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保護性耕作是國際農業(yè)技術發(fā)展 保性耕作是國際農業(yè)技術發(fā)展的重要趨勢,秸稈還田技術是機械化保護性耕作中關鍵的一項技術。使用機械化秸稈還田技術可以有效地解決農忙期間爭農時、爭勞力的矛盾,有力推動秸稈還田的農業(yè)全程機械化進程,避免由于焚燒秸稈產生的環(huán)境污染。本著一機多用、降低生產成本的原則,研制了既能滿足玉米秸稈、根茬直接粉碎還田,又能單獨實現旋耕作業(yè)的新型多功能玉米秸稈還田機。 (1)在對秸稈粉碎及滅茬基本理論分析的基礎上,提出多功能玉米秸稈還田機總體結構設計方案。 采用臥式結構,主要由懸掛裝置、變速箱、皮帶傳動、秸稈粉碎機構、滅茬旋耕機構、限深滾筒等組成。拖拉機輸出動力經萬向節(jié)傳遞給變速箱,變速箱一軸經齒輪、皮帶輪兩級增速后,帶動粉碎刀輥工作;另一軸經變速箱、皮帶輪變速后帶動滅茬旋耕刀輥工作。 (2)設計了新型變速箱,實現了秸稈粉碎、滅茬、旋耕的復合或單項作業(yè),結構簡單,一機多用。 主要由錐齒輪傳動、撥叉、撥叉套、滾針軸承等組成。利用撥叉套與從動齒輪的離合來實現粉碎、旋耕動力的分離與結合,從而分別完成秸稈粉碎與滅茬復合作業(yè)或旋耕單項作業(yè),實現一機多用之功能。 (3)對樣機進行了田間試驗,作業(yè)質量滿足農藝要求。 試驗結果表明:對秸稈和根茬具有良好的切碎效果,秸稈切碎平均長度為5.2 cm,粉碎合格率≥98%,滅茬率≥90%,碎茬拋撒均勻、覆蓋率高,作業(yè)性能穩(wěn)定。旋耕單項作業(yè)時,旋耕深度可達16 cm,碎土率85.7%,作業(yè)后土碎地平,滿足農藝要求,可直接進行后續(xù)播種作業(yè)。 作物秸稈是農作物生產系統(tǒng)中一項重要的生物資源，作物秸稈資源的利用既涉及到整個農業(yè)系統(tǒng)中的土壤肥力、水土保持，也涉及到環(huán)境安全以及再生資源的有效利用等可持續(xù)發(fā)展問題。秸稈機械還田是解決秸稈處理問題的有效途徑之一。 目前，秸稈機械還田機具已成為我國農機近期研究的一個重要領域。關于稻麥秸稈整株還田的機具研究目前還存在很多問題。為了研究水稻整株秸稈還田機具各部件的結構參數、工作參數等因素對功率的影響，降低秸稈整株還田機具功率消耗，本文對秸稈還田機具的各參數進行了設計和試驗研究。 (1)提出試驗臺的總體設計方案，通過對秸稈還田機的機理分析，選擇(出)影響還田機作業(yè)質量的結構參數、工作參數作為主要研究因素； (2)對刀盤間距、刀的排列方式、刀片滑切角以及刀片安裝角等主要工作部件的結構參數進行理論分析與優(yōu)化設計； (3)合理選擇、設計、加工測試系統(tǒng)的傳感器部分，并對整個測試系統(tǒng)進行標定； (4)在影響參數中，選擇了對機具作業(yè)狀態(tài)和功率消耗有較大影響的刀盤間距、機器前進速度以及刀滾旋轉速度三個參數作為試驗因子，按照二次正交旋轉組合設計試驗方法，給出試驗方案并進行了試驗研究； (5)通過對試驗數據的處理分析，得到刀盤間距、機器前進速度以及刀滾旋轉速度這三個因素對轉矩影響的數學模型，并分析了這三個因素對轉矩的影響規(guī)律； (6)通過對得到模型的理論分析，最終得到刀盤間距、機器前進速度以及刀滾旋轉速度這三個因素對作業(yè)機具功率消耗的數學模型，并分析了這三個因素對功率消耗的影響規(guī)律。 本文通過上述的試驗和分析，給出了刀盤間距、機器前進速度以及刀滾旋轉速度這三個因素在滿足作業(yè)要求(覆蓋率、埋草深度、碎土率)的前提下，降低功耗的最優(yōu)組合方案，為進一步進行整機參數優(yōu)化設計提供了重要的理論依據。 長期定位肥料試驗作為農田生態(tài)系統(tǒng)的重要研究方法,具有常規(guī)試驗不可比擬的優(yōu)點。本試驗選用山東省齊河縣華店鄉(xiāng)和焦斌鄉(xiāng)兩地代表黃淮海農區(qū)的潮土,設置秸稈不同用量與氮磷肥配施為 6 個主處理、兩種土質為副處理,進行盆栽試驗,對麥玉兩熟長期不同施肥條件下土壤理化性質的動態(tài)變化、土壤鉀庫形態(tài)的轉化、土壤養(yǎng)分的平衡狀況、土壤酶的活性及微生物區(qū)系等進行了系統(tǒng)研究,初步探討秸稈還田改土培肥的增產效應與機理,主要研究結果如下: 1 秸稈還田量與土壤鹽分呈顯著正相關。秸稈與化肥配施的土壤可溶性鹽分有增加趨勢。砂壤土含鹽量高于中壤土。另外,土壤鹽分也與氣候和作物生育期等因素有關。 2 秸稈還田能改善土壤的通氣狀況,降低土壤容重和 pH 值,協(xié)調土壤水肥氣熱等生態(tài)條件,為根系生長創(chuàng)造良好的土壤環(huán)境。 3 秸稈還田能顯著增加土壤有機質積累,提高土壤養(yǎng)分的有效性。兩種質地的土壤,其有機質季節(jié)積累和養(yǎng)分生物有效性的變化動態(tài)相似,即 6 月 2 日最高,6 月 22 日最低。土壤有機質及有效養(yǎng)分含量都隨施肥年限的延長而遞減,且中壤土的各肥力指標均大于砂壤土。 4 秸稈還田量與水溶性鉀、非特殊吸附鉀、特殊吸附鉀和非交換鉀含量呈顯著正相關,與礦物鉀呈顯著負相關。長期秸稈還田土壤鉀素年度變化規(guī)律:非交換鉀、特殊吸附鉀呈逐年上升趨勢;水溶性鉀、非特殊吸附鉀、礦物鉀呈逐年下降趨勢。 5 秸稈還田量與土壤有效鐵、鋅、錳之間呈顯著正相關,與速效銅相關性不好;兩種不同質地土壤微量元素均有類似規(guī)律: 除有效銅外,土壤有效鋅、錳、鐵季節(jié)性變化都較明顯。 6 兩種質地的土壤脲酶和磷酸酶活性強度變化趨勢是 N1P1M3>N1P1M2>N1P1M1>N0P0M2>N1P1M0>N0P0M0。在 NP 肥用量相同的各處理中,秸稈還田量與土壤脲酶、磷酸酶活性密切相關。兩種土質的土壤脲酶、磷酸酶與有機質、有效氮、有效磷、有效鉀均呈極顯著相關。 1長期秸稈還田改土培肥綜合效應的研究兩種酶都有隨施肥年限的延長而遞減的趨勢。 7 秸稈還田后,土壤細菌、真菌、放線菌的數量均有所增加,且細菌>放線菌>真菌。在小麥分蘗期,各處理的微生物數量最少;小麥返青期后菌類數量迅速增加;微生物數量的高峰期出現在玉米拔節(jié)期和大喇叭口期。 8 秸稈還田能顯著提高作物產量,中壤土的增產效果比砂壤土好?？偖a量與秸稈還田量呈顯著正相關;小麥的千粒重和生物量都與秸稈還田量呈顯著正相關,而株高、穗粒數和有效穗數與秸稈還田量的相關性不顯著;玉米的穗粒重、千粒重與秸稈還田量之間達到了顯著水平,而穗粒數和穗行數與還田量的相關性不顯著。 9 作物對 N、P、K 的吸收量隨秸稈還田量的增加而提高;在 N、P、K 投入量相同的條件下,中壤土中作物對養(yǎng)分的吸收量大于砂壤土;在化肥施入量相同的條件下,土壤氮素始終保持盈余狀態(tài),而磷素和鉀素均處于虧缺狀態(tài)。 