土壤微生物生物氮与植物氮吸收的关系

The contents of the soil microbial biomass nitrogen (SMBN) in the soils sampled from the Loess Plateau of China were determined using chloroform fumigation aerobic incubation method (CFAIM),chloroform fumigation anaerobic incubation method (CFANIM) and chloroform fumigation-extraction method (CFEM). The N taken up by ryegrass on the soils was determined after a galsshouse pot experiment. The flushes of nitrogen (FN) of the soils obtained by the CFAIM and CFANIM were higher than that by the CFEM, and there were significantly positive correlations between the FN obtained by the 3 methods. The N extracted from the fumigated soils by the CFAIM,CFANIM and CFEM were significantly positively correlated with the N uptake by ryegrass. The FN obtained by the 3 methods was also closely positively correlated with the N uptake by ryegrass. The FN obtained by the 3 methods was also closely positively correlated with the plant N uptake. The contributions of the SMBN and mineral N and mineralized N during the incubation period to plant N uptake were evaluated with the multiple regression method. The results showed that the N contained in the soil microbial biomass might play a noticeable role in the N supply of the soils to the plant.     

两种测定土壤微生物量氮方法的比较初探

用氯仿熏蒸-0.5mol/L的K2SO4直接浸提,280nm紫外比色法和熏蒸-淹水培养法测定了20种有机质、全氮和速效氮差异较大的土样的土壤微生物量N。研究结果表明,两种方法测得20种土样的土壤微生物量N数值呈极显著正相关;280nm紫外比色法操作步骤简单、产生误差的环节少、测定所需时间短、且测定数据比熏蒸-淹水培养法有更好的重现性。初步认为,280nm紫外比色法来反映土壤微生物量的大小。结果还表明,两种方法的测定结果都与土壤的全氮含量呈极显著正相关关系,与有机碳含量有一定的正相关关系,与速效氮无明显的相关关系;但在不同的土壤类型上,与全氮、有机碳和速效氮的相关性有所不同。用280nm紫外比色法测定两种土壤的新鲜和风干样的微生物生物量的结果说明,可用风干土经预培养后测定土壤微生物生物量。风干土样的预培养时间初步确定为10天。     

氨的固定对土壤微生物氮的测定的影响

The effect of ammonium fixation on the estimation of soil microbial biomass N was studied by the standard fumigation-incubation(FI) and fumigation-extraction (FE) methods,NO3-N content of fumigated soil changed little during incubation,while the fixed NH4^ in soils capable of fixing NH4^ increased with the increase of K2SO4-extractable NH4-N.one day fumigation increased both extractable NH4^ and fixed NH4^ ,However,prolonged fumigation gave no further increase.One day fumigation caused significant loss of NO3-N,while prolonged fumigation caused no further loss.For soils tested,the net increases of fixed NH4^ in fumigated soil equaled to 0-94% of NH4-N flush measured by the FI metod,and 1-74% of extractable N measured by the FE method.depending on different soils.It is concluded that the ammonium fixation was one of the processes taking place in soils during fumigation as well as incubation ofter fumigation and should not be neglected in the estimation of microbial biomass nitrogen by either FI or FE method.     

