Enzyme activities and microbial community structure in semiarid agricultural soils

This study investigated the effect of management on -glucosidase, -glucosaminidase, alkaline phosphatase, and arylsulfatase activities and the microbial community structure in semiarid soils from West Texas, USA. Surface samples (0–5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton ( Gossypium hirsutum L.) or in cotton rotated with peanut ( Arachis hypogaea L.), sorghum ( Sorghum bicolor L.), rye ( Secale cereale) or wheat ( Triticum aestivum L.), and had different water management (irrigated or dryland), and tillage (conservation or conventional). The enzyme activities were higher in the loam and sandy clay loam than in the fine sandy loam. Soil pH was not affected by management, but the soil organic C and total N contents were generally affected by the different crop rotations and tillage practices studied. The trends of the enzyme activities as affected by management depended on the soil, but in general crop rotations and conservation tillage increased the enzyme activities in comparison to continuous cotton and conventional tillage. The soil enzyme activities were significantly correlated with the soil organic C ( r -values up to 0.90, P< 0.001), and were correlated among each other ( r -values up to 0.90, P <0.001). There were differences in the fatty acid methyl ester profiles between the fine sandy loam and the sandy clay loam and loam, and they reflected the differences in the enzyme activities found among the soils. For example, a 15:0 ranged from 1.61±0.25% in cotton-peanut/irrigated/no-till in the fine sandy loam to 3.86±0.48% in cotton-sorghum/dryland/conservation tillage in the sandy clay loam. There were no differences due to management within the same soil.Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS     

秸秆还田条件下腐熟剂对不同质地土壤真菌多样性的影响

为因地制宜鉴选适宜的秸秆腐熟剂,在西辽河平原灌区选择秸秆还田的砂壤土和中壤土连作玉米地,分别配施中农绿康腐熟剂、人元腐熟剂和农富康腐熟剂(简称中农、人元、农富康),以秸秆还田不施腐熟剂为对照,在玉米吐丝期取0～15 cm、15～30 cm、30～45 cm土层样品,采用高通量测序技术,研究不同质地土壤秸秆还田配施腐熟剂情况下土壤真菌群落结构的多样性。结果表明,砂壤土秸秆还田配施腐熟剂处理特有OTU(operational taxonomic units)数均比对照多,中壤土则相反。所有处理土壤中被孢霉门(Mortierellomycota)、子囊菌门(Ascomycota)、担子菌门(Basidiomycota)相对丰度较高;优势属均为被孢霉属(Mortierella)和低温酵母(Guehomyces)。不同腐熟剂对土壤质地产生不同影响,中壤土秸秆还田配施中农和农富康对土壤真菌组成及丰度无显著影响,而配施人元显著改变中壤土真菌组成及丰度;砂壤土秸秆还田配施中农和人元显著增加土壤真菌组成及丰度。LEfSe分析可知,砂壤土秸秆还田配施中农、中壤土秸秆还田配施人元和农富康3个处理土壤真菌多样性存在差异,对真菌多样性差异发挥显著性作用的门为担子菌门、子囊菌门,纲为伞菌纲(Agaricomycetes),目为腔菌目(Pleosporales)和伞菌目(Agaricales),种为Mortierella fimbricystis。这种响应差异也体现在同一腐熟剂对中壤土和砂壤土不同土层真菌的影响;随土层的下移,砂壤土和中壤土对照中被孢霉属相对丰度先增加后下降,低温酵母相对丰度下降;施用腐熟剂后(中壤土农富康除外),深层土壤低温酵母相对丰度比表层土壤高。砂壤土秸秆还田配施中农后0～15 cm土层中上述2个优势菌属相对丰度显著提高;而中壤土秸秆还田配施人元增加0～15 cm土层低温酵母相对丰度和15～30 cm、30～45 cm土层被孢霉属相对丰度。由此可见,秸秆还田条件下腐熟剂与土壤质地间响应不同,所以秸秆腐熟剂配施应因地制宜。     

CO2 fluxes and drivers as affected by soil type,tillage and fertilization

Abstract

Importance of agricultural practices for greenhouse gases mitigation is examined worldwide. However, there is no consensus on CO₂ emissions as affected by soil management practices. Deeper understanding of soil CO₂ fluxes and drivers under different management practices are needed. The investigation of net CO₂ exchange rate as dependent variable and drivers (soil water and temperature, air temperature) as affected by soil type (loam and sandy loam), tillage (conservation and no-tillage) and fertilization are presented.