秸稈是自然界和農業(yè)生態(tài)系統(tǒng)中一種重要的資源,秸稈還田對于土壤的肥力狀況及其質量和健康都有著非常重要的意義。土壤微生物尤其是其中與纖維素降解有關的微生物在秸稈的降解過程中起著關鍵性的作用。本文對秸稈還田土壤中與纖維素降解有關的微生物進行了分子生態(tài)學研究,研究內容共分為三個部分: 第一部分:應用PCR-DGGE分子技術并結合聚類分析、主成份分析(PCA)等統(tǒng)計分析方法,對土壤微生物在幾種不同的纖維素富集培養(yǎng)條件下的多樣性進行了分析。結果發(fā)現,不同的纖維素富集培養(yǎng)條件對土壤微生物的多樣性有不同程度的影響:CMC和PCS兩種培養(yǎng)基在50℃時所回收的土壤微生物的菌群結構和組成比較相似;而纖維素富集培養(yǎng)基(J培養(yǎng)基)同CMC兩種培養(yǎng)基所回收的土壤微生物菌群結構和組成卻有很大的差異;此外50℃條件下所回收的土壤微生物其菌群結構和組成同28℃、37℃兩個溫度相比也相差較大。這一結果表明,組合不同的纖維素富集培養(yǎng)條件,結合分子和統(tǒng)計分析,可以對土壤樣品在不同纖維素富集培養(yǎng)條件下微生物的多樣性進行檢測和評估,同時還可以為分離目標菌時富集培養(yǎng)條件的選擇提供很有價值的參考。 第二部分:通過建立秸稈還田模擬體系,并應用PCR-DGGE分子技術與聚類分析、主成份分析(PCA)以及偏最小二乘法顯著性分析。 本研究采用尼龍網袋法、砂濾管法和植物組織切片的方法對秸稈在不同還田方式下的腐解速率及養(yǎng)分釋放規(guī)律，以及秸稈還田對土壤肥力和作物產量的影響進行研究。針對農業(yè)生產中出現的稻草覆蓋影響小麥生長的問題，采用室內培養(yǎng)實驗研究了稻草對小麥的化感作用，以期找到解決稻草還田抑制小麥生長的技術和方法，為大面積農業(yè)生產提供急需的技術支撐和指導。本研究取得的主要研究結果如下： 1．麥稈、油菜稈還田后，腐解速率均表現為前期快，后期慢。整個試驗期間(100d)，麥稈、油菜稈的累計腐解率分別為66.18％和55.62％，麥稈高于油菜稈。兩種秸稈在養(yǎng)分釋放上均表現為，鉀(K)最快，磷(P)次之，氮(N)最慢。在還田初期(前10d)K釋放率分別達到了98.92％和98.74％，已基本釋放完全。通過進一步研究發(fā)現，在麥稈、油菜稈還田6d后，K的釋放就已達95％左右，釋放率分別為94.76％和95.93％。在麥稈還田腐解的過程中，組織結構的破壞主要發(fā)生在基本組織的薄壁細胞及其所包圍的維管束，表皮和機械組織以及其所包圍的維管束的破壞不明顯。且麥稈的基本組織及其所包圍的維管束的破壞在腐解前期(50d前)并不明顯，主要發(fā)生在麥稈腐解的后期(50d后)。在油菜稈腐解過程中，組織結構的破壞主要發(fā)生在腐解的前10d。在10d之內，次生木質部以上的維管形成層、韌皮纖維、皮層薄壁組織和表皮均受到破壞而脫落。 2．稻草還田后，前期腐解快，后期較慢。翻埋還田的稻草腐解速率明顯快于覆蓋還田稻草，整個試驗期間(210 d)翻埋還田的稻草累計腐解率達到76.55％，而覆蓋還田的稻草僅為53.50％。稻草覆蓋與翻埋兩種還田方式下養(yǎng)分釋放速率均以鉀(K)最快，磷(P)次之，氮(N)最慢。還田10d內，兩種方式下K分別釋放了50.32％和90.13％。稻草與土壤充分混合條件下，稻草和土壤礦化釋放的氮主要以NO_3-N形態(tài)(＞80％)存在，NH_4-N和可溶性有機氮較少；在稻草還田后的前40d存在土壤微生物與作物競爭土壤礦質氮的現象，40d之后此現象消失，稻草開始氮的凈礦化；在稻草埋入土壤時同時配施適量的氮肥，可以消除微生物的奪氮現象。在稻草還田腐解過程中，組織結構的破壞主要發(fā)生在基本組織的薄壁細胞及其所包圍維管束，表皮和機械組織以及其所包圍的維管束的破壞不明顯。兩種還田方式比較，在還田初期，翻埋還田較覆蓋還田對組織結構的破壞嚴重。隨著腐解的進行，當稻草中易被破壞的基本組織及其所包圍的維管束被破壞之后，兩種還田方式對稻草中難以被破壞的表皮和機械組織及其所包圍的維管束的破壞程度差別不大。 3．秸稈還田能夠降低土壤容重，增加土壤孔隙度，改善土壤結構，增加土壤速效養(yǎng)分，促進作物對養(yǎng)分的吸收，增加作物的產量。秸稈還田后土壤容重比試驗前降低了0.03g／cm~3，土壤總孔隙度比試驗前增加了0.99％，土壤速效磷和速效鉀的含量增加，尤其是速效鉀，增加效果顯著。在大春階段，麥稈還田后水稻增產5.61％，油菜稈還田水稻增產1.31％；在小春階段，稻草還田小麥增產6.16％，油菜增產7.08％。 4．通過測定水稻秸稈水浸提液對小麥發(fā)芽率、幼苗高度和根長的影響，研究了不同浸提液濃度對小麥幼苗的化感作用。結果表明：水稻秸稈水浸提液對小麥發(fā)芽和幼苗生長的影響總體上表現為低促、高抑，即低濃度的浸提液對小麥發(fā)芽有促進作用，隨著濃度的增加浸提液對小麥發(fā)芽開始產生抑制作用，濃度越高，抑制作用越強。在浸提液質量濃度為0.01g／ml(低)時，浸提液對小麥發(fā)芽和幼苗生長都具有促進作用。在浸提液質量濃度為0.02g／ml(中)時，浸提液對小麥發(fā)芽和幼苗生長產生抑制作用，且在小麥幼苗生長階段的抑制作用強于發(fā)芽階段。在此浸提液濃度下，加入外源激素的處理，不但能夠消除浸提液對小麥幼苗生長的抑制作用，還能對小麥幼苗的生長產生明顯的促進作用。在浸提液質量濃度為0.04g／ml(高)時，小麥發(fā)芽和幼苗生長受到嚴重抑制。在此情況下，加入外源激素赤霉素或黃腐酸也不能對此抑制作用產生影響。 Conservation tillage is an important international trend of development of agricultural technology The protection cultivation is the most important international agricultural technology development tendency. The smashed straw technology is one essential technology of the mechanized protection cultivation. Using smashed straw machines can effectively solve the problems that striving for time and labour during the busying farming time, and can make the agricultural entire mechanization come to truth. It also