棉隆熏蒸与微生物有机肥联用对西瓜枯萎病的防控研究

通过田间试验评估了土壤熏蒸和微生物有机肥联用对西瓜枯萎病的防控效果及对西瓜产量与品质的影响。试验设置3个处理:对照(CK)、棉隆熏蒸结合普通有机肥处理(OF)、棉隆熏蒸结合微生物有机肥处理(BOF)。结果发现:与CK相比,BOF处理和OF处理均显著降低西瓜枯萎病发生率,病害防治效果分别为65.8%和54.1%;BOF处理还显著增加连作西瓜产量(增幅达33.4%),提高西瓜中心糖含量(增幅达15.9%)和糖酸比(增幅达13.4%)。棉隆熏蒸处理土壤细菌和真菌数量均显著低于CK,尖孢镰刀菌数量下降3个数量级;土壤脲酶、蔗糖酶、荧光素二乙酸酯酶活性以及土壤微生物碳源利用多样性指数、均一性指数较CK均显著降低。棉隆熏蒸后施用有机肥可使土壤微生物数量、土壤酶活性及微生物碳源利用多样性逐步恢复,其中BOF处理土壤微生物数量和酶活性恢复速度和强度更大、病原菌数量及病原菌与真菌数量比最低、微生物碳源利用多样性指数最高。结果表明,利用棉隆对连作西瓜土壤熏蒸20 d能显著减少病原菌数量,配合施用微生物有机肥,能快速改善土壤微生物区系和恢复土壤酶活性,降低枯萎病的发生,并有效促进西瓜生长,提高西瓜产量及品质。     

Effects of methyl bromide fumigation,chloropicrin fumigation and steam sterilization on soil nitrogen dynamics and microbial properties in a pot culture experiment

Abstract

The effects of steam sterilization (SS), methyl bromide (MeBr) fumigation and chloropicrin (CP) fumigation on soil N dynamics and microbial properties were evaluated in a pot experiment. All disinfection treatments increased the NH⁺ ₄-N level and inhibited nitrification. The additional NH⁺ ₄-N in the CP treatment probably originated from the decomposition of microbial debris by surviving microbes, while that in the SS treatment was attributable to deamination processes of soil organic N occurring in a less labile fraction in addition to the decomposition of microbial debris. The MeBr fumigation increased the level of NH⁺ ₄-N without changing the soil microbial biomass. Based on the determinations of soil microbial biomass, substrate utilization activity (Biolog method) and microbial community structure (phospholipid fatty acid method), the effects of the MeBr, CP and SS treatments on the microbial community were compared. The MeBr fumigation had relatively mild and short-term effects on microbial biomass and activity, but altered the community structure drastically by promoting the growth of gram-positive bacteria. The CP fumigation had large and long-term impacts on microbial biomass and activity; the community structure remained unaffected except for the gram-negative bacteria. Steam sterilization had severe and persistent effects on all parameters. The severity of the effects decreased in the order SS ≥ CP > MeBr.     

CH4 production potential in a paddy soil exposed to atmospheric CO2 enrichment

Abstract

An anaerobic incubation experiment was conducted to investigate methane (CH₄) production potential in soil samples collected from a paddy field after exposure to free-air CO₂ enrichment (FACE). The FACE experiment with two CO₂ levels, ambient and ambient + 200 p.p.m.v CO₂ during the rice growing season, was conducted at Shizukuishi, Iwate Prefecture, Japan. The soil was a wet Andosol. Soil samples were taken from the surface (0–1 cm) and the sub-surface (1–10 cm) soil layers 2 months after rice harvest. Sub-samples of the fresh soils were put into glass bottles and submerged under N₂ gas headspace during the incubation. The results showed that, prior to incubation, the contents of total C and dissolved organic C (DOC) were significantly greater in FACE soil than ambient soil. During the incubation, CH₄ production potential was approximately 2–4-fold higher in FACE soil than ambient soil and approximately 500–1,000-fold greater in surface soil than sub-surface soil. In general, the FACE soil contained more DOC than ambient soil, particularly in the surface soil layer. These findings suggest that FACE treatment exerted long-term positive effects on CH₄ production and increased organic C content in this paddy soil, particularly in the surface soil layer.     

