有机无机肥配施对酸性菜地土壤硝化作用的影响

通过室内培养和田间试验, 研究了有机无机肥配施对酸性菜地土硝化作用的影响。培养试验条件为60%土壤最大持水量和25 ℃。 结果表明,土壤硝化作用模式为指数方程,延滞期10天。与纯化肥处理（NPK）相比,鲜猪粪配施无机肥（FPM+NPK）和猪粪堆肥配施无机肥（CPM+NPK）均能降低土壤硝化势和氨氧化潜势,猪粪堆肥配施无机肥还能增加土壤微生物量碳、 氮。鲜猪粪配施无机肥和猪粪堆肥配施无机肥处理在硝化培养和田间试验期间N2O释放量均没有差异,但硝化培养期间鲜猪粪配施无机肥的N2O释放量显著低于纯化肥处理,田间试验期间猪粪堆肥配施无机肥的N2O释放量显著低于纯化肥处理。培养试验结束后的土壤pH值与土壤硝化势间,以及硝化培养期间N2O累积释放量与土壤硝化势间均存在显著正相关关系。本研究表明, 有机无机肥配施显著影响土壤硝化作用以及硝化培养期间和田间N2O释放。     

有机无机氮肥配施对莴苣土壤N2O排放的影响

采用静态箱–气相色谱法研究不同种类有机无机氮肥配合施用对盆栽莴苣土壤N_2O排放规律及排放量的影响。试验设置不施肥(CK)、不施氮肥(PK)、施纯化肥(NPK)、有机无机肥配施1(20%猪粪氮+80%化肥氮,NPKM1)、有机无机肥配施2(20%沼渣沼液氮+80%化肥氮,NPKM2)和有机无机肥配施3(20%猪粪堆肥氮+80%化肥氮,NPKM3)共6个处理。结果表明:莴苣生育期各处理施肥后土壤N_2O排放出现多个峰值,出峰时间和大小不一;累积排放量随着生育期的进程逐渐增加,处理间差异更为明显。莴苣生育期各处理土壤N_2O平均排放通量及累积排放量范围分别为0.10～0.25 mg/(m2·h)和1.37～3.42 kg/hm2,大小均表现为NPKNPKM2PKNPKM1NPKM3CK。土壤N_2O排放系数范围为0.13%～0.68%,大小表现为NPKNPKM2NPKM1NPKM3。与NPK处理相比,NPKM1、NPKM2和NPKM3处理莴苣土壤N_2O累积排放量均分别降低48.08%、25.75%和48.30%,产量分别增加48.66%、22.13%和53.76%。总之,施用纯化肥会促进菜地土壤N_2O的排放,而不同种类有机无机氮肥配施能有效减少N_2O排放且提高作物产量,以猪粪类配施效果最佳。因此,有机无机配施是菜地N_2O减排、降低蔬菜种植中氮素损失的重要途径。     

有机无机氮肥配施下洛阳烟田土壤N2O排放特点及其控制因素

随着农田化肥使用量的逐年增加和土壤退化问题日趋严重,农田温室气体排放关注度持续提高,为研究旱作植烟土壤N_2O排放特征及影响机理,设置6个田间试验处理,分别为CK0(不施肥处理)、CK1(100%无机氮)、T1(50%无机氮+50%饼肥氮)、T2(50%无机氮+50%羊粪肥氮)、T3(25%无机氮+75%饼肥氮)、T4(25%无机氮+75%羊粪肥氮),各处理施氮量均为45 kg/hm²,烟田施用基肥后起142天内测量不同处理土壤N_2O排放通量、硝态氮、铵态氮含量、根层温度和含水率。结果表明:(1)基肥施入后的3~7天内,土壤N_2O排放通量进入高峰,无机肥处理和有机无机肥配施处理的高峰期分别可维持20,9天,追肥后3天再次出现排放峰并持续9天,随后伴随烟株的生长发育,烟地N_2O排放通量逐渐趋向稳定。(2)基肥施用后仅1个月内N_2O累积排放量可达到总排放量的27.4%~32.6%;处理间N_2O排放量和排放系数均表现为无机>有机+无机(1∶1)>有机+无机(3∶1),无机肥配施有机肥明显降低了肥料中氮素以N_2O形态的损失量;与无机肥相比,T1和T2烟叶产量分别增加9.44%和6.37%,T1、T2、T3和T4处理的N_2O排放强度有着不同程度的降低。(3)主成分分析结果显示,在不施肥烟地中0—5 cm土壤温度和含水率是N_2O排放通量主导因子,利用相关性分析此环境下温度和水分分别与N_2O排放通量间呈现显著和极显著正相关关系;施肥后土壤铵态氮含量和土壤含水率是烟地N_2O排放通量的主导因子且相关性分析均呈现极显著正相关关系。综上,旱地植烟土壤N_2O排放受氮肥种类影响较大,施肥后N_2O排放通量对土壤温度响应减弱,主要受土壤铵态氮含量和含水量的影响;在总氮量相同情况下,有机无机肥配施比例为1∶1时明显降低土壤N_2O排放并提高了产量,该比例饼肥和羊粪肥处理分别将烟地N_2O排放强度降低20.4%和23.7%。     

