添加玉米和水稻秸秆对淹水土壤pH、二氧化碳及交换态铵的影响

通过温室土壤培养试验,研究了不同添加量玉米和水稻秸秆对淹水土壤pH、CO₂及交换态铵的影响.结果表明：在接近中性的土壤中加入秸秆可使土壤pH值降低,4 g·kg^-1玉米和水稻秸秆处理的土壤pH值均与对照差异显著（P＜0.05）,而1 g·kg^-1玉米和水稻秸秆处理与对照差异不显著（P＞0.05）.土壤溶液中的CO₂含量随秸秆添加量的增加而增大,1 g·kg^-1玉米和水稻秸秆处理的土壤溶液CO₂含量最大值分别为35.9％和31.9％（v/v）,与对照（25.8％）差异达显著水平（P＜0.05）,但两者间差异不显著（P＞0.05）;4 g·kg^-1玉米和水稻秸秆处理的土壤溶液CO₂含量最大值分别为54.2％和41.8％（v/v）,与对照差异极显著（P＜0.01）,两者间差异也达显著水平（P＜0.05）.在不施氮肥的情况下,添加秸秆可降低土壤铵态氮浓度,且铵态氮浓度随秸秆添加量的增加而降低,不同添加量处理间差异显著（P＜0.05）;在施入氮肥的情况下,1 g·kg^-1玉米和水稻秸秆处理提高了土壤铵态氮浓度,而4 g·kg^-1玉米和水稻秸秆处理降低了土壤铵态氮浓度.无论是否施入氮肥,玉米和水稻秸秆处理的土壤铵态氮浓度差异不显著（P＞0.05）.     

强化还原处理对海南西瓜连作障碍土壤性质的影响

以海南省三亚市西瓜生长发生障碍的土壤为研究对象,设置对照、淹水、淹水+覆膜、淹水+覆膜+7500 kg·hm-2紫花苜蓿(称为强化还原处理)4个处理,处理时间20 d,研究了强化还原处理对海南西瓜连作障碍土壤物理、化学、生物性质的影响。结果表明:强化还原处理能够明显降低土壤中大土块(直径大于5 mm)的比例,有效改良土壤板结问题;强化还原处理过程中土壤氧化还原电位(Eh)和硝态氮含量快速下降,pH显著提高,铵态氮含量快速上升;土壤中真菌和尖孢镰刀菌数量显著降低;土壤淹水同时添加有机物料的强化还原处理方法可能是改良连作障碍土壤的一种高效、环保的方法。     

土壤强还原处理对根结线虫数量、番茄生长及土壤性质的影响

土壤强还原处理是指高温条件下向土壤中施加大量有机物料并淹水覆膜,是一种防控土传病害的高效、环保、广谱的方法,但在防治根结线虫上的应用很少。本试验研究强还原处理对番茄上根结线虫的防治效果以及对土壤理化性质的影响。结果显示:处理20天后,强还原处理土壤中根结线虫2龄幼虫数量与阿维菌素处理效果相当,与CK和淹水覆膜处理存在显著性差异,强还原处理2龄幼虫数量比CK下降了58.8%~97.2%,比淹水覆膜处理下降了50.1%~96.6%;有机物料添加量为4.16 g·kg~(-1)时,强还原处理能够显著促进番茄根系伸长,增加根表面积,提高番茄地上部生物量;强还原处理土壤p H比CK平均提高了5.1%,土壤全氮和有机质含量分别平均提高了12.8%和3.4%。表明淹水添加有机物料创造强还原环境可以有效抑制根结线虫的繁殖,改良土壤理化性质。     

