Diagnostic techniques for cereals based on plant analysis II. Diagnosis and yield prognosis models

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Abstract
In a relationship between the grain yields and concentrations of a nutrient element at a well defined stage of development under varying growing conditions, i.e. 2.0 g Dry Matter weight (DMw) per hill, the boundary line concept dictates that the grain yield corresponding to the points along the boundary of data points is predominantly determined by the varying concentrations of the respective nutrient element. These concentrations, defined as “Pure‐effect Concentrations,”; form the bases to develop the pure‐effect yield curves. Pure‐effect yield curves were developed for N, P, K, Ca, Mg and Na. The absolutely optimal concentrations or absolute reference values, i.e. the concentrations of various nutrient elements at 2.0 g DMw level corresponding to maximum grain yield, were found to be 3.3% N, 0.36% P, 3.9% K, 1.3% Ca, 0.25% Mg and 0.03% Na. The relationships were developed between the concentrations of other nutrient elements corresponding to pure‐effect concentrations of a nutrient element in question in all combinations by treating each nutrient element as pure‐effect nutrient at a time. These relationships enable one to determine the varying optimal concentrations of other nutrient elements corresponding to the concentrations of the pure‐effect nutrient. These concentrations are defined as “Relatively Optimal Concentrations”; or “Relative Reference Values.”; The absolute and relative reference values are the bases for developing the diagnosis and yield prognosis models which can be used to evaluate the nutritional status of lowland rice plants and to predict the grain yield based on the elemental composition of plants at 2.0 g DMw per hill. The procedure for the application of diagnosis and yield prognosis models is demonstrated. A very good agreement was found between the grain yield predicted by using these models and the actual yields, thus indicating a high degree of accuracy in predicting the grain yield.