| To long term monocropping, one of the main obstacle factors of soil is lack or imbalance of nutrients which caused by long-term specific absorption of the same crop. In Xinjiang, the cotton planting either occupy highly proportion or has long continuous monoculture history. Farmland intensive management combination as high degree mechanized operations, large amount chemical fertilizer input, advanced water-saved dripping irrigation, and entire straw returning etc. formed during long term cotton production process, and make the production amount of Xinjiang cotton raise stably year by year. However, weak growth vigour, plants presenility, widespread dead seedling, serious diseases and pests, the raising dosage of pesticide and chemical fertilizer of Xinjing contiuous cropping cotton has appered in recent years which induced the ratio of outputs and inputs glided constantly, law diminishing return occurred seriously impact on sustainable production of cotton in Xinjiang. Based on the above issues, and combined the fertilizer input characters in Xinjiang farmland about emphasis on N and P fertilizer application, no K fertilizer, less or blindly application of microelement fertilize trace element fertilizer, this paper studied the nutrients variation laws of cotton farmland in different continuous cropping years from the angle of temporal and spatial variation of nutrients, discuss the consumption characters of cotton farmland nutrients and the regulating effect of different cultivation practices. The result could supplied theoretical basis for the scientific management to nutrients and soil sustainable utilization of the sustainable production of Xinjiang cotton.The study was conducted in Shajingzi of south Xinjiang where question of monoculture stood out and has more types of improved tillage practices. The study adopted the method of spatial substitution, choose the cotton field with different continuous cropping years (reclaimed for 1year,continuous cropping for 5 years,15 years,20 years, and 30 years) and the farmland improved by different tillage practices of cotton (deep tillage of 60cm or rice-cotton rotation after obstacles occurred on long term monoculture cotton field), analysised either the variation characteristics of the main nutrient included soil organic matter, macro-elements (N, P, K), micro-elements (Mo,Cu Zn, Mn, Fe), base salinization elements (Ca, Mg, Na) etc. in the 0-100cm soil profile of the cotton field of different continuous cropping years and improved by different methods, or the characteristics of nutrient bio-cycling under the modern intensive management models, and got the following main results:1. The soil organic carbon pool rises constantly in long term monocultural cotton field due to long term straw returning in Xinjiang. The organic carbon content of 0-40cm soil depth tended to increase year by year and brings carbon sequestration functions into play. To the cotton field improved by deep tillage, soil of 0-60cm depth gets sufficent mixing, the organic matter content of relative deep soil layer which below the plowing layer (0～20cm) rieses significantly in short term, but the organic matter decompose rapiddly during the growth of following cotton, and its content significantly decreased till harvest time, especially deep tillage in spring, organic matter content declined quicker than in winter. To the cotton field improved by rotation for one season, organic matter content redued inordiniately of different profile after dry and wet alternation in soil, In the sandy loam, the organic matter content of 0-60cm soil depth was significantly decreased, and the reduce in heavy loam is not significant in short term, but significant during the growing period of following cotton.2. Due to long term laying particular stress on the input of N and P fertilizer in Xinjiang, the soil N and P content in monocultral cotton field rises year by year. The content of Total-N, Alkeline-N, Total-P, available-P in various layers with 0-40cm profile rises constantly with the extending of the continuous cropping years. The content of Total-N, Alkeline-N, and Total-P rises quickly with the extending of years while available phosphorus rises slowly after 15-year continuous cropping. Deep tillage breaks the profile differentiation situation of N and P formed with long term continuous cropping, the two nutrients reach peak content value in 20～40cm, rise quickly together with the content in 40～60cm soil layer, and make the soil layer section keeping high efficient content during the key growing stage of the whole growth of following cotton. To the cotton field improved by rice rotation, the content of Total-N, Alkeline-N, and Total-P, available-P in heavy soil do not change significantly while the content of Total-N and Total-P of 0～40cm soil layer in sandy soil significantly dropped, and Total-N in profile moves to the bottom significantly while Alkeline-N and available-P have no significant change.3. Due to not fertilize potassium