稻田自然免耕体系土壤微生物及有机质周转研究

【作者】 张磊；

【导师】 谢德体； 魏朝富；

【作者基本信息】 西南农业大学 ， 土壤学， 2002， 博士

【摘要】 免耕制是一种保护性耕作制，指同一块土壤在一定年限内，不仅免除播前耕作(犁耕和深翻)，也免除播后中耕，作物收获后直接将作物残茬留在土壤中的耕作方式。在免耕体系中，有限的耕作只在播种行上进行，耕作区达总田面的25％，包括免耕、浅耕播种、中耕机开沟播种、旋耕机具条耕播种等，所以免耕制(no-tillage)也叫“零耕”(zero-tillage)、“化学耕作”(chemical tillage)、”无犁耕作”(no-plowtillage)、“喷—种—收”等名称。科学文献中通常采用免耕法和零耕这一术语。 比较各种免耕方式，最主要的区别是作物残茬返还的方式。作物收获后，作物地上部被从地表带走，地下部的根系等原位保留，直接播种的免耕方式暂时称为残茬免耕；直接播种，并将前作地上部有秩序地平铺在地表进行覆盖的免耕称为覆盖免耕。通常所指的免耕就是这两种方式。适于平作早地保墒和减少土壤侵蚀。 1982年侯光炯院士根据四川农民和农村科技工作者的实践经验，在总结覆盖免耕和残茬免耕的基础上提出了自然免耕制，其名称有两方面的涵义，一是模拟自然土高肥力的生理生态特征；二是说明高肥力的基本特征是免耕。 实行免耕制，关键是有机残体的返还。研究表明，一旦免耕与覆盖分离，则免耕即不能提高有机质和有机氮水平，导致土壤退化和减产。覆盖免耕使土壤上层的有机质和氮素稳定增加，这主要来自被激发的微生物繁殖时对碳和氮的生物固定，而传统耕作则由于耕翻加速了有机物的矿化，0-10cm土层微生物碳含量均一，其数值几乎为免耕系统的一半。所以长期的覆盖免耕使有机氮库越来越大，传统耕作下有机氮库则变得越来越小。 与残茬免耕和覆盖免耕相比， 自然免耕更加重视有机残体的返还及良好的分解条件的建立。自然免耕技术要则包括：(1)改造土壤水文，以连续的垄沟地形，扩充毛管水影响范围，用连续植被法提高复种指数，保证土不离根，最大限度地改土面蒸发为叶面蒸腾，让土壤长期处于毛管水浸润状态，保证七壤没有变干的危险，即连续植被、连续垄作；(2)严格执行免耕技术，保证土壤结构不会断裂和破坏，即连续免耕；(3)严格按照土壤生理类型和区域类型适土适种、适地适种、按土施肥、看苗施肥；(4)严格控制构内水位，使之适应根系生理的需要，即连续浸润。将秸秆混入土壤中分解，垄、沟搭配，保持土壤的浸润状态和连续植被，不仅解决了覆盖免耕制中有机质分解、转化慢的问题，而且使输入土壤的有机质分解、转化更加迅速，所以在促进土壤有机质循环方面自然免耕制表现出明显的优越性，土壤有机质遂表现为快速的增长。 土壤微生物是影响有机残体分解利用的最主要的因素，是推动土壤有机质分解、转化和循环的动力。对土壤有机物分解、转化的研究某种程度上就是有机物分解、转化与微生物关系的研究。但目前国内外对有机残体周转与微生物关系的深入研究较少，影响了有机残体的返还和利用。自然免耕在这方面提供了极好的素材，在本文中正是以自然免耕的有机残体物质循环为切入点，研究土壤中有机质的周转与微生物的关系。 在本论文中，有机残体的分解是自始至终的研究内容，有机残体的分解、转化与微生物的关系是论文的研究中心。首先通过对自然免耕定位试验的有机残体的分解与转化的动态特征研究，得出有机残体分解转化过程中的有机质、养分、微生物及出和Eh的动态特征，总结出有机残体分解与微生物关系的一般规律。在此基础上，设计了盆钵分解试验，在统一水分、统一养分和无植物干扰情况下验证有机残体分解周转与微生物的关系，探讨通过接种有益微生物加速有机残体转化的可能性和途径。之后，利用模拟试验研究了自然免耕使土壤有机质积累的微生物方面的原因所在，并探讨了对自然免耕土壤接种有益微生物菌种的影响和设置。最后，在大量士壤理化性质、土壤微生物特征值及气候数据的基础上，利用现有的土壤有机碳周转的计算机模型对自然免耕试验地的有机质积累趋势进行预测，从而在氏远发展上对自然兔耕地土壤有机质及其它性质的变化方向上有所了解和把握。 通过上述研究，主要得到以下结论： （l）对自然免耕的研究表明：经过门年的定位试验，士壤有机质含量迅速提高，增幅甚至达 90．0％和 SS 3％，而冬水免耕处理的土壤有机质的增幅不大。可见，大量的有讥残体的返还是土壤有机质增加的充分条件：影响土壤有机质的积累的表面上是耕作和轮作制度，而实质是有机残体的返还量及其适宜的分解、周转条件。自然免耕恰好提供这些条件。在自然免耕定位试验的施肥水平－卜，十壤的全氮量缓慢积累，速效氮在冬季有机残体分解量低时下降，总量保持增长；P、K养分供应不足，各处理的P、K含量提高较少，甚至在地上部作物旺盛生长时明显下降，尤以垄作免耕明显。P、K肥施肥不足及淹水条件下微生物分解作用受到抑制是主要原因，而籽粒带走一部分钾素也造成了缺钾。相比之下，沟内的分解作用因为淹水而较缓慢，分解产物含量的最高值的大小与有机残体的返还量有关。沟内上层上壤全量和有效N、P、K的最终积累水平均为：垄作兔?更多还原

