Effect of bensulfuron-methyl (a sulfonylurea herbicide) on the soil bacterial community of a paddy soil microcosm

The effect of bensulfuron-methyl (BSM) on a soil microbial community in a model paddy microcosm was studied. Total bacterial numbers in the overlying water and surface soil were monitored for 2 months after the application of BSM at the field rate and a ten-fold field rate. Pentachlorophenol (PCP) was used for comparison. Neither chemical affected the total bacterial numbers remarkably, either in the overlying water or in the surface soil. In contrast, the nitrification potential was significantly suppressed by the BSM application. The bacterial community structure, as evaluated by the denaturing gradient gel electrophoresis (DGGE) of PCR amplification products from bacterial 16S rDNA, was unaffected by the BSM treatments over 8 weeks in the surface soil, compared with the control (no pesticide). In contrast, the surface soil exposed to PCP at a ten-fold field rate showed different patterns from the controls at 4 weeks and 8 weeks after application. The DGGE patterns of the overlying water were much more variable than those of the surface soil in any treatments. Cluster analysis showed that the BSM plots were classified within the same group as the control at 1 week after application and that the BSM and PCP plots from 2 weeks onward after application were grouped differently from the control. Of 22 clones excised from the DGGE gels, 20 clones belonged to the Proteobacteria and two belonged to the Verrucomicrobia. It was considered that the impact of BSM on the overall microbial community (total numbers, community structure of soil) was negligible, although BSM had an impact on some specific functions of the soil microbial community (nitrification) and a part of the community (overlying water).     

Cloning, functional expression, and characterization of cystatin in sesame seed

A cDNA fragment encoding cystatin, a cysteine protease inhibitor, was obtained from maturing sesame seeds. The clone was constructed in a nonfusion or fusion vector and then overexpressed in Escherichia coli. The recombinant cystatins were found in the soluble fraction of cell extract and were demonstrated to be functionally active in a reverse zymographic assay. The corresponding endogenous 22 kDa cystatin of low abundance in mature seeds was purified to homogeneity via a papain-coupling affinity column and confirmed by western blotting with antibodies against the recombinant cystatin. Both endogenous and recombinant cystatin proteins showed effective inhibitory activities against papain with K(i) values of 7.89 x 10(-8) M and 2.77 x 10(-8) M, respectively. Immunodetection indicated that cystatin was specifically expressed in maturing seeds and rapidly degraded in germination. Accordingly, zymographic and inhibition analyses showed that sesame cystatin could not inhibit the de novo synthesized proteases in germinating seeds. It is suggested that sesame cystatin may play a role in the regulation of endogenous cysteine proteases during seed maturation and germination.     

Hydrolase activity, microbial biomass and community structure in long-term Cd-contaminated soils

Long-term effects of high Cd concentrations on enzyme activities, microbial biomass and respiration and bacterial community structure of soils were assessed in sandy soils where Cd was added between 1988 and 1990 as Cd(NO₃)₂ to reach concentrations ranging from 0 to 0.36 mmol Cd kg⁻¹ dry weight soil. Soils were mantained under maize and grass cultivation, or ‘set-aside’ regimes, for 1 year. Solubility of Cd and its bioavailability were measured by chemical extractions or by the BIOMET bacterial biosensor system. Cadmium solubility was very low, and Cd bioavailability was barely detectable even in soils polluted with 0.36 mmol Cd kg⁻¹. Soil microbial biomass carbon (B_C) was slightly decreased and respiration was increased significantly even at the lower Cd concentration and as a consequence the metabolic quotient (qCO₂) was increased, indicating a stressful condition for soil microflora. However, Cd-contaminated soils also had a lower total organic C (TOC) content and thus the microbial biomass C-to-TOC ratio was unaffected by Cd. Alkaline phosphomonoesterase, arylsulphatase and protease activities were significantly reduced in all Cd-contaminated soils whereas acid phosphomonoesterase, β-glucosidase and urease activites were unaffected by Cd. Neither changes in physiological groups of bacteria, nor of Cd resistant bacteria could be detected in numbers of the culturable bacterial community. Denaturing gradient gel electrophoresis analysis of the bacterial community showed slight changes in maize cropped soils containing 0.18 and 0.36 mmol Cd kg⁻¹ soil as compared to the control. It was concluded that high Cd concentrations induced mainly physiological adaptations rather than selection for metal-resistant culturable soil microflora, regardless of Cd concentration, and that some biochemical parameters were more sensitive to stress than others.     

