Transport of bacterial inoculants through intact cores of two different soils as affected by water percolation and the presence of wheat plants

Abstract Water flow-innduced transport of Burkholderia cepacia strain P2 and Pseudomonas fluorescens strain R2f cells through intact cores of loamy sand and silt loam field soils was measured for two percolation regimes, 0.9 and 4.4 mm h⁻¹, applied daily during 1 hour. For each strain, transport was generally similar between the two water regimes. Translocation of B. cepacia , with 4.4 mm h⁻¹, did occur initially in both soils. In the loamy sand soil, no change in the bacterial distribution occurred during the experiment (51 days). In the silt loam, B. cepacia cell numbers in the lower soil layers were significantly reduced, to levels at or below the limit of detection. Transport of P. fluorescens in both soils also occurred initially and was comparable to that of B. cepacia . Later in the experiment, P. fluorescens was not detectable in the lower soil layers of the loamy sand cores, due to a large decrease in surviving cell numbers. In the silt loam, the inoculant cell distribution did not change with time. Pre-incubation of the inoculated cores before starting percolation reduced B. cepacia inoculant transport in the loamy sand soil measured after 5 days, but not that determined after 54 days. Delayed percolation in the silt loam soil affected bacterial transport only after 54 days. The presence of growing wheat plants overall enhanced bacterial translocation as compared to that in unplanted soil cores, but only with percolating water. Percolation water from silt loam cores appeared the day after the onset of percolation and often contained inoculant bacteria. With loamy sand, percolation water appeared only 5 days after the start of percolation, and no inoculant bacteria were found. The results presented aid in predicting the fate of genetically manipulated bacteria in a field experiment.     

Soil types with different texture affects development of Rhizoctonia root rot of wheat seedlings

The effect of different soil textures, sandy (97.5% sand, 1.6% silt, 0.9% clay), loamy sand (77% sand, 11% silt, 12% clay) and a sandy clay loam (69% sand, 7% silt, 24% clay), on root rot of wheat caused by Rhizoctonia solani Kühn Anastomosis Group (AG) 8 was studied under glasshouse conditions. The reduction in root and shoot biomass following inoculation with AG-8 was greater in sand than in loamy sand or sandy clay loam. Dry root weight of wheat in the sand, loamy sand and sandy clay loam soils infested with AG-8 was 91%, 55% and 28% less than in control uninfested soils. There was greater moisture retention in the loamy sand and sandy clay loam soils as compared to the sand in the upper 10–20 cm. Root penetration resistance was greater in loamy sand and sandy clay loam than in sand. Root growth in the uninfested soil column was faster in the sand than in the loamy sand and sandy clay loam soils, the roots in the sandy soil being thinner than in the other two soils. Radial spread of the pathogen in these soils in seedling trays was twice as fast in the sand in comparison to the loamy sand which in turn was more than twice that in the sandy clay loam soil. There was no evidence that differences among soils in pathogenicity or soil spread of the pathogen was related to their nutrient status. This behaviour may be related to the severity of the disease in fields with sandy soils as compared to those with loam or clay soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of soil pH on the nitrate-reducing microbial populations and their potential to reduce nitrate to NO and N2O

Abstract After the introduction of Rhizobium leguminosarum biovar trifolii into natural loamy sand and silt loam, bacterial numbers increased only directly after inoculation. Thereafter, bacterial numbers decreased until an equilibrium was reached. This decrease was exponential on a log scale and could be described by the function Y = A + B − R ', where Y is the log number of rhizobial cells at time: T ; A represents the lgo of the final population size; B is the difference between the log (initial number of bacteria) and A ; R is the daily reduction factor of Y−A and t is time in days after inoculation. The final population sizes increased with increasing inoculum densities (10⁴−10⁸ bacteria/g soil). In sterilized soil, however, the populations increased up to an equilibrium, which was not affected by the inoculum density.
The final population sizes were higher in silt loam than in loamy sand in natural, as well as in sterilized soil. The final population size was reached earlier in natural silt loam than in loamy sand. Also the growth rate in sterilized soil was higher in silt loam than in loamy sand. The growth rate of low inoculum densities in silt loam was exponential and approximately the same as in yeast extract mannitol broth. The growth rate in loamy sand could be improved by incresing the bulk density of the soil from 1.0 to 1.4 g/cm³.     