can avoid environment pollution caused by straw setting on fire. According to multi-function and reducing production cost, multi-function smashed straw machine was developed. It not only can smash straw together with the stubble and put it back to the farmland to increase the nutrient once time but also can according to our practical necessity to choose rotary tilling single function. (1) On the basic of studying the elementary theory of smashing straw, the integral structure design plan of multi-function machine was introduced. The machine is mainly composed of hanging system, gearbox, belt transmission system, stalk-soil returning roller, rotary tiller roller, and depth limit roller. Power is transmitted from the tractor power output shaft to the gearbox. One shaft of the gearbox is accelerated by both bevel gears and strap transmission. And then it drives the stalk-smashing knives revolving quickly. Another shaft is moved by the bevel gears and strap wheel to drive the rotary tiller working. (2) The innovative point is the design of new gearbox, which has realized the composite work or single work of smashing straw, stubble and rotary tillage for the first time. It makes one machine has two uses. The gearbox is mainly composed of bevel gears, poking fork, clutch, and bearings. Using the separation or union between the clutch and gears, the separation or union of the power can be realized. So, the machine can choose smashed straw work or rotary tillage work. And the intension of bevel gears, belts, axes are checked. (3) The experiment of the machine is carried on the field. The results of the experiment can satisfy the agronomy request. The test result indicates that, the machine has good qualities to smash the straw and stubble. The average length of the smashed straw is 5.2 cm. The smashing qualified rate is 98%. The stubble smashed rate is 90%. The smashed straw is thrown equably. The fraction of coverage is high. The work performance is stable. When the machine chooses the single rotary tillage work, the rotary tillage depth can arrive at 16 cm. The crumble rate is 85.7%. After rotary tillage work, the farmland is smooth. It can satisfy the agronomy request and can carry on the following sowing seeds work directly. The crop straw is an important biologic resource in agricultural production system. Theapplication of the crop straw resource is involved with not only the soil fertility, water and soilconservation in the whole agricultural system, but also sustaining development problems such asthe environmental safety and the effective utilization of the regenerative resources. The straw returnin mechanical method is one of the effective ways to solve the straw processing. At the present time, the straw return machine has become of an important field in agriculturalmachinery study in China. However there are still lots of problems existed in the study of the strawreturn machine