Hydrogen oxidation activities in soil as influenced by pH,temperature, moisture,and season

Summary Hydrogen oxidation in soil was measured at low (1 ppmv) and high (300 ppmv) H₂ concentrations to distinguish between the activities of abiontic soil hydrogenases and Knallgas bacteria, respectively. The two activities also showed distinctly different pH optima, temperature optima, and apparent activation energies. The pH optima for the soil hydrogenase activities were similar to the soil pH in situ, i.e., pH 8 in an slightly alkaline garden soil (pH 7.3) and pH 5 in an acidic cambisol (pH 4.6–5.4). Most probable number determinations in the alkaline acidic soils showed that Knallgas bacterial populations grew preferentially in neutral or acidic media, respectively. However, H₂ oxidation activity by Knallgas bacteria in the acidic soil showed two distinct pH optima, one at pH 4 and a second at pH 6.4–7.0. The soil hydrogenase activities exhibited temperature optima at 35–40°C, whereas the Knallgas bacteria had optima at 50–60°C. The apparent activation energies of the soil hydrogenases were lower (11–23kJ mol^-1) than those of the Knallgas bacteria (51–145 kJ mol^-1). Most of the soil hydrogenase activity was located in the upper 10 cm of the acidic cambisol and changed with season. The seasonal activity changes were correlated with changes in soil moisture and soil pH.     

Growth rates of Aporrectodea caliginosa (Oligochaetae: Lumbricidae) as influenced by soil temperature and moisture in disturbed and undisturbed soil columns

Earthworm growth is affected by fluctuations in soil temperature and moisture and hence, may be used as an indicator of earthworm activity under field conditions. There is no standard methodology for measuring earthworm growth and results obtained in the laboratory with a variety of food sources, soil quantities and container shapes cannot easily be compared or used to estimate earthworm growth in the field. The objective of this experiment was to determine growth rates of the endogeic earthworm Aporrectodea caliginosa (Savigny) over a range of temperatures (5–20 °C) and soil water potentials (−5 to−54 kPa) in disturbed and undisturbed soil columns in the laboratory. We used PVC cores (6 cm diameter, 15 cm height) containing undisturbed and disturbed soil, and 1 l cylindrical pots (11 cm diameter, 14 cm height) with disturbed soil. All containers contained about 500 g of moist soil. The growth rates of juvenile A. caliginosa were determined after 14–28 days. The instantaneous growth rate (IGR) was affected significantly by soil moisture, temperature, and the temperature×moisture interaction, ranging from −0.092 to 0.037 d⁻¹. Optimum growth conditions for A. caliginosa were at 20 °C and −5 kPa water potential, and they lost weight when the soil water potential was −54 kPa for all temperatures and also when the temperature was 5 °C for all water potentials. Growth rates were significantly greater in pots than in cores, but the growth rates of earthworms in cores with undisturbed or disturbed soil did not differ significantly. The feeding and burrowing habits of earthworms should be considered when choosing the container for growth experiments in order to improve our ability to extrapolate earthworm growth rates from the laboratory to the field.     

Bacteria and protozoa in soil microhabitats as affected by earthworms

The effects of incorporation of elm leaves (Ulmus glabra) into an agricultural sandy loam soil by earthworms (Lumbricus festivus) on the bacterial and protozoan populations were investigated. Three model systems consisting of soil, soil with leaves, and soil with leaves and earthworms, respectively, were compared. The total, viable, and culturable number of bacteria, the metabolic potentials of bacterial populations, and the number of protozoa and nematodes were determined in soil size fractions. Significant differences between soil fractions were shown by all assays. The highest number of microorganisms was found in microaggregates of 2–53 μm and the lowest in the <0.2μm fraction. A major part of the bacteria in the latter fraction was viable, but non-culturable, while a relatively higher number of culturable bacteria was found in the macroaggregates. The number of colony-forming units and 5-cyano-2,3-ditolyl tetrazolim chloride (CTC)-reducing bacteria explained a major part of the variation in the number of protozoa. High protozoan activity and predation thus coincided with high bacterial activity. In soil with elm leaves, fungal growth is assumed to inhibit bacterial and protozoan activity. In soil with elm leaves and earthworms, earthworm activity led to increased culturability of bacteria, activity of protozoa, number of nematodes, changed metabolic potentials of the bacteria, and decreased differences in metabolic potentials between bacterial populations in the soil fractions. The effects of earthworms can be mediated by mechanical mixing of the soil constituents and incorporation of organic matter into the soil, but as the earthworms have only consumed a minor part of the soil, priming effects are believed partly to explain the increased microbial activity. Received: 7 January 1996     