Soil management practices and weather conditions affected the CO₂ flux through effects on soil water and temperature regime. Mean net CO₂ exchange rate on sandy loam was 8% higher than on loam. No-tillage, as a moisture-conserving tool, could be an appropriate tool for CO₂ emissions mitigation in any weather conditions on sandy loam; however, the advantage of no-tillage on loam was negligible. Mineral NPK fertilizers promoted significantly higher net CO₂ exchange rate in both soils, but suppressed it by 15% on sandy loam during a normal year. Effect of soil water content on net CO₂ exchange rate was direct in all tillage and fertilization treatments in both loam and sandy loam, whereas this effect was positive only in dry and normal weather conditions. In wet weather conditions, the direct effect of soil water content on net CO₂ exchange rate was negative. Soil and air temperature acted indirectly on net CO₂ exchange rate. The increase in temperature markedly suppressed the positive direct impact of soil water content on net CO₂ exchange rate in dry weather conditions, but did not reduce the direct effect of soil water content in normal weather conditions. In a wet year the negative indirect effect of increased temperature enhanced the negative direct impact of soil water surplus on net CO₂ exchange rate.     

Response of maize (Zea mays L.) and mungbean (Vigna radiata L.) to tillage in relation to water table depth in tropical lowland rice soils

The effects of zero, minimum and conventional tillage on soil physical properties and on the growth and yield of mungbean (Vigna radiata L.) grown after lowland rice (Oryza sativa L.) were studied in field experiments conducted during the 1984 and 1985 dry seasons (DS) at two Philippine sites (clay loam, Vertic Tropaquept, with shallow water table and sandy loam, Aeric Tropaquept, with deep water table). Effects on maize (Zea mays L.) were studied only in 1984 on clay loam soil.All parameter measurements were not significantly different with minimum and conventional tillage. Tillage, averaged over minimum and conventional and in both seasons, significantly lowered bulk density (10%) and increased aeration porosity (120%) of the 0–0.10 m clay loam soil layer. In sandy loam soil in 1985, it decreased bulk density by 7% and increased aeration porosity by 61%. Tillage only slightly affected the matric suction, strength and temperature of both soils.Maize seedling emergence was 15% higher with zero tillage than with minimum and conventional tillage. Tillage, however, did not affect mungbean emergence. It significantly increased maize plant height (42%) and root length (61%) as compared with no tillage. In mungbean, tillage increased plant height (18%) and root length (60%), as averaged over both sites and seasons. In clay loam soil, tillage increased grain yield of maize by 242%. On the same field, tillage increased mungbean grain yield by 78% in 1984 and 20% in 1985. In sandy loam, tillage produced 38% more mungbean grains than without tillage.     

Effect of Induced Soil Compaction on Changes in Soil Properties and Wheat Productivity under Sandy Loam and Sandy Clay Loam Soils: A Greenhouse Experiment