of whole rice stems. (such as power consumption is too much) In order to solve theimpact of those factors on the power consumption, such as structural parameters, operatingparameters and so on of each component in the machine, and reduce power consumption, thepaper implemented a design and experimental investigation on the parameters of the straw returnmachine. (1) The integrated design plan on test stand was put forward in this paper and throughmechanics analysis of the straw return machine, the structural parameters and operatingparameters which affected the operating quality of straw return machine are chose as the mainresearch factors. (2) The theoretical analysis and optimizing design were implemented to the structuralparameters of major working components, such as the clearance between cutter heads, thearrange of bent blade, grass removing angle and setting angle. (3) The sensor section has been chose, designed and processed logically, and then the testsystem was calibrated. (4) Among those influencing parameters, the paper chose the clearance between cutterheads, machine forward speed and knife roll revolving speed as experimental factors, whichhave a great influence on working status and power consumption (about the straw return machine),then put forward the experimental scheme and conducted experimental investigation as per the twotimes orthogonal rotational regressive test plan. (5) Through the analysis of data processing about the test date, a mathematical modelregarding the influence of the clearance between cutter heads, machine forward speed and rollrotational speed on the torque of the machine was achieved and the rule of impacts of these threefactors on the torque were analyzed as well. (6) Through the theory analysis about the model forenamed, another mathematical modelregarding the influence of the clearance between cutter heads, machine forward speed and rollrotational speed on the power consumption of the machine was achieved and the rule of impacts ofthese three factors on the power consumption were analyzed as well. Through the forementioned experiment and analysis, the optimal association schemes of theclearance between cutter head, machine forward speed and roll rotational speed on powerconsumption were given in the paper, on the premise that the operation requirements (such aspercentage of coverage, the tiling depth, and hack) were fulfilled. It provides the importanttheoretical foundation for further optimal design of parameters for whole machine. By comparison with routine fertilizer experiments, long—term fixedposition experiments that is an important means by which corn fieldecosystem are studied have many advantages. Experiment was carried outwith flouvo-aguic soils of Huang-Huai-Hai Plain coming from Huadian andJiaobin village of Qihe Shandong Province. Pot experiment, setting six maintreatments of straw combination to fertility and two subsidiary