Presidedress Soil Nitrate Test Evaluation in Maryland

Abstract Nitrate enrichment of groundwater and the Chesapeake Bay are major concerns in the Mid‐Atlantic area. A soil N test could increase N use efficiency and decrease NO 3 losses to the environment. This research evaluated the presidedress soil nitrate test (PSNT) for corn ( Zea mays L.) in the Piedmont and Atlantic Coastal Plain regions of Maryland. Soil samples were collected to a 30‐cm depth when corn was 15‐ to 30‐cm tall from replicated N rate experiments that included seven soil types and five growing seasons. Soil NO 3 ‐N and (NO 3 + NH 4 )‐N were determined by steam distillation on PSNT evaluation plots. Corn grain yields were measured on PSNT evaluation plots and on corresponding non‐N‐limited plots to estimate relative yields. Experimental variables included: poultry manure (PM), dairy manure (DM), composted sludge (CS), tillage, and incorporated cover crops that gave 47 treatment‐year combinations. The PSNT accurately reflected differences in corn N availability due to prior N inputs from manure, composted sludge, and cover crops. The relationship between relative yield and soil NO 3 ‐N was similar for both no‐tillage and plow‐tillage. Soil NO 3 ‐N concentrations >22 mg kg −1 soil, or (NO 3 + NH 4 )‐N concentrations >27 mg kg −1 soil, were associated with relative yields of 0.95 or higher. The variation in relative yields at soil N concentrations less than the above critical values was too large for predictive use. The relative yield vs. PSNT relationship was better with (NO 3 + NH 4 )‐N than with NO 3 ‐N alone. The PSNT successfully identified N‐sufficient sites across a range of textures, drainage classes, and years. By identifying N‐sufficient sites, the PSNT will help farmers conserve fertilizer N and reduce NO 3 ‐N losses to the environment.