Correlation of several soil n indices for wheat

Abstract

A study relating N uptake by wheat to several N soil tests was conducted throughout North and South Dakota. Sixty nine sites were utilized over a period of 5 years. The N soil tests and their respective r values with N uptake are: Soil Nitrate‐N 0–15 cm (N15), r=0.50; nitrate‐N 0–30 cm (N30), r=0.58; nitrate‐N 0–60 cm (N60), r=0.51; nitrate‐N 0–120 cm (N120), r=0.43; Kjeldahl N (TN), r=0.27; Organic matter (OM), r=0.24; absorbance of 0.01 M NaHCO₃ extract (SB), r=0.21; and ammonia distilled from autoclaved 0.01 M CaCl soil slurry (AN), r=0.21. Regression equations were used to predict N uptake by wheat using the soil test indices as independent variables. Soil tests that were useful in these equations were N30, AN, SB, and OM. Over all site years, only 29% of the variability in N uptake was explained using the 0–30 cm nitrate content. For the years of 1984 and 1985, approximately 60% of the N uptake variability was explained.