Effects of glucose and rhizodeposits (with or without cysteine-S) on immobilized-35S, microbial biomass-35S and arylsulphatase activity in a calcareous and an acid brown soil

Our aim was to study the effects of C (as glucose and artificial rhizodeposits) on S immobilization, in relation to microbial biomass‐S and soil arylsulphatase (ARS) activity, in contrasting soils (a calcareous and an acid brown soil). The glucose‐C and artificial rhizodeposit‐C with or without cysteine were added at six rates (0, 100, 200, 400, 600 and 800 mg kg^?1 soil) to the two soils and then incubated with Na₂³⁵SO₄ for 1 week prior to analysis. The percentages of ³⁵S immobilized increased when C as glucose and rhizodeposit (without cysteine) were added to both soils. With cysteine‐containing rhizodeposit, the percentages of ³⁵S immobilized remained relatively stable (23.5% to 29.9%) in the calcareous soil, but decreased in the acid brown soil (52.7% to 31.5%). For both soils, cysteine‐containing rhizodeposit additions showed no significant correlation between immobilized‐³⁵S and microbial biomass‐³⁵S, suggesting that microorganisms immobilized cysteine‐S preferentially instead of ³⁵S from the tracer (Na₂³⁵SO₄). In the calcareous soil, a positive and significant correlation was found between ARS activity and microbial biomass‐³⁵S (r = 0.85, P < 0.05) when glucose was added. We also saw this correlation in the acid brown soil when rhizodeposit‐C without cysteine was added (r = 0.90, P < 0.05). Accordingly, the results showed the presence of extracellular arylsulphatase activity of 48.7 mg p‐nitrophenol kg^?1 soil hour^?1 in the calcareous soil and of 27.0 mg p‐nitrophenol kg^?1 soil hour^?1 in the acid brown soil.     

Die Rolle der mikrobiellen Biomasse und des mineralisch fixierten Ammoniums bei den Stickstoff-Transformationen in niedersächsischen Löß-Ackerböden unter Winter-Weizen. I. Poolgrößenveränderungen

Significance of microbial biomass and non-exchangeable ammonium with respect to the nitrogen transformations in loess soils of Niedersachsen during the growing season of winter wheat. I. Change of pool sizes Nitrogen transformations in loess soils have been examined by laboratory and field experiments. After straw application (· 8 t · ha^?1), N in microbial biomass (N_mic) increased by about 20 mg · kg^?1 soil (· 90 kg N · ha^?1 · 30 cm^?1) after 9 days of incubation (20 °C). Another laboratory experiment yielded an increase of about 400 mg of NH₄+-N · kg^?1 fixed by minerals within 1 h after addition of 1 M NH₄+-acetate. Defixation of the recently fixed NH₄+ after addition of 1 M KCl amounted to only 60 mg · kg^?1 within 50 days. In a field experiment with winter wheat 1991, an increase in N_mic of about 80 kg N · ha^?1 · 30 cm^?1 was observed from March to June. After July, growth of the microbes was limited by decreased soluble carbon concentrations in the rhizosphere. Different levels of mineral N-fertilizer (0, 177 and 213 kg N · ha^?1) did not affect significantly the microbial biomass. The same field experiment yielded a decrease of non-exchangeable ammonium on the “zero”-fertilized plot in spring by 200 kg N · ha^?1 · 30 cm^?1. The pool of fixed ammonium increased significantly after harvest. After conventional mineral N-fertilizer application (213 kg N · ha^?1). NH₄+-defixation was only about 120 kg N · ha^?1 · 30 cm^?1 until July.     

Appropriate nitrogen supply could improve soil microbial and chemical characteristics with Sophora davidii seedlings cultivated in water stress conditions