Effect of long-term application of animal manure on physical properties of three soils

Surface soil samples to 15 cm depth were taken from replicated plots in an ongoing long-term field experiment involving application of animal manure on three soils in Virginia. The sampled plots had received either no manure or the equivalent of 289,000 kg ha^–1 of manure as dry weight. The manure was applied annually at the beginning of each spring for 15 years from 1978 through 1992. The plots were cropped similarly since 1978. Soil textures were a fine sandy loam at Holland in the Atlantic Coastal Plain region, a silt loam at Blacksburg in the Appalachian region, and a clay loam at Orange in the Piedmont region of Virginia. The following measurements were made on subsamples: liquid and plastic limits, wet aggregate stability, aggregate size distribution, dispersible clay percentage, water retention at 0. 03, 0.1, 0.3, 0.5, 1.0, and 1.5 MPa tension, and modulus of rupture of moulded briquettes at a water content corresponding to 0.1 MPa tension. Organic matter content by the Walkley-Black method was significantly higher in the manure-treated soils at all three locations. Increases were 3% for the sandy loam and 25% for the silt loam and clay loam. From these values it was estimated that at least 95% of the total applied manure had been degraded over the 15 years. Results showed that the liquid and plastic limits for all three soils were higher (p<0.05) for the manure-treated samples. However, the differences in the limits were only 2 to 3%. The modulus of rupture values were lowered by addition of the animal manure. Decreases (p<0.05) occurred for the silt loam and clay loam samples. The wet aggregate stability increased and the dispersible clay decreased in the manure-treated soils. Increases (p<0.05) in wet aggregate stability occurred for the sandy loam and silt loam samples. Decreases (p<0.05) in dispersible clay were measured for the sandy loam and clay loam samples. Water retention was consistently, but only slightly, increased by manure addition. The increases, in the order of sample texture, were clay loam > sandy loam silt loam. Increases tended to be higher at the lower values of tension. Manure addition consistently increased the weight percentages of aggregates passing a given mesh size. Increases, in order of sample texture, were silt loam > clay loam > sandy loam. In their entirety, these results show that the manure produced measurable changes in the soil physical properties. The magnitude of the changes, in most cases, were small and depended on the soil texture. Given the high total amount of manure applied, the results indicate that manure-induced physical changes in the soil were small and evidently did not accumulate over time. Rapid microbial degradation of the manure could be responsible for the lack of marked changes in the soil physical properties.     

Electronic nose evaluation of onion headspace volatiles and bulb quality as affected by nitrogen, sulphur and soil type

Edaphic factors affect the quality of onions (Allium cepa). Two experiments were carried out in the field and glasshouse to investigate the effects of N (field: 0,120 kg ha⁻¹; glasshouse: 0,108 kg ha⁻¹), S (field: 0, 20 kg ha⁻¹; glasshouse: 0, 4.35 kg ha⁻¹) and soil type (clay, sandy loam) on onion quality. A conducting polymer sensor electronic nose (E-nose) was used to classify onion headspace volatiles. Relative changes in the E-nose sensor resistance ratio (%dR/R) were reduced following N and S fertilisation. A 2D Principal Component Analysis (PCA) of the E-nose data sets accounted for c. 100% of the variations in onion headspace volatiles in both experiments. For the field experiment, E-nose data set clusters for headspace volatiles for no N-added onions overlapped (D²= 1.0) irrespective of S treatment. Headspace volatiles of N-fertilised onions for the glasshouse sandy loam also overlapped (D²=1.1) irrespective of S treatment as compared with distinct separations among clusters for the clay soil. N fertilisation significantly (P < 0.01) reduced onion bulb pyruvic acid concentration (flavour) in both experiments. S fertilisation increased pyruvic acid concentration significantly (P < 0.01) in the glasshouse experiment, especially for the clay soil, but had no effect on pyruvic acid concentration in the field. N and S fertilisation significantly (P < 0.01) increased lachrymatory potency (pungency), but reduced total soluble solids (TSS) content in the field experiment. In the glasshouse experiment, N and S had no effect on TSS. TSS content was increased on the clay by 1.2-fold as compared with the sandy loam. Onion tissue N: water-soluble SO₄²⁻ ratios of between five and eight were associated with greater %dR/R and pyruvic acid concentration values. N did not affect inner bulb tissue microbial load. In contrast, S fertilisation reduced inner bulb tissue microbial load by 80% in the field experiment and between 27% (sandy loam) and 92% (clay) in the glasshouse experiment. Overall, onion bulb quality discriminated by the E-nose responded to N, S and soil type treatments, and reflected their interactions. However, the conventional analytical and sensory measures of onion quality did not correlate with %dR/R.     

