| A comparative experiment was carried out with direct seeding method of different sowing date during year2008-2010in Sunan Taihu Lake rice district in Changshu (N31.4°), Suzhong Lixiahe rice district in Jiangyan (N32.3°) and Subei Huaibei rice district in Donghai (N34.5°), Jiangsu province. The experiment was selected suitable variety growth stage types for local and its main popularizing representative varieties according to the heat conditions in different latitude regions and possible safety growth days of direct seeding rice in the rice-wheat cropping system. Systematic comparative studies on growth stage and utilization of temperature and illumination, yield, characteristics of photosynthetic and matter production, nitrogen uptake and utilization and rice quality of direct seeding rice under different sowing date, and then the direct seeding rice comprehensive productivity and use of different sowing date and verieties in the lower Yangtze and Huai valleys was comparative evaluated, in order to provide a scientific basis for direct seeding rice rational distribution of this region.The main results were as follows:(1) Along with the delayed sowing date, the date of jointing, heading and maturity of all varieties were corresponding delayed, growth stages significantly reduced that growth stages reduced about0.6days when the sowing date delayed one day. For the same type varieties, the date of jointing, heading and maturity gradually delayed and the growth stages gradually increased with latitude increasing. In the same site, the number of days of growth stages of late japonica rice reduced slightly more than the medium japonica rice with the delayed sowing date. Growth stages reduced with the delayed sowing date because of the vegetative growth period and the vegetative and reproductive growth period reduced which in range of2to24days, the reproductive growth period was relatively stable which in range of-2to1days. Accumulated temperature and illumination hours of growth stages of all varieties reduced significantly or very significantly, which because of the accumulated temperature and illumination hours before heading, especially before jointing, the difference was significant or very significant.In the same site, accumulated temperature and illumination hours of growth stages of late japonica rice were more than the medium japonica rice; For the same type varieties, with latitude increased. accumulated temperature reduced, illumination hours reduced except for japonica hybrid rice. The utilization of temperature and illumination of all varieties reduced significantly or very significantly with the delayed sowing date.The number of days from sowing to heading and growth stages increased linearly with the increase of accumulated temperature and decreased linearly with the increase of illumination hours; The number of days from heading to maturity were different between different treatments with the increase of accumulated temperature or illumination hours. Sowing date had great effects on growth stage and utilization of temperature and illumination of direct seeding rice. Accordingly, we made a preliminary division for the direct seeding rice of different variety types, in order to provide reference for the production of the large area.(2) During the sowing date set in the study, along with the delayed sowing date, the yields of direct seeding rice of different maturity type and different ecological regions reduced very significantly, the changing degree was different that late-maturing varieties were higher than early-maturing varieties, and some types in three ecological regions could not be mature when the sowing date was so late. The changing degree of yield components along with the delayed sowing date was divided into two groups that the group of small changes was1000-grain weight and panicles, the other was spikelets per panicle and filled grain percentage which was the main reason of yield reducing. It showed significant or very significant correlation between total spikelets, filled grain Percentage, yield and accumulated temperature and illumination hours of whole growth stages, the effect of temperature and sunlight conditions in different growth stages on1000-grain weight was not significant. We made a regional planning for the direct seeding rice of different variety types and their suitable sowing dates in Jiangsu, in order to provide reference for the production of the large area.(3)①Along with the delayed sowing date, dry matter weight of single stem and population at jointing, booting, heading, waxy stage and maturity both showed a apparent downward trend, and the difference was increasing with the growing process.②Along with the delayed sowing date, the proportion of dry matter accumulation from sowing to jointing and from jointing to heading increased, but from heading to maturity decreased, while the dry matter accumulation of every stages reduced significantly or very significantly.③With the growing process, leaf weight per stem and sheath weight per stem decreased, stem weight per stem first increased and then decreased, and panicle weight per stem increased; along with the delayed sowing date, leaf weight per stem and sheath weight per stem decreased significantly or very significantly at booting and heading, little difference at waxy stage and increased a little at maturity, stem weight per stem and panicle weight per stem decreased significantly or very significantly at all stages.④With the growing process, the proportion of leaf, stem, sheath and panicle in the later growth period had the same changes as the dry matter weight; along with the delayed sowing date, the ratio of leaf and sheath decreased a little at booting, little difference at heading and increased significantly or very significantly at waxy stage and maturity, the ratio of stem decreased a little at booting and heading, increased a little at waxy stage and decreased at maturity, the ratio of panicle increased a little at booting, little difference at heading and decreased significantly or very significantly at waxy stage and maturity.⑤Along with the delayed sowing date, the exportation, export rate and transformation rate of leaf, stem and sheath decreased significantly or very significantly.⑥Along with the delayed sowing date, the leaf area index had a little difference at jointing, decreased significantly or very significantly at booting, heading and waxy stage, and decreased a little at maturity, the photosynthetic potential from sowing to jointing, jointing to heading and the whole growth period decreased significantly or very significantly, and decreased from heading to maturity, but the difference was little.⑦Along with the delayed sowing date, the crop growth rate from sowing to jointing increased significantly, little difference from jointing to heading and decreased significantly from heading to maturity, the net assimilation rate from sowing to jointing and from jointing to heading increased obviously, but decreased obviously from heading to maturity. Sowing date had great effects on characteristics of photosynthesis and matter production of direct seeding rice. Compared to sowing late, sowing early has the advantages that the dry matter accumulation is appropriate in the early stage and significantly higher in the middle and late stage, so the total dry matter accumulation is significantly higher and its distribution is reasonable, the export and transformation rate is high, and the photosynthetic production capacity is great after heading.(4) Along with the delayed sowing date,①N content in plant of jointing stage increased but the heading and maturity stage decreased, the differences were not significant;②N uptake in plant of jointing, heading and maturity all showed a significant downward trend;③N accumulation before jointing decreased, but its ratio to total rised, N accumulation and its ratio to total both from jointing to heading and from heading to maturity showed a gradual downward trend.④N uptake rate from sowing to jointing rised and the difference was not significant, but both from jointing to heading and from heading to maturity showed a significantly or very significantly downward trend.⑤N recovery efficiency, N agronomic efficiency, N physiological efficiency and N partial factor productivity showed a downward trend of different degrees.⑥Correlation analysis indicated that there existed significant or very significant positive correlations between yield and N accumulation, N uptake rate and N use efficiency except N uptake rate from jointing to heading. Under the experimental conditions, compared with sowing late, yield, N uptake of every stage, N accumulation of every period, N uptake rate after jointing and N use efficiency of direct seeding rice which sowed early were higher. It was obvious that early sowing of direct seeding rice is in favor of the N efficient absorption and utilization and high yield.(5) Along with the delayed sowing date, the yields of three types of rice cultivars were all significantly decreased, and the changing degree was different; the yield decreasing caused by the decline of spikelets per panicle and filled grain percentage, panicles and1000-grain weight had a little change. The law of changing of main direct seeding rice quality traits between different types under the conditions of different sowing date showed some similarities and differences:along with the delayed sowing date, appearance quality and cooking and eating quality had the same effect, but the trend was different, appearance quality became better while cooking and eating quality became worse; Milling quality and nutrient quality had the different effect, milling quality of the type of medium-maturing and late-maturing medium japonica rice became better but worse the nutrient quality, milling quality of the type of early-maturing late japonica rice became worse but better the nutrient quality. The direct seeding rice should be sowed as early as the time for harvesting the previous crop allows to attain high yield and improve cooking and eating quality, but reduce the appearance quality. Effects of sowing date on milling quality and nutrient quality were different because of types and varieties. |
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