Reducing Water in Rice Cultivation

by Laura Van Vliet

A recent study revealed by scientists has shown that the use of ammonium as a fertilizer rather than a nitrate and ammonium mixed fertilizer can increase the tolerance of rice (Oryza sativa L.) to water stress.

Researchers at the Nanjing Agricultural University in Nanjing, China, used rice seedlings grown by hydroponics (where water stress was simulated through the addition of PEG, 6000) and greenhouse grown (in pots) rice seedlings to study the drought tolerance of the plants. Under non-water stress conditions, the researchers found that the two different treatments had little effect on rates of photosynthesis, water uptake, and general nutrient flow in the plants. However, the study, headed by Yong Li and Yingxu Gao, showed during water stress significantly less negative effects on plant growth and photosynthetic activities when ammonium was provided to the plants, compared when the nitrate and ammonium mix was. Under water stress, it was also shown that the dry mass of the rice shoots was decreased by 25% for the ammonium treatment versus 43% for the nitrate mix. There was also a major increase in the water uptake and general nutrient flow in the plants treated with ammonia. This suggests an increased capacity to produce grain when higher levels of ammonium are present under water stress conditions.

A key difference between rice fields which are flooded (non-water stress) compared to those which are not (water stress) is the form of nitrogen which was available to the plants. Flooded fields generally contain more ammonium, while those not flooded have a higher level of nitrates. This study suggests that by artificially creating high levels of ammonium during water stress, we may be able to combat the major effects of low water levels on rice cultivation.

This study suggests that rice may be able to be cultivated in areas where water stress may normally have prevented a viable crop. Or similarly that water-saving irrigation techniques which have been developed but cast aside - because water stress prevented there use being profitable - may be put into place to avoid the wasteful over-usage of fresh water. In today’s world, this is especially important. Food prices worldwide have been on the rise in past few years, due to crop failures and low levels of food stocks (FAO, 2008). Compounding this issue is water quality and supply problems in many parts of the world. A large amount of water is crucial to rice farming. For each kilogram of rice produced by farmed, 2 m3 of water is required, and over 80% of this water is lost through evaporation and leakage (Li, Yong et al, 2009). This is two to three times more than other cereals, but rice is a staple food for over half of the world’s population (Aragon et al., 2008). In a world where clean and fresh water is rapidly disappearing, the use of ammonia to increase rice productivity in conditions of water scarcity could be crucial to the solving water conflicts in the future.

References

Li, Yong et al, 2009. Ammonium enhances the tolerance of rice seedlings (Oryza sativa L.)
to drought condition. Agricultural Water Management 96 (2009), pp. 1746-1750. Available at http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T3X-4X3DRY7-1&_user=1067211&_coverDate=12%2F31%2F2009&_rdoc=10&_fmt=high&_orig=browse&_srch=doc-info%28%23toc%234958%232009%23999039987%231505120%23FLA%23display%23Volume%29&_cdi=4958&_sort=d&_docanchor=&_ct=22&_acct=C000051237&_version=1&_urlVersion=0&_userid=1067211&md5=feb25e6c2b767c7841fcf3b8855903e2

Aragon, C.T. et al. 2008. The United Nations Must Manage a Global Food Reserve. UN Chronicle. Accessed on 14 October 2009. Available at http://www.un.org/Pubs/chronicle/2008/issue2_3/2_308p58.html

Food and Agricultural Organization of the United Nations (FAO). 2008. FAQs on Food Situation. Accessed on 14 October 2009. Available at http://www.fao.org/worldfoodsituation/wfs-faq/en/