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PRODUCTION PAPER

Selecting the High-Yield Subpopulation for Diagnosing Nutrient Imbalance in Crops

^a Dep. of Soil Sci. and Agri-Food Eng., Laval Univ., Paul-Comtois Building, Sainte-Foy, QC, Canada G1K 7P4
^b Hortic. Res. and Dev. Cent., 430 Gouin Blvd., St-Jean-sur-Richelieu, QC, Canada J3B 3E6

* Corresponding author (leon-etienne.parent{at}sga.ulaval.ca)

Received for publication August 10, 2000. Plant nutrient status is currently diagnosed using empirically derived nutrient norms from an arbitrarily defined high-yield subpopulation above a quantitative yield target. Generic models can assist Compositional Nutrient Diagnosis (CND) in providing a yield cutoff value between low- and high-yield subpopulations for small databases. Our objective was to compute the minimum yield target for sweet corn (Zea mays L.) and the corresponding critical CND nutrient imbalance index using a cumulative variance ratio function and the chi-square distribution function. Population (40 observations) and validation (20 observations) data were selected at random from a survey database of 240 observations including commercial yields and leaf nutrient concentrations. A filling value (R_d) was computed as the difference between 100% and the sum of d nutrient proportions [R_d = 100 - (N + P + K + ...)]. The CND nutrient expressions were the row-centered ratios of N, P, and R_d proportions in tissue specimens. Variance ratio computations of CND nutrient expressions among two subpopulations arranged in a decreasing yield order were iterated across population data. The proportion of low-yield subpopulation computed at the inflection point of a cubic cumulative variance ratio function was 67.5%, the minimum proportion of low-yield specimens. That exact probability corresponded to a theoretical chi-square value (CND r²) of 1.5 for three components. The critical CND r² value was validated using independent samples and the sum of the squared CND nutrient indices. The procedure is applicable to small-size crop nutrient databases for solving nutrient imbalance problems in specific agroecosystems. A calculation example is presented.

Abbreviations: CND, Compositional Nutrient Diagnosis • CVA, Critical Value Approach • DRIS, Diagnosis and Recommendation Integrated System

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