Huo Zhongyang

Characteristics of Leaf Senescence in Rice Genotypes with Different Nitrogen Use Efficiencies

Although excessive use of N fertilizer can result in the rapid decrease of N use efficiency and other serious environment problems,N fertilizer is yet the most important and largest input in modern rice production. Previous researches have been demonstrated that variation in N use efficiency existed among rice genotypes. Therefore,it is of urgent importance to elucidate the physiological mechanism of rice N absorption and utilization for increasing N use efficiency. In this research,field experiment with 225 kg ha-1 N fertilizer application was carried out in 2006 on the farm of Yangzhou University,Jiangsu province,China. Twelve rice genotypes (six N efficient and six N inefficient) selected from one hundred and twenty rice cultivars grown in Yangzhou during 2004 and 2005 were adopted to investigate the characteristics of N absorption and accumulation. Compared with N inefficient genotypes,N efficient genotypes had more obvious advantages in N absorption rate,the amount and the percentage of N accumulation during the growth phases from elongating to heading and from heading to maturing. And of which the advantage during the growth phase from heading to maturing was particularly significant. Since rice organs aged and the plant physiological functions declined gradually from heading to maturing,the characteristics of rice senescence was then studied to understand the relationships between rice senescence and the N absorption and accumulation,and the N use efficiency. Results showed that,during the period of grain filling,the activities of superoxide dismutase (SOD),peroxidase (POD),and catalase (CAT) in flag leaf of N efficient genotypes were obviously higher than those of N inefficient genotypes. Contrarily,content of malondialdehyde (MDA),which is the product of membrane lipid peroxidation,was lower in N efficient genotypes than in N inefficient genotypes significantly. After the stage of full heading,N use efficiency was positively correlated to the activities of SOD,POD,and CAT in flag leaf of rice and negatively correlated to the content of MDA. So it reveals that,at late growth stages of rice,the activities of SOD,POD,and CAT of N efficient genotypes were higher than those of N inefficient genotypes in flag leaves,which could eliminate reactive oxygen species,inhibit the membrane lipid peroxidation and decrease the content of MDA more efficiently in N efficient rice genotypes. Therefore,compared with the N inefficient genotypes,the leaf senescence of N efficient genotypes was relatively slower,which could prolong the functional period of leaves,enhance the organic matter accumulation and improve the efficiency of N absorption and utilization.

Effects of seedlings number per hill on grain yield and quality in different panicle types of mechanical transplanted japonica rice.

Field experiment was conducted under the rice-wheat two-ripe systems at the Lixia River area during the year 2006-2007,three mid-season japonica rice cultivars including Yanjing 9(small panicle type),Huaidao 9(medium panicle type) and 9 you 418(large panicle type) were adopted to investigate the effects of five planting densities on yield and quality of me-chanical-transplanted rice.Results showed that with the increase of seedlings per hill,the final panicles per plant increased while the number of grains per panicle,the grain filling rate and the 1000-grain weight decreased;and the yield of three cultivars increased first and then decreased.The highest yield was obtained when rice was transplanted with 4 seedlings per hill for small panicle type,with 3 seedlings per hill for medium panicle type and with 2 seedlings per hill for large panicle type.With the increasing of seedlings per hill,the chalkiness degree,the chalkiness rate and the amylose content increased while the milled rice qualities and the protein content decreased,and the gel consistency became longer.Among all of the RVA profiles,the peak viscosity,hot viscosity,breakdown,the final viscosity and the pasting temperature increased first and then decreased.The setback decreased first and then increased.Considering the grain yield together with quality,we suggest that for the coordination of high-yielding and high quality rice transplanting should be with 4 seedlings per hill for small panicle type rice,3 seedlings per hill for medium panicle type rice and with 2 seedlings per hill for large panicle type.

Effects of nitrogen application rate and growth-development type on milling quality in japonica rice.