有机物料对喀斯特地区石灰土有效N、Fe、Zn含量的影响

为研究不同有机物料对喀斯特石灰土元素有效性的影响,采用40 d的室内培养实验,比较了单独添加不同比例（1%、3%、5%）的生物质炭、鸡粪肥、羊粪肥对喀斯特石灰土有效N、Fe、Zn含量的影响。结果表明：添加生物质炭提高了喀斯特石灰土的pH值,而添加鸡粪肥和羊粪肥降低了喀斯特石灰土的pH值;添加3种有机物料均增加了喀斯特石灰土的有机质含量,大小关系为：生物质炭 > 鸡粪肥 > 羊粪肥,但添加鸡粪肥和羊粪肥土壤有机质的化学活性和微生物活性更高。受pH、有机质活性、碳氮比等因素的影响,添加鸡粪肥和羊粪肥能增加土壤有效N含量,但两种有机肥对土壤有效N的提高效果相差不大,而添加生物质炭反而降低了土壤有效N的含量;3种有机物料均能提高土壤的有效Fe和有效Zn含量,其中鸡粪肥效果最佳,其次为羊粪肥和生物质炭。当3种有机物料的添加比例为5%时,生物质炭处理土壤的有效N、Fe、Zn含量分别是对照处理的0.92、1.13、1.21倍;鸡粪肥处理土壤的有效N、Fe、Zn含量分别是对照处理的1.22、1.63和3.39倍;羊粪肥处理土壤的有效N、Fe、Zn含量分别是对照处理的1.27、1.34和2.59倍。所以,相对于生物质炭,有机粪肥对喀斯特地区的石灰土有更好的改良效果。     

氨水熏蒸对高发枯萎病蕉园土壤微生物区系及发病率的影响

采用涂布计数及荧光定量PCR和PCR-DGGE技术,研究了氨水熏蒸对土壤微生物区系的影响,并研究氨水熏蒸对高发枯萎病香蕉园枯萎病的防控效果和对香蕉产量的影响。结果表明:与熏蒸前相比,高发枯萎病香蕉园土壤施用130 L/667 m²的氨水熏蒸后,尖孢镰刀菌的数量下降了1个log单位;与对照处理相比,下降了0.5个log单位。氨水熏蒸后土壤可培养细菌数量与对照相比没有显著差异,但显著低于熏蒸前,可培养真菌的数量显著低于熏蒸前和对照;可培养细菌真菌的比值与熏蒸前相比没有显著差异,但显著高于对照。与对照及熏蒸前相比,氨水熏蒸后土壤中总细菌及总真菌的数量显著下降;熏蒸前后及对照处理总细菌真菌的比值没有明显差异。各土壤样品总细菌及真菌群落结构的PCR-DGGE分析结果表明,氨水熏蒸后土壤微生物在聚类上和条带组成上均与熏蒸前及对照有显著性差异。与对照相比,氨水熏蒸处理使香蕉枯萎病的发病率降低了20%,每666.7m²增产1.25t。以上结果表明,利用合适浓度的氨水对高发枯萎病香蕉园的土壤熏蒸,能够有效改良土壤微生物区系和降低枯萎病的发生。     

菜籽饼肥对香蕉枯萎病的防效及其对土壤细菌的影响

研究菜籽饼肥对香蕉枯萎病的防治效果,探究菜籽饼肥施用后对土壤细菌群落的影响.设置2组实验,CN组为菜籽饼肥处理组,YN组为对照实验组.种植120d后,统计各组的发病率;利用qPCR技术检测2组中的FOC4孢子数量;采集2组土壤,利用Illumina Miseq高通量测序平台对CN处理组与YN对照组的土壤细菌群落结构和差异进行分析对比.实验研究发现:(1)施菜籽饼肥的CN处理组枯萎病发病率比YN对照组低63.33％;施用菜籽饼肥的处理土壤中FOC4的数量由2.94×104个/克土下降为1.96×103个/克土,YN对照组土壤中FOC4孢子的数量由2.94×104个/克土上升为4.55×105个/克土,CN处理组较YN对照组枯萎病菌数量下降了 2个数量级;(2)土壤细菌宏基因组微生物分类测序结果显示,CN处理组的Alpha多样性指数均优于YN对照组,这表明施用菜籽饼肥后增加了土壤细菌群落的丰度及多样性;(3)在门水平上,菜籽饼肥处理增加了变形菌门(Proteobacteria)和拟杆菌门(Bacteroidetes)的相对丰度,同时也降低了酸杆菌门(Acidobact-eria)、厚壁菌门(Firmicutes)和Patescibacteria等菌门的相对丰度;在属水平,CN处理组中的不动杆菌属(Aci-netobacter)、水杆菌属(Aquabacterium)、热单胞菌属(Thermomonas)、产黄杆菌属(Rhodanobacter)、假单胞菌属(Pseudomonas)和奥托氏菌属(Ottowia)等菌属的相对丰度较YN对照组有明显提高,而酸热菌属(Acidother-mus)、Bryobacter菌属以及Acidipila等菌属相对丰度较YN对照组有所减少.施用菜籽饼肥可以改变土壤中细菌的群落结构,显著降低土壤中FOC4孢子数量,从而降低香蕉枯萎病的发病率.本研究结果为菜籽饼肥用于香蕉枯萎病综合防控提供了理论依据.     

