【作者】 徐海；

【导师】 王益权；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2011， 博士

【摘要】 人口增长、土地面积缩减、人与土地矛盾日益尖锐,迫使人们不得不采取集约化或密集型农业生产。在人为高强度利用、高负荷生产条件下,农田土壤质量发生着程度不同地宏观变化(退化)和微观变化(疲劳)过程,研究现代密集型生产模式下土壤质量演化趋势和变化程度无疑是土壤科学重点内容。虽然土壤是具有“再生作用”的宝贵资源,是具有一定生理机能的“类生命体”,这些都是建立在“用之得宜”的基础上。任何对土壤过度使用、管理不当,轻者使土壤“生理机能”受损,出现各种疲劳症;重者则发生明显退化,失去生产力,直至荒芜。其中土壤疲劳症是在发生在“连年高产”,仍追求“高产再高产”目标过程中,其生理机能(协调能力)的一种衰退过程,是土壤发生退化的前奏。土壤退化早已被人们所关注,可是,土壤疲劳至今却最被忽视。研究农田土壤疲劳症状、发生原因与机理,探索土壤抗疲劳的物质基础,是揭示人为强度利用对土壤质量演化作用与影响规律、深刻认识土壤本质属性、全面掌握土壤生理机能、探求土壤永续利用有效途径、确保农业及生态环境可持续发展的迫切需要。本文以半干旱偏湿润关中地区的旱地农田为研究对象,以建立涵盖空间尺度、时间尺度的新的土壤养分状况理论为主要目标、以长期大量使用无机化肥情况下,石灰性富钙土壤的钙饱和度演变为指标,采用定位监测、室内过程模拟以及生物效应试验等技术手段,分析现代密集型农业生产条件下土壤营养疲劳症及其发生机理。通过研究得出如下主要结论:1.完整的能够真实体现对作物营养供给能力的“土壤养分状况”概念必须是指在一定时段(一般是作物生育期)一定厚度土层(一般是根系主要发育层)的土壤中某种速效(有效)养分含量的动态变化过程,而不应当是作物播种前耕层土壤养分的含量。关中旱地农田土壤养分状况呈现出明显的季节性和区间性变化特征(农田营养疲劳症时空变异),既体现着施肥习惯、又体现着旱地作物养分迁移和生物吸收特点。土壤剖面碱解氮素时空变化特征分为两个不同变化区域。在0~50 cm是体现着施肥模式的具有从上向下递减显著特征的“垂直梯度”区域;50~100 cm是体现作物根系吸收、养分迁移过程特征的“时间梯度”区域。其中0~20 cm以上土层的垂直向梯度不明显,终年基本上能够维持在70 mg/kg范围以上,只有几个短暂时间性质的变化梯度,属于土壤“碱解氮丰富的等值区域”,显然,与作物生长过程关系不密切,如若作为土壤营养诊断区域不够可靠;20~50 cm处土壤碱解氮素含量变化在50~70 mg/kg范围,垂直梯度等值线较为密集,尤其是在30~40 cm处,体现碱解氮含量垂直梯度的曲线极为密集,该梯度成为氮素向深层迁移的动力,意味着该区域应当属于氮素深层移动的“传导区域”。50~100 cm处土壤碱解氮素含量终年变化在50 mg/kg以下,该区域等值线多呈现纵向延伸,意味着该区域土壤碱解氮含量的变化梯度体现着作物的生长发育过程,属于土壤碱解氮的“活动区域”。土壤速效磷含量变化呈现两个显著的时间变化特征段。在小麦全生育季节里土壤剖面上有效磷含量呈现出典型的垂直空间变异梯度特征,其中在0~50 cm以上区间梯度大,50 cm以下梯度明显变缓,在小麦返青到成熟阶段对深层60 cm以下土壤速效磷消耗非常明显;在玉米生育季节里土壤剖面上磷素呈现出明显的时间变异梯度特征。在玉米苗期深层土壤速效磷含量有递增趋势,随生育期延伸土壤剖面上速效磷含量明显递减,尤其是在玉米成熟期间,深层土壤速效磷素递减非常明显。在0~100 cm范围内查明土壤速效钾随时间的变化梯度非常明显,而上下土层之间没有明显的梯度。随作物生育期延伸0~100 cm范围土壤速效钾含量整体上呈显著地递减趋势。从小麦返青期前土壤剖面速效钾含量为140 mg/kg以上逐渐递减到玉米收获期土壤剖面上速效钾含量的70 mg/kg,减少了一半多。终年时间段内土壤剖面上速效钾含量变化过程具有明显的“稳与降”的交替进行过程。从小麦播种到越冬期土壤剖面速效钾含量随时间变化不很剧烈,基本稳定在150 mg/kg高水平范围,属于“富钾的稳定阶段”;从小麦返青到拔节期土壤剖面速效钾为“富足性快速递减过程”;从小麦拔节后到成熟阶段土壤剖面维持着100 mg/kg的速效钾含量水平,过程变化梯度不明显,土壤处于速效钾处于“中等水平的稳定阶段”。在夏玉米生育期间,土壤剖面速效钾含量又一次显著地递减,属于钾素的“胁迫性递减阶段”。旱地农田土壤速效养分状况充分体现着施肥习惯,存在着极为明显的“上肥下瘦、上干下湿”剖面特征。上层土壤水分含量低且不稳定限制了养分利用,成为土壤营养疲劳发生的重要环境因素。由此得出,肥料表施是旱地土壤养养疲劳发生的人为因素、上层土壤水分含量低且不稳定限制养分利用,使土壤营养疲劳发生的重要环境因素。2.关中农田土壤主要肥力性状存在着明显的水平空间变异特征(农田土壤营养疲劳症的空间变异),充分印证了当地施肥习惯和历史。历史上以有机肥料培肥为主,采用就近施肥的原则,在土壤中印记着亚表层有机质含量水平变异程度相对较高的痕迹;现代以无机培肥为主,表层土壤有机质水平变异程度不大,田间土壤有机质含量的水平空间分布趋势与土壤碱解氮相反,0~40 cm范围内农田土壤碱解氮变化趋势与有机质变化不一致的特征,反映着当今大量使用无机氮肥,导致土壤剖面氮素累积结果。长期使用无机化肥,即就是石灰性的富钙土壤,同样也会具有钙饱和度明显递减的问题,关中农田土壤钙饱和度变异在55.76%~72.76%,平均值在61%左右。农田0~40 cm范围内土壤钙饱和度水平分布趋势与土壤有机质相似,与土壤氮素分布趋势相反,表层土壤钙饱和度的变异性大等特征,佐证了现代大量使用无机氮肥对土壤营养疲劳的作用与影响。土壤钙饱和度显著变化应当属于“隐性退化”----“营养疲劳”症状之一。3.施入不同类型及浓度的氮肥均能引起石灰性土壤钙素退化,同时,氮肥品种间差异体现着明显的陪伴离子效应。石灰性土壤在NH4Cl、1/2(NH4)2SO4、NH4NO3三种同体积不同浓度铵态氮溶液的淋洗后,土壤中交换性钙含量的下降程度呈现为NH4NO3 < NH4Cl < (NH4)2SO4。尿素对石灰性土壤中交换性钙也具有明显的影响,施入尿素后的土样培养7天,土壤交换性钙含量明显降低;培养7天之后土壤交换性钙降低趋势趋于平稳。从整体上看,大量施用氮肥使石灰性土壤钙饱和度平均下降到50%以下水平。4.石灰性土壤使用磷肥也能引起钙饱和度下降。以氯化钾为对照,以不同浓度磷酸二氢钾溶液淋洗土壤后,土壤中交换性钙含量均呈现不同程度的下降,土壤有效钙和交换性钙含量与溶液浓度呈明显的负相关关系,其中磷酸二氢钾溶液对土壤钙素影响十分明显。剔除钾素对土壤中钙离子的影响,得出随磷酸根溶液浓度的增加,对土壤中有效钙素和交换性钙素的影响较大。土壤碳酸钙含量也与溶液浓度成明显的负相关关系,在磷酸二氢钾溶液浓度达到0.2 mol/L以上时脱钙作用明显。随磷素浓度增加对土壤钙饱和度明显递减。5.土壤物理状态是发生营养疲劳的重要因素之一。土壤紧实胁迫对玉米苗期生长及钙素养分的吸收影响研究,得出玉米从播种到生长15 d期间,玉米生育前期株高对不同容重紧实胁迫的反映不明显,15 d后地上部分生长速度随土壤容重增加而受到明显抑制,玉米株高随土壤容重变化顺序为R1.20 g/cm3>R1.10 g/cm3>R1.30 g/cm3>R1.40 g/cm3>R1.50 g/cm3,其中R1.10 g/cm3处理因土壤容重过小,根系与土壤接触面减小,不利于对水肥的吸收利用,因此其株高反而小于R1.20 g/cm3。玉米根系生长也由于土壤紧实胁迫而受阻,根系干物质质量下降,根系活力减小,影响钙素养分的吸收。玉米幼苗中钙素含量最低为11.78 g/kg,最高为16.67 g/kg,其值分别出现在土壤容重1.1 g/cm3和1.2 g/cm3处理中,土壤容重较小,根系与土壤表面接触少,作物对养分的吸收不易,而随着土壤紧实的增加,根系活性减小,同样使作物根系对钙素的吸收减少、作物抗性下降,导致作物提前衰老。因此,土壤容重影响土壤中养分的有效性,土壤过松或过紧实均不利于作物的生长。更多还原

