Effects Of Water Regime Or Combined With Nitrogen Fertilization On Physiology And Yield Of Rice Hybrids

In this paper, we conducted a pot and a field experiment to study the effects of drought stress on growth, physiology, yield and quality of different rice hybrids during different growth stages. We also investigated the responses of photosynthetic performance,resistance, yield and quality to water-saving irrigation and nitrogen addition, to explore the ways and mechanism of water saving, high yield and high efficiency cultivation. The main results were as follows:1.Effects of drought stress on growth, physiology and yield of various rice cultivars:Results showed that drought significantly affected the height, tillering dynamic, leaf area and leaf water content of rice paddy. Drought reduced the height of rice, but to different degrees based on different cultivars. In addition, some high drought-resistance cultivars would enhance shoot height. The physiological traits such as concentration of methane dicarboxylic aldehyde(MDA), activity of Peroxidase(POD) and superoxide dismutase(SOD), and content of proline and soluble sugar were all significant in response to drought. As regards the yield, Xinliangyou 6, Xinliangyouxiang 4 and Liangyou0293 had high drought resistance among 9 rice cultivars. Especially, the yield of Xinliangyou 6reduced the least amount by 3.32-4.27% compare with control. Xingliangyouxiang 4 and Liangyou 0293 also only reduced the yield by less 10% than control. Results showed that drought would negatively influence the rice’s appearance and processing quality but not affect its nutritional quality. During the tillering and booting stages, drought decreased the mass od Liangyou 0293 and Wandao 153, while other cultivars increased mass under drought treatment. Xingliangyou 6 had the highest of brown rice percentage, head rice rate and milled rice rate. However, the head rice rate had no significant response. In the respect of appearance, Yangliangyou 6, Xinliangyou 6 and Xinliangyouxiang 4 had higher drought-resistance. By the view of yield and quality, Xingliangyou 6, Xingliangyouxiang 4and Liangyou 0293 had higher drought-resistance.2. Effects of drought lasting different time on physiological traits and yield of rice during tillering stage. Drought stress resulted in the significant decrease of plant height at tillering stage. Lasting different days of drought treatment, plant height showed T0(CK)>T1(3d)> T2(5d)>T3(7d). Applied 7 days of drought treatment, the height of stem was lowest which might result in a decreased reproductive allocation or the yield of rice.Tiller number showed T0>T2>T1>T3. There was no significant difference in duration of tillering stage between T0 and T1. Tillering stage for T2 delayed 7 days compared with T3.Rice performed best for T1 to contribute to stimulate photosynthetic potential and enhance their tillering capacity. Plant physiological traits showed positive responses under drought.Drought caused significant change of content of MDA, proline, and soluble sugar. In addition, we found that short-time of applied drought made plants more sensitive to water so that rapidly recover or even simulated the growth. Hence, this would explain the yield increased by 9.21% after applied short time drought treatment(3days). Our results suggested reasonable irrigation during the tillering stage would not influence the yield of rice neither waste water. However, if the drought lasted long, it would seriously decrease the yield. For instance, in our experiment when the soil water potential(SWP) reduced to-75 k Pa for 7 days, the yield decreased by 24% in tillering stage.3. Effects of drought lasting different time on physiological traits and yield of rice during booting stage. Drought stress inhibited the growth of rice and the expansion of leaf area. Leaf area index of rice significantly decreased when drought stress duration was prolonged during the booting stage. When we applied same time water stress at-75 Pa during booting stage, Leaf SPAD value showed B1>T0>B2>B3, and the difference was significant among them. Proline content was related to the stress duration in soil. We also found a positive correlation between the stress duration and the content of MDA. In addition, when the stress duration was prolonged, the content of soluble sugar in leaf increased first and then decreased after a period of time. The content was the highest with drought duration of 3 days(B1). Different stress duration would affect the scenarios of net photosynthetic rate. The net photosynthetic rate showed diauxie curve for T0(0 days) and B1(3 days) but single-peak curve for B2(5 days) and B3(7 days). The daily trend of transpiration rate showed a single-peak curve among all treatments. Before 10 a.m., the leaf intercellular CO2 concentration ranked in order: B3>B2>B1>T0, but it was changed to B1>T0>B2>B3 after 12 a.m. When the drought was ceased, T0 received the highest accumulation of dry mass, and there were significant differences in that among B1, B2 and B3. After we had watered for 10 days, the accumulation of dry mass for T0 compared with B1, B2 and B3 was increased 15.99%, 37.62% and 39.69%, respectively. When the rice was harvested, the dry mass of stem, leaf and spike were shown T0>B1>B2>B3, and the differences were extremely significant(P<0.01). Panicle number, grain number per spike,1000-grain weight, seed setting rate and yield all significantly displayed T0>B1>B2>B3. When drought stress was applied during booting stage, the yield of B1, B2 and B3 decreased relative to T0 by 20.51%,40.44% and 42.2%, respectively. The differences were extremely significant.4. Effects of drought lasting different time on physiology and yield of rice during whole tillering and booting stage. During the tillering(21st-30 thday after plant was planted) and booting(61st-70 th day after plant was planted) stage we applied 3-day(short time) drought stress(TB1), and found that the rice outperformed the best. It would stimulate the photosynthesis, increase the tillering capacity and lodging resistance. The content of methane dicarboxyic aldehyde(MDA), proline content and total soluble sugar all had significant variety of different change under drought condition during a whole tillering and booting stage relative to control(T0). When re-watered, the plants were very sensitive to water so that they could rapid recover themselves and even achieve higher growth and production. Overall, the dry mass and economic yield showed T0>TB1>TB2>TB3. When drought lasted 7 days, yield decreased 29.16% compared with control. During the whole tillering and booting stage, if drought lasted more than 5 days, the number of panicles per plant and number of grains per panicle would negative correlated with the time in a way to reduce yield of rice significantly.5. Effects of water regime combined with nitrogen fertilization on physiology, yield and quality of rice hybrids: We found that: there were significant influences of water regime and nitrogen addition on the growth, photosynthesis, physiological resistance, yield and quality. Regardless of water regime, the reproduction period would shorten 2-3 days for low nitrogen addition but extend 2-5 days compared with middle nitrogen addition.Compared with the conventional irrigation, controlled irrigation would decrease the height and valid panicle number, enhance water use efficiency, panicle number and seeds production but have no difference on tillering. Suitable water irrigation and nitrogen addition would enhance the water use efficiency. When the amount of nitrogen addition increased, valid panicle number and panicle number would increase, but the seeds setting rate and 1000-grain weight decreased. In addition, the yield and water use efficiency increased first and then decreased. Considering the interaction effects, the yield showed C2N2>C1N2 >C2N3>C1N3>C1N1 >C2N1, and the water use efficiency showed C1N2 >C1N1 >C1N3 >C2N2 >C2N3 >C2N1. The water use efficiency elevated by21.2-43.0% for controlled irrigation relative to conventional irrigation. As the amount of nitrogen increased, the water use efficiency increased first and then decreased. Under controlled irrigation, inputting nitrogen would offset the negative effects on yield and quality of rice from shortage of water. For instance, applying nitrogen at 180 kg N hm-2and 270 kg N hm-2 would achieve the yield at 11489 kg hm-2 and 10126 kg hm-2,respectively, which were significant higher than the yield for C1N1 and C2N1. For the palatability value evaluation, the value is the highest for C1N2 which reached 79.3 and had high comprehensive quality. Overall, when nitrogen application reached at 180 kg N hm-2under controlled irrigation, we would achieve the yield-cost optimization in a way to fulfill enhancing the water use efficiency and promoting agricultural production efficiency.