有机肥与无机肥配施对菜地土壤N2O排放及其来源的影响

该研究采用同位素自然丰度法,通过室内培养试验研究北京地区菜地有机肥和无机肥配施对土壤释放N2O及同位素位嗜值SP（site preference）的影响,以期获得不同肥料及其配比下土壤N2O的来源及变化规律。结果表明：施用无机肥释放的N2O显著高于有机肥,其累积排放量是有机肥的6.63倍,且无机肥施用比例越高,排放量越大;各肥料组合在施用后7天内均以反硝化作用生成N2O为主,贡献最高达到78.89%,SP为6.97‰,之后硝化作用逐渐增强并成为主要途径,最高占比达76.48%,SP为25.24‰;培养期内施用无机肥可以促进反硝化作用,平均占比52.98%,SP为15.52‰,而有机肥会使硝化作用增强,平均占比71.35%,SP为23.55‰。因此,在北京潮褐土地区菜地土壤施用有机肥对N2O有良好的减排效果,可为蔬菜生产中肥料的合理应用提供科学依据。     

长期施肥下黑土玉米田土壤温室气体的排放特征

研究不同施肥措施下东北黑土区玉米农田温室气体(CO_2、N_2O和CH_4)的排放量及其增温潜势,将为制定农业温室气体减排措施提供理论依据。本研究以国家(公主岭)黑土长期定位试验为平台,采用静态箱-气相色谱法对不同施肥措施下玉米农田土壤温室气体排放通量进行了监测,并分析了不同施肥处理间玉米田的综合温室效应差异。结果表明:各施肥处理土壤温室气体CO_2和N_2O的排放高峰均出现在玉米拔节期。农家肥和化肥配施(M_2NPK)处理土壤CO_2、N_2O排放通量和CH_4吸收量均显著高于施化肥处理(P0.05);施用化肥处理土壤CO_2、N_2O排放通量高于不施肥处理;撂荒区土壤CO_2排放通量最高,而土壤N_2O排放通量显著低于施肥处理;等施氮量条件下,化肥(NPK)处理土壤N_2O排放通量明显高于秸秆还田(SNPK)处理,而土壤CH4净吸收量结果则截然相反。从土壤综合温室效应和温室气体强度可分析出,与不施肥(CK)比较,偏施化肥N和NPK处理的综合温室效应(GWP)分别增加了142%和32%,SNPK综合温室效应降低了38%;尤其是有机无机配施(M_2NPK)处理的综合温室效应为负值,为净碳汇。平衡施肥NPK和有机无机肥配施(SNPK和M_2NPK)温室气体排放强度(GHGI)较弱,显著低于不施肥(CK)和偏施化肥(N)处理,其中M2NPK为-222 kg CO_2-eq·t~(-1)。因此,为同步实现较高的玉米产量和较低的温室气体排放强度,有机无机肥配施是东北黑土区较为理想的土壤培肥方式。     