Effect of soil type on infectivity and persistence of the entomopathogenic nematodes Steinernema scarabaei, Steinernema glaseri, Heterorhabditis zealandica, and Heterorhabditis bacteriophora

We tested the effect of soil type on the performance of the entomopathogenic pathogenic nematodes Steinernema scarabaei, Steinernema glaseri, Heterorhabditis zealandica, and Heterorhabditis bacteriophora. Soil types used were loamy sand, sandy loam, loam, silt loam, clay loam, acidic sand, and a highly organic potting mix. Infectivity was tested by exposing third-instar Anomala orientalis or Popillia japonica to nematodes in laboratory and greenhouse experiments and determining nematode establishment in the larvae and larval mortality. Infectivity of H. bacteriophora and H. zealandica was the highest in potting mix, did not differ among loamy sand and the loams, and was the lowest in acidic sand. Infectivity of S. glaseri was significantly lower in acidic sand than in loamy sand in a laboratory experiment but not in a greenhouse experiment, and did not differ among the other soils. Infectivity of S. scarabaei was lower in silt loam and clay loam than in loamy sand in a greenhouse experiment but not in a laboratory experiment, but was the lowest in acidic sand and potting mix. Persistence was determined in laboratory experiments by baiting nematode-inoculated soil with Galleria mellonella larvae. Persistence of both Heterorhabditis spp. and S. glaseri was the shortest in potting mix and showed no clear differences among the other substrates. Persistence of S. scarabaei was high in all substrates and its recovery declined significantly over time only in clay loam. In conclusion, generalizations on nematode performance in different soil types have to be done carefully as the effect of soil parameters including soil texture, pH, and organic matter may vary with nematode species.     

A comparison of fine root distribution and water consumption of mature Caragana korshinkii Kom grown in two soils in a semiarid region, China

Water is a key limiting factor for vegetation restoration in the semi-arid areas of China. Caragana korshinkii Kom is a shrub that is widely planted in this region to control soil erosion and land desertification. The objective of this study was to investigate the fine root distribution of mature C. korshinkii and its water consumption, when grown in either silt loam or sandy soils, in order to understand differences between the water cycles of two such soils found in the transition zone between fertile loess hills and desert of the Northern Loess Plateau. Fine root distributions were measured using the trench-profile method. Soil water dynamics were monitored with a neutron probe during two growing seasons. The results showed that fine root area density (FRAD) declined with increasing soil depth in both soils, with 70.7% and 96.6% of the total fine roots being concentrated in the upper 1-m layer of the silt loam and sandy soils, respectively. Water consumption by C. korshinkii in the silt loam was close to that in the sandy soil. Most water consumption in both soil types was from the upper 1-m layer. Little variation in plant available water (PAW) occurred in the 3–6 m soil layer during the whole study period. However, in this layer, the PAW was significantly lower in the silt loam soil than in the sandy soil. Total actual evapotranspiration (ET_a) was slightly higher from the sandy soil plots than from those of the silt loam soil during both growing seasons. Our study indicated that mature C. korshinkii effectively uses about the same amount of water from either the silt loam or sandy soils, but that more soil water at depth was extracted from silt loam soil than from sandy soil.     