Earthworm populations as affected by crop practices on clay loam soil in a Mediterranean climate

Abstract

Earthworms influence soil fertility, and their population is known to be influenced by fertilization. The objective of this study is to characterize the abundance of earthworms under three different kinds of rotation-crops (Rotation: cereals–legumes for green manure-cotton), three tillage systems (Conventional Tillage CT, Minimum Tillage MT, & No-Tillage NT) and fertilization (NP: inorganic and FYM: farmyard manure-organic). Significantly higher populations of earthworms were found under the legumes and NT system in contrast to the lowest abundance determined under the cotton and CT system. Earthworm populations benefited more from organic fertilization than from NP. Our study showed that the most important factors for earthworm abundance are the macropores and C_org under Mediterranean conditions. No-till management considerably influenced the improvement of the physical and chemical soil properties and increased the earthworm abundance.     

Assessing the impact of Diplocardia ornata on physical and chemical properties of compacted forest soil in microcosms

 The influence of compaction on Diplocardia ornata (Smith) burrowing and casting activities, soil aggregation, and nutrient changes in a forest soil were investigated using pot microcosms. Treatments included two levels each of compaction, organic matter, and earthworms. Both burrowing and casting activities were more abundant in uncompacted soil than in compacted soil. Bulk density decreased in microcosms of compacted soil containing D. ornata from 1.76 g cm^–3 to 1.49 g cm^–3 over the study period. The overall percent of aggregates in the same size classes in compacted soil was less than the percent of aggregates in uncompacted soil. The mean percent of aggregates in earthworm casts for size classes 0.25–1.00 mm was higher for compacted soil than for uncompacted soil. The reverse was true for aggregates in class sizes 2.00–4.00 mm. Soil compaction also affected soil microbial biomass carbon and soil inorganic N concentrations. These results indicate that the burrowing and casting activities of earthworms in compacted forest soils, as in soils of agricultural and pastured lands, can help ameliorate disturbed soils by improving aggregation, reducing bulk density, and increasing nutrient availability. Received: 1 September 1999     

The response of Aporrectodea rosea and Aporrectodea trapezoides (Oligochaeta: Lubricidae) to moisture gradients in three soil types in the laboratory

The question of whether the response of earthworms to soil moisture is governed by their reaction to soil wetness (moisture content) or to soil water energy (matric suction) was examined in two species of earthworm using moisture gradients in three contrasting soil types with clay contents varying from 4 to 39%. Gravimetric moisture gradients ranging over 5–30% were established in horizontal cores comprising 12 or 14 sections containing loosely packed soil. Earthworms were introduced to each section at the beginning of each experiment. The earthworms moved from sections containing dry soil into adjacent sections containing moister soil. Clear effects were evident after 6 h but these became more obvious after 96 h. For the earthworm Aporrectodea rosea, the threshold soil mositure level at which earthworms were induced to move away from dry soil was a matric suction of about 300 kPa (pF 3.4) and was independent of soil type. In contrast, for A. trapezoides, the threshold soil moisture varied with soil type (sandy loam 15 kPa, loam 25 kPa, clay 300 kPa). We conclude that, for the earthworm A. rosea, matric suction and not water content of soil provided the cue by which the earthworm recognized dry soil. For A. trapezoides, there was an interaction between matric suction and soil type in which the response of A. trapezoides to soil moisture varied with soil texture and the threshold for avoidance of dry soil ranged from a matric suction of 300 kPa (20% w/w) in clay to 15 kPa (10% w/w) in sandy loam.     