旱地土壤N_2O排放特征及影响因素分析

N_2O是重要的温室气体之一,其增温效应是CO_2的150~200倍。旱地土壤是N_2O主要排放源,其排放通量在介于0~1000μg m~(-2) h-1,旱地作物生长期土壤N_2O排放通量一般呈现1~3次峰值。通过对旱地N_2O排放影响因素分析,总结出:正常施肥结合秸秆还田农民传统施肥或习惯性施肥优化施肥、优化施肥+有机肥、控释肥+有机肥、控释肥,有机肥有机无机混肥缓释尿素、生物质碳、硝化抑制剂;土壤N_2O的排放量与土壤含水量、土壤温度呈正相关,微咸水再生水、清水;栽培模式对旱地N_2O排放的影响不明确,结果存在分歧;单种作物混合作物;菜地玉米地小麦大豆;农林系统撂荒地农草系统纯玉米地系统;硝化和反硝化作用、土壤中的硝化细菌、地表温度、土壤温度、酸雨、土壤PH值等其他因素也影响N_2O的排放。     

氮肥与氮转化调控剂配施降低夏玉米-冬小麦农田N2O排放

针对农业生产中氮肥施用不合理导致氮肥利用率低、N_2O排放增加及经济效益下降等问题,采用田间试验法研究了不同氮肥与氮转化调控剂配施模式的夏玉米-冬小麦一年两作农田N_2O排放特征及经济效益。结果表明:与农民施氮肥处理(FN)相比,各推荐施氮处理在夏玉米季和冬小麦季的N_2O平均排放通量分别降低29.2%~65.4%(P0.05)和26.9%~74.9%(P0.05),N_2O排放总量分别降低1.05~2.72(P0.05)和1.10~2.47(P0.05)kg/hm~2;整个轮作季纯收益增加967.5~3 887.0元/hm~2。同等施氮量条件下,与推荐施氮处理(RN)相比,夏玉米季推荐施氮配施双氰胺处理(RN+DCD)和推荐施氮配施吡啶处理(RN+CP)分别使N_2O平均排放通量降低41.5%(P0.05)和31.2%(P0.05);而在冬小麦季则分别下降63.0%(P0.05)和65.7%(P0.05);整个轮作季RN+DCD和RN+CP处理N_2O排放总量分别降低了52.5%(P0.05)和49.0%(P0.05),纯收益分别增加312.6和708.9元/hm~2。夏玉米季,土壤N_2O阶段排放峰值出现在三叶期-拔节期和大喇叭口期-抽雄期;而冬小麦季土壤N_2O阶段排放峰值出现在播种-冬前苗期和返青-拔节期。考虑作物产量、N_2O排放以及经济效益,RN+DCD和RN+CP处理经济效益较高,N_2O排放总量较少,是兼顾作物产量、农民收入及大气环境的推荐氮肥管理措施。     

不同灌溉施肥措施对夏玉米-冬小麦农田N2O排放和产量的影响

为明确不同灌溉施肥措施下夏玉米-冬小麦轮作农田N_2O的排放特征,寻求既能减少N_2O排放又保证粮食产量的灌溉施肥方法,以华北地区夏玉米-冬小麦轮作农田为研究对象,利用静态暗箱-气相色谱法对土壤N_2O排放特征进行了周年(2015年6月15日-2016年6月12日)观测,探讨了常规施氮量(夏玉米:205.5 kg/hm2;冬小麦:250 kg/hm2)下传统灌溉施肥(FP100%)、滴灌+传统施肥(DN100%)、滴灌水肥一体化(FN100%)以及滴灌水肥一体化下不同施氮量(减氮60%(FN40%)、减氮30%(FN70%)、常规氮量(FN100%)和增氮30%(FN130%))下农田N_2O排放特征及土壤温湿度对农田N_2O排放的影响,另设滴灌+不施氮肥(CK)为对照。结果表明:在夏玉米-冬小麦轮作体系中小麦季农田土壤N_2O排放通量高于玉米季,夏玉米季土壤N_2O阶段排放峰值出现在拔节期和抽雄期;而冬小麦季土壤N_2O阶段排放峰值出现在冬前苗期和拔节期。与FP100%处理相比,FN40%处理在夏玉米和冬小麦季的N_2O平均排放通量分别降低了70.8%和66.7%,N_2O排放总量分别减少了58.7%和66.3%;整个轮作季周年产量没有显著减少,N_2O排放总量显著降低了62.9%(P0.05)。FN40%处理夏玉米季和冬小麦N_2O排放系数分别为0.06和0.01,显著低于其他施肥处理(P0.05)。土壤温湿度均影响农田N_2O排放,但不同处理在夏玉米和冬小麦生长季与土壤温度和土壤湿度的相关性并不相同。综合考虑N_2O排放量和作物产量,研究认为,在华北地区夏玉米-冬小麦轮作系统下,若采用滴灌,则根据作物需肥规律同时采用水肥一体化方式进行施肥才既有增产,又减少农田N_2O排放的效果,并且在滴灌水肥一体化技术下,减少60%施氮量在保障粮食产量的同时,可以有效地减少N_2O排放,是兼顾作物产量及大气环境的推荐管理措施。     