Impact of soil fumigation practices on soil nematodes and microbial biomass

This study was designed to understand the impact of methyl bromide (MB) (CHaBr) and its alternatives on both free-living and root-knot nematodes in the soil. A randomized complete block experiment with six treatments and 4 replicates (each replicate in a separate greenhouse) was established in Qingzhou, Shandong Province, China. In addition to MB and untreated control (CK) treatments there were four alternative soil fumigation practices including MB virtually impermeable films (VIF), metam sodium (MS), MS VIF and soil solarization combined with selected biological control agents (SS BCA). Two tomato (Lycopersicum esculentum Mill.) cultivars, cv. Maofen-802 from the Xian Institute of Vegetable Science, China, and cv. AF179 Brillante from the Israeli Hazera Quality Seeds, were selected as test crops. The results indicated that Rhabditidae was the most dominant population with percentage abundance as high as 85% of the total number of identified free-living nematodes, followed by that of Cephalobidae. Methyl bromide and its alternatives except for the non-chemical SS BCA treatment controlled the target pest, root-knot nematodes. Also, the impact of the three chemical alternatives on free-living nematode number and functional group abundance was similar to the impact associated with a typical methyl bromide application. Chemical fumigation practices, especially that with MB, significantly reduced the number of nematodes in the soil and simultaneously significantly reduced the number of nematode genera thereby reducing nematode diversity. All the four soil chemical fumigation activities decreased soil microbial biomass and had an obvious initial impact on microorganism biomass. Furthermore, both plant-parasitic and fungivore nematodes were positively correlated with soil microbial biomass.     

Microwave irradiation of soil for routine measurement of microbial biomass carbon

 Microwave irradiation was evaluated as a non-toxic alternate to chloroform fumigation for routine measurement of soil microbial biomass C. Microwave energy was applied to moist soil to disrupt microbial cells. The flush of C released was then measured after extraction or incubation. Microwave irradiation at 800 J g^–1 soil was optimal because this level resulted in an almost instantaneous rise in soil temperature (≥80  °C), an abrupt reduction in microbial activity, maximal release of biomass C, and minimal solubilization of humic substances. Both incubation-CO₂ titration and extraction-colorimetry methods were used on separate 20-g subsamples to compare the labile C in the microwave-treated and untreated soil samples. The incubation-titration method was also used to measure C in chloroform-fumigated soil samples. Averaged across soils, the chloroform fumigation yielded 123.3±5.1 mg CO₂-C kg^–1. Microwave irradiation yielded 93.6±3.9 mg CO₂-C kg^–1 soil determined by incubation and 52.4±2.4 mg C kg^–1 soil determined by extraction, accounting for 76% and 42% of the net flush of C measured by the chloroform fumigation. Microwave-stimulated net flushes of C were correlated closely (r ²=0.974 for incubation or 0.908 for extraction) with microbial biomass C measured by the chloroform fumigation. Little correlation was found with the total soil organic C (r ²=0.241 for incubation or for 0.166 extraction). Mean efficiency factors for incubation (K _MI) or extraction (K _ME) were used to calculate microbial biomass C from net flushes of C between microwaved and unmicrowaved soils. Values of K _MI and K _ME were not affected by soil pH, bulk density or clay contents. Extraction of microwaved soil by 0.5M K₂SO₄ proved to be a simple, fast, precise, reliable, and safe method to measure soil microbial biomass C. Received: 12 September 1997     

Microbial biomass and metabolic activity in four acid soils

The fumigation method was used to estimate microbial biomass C in four Haplumbrepts developed over different kinds of rock. In order to investigate the relationship between metabolic activity and microbial biomass and population density, CO₂ release from the glucose-enriched and unenriched soils was measured during 28 days of incubation.

Biomass C levels lay between 36 and 112 mg 100 g⁻¹ of dry soil, and made up only a small proportion of total soil C (0.77–1.38%). Only a small fraction of this biomass was detected by counting viables, but the microbial population was nevertheless significantly correlated with the biomass determined by fumigation. Among the physico-chemical properties of the soils, microbial biomass and population size were both chiefly affected (favourably) by humidity, total C and N and Al gel content. Metabolic activity was slight, either because part of the micro-organisms are inactive or because of a limited supply of substrate (the organic matter present may be unsuitable as a substrate or protected from microbial attack). Percentage C mineralization was inversely related to organic matter, silt and Al gel contents, and likewise failed to exhibit positive correlation with respiration, the biomass determined by fumigation or the counted population. The metabolic activity of the biomass appeared to depend upon the quality and nature of soil organic matter rather than its quantity, which nevertheless controlled microbial population size.

