| The suitable sowing date is changed due to the use of the straw bundles, a mode of partial coverage that the places planted crops don‘t use the straw bundles, and the places used the straw bundles don‘t plant crops, is different to the traditional cover system affecting on soil water and temperature. Six treatments of sowing date is September 14 th, September 19 th, September 24 th, September 29 th, October 4th and October 9th, and September 24 th is the usual seeding time of production(CK) in this experiment by taking winter wheat as the research object, which was carried out in northwest semiarid and rainfed region. Effects of different sowing dates on soil water, soil temperature, growth indexes and yield were studied to determine the suitable sowing date of winter wheat with the use of the straw bundles in northwest semarid and rainfed region, research results would provide evidence for the use of the bundled straw covering technique and a further study on this technique. The main results are as following:1. Winter wheat should be early seeding at appropriate period with the use of the straw bundles. Sowing dates had an obvious effect on winter wheat yield, and the maximum nt differences among treatments was 44.00%; yield of the treatment September 19 th, which was 5096.00 kg·hm-2, was the highest amount of higher grain number per spike, ear number per unit area and 1000-grain weight, and increased by 5.76% over CK, otherwise it would be decreasing-yield. Yield of the treatment October 9th was the lowest and decreased by 26.55% compared with CK. The yield difference among treatments mainly resulted from grain number per spike and ear number per unit area, variation tendency of 1000-grain weight was stable. The maximum nt difference of grain number per spike, ear number per unit area and 1000-grain weight was 24.99%, 21.17% and 6.50%, respectively.2. Effects of sowing date on soil water of winter wheat during the whole growth stage were obvious. The maximum difference of average soil moisture content of 0~200 cm soil layer was 0.75 percentage point among treatments. Soil moisture content of the treatment October 9th was the highest, which was 15.65% while that of CK was the lowest for 14.90%. The average soil moisture content both early and late sowing increased by 0.48 and 0.45 percentage point over CK. And average soil moisture content during the whole growth stage gradually decreased with the delaying of sowing date after September 24 th.Soil water content of 0~200 cm soil layer among treatments was decreasing in the growth stage and that of wintering was the highest. Difference of soil water after jointing was much greater than that before jointing and that at floweing stage was the greatest, which was 2.18 percentage point and rate of soil water variation among treatments was 19.22%. The difference of the treatment both October 4th, soil moisture content of which was higher, and September 29 th, soil moisture of which was the lowest, was 0.65 percentage point and the maximum difference was 359% before jointing, while the difference of soil water content both the treatment October 9th, which was the highest generally, and CK, which was the lowest generally, was to 1.44 percentage point and the rate of variation was 12.17% after jointing. And average soil moisture of treatments both early and late sowing increased by 0.82 and 0.69 percentage point over that of CK after jointing.At different soil layer and growth period, inflection point of soil water content was in 60~90 cm soil layer and heading stage. Generally speaking, soil moisture content of the treatment September 14 th in 0~90 cm soil layer was the highest, which was 14.26%, the difference among other treatments was not obvious; soil moisture content of treatments both October 9th and September 19 th in 90~200 soil layer increased by 1.40 and 1.15 percentage point over CK, respectively in the aspect of soil water at different stage and soil layer, which of October 9th was the highest and was 17.48% and that of September 19 th was 17.27%, which was next to October 9th.3. The difference of water use efficiency(WUE) among treatments was obvious, the difference of WUE of treatments both September 19 th and October 9th was 40.71%, which resulted from yield difference. And WUE of the treatment September 19 th was the highest for 16.9716.97 kg·hm-2·mm-1.4. The difference of soil temperature at different growth stage and soil layer was much more obvious among treatments. Difference of soil temperature among treatments from returning green stage to jointing stage was the greatest, the next was that of from heading stage to flowering stage, and that at emergence stage was the lowest at the side of different growth stage. And the difference of soil temperature among treatments decreased with the delaying of sowing date, but the difference of soil temperature in 5 cm soil layer was the greatest.Average soil temperature of the treatment in 0~25 cm soil layer during the whole growth stage was the highest, which was 13.42℃, and that of the treatment October 4th was the lowest, which was 12.68℃. The difference of soil temperature among treatments in 0~25 cm soil layer was the least at emergence stage at the side of different growth stage, and soil temperature of the treatment October 9th was generally the highest while that of the treatment October 4th was the lowest from returning green stage to maturity stage, the difference of treatments both October 9th and October 4th was 1.17℃. And the difference of average temperautue in 0~15 cm of treatments both October 9th and October 4th was 1.01℃, the variation of average soil temperature in 15~25 cm of the treatment September 29 th, average soil temperature of which was the highest, was 1.08℃ with the treatment September 19 th, average soil temperature of which was the lowest comparing with average soil temperature in different soil layer.5. Effects of sowing date on accumulation and distribution of dry matter before anthesis were outstanding. Generally, contribution rate to grain from dry matter accumulated before anthesis increased with the delaying of sowing date. Meanwhile, sowing date had an effect on distribution proportion of dry matterin different positions of wheat plant. The rato of grain dry weigh was the highest, that of leaf and sheath was the next, and grain husk and spike axis was the lowest on average. Distribution proportion of dry matter in grain generally decreased with the postponement of sowing date. Early seeding at appropriate period would improve the distribution proportion of dry matter at maturity in grain or harvest index, that of the treatment September 19 th was the highest for 60.50%, and the maximum difference of the distribution proportion of dry matter at maturity in grain among treatments was 10.70 percentage points.6. The whole growth period was prolonged by early sowing, otherwise, the growth stage would cut down with sowing date delayed, and the growth period would shorten 1.5 days averagely if the date of sowing was postponed every 5 days. The period of the whole growth period of the treatment September 19 th was the longest for 290.3 days, which was longer by 15.3 days than that of the treatment October 9 th, the whole growth period of which was the shortest days of 275 days. |
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