| Tobacco is one of the most important economic crops in China, continuous cropping crop of tobacco is a jealous crop, but in recent years, driven by external conditions and economic profit, more and more serious phenomenon of continuous cropping of tobacco, thereby restricting the sustainable development of tobacco. Phosphorus is one of the essential macronutrient by plants for growth and development. Poor mobility of phosphorus in soils, easily soil minerals and clay and other substances adsorption fixed, resulting in low availability of soil phosphorus limits the growth of crops, improve crop yields for a large number of chemical fertilizer is applied to the soil, which not only caused excess phosphorus migration to risk environment, but also increase crop production costs. Field investigation and laboratory analysis using a combination of methods to explore the basis of different tobacco continuous cropping and tobacco garlic intercropping soil phosphorus content and phosphorus fraction changes under different number of years, through field plot trials under different planting patterns in tobacco rhizosphere soil phosphorus fraction variation, revealing tobacco garlic crop rotation, intercropping effects of planting pattern on tobacco yield and different forms of phosphorus in the soil, the main research results are as follows:(1) With the increasing length of continuous cropping of tobacco, soil available phosphorus content increased significantly, soil available phosphorus content under continuous cropping of tobacco in 15 age were 1.55 and 1.89 times as high as that under continuous cropping of tobacco in 5 age and 10 age.Under two cropping ways of soil inorganic phosphorus in size as follows:Fe-P> O-P>Caio-P> Al-P>Ca8-P> Ca2-P, and the sum of O-P and Fe-P content accounted for much than 65% of the total inorganic phosphorus content. Ca2-P, Cas-P and Al-P content in continuous cropping of tobacco increased significantly. O-P content under continuous cropping of tobacco in 15 age were 1.37 and 1.45 times as high as that under continuous cropping of tobacco in 5 age and 10 age. Tobacco garlic intercropping soil O-P content with the increase of the fixed number of year of the intercropping dropped significantly, the Caio-P content also assumes the declining trend of fluctuations. The moderate labile organic phosphorus was dominant in the organic phosphorus fraction, followed by the high resistant organic phosphorus and moderate resistant organic phosphorus, while labile organic phosphorus was the lowest in soil of tobacco continuous cropping and tobacco garlic intercropping. Increase with continuous cropping years in continuous cropping of tobacco, high resistant organic phosphorus content is lower, but the ratio has increased. Tobacco garlic intercropping not only can stabilize the soil available phosphorus and strong activity Ca2-P content, can also reduce the content of O-P in soil and proportions.(2)The tobacco yield were higher in tobacco garlic crop rotation and tobacco garlic crop intercropping growth conditions than in the tobacco monoculture growth condition. In 2013 and 2014, tobacco yield under tobacco garlic crop rotation and tobacco garlic intercropping were tobacco was 1.35 and 1.18 times,1.18 and 1.22 times as high as that under tobacco monoculture. In 2013, the rhizosphere soil available phosphorus content under garlic crop rotation and tobacco garlic crop intercropping were 1.35 and 1.70 times, 1.03 and 1.51 times,1.10 and 1.15 times as high as that under tobacco monoculture at mature stage of lower leaf, mature stage of middle leaf, mature stage of upper leaf. In 2014, the rhizosphere soil available phosphorus content under garlic crop rotation and tobacco garlic crop intercropping were 1.09 and 1.70 times,1.06 and 1.72 times as high as that under tobacco monoculture at mature stage of lower leaf, mature stage of middle leaf. Description tobacco garlic crop rotation and intercropping can improve the rhizosphere soil available phosphorus content.(3)In a whole, the concentration of inorganic P fractions showed the same tendency in rhizosphere and non-rhizosphere soils. The highest content of O-P and Fe-P, followed by Ca2-P and Al-P, Ca8-P and Ca10-P at different stages under different planting patterns, and the sum of O-P and Fe-P content accounted for much than 70% of the total inorganic phosphorus content. The Ca2-P concentration in rhizosphere soil under tobacco garlic crop rotation treatment was 97.06% and 85.66%,81.82% and 43.26% of that under tobacco monoculture at mature stage of upper leaf and mature stage of upper leaf in 2013 and 2014. While the concentration of Cas-P also had the same changes at mature stage of lower leaf in 2013. The O-P concentration under that tobacco garlic crop rotation and tobacco garlic crop intercropping was significant lower than that under tobacco monoculture in rhizosphere soil. In 2013 and 2014, the Caio-P concentration in rhizosphere soil in of tobacco garlic crop rotation was significant lower than that in tobacco monoculture and tobacco garlic crop intercropping at mature stage of middle leaf. The moderate labile organic phosphorus and high resistant organic phosphorus were dominant in the organic phosphorus fraction, followed by the moderate resistant organic phosphorus, while labile organic phosphorus was the lowest in rhizosphere soils. The labile organic phosphorus concentration under tobacco garlic crop rotation was 2.11 and 5.09 times,1.23 and 1.20 times higher respectively than that under tobacco monoculture in rhizosphere soil at mature stage of middle leaf and mature of upper leaf in 2013 and 2014. The high resistant organic phosphorus concentration under that tobacco garlic crop rotation was lower than that under tobacco monoculture and tobacco garlic crop intercropping in rhizosphere soil. Description tobacco garlic crop rotation can enhance the ability to activate the rhizosphere, the soil organic phosphorus fractions insoluble converted to higher availability of phosphorus forms.(4) In garlic season and tobacco season, the soil Ca2-P, Ca8-P and Caio-P content of the change is very small under tobacco garlic garlic crop rotation and intercropping. And the soil Fe-P and O-P content decreased by 12.85 and 15.50 mg·kg-1 under tobacco garlic rotation; tobacco garlic intercropping in garlic season, soil available phosphorus content is 1.20 times that of tobacco season, soil O-P content drop of 33.66%. The soil high resistant organic phosphorus content decreased by 22.55 and 15.64 mg·kg-1 under tobacco garlic rotation and tobacco garlic intercropping. Combined with tobacco maturity characteristics of soil phosphorus fractions under different cropping ways and tobacco yield change, indicating that tobacco and garlic rotation is a better crop model. |
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