacks to the standard testing procedure that discourages farmer adoption of such tests. Recent developments of an on-farm soil testing methodology referred to as the soil nitrate quick test (SNQT) have shown great promise in overcoming the drawbacks associated with standard testing procedures. The proper steps needed to encourage widespread adoption of on-farm soil testing technology include accuracy assessment across regional soil types as well as crop and site specific calibration. We assessed the accuracy of the SNQT in agricultural soils throughout Hawaii, across a diversity of soil types as well as a wide range of soil nitrate concentrations. We also calibrated the SNQT on a Rhodic Haplustox for napa cabbage (Brassica rapa subsp. pekinensis) by identifying soil nitrate-N (NO3-N) critical concentrations beyond which response to N fertilizer is unlikely. The results indicate that the SNQT provides an acceptable estimation of soil NO3-N concentration that is similar to results using the standard soil testing methodology (r2 =0.95). We also propose an SNQT critical concentration for napa cabbage of 38 mg kg-1 NO3-N when the test was used as a pre-sidedress soil test (PSNT) two weeks after planting. Overall evaluation of the SNQT indicates that the test is a suitable diagnostic tool for Hawaii farmers.
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