Neither microbial biomass estimates nor viable population counts faithfully reflected metabolic activity in the soils.     

Short-term partitioning of <Superscript>14</Superscript>C-[U]-glucose in the soil microbial pool under varied aeration status

The effect of soil aeration status on carbon partitioning of a labelled organic substrate (¹⁴C-[U]-glucose) into CO₂, microbial biomass, and extra-cellular metabolites is described. The soil was incubated in a continuous flow incubation apparatus under four different aeration conditions: (1) permanently aerobic, (2) permanently anaerobic, (3) shifted from anaerobic to aerobic, and (4) shifted from aerobic to anaerobic. The soil was pre-incubated for 10 days either under aerobic or under anaerobic conditions. Afterwards, glucose was added (315 g C g^–1) and the soils were incubated for 72 h according to four treatments: aerobic or anaerobic conditions maintained, aerobic conditions shifted to anaerobic conditions and anaerobic conditions shifted to aerobic conditions. Carbon partitioning was measured 0, 8, 16, 24, 48 and 72 h after the glucose addition. In permanently aerobic conditions, the largest part of the consumed glucose was built into microbial biomass (72%), much less was mineralised to CO₂ (27%), and only a negligible portion was transformed to soluble extra-cellular metabolites. Microbial metabolism was strongly inhibited when aeration conditions were changed from aerobic to anaerobic, with only about 35% of the added glucose consumed during the incubation. The consumed glucose was transformed proportionally to microbial biomass and CO₂. In permanently anaerobic conditions, 42% of the consumed glucose was transformed into microbial biomass, 30% to CO₂, and 28% to extra-cellular metabolites. After a shift of anaerobic to aerobic conditions, microbial metabolism was not suppressed and the consumed glucose was transformed mainly to microbial biomass (75%) and CO₂ (23%). Concomitant mineralisation of soil organic carbon was always lower in anaerobic than in aerobic conditions.     

Dichromate Digestion–Spectrophotometric Procedure for Determination of Soil Microbial Biomass Carbon in Association with Fumigation–Extraction

A dichromate digestion and spectrophotometric procedure is proposed for estimating soil microbial biomass carbon (C) in association with fumigation–extraction. The recommended procedure uses a volume (1.6 ml) of 0.5 M potassium sulfate (K₂SO₄) soil extracts and oxidant solution (dichromate–sulfuric acid, 2.4 mL), mixed with a volume (4 mL) for digestion at 140 °C for 30 min. The digested solution is then directly read for absorbance at 350 nm using a spectrophotometer, and the C in the digested soil extracts is measured against glucose standards. The K_EC (indicating the extractable part of microbial biomass C after fumigation) value is estimated as 0.33 for the proposed method. There are good correlations between soil microbial biomass C measured by the proposed method, the dichromate digestion titration, and oven oxidation by total organic C (TOC) analytical method. This method is a simple, rapid, and economical procedure associated with fumigation–extraction for biomass C analysis.     

Limitations when quantifying microbial carbon and nitrogen by fumigation‐extraction in rooted soils