【Abstract】 Intensive agricultural production had to be used, because of the contradiction between population increasing and acreage reduction. Under the condition of artificial high intensity using and high load production, farmland soil quality occurred variations including macroscopic(degradation) and microscopic(fatigue) processes to different extent. So, study of soil quality evolvement trend and variation degree under model of modern intensive production was key content of soil science.Although soil was a gold resource, which was reclaiming action and some physiological function, all properties based on rational utilization. Overuse soil and mismanagement would result in damage of soil physiological function, especially appeared significantly degradation, lost the fertility at last. Soil fatigue appeared in process of blindly pursuing highyield, and it was a decline process of physiological function, and it was prelude of soil degradation. People paid more attention to soil degradation, but ignored soil fatigue. Studying farmland soil fatigue symptom, reason and mechanism, exploring material basis of soil anti-fatigue, which was urgent need of opening out soil quality evolvement and effect law under artificial intensive using, profound understanding soil properties, comprehensively mastering soil physiological function, searching for effective approach of soil permanent utilization and ensuring sustainable development of agriculture and ecological environment.The research analysed soil nutrient fatigue and its occurrence mechanism by taking farmland in semiarid area liable to humid as the research object and taking spatiotemporal soil nutrient status theory as the main goal, and it used the methods including located monitoring, indoor simulation and biological effect experiment by taking degree of calcium saturation in calcareous soil as index. The conclusion:1. The full concept of“soil nutrient status”which could embody crop nutrient supply ability was dynamic variation process of soil available nutrient in certain period of time(crop growth stage) and certain soil layers(root developoment layer). The seasonal and regional variation of farmland soil nutrient status showed the fertilization habit and the characteristics of nutrient transfer in dry land and biological absorption in Guanzhong Area.There were two different variation regions in soil available N spatiotemporal variation characteristics.“Vertical gradient”area was in 0~50 cm, which was significantly decreasing characteristics from up to down;“time gradient”area was in 50~100 cm, which embodied characteristics of crop root absorption and nutrient transfer process. And vertical gradient was not obvious in 0~20 cm soil layer, its content was above 70 mg.kg-1. Only some brevity time variation gradient was“available N abundant equivalent region”, obviously, it was not close with crop growth process, and it was not reliable as soil nutrient diagnosis area. The content of soil available N was 50~70 mg/kg in 20~50 cm soil layers, and its vertical gradient