The continuous use of heavy machinery and vehicular traffic on agricultural land led to an increase in soil compaction, which reduces crop yield and deteriorates the physical conditions of the soil. A pot experiment was conducted under greenhouse conditions to study the effects of induced soil compaction on growth and yield of two wheat (Triticum aestivum) varieties grown under two different soil textures, sandy loam and sandy clay loam. Three compaction levels [C₀, C₁, and C₂ (0, 10 and 20 beatings)], two textural classes (sandy loam and sandy clay loam), and two genotypes of wheat were selected for the experiment. Results indicated that induced soil compaction adversely affected the bulk density (BD) and total porosity of soil in both sandy loam and sandy clay loam soils. Compaction progressively increased soil BD from 1.19 Mg m^?3 in the control to 1.27 Mg m^?3 in C₁ and 1.40 Mg m^?3 in C₂ in sandy loam soil while the corresponding increase in BD in sandy clay loam was 1.56 Mg m^?3 in C₁ and 1.73 Mg m^?3 in C₂ compared to 1.24 Mg m^?3 in the control. On the other hand, compaction tended to decrease total porosity of soil. In case of sandy loam, porosity declined by 5% and 17% in C₁ and C₂, respectively, and declined in sandy clay loam by 29% and 54%, respectively. Averaged over genotypes and textures, shoot length decreased by 15% and 26% at C₁ and C₂, respectively, and straw yield decreased by 21% and 61%, respectively. The compaction levels C₁ and C₂ significantly decreased grain yield by 12% and 41%, respectively, over the control. The deleterious effect of compaction was more pronounced on root elongation and root mass, and compaction levels C₁ and C₂ decreased root length by 47% and 95% and root mass by 41% and 114%, respectively, over the control. Response of soil texture to compaction was significant for almost all the parameters, and the detrimental effects of soil compaction were greater in sandy clay loam compared to sandy loam soil. The results from the experiment revealed that soil compaction adversely affected soil physical conditions, thereby restricting the root growth, which in turn may affect the whole plant growth and grain yield. Therefore, appropriate measures to avoid damaging effects of compaction on soil physical conditions should be practiced. These measures may include soil management by periodic chiseling, controlled traffic, conservation tillage, addition of organic manures, and incorporating crops with deep tap root systems in a rotation cycle.     

Desorption behaviour of lead in two calcareous soils as affected by Pb level without and with compost supply

A laboratory study was performed to investigate the influence of soil texture (sandy loam vs. clay loam), Pb supply (as Pb(NO₃)₂ without or with compost) and Pb levels on the extraction of available Pb by diethylene triamine pentaacetic acid (DTPA) and its desorption patterns at ten shaking periods. The soils were polluted with five Pb levels without or with compost and incubated for 1 month. Kinetic models commonly used to study the release of the nutrients were used in this study. Results showed that Power function model described the pattern of Pb desorption better than other models. The amount of extracted Pb increased as the Pb levels increased and was found to be higher in sandy loam soil treated with Pb without compost than that of clay loam soil treated with Pb with compost. The a value (Pb desorption constant) was the highest in sandy loam soil amended with Pb without compost. The lowest value of a, however, was observed in clay loam soil amended with Pb with compost. The ab coefficient (initial desorption rate of Pb) was higher in sandy loam than clay loam soil, demonstrating higher initial release rates of Pb in the coarser-textured soil. Addition of Pb without compost resulted in a higher increase in ab value in comparison with Pb with compost, in both the soils.     

Effect of tillage and residue management on properties of two coarse-textured soils and on yield of irrigated wheat and groundnut

Changes in soil properties and yield response in relation to tillage and residue management treatments in an irrigated groundnut (Arachis hypogea L.)—wheat (Triticum aestivum, L.) rotation on a sandy soil (1972–1974) and on a sandy loam soil (1974–1976) were evaluated. Tillage treatments (T₁ and T₂) did not cause significant changes in soil properties. Incorporation of crop residues (5 t residue per ha per crop, T₃) caused a substantial increase in organic C, available N, and NaHCO₃ -extractable P contents in the top 15 cm of both soils. Residue management treatments (T₃, T₄ and T₅) showed no significant effect on soil bulk density and exchangeable K. Crop yields under no-tillage (T₁) and conventional tillage (control, T₂) were comparable on sandy soil but on the sandy loam soil, no-tillage yielded significantly lower than conventional tillage. Compared with the control, incorporation of crop residues (T₃) caused higher yields on sandy soil for groundnut and wheat by 34.1 and 47.4%, respectively, and on sandy loam by 17.1 and 7.2%, respectively. Mulching with crop residues conserved soil moisture and reduced maximum soil temperature (1.5–5.3°C in groundnut and 1.5–2.9°C in wheat) but other measured soil properties were not significantly affected. Significant yield increase due to residue mulching (T₄) was observed in sandy soil but it was significantly less than when total crop residue was incorporated (T₃). Increased wheat root-weight density in the top 15 cm soil with residue mulching was not reflected in grain yield. Compared with the incorporation of the total amount of crop residue (T₃), incorporation of half the amount and application of the other half as mulch (T₅) caused lower yields — on sandy soil for groundnut and wheat by 31.5 and 15.7%, respectively, and on sandy loam by 4.8 and 3.6%, respectively.     

