| This study was based on the factors of the soil quality declining to some extents and incompatible soil nutrient due to the long-term tobacco-rice continues rotation, and thus unreasonable fertilizing, aimed at high quality, high efficiency, sustainable develepment of tobacco production in Hunan, taken tobacco variety Yunyan 87 and green manure as experiment material, through analysis and research of the reason of soil quality declining,and technical measures as green manure cropping patterns changing, the turnover and conservation of green manure, in order to better soil fertility, improve soil structure, change the condition of nutrient supply, regulate some soil physicochemical property and raise the soil microorganism. It has provided theoretical foundation and techenical support for protection of tobacco continues cropping obstacles and fertilization of new tobacco planting soils. The results are as follows:1.It was diverse multiple cropping years that has certain influence on the tobacco planting soil structure and variation. The study demonstrated that pH has a remarkable relate with soil fertilizer. When the pH was 5.5-6.5, the soil nutrient form was beneficial to absorb and utilize. It also showed that the soil acidification was more serious when the tobacco-rice continuously crop over 7 years. The soil organic matter was suitable when the period of continuous cropping was during 1-7 years, meanwhile considering that the organic matter get higher over 10 years continuous cropping, it was not benefit for the late stage growth and development of flue-cured tobacco. With the tobacco-rice continuous cropping years prolonged, the change trend of soil alkeline nitrogen decreased firstly, then increased. Thereinto, the soil alkeline nitrogen content reached the minimum value as 145.6 mg/kg of the 7th year continuous cropping, moreover the soil alkeline nitrogen content gradually increased after 7 years; as the tobacco-rice continuous cropping years prolonged, the soil active potassium content groew. It was closely related to the utilization of potash fertilizer in tobacco planting soil every year, as well as the soil active phosphorous content was stable, average 11.18mg/kg. It was the highest soil active phosphorous when the period of continuous cropping was 4 years, and the lowest in 7 years. The extent of variation was 1.3 mg/kg. In Hengyang tobacco planting area, within 7 years tobacco-rice continuously cropping, the secondary element content all decreased to some extent, thus it had a certain effect on the growth and quality of tobacco. Zinc, copper, manganese, iron content in soil all are the lowest. It explained that the effectiveness of zinc, copper, manganese, iron was better before 7 years. From the 7th year on, the trend in tobacco yield and quality declined. It can obtain a certain degree of economic benefits and high quality tobacco leaves under 7 years. After 7 years, with the continuesly cropping year prolonged, the quality of tobacco leaves declined.2.It was obviously that diverse green manures varieties and mixed sowing and returning to soil have effect on the conservation of tobacco planting soil. The biological characteristics (basic seedlings, branch number, plant height, fresh weight per plant) of milk vetch were comprehensively the best and grass yield the highest among different green manure; nitrogen, phosphorus and potassium content of Grass yield which was converted into a scalar in milk vetch treatment,is 4.29 kg/667m2,4.23 kg/667m2 and 1.03 kg/667m2. the indicators of phosphorus, potassium were on the first place among the three indexes of pure nitrogen, phosphorus and potassium; the total Soil microbial biomass increased by 20.4%-20.4%, compared with CK. It was most obvious that the number of actinomycetes increased by 72.3%?72.3%, and fungi increased by 38.9%-38.9%. The number of bacteria was especially relatively stable as a whole; However among different green manures, the Influence on The tobacco soil borne disease was not big, and it had a certain influence on the economic character of tobacco leaves and proportion of high and middle grade tobacco after green manures has turnovered and retted. Compared with CK, yield improvements of milk vetch, sand vetch, vicia sativa and mixed sowing were 19.4,15.8,4.8 and 12.2 kg/667 m2 respectively; increasing economic values were 535.53,415.23,111.57 and 305.61 yuan respectively; proportion of high and middle grade tobacco increased 4.2%,2.7%,0.4% and 1.5% respectively. Under this condition of experiment, the more the green manure turnovered and retted, the better integrated characters were; It benefited the effect on the inner quality of tobacco leaves the most after flue-curing by milk vetch, wherein the starch, reducing sugar, total sugar, nicotine content are 6.28%,32.18%,36.37% and 2.17% respectively. To summarize, the best variety of green manure was milk vetch which was efficient for soil fertilization in tobacco-rice continues cropping area.3.In winter fallow cropland of tobacco-rice rotation district which plants green manure to improve soil quality. It was better to regularly intercrop tobacco in the growth of green manure in the second year in March, according to preparation of tobacco planting soil after the late rice harvest, firstly ridging and soil preparation, finally green manure sowing in ridged tobacco planting soil. The results showed that the biological yield of ridging planting astragalus sinicus is higher than no ridge planting astragalus sinicus. The average grass yield of 1144.4 kg/667 m2, after flue-cured tobacco transplanting, it has reached an average of 1691.8 kg/667 m2, biological yield increased by 63%, branch number, plant height, fresh weight per plant of ridging planting astragalus sinicus and other comprehensive advantages appear obviously and prominent to some extent. The main reason why mass demonstration of green manure in southern Hunan was not success, was the conflict that green manure and tobacco shared the same planting season. Through the pattern of firstly ridging then green manure sowing, to extend the growth duration of green manure. The green manure turnover was that the green manure was putted on the ridge through cultivation and earthing up. It measured such green manure planting patterns to increase soil fertility, decrease soil bulk density, enhance permeability. It had significantly improved tobacco planting soil physical and chemical properties, microbial activity and the growth and development of tobacco plant. The microbial amount increased by 42.2%?52.2%, of which the largest number was bacteria of maximal 75.7%, secondly number of fungi increased of maximal 24.9%, actinomyces increase of maximal 9.0%. The turnover and retting after planting green manure has a certain effect on tobacco agronomy character. The more quantity of green manure turnovered, the better the tobacco agronomy character was, wherein the unridged test of tobacco agronomy character is the best; Planting green manure has remarkable effect on leaf yield of tobacco. Compared with CK, yield improvements of ridged and unridged were 5.93kg/667m2,1.07kg/667m2; increasing economic values were 163.5 yuan,36.9 yuan; proportion of high and middle grade tobacco increased 0.87%,0.68%. Ridged and unridged did not have remarkable effect on quality and quantity of tobacco leaves, so it should be advocate to plant green manure to return to soil in tobacco production, in order to prove tobacco agronomy character, raise the ratio of the first and secondary class leaves, finally reached quality and effects improvement. |
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