Improved Zinc Management Strategies for Rice Scientists and Farmers.

Many rice soils are zinc deficient, resulting in yield loss and grain with low levels of Zn, which is suboptimal for human nutrition. Recommendations for Zn fertilization of rice have been in the literature since the 1970’s, but with the subsequent development of more Zn-efficient varieties, the new goal of high grain Zn, and the steady increase of Zn fertilizer prices, it is important to update these recommendations. Because Zn fertilizer added to soil becomes rapidly unavailable after flooding, the Zn fertilizer use efficiency from traditional recommendations is quite low (1-5%). A supply of high quality Zn fertilizer is hard to maintain because it is not carefully regulated in most Asian countries and it is easy for unscrupulous traders to adulterate.  From the scientist’s perspective, it is important to add appropriate amounts of Zn at appropriate times with optimal water management in order to determine if there is a real response to Zn fertilization. From the farmer’s perspective, it is important not to waste money on bad fertilizer or on unnecessary amounts of high-quality fertilizer. Optimal strategies for testing Zn fertilization methods under varying environmental conditions have been studied in field and greenhouse experiments, and suggestions for timing of Zn fertilization and water management are made based on the two goals of providing enough Zn for rice to grow well in Zn-deficient soil, and providing enough Zn to increase the amount of Zn in grain under multiple soil environments.