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Deriving Fertilizer Recommendations with a Flexible Functional Form
Author(s) -
Sain Gustavo E.,
Jauregui Mario A.
Publication year - 1993
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1993.00021962008500040027x
Subject(s) - fertilizer , mathematics , sowing , agronomy , crop , soil test , nutrient , statistics , soil water , environmental science , soil science , biology , ecology
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 (NO 3 ‐N and Bray‐1 P), rainfall from sowing to maturity, and previous crop. The economic analysis was performed for relevant nutrient/grain price ratios r o = 8.0 and r p = 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 (In Y ), with R 2 =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).