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This article in AJ

  1. Vol. 73 No. 1, p. 128-135
    Received: Nov 13, 1979

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An Index of Nutrient Efficiency and Its Application to Corn Yield Response to Fertilizer N. I. Derivation, Estimation, and Application1

  1. Eduardo Capurro and
  2. Regis Voss2



Improving the efficiency of use of applied nutrients in crop production are agronomic, economic, and environmental goals. The purpose of this study was to develop a methodology for studying the efficiency of fertilizer use, to apply it to the yield response of corn (Zea mays L.) to fertilizer N, and to use these results to estimate fertilizer N needs for a range of relative corn yields.

The derived nutrient efficiency was divided into two components: (a) one depending on the level of relative yield expressed as a percentage of maximum yield (hence, it depends on the nutrient rate and can be estimated from soil test or plant analysis values) and (b) a component termed relative efficiency index (Ex), which can be defined generally as the nutrient efficiency at 99% of maximum yield and is independent of the nutrient rate. for the quadratic polynomial, Ex is equal to one-fifth of the product of the square roots of the quadratic coefficient and of the maximum yield.

Relative efficiency index for N, EN, were obtained from quadratic regressions of corn yield on fertilizer N rates for each of 33 experiments conducted on well, moderately well, and somewhat poorly drained soils in Iowa. EN was closely related to the square root of the quadratic coefficient. Values of EN ranged from 2.5 to 9.3, and maximum grain yields varied from 3,600 to 10,200 kg/ha. Nutrient efficiencies were calculated from given values of EN and relative yield, e.g., this gave efficiencies in kg grain/kg N of 14 for EN of 2 and 42 for EN of 6 at a relative yield of 50%. The required increase in N rate for economic optimum yield was calculated from given values of EN, relative yield, maximum yield, and the N to corn price ratio.

The Ex seems to be a useful index to characterize the response of crop yields to applied nutrients and to derive yield-applied nutrient relationships.

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