Turnover of root-derived material and related microbial biomass formation in soils of different texture

Wheat plants were grown on two soils of different texture, a sandy soil and a silty clay loam, in an atmosphere containing ¹⁴CO₂. The ¹⁴C and total C content of the shoots, roots, soil rhizosphere CO₂ and soil microbial biomass were measured 21, 28, 35 and 42 days after germination. There was a pronounced effect of soil texture on the turnover of root-derived C through the microbial biomass. Turnover was relatively fast and at a constant rate in the sandy soil but slowed down in the clay soil, following an initial high assimilation of root products into the microbial biomass.Four percent of the total fixed ¹⁴C was retained in the clay loam after 6 weeks compared with a corresponding value of 1.2% for the sandy soil. The proportion of fixed ¹⁴C recovered as rhizosphere CO₂ at each of the sampling times was relatively constant for the sandy soil (ca 19%) but decreased from 17% at day 28 to 11% at day 42 in the clay soil. The proportion of total fixed ¹⁴C in the soil biomass as measured by a fumigation technique increased to a maximum value of 20% after 6 weeks in the sandy soil but decreased in the clay soil from 86% at day 21 to 26% after 42 days plant growth.     

Influence of ammonia fertilization on cotton production in conservation tillage systems

Abstract

Field studies were conducted to determine the influence of ammonia fertilization on cotton grown in conservation tillage systems. The studies were located on a Decatur silt loam (Rhodic Paleudult) in the Limestone Valley and a Norfolk sandy loam (Typic Paleudult) in the Coastal Plain of Alabama. Winter annual legumes, crimson clover (Trifolium incarnatum L. at the Norfolk site) and hairy vetch (Vicia villosa Roth at the Decatur site) were established as whole plots along with a winter fallow area. Sources of fertilizer differing widely in their NH₄+‐N contents were used for split plot treatments applied at time of cotton (Gossypium hirsutum L.) planting. Fertilizer treatments included calcium nitrate, ammonium nitrate, urea, urea with dicyandiamide, and a no N check. The cotton was planted with a strip‐till conservation planter. Nitrogen production by winter legumes was adequate to meet N requirements for cotton on the Decatur silt loam (67 kg N/ha) but not at the Norfolk sandy loam site (101 kg N/ha). Cotton populations were 24% higher in fallow than legume whole plots. Differences in plant growth and N concentrations were highly variable and treatment trends were not found. Seed cotton yields were 4% higher in fallow than legume plots. Maximum populations and yields were achieved with ammonium nitrate in fallow area and urea in legume areas.     

Effects of thiamine and nitrogen fertilizer form on the number of N2−fixing and total bacteria in the rhizosphere of maize plants

