【作者】 韩春丽；

【导师】 张旺锋；

【作者基本信息】 石河子大学 ， 作物栽培学与耕作学， 2010， 博士

【摘要】 单一作物长期连作,由于作物专性吸收而引起土壤某些养分亏缺或比例失衡是连作的主要障碍因子之一。新疆棉花种植比例高,连作年限长,在长期棉花生产过程中,集成了高度机械化作业,增加化肥投入,采用先进的节水滴灌以及全面秸秆还田等农田集约管理组合,使得新疆棉花产量水平稳步提高。然而近年来新疆长期连作棉田棉花生长势差、早衰、死苗等现象普遍,病虫为害严重,农药、化肥用量不断上升,而产出和投入比不断下滑,出现明显的报酬递减规律,严重影响了新疆棉花的可持续生产。基于上述问题,结合新疆农田偏重氮磷施用,不施钾肥,少施或盲目施用微量元素肥料的施肥管理特点,本论文从土壤养分时空变化角度,研究了不同连作年限棉田养分变化规律,探讨棉田养分消耗特征及不同耕作方式的调节效应,为新疆棉花生产中养分科学管理和土壤可持续利用提供理论依据。试验地点选择在棉花连作问题突出,同时改良措施类型多的南疆沙井子垦区进行；研究采用空间替代法,以不同连作年限棉田(初垦1年、连作5年、15年、20年、30年)以及经不同耕作措施改良的棉田(长期连作棉田出现障碍后进行深翻(翻60cm)或稻棉轮作)为研究对象,系统分析了现代集约综合管理模式下,土壤有机质、大量元素(N、P、K)、微量元素(Mo、Cu、Zn、Mn、Fe)、盐基元素(Ca、Mg、Na)等几种主要养分,在不同年限连作棉田和经不同方式改良的棉田土壤100cm剖面中的变化特征及生物循环规律,取得以下主要研究结果：1.新疆棉花长期连作伴随秸秆还田,长期连作棉田土壤有机碳库持续增加,随连作年限延长,剖面0～40cm各土层有机质含量均呈逐年上升态势,具有碳汇功能。经深翻改良的棉田,0-60cm土壤得以充分混合,短期内耕作层(0～20cm)以下相对较深土层有机质含量显著增加,而在后茬棉花生长期间,有机质分解较快,至收获期含量大幅下降,春季深翻较冬季深翻下降更快。经一季水稻轮作改良的棉田,土壤经干湿交替,剖面不同深度有机质含量有不同程度下降,砂性质地土壤中,0～60cm均显著降低,而重壤质地土壤中,短期内下降不明显,但在后茬棉花生长期间下降较多。2.由于长期偏重氮、磷肥投入,长期连作棉田土壤氮、磷养分含量逐年上升,剖面0～40cm各土层全氮、碱解氮、全磷、有效磷含量均随连作年限延长而持续增加。全氮、碱解氮、全磷含量随连作年限延长大幅度提高,而有效磷在连作15年以后,增长速度明显减慢。深翻打破了土壤氮、磷养分在长期连作下形成的剖面分化格局,两种不同形态养分均在20～40cm达含量峰值,与40～60cm土层的含量一并得到大幅度提升,并使该土层段在后茬棉花全生育期的关键生育时期一直保持较高的有效含量。经水稻轮作改良的棉田,重壤质地土壤中,全氮、碱解氮、全磷、有效磷含量未发生明显变化,而砂壤质地土壤中,0-40cm全氮和全磷含量显著降低,且全氮在剖面中呈明显向底部迁移的运移趋势,而碱解氮和有效磷变化不大。3.新疆农田一般不施钾,在秸秆还田和棉花生物吸收作用下,棉花长期连作土壤钾含量在剖面不同深度发生分异。随连作年限延长,上部0-20cm耕作层含量先升后降,一般在棉花连作15年以后开始下降；中部20-70cm逐年下降,砂壤土中以40-50cm耗竭最重,重壤土中较浅,以20-30cm下降最快；下部70-100cm有累积趋势,但在年限之间无明显规律。深翻打破了钾在剖面中自上而下先降后升的分布状态,使0-60cm各土层含量趋于平均化,并促进速效钾的释放,使中部土层在棉花全生育期维持较高的速效钾含量。稻棉轮作虽然在克服连作障碍中有积极作用,但易造成土壤钾沿剖面向底部的淋溶损失,尤其在砂壤质地土壤上种植水稻,下茬棉花全生育期0-40cm土层速效钾水平普遍较低,因此应注重对下茬作物的钾肥补充。4.新疆棉田微量元素施用少,通过秸秆归还和产品器官输出,棉花长期连作,耕作层0-20cm土层全Mo随连作年限增加持续下降,与连作年限呈一元负线性关系；全Cu、全Zn、全Mn含量随年限增加先升后降,与年限呈二次函数关系,分别在连作7-10、10-12、17-18年达到最高累积量,之后持续下降,分别在14-17、20-22、32-34年回到初垦水平。0-30cm有效Cu、有效Mn、有效Fe含量亦随连作年限增加先升后降,在15-20年之后转而下降。中部20-70cm一定深度会因棉花大量吸收消耗而形成低谷,并随连作年限延长而逐年下降,与年限呈一元负线性关系,砂壤土表现较深,一般位于30-50cm处,重壤土中较浅,位于20-30cm处。深翻对微量元素全量和有效含量的剖面分布均有明显的影响,有较强的匀化土层养分的作用；稻棉轮作能明显提升耕作层微量元素有效性,这种作用在重壤土上尤为明显,而在砂壤土上,可使有效Zn在剖面产生一定程度的淋溶。5.新疆农田土壤盐碱化较重,在传统冬灌压盐和生育期膜下滴灌作用下,棉花长期连作,随连作年限延长,Ca、Mg元素由表层向底部迁移的趋势增强,使得耕作层0-20cm及以下20-40cm土层含量有不同程度下降,Na在重壤土表层含量增加,而在砂壤土中30-50cm随连作年限延长逐渐累积。深翻由于人为强烈的扰动,翻耕涉及的深度范围内盐基元素出现平均化分配格局；稻棉轮作在水分的淋洗作用下,盐基元素自上而下运移,可使土壤向脱盐方向转变。6.由于棉花对不同元素的吸收以及不同器官富集养分能力的差异,棉花对土壤不同元素的消耗量和归还量各异。经过多年棉花的连续生产,棉田土壤中部分微量元素和常量元素均有一定程度的贫化趋势,且在土壤中含量水平越低的元素,贫化越明显。棉花对Mo的吸收能力最强,导致长期连作土壤中Mo耗竭最重；随籽棉的收获,棉田微量元素Zn、Cu和常量元素Mg、K的输出较多,而Mn、Fe、Ca、Na等元素在秸秆中富集较多,会随秸秆还田归还农田,消耗不大。7.在现代集约综合管理模式下,新疆棉花长期单一种植,应适当减少N、P肥投入量,改进措施提高养分有效性；应重点补充Mo、Zn和Cu微量元素肥料,酌情补充Mg、K常量元素肥料。并对连作达20年以上的棉田结合土壤深度翻耕,肥料深施等措施提高中部土层K及微量养分含量。棉田Ca、Na含量较新疆士壤背景低,预示着棉田土壤在向着脱盐碱方向发展,然而两元素在秸秆中的比例较高,因此棉花长期连作农田,应注意防止耕作层土壤向次生盐碱化方向发展。更多还原

【Abstract】 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.更多还原