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This article in AJ

  1. Vol. 85 No. 4, p. 934-937
     
    Received: Oct 22, 1990
    Published: July, 1993


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doi:10.2134/agronj1993.00021962008500040027x

Deriving Fertilizer Recommendations with a Flexible Functional Form

  1. Gustavo E. Sain  and
  2. Mario A. Jauregui
  1. E conomics Program, Int. Maize and Wheat Improvement Ctr. (CIMMYT), Lisboa 27, Col. Juáirez, Deleg. Cuauhtémoc, Apdo. Postal 6-641, 06600 México, DF, México
    F ac. de Ciencias Agrarias, Univ. Nac. de Cuyo, Almirante Brown 500, 5505-Chacras de Coria, Mendoza, Argentina

Abstract

Abstract

General fertilizer response models are useful to derive robust recommendations for farmers who face different circumstances. This paper shows that a flexible functional form such as the transcendental can be applied to develop both agronomically and economically sound recommendation tables using a set of soil test, climate, and management variables. Data from thirty-eight experiments on wheat response to N and P in the Humid Pampa, Argentina, were used to build a general response model that incorporates the initial levels of soil test measures (NO3-N and Bray-1 P), rainfall from sowing to maturity, and previous crop. The economic analysis was performed for relevant nutrient/grain price ratios ro = 8.0 and rp = 18.3 for N and P, respectively. A table of fertilizer recommendations for wheat was derived for different combinations of rainfall expectations, previous crop, and soil test values. The following results were obtained: (i) the estimated model not only accounted for a significant percentage of the total variability in the dependent variable (InY), with R =0.56, P = 0.01, but it also gave coefficients with signs in conformity with agronomic expectations; (ii) the economic optima for N (N*) and P (P*) are compatible with the range of optima computed with per-site economic analyses; (iii) N* and P* increased as rainfall increased; (iv) N* was lower for wheat after soybeans than for wheat after maize; (v) N* was higher for smaller values of soil N, while P* was practically unaffected by soil N; and (vi) P* was higher for smaller values of soil P, while N* was affected by soil P, with a pattern that depended on both previous crop and rainfall. Similar tables can be derived for groups of farmers under different economic circumstances (i.e., different input/output price ratios).

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