石灰碳铵熏蒸与施用生物有机肥对连作黄瓜和西瓜枯萎病及生物量的影响

采用稀释涂布平板计数法,研究了石灰碳铵及碳铵熏蒸对黄瓜和西瓜连作土壤尖孢镰刀菌数量的影响,以及熏蒸后施用生物有机肥对黄瓜和西瓜枯萎病的防控效果及植株生长的影响.结果表明:与对照相比,石灰碳铵及碳铵熏蒸后,连作土壤中黄瓜尖孢镰刀菌的数量分别下降95.4%及71.4%,西瓜尖孢镰刀菌的数量分别下降87.2%及64.2%;多因素方差分析表明,熏蒸、施用有机肥及作物种类均对土壤中尖孢菌数量、枯萎病发病率、防控率及生物量有显著影响;与未熏蒸施用普通有机肥对照相比,石灰碳铵熏蒸后施用生物有机肥能显著减少后茬黄瓜或西瓜土壤中尖孢镰刀菌的数量并显著降低枯萎病发病率,防控率高达91.9%及92.5%,同时显著增加了植株的株高、茎粗、SPAD值及干质量.表明石灰碳铵熏蒸及施用生物有机肥能够降低土壤中尖孢镰刀菌数量,有效防控黄瓜和西瓜枯萎病的发生并促进其植株生长.     

有机物料与锌肥配施对石灰性土壤锌有效性及形态转化的影响

采用尼龙网袋田间填埋培养法探究了外源施锌条件下石灰性土壤Zn有效性及形态转化对不同有机物料(作物秸秆、生物菌肥、黄腐酸和腐熟鸡粪)的响应.结果表明:与对照相比,Zn肥单施和与有机物料配施均显著提高了土壤全Zn含量(7.2%~13.8%)和DTPA-Zn含量(2.1~2.8倍).在施Zn条件下,有机物料对土壤全Zn和DTPA-Zn的贡献量表现为腐熟鸡粪>生物菌肥>玉米秸秆>黄腐酸,但外源锌的DTPA-Zn转化率以添加秸秆和生物菌肥处理最高.与单施Zn肥相比,有机物料与Zn配施处理显著提高了土壤有机质含量,促进了松结有机态Zn的形成,进而提高了土壤Zn转移因子,降低了Zn分配指数.不同物料与Zn肥配施土壤Zn有效性及形态转化之间存在差异,这可能与有机物料自身性质如腐熟度和含Zn量有关.尽管秸秆与Zn配施对DTPA-Zn含量的提升效果不及生物菌肥或腐熟鸡粪与Zn配施,但综合考虑环境和经济效益,其仍是改善缺锌石灰性土壤Zn有效性的最佳选择.     

石灰碳铵熏蒸联合生物有机肥对香蕉枯萎病和细菌群落的影响

以连续种植的香蕉枯萎病高发病蕉园为试验点,通过实时定量PCR和高通量测序等方法,研究了田间条件下石灰碳铵熏蒸联合生物有机肥施用对香蕉枯萎病的防治效果,以及对土壤细菌群落结构和组成的影响。结果表明: 与不熏蒸施用有机肥(OF)相比,香蕉枯萎病发病率在施用有机肥前使用石灰碳铵进行熏蒸处理(LAOF)和施用生物有机肥前使用石灰碳铵进行熏蒸处理(LABF)中分别降低了13.3%和21.7%,病原菌的拷贝数分别降低了22.4%和33.0%。与OF处理相比,石灰碳铵熏蒸联合不同肥料施用均显著降低了细菌的丰富度和多样性,形成了明显不同的群落结构,且熏蒸对群落组成的差异产生了决定性的影响。LABF的细菌丰富度和多样性均低于其他处理,群落组成也与其他处理存在明显差异。与OF处理相比,熏蒸处理(LAOF和LABF)显著增加了土壤中水恒杆菌、布鲁式菌和漯河杆菌属的相对丰度,且在LABF中的相对丰度均高于LAOF,水恒杆菌和布鲁式菌的相对丰度差异显著。在田间条件下,施用生物有机肥之前使用石灰碳铵进行熏蒸处理能够显著降低病原菌数量,改变土壤细菌群落结构,激发土壤有益微生物,从而减少香蕉枯萎病的发生。     

