水稻田水資源及水分利用效率之探討

Abstract

我國年平均降雨量高達2,500公壓以上，和世界年平均降雨量相較，是屬於雨量豐沛的區域，然而，受限於地形和季節因素的影響，河流短促且降雨分布不平均，多數雨水逕流入海，在豐水期的逕流量高達85％以上。因此，如何有效的調控水資源，以滿足各項用水需求是重要的課題。水稻是我國種植面積最廣，同時也是需水量最大的糧食作物，如何開發水分管理系統以減少灌溉用水量及增加水分利用效率是需要努力的工作。水稻水分利用效率數值在0.5-1.69kg-1間，若以進水量作為基值，水分利用效率大約為0.3-0.79kg-1，均較小麥（0.8-1.65kg-1）及玉米（1.6-3.99kg-1）為低。偏低的原因為水田較其他作物有較高的滲漏及滲流，這種無助於水稻生產之耗水量，主要在於整田及生育期問維持湛水狀態所致。作物缺水時，光合作用下降主要是氣孔關閉所致，而CO2同化的限制使電子傳送反應受阻，有過多還原力造成活化氧族的產生，導致光氧化及光抑制的傷害。作物有複雜的抗氧化系統以對抗活化氧族的傷害，在不同耐旱程度之品種或基因型，降低氣化傷害和增加抗氧化系統有密切關係。 The average rainfall in Taiwan is about 2,500 mm. When compared with the whole world rainfall standard, Taiwan is belonged to abundant rainfall area. However, the rainfall distribution in Taiwan is disproportionate and the landform is high and precipitous. It will be nearly 85 percent of runoff flowing into the sea directly. For this reason, how to use water resource effectively in order to satisfy water requirement on each purpose is an important issue. Rice (Oryza saliva L.) is the most widely grown and produced crop in Taiwan, but it is also the greatest consumer of water among all crops. In the present time, efforts must be made to develop new water management systems aimed at reducing irrigated water input and increasing water use efficiency in rice production in Taiwan. When comparing the water use efficiency (WUE) among rice and other crops in field during the growth period, data show that the WUE of rice is about 0.3-0.7 g kg-1, while it is 0.8-1.6 g kg-1 for wheat and 1.6-3.9 g kg-1 for corn. There are higher seepage and percolation in paddy field during rice growth. Those non-beneficial depletions and outflows are due to maintaining the flooded water layer on the soil surface during crop growth and land preparing stage in traditional rice cultivation. When rice grown under drought conditions during soil water deficit, the photosynthesis decreases due mainly to stomatal closure. The limitation of CO2 assimilation will cause the inactivation of electron transfer reaction, an excess of reducing power is frequently generated in water-stressed plants. The over-reduction of photosynthetic electron chain may result in the formation of active oxygen species (AOS) that can lead to photoinhibitory and photooxidative damages. Plants are endowed with a complex antioxidant system to cope with AOS. Among different drought-tolerant varieties or genotypes, to increase the expression of antioxidant system is associated to decrease oxidative damages.