Impact of Rotylenchulus reniformis on Cotton Yield as Affected by Soil Texture and Irrigation

The effects of soil type, irrigation, and population density of Rotylenchulus reniformis on cotton were evaluated in a two-year microplot experiment. Six soil types, Fuquay sand, Norfolk sandy loam, Portsmouth loamy sand, Muck, Cecil sandy loam, and Cecil sandy clay, were arranged in randomized complete blocks with five replications. Each block had numerous plots previously inoculated with R. reniformis and two or more noninoculated microplots per soil type, one half of which were irrigated in each replicate for a total of 240 plots. Greatest cotton lint yields were achieved in the Muck, Norfolk sandy loam, and Portsmouth loamy sand soils. Cotton yield in the Portsmouth loamy sand did not differ from the Muck soil which averaged the greatest lint yield per plot of all soil types. Cotton yield was negatively related to R. reniformis PI (initial population density) in all soil types except for the Cecil sandy clay which had the highest clay content. Supplemental irrigation increased yields in the higher yielding Muck, Norfolk sandy loam, and Portsmouth loamy sand soils compared to the lower yielding Cecil sandy clay, Cecil sandy loam, and Fuquay sand soils. The Portsmouth sandy loam was among the highest yielding soils, and also supported the greatest R. reniformis population density. Cotton lint yield was affected more by R. reniformis Pi with irrigation in the Portsmouth loamy sand soil with a greater influence of Pi on lint yield in irrigated plots than other soils. A significant first degree PI × irrigation interaction for this soil type confirms this observation.     

Fungicidal control of Rhizoctonia solani in relation to soil texture, organic matter and clay minerals

In pot tests, MEMC, quintozene, captafol, carboxin, thiabendazole, carbendazim, benomyl and thiophanate-methyl used as seed treatments gave much better control of cowpea seedling rot in light-textured sandy and loamy sand soils than in heavy-textured loam and silt loam soils inoculated with Rhizoctonia solani. Disease control by chloroneb was not altered by soil texture. Amendment of sandy soil with montmorillonite reduced disease control with all fungicides, except chloroneb and carboxin; similar amendments with kaolinite decreased efficacy of MEMC and captafol. Green manuring with cluster bean reduced disease control by MEMC, captafol, benomyl and thiophanate-methyl; sunnhemp reduced efficacy of MEMC. Most fungicides gave poor disease control when farm yard manure or biogas sludge was added to soil, the sludge having the more marked effect. All the fungicides tested, except carboxin, were inactivated to different extents by humic acid extracted from farm yard manure.     

Effect of Substrate Type and Moisture on Pupation and Emergence of <Emphasis Type="Italic">Heortia vitessoides</Emphasis> (Lepidoptera: Crambidae): Choice and No-Choice Studies

Heortia vitessoides Moore is the most destructive defoliator of Aquilaria sinensis (Loureiro) Sprenger, an endangered and economically important plant that produces the high-prized agarwood. After maturing, H. vitessoides larvae will leave the A. sinensis and pupate in soil, however, factors affecting this behavior have not been previously addressed. In the present study, choice and no-choice tests were conducted to study the effects of substrate type (sand, sandy loam A, sandy loam B, and silt loam) and moisture condition (0 %, 20 %, 40 %, 60 %, 80 %, and 100 % water saturation) on burrowing, pupation and emergence behaviors of H. vitessoides under laboratory conditions. Six-choice tests showed that significantly fewer larvae burrowed and pupated in each substrate under extremely dry (0 % saturation) or wet (80 % and 100 % saturation) conditions. Four-choice tests showed that at 20 % saturation a significantly lower percentage of larvae burrowed and pupated in silt loam as compared to other substrates, whereas at 40 % saturation sand was least preferred. At 60 % saturation, however, there was no significant difference in burrowing and pupation among the four substrates. No-choice test showed that either or both 0 % and 80 % water saturation suppressed burrowing behavior and emergence success compared with the intermediate saturation levels in sandy loam (A and B) and silt loam, but not in sand. In addition, the effect of substrate type varied with saturation level. Our study enhance the understanding of pupation ecology of H. vitessoides, and applied implications are discussed.     