有机物料发酵流体和堆肥对苹果连作土壤环境及平邑甜茶幼苗生物量的影响

为探讨不同有机物料的发酵流体(厌氧发酵产物)和堆肥(有氧发酵产物)对苹果连作土壤环境的影响,以盆栽平邑甜茶幼苗为试验材料,分别设置猪粪+秸秆、鸡粪+秸秆、羊粪+秸秆、猪粪+鸡粪+羊粪+秸秆4个不同有机物料组合并进行厌氧发酵和有氧发酵,并将发酵产物分别施入连作土中,研究其对平邑甜茶幼苗生物量、连作土壤中微生物、土壤酶活性、土壤酚酸等的影响。结果表明:与有机物料堆肥相比,各有机物料发酵流体处理的平邑甜茶幼苗干重、鲜重较高,其中猪粪发酵流体处理显著提高了幼苗干、鲜重,7月份为对照的1.57、1.26倍,9月份为CK的1.55、1.86倍;两类发酵产物均增加了土壤微生物的数量,且发酵流体处理显著增加了土壤中细菌和放线菌的数量,其中羊粪发酵流体效果最明显,分别为CK的2.95倍和2.37倍,在堆肥处理中,真菌数量显著增高;两类发酵产物也影响了土壤中酚酸总量,表现为猪粪、鸡粪发酵流体和猪粪堆肥处理含量下降,至9月份分别下降到CK的0.45、0.39倍和0.36倍。     

Effect of Sesbania,Azolla and rice straw incorporation on the kinetics of NH4, K,Fe, Mn,Zn and P in some flooded rice soils

In a greenhouse study, with and without rice plants, of five flooded Philippine rice soils whose organic C (OC) content varied from 0.5 to 3.6%, incorporation ofSesbania rostrata, Azolla microphylla and rice straw affected the kinetics of soil solution NH ₄ ⁺ −N, K⁺, Fe²⁺, Mn²⁺, Zn²⁺, and P. Sesbania and Azolla increased NH ₄ ⁺ −N concentration above the control treatment, whereas rice straw depressed it. In all soils Azolla released less NH ₄ ⁺ −N than Sesbania. The apparent net N release depended on the soil and ranged from 44–81% for Sesbania and 27–52% for Azolla. These effects persisted throughout the growth of IR36. Soil solution and exchangeable NH ₄ ⁺ −N increased initially but levelled off between 30 to 80 days and between 20 to 40 days after flooding (DF), respectively. With rice, soil solution NH ₄ ⁺ −N concentration, reached a peak at 15–40 DF and declined to very low levels (<4mg L⁻¹). In the 3 soils of low OC content nitrogen derived from green manure ranged from 34–53% and the apparent revovery of added green manure N varied from 29–67%. Almost all N released from both Azolla and Sesbania were recovered in the rice plant in all soils except Concepcion with only 77%. The concentration of K⁺, Fe²⁺, Mn²⁺ and P in the soil solution were higher with rice straw than Sesbania and Azolla in all soils except Hanggan which showed no change in Fe²⁺ and Mn²⁺ but increased K⁺ and P. In general, rice straw, Sesbania and Azolla decreased Zn²⁺ concentration in all soils.     