橡胶林土壤呼吸速率及其与土壤温湿度的关系

利用Li-6400光合仪研究4 a、12 a和19 a橡胶林的土壤呼吸及其各组分(微生物呼吸、根系呼吸、凋落物呼吸)呼吸速率的日变化和年变化特征,探索土壤温度和湿度对土壤呼吸速率的影响。结果表明: 不同树龄橡胶林土壤呼吸速率在全天观测期间,出现最大值和最小值的时刻有很大差异,但在9:00~11:00时刻的测定值均接近日均值;在不同树龄橡胶林中各组分呼吸速率日变化大小虽不一致,但均表现为凋落物呼吸速率最小。4 a、12 a和19 a橡胶林土壤呼吸速率均有明显的月变化,月均值分别是2.45、2.63和2.96 μmol m-2 s-1;最大值出现在7月和8月,最小值出现在2月和3月;不同树龄橡胶林土壤呼吸速率月变化相互间差异不显著;土壤微生物呼吸占土壤呼吸的比例最高(为43.6%),根系呼吸次之(为36.1%),凋落物呼吸较小(为20.4%)。土壤呼吸速率与土壤温度之间具有显著的指数函数关系,但与土壤湿度的相关性不显著,从而得知海南橡胶林土壤温度与土壤呼吸速率有着密切的关系,土壤水分与土壤呼吸速率可能没有直接的关系。     

黄土高原旱地土壤质量评价指标研究

基于设置在陇中黄土高原半干旱区的长期定位试验,运用综合评价模型,定量评价了小麦→豌豆双序列轮作系统6种不同耕作方式对土壤质量的影响。结果表明,采用加权综合法和加乘法则对土壤质量进行综合评价,能够较好地反映土壤质量的实际情况,敏感地反映耕作方式对土壤质量的影响。运用逐步判别分析法对6种不同耕作方式[传统耕作(T)、免耕作(NT)、传统耕作秸秆还田(TS)、免耕秸秆覆盖(NTS)、传统耕作地膜覆盖(TP)、免耕地膜覆盖(NTP)]下29项土壤属性指标进行筛选,建立了包括团粒结构、全氮、速效氮、有机质、蔗糖酶活性、作物产量、种植纯收益和产投比8项因子的简化评价指标体系。原始评价指标体系下2种轮作序列土壤质量指数排序均为NTSTSNTPNTTPT;简化评价指标体系下豌豆→小麦轮作序列土壤质量指数排序为NTSTSNTPNTTTP,而小麦→豌豆轮作序列土壤质量指数排序为NTSTSNTNTPTTP。进一步相关分析和方差分析表明,应用逐步判别分析法建立的简化指标体系具有较高的代表性,可适用于黄土高原半干旱区土壤质量评价。     

河北省土壤温度与干湿状况的时空变化特征

土壤温度和干湿状况是表征土壤特性的重要参数,在土壤系统分类中作为诊断土壤某些亚纲、土类及亚类划分的参考依据。基于河北省142个气象观测站1951—2010年的日值气象数据,利用GIS空间分析技术,对河北省近60年的土壤温度和干湿状况的时空变化规律进行了分析。结果表明:(1)1951—2010年的平均土温和平均干燥度指数呈现上升趋势,且1981—2010年的上升速率均高于1951—1980年。(2)河北省主要有冷性和温性两种土壤温度状况,与1951—1980年相比,1981—2010年的温性土壤向北有所移动,移动的距离和面积大约为14.26 km和5 665 km2。(3)河北省的土壤干湿状况分布具有明显的地域差异,地表干湿状况可分为湿润、半湿润和半干旱三个等级;东部和北部区域气候湿润状况优于西部和南部,也间接表明了土壤的干湿分布状况。该研究结果为土壤系统分类定量化的诊断特性取代传统土壤分类中的地带性概念提供参考。     

黑土土壤水分反射光谱特征定量分析与预测

选择单一土类黑土作为研究对象, 并准确调配其不同含水量,实验室测定土壤高光谱反射率,利用光谱分析与统计方法,定量描述了不同含水量黑土反射光谱特征,并建立了黑土含水量反射光谱预测模型,结果表明,随土壤含水量的增加,达到一定阈值（300 g kg-1）,反射率存在过饱和现象,但其倒数对数微分可以有效去除饱和问题;土壤反射率倒数对数微分对土壤含水量的响应表现出三个变化阶段,导致1 870 nm波段的倒数对数微分也表现为非线性变化,需要利用分段函数进行土壤含水量的光谱精确速测。     

Influence of earthworms and leaf litter on edaphic variables in sewage-sludge-treated soil microcosms