Effect of bovine manure on fecal coliform attachment to soil and soil particles of different sizes

Manure-borne bacteria can be transported in runoff as free cells, cells attached to soil particles, and cells attached to manure particles. The objectives of this work were to compare the attachment of fecal coliforms (FC) to different soils and soil fractions and to assess the effect of bovine manure on FC attachment to soil and soil fractions. Three sand fractions of different sizes, the silt fraction, and the clay fraction of loam and sandy clay loam soils were separated and used along with soil samples in batch attachment experiments with water-FC suspensions and water-manure-FC suspensions. In the absence of manure colloids, bacterial attachment to soil, silt, and clay particles was much higher than the attachment to sand particles having no organic coating. The attachment to the coated sand particles was similar to the attachment to silt and clay. Manure colloids in suspensions decreased bacterial attachment to soils, clay and silt fractions, and coated sand fractions, but did not decrease the attachment to sand fractions without the coating. The low attachment of bacteria to silt and clay particles in the presence of manure colloids may cause predominantly free-cell transport of manure-borne FC in runoff.     

Effect of Bovine Manure on Fecal Coliform Attachment to Soil and Soil Particles of Different Sizes

Manure-borne bacteria can be transported in runoff as free cells, cells attached to soil particles, and cells attached to manure particles. The objectives of this work were to compare the attachment of fecal coliforms (FC) to different soils and soil fractions and to assess the effect of bovine manure on FC attachment to soil and soil fractions. Three sand fractions of different sizes, the silt fraction, and the clay fraction of loam and sandy clay loam soils were separated and used along with soil samples in batch attachment experiments with water-FC suspensions and water-manure-FC suspensions. In the absence of manure colloids, bacterial attachment to soil, silt, and clay particles was much higher than the attachment to sand particles having no organic coating. The attachment to the coated sand particles was similar to the attachment to silt and clay. Manure colloids in suspensions decreased bacterial attachment to soils, clay and silt fractions, and coated sand fractions, but did not decrease the attachment to sand fractions without the coating. The low attachment of bacteria to silt and clay particles in the presence of manure colloids may cause predominantly free-cell transport of manure-borne FC in runoff.     

Passive volatilization of gasoline from soil

Gasoline spills were simulated in the laboratory with three air‐dried soils, using a synthetic gasoline and unsaturated soil to quantify passive volatilization over a period of up to 16 d. The total and individual gasoline components were monitored as a function of time and depth in the soil.

The time required to deplete the overall gasoline concentration in the soil to 40% of the initial concentration ranged from 0.25 to 10 d for the three soils. Sand was the fastest, followed by loamy sand and silt loam. The volatilization rate of gasoline from soil was found to be dependent on soil, chemical type, and depth. Observation of individual components indicated that a wicking mechanism contributed to the gasoline flux toward the surface.     

Effects of three soil-applied herbicides on populations of plant disease suppressing bacteria in the cotton rhizosphere

The potential impact of three widely used herbicides, pendimethalin, prometryn, and trifluralin, on populations of five plant disease suppressing bacterial isolates (three isolates of Pseudomonas fluorescens and two isolates of Burkholderia cepacia) in the rhizosphere of cotton seedlings was investigated. All isolates are efficient cotton root colonizers and each is capable of suppressing a plant disease. In microcosm experiments, application of each of the test herbicides at the rates of 1, 2, and 4 µg active ingredient (a.i.) g^-1 soil caused significant (p<0.05) reductions in populations of most of the isolates in the rhizosphere, 14 days after the release of bacteria into the soil by seed coating. The responses of the isolates to the herbicides varied depending on the isolate and the type and concentration of the herbicides. In microcosm experiments the impact of pendimethalin, prometryn, and trifluralin at the respective concentrations of 2.4, 3.6, and 1.8 g a.i. g^-1 soil on the population of isolate D1 in the cotton rhizosphere declined with time during a four week period of monitoring following the release of the isolate into the soil by seed coating. The impact of soil applied test herbicides on the population sizes of D1 in cotton rhizosphere was also studied in two field experiments (Safford and Tucson, Arizona) where the bacteria were added as a soil drench. In the Safford experiment pendimethalin and prometryn, but not trifluralin, caused significant (p <0.05) reductions in the population of the bacterium 15 days after sowing. In the Tucson experiment a significant (p < 0.05) reduction in the population of the bacterium was observed 15 and 25 days after sowing in soils treated with pendimethalin and prometryn and 25 days after sowing in soils treated with trifluralin.     