Soil microbial C and N (C_mic, N_mic) estimation by the chloroform fumigation‐extraction method is erroneous in densely rooted soils due to CHCl₃‐labile C and N compounds. The effect of a pre‐extraction with 50 mM K₂SO₄ and a pre‐incubation (conditioning at 25 °C for 7 days) on the flush in extractable, CHCl₃‐labile C (C‐flush) and N (N‐flush) was tested with reference to rooting density (0.3—75 mg root dry matter g^—1) in one arable and 3 grassland soils. In the arable soil and in the second horizon (10—20 cm) of a grassland soil, C‐flush values were not affected by the pre‐extraction. However, the pre‐extraction considerably reduced C‐flush values in the top soils of the grassland (above 10 cm). Only about 42 % was found in the pre‐extracted roots and the rest was lost during the pre‐extraction. The estimated concentrations of N_mic decreased due to pre‐extraction of soil samples with low root biomass. Clearly, the concentrations of N_mic were underestimated by introducing the pre‐extraction. Soil pre‐incubation reduced C‐flush values only slightly, whereas N‐flush values were not affected. It can be concluded that (1) CHCl₃‐labile root C and N is partly extracted with K₂SO₄ after pre‐incubation and (2) CHCl₃‐labile C and N removed with the roots during pre‐extraction is partly derived from microbial biomass. Soils with low rooting density (arable soils, grassland soils below approximately 10 cm depth) should therefore be fumigated and extracted without pre‐extraction. In densely rooted soils, fumigation extraction with and without pre‐extraction probably gives estimates for the minimum and maximum of C_mic and N_mic.     

Microbial biomass C measurements in soil of the central highlands of Mexico

Microbial biomass is the key factor in nutrient dynamics in soil, but no information exist about it in soils of the central highlands of Mexico, a major agricultural area. We determined the microbial biomass in soils with a wide range of organic C and belonging to three soil texture classes. Twenty-four soils under different types of cultivation were sampled while microbial biomass C was measured with the chloroform fumigation incubation (CFI) and extraction technique (CFE). Microbial biomass C as measured with the CFI technique ranged from 138 to 2195 mg C kg⁻¹. The ninhydrin-positive compounds (NPC) and extractable C released with CFE increased with increased time of exposure to chloroform and on average 53% of NPC and 83% of extractable C was released after 1 day compared to that released after 10 days. The ratio of microbial biomass C as measured with the CFI method related to the NPC was 31.8 after 1 day and 20.0 after 10 days while the relationship with extractable C was 3.18 and 2.69, respectively. The relationship between microbial biomass C as measured by the chloroform fumigation incubation technique and the soluble C and ninhydrin-N rendered extractable after 1 and 10 days of chloroform fumigation for soils of the central highlands of Mexico were comparable to values reported for soils in other regions of the world. The factors determined in this study can thus be used to determine microbial biomass.     

A rapid chloroform-fumigation extraction method for measuring soil microbial biomass carbon and nitrogen in flooded rice soils

 A chloroform-fumigation extraction method with fumigation at atmospheric pressure (CFAP, without vacuum) was developed for measuring microbial biomass C (C_BIO) and N (N_BIO) in water-saturated rice soils. The method was tested in a series of laboratory experiments and compared with the standard chloroform-fumigation extraction (CFE, with vacuum). For both methods, there was little interference from living rice roots or changing soil water content (0.44–0.55 kg kg^–1 wet soil). A comparison of the two techniques showed a highly significant correlation for both C_BIO and N_BIO (P<0.001) suggesting that the simple and rapid CFAP is a reliable alternative to the CFE. It appeared, however, that a small and relatively constant fraction of well-protected microbial biomass may only be lysed during fumigation under vacuum. Determinations of microbial C and N were highly reproducible for both methods, but neither fumigation technique generated N_BIO values which were positively correlated with C_BIO. The range of observed microbial C:N ratios of 4–15 was unexpectedly wide for anaerobic soil conditions. Evidence that this was related to inconsistencies in the release, degradation, and extractability of N_BIO rather than C_BIO came from the observation that increasing the fumigation time from 4 h to 48 h significantly increased N_BIO but not C_BIO. The release pattern of C_BIO indicated that the standard fumigation time of 24 h is applicable to water-saturated rice soils. To correct for the incomplete recovery of C_BIO, we suggest applying the k _C factor of 2.64, commonly used for aerobic soils (Vance et al. 1987), but caution is required when correcting N_BIO data. Until differences in fumigation efficiencies among CFE and CFAP are confirmed for a wider range of rice soils, we suggest applying the same correction factor for both methods. Received: 1 June 1999     

