DERIVATION AND ASSESSMENT OF DRIS NORMS FOR GREENHOUSE TOMATOES

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Abstract
Diagnosis and recommendation integrated system (DRIS) norms were developed in Quebec from the 30% top yielding plants among 733 observations on marketable yields and foliar analyses of spring-grown greenhouse tomato plants. These crops produced between 4 and 6.5 kg plant−1 cumulated over 8 wk of harvest. Fifteen optimum nutrient ratios and concentrations were computed from N, P, K, Ca and Mg analytical results. DRIS norms developed irrespective of plant developmental stage were less sensitive than norms developed for selected sampling periods. Including a dry matter index in DRIS did not modify the nutrient ranking of independent samples, but DRIS and the critical value approach produced different diagnoses. The dry matter index may not only help in the separation of limiting from nonlimiting nutrient but can also become an indicator for modifying carbon accumulation in tomato plants. Since DRIS describes numerically the nutrient equilibrium in plants, fertigation regimes could be adapted to the actual plant requirements.Key words: Tomato, Lycopersicon esculentum L., tissue diagnosis, nutrient ratio, diagnosis and recommendation integrated system.

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