Soil composition affects the nesting behavior of blue-tailed bee-eaters (Merops philippinus) on Kinmen Island

The blue-tailed bee-eater (Merops philippinus) is a summer migrant that breeds on Kinmen Island, located off the west coast of Taiwan, about 5 km from the southern coast of mainland China. The aim of this study was to investigate why blue-tailed bee-eaters build their nests in sandy loam and sandy clay loam, but not in clay loam. Soil chemical and physical properties, and mineralogical composition were measured for the different soil types. Clay loam had a significantly lower pH, Na, and base saturation than did sandy loam or sandy clay loam. Clay loam had a significantly higher N, cation-exchange capacity (CEC), K, and free iron (Fe_d) and aluminum oxide (Al_d) contents than the other soil types. Clay loam had significantly lower sand and higher clay content, and higher bulk density and penetration resistance than the other soil types. The correlation coefficients (r ²) between penetration resistance and Fe_d, Al_d, and clay contents were 0.997, 0.848, and 0.779, respectively. Soil strength and compaction are important criteria for bee-eaters nesting-site selection. The lower pH of clay loam would enhance the exchangeable Al and acidity, further increasing the soil aggregation. Thus, it might prevent the bee-eaters from excavating nesting burrows.     

Effects of D-D, Telone or dazomet applied to potato ridges in spring on potato cyst-nematode, Heterodera rostochiensis, in sandy loam and silt loam soils

Large amounts of dazomet (329, 439 kg/ha) applied to potato ridge soil in spring, before potatoes were planted, controlled potato cyst-nematode (Heterodera rostochiensis) in sandy loam and silt loam more effectively than large amounts of D-D (359, 448 kg/ha). In heavily infested sandy loam, 329 kg dazomet/ha or 857 kg methyl bromide/ha applied in spring 1969 or 439 kg dazomet/ha applied in autumn 1968, greatly decreased the number of larvae able to invade potato roots, so Majestic potatoes grew and yielded well without increasing the number of nematodes left in the soil after harvest. Large amounts of D-D or Telone applied to the topsoil in autumn or to the ridges in spring were less effective in controlling potato cyst-nematode or increasing potato yields. Applied in spring 1969 to silt loam ridges, 439 kg dazomet/ha had more effect than 448 kg D-D/ha on potato cyst-nematode and on the increase in yield of Majestic potato. The yield of Maris Piper potatoes (resistant to H. rostochiensis pathotype A) in infested silt loam was increased greatly by D-D, as much by 112 as by 224 or 448 kg/ha.     

Effects of antibiotics in soil on the population dynamics of transposon Tn5 carrying Pseudomonas fluorescens

The effects of kanamycin and streptomycin added to soil on the survival of transposon Tn5 modified Pseudomonas fluorescens strain R2f were investigated. Kanamycin in high (180 g g^-1 dry soil) or low (18 g g^-1) concentration or streptomycin in low concentration in Ede loamy sand soil had no noticeable effect on inoculant population dynamics in soil and wheat rhizosphere, whereas streptomycin in high concentration had a consistent significant stimulatory effect, in particular in the wheat rhizosphere. Streptomycin exerted its effect by selecting P. fluorescens with Tn5 insertion whilst suppressing the unmodified sensitive parent strain, as evidenced by comparing the behaviour of these two strains in separate and mixed inoculation studies.Soil textural type influenced the effect of streptomycin on the Tn5 carrying inoculant; the effect was consistently detected in rhizosphere and rhizoplane samples of wheat grown in Ede loamy sand after 7 and 14 days incubation, whereas it was only apparent after 7 days in rhizoplane or rhizosphere (and bulk soil) samples of wheat grown in two silt loam soils. Modification of soil pH by the addition of CaCO₃ or bentonite clay resulted in an enhancement of the selective effect of streptomycin by CaCO₃ and its abolishment by bentonite clay.The addition to soil of malic acid or wheat root exudate, but not of glucose, enhanced the streptomycin selective effect on the Tn5-modified P. fluorescens strain. Neither the streptomycin producer Streptomyces griseus nor two non-inhibiting mutants obtained following UV irradiation affected the dynamics of P. fluorescens (chr::Tn5) in soil and wheat rhizosphere.The effect of streptomycin in soil on inoculant Tn5 carrying bacteria depends on conditions such as soil type, the presence of (wheat) root exudates and the type of available substrate.     