Summary A series of 48 greenhouse soil microcosms were established and treated with combinations of sewage sludge, Acer saccharum leaves, and the earthworms Eisenia fetida and Lumbricus terrestris. The microcosms were incubated at constant moisture for 110 days. Samples were then taken and analysed for sludge depth, organic-matter content, and waterstable soil aggregates. Weights of surface leaves and weights and numbers of surviving earthworms were determined for each microcosm. L. terrestris significantly reduced sludge depth and the surface organic-matter content of microcosm soil and significantly increased percentages of 4-mm diameter water-stable aggregates. Leaf litter also significantly reduced sludge depth and increased 4-mm water-stable aggregates. E. fetida inhibited surface feeding by L. terrestris, reduced its 110-day survival rate, and inhibited the production of 4-mm water-stable aggregates in L. terrestris treatments. Numbers of E. fetida increased in L. terrestris treatments. Sludge depth, organic-matter content and water-stable aggregates were not significantly different from controls in E. fetida treatments.     

Wheel traffic impact on soil conditions as influenced by tillage system in Central Anatolia

The increased limiting effects of soil compaction on Central Anatolian soils in the recent years demonstrate the need for a detailed analysis of tillage system impacts. This study was undertaken to ascertain the effects of seven different tillage systems and subsequent wheel traffic on the physical and mechanical properties of typical Central Anatolian medium textured clay loam soil (Cambisol), south of Ankara, Turkey. Both tillage and field traffic influenced soil bulk density, porosity, air voids and strength significantly except the insignificant effect of traffic on moisture content. Traffic affected the soil properties mostly down to 20 cm. However, no excessive compaction was detected in 0–20 cm soil depth. The increases of bulk density following wheel traffic varied between 10–20% at 0–5 cm and 6–12% at 10–15 cm depth. In additions, traffic increased the penetration resistance by 30–74% at 0–10 cm and 7–33% at 10–20 cm. Less wheel traffic-induced effects were found on chisel tilled plots, compared to ploughed plots. Soil stress during wheel passage was highly correlated with soil strength. Also, both tillage and traffic-induced differences were observed in mean soil aggregate sizes, especially for mouldboard ploughed plots. The obtained data imply that chisel+cultivator-tooth harrow combination provides more desirable soil conditions for resisting further soil compaction.     

不同深度土壤控水对稻田土壤微生物区系及细菌群落多样性的影响

为研究不同深度土壤控水对壤土稻田土壤水势、微生物区系和细菌群落多样性的影响,通过土培池栽试验,在水稻生育后期设置土壤深度0~5 cm（S05）、0~10 cm（S10）和0~15 cm（S15）控水处理,以保持水层为对照,分析了不同深度控水处理下5 cm、10 cm、15 cm深土壤水势与土壤微生物区系、细菌群落多样性的变化。结果表明：土壤5 cm、10 cm、15 cm深度的水势随着控水深度增加而降低,S05控水处理主要影响上层（5 cm）土壤水势,S10控水处理影响上、中层（10 cm）土壤水势,S15控水处理土壤水势随土层深度的增加而升高。花后8 d和32 d,S05控水处理上层土壤细菌数量显著高于S10、S15控水处理;花后16~24 d,S05控水处理中层、下层（15 cm）土壤细菌数量均显著高于S15控水处理;土壤水势与水稻生育后期中、下层土壤细菌数量呈极显著正相关关系。S05控水处理10 cm、15 cm土层的细菌丰富度Chao指数均显著高于S15控水处理及CK。3个控水处理中,5 cm土层细菌的多样性Shannon指数以S05控水处理最低。优势细菌菌群分析发现,优势群落主要为变形菌门、绿弯菌门、酸杆菌门、拟杆菌门,四者总相对丰度在80%以上;S15控水处理中层土壤变形菌门相对丰度低于S05和S10控水处理。3个控水处理土壤样品中优势纲（相对丰度大于2%）达15个,主要包括α-变形菌纲、β-变形菌纲、δ-变形菌纲、厌氧绳菌纲等,这4个纲的总相对丰度在47%以上,其中厌氧绳菌纲相对丰度最高;上层土壤中S05控水处理的β-变形菌纲相对丰度显著低于S10和S15控水处理。因此,不同深度土壤控水对壤土土壤水势、细菌数量存在影响,改变了细菌的多样性及丰富度,对土壤细菌优势菌种类无显著影响。     