Abstract

A greenhouse experiment was conducted to investigate the changes of soil microbial activities and chemical properties under different water and nitrogen (N) supply conditions. A completely randomized design was subjected to three water regimes (80%, 40% and 20% water field capacity (FC)) and three N supply regimes (control, N0: 0 mg N kg^?1 soil; low N supply, Nl: 92 mg N kg^?1 soil; and high N supply, Nh: 184 mg N kg^?1 soil) by potting with 2-month-old Sophora davidii seedlings. Water stress decreased the content of soil organic carbon (C), available N and phosphorus (P), the ratio of C/N, the ratio of C/P, as well as activities of soil invertase, urease and alkaline phosphatase, but not reduced microbial biomass C, N and P contents. Soil microbial and chemical characteristics also exhibited strong responses to N supply, and these responses were inconsistent among N supply levels. The contents of soil organic C and available P showed stronger positive responses to Nl than to Nh, while the available N content increased with increasing N supply. Additionally, Nl rather than the other two N treatments led to increased microbial biomass N and invertase activity under 20% FC treatment, even though the invertase activity increased in Nh treatment under 40% FC and 80% FC treatments. Nl treatment also increased the C/P ratio and alkaline phosphatase activity. These results suggest that water and N co-limited nutrient mineralization and microbial activity, and that these characteristics responded positively to Nl. Therefore, appropriate or low N supply is recommended to increase soil quality restrained by water stress, thereby facilitating S. davidii seedling establishment under water deficit conditions.     

Microbiological and biochemical characteristics of a range of New Zealand soils under established pasture

Twenty one topsoils, selected to represent major New Zealand soil groups were collected from developed, grazed pasture and examined for microbiological and biochemical characteristics. Organic C and total N levels ranged from 2.4–46% (mean 8.7%) and 0.22–2.31% (mean 0.65%), respectively. The characteristics examined included microbial biomass (mean 1240 μg Cg^?1 soil), min-N flush (mean 85 μg N g^?1 soil), microbial P (mean 52 μg P g^?1 soil), min-N and CO₂ produced, nitrification index, urease, protease, phosphatase and arylsulphatase activities. Most of these characteristics were generally higher than the values already published possibly due to high levels of organic matter.Principal component analysis of the correlation matrix showed two distinct groups of characteristics: CO₂ produced, N mineralized, total N, organic C, microbial biomass, microbial P and phosphatase comprising one group and arylsulphatase, min-N flush, urease and nitrification index comprising the other group. Protease activity and soil pH were not strongly associated with each other or the other groups.     

Soil Fertility Index,Soil Evaluation Factor,and Microbial Indices under Different Land Uses in Acidic Soil of Humid Subtropical India

A study was conducted to examine the impact of land use on soil fertility in an Entisol in the Jalpaiguri District of humid subtropical India. The natural forest served as a control against which changes in soil properties were compared. Soil samples were collected from four different depths (0–25, 25–50, 50–75, and 75–100 cm) of soil from four land uses (viz. forest, home garden, arecanut plantation, and agriculture) and examined for pH, organic carbon (OC), electrical conductivity (EC), cation exchange capacity, available nitrogen (N), phosphorus (P), exchangeable calcium (Ca), magnesium (Mg), potassium (K), aluminum (Al), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and dehydrogenase activity (DHA). Soil pH (5.7), OC (2.29%), N (386 kg ha^?1), and P (22.54 kg ha^?1) were greatest in forest soil, followed by soil from arecanut plantation, agriculture, and home garden. The greatest Ca (0.892 cmol kg^?1), Mg (0.527 cmol kg^?1), and Al (1.86 cmol kg^?1) were found in the arecanut plantation, whereas K (0.211 cmol kg^?1) was greatest in forest. The greatest content of diethylenetriaminepentaacetic acid–extractable copper, zinc, manganese, and iron (2.25, 1.66, 4.86, and 7.65 ppm, respectively) were found in forest. MBC (558 mg kg^?1), MBN (26.67 mg kg^?1), and DHA (33.03 μg TPF 24 h^?1 g^?1) was greatest in forest soil. Soil fertility index varied from 13.13 in arecanut plantation to 18.49 in forest. The soil evaluation factor ranged from 5.32 in agriculture to 6.56 in forest. Pearson's correlation matrix revealed strongly significant positive correlation of soil fertility index and soil evaluation factor with soil properties.     