【Abstract】 Being a protective tillage, the no-tillage means getting rid of not only the tillage before sowing, but also the intertill after sowing, and leaving the plant residue after harvesting. Under its principle, limited tillage is carried out only on the sowing lines which occupy 25% of the field. So it’s also called zero-tillage, chemical-tillage, and no-plowtillage etc.There are different types of no-tillage according to different types of leaving the plant residue. The type is temporarily called root-no-tillage with only the root left in soil and direct drilling; sowing directly and placing the past plant stalk orderly over the soil is called mulch-no-tillage. They are both of the content when refers to no-tillage generally and are adapted to keep moist in or keep from soil erosion in drying land.Academician Hou Guangjiong, who summarized the experiences from peasants in Sichuan province, promoted the no-tillage and ridge culture in 1982 that has two sides of meaning of its name: one is simulating the physical and ecological characteristics of originally moist soil; the other means rhat the basic characteristic of perfect soil fertility is no-tillage.The key of no-tillage is the supply the past crop residue to soil. Not only couldn’t the quantity of soil organic matter and organic N be lifted up, but also did it lead, to soil erosion and output declining under nc-ti!!age system without crop residue adding. By the crop residue input, priming effects of soil irJcrobe will take place, and decomposition and bio-fixation give rise to soil organic matter arid M in the up layer of soil. On the other hand, tillage accelerate; the organic matter mineralization and leads to the quantity of organic matter decreasing in..Or 10cm.layer which is about 1/2 of soil organic matter under no-tillage. So the pool of soil organic matter in soil become bigger anci bigger under no tillage while smaller and smaller under tillage.The no-tillage and culture focus more on creating better conditions for microbe decomposing the crop residue compared with no-tillage. There are four principle in it: 1) successive capillary water circulation; 2) successive no-tillage; 3) successive multiple crop rotation; and 4) successive "ridge and furrow culture". By these devices taken, the soil accumulate more organic matter in shorter period compared with general no-tillage.As we all know: the chief part in decomposing the plant residue is soil microbe. It’s microbe’s metabolism that promotes the turnover of substance and organic matter in soil. The study about the turnover of organic matter in soil is the same as the study about the relationship between the microbes and organic decomposition in some extent. But there is few report on exactly the relationship till now. The no-tillage and ridge culture is just the good example to study it. And the models of the turnover and circulation of organic matter in no-tillage and ridge culture are be used as a base and a start to the relationships.This study takes the relationships between the turnover of organic matter and microbe as its goat by researching the course of plant residue decomposition and mineralization. First, the dynamics of soil properties in different period during a year from the long-term no-tillage and ridge culture experiment field are researched in order to get the general dynamic properties of organic matter,chemical substances, microbe, pH and Eh in soil. The plant residue decomposing simulated experiment in containers is managed according to those general properties afterward with aims to test and verify them. Besides this, the possibility to accelerate the plant residue decomposing by inoculate promoting strains, such as cellulose decomposing microbe and nitrogen-fixating bacterium, is also be consulted. Then, in order to pursue effect of soil humidity to the relationship between the turnover of organic matter and the micro flora, the no-tillage and ridge culture simulated experiment is carried out to find out the exactly reasons for the high level of organic matte更多还原