| The technology of no-tillage cultivation can not only increase the content of organic matter and moisture in soil, improve moisture efficiency, decrease the erosion of soil by wind and water and slow down soil degradation, but effectively relieve the crop contradiction, save labor and energy resources and reduce investments. The technology of returning rice straw to the field can increase crop yield by improving soil characteristics, balancing crop nutrition and adjusting soil temperature and humidity. It also avoids environmental pollution caused by straw burning. The combination of the two technologies can effectively solve the problems of low fertilizer utilization rate, later shortage of fertilizer as well as early aging existing in the no-tillage cultivation mode. As a result, it plays an important role in increasing the yield and farmers’incomes. However, there is little research on the cultivation mode of combing rice straw mulching returning with rapeseed no-tillage direct-seeding. Therefore, this thesis presents the design of crack area test, discusses the impacts of the sowing time of rapeseed, its planting density as well as the amount of rice straw returned to the field on the growth, development, yield and quality of rape in the combination model. The results of this study are as follows:1. Impacts of the sowing time of rapeseed on the growth of rape in different periods, its yield and quality. Index of each stage, final yield and quality of early-planted rapeseed are all better than those of late-planted rapeseed:during the over-wintering stage, budding stage, flowering stage and podding stage, compared with early-planted rapeseed, seedling height of late-planted rapeseed decreases by44.1%,57.9%,31.6%and7.5%respectively; green leaves (the first three growing periods) decreases by53.8%,30.9%and18.8%respectively; overground dry weight decreases by80.5%,59.9%,63.6%and9.6%respectively; root dry weight decreases by94.2%,77.8%and78.9%,31.7%respectively. At the maturity stage, the number of primary branch, the effective length of main inflorescence, the main inflorescence pods, pod number per plant, seed number per pod, a thousand seeds weight and yield per plant of late planted rapeseed are down by10.9%,12.9%,15.5%,9.6%,2.7%,35.3%and25.8%respectively compared with early-planted rapeseed. If sowing time is delayed, rapeseed yield declines. Yield of rapeseed sowed on October30th is66.32kg/667m2, less than that sowed on September15th with210.51kg/667m2, decreases by68.5%. When sowing time is delayed from September15th to October30th, rapeseed protein content increases by10.97%, which reaches the significant level; and oil content falls by7.42%, which also reaches the highly significant level.2. Impacts of the planting density of rapeseed on the growth of rape in different periods, its yield and quality. Increase of the planting density of rapeseed causes the decrease of individual index such as seedling height, green leaves, root thick, dry matter weight per plant and the increases of leaf area index, group dry matter weight. When the density increases from D1(12000plants/667m2) to D4(48000plants/667m2), during over-wintering stage, budding stage, flowering stage and podding stage, seedling height decreases by12.0%,8.9%,7.1%and3.3%respectively; green leaves (the first three growing periods) decrease by21.2%,7.3%and17.8%respectively; root thick is down by14.5%,20.5%,23.6%and22.2%respectively; and the individual root dry weight decreases by47.6%,40.1%,45.9%and40.1%respectively; the individual overground dry weight decreases by41.2%,36.6%,41.8%and37.8%respectively; Leaf area index increases respectively by99.4%,218.9%,144.9%and148.4%; group root dry weight increases by109.2%,139.7%,116.4%and139.8%respectively; group overgroud dry weight increases by135.4%,153.7%,132.7%and148.9%respectively. At the maturity stage, the number of primary branch, the effective length of main inflorescence, inflorescence pods, pod number per plant, seed number per pod, a thousand seeds weight and yield per plant decrease with the increase of density, and the declining rates of D4(48000plants/667m2) treatment are25.0%,11.8%,14.8%,34.4%,13.4%,5.9%and50.5%, respectively compared with the D1(12000plants/667m2) treatment. Yield increases by29.3%with the increase of density. Protein and linoleic acid content increase at first and decrease later with the increase of density, maximum are D2(24000plants/667m2processing; while oil content and the stearic acid, oleic acid content show the opposite trend.3. Impacts of the amount of rice straw returned to the field on the growth of rape in different periods, its yield and quality. Rice straw returning effectively promotes the rapeseed growth and development. Seedling height, root thick, effective length of main inflorescence, effective branch number, yield per plant and total yield of straw returning treatments are higher than the control group. With the increase of straw returning mass, during over-wintering stage seedling height, green leaves, leaf area index, open quotation degrees, root thick, root dry weight, overground dry weight significantly increase at first and decline later, and reach the maximum at400kg/667m2treatment. Growth of green leaves, root thick, root dry weight and overground dry weight in buding stage of straw returning mass by600kg/667m2processing are more than that of400kg/667m2processing. On maturity stage, the effective branche height, the effective length of main inflorescence, primary branch number, pod number per plant, a thousand seeds weight and yield per plant of straw returning processings are higher than control. Straw returning mass of400kg/667m2processing increases by8.6%,0.8%,2.0%,2.1%,6.9%,8.6%, respectively. Total yields of straw returning processings are significantly higher than control, but yields decline when straw returning mass adds. Treatment of200kg/667m2rapeseed reaches the highest yield,167.89kg/66m2and the growth rate is25.4%. The straw returning influence to the quality of rapeseed is not significant, and compared to control, protein, linolenic acid, linoleic acid and stearic acid content increase, while oil and oleic acid content reduce, comprehensive all indicators, rice straw returning mass should be400kg/667m2which is most conducive to form high rapeseed quality.4. Effect analysis of the interaction between the sowing time of rapeseed, its planting density and the amount of rice straw returned to the field. According to the variance analysis, influences of rapeseed sowing time, rapeseed planting density and rice straw returning mass reach highly significant level among each treatment; F values show that, in three factors sowing date makes the most influence to rapeseed final yield, second for the planting density, and last for rice straw returning mass. The analysis indicates that the interaction effect between straw returning mass and sowing date reaches a very significant level, and interaction effect between planting density and straw returning mass as well as that between planting density and sowing date reach significant level.5. The establishment of no-tillage direct-seeding rapeseed cultivation mode based on rice straw mulching returning. Under the experimental condition, when sowing on September15th with planting density of24000plants/667m2, rice straw returning mass is200kg/667m2, yield could reach the maximum of268.13kg/667m2.The results of variance analysis show that the interaction effect between straw returning mass and sowing date reaches a significant level, both the sowing date and straw returning mass should be paid attention to in production. Straw returning mass can be added appropriately when rapeseed is sowed early, it should be decreased relatively when rapeseed sowed late and add planting density to ensure high yield. According to the production data, equation for optimal simulation can be set up, we can establish the pilot high yield mode:under no-tillage direct-seeding conditions, with nitrogen fertilizer used15kg/667m2, rice straw returning mass is362kg/667m2, with planting density of37500plants/667m2,sowing on September18th, rapeseed potential yield could be up to237kg/667m2. |
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