秋施有机肥对土壤生物学、理化性状及玉米产量的影响

以黑龙江省海林农场白浆土为研究对象,在等氮量条件下（秋季有机肥配施来年春季无机肥）,设置100%有机肥（T₁）,30%有机肥+70%无机肥（T₂）,20%有机肥+80%无机肥（T₃）,100%无机肥（T₄）和不施肥（CK）5个处理,研究长期施肥对土壤生物学、理化性状以及玉米产量的影响。结果表明:玉米生育期内,土壤微生物数量呈先升高后降低的变化趋势,且施用高量有机肥有助于细菌和放线菌群落结构的形成,无机肥和不施肥适于真菌生长;有机无机肥配施处理在提高土壤酶活性方面占据绝对优势,脲酶和蔗糖酶活性始终显著高于其他处理,且有机肥较无机肥处理更能提高玉米生育期内土壤微生物生物量;有机无机肥配施可明显提高土壤全量和速效养分,培肥地力,单施效果稍差,且差异不大,而高量有机肥在降低土壤容重、增加总孔隙度百分比方面作用显著;两年玉米累计产量30%有机肥（T₂）最高,分别比100%有机肥（T₁）和100%无机肥（T₄）提高57.34%和4.59%,稳产并高产。总体来讲,30%有机肥+70%无机肥为最佳施肥模式。     

有机无机肥配施对我国主要粮食作物产量和氮肥利用效率的影响

  【目的】  近年来，化肥的投入使我国作物单位面积产量的大幅提高，但是化肥的过量施用也导致了土壤及生态环境一系列的问题。此外，我国有机物料的种类与数量不断丰富，而循环利用率较低，因此，开展有机物料农田投入对作物增产和氮肥替代能力的研究十分重要。  【方法】  本研究基于文献查阅，收集并整理了我国三大粮食作物 (小麦、玉米、水稻) 在不同施肥处理 (不施肥对照、化肥、有机肥、有机无机肥配施) 下的相关试验数据 (试验年限 ≤ 5)，旨在比较不同施肥处理下三大粮食作物的产量差异，并明确化肥与有机无机肥配施处理下的氮肥用量及氮肥利用效率。  【结果】  化肥、有机肥和有机无机肥配施处理较对照分别增产58.7%、32.1%和61.8%；与化肥处理相比，有机肥处理的作物产量无显著变化，而有机无机肥配施处理显著提高作物产量 (7.4%)，且不同的作物类型均表现出相似的规律。对同时设置对照、化肥、有机肥、有机无机肥配施4个处理的试验数据进行统计分析表明，4个处理的作物平均产量分别为4778、7000、6009和7422 kg/hm2。与对照相比，施肥显著提高了作物产量，化肥和有机无机肥配施处理间无显著性差异，但均显著高于有机肥处理。同时，研究发现不同处理的作物产量会受到作物类型、有机物料种类的影响。从氮肥施用总量分析，有机无机肥配施处理的化肥氮用量在小麦、玉米试验中与化肥处理基本相等，在水稻试验中则显著降低。总体来看，有机无机肥配施的氮肥偏生产力较化肥处理平均显著提高了32.5%，在小麦、玉米、水稻上，氮素偏生产力由化肥处理的35.0、45.2、42.8 kg/kg分别增加到有机无机肥配施处理的45.2、60.6、56.4 kg/kg。不同有机物料替代化肥提高氮肥偏生产力的潜力不同，秸秆还田、农家肥与化肥配施处理中，化肥氮用量未发生显著变化，而氮肥偏生产力显著提高9.4%、71.7%；配施堆肥的化肥氮用量也无显著降低，氮肥偏生产力较化肥处理没有明显提高；配施沼渣的处理中，氮肥用量显著降低，氮肥偏生产力显著提高 90.3%。  【结论】  综合我国历年田间试验中有机无机肥配施和化肥处理的结果，表明适宜的化学氮肥投入是保证我国小麦、玉米和水稻产量的重要措施。在当前我国土壤肥力条件下，在不减少化肥氮用量的前提下配施有机物料，可以进一步增加产量，提高土壤肥力。在总氮量不变的情况下，以有机物料替代部分化肥氮可以保证粮食产量不降低，且可提高氮肥偏生产力。在有机物料中，粪肥和沼渣替代部分化肥的效果较好，而配合秸秆还田应注意维持化肥氮素的投入量。     

