| Regulated deficit irrigation (RDI) was first coined as a new irrigation term abroad in mid-1970based on principles of traditional irrigation. The principal concept of RDI was that based on understanding of genetics and eco-physiological characteristics of crops, a prescribed limits of water deficit was imposed for a prescribed part or parts of the seasonal cycle of plant development, to regulate the Distribution of photosynthate in different tissues or organs, to coordinate growth of aboveground parts of plant and roots, to improve reproductive growth and development and control vegetative growth, to increase economic yield, and finally to realize the objectives of water-saving, high-yield, good-quality, and high efficiency crop production and extend irrigation area. In brief, RDI method was a more scientific and efficient irrigation strategy which paved the best way for regulating the water-soil-plant-environment relations. Therefore, studying on RDI in such water resources deficiency area as Huang Huai Hai plain of china was of important theoretical value and practical significance. In this study, different crops were used as experimental materials to expend research and application area of RDI. Firstly, the theoretical basis and eco-physiological mechanism were investigated. By the systematic analysis method, eco-physiological changes of crops in water deficit period were not only studied,. but also emphasized particularly on crops physiological metabolism and compensation mechanism after re-watering. Secondly, RDI models were established according to the coupling relationship between crop transpiration and photosynthesis with the objective to reduce water losses and improve photosynthate translocation efficiency. Finally, combinations of RDI and nutritional regulation and their mathematical models were studied and, therefore, improve the scientific characters, practicality and maneuverability of RDI techniques.The studies were carried out under rain-proof shelter conditions, by pot, plot and pond culture, with winter wheat (Triticum aestivum L.), summer maize (Zea mays L.) and cotton (Gossypium hirsutum L.) as materials. The research was developed qualitatively and quantitatively using conventional methods and advanced techniques, with help of a series of instruments and equipments. The main results were as follows:1. Under rain-proof shelter condition and cultivated in plots with winter wheat, summer maize and cotton, the effects of RDI on crop morphology were studied. The results indicated that there were differences in effects of RDI on crop morphological development due to different crops, growing stages and degree of water deficit. Moderate water deficit imposed (degree of water deficit was50%～55%FC) from jointing to heading in winter wheat or in summer maize could effectively inhibit plant height, promote plants to grow healthily, prevent lodge at late stages and finally obtain higher economic yield. However, cotton plant height didn’t decrease under different water deficit treatments. Growth of root system in winter wheat was restrained severely during water stress period before jointing, but there was a super-compensation effect in root growth after re-watering. Comparatively, water deficit imposed at middle or late growing stages in maize not only promoted root growth but also delayed root senescence, indicating that adaptability of maize plants to water stress at late growing stages was stronger than that at earlier stages. RDI didn’t change the general trend of cotton root growth but accelerated root growth rate, which was rather different from that either of winter wheat or summer maize. RDI in winter wheat could increase the ratio of root to shoot (R/S), and R/S increased with the degree of water deficit. R/S of maize increased significantly during water stress period from jointing to heading, distribution of photo synthetic products in roots and shoots reached balance after re-watering. The moderate water deficit (degree of water deficit was50%～55%FC) at different growing stages in cotton accelerated significantly root growth rate and kept higher dry root weight during water deficit period, enhanced the effects in compensatory growth and delayed senescence of roots, and kept higher R/S value at late stages.2. Under conditions of mobile rain-proof shelter and cultivated in pots with winter wheat, summer maize and cotton, effects of RDI on photosynthetic characteristics and accumulation and distribution of crop photosynthates were studied. The results showed that under appropriate degree of water deficit at suitable growing stages, there were compensation or super-compensation effects in photosynthesis and accumulation of photosynthetic products after re-watering. The proportion of photosynthetic products partitioned to the economic organs increased. The suitable growing stages to introduce RDI in winter wheat was jointing stage and before, and the degree of water deficit was50%～60%FC. For maize, the suitable growing stages were either before jointing, and the degree of water deficit was50%～55%FC, or from jointing to tassel, and the degree of water deficit was60%～65%FC. For cotton, RDI imposed at seedling or boll-opening