土壤微生物体氮的季节性变化及其与土壤水分和温度的关系

以杨陵土垫旱耕人为土(中等肥力红油土)为供试土壤进行田间试验和室内培养试验,研究土壤微生物体氮的动态变化及其土壤含水量和温度的关系。结果表明,田间土壤微生物体氮的变化有明显的季节性;夏季最高,冬季最低,其它时期居中;且与土壤温度有显著或极显著的正相关性,相关系数在0.855以上;试验期间土壤水分含量在10%以上,基本能满足微生物活动所需,因而微生物体氮的变化与水分关系并不密切。应用培养试验结果进一步证明了田间试验结果,即在4～36℃范围内,微生物体氮与温度呈线性相关,而在土壤含水量为6.75%～23.23%范围内,与水分呈指数相关关系,当土壤水分小于10.87%时,水分对微生物体氮有突出结果,当超过10.87%后,几乎没有影响。频繁的干湿交替会使微生物体氮显著减少,但冻融交替却无明显影响。     

发酵脱氢产氢过程对微生物铁还原的影响

发酵型微生物是铁还原菌中的主要类群,但其发酵产氢过程对铁还原的作用尚不清楚,为此采用接种水稻土浸提液混合培养的方法对微生物分别利用葡萄糖、丙酮酸盐和乳酸盐为碳源时,Fe（Ⅲ）还原过程中脱氢酶活性变化、培养体系pH、氢气分压及铁还原特征进行分析,探讨了发酵微生物脱氢产氢过程与微生物Fe（Ⅲ）还原的内在关系。结果表明：2种水稻土浸提液中的微生物均能够以葡萄糖为优势碳源进行脱氢、产氢及还原氧化铁,Fe（OH）,可以诱导脱氢酶的产生,利用葡萄糖时脱氢酶活性在厌氧培养的4-6d出现最大峰值,利用丙酮酸盐和乳酸盐时脱氢酶活性出现峰值的时间分别为培养的15d和21-22d,脱氢酶活性出现峰值的时间与最大铁还原速率Vmax显著负相关、与最大反应速率对应的时间zk存在显著正相关关系。脱氢产氢过程中产生的H＋导致培养体系pH的变化是影响铁还原过程的主要原因,培养体系pH与体系氢气分压及Fe（Ⅱ）累积量呈极显著负相关。微生物利用不同碳源产氢时,利用葡萄糖的产氢能力最高,丙酮酸盐次之,乳酸盐最低。Fe（OH）3的加入增加了氢气的消耗量,培养体系氢气分压与Fe（Ⅱ）累积量存在极显著正相关关系。     

旱作褐土中氧化铁的厌氧还原与光合型亚铁氧化特征

土壤中铁的氧还过程与碳氮转化及自净能力关系密切,已还原亚铁的氧化受土壤性质的影响。采用室内恒温培养试验研究了旱作褐土中铁还原氧化过程、及其与水溶性碳、NO3-、SO42-的关系。结果表明旱作褐土中铁氧化物在厌氧光照条件下可先被还原后被再次氧化,其再氧化量介于1.46~3.00 mg g-1之间,平均2.09 mg g-1;再氧化速率常数介于0.23~0.80 d-1之间,平均0.48 d-1。再氧化量与土壤无定形铁、水溶性硫酸盐含量、阳离子交换量显著负相关,与土壤总氮、总磷显著正相关;再氧化速率常数与土壤有机碳显著负相关,与黏粒含量极显著正相关。厌氧光照培养可使旱作褐土水溶性无机碳平均降低52.74%,水溶性NO3-降低92.15%,水溶性SO42-增加55.38%。研究结果为深入理解旱作土壤潜在的微生物铁循环转化方式提供理论支持。     