The effects of thiamine (vitamin B1) application as seed dressing and of N form supplied (NH₄⁺ versus NO₃^?) on rhizosphere pH and on rhizosphere microorganisms were evaluated in two different soils. Imbibition of maize (Zea mays L.) seeds with thiamine (1 g kg^?1) increased seed thiamine content by a factor of 370. Maize plants from untreated and treated seeds were cultivated in a growth chamber under controlled conditions for 10 d in a sandy loam soil, pH 7.1 (Mascherode soil) or in a sandy soil, pH 4.8 (Niger soil) fertilized with two different N sources (NO₃?N or NH₄?N with dicyandiamide, 100 and 250 mg N kg^?1 soil). The rhizosphere pH was not affected by thiamine, only slightly affected by N source in the Mascherode soil, but markedly affected in the Niger soil. Thiamine application and N source affected the most probable number (MPN) of diazotrophs and total bacteria isolated from the rhizosphere soil of 10 d old maize plants. In the Mascherode soil, thiamine application increased MPN of diazotrophs 4-fold and total bacteria 2-fold when the soil was fertilized with 100 mg NO₃?N compared to untreated seedlings. Compared to Mascherode soil, in the Niger soil, MPN of diazotrophs was extremely low, especially after NH₄?N treatment which significantly decreased pH of the rhizosphere. Thiamine application had only marginal effects on the MPN of diazotrophs and total bacteria. Total bacteria isolated from Niger soil fertilized with NH₄?N were about 10-fold lower compared to the soil from Mascherode. However, in the other two treatments, total bacteria were higher in the Niger soil compared to the Mascherode soil. In the Niger soil, apparently some of the heterotrophs (the Actinomycetes dominated in this soil) might have suppressed the diazotrophs. The results of the present study demonstrate that in many cases seed treatment with thiamine enhances MPN of diazotrophs and total bacteria in the rhizosphere of maize seedlings.     

A study of some tillage practices for sustainable crop production in India

Soil tilth has been defined in terms of a ‘Physical Index’ based on the product of the ratings of eight physical properties — soil depth, bulk density, available water storage capacity, cumulative infiltration or apparent hydraulic conductivity, aggregation or organic matter, non-capillary pore space, water table depth and slope. The Physical Index and a tillage guide were used to identify the tillage requirements of different soils varying in texture from loamy sand to clay in the semi-arid tropics. The physical index was 0.389 for a loamy sand, 0.518 for a black clay loam and 0.540 for a red sandy loam soil and the cumulative rating indices in summer and winter seasons were 45 and 44 for loamy sand, 52 and 51 for red sandy loam and 54 and 52 for black clay loam soils, respectively. The compaction of the loamy sand by eight passes of a 490 kg tractor-driven roller (0.75 m diameter and 1.00 m length) increased the physical index to 0.658 and chiselling of the red sandy loam and black clay loam increased the physical indices to 0.686 and 0.729, respectively. The grain yields of rainfed pearl millet and guar and irrigated pearl millet, wheat and barley increased significantly over the control (no compaction) yields by compaction.

The chiselling of the soils varying in texture from loamy sand to clay at 50 to 120-cm intervals up to 30–40 cm depth, depending upon the row spacing of seedlines and depth of the high mechanical impedance layer, increased the grain yields of rainfed and irrigated maize on alluvial loamy sand, rainfed maize on alluvial sandy loam and red sandy loam, rainfed sorghum on red sandy loam and black clay loam, irrigated sorghum on black clay loam and rainfed black gram on red sandy loam, pod yield of rainfed groundnut, tuber yield of irrigated tapioca and fresh fruit yield of rainfed tomato on red sandy loam and sugarcane yield on black clay soil, significantly over the yields of no-chiselling systems of tillage such as disc harrow and country plough.     

Conservation tillage and optimal water supply enhance microbial enzyme (glucosidase,urease and phosphatase) activities in fields under wheat cultivation during various nitrogen management practices

Field experiments were conducted on sandy clay loam soil at New Delhi, during the winter season of 2007 and 2008 to investigate the effect of tillage, irrigation regimes, i.e. sub-optimal, optimal and supra-optimal water supply, and integrated nutrient management practices (INM) on soil enzymatic activities after cultivation of wheat (Triticum aestivum). Soil glucosidase (54.5%), urease (88.8%), acid phosphatase (97.4%) and alkaline phosphatase (85.3%) activities increased significantly under conservation tillage compared with conventional tillage fields. An optimal water supply (i.e. three irrigations) led to a significant increase in soil enzymatic activity over sub-optimal (i.e. two) and supra-optimal (five) irrigation. Urease activity was slightly lower in the sub-optimal irrigations, but higher in supra-optimal irrigations by 15.5% than in optimal irrigation in conventional tillage. This study suggests that inorganic and organic nutrient combinations with conservation tillage and optimal water supply significantly improved soil enzymatic activities.     

