DRIS Evaluation of the Nutritional Status of Crisphead Lettuce

Diagnosis and Recommendation Integrated System (DRIS) norms were derived for crisphead lettuce (Lactuca sativa L.) from field fertility experiments conducted over the past 20 years on mineral and organic soils in Florida. Preliminary testing indicates that DRIS diagnoses generally agree with diagnoses using the sufficiency range approach, with the advantage of predicting the degree of nutrient limitation. DRIS also appeared to correctly predict a response to K where sufficiency ranges currently used did not. Overall, DRIS appears to be a useful adjunct to the sufficiency range approach currently used to diagnose nutritional deficiencies in crisphead lettuce. The Diagnosis and Recommendation Integrated System (DRIS) method of interpreting nutrient content of plant tissue has received considerable attention since being detailed by Beaufils (1973). The DRIS approach stresses nutrient balance and provides a means for comparing the degree to which various nutrients limit yield, either as a result of deficiency or excess (Walworth and Sumner, 1987). Because the DRIS approach uses nutrient ratios, it is sometimes less sensitive than the sufficiency range (SR) approach to differences caused by leaf position, tissue age, climate, soil conditions, and cultivar effects. However, a shortcoming of using nutrient ratios is that DRIS may indicate a nutrient limitation for a nutrient that is low relative to others, even though the nutrient may not be limiting yield (Beverly et al., 1984). The incorporation of nutrient concentrations in the DRIS evaluation has been proposed and used as a means of minimizing these erroneous diagnoses (Hallmark et al., 1987; Parent and Granger, 1989). The DRIS approach has been found to provide reliable diagnosis for agronomic crops (Elwali and Gascho, 1984; Sumner, 1977; Walworth et al., 1986) and for orchard crops (Beverly et al., 1984; Parent and Granger, 1989). However, the possibility of using the DRLS approach for fast-growing short-season leafy vegetables, such as crisphead lettuce, has not been evaluated. The objectives of this work were to derive DRIS norms for crisphead lettuce and perform a preliminary evaluation of the DRIS approach as a tool for diagnosing nutrient deficiencies in lettuce. The data used for this investigation consisted of 3316 observations from numerous lettuce field fertility experiments conducted between 1971 and 1989 on both mineral and Received for publication 26 Apr. 1990. Univ. Fla. Expt. Sta. Journal Series no. R-O0624. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 274 organic soils in southern Florida. About 20% of the observations came from experiments conducted on mineral soils, and 80% of the observations came from experiments conducted on organic soils (Histosols). Details of experimental procedures are presented elsewhere (Sanchez and Burdine, 1988; Sanchez et al., 1988, 1990). The outermost sound leaf was collected from several plants in each plot in each experiment during the growing season (generally early to midgrowth). The leaves were dried at 60C and ground for analysis. From 1972 to 1983, N was determined by steam distillation after micro-Kjeldahl digestion. During this same period, P was determined calorimetrically, K and Na by flame-emission spectroscopy, and Ca, Mg, Fe, Zn, Mn, and Cu by atomic absorption spectroscopy, after digestion with HN03/HCIO4 acid. During this period, B was determined using the quinalizarin method (McDougall and Biggs, 1952). In 1984, our laboratory changed to a H 2O 2/H2SO 4 digestion (Wolf, 1982), after which time N was determined colorimetrically and B by inductively coupled plasma spectroscopy. Comparisons of digestion methods before the change was made indicated that both methods gave similar results. Because quality is often the overriding factor determining the market value of lettuce, we used a combined yield-quality index to separate superior and inferior subpopulations rather than yield alone. Lettuce yields were assigned a rating ranging from 1 through 5 for marketable yield levels of O to 14, 15 to 28, 29 to 42, 43 to 56, and >56 Mg·ha-1, respectively. The quality of lettuce was rated from 1 to 5 as very poor, poor, fair, good, and excellent, respectively. The lettuce was rated based on head firmness, head size, and the presence of marketing defects, such as tipburn, cracked stems, ribbiness, and rib discoloration (U.S. Dept. Agr., 1973). A yield–quality index was calculated as the multiple of the yield and quality ratings. Marketable yields >50 Mg·ha-l are generally only obtainable in the winter–spring (January to March) growing period when the weather is cool and irradiance is relatively high. Limiting yields in the range of 40 to 56 Mg·ha-1 are more frequent; hence, a yieldquality index of 16 was used to separate the