isoline was relatively dense, especially in 30~40 cm, so the region was“conduction region”of nitrogen deep moving. The content of available N in 50~100 cm soil layer was below 50 mg.kg-1 all the year round, the isoline in the area was vertical extension, the variation gradient of available N content embodied crop growth process, it was“activity region”.There were two significantly temporal variation characteristics in soil available P content variation. The gradient of spatial distribution of the soil available P was very obvious in wheat growth stage, especially in 0~50 cm, and soil available P consumed obviously below 60 cm from wheat turning green stage to mature stage. Then, the content of soil available P in maize growth stage was obviously temporal variation gradient. In deep layers, soil available P content was increasing in maize seedling stage, then decreasing was significant after seedling stage, especially in maize mature stage.The time variation gradient of soil available K was very obvious in 0~100 cm, and the gradient among different layers were not obvious. The soil available K content in 0~100 cm soil layer showed general decline trend in time domain, which decreased from over 140 mg.kg-1 in wheat turning green stage to 70 mg.kg-1 in maize mature stage. The annual variation process of soil available K was significant“steady and drop”alternative process. The soil available K content was about 150 mg.kg-1 from sowing stage to overwintering stage, which was“rich-K stable stage”; the soil available K content variation was“affluence rapid decline process”from wheat turning green stage to jointing stage; the soil available K content was maintaining about 100 mg.kg-1 from jointing stage to mature stage, which was“middle level stable stage”. And in maize growth stage, the soil available K content obviously decreased again, which was“stress decline stage”of potassium.The fertilizing custom by farmland soil available nutrient status in dry land, and the characteristics of“upside fertility and underside leanness, upside dry and underside wet”was very significant on soil profile. Low and unstable surface soil moisture limited to nutrient using, which was important environment factor of leading to soil fatigue.2. The horizontal space variation characteristics(the space variation of farmland soil fatigue) of main farmland soil fertility properties were obvious in Guanzhong area, which showed the local fertilizing custom and history.In history, farmer mainly cultured fertilizer by organic fertilizer before, which followed the principle of proximity, however, in current years, we mainly cultured fertilizer by chemical fertilizer, the soil organic matter content decreases more gradually as the distance from the village increases.in the horizontal direction, it showed a changeable tendency consistent with that of soil organic matter content, whilst this trend was opposite to that of soil available N content in 0~40 cm, which showed that slather inorganic nitrogen fertilizer lead to nitrogen accumulation on soil profile.Slather inorganic fertilizer would lead to the decline of degree of calcium saturation, even in calcareous soil, and the variation of farmland soil Ca saturation in Guanzhong was 55.76%~72.76%, the