Correlation of soil test nitrogen with potato yields

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Abstract
Yield response of Idaho Russet Burbank potatoes to nitrogen fertilizer was related to soil test for inorganic N (NO3 ‐ and NH4 +) in a total of 27 field experiments over a 3‐year period using polynomial correlation and regression analysis. Nitrate plus ammonium nitrogen content in the surface foot of soil was found to be useful in predicting yield response of potatoes to applied nitrogen. Correlations between yield and extractable N were considerably better when the data from each cropping system were analyzed separately than when all locations were analyzed as one group. Additional improvement was obtained by including extractable ammonium nitrogen and nitrogen in the second foot of soil respectively. The best correlation with yield was found using (NO3 ‐ + NH4 +)‐N in the surface foot following grain and the top two feet following non‐grain crops with R2 values of 0.875 and 0.821 respectively.