Seasonal changes in fluxes of methane and volatile sulfur compounds from rice paddies and their concentrations in soil water

Rice paddies emit not only methane but also several volatile sulfur compounds such as dimethyl sulfide (DMS: CH₃SCH₃). However, little is known about DMS emission from rice paddies. Fluxes of methane and DMS, and the concentrations of methane and several volatile sulfur compounds including hydrogen sulfide (H₂S), carbonyl disulfide (CS₂), methyl mercaptan (CH₃SH) and DMS in soil water and flood water were measured in four lysimeter rice paddies (2.5 × 4 m, depth 2.0 m) once per week throughout the entire cultivation period in 1995 in Tsukuba, Japan. The addition of exogenous organic matter (rice straw) was also examined for its influence on methane or DMS emissions. Methane fluxes greatly differed between treatments in which rice straw had been incorporated into the paddy soil (rice straw plot) and plots without rice straw (mineral fertilizer plot). The annual methane emission from the rice straw plots (37.7 g m^-2) was approximately 8 times higher than that from the mineral fertilizer plots (4.8 g m^-2). Application of rice straw had little influence on DMS fluxes. Significant diurnal and seasonal changes in DMS fluxes were observed. Peak DMS fluxes were found around noon. DMS was emitted from the flood water in the early growth stage of rice and began to be emitted from rice plants during the middle stage. DMS fluxes increased with the growth of rice plants and the highest flux, 15.1 µg m^-2 h^-1, was recorded before heading. DMS in the soil water was negligible during the entire cultivation period. These facts indicate that the DMS emitted from rice paddies is produced by metabolic processes in rice plants. The total amount of DMS emitted from rice paddies over the cultivated period was estimated to be approximately 5–6 mg m^-2. CH₃SH was emitted only from flood water during the first month after flooding.     

Solid-state fermentation of agro-industrial wastes to produce bioorganic fertilizer for the biocontrol of Fusarium wilt of cucumber in continuously cropped soil

Agro-industrial wastes of cattle dung, vinegar-production residue and rice straw were solid-state fermented by inoculation with Trichoderma harzianum SQR-T037 (SQR-T037) for production of bioorganic fertilizers containing SQR-T037 and 6-pentyl-α-pyrone (6PAP) to control Fusarium wilt of cucumber in a continuously cropped soil. Fermentation days, temperature, inoculum and vinegar-production residue demonstrated significant effects on the SQR-T037 biomass and the yield of 6PAP, based on fractional factorial design. Three optimum conditions for producing the maximum SQR-T037 biomass and 6PAP yield were predicted by central composite design and validated. Bioorganic fertilizer containing 8.46 log₁₀ ITS copies g⁻¹ dry weight of SQR-T037 and 1291.73 mg kg⁻¹ dry weight of 6PAP, and having the highest (p < 0.05) biocontrol efficacy, was achieved at 36.7 fermentation days, 25.9 °C temperature, 7.6% inoculum content, 41.0% vinegar-production residue, 20.0% rice straw and 39.0% cattle dung. This is a way to offer a high value-added use for agro-industrial wastes.     

The significance of denitrification of applied nitrogen in fallow and cropped rice soils under different flooding regimes I. Greenhouse experimènts

The role of nitrification-denitrification in the loss of nitrogen from urea applied to puddled soils planted to rice and subjected to continuous and intermittent flooding was evaluated in three greenhouse pot studies. The loss of N via denitrification was estimated indirectly using the¹⁵N balance, after either first accounting for NH₃ volatilization or by analyzing the¹⁵N balance immediately before and after the soil was dried and reflooded. When urea was broadcast and incorporated the loss of¹⁵N from the soil-plant systems depended on the soil, being about 20%–25% for the silt loams and only 10%–12% for the clay. Ammonia volatilization accounted for an average 20% of the N applied in the silt loam. Denitrification losses could not account for more than 10% of the applied N in any of the continuously flooded soil-plant systems under study and were most likely less than 5%. Intermittent flooding of soil planted to rice did not increase the loss of N. Denitrification appeared to be an important loss mechanism in continuously flooded fallow soils, accounting for the loss of approximately 40% of the applied¹⁵N. Loss of¹⁵N was not appreciably enhanced in fallow soils undergoing intermittent flooding. Apparently, nitrate formed in oxidized zones in the soil was readily denitrified in the absence of plant roots. Extensive loss (66%) of¹⁵N-labeled nitrate was obtained when 100 mg/pot of nitrate-N was applied to the surface of nonflooded soil prior to reflooding. This result suggests that rice plants may not compete effectively with denitrifiers if large quantities of nitrate were to accumulate during intermittent dry periods.     