Effects of seed priming with plant growth-promoting rhizobacteria on wheat yield and soil properties under contrasting soils

In the present investigation, different strains of Plant growth-promoting rhizobacteria (PGPR), namely Bacillus megaterium, Pseudomonas fluorescens and Bacillus subtilis were evaluated for their growth-promoting effects on wheat as well as on soil properties under field conditions at two different sites having sandy loam and silt loam type of soils. PGPR strains were evaluated either singly or in consortia. Amongst all the treatments, wheat inoculated with consortia was found most effective as it increased grain yield up to 53% over control in silt loam soil, whereas, corresponding effects in sandy loam soil were less pronounced as an increase of 31% was observed in corresponding treatments, respectively. Enhanced effects on soil properties were also more intense in silt loam as there was an increase of 205% organic matter as against sandy loam soil where this value was 110%.     

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.     

Effects of alternative tillage systems on soil quality and yield of spring cereals on silty clay loam and sandy loam soils in the cool, wet climate of central Norway

Tillage trials were established on a poorly drained silty loam overlying silty clay loam and on a freely drained sandy loam overlying medium sand, in 1988 and 1989, respectively. Autumn and spring ploughing and two ploughless systems were compared for 12–13 years, with three replications at each site. The ploughless treatments comprised deep versus shallow spring harrowing until 1999, and thereafter autumn plus spring harrowing versus spring harrowing only. In 6 years, treatments with and without fungal spraying of the cereal crops were included. In other years, fungicides were not used. Perennial weeds were controlled by herbicides as necessary, on nine occasions up until 2001. Average spring barley (Hordeum vulgare L.) and spring oat (Avena sativa L.) yields were similar with spring ploughing as with autumn ploughing at both sites. In treatments without ploughing, average yields on the silty loam over clay were 93% of those obtained with ploughing, and on the sandy loam over sand they were 81%. Smaller and non-significant yield differences were found between spring harrowing versus deep spring harrowing, and between autumn plus spring harrowing versus spring harrowing only. Fungal spraying increased yields markedly at both sites (25%), but there was no significant interaction between this treatment and tillage system. Oat was compared with barley in 2 years, with oat performing better under ploughless tillage. At both sites increases in penetrometer resistance occurred in the topsoil of unploughed treatments. These were considered particularly limiting on the sandy loam. On the silty loam there was an increase in surface horizon porosity in the absence of ploughing, which was associated with an increase in topsoil organic matter content. On this soil there was also a tendency toward lower penetrometer resistance at >30 cm depth on autumn plus spring harrowed soil than on ploughed soil, indicating that the plough pan may have diminished. This was supported by observations of greater earthworm activity on unploughed soil. Soil chemical analyses revealed that mineral N and plant-available P and K accumulated in the upper horizon under ploughless tillage. The percentage yields obtained in individual years with autumn as opposed to spring ploughing, were positively correlated with air temperature during 0–4 weeks after planting on the silty loam, and with precipitation during 0–12 weeks after planting on the sandy loam. In the case of yields obtained with spring harrowing only, relative to spring ploughing, positive correlations were found with 0–4 week temperature on both soil types, suggesting that low early season temperatures may limit yields under ploughless tillage.     