Recovery of cover-crop-N in the soil-plant system in the Guinea savannah zone of Ghana

In order to understand the efficiency of residue-N use and to estimate the minimum input required to obtain a reasonable level of crop response, it is important to quantify the fate of the applied organic-N. The recovery of N from ¹⁵N-labelled Crotalaria juncea was followed in the soil and the succeeding maize crop. Apparent N recovery (ANR) by maize from unlabelled Crotalaria juncea, Crotalaria retusa, Calopogonium mucunoides, Mucuna pruriens and mineral fertilizer at three locations were also evaluated. The maize crop recovered 4.7% and 7.3% of the ¹⁵N-labelled C. juncea-N at 42 days after sowing (DAS) and at final harvest, respectively. The corresponding ¹⁵N recovery from the soil was 92.4% and 58.5%. The highest mean ANR of 57.4% was with mineral fertilizer, whereas the mean ANR of 14.3% from C. retusa was the lowest. A large pool substitution and added-N interaction effect was observed when comparing N recovery from the labelled and unlabelled C. juncea. The amount of residue-N accounted for by the isotope dilution method at 42 DAS was 97.1% and at final harvest 65.8%. The large residue-N recovery in the soil organic-N pool explains the residual effect usually observed with organic residue application.     

Nitrogen and carbon mineralisation of leather meal in soil as affected by particle size of fertiliser and microbiological activity of soil

Carbon and nitrogen mineralisation of leather meal fertilisers were studied in two soils characterised by different respiration activity. Both C and N mineralisation were highest in the most active soil, and when leather meal was added as a powder rather than as 2- to 4- and 4- to 6-mm particles. Fast and slow soluble N pools were determined after extraction with cold water and with hot buffer, respectively. The N remaining after the second extraction with hot buffer was named slow-release N. The percentage of slow-release N rose as the size of the applied leather meal particles increased, whereas fast soluble N was highest in the coarsest (4-6 mm) fertiliser.     

Effect of harvesting and drying conditions on chlorophyll levels of soybean (Glycine max L. Merr)

Chlorophyll in soybean represents a downgrading factor for the crops. Five Brazilian cultivars were harvested between R(6) and R(8) stage of development (Fehr & Caviness scale) and dried at 25 degrees and 40 degrees C. The effect of maturity stages and two drying conditions after harvest were studied to achieve reduction of moisture and chlorophylls to acceptable levels. When seeds were dried at 25 degrees C, even harvesting at early stages of development such as R(6), the green pigments were almost degraded, and 16 ppm of chlorophyll were found at maximum, accompanied by loss of moisture. Moisture and chlorophyll declines as seed matures, but at intermediary stages (R(6)-R(7)), chlorophyll degrades first, so the rate of moisture loss should not be used to predict chlorophyll contents. At 40 degrees C, complete degradation of chlorophyll pigments is only achieved when seeds are swathed from R(7) stage up, otherwise the seed quality could be compromised. Slow drying allows almost complete removal of green pigments, even when seeds are swathed a few days before the physiological maturity stage.     