Relationships between soil aggregation and mycorrhizae as influenced by soil biota and nitrogen nutrition

 The effect of the form of N nutrition on soil stability is an important consideration for the management of sustainable agricultural systems. We grew soybean [Glycine max (L.) Merr.] plants in pot cultures in unsterilized soil, and treated them by (1) inoculating them with Bradyrhizobium japonicum, fertilizing with (2) nitrate or (3) ammonia, or (4) by providing only minimum N amendment for the controls. The soils were sampled at 3-week intervals to determine changes in water-stable soil aggregates (WSA), soil pH, the development of roots, arbuscular mycorrhizal (AM) soil and root colonization, and selected functional groups of soil bacteria. The soil fauna was assayed at the end of the experiment (9 weeks). WSA was correlated positively with root and AM soil mycelium development, but negatively with total bacterial counts. Soil arthropod (Collembola) numbers were negatively correlated with AM hyphal length. Soils of nodulated and ammonia-fertilized plants had the highest levels of WSA and the lowest pH at week 9. Sparse root development in the soils of the N-deficient, control plants indicated that WSA formation was primarily influenced by AM hyphae. The ratio of bacterial counts in the water-stable versus water-unstable soil fractions increased for the first 6 weeks and then declined, while counts of anaerobic bacteria increased with increasing WSA. The numbers of soil invertebrates (nematodes) and protozoans did not correlate with bacterial counts or AM soil-hyphal lengths. Soil pH did not affect mycorrhiza development, but actinomycete counts declined with decreasing soil pH. AM fungi and roots interacted as the factors that affect soil aggregation, regardless of N nutrition. Received: 20 December 1997     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

黄土丘陵区枣林地土壤水分时空变化研究

为探索枣树种植对黄土丘陵沟壑区土壤水分的影响,在陕西省米脂县,以5 a和15 a枣林地及14 a更新枣林地(与15 a枣林同年栽植,14 a时截枝截干更新)为研究对象,对枣林地土壤水分进行长期定位观测,分别研究了不同树龄枣林地的土壤水分差异、土壤水分与土壤质地关系、枣树耗水深度以及土壤干燥化问题。结果表明:1)不同树龄枣林地土壤水分存在显著差异,随树龄增加,枣树年耗水量增大,枣树耗水深度增加。2)枣林地枣树根系吸水影响范围内的土壤水分与粉粒含量呈显著正相关关系。3)不同树龄枣林地的耗水深度分别为5 a枣林地440 cm、14 a更新枣林地800 cm、15 a枣林地840 cm。4)5 a枣林地在根系吸水影响范围内出现了100 cm深的重度干燥化土层(土层深度为400~500 cm),14 a更新枣林地在根系吸水影响范围内出现了300 cm深的重度干燥化土层(土层深度为300~600 cm),15 a枣林地在根系吸水影响范围内分别出现了100 cm深的重度干燥化土层(土层深度为200~300 cm)和300 cm深的极度干燥化土层(土层深度为300~600 cm)。枣林地土壤水分状况与树龄、土壤质地相关,截干更新具有减少耗水的作用。研究结果可为今后半干旱山地枣林可持续经营及防治林地土壤干层研究提供一定理论依据。     

Nitrate leaching as influenced by soil tillage and catch crop

Because of public and political concern for the quality of surface and ground water, leaching of nitrate is of special concern in many countries. To evaluate the effects of tillage and growth of a catch crop on nitrate leaching, two field trials were conducted in spring barley (Hordeum vulgare L.) under temperate coastal climate conditions. On a coarse sand (1987–1992), ploughing in autumn or in spring in combination with perennial ryegrass (Lolium perenne L.) as a catch crop was evaluated. Furthermore, rotovating and direct drilling were included. The experiment was conducted on a 19-year-old field trial with continuous production of spring barley. On a sandy loam (1988–1992), ploughing in autumn or in spring in combination with stubble cultivation and perennial ryegrass, in addition to minimum tillage, was evaluated in a newly established field trial. For calculation of nitrate leaching, soil water isolates from depths of 0.8 or 1.0 m were taken using ceramic cups. No significant effect of tillage was found on the coarse sand; however, a significant effect of tillage was found on the sandy loam, where leaching from autumn ploughed plots without stubble cultivation was 16 kg N ha⁻¹ year⁻¹ higher than leaching from spring ploughed plots. Leaching was significantly less when stubble cultivation in autumn was omitted. Leaching on both soil types was significantly reduced by the growth of a catch crop which was ploughed under in autumn or in spring. It was concluded that soil cultivation increased leaching on the sandy loam but not on the coarse sand, and that the growth of perennial ryegrass as a catch crop reduced leaching on both soil types, particularly when ryegrass was ploughed under in spring.     

