Water-Saving Irrigation Techniques For HighYield And Good Quality Of Rice And Their Physiological Bases

Rice is the foremost stable food crop in China and the greatest water consumer in agriculture. With the population growth, urban and industrial development, and the aggravation in environmental pollution, the increase in total food production is necessary, meanwhile this increase needs to be accomplished under increasing scarcity of water resources. Therefore, it would have great significance to establish the water-saving techniques for high yield and good quality in promoting rice production and ensuring food security. This study investigated the characteristics of grain yield and grain quality of rice under different water-saving irrigation techniques and their physiological mechanism. The main results were as follows:1. Effect of furrow irrigation and alternate wetting and moderate drying irrigation on the grain yield and quality of riceFurrow irrigation and alternate wetting and drying irrigation have been considered as two new water-saving techniques in rice production. This study aimed to investigate yield performance in terms of quality and quantity under such practices. Two cultivars, Yangdao6(an indica hybrid cultivar) and Yangjing4038(a japonica cultivar) were field-grown and three treatments were imposed from transplanting to maturity:conventional irrigation as control (CI), furrow irrigation (FI) and alternate wetting and moderate drying (WMD, re-watered when soil water potential reached to-15kPa at15-20cm). Compared with CI, both FI and WMD enhanced percentage of productive tillers, area and length of top three leaves, grain-leaf area ratio, light transmission rate, dry matter accumulation from heading to maturity, leaf membrane lipid peroxidation, photosynthetic rate, root activity and contents of indole-3-acetic acid and zeatin+zeatin riboside in roots, and significantly increased yield by9.43%-11.6%and6.16%-9.94%respectively. Both FI and WMD either significantly increased the rates of brown rice, milled rice, head rice and contents of albumin and glutelin proteins, and peak viscosity and breakdown value of rapid visco-analyser (RVA) profiles, and reduced chalky kernels, chalk size, chalkiness and content of prolamin in grain and setback values. The two cultivars showed similar trends in quality and quantity of rice yield. Both FI and WMD could increase grain yield and quality. Improvement in root and canopy performance under FI and WMD contributed to a higher grain yield and better quality of rice.2. Effect of alternate wetting and severe drying irrigation on grain yield and quality of drought-resistant rice cultivars A field experiment was conducted with a local high-yielding cultivar, Yangfujing8and three drought-resistant cultivars, hanyou113, hanyou3and hanyou8. Two irrigation treatments, conventional irrigation as control (CI) and alternate wetting and severe drying irrigation (WSD) were imposed from transplanting to maturity. Characteristics of the grain yield and quality of water-saving and drought-resistant cultivars under WSD were investigated. Compared with CI, the WSD increased grain yield of drought-resistant cultivars by-3.2%-3%, the difference was not significant between CI and WSD. The grain yield of the local high-yielding cultivar was significantly reduced by21.4%under the WSD. The WSD significantly increased head rice and breakdown, and reduced chalkiness degree and setback of Hanyou113. Apart from Gel consistency, the differences in milling quality and appearance of Hanyou3or Hanyou8were not significant between CI and WSD. Compared with the local high-yielding cultivar, water-saving and drought-resistant cultivars under WSD significantly increased photosynthetic rate of the flag leaf, root dry weight, ratio of root to shoot, root activity, contents of zeatin+zeatin riboside (Z+ZR) in roots and activities of the key enzymes involved in the sucrose-starch metabolic pathway in grains at the mid and late grain filling stage, which would be an important physiological foundation for higher grain yield, better quality and higher water use efficiency of water-saving and drought-resistant cultivars under WSD.3. Effect of the interaction between nitrogen rates and irrigation regimes on grain yield, grain quality and nitrogen use efficiency of riceWith Liangyupeijiu (indica) and Yangjing4038(japonica) as materials, the effect of different nitrogen levels, ON (0kg hm-2), MN (240kg km-2) and HN (360kg hn-2), on growth and development, grain yield, grain quality and fertilizer-N use efficiency under three irrigation regimes, conventional irrigation (CI), alternate wetting and moderate drying (WMD) and alternate wetting and severe drying (WSD) were studied. The results showed that there was a significant interaction between irrigation regimes and nitrogen applications, the yield of WMD+HN combination was the highest, whereas, the difference was not significant between WMD+HN and