Conventionally Tilled and Permanent Raised Beds with Different Crop Residue Management: Effects on Soil C and N Dynamics

Conservation tillage in its version of permanent bed planting under zero-tillage with crop residue retention has been proposed as an alternative wheat production system for northwest Mexico. However, little is known about the dynamics of C and N in soils under wheat/maize on permanent beds (PB) where straw was burned, removed, partly removed or retained, as opposed to conventionally tilled beds (CTB) where straw was incorporated. We investigated the dynamics of soil C and N and normalized difference vegetative index (NDVI) crop values in zero-tilled PB and CTB after 26 successive maize and wheat crops. Organic C and total N were respectively, 1.15 and 1.17 times greater in PB with straw partly removed and with straw retained on the surface, than in CTB with straw incorporated. Organic C and total N were 1.10 times greater in soils with 300 kg N ha⁻¹ added than in unfertilized soil. Cumulative production of CO₂ was lower under CTB with straw incorporated than under PB treatments, and CO₂ production increased with increments in inorganic fertilizer. The N-mineralization rate was 1.18 times greater than in unamended soils when 150 kg inorganic N ha⁻¹ was applied, and 1.48 times greater when 300 kg inorganic N ha⁻¹ was added. The N-mineralization rate was significantly (1.66 times) greater in PB where the straw was burned or retained on the surface than in CTB where the straw was incorporated, but significantly (1.25 times) lower than in PB with straw partly removed. The NDVI values reached a maximum 56 days after planting and decreased thereafter. The NDVI for unfertilized soil were similar for CTB with straw incorporated, PB with straw partly removed, and PB with straw retained on the surface, but significantly lower for PB with straw burned and PB with straw removed. In soils to which 150 or 300 kg N ha⁻¹ was added, NDVI was significantly lower for PB with straw burned than for other treatments. Among other things, this suggests the utility of rotating maize or wheat with crops whose residues have lower C–N ratios, thus avoiding immobilization of large amounts of N for extended periods. PB with residue burning, however, is an unsustainable practice leading to low crop performance and soil and environmental degradation.     

Comparison of the rates of enzymatic hydrolysis of pretreated rice straw and bagasse with celluloses

The rates of enzymatic hydrolysis of pretreated rice straw and bagasse have been studied and compared with the hydrolysis rates of microcrystalline cellulose powder (MCCP) and Solka Floc. The effects of particle size reduction and enzyme loading on the rates of hydrolysis of rice straw and bagasse were also studied. It was found that the rates of hydrolysis of pretreated rice straw and bagasse are much higher than that of MCCP and Solka Floc. For both rice straw and bagasse, particle size reduction had very little effect in enhancing the rate of hydrolysis. Lignin present at <10% did not seem to hinder the accessibility of the enzyme to the cellulose surface. An enzyme loading > 40 Ug^?1 had no effect on the hydrolysis rate of rice straw or bagasse.     

Amelioration of growth reduction of lowland rice caused by a temporary loss of soil-water saturation

Decreases in nutrient availability after loss of soil-water saturation are significant constraints to productivity in lowland rainfed rice soils. The effectiveness of soil amendments like lime and straw in ameliorating these constraints are poorly understood. This pot experiment was conducted in Cambodia to investigate changes in soil chemical properties and nutrient uptake by rice after applying lime or straw to continuously flooded or intermittently flooded soil. In continuously flooded soils, exchangeable Al decreased to below 0.2 cmolc/kg. Liming (pH 6.5–6.8) the continuously flooded soil decreased the levels of acetate extractable Fe and P, plant P uptake and shoot dry matter, but had no effect on either Bray-1 or Olsen extractable P values. By contrast, the addition of straw (3.5 g dry straw/kg soil) increased Bray-1, Olsen, and acetate extractable P, plant P uptake, shoot P, and shoot dry matter. The non-amended soils became strongly acidic after loss of soil water saturation: extractable Al increased to 1.0 cmol_c/kg, a potentially harmful level for rice. By contrast, extractable P decreased markedly under loss of soil water saturation as did plant P uptake, shoot P, and shoot dry matter. With loss of soil water saturation, liming substantially depressed the levels of Al but it did not increase plant P uptake, shoot P, and shoot dry matter. Straw addition not only decreased extractable Al levels to well below 0.6 cmol_c/kg under loss of soil water saturation, but it also increased extractability of soil P, plant P uptake, shoot P, and shoot dry matter. Thus, in rainfed environments, the incorporation of straw may be more effective than liming to pH 6.8 for minimising the negative effects of temporary loss of soil-water saturation on P availability, P uptake, and growth of rice.     