Absorption and transport of Na and Cl in rice cultivars differing in their tolerance to salinity: An examination of the effects of ammonium and potassium salts

The absorption and transport of Na and Cl from 0.1 mM and 10 mM ²²Na labelled NaCl or ³⁶Cl labelled KCl were examined in 15 days old seedlings of 3 cultivars of rice differing in their tolerance to salinity. Furthermore, the effects of 10, 100 and 1000 ppm (N)₂S on their uptake were studied. It was found that in general, the salt‐tolerant cultivars BR and PNL‐1 absorbed more Na and translocated a lesser proportion of it to the shoot, compared to the salt‐sensitive IR‐8, from 0.1 mM NaCl. The presence of (N)₂S reduced the uptake of Na in all the cultivars. It was also found that the presence of 100 ppm K, KN or NNreduced Na absorption from 0.1 mM NaCl significantly in all the cultivars, and the translocation to shoot in BR‐ Chloride transport from 0.1 mM NaCl was reduced by (N)₂S in all the cultivars. The 3 cultivars differed significantly in the rates of absorption and transport of Na and Cl. The results indicate that PNL‐1 which is a cross of IR‐8 X BR, has inherited the salt tolerance trait from BR. Lower rates of Na translocation to the shoot can be used as an index of salt tolerance in rice.     

An examination of the total analysis of major elements in soil samples

Recently conventional chemical analyses were mostly replaced by instrumental analysis. Although results from both methods were examined in details after the samples had been solubilized or extracted by appropriate techniques, the solubilization method was considerably altered so as to be convenient for the following analysis. In atomic absorption spectrophotometry (AAS), for example, fusion technique was mostly inadequate because of the higher salts concentration in the obtained solution. The use of H₂SO₄ must also be avoided in acid digestion for SO₄ ^2- precipitates with Sr²⁺ or La³⁺ which must be added to eliminate interferences in the succeeding procedure. Therefore, it is essential to consider the whole scheme including sample treatments to evaluate the suitability of instrumental analysis. In this experiment, the suitability of the methods which have been employed in our laboratory was examined by analyzing 9 rock standards.     

Availability and extractability of soil manganese in a liming experiment

Abstract

The availability of soil Mn to corn in relation to extractability of soil Mn by EDTA, Mg(NO₃)₂, CH₃COONH₄, hydroquinone, H₃PO₄, and NH₄H₂PO₄ as affected by liming was evaluated under field conditions on a single soil type. EDTA, Mg(NO₃)₂ and CH₃COONH₄‐extractable Mn were related inversely to available Mn. No useful relationships were found between hydroquinone, H₃PO₄, and NH₄H₂PO₄‐extractable soil Mn and Mn uptake by sweet corn.     

Denitrification potential in a grassland subsoil: effect of carbon substrates

We examined the potential of a subsoil to denitrify nitrate under optimal anaerobic conditions in a laboratory-based incubation when supplied with a range of C substrates of increasing recalcitrance. Both topsoil and its associated subsoil were supplied with nitrate and either glucose, starch or cellulose. Microbial respiration and the evolution of N₂O and N₂ were measured. The subsoil supported low amounts of microbial activity and responded only to the glucose treatment; with less than one-fifth of the N₂O production measured in the top soil. Overall, our findings demonstrated that the denitrification potential of this particular subsoil is relatively low and that only simple carbohydrates could be utilised readily by the resident microorganisms.     

