In the Hetao Irrigation Districts of the Ningxia autonomous region, Upper Yellow River Basin, the "con-tinuous deep flooding irrigation" method is used for the rice paddies. The field irrigation water use during the rice-growing season is two to three times higher than in other regions of North China where water-saving practices have been introduced. This paper, based on the data measured in experimental rice fields and sub-branch canal systems, presents main results concerning crop evapotranspira-tion, percolation and irrigation requirements for deep and shallow water irrigation. Causes for water waste relate to both the lack of regulation in supply and distribution canals and to the poor management of paddy fields. The potential for water saving is discussed using water bal-ance data. Improved irrigation techniques and water man-agement strategies, including the shallow water irrigation method, are suggested considering the expected impacts and benefits. Replacing the current continuous deep flood-ing with the shallow-ponded water irrigation method may reduce the growing season irrigation water use from 1,405 to 820mm in average, with a likely increase in yields of 450kg/ha. Water productivity would then increase from 0.49 to 1.03kg/m3. Adopting improved canal manage-ment and modernization of regulation and control struc-tures may lead to decreasing the gross irrigation demand from the present 3,100mm to about 1,280mm, which would highly benefit the environmental conditions in the area.

In the southern part of China over 70% of the cultivated area is under rice. A tremendous amount of water is used for the rice fields under the traditional irrigation method, termed 'shallow flooding irrigation1. Since the 1980s, in some provinces in south China, a new irrigation technique for rice, termed 'water-saving irrigation', has been advanced. In recent years this new technique has become widespread. The basic feature of this new irrigation technique is that there is no water layer above the soil surface in rice fields during the growing season of rice after the stage of recovering. This technique not only saves water and increases the rice yields, it also: reduces soil and water pollution; improves soil aeration; improves the field's microclimatic condition; reduces rice diseases and insect pests; and improves the regional water balance. This paper discusses the details of the water-saving irrigation technique for rice, and its potential environmental impact in south China.

A network of about 30 basic and more than 150 ordinary irrigation experiment stations for observing the evopatransptration of rice the soutern and middle parss of China has been formed. In this paper, based on the analysis of the observation data from the majority of the besic and a port of the ordinary stations, the patterns of vanation of evaputran-sptrotian of rice in space and time are expounded. Based on the inference, calcutation. and verification by the observation data from the above stations, the main method for cal-culating the evapotransptration of rice in China are exponded and recommended. In par-ticular, three new methods are introduced and discussed Finally. the method and results of making the isoline maps of evapotranspiration of rice in China are introduced.

The forecast of cropevapotranspiration (ET) is one of the essential parts of the work for compiling e dynamic plan of imigation water use. It plays an important role in saving water, ineressing ropyields and economic benefits in en imigation area. In this paper, amocile for a shortrange glass than 15 days forocasl of ET is introduced and ciscussoid The ralationship between ET ard the melecrological factors and ono-motoorological tactors such as tho factors of plant and scil are enalysed. The models which express the effects of meteorology. Plant and soil on ET separately are recommended, Based on these moreis a combined model for the forecast of ET and the eonerete methods of the short-range forecast of ET are presented.

本文根据作者在全国协作研究作物需水量等值线图（湖北协作组）工作中取得的成果及经验，并暧取兄弟省、市、自治区及国外经验，就作物需水量等值线图的类别、绘制原理和方法以及应甩等方面进行论述。从满足生产需要出发，提出绘制四种等值线圈：（1）垒年各月的日平均参照作物需水量等值线图；（2）作物生育期内各月的日平均作物稚水量等值线图；（3）作物全生育期需水量等值线图，（4）作物全生育期日平均需水量等值线图。阐述了每种图的依据、作用及绘制方法。推荐用“改进的彭曼法”及“作物系数”计算作物需水量；指出应用此法时在推算净辐射及空气动力学项中常产生的错误，分析错误的原因，提出正确的算法。最后，阐述应用需水量等值线图绘制净灌溉定额等值线图的方法，以便用该图进行灌溉区划和灌溉工程的规划、设计与管理；用实例说明利用需水量等值线图综合分析需水量在空间和时间两方面的变化规律，藉以指导抗旱和调整农业布局。