Microbial Biomass and Tolerance of Microbial Community on an Aged Heavy Metal Polluted Floodplain in Japan

The objective of the present study was to increase understanding of the effects of heavy metal pollution and soil properties on microorganisms in relation to the biomass and microbial functional community. Soil samples were collected from aged polluted and reference sites on a floodplain. The soil Cu, Zn and Pb total concentrations were much higher at the polluted sites (average 231.6–309.9 mg kg^?1, 195.7–233.0 mg kg^?1, and 72.4–86.0 mg kg^?1, respectively) than at the reference site (average 33.3–44.0 mg kg^?1, 76.7–98.0 mg kg^?1, and 30.8–41.6 mg kg^?1, respectively), while the available heavy metal concentrations in CaCl₂ extraction were similar in all sites. Small seasonal variations in the size of microbial biomass were observed. Ambient soil properties (e.g. total C, N, pH, moisture content, and CEC) affected the soil microbial biomass more than the heavy metal pollution. However, the aged pollution tended to impact on the composition of the microbial community. PICT (pollution-induced community tolerance) test using BIOLOG Ecoplates showed enhanced tolerance of the microbial community to Cu stress in the polluted site. In non polluted but low nutrient, low pH and low moisture soil, the microbial biomass was lower and the microbial community was more vulnerable to Cu stress. In spite of the low heavy metal availability due to ageing, the BIOLOG technique provided sensitive detection of microbial community level changes in PICT analysis.     

Influence of lanthanum on microbial biomass C,P and C- and P-cycling enzyme activities in tea garden soil

At present, reports of the effect of lanthanum on nitrogen cycling in the soil are very detailed, but information on carbon (C) and phosphorus (P) cycling is less reported. We present an investigation into the effects of lanthanum on the pH, microbial biomass C and P and enzyme activities (such as that of β-glucosidase, peroxidase, polyphenol oxidase, acid phosphomonoesterase, phosphodiesterase and phosphotriesterase) in soil in an indoor culture experiment. The results show that the application of lanthanum decreased the pH and had an inhibitory effect on microbial biomass C and P throughout the experiment. The application of lanthanum significantly inhibited most of enzyme activities at the 14th day of the experiment. However, soil samples treated with 100 mg kg^?1 of lanthanum significantly stimulated the activity of polyphenol oxidase at the 14th day, and the range 100–300 mg kg^?1 stimulated the activities during the 28th day to the 56th day. From the 42nd to the 56th day, the pH and all enzyme activities gradually increased. We inferred that the lanthanum had different effects on microbial biomass C and P and enzymes. We recommended that the amount of the rare earth element applied in a tea garden should be lower than 100 mg kg^?1.     

氮素浓度和水分对水稻土硝化作用和微生物特性的影响

为了明确不同氮素浓度和水分对土壤硝化作用和微生物特性的影响,特别是高氮素浓度下的响应特异性,以红壤水稻土为供试土壤,设置4个硫铵用量水平[0(CK)、120 mg(N).kg-1(A1)、600 mg(N).kg-1(A2)、1 200 mg(N).kg-1(A3)],调节土壤水分为饱和持水量(WHC)的40%、60%和80%,研究了短期内不同氮素浓度和不同水分条件下土壤硝化作用、微生物生物量碳和微生物功能多样性的变化。结果表明:在40%、60%和80%WHC水分条件时,硫铵A2、A3浓度处理土壤硝化率和硝化速率普遍较低,硫铵A1浓度处理硝化率和硝化速率随土壤含水量的升高而升高;同含水量时随硫铵用量的升高而显著降低。在40%、60%和80%WHC水分条件时,微生物生物量碳随硫铵浓度的升高而降低;同浓度硫铵用量水平时,微生物生物量碳的变化基本表现为:60%WHC80%WHC40%WHC。分析发现不同水分和硫铵处理之间存在交互作用。BIOLOG分析显示:不同氮素浓度和不同水分处理,60%WHC下A1处理的平均吸光值(AWCD)和Shannon、Simpson、McIntosh指数最大,其次为60%WHC的硫铵CK处理,而不同水分下硫铵A2、A3处理,其AWCD值和Shannon、Simpson、McIntosh多样性指数都较低,进一步说明过量施肥导致微生物活性降低。不同氮素浓度和水分条件下土壤微生物和生化性状不同,过量施用化肥后将有可能造成土壤微生物性状和生化功能衰减。     

Effect of lead pollution on soil microbiological index under spinach (Spinacia oleracea L.) cultivation

Purpose

Lead (Pb) pollution is appearing as an alarming threat nowadays in both developed and developing countries. Excessive Pb concentrations in agricultural soils result in minimizing the microbiological activities which leads to the decrease in crop production. A pot experiment was conducted with the purpose to examine the deleterious effect of Pb on microbiological index under spinach cultivation.