Land-use impacts on surface runoff and soil detachment within agricultural sloping lands in Northern Vietnam

Two consecutive years of investigation on soil surface features, surface runoff and soil detachment within 1-m² microplots on 40% slope highlighted the effects of land-use change, vegetation cover and biological activity on the water pathways in Northern Vietnam. Three replicate plots were set up on each of five land-uses: cassava (CAS), grass fodder of Bracharia ruziziensis (BRA), a 3-year old fallow (FAL), tree stands of Acacia mangium and Venicia montana (FOR), and a fallow with regrowth of Eucalyptus regularly cut (EUC). The second year, two of the microplots under FAL and EUC were treated with herbicide (FALh, EUCh), one of them was burnt (FALh+b, EUCh+b). The highest yearly surface runoff coefficient of 16%, and soil detachment rate of 700 g m^− 2 yr^− 1 in average with a maximum of 1305 g m^− 2 yr^− 1 have been recorded under CAS. On FALh and FALh+b, runoff ratios were 8.7 and 13.5%, respectively and detachment rates were 86 and 389 g m^− 2. On FAL and BRA the yearly runoff ratio varied from 5.9 to 9.8% but the detachment rate was limited at 24 to 35 g m^− 2. FOR and EUC annual runoff was ≤ 3.1% and annual soil detachment ≤ 71 g m^− 2. These values were very low compared to the values reported on steep slopes in Laos within similar climate and vegetation cover.The runoff and detachment rates underlined the importance of rainfall intensities, soil physical properties, soil surface features, soil vegetation cover and biological activity. The annual surface runoff was highly correlated to the soil surface crusting. CAS and BRA plots were prone to crusting especially after weeding at the onset of the rainy season, when the soil surface was still uncovered. Soil bioturbation (earthworm casting activity) was the second factor that explains local variation of surface runoff and soil detachment. The continuous production of earthworms casts on soil surface, especially on FOR and EUC microplots, induced a marked surface roughness and reduced the surface runoff. The production of casts was very limited in FAL and completely absent in CAS microplots. So it is evident that our results confirm the deleterious effects of cassava on soil and water conservation.     

Enzymatic activities and microbial biomass in soil as influenced by metalaxyl residues

A laboratory experiment was conducted to study the impact of metalaxyl application at different concentration levels on microbial biomass and the biochemical activities in soil. A dissipation study of metalaxyl highlighted 52.5-56.8% loss of metalaxyl due to the presence of microbial activity. However, a small but significant decline in microbial biomass was observed on 60 d of incubation period. Metalaxyl showed a highly significant effect in decreasing total N and organic C content in soil from 0 to 30 d of incubation. Dehydrogenase, phosphatase, urease, arylsulphatase and β-glucosidase activities were monitored in metalaxyl treated soils. Except urease, all the enzymatic activities initially increased and then decreased. Urease activity showed a continuous gradual decrease throughout the experimental period. Thus, metalaxyl might influence the growth and development of crop-plants, since it has direct impact on nutrient recycling and energy flow in soil.     

不同浸提剂以及保存方法对土壤矿质氮测定的影响

为探明影响土壤矿质氮测定的因素,从棕壤、潮土和黄棕壤3种类型土壤中各采集10个经不同施肥处理的土样,用连续流动注射分析仪测定经不同浸提剂以及不同保存方法处理后土样的NO3-N和NH4-N含量。结果表明:不论是棕壤、潮土还是黄棕壤,2 mol.L?1 KCl提取硝态氮的数量与0.01 mol.L?1 CaCl2提取的数量相关性均达到P<0.01水平;3种土壤各个土样硝态氮含量的测定值多表现为新鲜土<冷冻土<风干土;将鲜样浸提后作短时间的冷冻处理,其效果与鲜样24 h内的测定结果较接近;土样不同保存方式以及浸提液的保存时间对3种土壤NH4-N测定结果的影响规律不及NO3-N明显。