WMD+MN. At either MN or HN rate, milling quality, appearance quality, and eating quality were significantly higher or better under the WMD regime than under the CI regime. At the MN rate, the WSD regime significantly decreased grain yield quality when compared with the CI regime. At the HN rate, however, grain quality showed no significant difference between the two irrigation regimes. The fertilizer-N use efficiency of WMD+MN was highest among all the combinations. Increases in dry matter weigh in maturity, root activity, photosynthetic rate of the flag leaf, activity of adenosine triphosphate enzyme (ATPsse) in grains and contents of indole-3-acetic acid, zeatin+zeatin riboside, and abscisic acid in roots during grain filling combination contributed to a higher yield better grain quality and a higher efficiency of rice4. Effects of non-flooded mulching cultivation on the yield and quality of riceTwo super rice cultivars, Wujing15(a japonica cultivar) and Liangyoupei9(an indica hybrid cultivar) and four cultivation treatments, traditional flooding as control (TF), non-flooded plastic film mulching (PM), non-flooded wheat straw mulching (SM), and non-flooded no mulching (NM), were imposed from transplanting to maturity. Compared with that under the TF, grain yield showed some reduction under all the non-flooded cultivations, but differed largely among the treatments. The reduction in yield was38.7%-6.5%under the NM,9.8%-17.4%under the PM, and1.7%-7.0%under the SM. The difference in grain yield was significant between the NM and the TF or between the PM and the TF, and was not significant between the SM and the TF. The SM significantly improved milling, appearance, and cooking qualities, whereas the PM or the NM decreased these qualities. SM also significantly increased the peak viscosity and breakdown value, and reduced setback value, and the PM or the NM had the opposite effect. The two cultivars showed similar trends in quality and quantity of rice yield. The SM significantly increased root oxidation activity, leaf photosynthetic rate, and activities of key enzymes in sucrose-to-starch conversion in grains during the grain filling period, whereas the PM and the NM significantly reduced these parameters. The results indicate that the SM could not only maintain a high grain yield, but also improve quality of rice. Increases in leaf photosynthetic rate, root activity, and activities of the key enzymes involved in the sucrose-starch metabolic pathway in grains under the SM contributed to a higher grain yield and better quality of rice.5. The relationship of grain filling with abscisic acid and ethylene under non-flooded mulching cultivationA field experiment was conducted with two high-yielding rice cultivars, Zhendao88(a japonica cultivar) and Shanyou63(an indica hybrid cultivar), and four cultivation treatments were imposed from transplanting to maturity:non-flooded plastic film mulching (PM), non-flooded wheat straw mulching (SM), non-flooded no mulching (NM) and traditional flooding as control (TF). Compared with that under TF, grain yield was reduced by21.0-23.1%under PM,50.9-55.4%under NM and1.4-1.8%under SM. Both PM and NM significantly reduced the proportion of filled grains and grain weight and were associated with decreased grain filling rates. In SM there was a significant increase in the grain filling rate. The concentration of abscisic acid (ABA) in the grains was very low at the early grain filling stage, reaching a maximum when the grain filling rate was the highest, and showed no significant differences between TF, PM and SM. However, it was significantly higher in NM. In contrast to ABA, the ethylene evolution rate and1-aminocyclopropane-l-carboxylic acid (ACC) concentration in the grains were very high at the start of grain filling and sharply decreased during the active grain filling period. Both PM and NM increased the ethylene evolution rate and ACC concentration, whereas these were reduced in SM. The ratio of ABA to ACC was increased under SM but decreased under PM and NM, indicating that ethylene was more enhanced than ABA when plants were grown under NM and PM, indicating that ethylene was more enhanced than ABA when plants were grown under NM and PM. The concentration of ABA correlated with the grain filling rate as a hyperbolic curve, whereas the ethylene evolution rate correlated with the grain filling rate as an exponential decay equation. The ratio of ABA to ACC significantly correlated with the grain filling rate with a linear relationship. Application of amino-ethoxyvinylglycine (inhibitor of ethylene synthesis by inhibiting ACC synthase) or ABA to panicles under TF and PM at the early grain filling stage significantly increased activities of the key enzymes involved in sucrose to starch conversion in the grains, sucrose synthase, ADP glucose pyrophosphorylase and soluble starch synthase, grain filling rate and grain weight. Application of ethephon (ethylene-releasing agent) or