Influence of phosphorus application on growth and cadmium uptake of spinach in two cadmium‐contaminated soils

A pot experiment was conducted to investigate the influence of phosphate (P) application on diethylene triamine pentaacetic acid (DTPA)–extractable cadmium (Cd) in soil and on growth and uptake of Cd by spinach (Spinacia oleracea L.). Two soils varying in texture were contaminated by application of five levels of Cd (NO₃)₂ (0, 20, 30, 40, and 60 mg Cd kg^–1). Three levels of KH₂PO₄ (0, 12, and 24 mg P kg^–1) were applied to determine immobilization of Cd by P. Spinach was grown for 60 d after seeding. Progressive contamination of soils through application of Cd affected dry‐matter yield (DMY) of spinach shoot differently in the two soils, with 67% reduction of DMY in the sandy soil and 34% in the silty‐loam soil. The application of P increased DMY of spinach from 4.53 to 6.06 g pot^–1 (34%) in silty‐loam soil and from 3.54 to 5.12 g pot^–1 (45%) in sandy soil. The contamination of soils increased Cd concentration in spinach shoots by 34 times in the sandy soil and 18 times in the silty‐loam soil. The application of P decreased Cd concentration in shoot. The decrease of Cd concentration was higher in the sandy soil in comparison to the silty‐loam soil. Phosphorus application enhanced DMY of spinach by decreasing Cd concentration in soil as well as in plants. The results indicate that Cd toxicity in soil can be alleviated by P application.     

Influence of growth-promoting bacteria on the growth of wheat in different soils and temperatures

Plant-growth-promoting bacteria isolated from the rhizosphere, phyllosphere and soil of the root zone in different climatic regions of Germany and Uzbekistan were analysed for plant-growth-promoting effects and nutrient uptake on winter wheat on different soils and under different temperature regimes. The investigations were carried out in pot experiments using loamy sand and sandy loam soils from Müncheberg, Germany and Calcisol soil from Tashkent, Uzbekistan. The temperature and soil types were found to influence growth-promoting effects. Inoculation with bacterial strains Pseudomonas fluorescens PsIA12, Pantoea agglomerans 050309 and Mycobacterium sp. 44 isolated from Müncheberg (semi-continental climate) was found to significantly increase the root and shoot growth of winter wheat at 16 °C compared to 26 °C in loamy sand. Mycobacterium phlei MbP18 and Mycoplana bullata MpB46 isolated from Tashkent (semi-arid climate) were found to significantly increase the root and shoot growth of winter wheat in nutrient-poor Calcisol at 38 °C as well as in nutrient-rich loamy sand at 16 °C. Bacterial inoculation also resulted in significantly higher N, P, and K contents of plant components. The bacteria isolates were able to survive in the rhizosphere and in the soil of winter wheat after root and shoot inoculation.     

干粉PAM溶解时间对土壤饱和导水率的动态影响

本试验选取两种质地土壤(黏壤土和砂壤土),采用3种干粉PAM施用水平(0、22.5 kg/hm~2和45 kg/hm~2),测定土样在10.25 mm/h入渗速度下的土壤饱和导水率(KS),然后根据土样团聚体含量和稳定性及团聚结构的微观图片,分析干粉PAM影响下土壤结构的变化特征,进而说明干粉PAM溶解时间对KS的影响机理。结果表明:施用PAM后,KS随干粉PAM在水中溶解时间的延长而逐渐减小,最终趋于稳定;干粉PAM溶解时间较短时,PAM处理的KS高于对照,其中PAM施用水平45 kg/hm~2时砂壤土KS提高幅度最大,较对照提高26.87%,但不同PAM施用量处理间的KS差异不显著。干粉PAM溶解时间足够长时,PAM处理的KS均显著低于对照,其中PAM施用水平45 kg/hm~2时黏壤土KS降低幅度最大,较对照降低10.86%,但是不同施用量处理间KS差异不显著。从影响机理上分析,PAM主要是通过增加土壤团聚体含量及稳定性来提高KS;而干粉PAM溶解时间足够长时,由于PAM易吸附土壤颗粒,水解后的PAM分子链不断伸张延长,堵塞了土壤孔隙,加上PAM本身的黏滞特性,从而降低了KS。研究干粉PAM溶解时间对KS的动态影响,可以为PAM在改善土壤导水能力方面的应用提供理论依据。