Changes in penetration resistance of Ultisols from southern China as affected by shearing

Shear stresses and soil properties modified due to stress play an important role during formation of seals in a series of rainfall events and during tillage. The objectives of the study were to evaluate the effects of the penetrometer geometry on the penetration resistance as affected by shearing under different initial soil conditions and to use the information on soil strength to elucidate shearing process. Nine homogenous air-dried soils (<2 mm) were sprayed and stored so as to obtain equilibrium soil water contents. The moist soils were sheared by horizontal displacement of layers of soil particles/aggregates in between hands in one direction. The soil cores were prepared with comparable bulk density before the measurement of maximum penetration resistance (P_max) with a small flat tip and a cone tip penetrometers. At a wide range from 0.05 to 6.2 MPa, P_max was linearly correlated between the small flat tip and the cone tip penetrometers. The conversion ratio was higher under the saturation condition irrespective of the shearing effect. The penetrometer with the small flat tip was more sensitive for the weak soils. Shearing generally increased P_max in most cases, but it decreased P_max for some sandy soils under both saturated and unsaturated conditions and for a clayey soil under the saturated condition. The soil consisting of swelling clay exerted a decrease in P_max. Rearrangement and/or sliding of particles/aggregates and increase in soil suction during shearing were attributed to the increase in P_max. Increase in porosity due to the aggregation during shearing was ascribed to the decrease in P_max. In addition, it was shown that agricultural cultivation resulted in a reduction in soil strength.     

Using soil temperature and moisture to predict forest soil nitrogen mineralization

Due to the importance of N in forest productivity ecosystem and nutrient cycling research often includes measurement of soil N transformation rates as indices of potential availability and ecosystem losses of N. We examined the feasibility of using soil temperature and moisture content to predict soil N mineralization rates (Nmin) at the Coweeta Hydrologic Laboratory in the southern Appalachians. We conducted seasonal laboratory incubations of A and AB horizon soils from three sites with mixed-oak vegetation using temperature and moisture levels characteristic of the season in which the soils were collected. The incubations showed that temperature and temperature-moisture interactions significantly affected net soil Nmin. We used the laboratory data to generate equations relating net Nmin to soil temperature and moisture data. Using field-collected temperature and moisture data we then calculated Nmin on similar forest sites and compared predicted rates with in situ, closed-core Nmin measurements. The comparison showed that the in situ Nmin was greater than rates predicted from laboratory generated equations (slope =3.22; r²=0.89). Our study suggests that while climatic factors have a significant effect on soil Nmin, other factors also influence rates measured in the laboratory and in situ.     

Soil management for Alfisols in the semiarid tropics: erosion, enrichment ratios and runoff

Abstract. Continuous cultivation of soils of the semiarid tropics has led to significant land degradation. Soil erosion and nutrient loss caused by high runoff volumes have reduced crop yields and contributed to offsite damage. We compared a number of soil management practices (tillage, mulch and perennial/annual rotational based systems) for their potential to improve crop production and land resource protection in an Alfisol of the semiarid tropics of India. Runoff and soil erosion were monitored and surface soil and sediment were analysed for nitrogen and carbon to determine enrichment ratios. Amelioration of soils with organic additions (farmyard manure, rice straw) or rotating perennial pasture with annual crops increased soil carbon and nitrogen contents and reduced runoff, soil erosion and nutrient loss. Soil erosion totalled less than 7 t ha^–1, but enrichment ratios were often greater than 2 resulting in up to 27 kg N ha^–1 and 178 kg C ha^–1 being lost in sediment. Up to an extra 250 mm of water per year infiltrated the soil with organic additions and was available for crop water use or percolation to groundwater. The results show that there are good opportunities for reducing degradation and increasing productivity on farms.     

Effect of Temperature on Bio-Kinetic Coefficients in UASB Treatment of Municipal Wastewater

Upflow anaerobic sludge blanket (UASB)reactors were used to treat municipal wastewater attemperatures of 6, 11, 15, 20 and 32 °C and athydraulic retention times (HRTs) ranging from 48 to 3 h overan operational period of approximately 860 days. The Monodmodel was used to evaluate substrate utilization. TheArrhenius model was used to calculate the activationenergies from which temperature coefficients weredetermined. It was found that the maximum specific substrateutilization rate constant (k) decreased from 0.387 d^-1(at 32 °C) to 0.041 d^-1 (at 6 °C). Thedecay rate constant (k_d), yield coefficient (Y_g),half velocity constant (K_s) and maximum specific growthrate (μ_m ) were also impacted by temperature in theUASB treatment of municipal wastewater.