fluridone (inhibitor of ABA synthesis) had the opposite effect. The results suggest that antagonistic interactions between ABA and ethylene may be involved in mediating the effect of non-flooded mulching cultivation on grain filling, and a high ratio of ABA to ethylene enhances grain filling rate.6. Effect of non-flooded straw-mulching cultivation on grain yield and quality of direct-seeding riceTwo rice cultivars currently used in the production, Yangdao6(an indica) and Yangjing4038(a japonica), were field grown using a direct-seeding method, and three treatments, non-flooded wheat-straw-mulching (SM), non-flooded and no mulching (NM), and traditional flooding and on mulching (Control, TF), were imposed from10days after sowing to maturity. Compared with that under TF, grain yield showed some reduction under both SM and NM. The reduction in yield was1.9%-6.6%under SM, and18.0%-27.6%under NM. The difference in grain yield was not significant between SM and TF, and was significant between NM and TF. SM significantly improved head rice, gel consistency, albumin, glutelin and eating quality, and significantly reduced chalky kernels, chalkiness and prolamin content, and NM had the opposite effect. The results indicate that non-flooded wheat-straw-mulching could maintain a high grain yield and improve grain quality of direct-seeding rice. Greater leaf photosynthetic rate, root activity, and content of IAA and Z+ZR under such a practice contributed to a high grain yield and better quality, whereas NM significantly reduced these physiological parameters and grain yield and quality were reversed under NM.7. Effect of direct-seeding with non-flooding and wheat residue returning patterns on grain yield and grain quality of riceTwo rice cultivars, Yangdao6(an indica) and Yangjing4038(ajaponica), were field grown using a direct-seeding method, and four treatments, wheat straw incorporation into soil and traditional flooding (SIF), non-flooding and wheat straw mulching (NSM), non-flooding and wheat straw incorporation into soil (NSI) and traditional flooding (no straw returned, Control, TF), were imposed from10days after sowing to maturity. Compared with TF, SIF increased in yield by10.19%-11.48%, NSI and NSM showed some reduction in yield and the reduction was2.96%-6.61%. The difference in increase was significant between SIF and TF, and was not significant between NSI and NSM or between NSM and TF. SIF, NSI and NSM significantly improved milling quality, appearance quality, cooking and peak viscosity and breakdown of RVA. Increases in photosynthetic rate of the flag leaf, root activity, Q enzyme activity in grains at the mid and late grain filling stage contributed to a higher yield and better quality under SIF, NSI and NSM.8. Effect of direct-seeding with non-flooding and wheat residue returning patterns on greenhouse gases emission of riceTwo rice cultivars currently used in the production, Yangdao6(an indica) and Yangjing4038(a japonica), were field grown using a direct-seeding method, and four treatments, wheat straw incorporation into soil and traditional flooding (SIF), non-flooding and wheat straw mulching (NSM), non-flooding and wheat straw incorporation into soil (NSI) and traditional flooding (no straw returned, Control, TF), were imposed from10days after sowing to maturity to study the effect of direct-seeding with non-flooding and wheat residue returning patterns on CH4, N2O and CO2emissions by using the method of static chamber-gas chromatographic techniques. The result showed that emission flux of CH4and CO2under TF and SIF exhibited a single peak curve, and NSI and NSM did not greatly changed, and emission flux of N2O showed multiple perk curves among all treatments. Compared with TF, SIF significantly increased mean emission flux of CH4and N2O, and decreased emission of N2O, and NSI and NSM significantly decreased the mean emission flux of CH4, and increased emission flux of N2O and CO2. Compared with TF, SIF increased Greenhouse Warm Potential (GWP) of CH4, N2O and CO2and the GWP per unit grain yield was increased by45.2%-51.6%,30.0%-38.3%, respectively. Both NSI and NSM decreased GWP by17.7%-25.9%,24.2%-30.2%, and the GWP per unit grain yield was decreased by15.0%-23.6%,18.4%-25.4%, respectively. The results indicate that both SIF and NSM could maintain a high yield and significantly reduce greenhouse effect of CH4, N20and CO2.In summarily, present results indicated that both FI and WMD could increase grain yield and grain quality, and SM could maintain a higher yield and better grain quality. The WMD could achieve a higher yield, better quality and higher nitrogen use efficiency when N rate was at240kg hm-2. Increases in photosynthetic rate, root oxidation activity, content of IAA, Z+ZR in roots, activities of the key enzymes involved in sucrose-to-starch conversion and ATPase in grains, and increases in ratio of ABA/ACC under FI, WMD and SM contributed to the high grain yield and good quality.