Cultivation Techniques For High-Yielding And High Nutrient Use Efficiency In Rice And Their Physiological Bases

Rice is the foremost stable food crop in China. With the growth of population and economic development, it is necessary to increase more crop yield. Meanwhile, this increase needs to be accomplished under high input of water and fertilizer resources. It remains debates whether it is necessary to input more water and fertilizer resources for more food, and whether higher grain yield and higher nutrient use efficiency can be coordinately achieved? It is not only always focusing of attention at home and abroad, but also an important scientific proposition in academic circles. In developed contries, the principle is adopted that environment takes for the first place. But, in China, there is less land and a shortage of resources for large population. It is an essential way for agricultural sustainable development to increase crop yield and meanwhile increase resource use efficiency.This study investigated the characteristics of grain yield and popoulation growth and development, nutrient absorption and utilization efficiency, physiological characteristics and rice quality under different cultivation patterns throgh integrating and optimizing cultivation techniques. The main results are as follows:1. The limiting factors and the cultivation techniques for high-yielding and high nutrient use efficiency in riceBy investigating, collecting evidence and useful information and conducting experiments, the main factors limiting high yielding and high nitrogen use efficiency were made known, i. e., improper cultivation measures, such as poor seedling quality, lower plant denstiny, higher fertilizer amount, and flodding irrigation which could result in poor quality of rice population directly and caused a waste of resources. Meanwhile, the cultivars with strong adaptability of fertilizer and the poor grain filling of inferor spikelets for a large panicle with numberios spikelets were also contributed to the reduction in grain yield and nutrient use efficiency in rice. A cultivation technique system was created and integrated by taking site-specific nutrient management(SSNM) and alternate wetting and moderate drying(WMD) as the two key techniques and some practices as supporting techqiques, including cultivating strong seedlings, increasing densitny, controlling fertilizer application, applying N fertilizer at later stage, spraying foliage fertilizer, and increasing silicon fertilizer application.2. The characteristics of population growth and development of rice under high-yielding and high nutrient use efficiency cultivation A high quality of population is necessary to achieve high grain yield in rice, but little information is avaliable on understanding how cultivation patterns affect population quality. In this study,two experiments were conducted.(1) two japonica hybrid rice cultivars Changyou3and Changyou5were grown in the field, with six cultivation patterns including no nitrogen application (ON), local high yielding cultivation (control), cultivation for high yielding and high efficiency(CHYHE), super high yielding cultivation (SHY), cultivation for super high yielding and high efficiency (SHYHE) and cultivation for high use efficiency of N (HUEN)(Experiment1). The results showed that, the average yields of two cultivars under CHYHE, SHY,SHYHE and HUEN were9.9t ha-1,12.01ha-1,10.9t ha-1and9.3t ha-1, respectively, and10.1%-41.9%’ higher than these of control.(2) Three rice cultivars Yangjing4038,Yangdao6and Lianjing6were grown in the field, with three treatments including local farmer’s practice (LFP), an improved crop management (ICM) and N omission (ON)(Experiment2).The results showed that, compared with LFP, the average grain yields of ICM increased by14.4%. Both experiment1and experiment2showed that, compared with control or LFP, CHYHE, SHY, SHYE and HUEN or ICM increased percentage of productive tillers, leaf area index(LAI) and efficient LAI, leaf area duration(LAD), crop growth rate (CGR), biomass from heading to mature, grain-leaf ratio, root biomass and root bleeding after heading. The results indicate that the population quality of rice could be improved and higher yield could be achieved through high-yielding and high nutrient use efficiency cultivation patterns.3. Nutrient absorption and utilization efficiency of rice under high-yielding and high nutrient use efficiency cultivationThe objiective of this study was to investigate if a cultivation technique could coordinately increase both grain yield and nutrient use efficiency of rice. In this study, two experiments were conducted. The results of experiment1showed that, compared with those under the control, nitrogen recovery efficiency (NRE) was increased by50.3%,87.4%,78.5%and44.3%, and nitrogen agronomic efficiency(NAE) was increased by74.7%,91.1%,97.1%and78.3%respectively, under CHYHE, SHY, SHYE and HUNE. The percentage of nitrogen (N), phosphors (P), potassium (K) translocation from heading to maturity under CHYHE, SHYE and HUNE were also increased. The accumulation of N, P, K from panicle initation to heading was very significantly and positively correlated with grain yield.The results of experiment2showed that, the average WUE, NRE and NAE under ICM were increased by35.6%,42.5%and64.1%, respectively, than those under LFP. The results of two experiments indicate that a higher yield and higher WUE and NUE can be achieved through integrating and optimizing cultivatin techniques in rice production. 4. Physiological traits of rice under high-yielding and high nutrient efficiency cultivationThe results from experiment1showed that, compared with the control, CHYHE, SHY, SHYE and HUEN increased SPAD values, photosynthetic rate (Phr) and activities of antioxidant enzymes, catalase (CAT), peroxidase (POD) and superoxide dismutase(SOD), in/of flag leaves, root oxidation activity (ROA), contents of zeatin+zeatin riboside(Z+ZR) in roots and grains and indoleacetic acid (IAA) in grains. The activities of key enzymes involved in nitrogen metabolism, nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT), showed no significant difference at mid-tillering stage, but were significantly higher than the control at the panicle initation, heading time and maturity stages. Results in experiment2showed that, compared with LFP, ICM increased Phr in flag leaves, ROA, activities of sucrose synthase (SuSase) and adenine diphosphogiucose pyrophosphorylase (AGPase) in garains during grain filling, and contents of Z+ZR in leaves, panicles and roots at mid and late growth stages. The results of two experiments suggest that an enhanced phsiological activties of shoot and root contributes to the increase in grain yield and nutrient use efficiency under the high-yielding and high nutrient use efficiency cultivation patterns.5. The rice qualities and contents of mineral elements in milled rice under high-yielding and high nutrient use efficiency cultivationThis study was to investigate the formation characteristics of rice quality under high-yielding and high nutrient use efficiency cultivation. In experiment1, the rice qualities and contents of mineral elemnts in milled rice were analyzed under six cultivation patterns. The results showed that, compared with the control, SHY and SHYE significantly increased head rice, contents of protein and mineral elements accumulation in milled rice, and increased the gel consistency and breakdown of rice, and reduced chalkness, amylose and setback. The results indicate that the milling quality, appearance quality and nutrient quality could be improved under the high-yielding and high nutrient use efficiency cultivation.In summary, a high-yielding and high nutrient use efficiency cultivation pattern could increase not only grain yield but also nutrient use efficiency and water use efffiency. A larger ROA and leaf area duration, higher activities of key enzymes involved in nitrogen metabolism in leaves, more remobilization of pre-stored NSC from stems to the grain, greater content of Z+ZR in plants, and enhanced activities of key enzymes involved in sucrose-to-starch conversion in grains during the grain filling period under the high-yielding and high nutrient use efficiency cultivation pattern may have contributed to achieving the dual goal of increasing grain yield and resource use efficiency. The SSNM and AWMD irrigation were two key techniques in the high-yielding and high nutrient use efficiency cultivation system of rice.