stage was suitable and the degree of water deficit was60%～65%FC or50%FC-～55%FC.3. Under conditions of mobile rain-proof shelter and cultivated in pots with winter wheat, summer maize and cotton as materials, effects of RDI on crop yield and water use efficiency were investigated. The results indicated that water-consumption of crops decreased with degree of water deficit, fitting a quadratic regression equation. Appropriate degree and of water deficit at suitable stages inhibited luxury transpiration and hence reduced water loss and increased crop yield. Water deficit before green-returning in winter wheat, before jointing in maize and at seedling stage in cotton not only increased yield but also save water significantly. The most appropriate degree of water deficit for improving WUE in winter wheat, summer maize and cotton was50%～55%FC,60%～65%FC and50%～60%FC, respectively. Based on above data, RDI models were suggested which could be used according to local conditions. 4. Under conditions of large-scale open-closed type rain-proof shelter in plot culture with winter wheat as material, effects of RDI on quality of crop economic product were studied. The results indicated that the correlations between grain protein content in winter wheat and soil water moisture were not all negative. There were differences in effects of RDI at different growing stages on grain protein content. The correlations between grain protein content of strong-gluten wheat cultivars and soil water moisture from jointing to heading stage were negative. Appropriate degree of water deficit at different growing stages increased amino acid content. Before heading, under conditions of different degrees of water deficit, amino acid content increased with postponing of introduction time of water deficit. Amino acid content was the most sensitive to water deficit from jointing to heading stage, next came that at grain filling stage. Light or middle degree of water deficit before jointing stage did not significantly reduce grain yield, protein yield and amino acid. However, water deficit after jointing stage resulted in reduced yields seriously, especially from jointing to heading stage, even though the degree of water deficit was light. Light degree of water deficit at grain filling stage did not significantly decrease grain yield, but enhanced the water-saving effects and significantly improved grain quality.5. The results from these studies also showed that the correlations between grain yield and protein content in winter wheat were not all negative. The situation would change in certain conditions. There were significant differences in effects of RDI at different growing stages on relationship between grain yield and quality characters. Therefore, it was suggested that coordinating high grain yield in contradiction to good grain quality might be possible, which modified the existing theory on relations of grain yield to quality. In these current studies, it was also preliminarily confirmed that RDI was a practicable technique for coordinating relationship between grain yield and quality characters in winter wheat.6. Under conditions of mobile rain-proof shelter and cultivated in pots and ponds with winter wheat, summer maize and cotton as experimental materials, effects of combinations of RDI and nutritional regulation were studied. A three-factor (degrees of water deficit, nutrient levels, and sowing rates) quadratic rotational regression combination design were employed in pond culture. The results showed that there was a significant interaction between water deficit and nutrient levels. Negative effects of RDI were compensated by rational fertilization. Two objective function mathematical models for economic yield and WUE in wheat, maize and cotton were established, respectively, based on the data from three-factor quadratic rotational regression design experiment. Analysis of the models suggested that plant population moderately be increased and be combined with other agronomic measures while RDI was introduced. Finally, optimal schemes for combinations of RDI and agronomic measures with different objectives were worked out by computerizing simulation.From what has been discussed above, it may be concluded that it was practical for RDI in field crops such as winter wheat, summer maize and cotton to realize the objectives to save water and obtain high grain yield, high grain quality and high WUE. Eco-physiological mechanism of RDI was like this:RDI reduced evaporation and transpiration significantly during the water deficit/stress period; luxury transpiration was significantly inhibited while photosynthetic rate decreased slightly; there were compensational or super-compensational effects of RDI on photosynthesis and photosynthetic product accumulation after re-watering; and the proportion of photosynthate partitioned to the economic organs increased. Appropriate degree of water deficit/stress at appropriate growing stages inhibited vegetative growth, promoted reproductive growth and development, coordinated R/S, and improved root absorption efficiency and material transformation efficiency in plant body. |
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