Nitrogen is the most important and largest input required in rice production although over use of N causes so many environment problems. The milling quality is one of the important aspects of rice quality. The effect of nitrogen application rate on milling quality is varied in different rice varieties, especially in different types. In this research, the field experiment for milling quality was carried out with 57 japonica rice varieties including five growth-development types, planting in the region of Yangtze River, under four nitrogen levels (zero, low, medium, and high) to investigate the difference of rice types under four nitrogen levels. Genotypic difference of head rice rate in response to nitrogen levels was discussed and their types were also classified. The main results were as follows: (1) As the increase of nitrogen application, the brown rice rate, milled rice rate and head rice rate of all the rice varieties were improved although the range of improvement decreased gradually. And there was no significant difference in head rice rate between medium and high nitrogen level. (2) In general, the longer of rice growth duration, the better of rice milling quality. According to this research, the milling quality of late japonica rice was better than that of medium japonica rice and the milling quality of late mature rice variety was superior to that of early mature rice varieties. The head rice rate of late japonica rice was higher than that of medium japonica rice by 19.07% on an average. (3) The response of head rice rate to nitrogen varied significantly. According to the variation coefficient of head rice rate under different nitrogen levels, rice varieties could be classified into three types including insensitive type, intermediate type and sensitive type. The varieties with high and stable head rice rate under all nitrogen levels and with high head rice rate at only high nitrogen application rate were recommended to be used in production.

Effects of Potassium Fertilizer Rate on Biomass Accumulation and Grain Yield of Yongyou Japonica/indica Hybrids Series

In order to investigate proper potassium application rate and its effects on growth and grain yield for Yongyou japonica/indica hybrids series, a field experiment was conducted using Yongyou 12 and Yongyou 538 with five treatments of 0, 75, 150, 225, and 300 kg ha potassium application. Results indicated that compared with check treatment (0 kg ha), potassium

Preliminary Study on Parameters of Precise and Quantitative Nitrogen Application in Rice Varieties with Different Growth Period Durations

The objective of this study was to expose the change law of the three parameters of the precise and quantitative N application based on the Stanford equation in different growth types of rice.Three levels of N fertilizer application rates of 0,225,and 300 kg ha-1 N were designed in a field experiment with early(125–135 d),medium(136–145 d),late-maturing(146–155 d) medium japonica and early(156–165 d),medium-maturing(166–175 d) late japonica rice in 2007 and 2008 on the farm of Yangzhou university,Jiangsu province,China.The results were as follows:(1) Under zero N application,soil basal N application(N accumulation for basal yield) increased with the extension of the rice growth duration,in which the parameter of calculating N accumulation for basal yield was the N requirement for 100 kg grains.There were only small differences in N requirement for 100 kg grains between medium,late-maturing medium japonica and early-maturing late japonica rice.For an average yield of 6 t ha-1(4.87–6.58),the N requirement for 100 kg basal yield was 1.58 kg(1.50–1.63).(2) Under N application,the N requirements for 100 kg grains were rather stable in medium,late-maturing medium Japonica and early-maturing late Japonica rice.With the average yield of 7.5 t ha-1,N requirement for 100 kg grains was 1.86 kg(1.85–1.87) under 225 kg ha-1 N level and 2.01 kg(1.98–2.05) under 300 kg ha-1 N level,respectively.With the average yield of 9 t ha-1,N requirement for 100 kg grains was 1.94 kg(1.91–2.04) under 225 kg ha-1 N level and 2.08 kg(2.01–2.19) under 300 kg ha-1 N level,respectively.With the average yield of 10.5 t ha-1,N requirement for 100 kg grains was 1.95 kg(1.93–2.01) under 225 kg ha-1 N level and 2.09 kg(2.08–2.10) under 300 kg ha-1 N level,respectively.These results suggested that N requirement for 100 kg grains increased with the rising of N ap-plication rates.Correlation analysis showed that there existed highly significantly positive conic correlation between yield and N requirement for 100 kg grains,and the correlation coefficients for early-maturing medium japonica and medium-maturing late Japonica were less than those for the other three types.(3) The N use efficiency decreased with the increase of N application rate,and increased with the extension of the growth duration except in the medium-maturing late japonica.N use efficiency was 31.32%,37.64%,38.5%,41.08%,and 38.11% under 225 kg ha-1 N level,and 28.74%,36.13%,37.16%,40.15%,and 39.42% under 300 kg ha-1 N level,for the five types of rice with extended growth duration respectively.(4) The parameters of N applica-tion displayed larger differences in early-maturing medium japonica and medium-maturing late japonica rice which were less suitable for local cultivation,compared with the other three types,while these parameters values of the prevailing varieties(headed varieties) were higher and more stable than those of common varieties.These results demonstrated that the changes of the parameters of N application were much larger,it is feasible for the N quantity required for target yield to be calculated accurately by using Stanford equation under the condition of reasonable variety selection and planting location.