Incorporation of C-labeled rice-straw-derived carbon into microbial communities in submerged rice field soil and percolating water

Rice straw is a major organic material applied to rice fields. The microorganisms growing on rice-straw-derived carbon have not been well studied. Here, we applied ¹³C-labeled rice straw to submerged rice soil microcosms and analyzed phospholipid fatty acids (PLFAs) in the soil and percolating water to trace the assimilation of rice-straw-derived carbon into microorganisms. PLFAs in the soil and water were markedly enriched with ¹³C during the first 3 days of incubation, which indicated immediate incorporation of rice-straw-derived carbon into microbial biomass. The enrichment of PLFAs in the percolating water with ¹³C suggested that microorganisms other than the population colonizing rice straw also assimilated rice-straw-derived carbon or that some bacterial groups were selectively released from the straw. The microbial populations could be categorized into two communities based on the carbon isotope data of the PLFAs: those derived from rice straw and those derived from soil organic matter (SOM). The composition of the PLFAs from the two communities differed, which indicated the assimilation of rice-straw-derived carbon by a subset of microbial populations. The composition of rice-straw-derived PLFAs in the percolating water was also distinct from that in the soil.     

4种熏蒸剂处理对土壤可溶性有机氮和微生物量碳氮的影响

采用室内恒温通气培养法,以北京大棚蔬菜地土壤为研究对象,以未使用熏蒸剂土壤为对照,研究4种熏蒸剂[氯化苦(Pic)、1,3-二氯丙烯(1,3-D)、二甲基二硫(DMDS)和威百亩(MS)]对土壤可溶性氮素和微生物量碳、氮的影响。结果表明,4种熏蒸剂处理均能增加土壤中可溶性有机氮的含量,熏蒸处理后敞气0 d时,Pic、MS、DMDS和1,3-D处理的土壤可溶性有机氮累积量分别为47.55 mg·kg-1、42.15 mg·kg-1、40.34 mg·kg-1和32.02 mg·kg-1,较对照(29.97 mg·kg-1)分别增加58.67%、40.65%、34.61%和6.87%。敞气后14~84 d,Pic、DMDS和MS处理DON含量仍持续上升,1,3-D和对照变化不大,各处理之间DON含量差异显著。4种熏蒸剂处理后短时间内,土壤中可溶性氨基酸(DAA)与对照相比大幅上升,在熏蒸后7 d达到最大值,其中Pic处理的上升幅度最大,为12.87 mg·kg-1,对照DAA含量最低,为5.74 mg·kg-1。4种熏蒸剂处理之后,土壤中微生物量碳和氮均呈现急剧下降的趋势,其中Pic处理对微生物的杀灭作用最强,敞气后0 d,Pic处理的微生物量碳和微生物量氮含量分别比对照下降69.39%和70.95%,MS和DMDS次之,1,3-D的杀灭作用最弱。     

Estimation of Changes in Available Soil Phosphate under Submerged Conditions Associated with Temperature during the Tillering Stage of Rice Plant in the Cool Climate Region of Japan

This study was performed to investigate changes in available soil phosphate associated with temperature under submerged conditions and to explore the possibility for estimating those under submerged conditions during the early growth (tillering) stage of rice plants (Oryza sativa L.). An incubation experiment was conducted under submerged conditions at three temperatures (10°C, 17.5°C and 25°C) using paddy soils collected over a widespread area in Japan. In most soils, significant positive correlations were observed between available soil phosphate and cumulative temperature to 650°C, which corresponded to the tillering stage in Japan. Relationships between the regression formulae of the available phosphate against cumulative temperature to 650°C and soil chemical properties measured in air-dried soil were investigated. The results indicate that the available phosphate of paddy soil against cumulative temperature during tillering stage under submerged conditions can be estimated from the results of air-dried soil analyses which can be conducted before a crop season.