| China has31%of the paddy fields in Asia and19%of paddy fields on Earth, more than any individual country and plays an important role on the stable of grain production in the world. Southern rice acreage accounted for90%of the country’s rice acreage. The area of the low-yield rice soil has always maintained above1/3(about one hundred million mu) of the total rice-cultivated area in China, restricting rice’s yield-increasing potential in the south, and it also has an impact on rice safety, even food safety all around the country. In the area of medium-and-low-yield fields in Hubei Province accounted for71.1percent of China’s total arable land. In major grain producing areas, Medium-and low-yield level fields in Hubei Province account for71.1%of the total cultivated area in China, and in the major grain producing areas, they are up to52.56%. The application of nitrogen is an important measure for farmers to guarantee a high rice yield. And excessive nitrogen application phenomenon has been widespread in each rice producing area due to blindness pursuit for yield increase. Our research was aimed at improving production technique of low-yield rice fields in south China. The low-yield rice soil in Hubei (yellow soil) are targeted to explore the appropriate nitrogen application level, the law of nitrogen demand and nitrogen utilization efficiency for high-, medium-and low-yield level fields, respectively, by studying the appropriate nitrogen application rate of different yield level rice fields and the screen of nitrogen efficiency for the main popularized rice cultivars in the south. The results were to provide theoretical bases for appropriate nitrogen application, rice yield increase and reduction of nitrogen input of the low-yield level fields.The main results are as follows:1. Study on optimal Nitrogen Application Rates on Rice Grain Yield and Nitrogen Use Efficiency in High-, Middle-, and Low-yield Paddy FieldsField plot experiments were carried out in Meijiadun, Huanggang, Hubei. The rice cultivar of Liangyoupeijiu was choosed to investigate the optimum nitrogen application rate in paddy fields with different yield levels (high, middle and low), and to observe the effect law of different nitrogen application rates on rice yield and its components, nitrogen fertilization contribution rate, soil nitrogen dependent rate and nitrogen use efficiency. The results obtained from2011to2013field trial showed that the high yield field have a significantly higher level of tillering than middle-and low-yield fields under the low nitrogen application rates. And the panicle rate of rice was in order:high yield field> middle yield field> low yield field. The tillering number and the SPAD value of rice top leaves increased with the increasing of nitrogen application rates.The SPAD value of high yield field was higher than the middle and low yield fields. Without N application rates, the rice yield was in the order:high yield field> middle yield field> low yield field. The rice yield increased as the increasing of nitrogen application rate. When the nitrogen application over the appropriate amount, the rice yield decreased as the increasing of nitrogen application rates.The increment of rice yield was in order:low yield field> middle yield field> high yield field.The product of panicle number and spikelet number in high yield field was higher than middle-and low-yield fields in the low nitrogen application level.There was no significantly difference among the1000-grain weight in high, medium and low yield fields at the same treatment.The nitrogen use efficiency increased with the increasing of nitrogen application rate in low nitrogen application level. Excess nitrogen appropriate application rate showed the nitrogen use efficiency decreased with the increasing of nitrogen application rate. The nitrogen use efficiency in high yield field was lower than medium and low yield fields. By the analysis of yield, yield components, nitrogen use efficiency, tiller dynamic and SPAD value,we concluded that the optimum nitrogen application rates are120-180kg/ha in high and middle yield fields, and are180-210kg/ha in low-yield fields. The optimum nitrogen application rate was in order:low yield field> middle yield field>high yield field.2. Study on Nitrogen Efficiency Screening and evaluating of Rice Cultivars Popularized in South ChinaIn this research,34rice cultivars popularized in south China were used to do the field trials and pot experiments under both normal and low nitrogen conditions. The high and low nitrogen efficient cultivars were identified by the analysis of several parameters, such as yield, yield components, leaf SPAD value and aboveground nitrogen accumulation rate of rice. The rice seed yield of all cultivars was between5000kg/hm2to9000kg/hm2under low nitrogen supply condition, but it was between7000kg/hm2to10000kg/hm2under normal nitrogen supply condition, in three years’cultivar Screening trials. The value nitrogen efficiency was between0.5to1.0. The results show that Huiliangyou6, Guangliangyou35and Tianyouhuazhan were found out to be high nitrogen efficient, and Xiushui134, Fudao2and Wufengyou7025were found out to be low nitrogen efficient from the field trials in2011. In2012, these rice cultivars were experimented both in fields and pots. We finally identified the high nitrogen efficient cultivar Guangliangyou35and the low nitrogen efficient cultivar Xiushui134.The physiological analysis between high and low nitrogen efficient cultivars revealed that the high nitrogen efficient cultivar has higher panicle number and spikelet number per panicle under low nitrogen supply condition, which led to the higher yields than the low nitrogen efficient cultivar. Although neither the leaf SPAD value nor the nitrogen accumulation rate in the aboveground showed significant differences between the high and low nitrogen efficient cultivars at the early growth stage, more nitrogen was accumulated in the high nitrogen efficient cultivar at the late growth stage, which enhanced photosynthesis, the nitrogen assimilation and improved yields as a result. |
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