Functions and ratio order of the nutrients at the establishment of DRIS norms in 'Valencia' sweet orange

Abstract

Diagnosis and Recommendation Integrated System (DRIS) has been a useful tool for nutrient diagnosis of several crops. This research aimed to establish adequate norms for DRIS through three methods (Beaufils, Elwali & Gascho and Jones) to calculate ratio functions and two criteria (Letzsch and Nick) for choosing the ratio order of the nutrients for 'Valencia' sweet orange budded on three rootstocks, in Mogi Guaçú, SP, Brazil. Data referred to yield, rootstock and concentrations of N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn and B in leaves of non fruiting terminals, for each plot, were processed for 1994 through 1998. Nutritional Balance Index (NBI) was calculated by the average of the sum (disregarding the sign) of all nutritional index values and dry matter index. DRIS and NBI indexes were calculated and the r² values (yield related to NBI) were obtained for each calculation method. DRIS calculation method of the ratio function, recommended by Jones, presented better correlation with yield. The criterion for choosing the ratio order of the nutrients recommended by Nick was more efficient. Specific populations, with reduced number of observations, standardized by rootstock and referred to one or two sampling years were more efficient data for calculation of DRIS norms.