Materials and methods

Pb was added to 5 kg soil in each pot (with 6 seeds/pot) using Pb(NO₃)₂ at the rate of 0, 150, 300, 450, and 600 mg kg^?1 with three replications in completely randomized design. All soil microbial, enzymatic, and chemical properties and plant growth parameters and nutrient uptake were measured by standard methods.

Results and discussion

Both soil and plant measured parameters decreased after the addition of Pb (150, 300, 450, and 600 mg Pb kg^?1 soil) treatments with the passage of time (from 15 to 60 days) compared with control (CK). However, high Pb levels had more suppressive effect, therefore, highest Pb level (600 mg Pb kg^?1 soil) significantly (P?<?0.05) decreased the microbial biomass carbon (5.59-fold); microbial biomass nitrogen (N; 11.71-fold); microbial biomass phosphorus (P; 25.1-fold); dehydrogenase (4.02-fold); phosphatase (9.40-fold); urease (9.26-fold); pH (1.40-fold); spinach shoot (2.17-fold) and root (2.54-fold) length; shoot (2.36-fold) and root (2.69-fold) fresh weight; shoot (3.90-fold) and root (3.50-fold) dry weight; chlorophyll content (5.60-fold); carotenoid content (4.29-fold); plant macronutrients uptake, i.e., N (4.38- and 2.97-fold), P (3.88- and 6.58-fold), K (3.88- and 4.6-fold), Ca (6.60- and 6.70-fold), and Mg (5.57- and 4.45-fold); and plant micronutrient uptake, i.e., Zn (2.39- and 3.05-fold), Cu (3.70- and 2.62-fold), Fe (4.13- and 3.23-fold), and Mn (4.17- and 4.09-fold) in spinach shoot and root, respectively. Conversely, highest Pb level, i.e., 600 mg Pb kg^?1 soil significantly (P?<?0.05) increased the biomass carbon (C)/nitrogen (N) (4.69-fold) and C/P (6.01-fold) ratios, soil extractable Pb (5.87-fold), and Pb uptake in spinach shoot (3.58-fold) and root (4.38-fold), respectively, at the end of the experiment, i.e., day 60.

Conclusions

Pb contamination significantly decreased the soil microbial and enzymatic activities, pH, spinach plant growth, and nutrients uptake in all the samples spiked with Pb. The degree of the influence increased with the increased Pb concentrations and incubation time, showing that Pb threshold is strongly associated with the extent of Pb concentration and time to accumulate. The soil microbial biomass, enzymatic activities, pH, and spinach physiological indices, could be used as a sensitive indicators to reflect environmental stress in soil ecosystems.     

Effects of microbial inoculations on soil chemical,biochemical and microbial biomass carbon of cassava (Manihot esculenta Crantz) growing Vertisols

Cassava is an important subsidiary food in the tropics. In Tamil Nadu, India, microbial cultures were used to eradicate the tuberous root rot of cassava. Hence, an experiment was conducted for two consecutive years to test the effects of coinoculation of microbes on soil properties. The surface soil from the experimental site was analysed for soil available nutrients, soil enzyme activities and microbial biomass carbon. The treatment of Azospirillum with Trichoderma at the 50% recommended N:P₂O₅:K₂O (NPK) rate (50:25:50 kg ha^?1) significantly increased soil available nitrogen (142.81 kg ha^?1) by 72.66% over uninoculated control. There was a significant increase in available phosphorus in soil by the inoculation of AM (arbuscular mycorrhizal) fungi with Trichoderma at the 50% recommended NPK rate (41.04 kg ha^?1) compared to other treatments. The application of Pseudomonas fluorescens with Trichoderma at the 50% recommended NPK rate significantly increased available iron (19.34 µg g^?1) in soil. The treatment of Azospirillum with Trichoderma increased urease enzyme activity at the recommended NPK rate (816.32 μg urea hydrolyzed g^?1 soil h^?1). Soil application of all cultures at the 50% recommended NPK rate significantly increased dehydrogenase activity (88.63 μg TPF g^?1 soil) and β-glucosidase activity (48.82 μg PNP g^?1 soil) in soil. Inoculation of Trichoderma alone at the 50% recommended NPK rate significantly increased microbial biomass carbon (3748.85 μg g^?1 soil). Thus, the microbial inoculations significantly increased soil available nutrient contents, enzyme activities such as urease, dehydrogenase and β-glucosidase activity and microbial biomass carbon by reducing the amount of the required fertilizer.     