treatments ofsoil texture, were carried out to study the dynamic change of soil properties,translation of potassium form, nutrient balance, activity of soil enzymes andmicrobe species in the condition of wheat/maize rotation system. The effectand mechanism of increase production were also discussed preparatory. Theresult showed: 1 Soil salinity was positive related to the amount of using strawmarkedly, and improved highest by straw combination to fertility. Medium loamsoil was higher than sandy loam soil. In addition, soil salinity were effectedby climate、growing season et al. 2 Straw back to soil improved porosity, reduced soil unit weight and pH,harmonizd ecological condition and created favorable soil environment. 3 Soil organs matter and available nutrient were improved by strawback to soil, and they had the same seasonal dynamic change, highest inJune 2 and lowest in June 22. Soil organs matter and available nutrientdecreased with year, and medium loam soil was higher than sandy loamsoil. 4 Soil non-exchangeable K, water soluble K, specifically absorbed Kand non-specifically absorbed K are all positively related to the amount ofstraw remarkably, while mineral K is negatively correlative. The variant 3 regularity of soil K is that non-exchangeable K and specifically absorbed Kare increasing, but the other forms of K are decreasing. 5 Soil available Zn、Fe、Mn were all positive related to the amount ofusing straw markedly, but soil available Cu was unmarked. Soilmicroelement had the same rule, N1P1M3>N1P1M2>N1P1M1>M2>N1P1M0 > N0P0M0, and they all had evident seasonal change exceptavailable Cu. 6 Soil urease and phosphatase had the same trend, N1P1M3>N1P1M2>N1P1M1>N0P0M2>N1P1M2>N0P0M0, and they were related to the amountof using straw nearly and all positive related to soil organs matter andavailable nutrient markedly. Soil urease and phosphatase decreased withyear. 7 Straw returning increased the quantity of soil bacteria, fungi andactinomycetes, and bacteria>actinomycetes>fungi. The quantity of microbewas least in tillering stage and increased after reviving stage, and cornjointing stage and male tetrad stage were its fastigium. 8 Straw returning increased yield notably, and the effect of mediumloam soil was better. Yield、1000-grain weight、biomass of wheat and spikegrain weight、1000-grain weight of corn were all positive related to theamount of using straw markedly, but plant height、grains/ear、effective/earof wheat and grains/ear、rows per spike of corn were unmarked. 