to the farmland, with of straw returning and the function biological uptake of cotton, soil K content differentiates in different depth of profile after long term monocultral cotton. With the extending of years, the soil K content in 0～20cm rises first and decreases later, generally decreases after 15 years for cotton monoculture; in 20～-70cm decreases year by year, the content of 40-50cm decrease most significantly in sandy loam, and the content of 20～30cm decreases quickest in heavy loam; in 70～100cm accumulates, but have no significant difference indifferent years. Deep tillage breaks the distribution of K which rise first then decrease from upper to bottom and in whole profile, makes the content in various layer within 0-60cm to equalize, promotes the release of available K, and makes the medium soil layer keeping high content of available K during the whole growth of cotton. Although rice-cotton rotation has positive function in overcoming the obstacle of continuous cropping, but it may cause leaching loss for potassium along profile to the bottom, especially cropping rice in sandy soil, available K content is low in 0-40cm soil layer during the whole growth of following cotton, hence, we should pat attention to the potassium supplementary for cotton after rice.4. Due to less fertilization of microelement, with the cropping going on, through straw returning and the output of crops organ, Total Mo of plowing layer (0～20cm) decreases with the extending of years of continuous cropping, in the plow layer (0～20cm) total Mo decreased, showing a unitary negative linear relationship, while total Cu, total Zn and total Mn first rose up, peaking in year 7～10,10～12 and 17～18, separately and then declined, dropping back in year 14～17,20～22 and 32～34 separately to the initial value, showing a quadratic functional relationship. The content of available Cu, available Mn and available Fe of 0-30cm layer rises first decrease later with the extending of continuous cropping years, and turns decrease in 15～20 years after continuous cropping. Certain position of 20～70cm in medium will form low valley due to the large absorption and consumption of cotton, decreases year by year with the extending of continuous cropping, takes on the relationship of unitary negative linear correlation, sandy soil distributes in 30～50cm depth, and heavy soil distribute in 20～30cm depth. Deep tillage has significant affect on the profile distribution of total element and available content of microelement, and has strong equalization function to soil layer. Rice-cotton rotation can significantly rise the availability of microelement in plowing layer, the function are more significant on heavy loam, and available Zn can have certain leaching on profile in sandy soil by the affect of the function.5. Due to high salinization and solonization, with conventional lavement in winter and mulch-drip irrigation during growth stage, Ca and Mg moved remarkably from surface to deep soil layer and bring the result as the content of Ca and Mg reduced differently. The content of Na increased in upper of heavy loam and accumulated in the depth of 30～50cm. Deep tillage, as strongly soil jamming, the content of base salinization elements were meaned at the depthes which deep tillage could touch. Rice-cotton rotation, under the eluviation, base salinizaton elelments were moved from upper to deep, it can take soil changes to desalinization.6. Nutrient consumption and return which come from cotton are different due to the difference of cotton absorbed nutrient or organs accumulated nutrient. To some extent, not only microelement but also microelement have leanness trend in the fields after long-term cotton monoculture.and the lower the microelement in content in the soil, the more apparent the fall of its content, such as Mo. With getting in the cotton, quantities and ratio of Zn and Cu have output much more in cotton fields, in the same Mg, K. most of Mn, Fe, Ca, Na were accumulated in the straw. with turning straw, there will be a lot in farming soils.7. Under the modern intensive management mode, Xinjiang cotton is monocrop for a long time which needs to be reduced the inputs of N, P fertilizer appropriately and improves the nutrient validity by updating the measures; at the same time, the microelement fertilizer of Mo, Zn and Cu should be added importantly and the microelements fertilizer of Mg, K should be added appropriately. Combined with the measures of soil deep tillage and fertilizer deep fertilizing, improves the content of K and microelement in the central earth layer. The content of Ca, Na is lower than background of Xinjiang soil which indicate that the cotton soil trends to the direction of desalinization, while the contents of two elements take higher percentage in the straws, the continuous cropping farmland with cotton for long time should be prevented the plough horizon soil to change to soil secondary salinization.
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