Internal Boron Requirement of Young Sunflower Plants: Proposed Diagnostic Criteria

Abstract

In a greenhouse study, a significant increase in sunflower (Helianthus annuus L., cv. Hysun 33) dry matter yield was observed with boron (B) application to a B-deficient (hot water-extractable, 0.23 mg B kg^?1) calcareous soil of Missa series (Typic Ustochrept). Six rates of B, ranging from 0 to 8 mg B kg^?1 soil, were applied as H₃BO₃ along with adequate basal fertilization of nitrogen (N), phosphorus (P), potassium (K), and zinc (Zn). Four plants of sunflower were grown in each pot; two were harvested after 4 weeks of germination and the other two after 8 weeks. Maximum crop biomass was produced with 1.0 mg B kg ^?1, and application of ≥2.0 mg B kg^?1 proved toxic, resulting in drastic yield suppressions. Critical B concentration range for deficiency diagnosis in 4‐week‐old sunflower whole shoots appears to be 46–63 mg B kg^?1. However, critical concentration in 8‐week‐old plants was much less (i.e., 36 mg B kg^?l), presumably due to a dilution effect. As plant's internal B requirement can vary, in fact manifold, depending on the species, plant part, and plant age, only a relevant criterion can help in diagnosing the deficiency effectively.     

Impact of Salinity on Soil Biological Activities: A Laboratory Experiment

In a laboratory study, the impact of sodium chloride (NaCl) on soil quality was examined through the monitoring of soil biological activity. Artificially salinized samples were prepared from the nonsaline soil by adding NaCl at electrical conductivities (EC) 2, 4, and 8 dS·m^?1 in saturated extracts. The samples were kept at 25 °C and at 50% field capacity during an incubation period of 40 days. The ATP, soil basal respiration, protease, amylase, alkaline phosphatase, dehydrogenase, and catalase activities were monitored. The biological index of fertility (BIF), the enzyme activity number (EAN), and the metabolic potential (MP) were calculated. A regression analysis was used to calculate parameters from cumulative data of carbon dioxide (CO₂) evolution. The size of microbial biomass, measured throughout the determination of ATP, was decreased by increasing salinity. Increasing concentrations of salt up to an EC of 4 dS·m^?1 led to an increase of soil respiration. During incubation, protease and dehydrogenase were inhibited by NaCl; however, amylase, alkaline phosphatase, and catalase were not affected by the salt addition. Between indices, EAN confirmed the general depressive effect of NaCl on the biological properties of soil, while MP showed a pattern similar to that of soil respiration. Results of this study chiefly indicate that ATP, soil respiration, protease, dehydrogenase, EAN, and MP were able to put in evidence the effects of NaCl on soil biological activity and may be regarded as suitable tools to show the physiological reaction of soil microbial biomass under saline stress.     

Effect of soil application of nickel on growth,micronutrient concentration and uptake in barley (Hordeum vulgare L.) grown in Inceptisols of Varanasi

A pot experiment was conducted in a glass house on low nickel containing alluvial soil in the Department of Soil Science and Agricultural Chemistry, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, during 2012–13 and 2013–14, to study the response of barley to soil application of nickel (Ni). There were ten treatments of Ni (0, 2.5, 5, 10, 15, 20, 30, 40, 50 and 60 mg kg^?1) studied with recommended dose of fertilizers nitrogen, phosphorus, potassium and sulfur (N:P:K:S :: 40:30:30:20 mg kg^?1).The results showed a significant increase in plant height, number of tillers, chlorophyll content, straw and grain yield, and 1,000 grains weight with application of 10 mg Ni kg^?1 soil during both years of study. The micronutrient concentration and uptake in straw and grain increased with application of <15 mg Ni kg^?1 soil and beyond that declined significantly. Diethylenetriaminepentaacetic acid-extractable micronutrient iron, manganese, copper, zinc and nickel (Fe, Mn, Cu, Zn and Ni) content in soil increased with increasing level of Ni. The maximum urease activity in post-harvest soil was noticed with application of 40 mg Ni kg^?1 soil. The microbial population viz. bacteria, fungi and actinomycetes were higher with 5, 30 and 10 mg Ni kg^?1 soil, respectively.     