9 Amount of N, P and K absorption increased with the amount of usingstraw, and medium loam soil was higher. Applying the same chemicalfertilizer, soil N was surplus, but soil P and K were waney. Straw are a crucial source of nutrients in both natural and agricultural ecosystems. It is a very essential method for soil fertility, quality and healthy by amending straw to the soil. The microorganisms in soil play an important role during the process of the straw decomposition after the straw was amended to the soil. The object of our study was an investigation on microorganisms related with cellulose decomposition in straw-amended soil. There are three parts in this study. In the first part, the diversity of soil microbe cultured at different cellulose enrichment culturing conditions was analyzed by molecular technology of DGGE combined with statistical methods of clustering analysis and PCA. Both cluster dendrogram analysis and PCA analysis demonstrated that different cellulose enrichment culturing conditions might cause different effect to the soil microbe. The structure and components of the samples incubated in CMC medium and PCS medium at 50℃showed a relatively high level of similarity, In contrast, those incubated in CMCmedium and J medium were significantly different Employing nylon net bags, carborundum tubers and plant straw/shoot sections, the decomposition rates and nutrient release patterns of straw returned to the field with different returning methods were studied. Soil fertility and crop yields in the field with straw treatments were examined. The allelopathic effect of rice straw on wheat germination was studied with indoors germination experiments in order to seek the solution to this allelopathic problem and offer practical techniques and gudence to farmers in rice straw mulching areas. The main results were achieved as below: 1. Wheat straw and rape shoot were decomposed much faster at the very beginning and slower at the later stages of the experiment. The wheat straw was easier to decompose than the rape shoot, giving a decomposing rate of 66.18% after 100 d for wheat straw against 55.62% for the rape straw. As for the nutrient release rates, it appeared that K was the fastest and followed by P and N from two types of straws. Within the first 10 d, amount of K released accounted for 98.92% for the wheat straw and 98.74 % for rape shoot, very close to its total content. The study further revealed that amount of K released accounted for 94.76% and 95.93 within 6 d. During the decayed process of wheat straw, the damage of straw tissues occurred predominately at thin parietal cells of fundamental tissue and its vascular bundle, epiderms and mechanical tissue had no evident damage.The fundamental tissue of wheat straw and its vascular bundle remained almost intact within first 50 d and decay was observed thereafter. During the decay process of rape shoot, the decomposition of organization structure started after 10 d. The vascular cambium, phloem fiber, parenchyma and epidermis above the secondary xylem, however, were started to decay and fall off within the first 10 d. 2. Employing nylon net bags and carborundum tubers, the decomposition rates and nutrient release patterns of rice straw in the field with different returning methods were studied. Results showed that rice straw decomposed