Fertilizer Zinc Efficiency in Flooded Calcareous Soils

Abstract

AbstractEffect of Zn sources and methods of application on rice (Oriza sativa var. Giza 159) was studied in relation to organic matter application and to N source. In addition to laboratory investigations, a pot experiment was conducted with 65Zn‐labelled soil (Vertic Torrifluvents) and two field experiments with labelled and nonlabelled Zn fertilizers.Zinc oxide (ZnO) was superior to ZnSO4 in increasing grain yield and Zn content of flooded rice and in maintaining higher Zn concentration in the soil solution. With different methods of ZnSO4 application, rice yield and Zn uptake were in the order: applied to surface water 2 weeks after transplanting ≫ mixed with soil = surface applied to soil. The corresponding percentages of plant Zn derived from fertilizer and of Zn utilization from the applied fertilizer were 11.2, 8.46, and 6.26%; and 2.9, 1.4, and 1.0%, respectively. Effectiveness of organic matter in increasing yield and Zn content was greater when applied 2 weeks before transplanting than when applied at transplanting, as it decreased soil solution Zn during the first 2 weeks of anaerobic decomposition. The organic matter induced a temporary reduction in Zn content early in the season, but a good correlation was obtained between grain yield and Y leaf Zn at the midtillering and panicle initiation stages.With combined Zn and organic matter application, urea as a N source resulted in higher yielding and Zn content than (NH4)2SO4. Specific activity measurements showed that under nonflooded conditions rice was largely dependent on the Zn labile pool, while flooded rice was able to derive Zn from an additional source. Results generally indicate that formation of sphalerite (ZnS) may play a major role in controlling Zn solubility in flooded calcareous soils.