Organic matter, microbial biomass and enzyme activity of soils under different crop rotations in the tropics

Soil organic matter level, soil microbial biomass C, ninhydrin-N, C mineralization, and dehydrogenase and alkaline phosphatase activity were studied in soils under different crop rotations for 6 years. Inclusion of a green manure crop of Sesbania aculeata in the rotation improved soil organic matter status and led to an increase in soil microbial biomass, soil enzyme activity and soil respiratory activity. Microbial biomass C increased from 192 mg kg^–1 soil in a pearl millet-wheat-fallow rotation to 256 mg kg^–1 soil in a pearl millet-wheat-green manure rotation. Inclusion of an oilseed crop such as sunflower or mustard led to a decrease in soil microbial biomass, C mineralization and soil enzyme activity. There was a good correlation between microbial biomass C, ninhydrin-N and dehydrogenase activity. The alkaline phosphatase activity of the soil under different crop rotations was little affected. The results indicate the green manuring improved the organic matter status of the soil and soil microbial activity vital for the nutrient turnover and long-term productivity of the soil. Received: 7 January 1996     

Effect of land‐use on soil nutrients and microbial biomass of an alpine region on the northeastern Tibetan plateau,China

Land‐use patterns affect the quantity and quality of soil nutrients as well as microbial biomass and respiration in soil. However, few studies have been done to assess the influence of land‐use on soil and microbial characteristics of the alpine region on the northeastern Tibetan plateau. In order to understand the effect of land‐use management, we examined the chemical properties and microbial biomass of soils under three land‐use types including natural grassland, crop‐field (50 + y of biennial cropping and fallow) and abandoned old‐field (10 y) in the area. The results showed that the losses of soil organic carbon (SOC) and total nitrogen (TN) were about 45 and 43 per cent, respectively, due to cultivation for more than 50 y comparing with natural grassland. Because of the abandonment of cultivation for about a decade, SOC and TN were increased by 27 and 23 per cent, respectively, in comparison with the crop field. Microbial carbon (ranging from 357·5 to 761·6 mg kg⁻¹ soil) in the old‐field was intermediate between the crop field and grassland. Microbial nitrogen (ranging from 29·9 to 106·7 mg kg⁻¹ soil) and respiration (ranging from 60·4 to 96·4 mg CO₂‐C g⁻¹ C_mic d⁻¹) were not significantly lower in the old‐field than those in the grassland. Thus it could be concluded that cultivation decreased the organic matter and microbial biomass in soils, while the adoption of abandonment has achieved some targets of grassland restoration in the alpine region of Gansu Province on the northeastern Tibetan plateau. Copyright © 2010 John Wiley & Sons, Ltd.     

Potted rice straw increased the antioxidase activity and growth of Chinese green cabbage seedlings and altered the soil microbial community

To reuse rice straw and decrease the environmental pollution and resource waste that are caused by burning rice straw in China, this agricultural resource is increasingly being used to make pots with added formaldehyde and other chemicals for cultivating vegetables. A study was conducted to investigate the effects of rice straw-based pot powder on the growth and antioxidase activity of Chinese green cabbage seedlings and the soil microbial community using a molecular analysis. The results showed that there was no negative effect from the powder on cabbage growth, given that the cabbage plants that were treated with powder (1.2–3.2 g kg^?1 rice straw pot powder) exhibited 1.8 to 2.5 times higher fresh biomass than the control (0 g kg^?1 powder). Minor differences were found among key reactive oxygen system enzyme activities, but the superoxide dismutase activity decreased by 33–55% (1.2–3.2 g kg^?1 powder). The phenylalanine ammonia-lyase activity of green Chinese cabbage that was treated with powder (1.2–3.2 g kg^?1 rice straw pot powder) was 1.5 times higher than the no-powder control. The soil microbial diversity was changed, and the community composition was altered depending on the rates of powder application, according to a polymerase chain reaction-denaturing gradient gel electrophoresis analysis.     