Influence of soil factors,fertilizers and manures on pathogenicity ofRhizoctonia solani onVigna species

Rhizoctonia solani caused maximum mortality of mung bean seedlings at 20°C, and the disease incidence decreased with increase of temperature; 30° was optimum for mycelial growth of the fungusin vitro. The fungus grew best in nutrient broth of pH 5.5 but infected mung bean and pea seedlings more severely in neutral and alkaline river sand than in the sand adjusted to acidic reaction. The disease incidence was higher in adequately moist sandy loam and less in soil under moisture stress. Incidence of cowpea seedling rot was higher in heavy-textured loam and silt loam soils than in light-textured sandy- and loamy sand. Addition of montmorillonite and kaolinite in the sandy soil increased the disease incidence, but these clays reduced fungus growth in culture. More seedling rot occurred in the sandy soil fertilized with urea, potassium nitrate, monocalcium phosphate, or potassium dihydrogen phosphate while soil application of ammonium nitrate, potassium chloride, or potassium sulphate decreased the disease. In tests with combined soil application of N (as urea), P (as monocalcium phosphate) and K (as potassium chloride), disease incidence was more in all combinations having P. Among the six micronutrients tested, only boron reduced the disease incidence significantly both in presence and absence of NPK fertilizers. Farm-yard manure and biogas sludge aggravated seedling rot but their water extracts decreased it. Humic acid, extracted from farm-yard manure, increased the disease incidence but was inhibitory to fungus growth in culture. Green manure also resulted in more disease.     

Biochar’s effect on crop productivity and the dependence on experimental conditions—a meta-analysis of literature data

Background and aims

For the last decade, there has been an increasing global interest in using biochar to mitigate climate change by storing carbon in soil. However, there is a lack of detailed knowledge on the impact of biochar on the crop productivity in different agricultural systems. The objective of this study was to quantify the effect of biochar soil amendment (BSA) on crop productivity and to analyze the dependence of responses on experimental conditions.

Methods

A weighted meta-analysis was conducted based on data from 103 studies published up to April, 2013. The effect of BSA on crop productivity was quantified by characterizing experimental conditions.

Results

In the published experiments, with biochar amendment rates generally <30 t ha^?1, BSA increased crop productivity by 11.0 % on average, while the responses varied with experimental conditions. Greater responses were found in pot experiments than in field, in acid than in neutral soils, in sandy textured than in loam and silt soils. Crop response in field experiments was greater for dry land crops (10.6 % on average) than for paddy rice (5.6 % on average). This result, associated with the higher response in acid and sandy textured soils, suggests both a liming and an aggregating/moistening effect of BSA.

Conclusions

The analysis suggests a promising role for BSA in improving crop productivity especially for dry land crops, and in acid, poor-structured soils though there was wide variation with soil, crop and biochar properties. Long-term field studies are needed to elucidate the persistence of BSA’s effect and the mechanisms for improving crop production in a wide range of agricultural conditions. At current prices and C-trading schemes, however, BSA would not be cost-effective unless persistent soil improvement and crop response can be demonstrated.     

Control of potato cyst-nematode, Heterodera rostochiensis, in three soils by small amounts of aldicarb, Du Pont 1410 or Nemacur applied to the soil at planting time

Aldicarb or Du Pont 1410 (S-methyl 1-(dimethylcarbamoyl)-N-[(methylcarbamoyl) oxy] thioformimidate) at 2.6–11.2 kg a.i./ha applied to the soil at planting time controlled potato cyst-nematode, Heterodera rostochiensis, in sandy loam, peaty loam and silt loam and greatly increased tuber yields of susceptible potatoes. Nemacur (O-ethyl-O-(3-methyl-4-methylthiophenyl) isopropylamido-phosphate) controlled potato cyst-nematode in sandy loam at 2.9–10.3 kg a.i./ha and in silt loam at 11.2 kg a.i./ha but did not control the nematode well in peaty loam even at 22.4 kg a.i./ha. In peaty loam aldicarb and Nemacur were more effectively incorporated by rotavation than by a modified power harrow.