Crop-specific sulfur management for optimizing productivity, quality and plant health
Silvia Haneklaus: Julius Kuehn-Institut, Institute for Crop and Soil Science
<div>The implementation of biological know-how into fertilizer practice is a major contribution to fully utilize potential crop yield and quality, and to strengthen crops against biotic stress. Sulfur Induced Resistance (SIR) is one constituent of the complex phenomenon of induced resistance (IR). S fertilization reduced the plant disease index (DI) for various host/pathogen relationships by 5 to 50 % (greenhouse) and 17 to 35% (field experiments), for instance <em>Verticillium</em> wilt in cotton from 0.708 to 0.375. Effective fertilizer rates can be higher than the physiological S demand and vary crop-specifically between 20 to 40 kg/ha S before winter and 50 to 100 kg/ha S during main vegetative growth in spring; a constant S supply over time provided best protection against soil-borne and foliar plant diseases. The magnitude and efficiency of SIR seems to be regulated by the external plant available S reserves and plant-inherent S pools and fluxes, whereby the strongest response to S can be expected when going from severe S deficiency to sufficiency. S fertilization increases plant S status, content/release of S-containing primary and secondary metabolites (cysteine, glutathione, glucosinolates, H<sub>2</sub>S and COS). All components show either a direct fungicidal/fungistatic effect or are involved in the induced resistance response. Based on a profound and robust statistical procedure, critical S concentrations (severe deficiency, optimum supply, toxicity) have been calculated for <em>Brassica</em> crops, legumes, pastures, Poaceae and root crops. These are recommended for adjusting fertilizer rates in order to maximize productivity and quality as well as enhance resistance against plant diseases.</div>
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