Influence of inorganic fertilizers and organic amendments on soil organic matter and soil microbial properties under tropical conditions

 Soil organic matter level, mineralizable C and N, microbial biomass C and dehydrogenase, urease and alkaline phosphatase activities were studied in soils from a field experiment under a pearl millet-wheat cropping sequence receiving inorganic fertilizers and a combination of inorganic fertilizers and organic amendments for the last 11 years. The amounts of soil organic matter and mineralizable C and N increased with the application of inorganic fertilizers. However, there were greater increases of these parameters when farmyard manure, wheat straw or Sesbania bispinosa green manure was applied along with inorganic fertilizers. Microbial biomass C increased from 147 mg kg^–1 soil in unfertilized soil to 423 mg kg^–1 soil in soil amended with wheat straw and inorganic fertilizers. The urease and alkaline phosphatase activities of soils increased significantly with a combination of inorganic fertilizers and organic amendments. The results indicate that soil organic matter level and soil microbial activities, vital for the nutrient turnover and long-term productivity of the soil, are enhanced by use of organic amendments along with inorganic fertilizers. Received: 6 May 1998     

Effect of boron and sulfur interaction on some important biological indices in an inceptisol

In most soil ecosystems, soil biological activity and associated processes are concentrated in the rhizosphere soil and is influenced by the external application of plant nutrients. The impacts of boron and sulfur on soil biological properties were evaluated in an Aeric Haplaquept (pH 5.7) growing rapeseed (Brassica campestris L.) as a test crop. Application of boron (B) at 2 mg kg^?1 in combination with sulfur (S) at 30 mg kg^?1 (B₂S₃₀) resulted in highest available Boron and sulfur of 0.239 and 15.4 mg kg^?1, respectively and registered 62.5% and 71.3% increase over control (B₀S₀) at 60 days of crop growth compared to individual applications. The microbial populations viz. phosphate solubilizing microorganisms (PSM) and nitrogen fixing bacteria (NFB) were the highest of 52.63 and 85.87 × 10⁵ g^?1 soil, respectively, CFU in B₂S₃₀ treatment at 60 days and adjudged as the best treatment combination for enhancement of soil biological indices and seed yield.     

Dissolved Organic Carbon in Association with Water Soluble Nutrients and Metals in Soils from Lake Okeechobee Watershed, South Florida

Water quality of Lake Okeechobee has been a major environmental concern for many years. Transport of dissolved organic matter (DOM) in runoff water from watershed is critical to the increased inputs of nutrients (N and P) and metals (Cu and Zn). In this study, 124 soil samples were collected with varying soil types, land uses, and soil depths in Lake Okeechobee watershed and analyzed for water-extractable C, N, P, and metals to examine the relationship between dissolved organic carbon (DOC) and water soluble nutrients (N and P) and metals in the soils. DOC in the soils was in 27.64?C400 mg kg^?1 (69.30 mg kg^?1 in average) and varied with soil types, land uses, and soil depth. The highest water-extractable DOC was found in soils collected in sugar cane and field crops (277 and 244 mg kg^?1 in average, respectively). Water soluble concentrations of N and P were in the range of 6.46?C129 and 0.02?C60.79 mg kg^?1, respectively. The ratios of water-extractable C/N and C/P in soils were in 0.68?C12.52 (3.23 in average) and 3.19?C2,329 (216 in average), and varied with land uses. The lowest water-extractable C/N was observed in the soils from dairy (1.66), resident (1.79), and coniferous forest (4.49), whereas the lowest water-extractable C/P was with the land uses of dairy (13.1) and citrus (33.7). Therefore, N and P in the soils under these land uses may have high availability and leaching potential. The concentrations of water soluble Co, Cr, Cu, Ni, and Zn were in the ranges of?<?method detection limit (MDL)?C0.33, <MDL?C0.53, 0.04?C2.42, <MDL?C0.71, and 0.09?C1.13 mg kg^?1, with corresponding mean values of 0.02, 0.01, 0.50, 0.07, and 0.37 mg kg^?1, respectively. The highest water soluble Co (0.10 mg kg^?1), Cr (0.26 mg kg^?1), Ni (0.31 mg kg^?1), and Zn (0.80 mg kg^?1) were observed in soils under the land use of sugar cane, whereas the highest Cu (1.50 mg kg^?1) was with field crop. The concentration of DOC was positively correlated with total organic carbon (TOC) (P <0.01), water soluble N (P <0.01), electrical conductivity (EC, P <0.01), and water soluble Co, Cr, Ni, and Zn (P <0.01), and Cu (P <0.05), whereas water soluble N was positively correlated with water soluble P, Cu, and Zn (P <0.01) in soils. These results indicate that the transport of DOC from land to water bodies may correlate with the loss of macro-nutrients (N, P), micro-nutrients (Cu, Zn, and Ni), and contaminants (Cr and Co) as well.