In-season soil nitrate testing as a guide to nitrogen management for annual crops

Abstract

In-season soil nitrate testing is most useful when there is reason to believe, based on field history, that N availability may be adequate. These reasons may include soil organic matter content, applied manure, compost, legumes in the rotation, or residual N fertilizer. Soil nitrate testing is not helpful when crops are grown on sandy, low organic matter content soils that are known from experience to be N deficient. Soil nitrate testing is useful for annual crops such as vegetables or corn for which supplemental N fertilization is a concern. Soft nitrate tests must be performed at critical crop growth stages, and the results must be obtained rapidly to make important decisions about the need for N fertilization. Soil nitrate-N (NO3-N) concentrations in the range of 25 to 30 mg·kg-1 (ppm) indicate sufficiency for most crops, but N fertilizer practice should be adjusted based on local extension recommendations.