Developmental patterns of lamellae and stroma fractions of chloroplasts in rice plants

On examining the changes in lamellae and stroma nitrogen during leaf development, it is demonstrated that the lamellae and stroma fractions ofrice chloroplasts develop in quite different ways. In the case of stroma, the stroma materials existing in the leaf section which has just emerged from a leaf sheath are quite limited and the major part of this fraction is derived from the successive protein synthesis, i.e., the synthesis of this fraction was markedly increased during leaf expansion. This developmental pattern of the stroma coincided with the changes in the high-molecular-weight water soluble leaf protein, which seemed to be mainly composed of Fraction I protein. A rapid increase in stroma nitrogen was found to be a major cause for an increase in the leaf nitrogen content during leaf development.

On the other hand, the developmental pattern of the lamellae fraction was characterized by the fact that a considerable amount of this fraction had already been prepared when a leaf emerged from a leaf sheath and thereafter, no outstanding increase was seen compared to that of the stroma. This developmental pattern of the lamellae fraction resulted in a lowering of the proportion of lamellae nitrogen to the total leaf nitrogen during leaf development.

A great change in the lamellae-stroma composition of chloroplasts was observed. The proportion of stroma nitrogen to the total chloroplast nitrogen tended to increase as a leaf develops. Since the developmental stage varied according to the regions of a leaf, variation of the lamellaestroma composition was seen even within a leaf, i.e., the proportion of stroma nitrogen increased from base to tip.

In order to compare the synthetic rate of chlorophyll with those of the stroma and lamellae fractions, the changes in the ratios of stroma nitrogen/chlorophyll and lamellae nitrogen/chlorophyll were examined. The lamellae nitrogen/chlorophyll ratio decreased as a leaf developed, whereas the stroma nitrogen/chlorophyll ratio increased. Then the synthetic rates of these fractions during leaf development turned out to be of the same order as the stroma fraction, chlorophyll, lamellae fraction.     

Soil Properties Influence Distribution of Extractable Boron in Soil Profile

Depth distribution of boron (B) extractable by hot calcium chloride (HCC), potassium dihydrogen phosphate (PDP), and tartaric acid (TA) in some typical B‐deficient Inceptisols, Entisols, and Alfisols in relation to soil properties was studied. The magnitude of B extraction followed the order HCC > PDP > TA for Inceptisols, TA > HCC > PDP for Entisols, and PDP > HCC > TA for Alfisols and showed a decrease along soil depth. The low pH of TA and effective desorption of B by phosphate of PDP are attributed to their higher efficiency in extracting B in Entisols and Alfisols, respectively. A decrease in organic carbon (C), clay, and amorphous iron oxide content was responsible for the observed decrease in extractable B along depth of soil profile. The HCC showed more efficiency than PDP and TA for extracting B in soils high in organic C. Multiple regression equations explained only 21, 57, and 59% of the variability in PDP‐, HCC‐, and TA‐extractable B content in soils by the soil properties analyzed, of which organic C and clay were the most important. There were dynamic equilibria among the amount of B extracted by the extractants, indicating B extraction by them from more or less similar pools in the soils.     

Acidifying emissions in The Netherlands

The emission of acidifying compounds to air in the Netherlands, expressed as acidifying equivalents, consisted in 1992 mainly of NO_X (45%), NH₃ (35%) and SO₂ (20%). Transportation, agriculture and large combustion plants each contributed about 30% to the national total emission of acidifying compounds. The emissions from transportation activities mainly consisted of NO_X, while in agriculture NH₃ emission strongly dominated. Combustion processes in large combustion plants resulted both in SO₂ emissions (especially from refineries) and NO_X emissions (especially from public power plants). The total emission of acidifying substances decreases steadily in the Netherlands. The emission in 1992 was 24% lower than in 1985. It is expected to decrease further in future. The emission levels in 1992 and 1993 still are more than twice as high as the emission objective for the year 2000, set by Dutch environmental policy.     