Methane emission from paddy soils as affected by wheat straw returning mode

To study influence of wheat straw returning mode on CH₄ emission from paddy soils, a field experiment was conducted at Jurong, Jiangsu Province, China in 2006. Five treatments, no wheat straw applied (CK), wheat straw evenly incorporated into the topsoil (WI), wheat straw buried in ditches (WD), wheat straw strip-mulched onto the field surface (WM) and wheat straw burned in-situ (WB), were laid out in a randomized block design. Results showed that seasonal CH₄ emissions ranged from 6.9 to 28.1 g CH₄ m^?2. Wheat straw incorporation significantly increased CH₄ emission. No significant difference was observed between Treatments WI and WD in total CH₄ emission. Compared with Treatment WI, Treatment WM reduced total CH₄ emission by 32% and Treatment WB by 42%. Treatment WM was about 27% higher than Treatment CK in grain yield. Based on the findings, the best management of wheat straw prior to rice cultivation is strip-mulching wheat straw onto the field surface, which largely reduced CH₄ emission from rice fields with no decrease in rice yield.     

15N2 incorporation by rhizosphere soil influence of rice variety,organic matter and combined nitrogen

Summary Heterotrophic nitrogen fixation by rhizosphere soil samples from 20 rice cultivars grown under uniform field conditions was estimated employing¹⁵N-tracer technique. Rhizosphere soil samples from different rice cultivars showed striking differences with regard to their ability to incorporate¹⁵N₂. Rhizosphere samples from rice straw-amended (3 and 6 tons/ha) soil exhibited more pronounced nitrogen-fixing activity than the samples from unamended soil; while the activity of the rhizosphere samples from soils receiving combined nitrogen (40 and 80 kg N/ha) was relatively low. However, the inhibitory effect of combined nitrogen was not expressed in the presence of rice straw at 6 tons/ha. Results suggest that plant variety, application of combined nitrogen and organic matter influence the rhizosphere nitrogen fixation.     

Combined Application of Rice Straw and Fungus Penicillium Chrysogenum to Remediate Heavy-Metal-Contaminated Soil

The search for cheap and environmentally friendly materials is essential for remediation of heavy-metal-contaminated agricultural soils. A pot experiment was undertaken to evaluate the application of rice straw and filamentous fungus Penicillium chrysogenum (P. chrysogenum) on the fractionation of copper (Cu) and cadmium (Cd), soil microbial properties, and Cu and Cd uptake by romaine lettuce (Lactuca sativa) in a contaminated agricultural soil. Rice straw was applied at three rates (0, 7.8, and 11.7 g kg^?1 soil), and in combinations with P. chrysogenum (1.0 × 10⁶ spores g^?1 soil). It was found that the combined treatment of rice straw and P. chrysogenum significantly decreased the acid-extractable Cu and Cd by 15.4–25.1% and 20.2–27.3%, and increased the oxidizable Cu and Cd by 16.1–18.0% and 72.1–98.4%, respectively. Soil microbial biomass and fresh weight of lettuce were also remarkably enhanced after rice straw plus P. chrysogenum addition. Rice straw combined with P. chrysogenum was more effective in reducing Cu and Cd uptake by lettuce than rice straw alone. The joint application of rice straw and P. chrysogenum remarkably reduced Cu and Cd concentrations in lettuce shoots by 13.6–21.9% and 32.9–41.7%, respectively. These results indicate that the combined application of P. chrysogenum and rice straw is a promising method to alleviate the bioavailability of metals, and to improve soil microbial properties and plant yield in heavy-metal-polluted agricultural soils.