average was 61%. The Ca saturation variation trend was similar to soil organic matter and was opposite to that of soil available N content in 0~40 cm, and the soil surface layer variation was larger than others, which showed the effect of soil nutrient fatigue on slather inorganic nitrogen fertilizer. The decline of Ca saturation is a hidden process of soil degradation, and it is the main symptom of soil fatigue.3. Using different types and concentration nitrogen fertilizers could result in calcium degradation in calcareous soil, and the difference among nitrogen varieties showed accompany ionic effect.Calcareous soil exchangeable calcium content did go down after leached by equal volume of NH4Cl, 1/2(NH4)2SO4 and NH4NO3 (different NH4+ concentration). The influence decreased in this order: NH4NO3 < NH4Cl < (NH4)2SO4. Soil exchangeable calcium content was significantly negatively correlated negatively with incubation time during 7 days after adding carbamide into the soil and became stable in the following days. Overall, the results indicate that topsoil exchangeable calcium content gradually decreases with long-term heavy nitrogen fertilizer usage in a calcareous soil. Decalcification can make soil calcium saturation lower, down to 50% or less.4. Using phosphorus fertilizers could result in the decline of Ca saturation in calcareous soil. Taking KCl treatment as control, the soil exchangeable calcium content did go down after leached by different concentration KH2PO4 solution. There was a negative correlation between soil potent calcium(exchangeable Ca) and solution concentration, and the effect of KH2PO4 solution on soil calcium was very obvious. Excluding influence of potassium, PO43- concentration was higher, the effect on soil potent calcium and exchangeable Ca was larger. There was a negative correlation between soil CaCO3 content and solution concentration, too. When KH2PO4 solution concentration was above 0.2 mol/L, the decalcification was obvious. The increasing of PO43- concentration resulted in soil Ca saturation decreasing significantly. 5. Soil physics status was one of important factors of nutrient fatigue.The research of the influence of soil hardness to maize growth and calcium absorption showed there was no significant influence of soil hardness to maize growth in the first 15 days after seeding, however, inhibited aboveground maize growth in the following days, and maize height orders were R1.20 g.cm-3 >R1.10 g.cm-3 >R1.30 g.cm-3 >R1.40 g.cm-3 >R1.50 g.cm-3. And the bulk density of R1.10 g.cm-3 was too low, root could not contact well with soil, which was disadvantage to water and nutrient absorption, so its plant height was lower than R1.20 g.cm-3.Root dry mass and activity both decreased because of the high soil hardness which had a negative effect on calcium absorption. The calcium content in maize seedling, the lowest was 11.78 g.kg-1(R1.10 g.cm-3), the highest was 16.67 g.kg-1(R1.20 g.cm-3). The increase of soil hardness causes root activity decrease which lead to the decrease of calcium absorption, thus, lower crop resistance to disease and cause insenescence in advance. It was concluded that soil bulk density was too high or too low, which were disadvantage to crop growing.更多还原