FOLIAR NUTRIENT REFERENCE LEVELS OBTAINED IN HYDROPONIC CULTURES AS PRELIMINARY NORMS FOR DRIS TO FERTIGATE CONIFERS

Abstract

Preliminary norms for foliar tissue were developed for Cupressus glabra grown on a sand culture for use in the diagnosis and recommendation integrated system (DRIS). These norms were generated from macronutrients nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) of high-quality plants growing in hydroponics cultures in controlled conditions. The values were those of foliar tissues from three periods of the growing cycle (July, September, and November). These norms were applied to perform DRIS in plants growing in five artificial potting mixes with different physico-chemical properties. The results show that hydroponics are a good system to obtain nutrient reference levels at a lower analytical cost than that of a survey for its use in DRIS. DRIS indices obtained by using hydroponic norms are much higher than those obtained for other crops by using survey norms, due to luxury consumption of some nutrients with the hydroponic system. The physico-chemical properties of the potting mixes have a great influence by changing significant nutrient concentrations in tissues and consequently diagnosis and interpretation. DRIS is able to detect nutrient imbalances caused by the own composition of the substrate (i.e., K and Ca limitation in substrates with sepiolite—release Mg—in their composition, or P limitation in substrates with high pH and Ca).

ACKNOWLEDGMENTS

The authors thank the Subdirección General de Investigación de la Consejeria de Economia of the Comunidad Autónoma (the Research Department of the Regional Government) of Madrid for financing the Project to which this study belongs.