much faster at the very beginning than at the later stages of the experiment. The straw decayed faster when it was buried into the soil, yielding a decomposition rate of 76.55% after 210 d against 53.50% for the surface mulching straw. Among the three nutrients, release of K from the straw was the fastest, followed by P and N, regardless of returning methods used. Within the first 10 d, amount of K released accounted for 50.32% for the surface mulching straw and 90.13% for the buried straw. When the straw was mixed into the soil, the major form of available N was nitrate (＞80%), with reminders of NH_4~+ and soluble organic nitrogen. Meanwhile, the phenomenon of soil microbes grabbing available N was observed during the first 40 d of straw decomposition and it disappeared thereafter, resulting in net N release from the soil with filtration. After N fertilizer was amended with buried straw, it offset the need of microbes for available N to decompose the buried straw. During the decayed process of rice straw, the damage of tissue structure started from thin parietal cell of fundamental tissue and its vascular bundle, while epiderms and mechanical tissue were not evidently damaged.In the early days of straw returning, the damage of tissue structure for the buried straw was more serious than the mulched. As decay proceeded, the changes in epiderms and mechanical tissue and its vascular bundle were not different btween the two different return methods, after the fundamental tissue of rice straw and its vascular bundle were decomposed. 3. Straw returned to the field enabled to reduce soil bulk density, increased soil porosity, improved soil structure, increased soil available nutrient and crop uptake and finally resulted in yield increases. Soil bulk density was reduced by 0.03g/cm~3 and soil porosity increased by 0.99% compared to the initial data of the experiment. The soil available phosphorus and potassium were increased, especially for potassium. Rice yield was increased by 5.61% with mulching wheat straw, and by 1.31% with mulching rape shoot. Wheat yield was increased by 6.16% and rape yield by 7.08% with mulching rice straw. 4. Allelopathic effect of water soaked rice straw extract on wheat germination was tested. Results showed that the extract significantly depressed germination and elongation of seedling and roots of wheat. It appeared that it showed a stimulating effect of the extract at lower concentrations (0.01 g/ml) and an inhibitory effect at higher concentrations (=0.02g/ml). The inhibition effect was more severe to seedling growth of wheat than its germination. With introduction of plant regulator gibberellin or humic acid to the extract, the inhibitory effect of the extract on wheat germination was relieved. As the concentration of the extract was greater than 0.04g/ml, a serious inhibitory effect was observed and this could not be reversed by addition of gibberelli