Effect of intermittent drainage in reduction of methane emission from paddy soils in Hokkaido,northern Japan

ABSTRACT

Emission of methane (CH₄), a major greenhouse gas, from submerged paddy soils is generally reduced by introducing intermittent drainage in summer, which is a common water management in Japan. However, such a practice is not widely conducted in Hokkaido, a northern region in Japan, to prevent a possible reduction in rice grain yield caused by cold weather. Therefore, the effects of intermittent drainage on CH₄ emission and rice grain yield have not been investigated comprehensively in Hokkaido. In this study, we conducted a three-year field experiment in Hokkaido and measured CH₄ and nitrous oxide (N₂O) fluxes and rice grain yield to elucidate whether the reduction in CH₄ emission can be achieved in Hokkaido as well as other regions in Japan. Four experimental treatments, namely, two soil types [soils of light clay (LiC) and heavy clay (HC) textures] and two water management [continuous flood irrigation (CF), and intermittent drainage (ID)], were used, and CH₄ and N₂O fluxes were measured throughout the rice cultivation periods from 2016 to 2018. Cumulative CH₄ emissions in 2016 were markedly low, suggesting an initially low population of methanogens in the soils presumably due to no soil submergence or crop cultivation in the preceding years, which indicates a possible reduction in CH₄ emission by introducing paddy-upland crop rotation. Cumulative CH₄ emissions in the ID-LiC and ID-HC plots were 21–91% lower than those in the CF-LiC and CF-HC plots, respectively, whereas the cumulative N₂O emissions did not significantly differ between the different water managements. The amount of CH₄ emission reduction by the intermittent drainage was largest in 2018, with a comparatively long period of the first drainage for 12 days in summer. Rice grain yields did not significantly differ between the different water managements for the entire 3 years, although the percentage of well-formed rice grains was reduced by the intermittent drainage in 2018. These results suggest that CH₄ emission from paddy fields can be reduced with no decrease in rice grain yield by the intermittent drainage in Hokkaido. In particular, the first drainage for a long period in summer is expected to reduce CH₄ emission markedly.     

Sulfur dioxide inhibition of photosynthesis at different CO2 and O2 concentrations in relation to photorespiration

The mechanism of SO₂ inhibition of photosynthesis in intact leaves of tomato and maze was studied to evaluate SO₂ inhibition of photorespiration. Leaf tissues were fumigated with SO₂ under photorespiratory (low CO, and/or high O, concentrations) and non-photo-respiratory conditions. When tomato leaf disks were fumigated with 10 ppm SO₂ at 2, 21 and 100° o O., SO₂ inhibited photosynthesis at 2% O₂ in the same degrees as at 21% O₂. SO₂ inhibition of photosynthesis was depressed at higher CO₂ concentrations when the disks were fumigated with SO₂ at different CO₂ concentrations. High CO₂ concentrations also reduced the photosynthesis inhibition of maize leaf disks. These results suggest that SO₂ inhibits photosynthesis through other mechanisms than photorespiration inhibition and confirm the view that SO₂ competes with CO₂ for the carboxylating enzymes in photosynthesis     

Effects of NaHCO3 on photosynthetic characteristics,and iron and sodium transfer in pomegranate

In order to study effects of sodium bicarbonate (NaHCO₃) stress in irrigation water on photosynthetic characteristics and iron (Fe) and sodium (Na⁺) translocation content of pomegranate plants, a factorial experiment was conducted based on completely randomized design with three cultivars of pomegranate (“Gorch-e-Dadashi,” “Zagh-e-Yazdi,” and “Ghermez-e-Aliaghai”) and four concentrations of NaHCO₃ (0, 5, 10, and 15 mM), with three replications. The results of plant analysis indicated that NaHCO₃ affected chlorophyll index, F_v/F_m, and performance index (PI) in upper and lower leaves of shoots and also the translocation of Na⁺ and Fe. The results also showed that Fe translocation from root to shoot reduced at 15 mM level of NaHCO₃. The highest Na translocation and the lowest Fe translocation were observed in Zagh-e-Yazdi and Ghermez-e-Aliaghai cultivars, respectively. The ratio of sodium/potassium (Na⁺/K⁺) in stems was higher than that in roots and leaves, and the observed chlorophyll content of upper leaves was also lower than that of lower leaves. Based on the measured parameters Gorch-e-Dadashi cultivar showed less relative sensitivity than other cultivars to NaHCO₃ of irrigation water through maintaining the lower Na⁺ transport to the shoots, and improvement of Fe transport to shoots.