Prediction of the Nitrogen Requirements of Field Crops Part I. Theoretical Models of Nitrogen Release¹

Abstract

Abstract Theoretical models for the prediction of the total supply of mineral nitrogen available for crop production have been developed. These models are based on the assumption that the supply of available N is determined by fertilizer N, native soil mineral N, and N released from organic matter. Model No. [1] is of the form Y = b 0 + b l X l + b 11 X 1 2 + b 2 X 2 + b 22 X 2 2 + b 12 X 1 X 2 , where: Y = yield or other parameter dependent on N supply, X l = fertilizer N plus available soil mineral N, X 2 = any index of organic N release, and b l , b 2 , b . . . are coefficients determined by regression techniques. Model No. [2] is of the form Y = B 0 + B 1 (X 1 + a X 2 ) + B 2 (X 1 + a X 2 ) 2 , where: a represents a release coefficient appropriate to a given X 2 ; B 0 , B 1 , B 2 are regression coefficients; and Y, X 1 , and X 2 are the same as in Model [1]. The release coefficient a can be evaluated by ratios of coefficients from Model [1], ratios of slopes from Model [1], or by a reiterative procedure. More sophisticated models based on Model [2], but assuming nonlinear release of organic N, have also been developed along with methods for evaluating the constants involved.