Loss of nitrate nitrogen in the soil surface layer in Japanese grassland during the heavy rainfall season and its enhancement by the root mat

Summary Measurement of nitrate and chloride in the soil profile have been made in a grassland field at the National Grassland Research Institute, Tochigi, which received heavy applications at the rate of 60 kg/ha of nitrogen and chloride as potassium nitrate and calcium chloride respectively, at 5 days intervals in the summer wet season. The chloride anion was utilized as a tracer of the nitrate anion. Compared with the plots without a root-mat zone (0–2.5 cm), those with a root-mat zone had a lower NO₃–N/Cl ratio in the soil surface layer (0–15 cm). Under intensive rainfall (17th July to 5th Sept., 519 mm) and high temperature (23°C), the surface root zone of the grass sward was assumed to be in a significantly reducing condition. From the change of NO₃–N/Cl ratio in the soil profile and the plant uptake of nitrogen and chloride, considerable reduction of NO₃–N and its loss from the root-mat zone was suggested.     

Evaluating spatial within plot crop variability for different management practices with an optical sensor?

Subsoil constraints to root growth exacerbate frequent water and nutrient limitations to crop yields in Mediterranean-type environments. Amelioration of subsoil constraints can relieve these limitations by opening root-access to subsoil water and nutrients. However, decisions in subsoil amelioration are hampered by seasonally variable yield responses in these environments. We used the APSIM model to analyse the impact of subsoil constraints on yield and yield variability. The simulated yield data were used to calculate the financial benefits of subsoil amelioration across several scenarios. There was a strong yield-dependence on accessible soil water governed by root depth. Root depth development was limited to a minimum of either the effect of subsoil constraints or the weather-dependent depth of the soil wetting front. Insufficient rainfall in dry years or in a drier region often resulted in shallow soil wetting fronts and correspondingly shallow roots even in the absence of subsoil compaction. In these situations, there is little response to subsoil amelioration. Positive yield responses and positive financial returns to subsoil amelioration are therefore greater in good rainfall years and are more likely in a wetter region. A yield response to amelioration is also greater in coarser textured sand than finer textured sandy loam in an average rainfall season because the same amount of rainfall results in a deeper wetting front in sand than in sandy loam. Hence, roots in a sand are required to grow deeper compared to a sandy loam to access the same amount of water and therefore benefited more from subsoil amelioration in an average rainfall year. In wet years, sands leach more nitrate than sandy loam, which decreases yields and the response to subsoil amelioration in sands is more than in the sandy loam. Environmental threats occur along with yield loss when roots cannot access subsoil water. These include increased nitrate leaching and deep drainage due to unused water remaining in the soil profile. By allowing roots to access deep soil water, ameliorating subsoil is expected to yield financial gains in average to good rainfall seasons and decrease the environmental risk of drainage and leaching loss. The financial gains are expected to offset potential financial losses in dry and dry finish seasons especially in coarser textured soils and wetter environment. Responsible Editor: Jan Vos.     

Transport of a genetically engineered Pseudomonas fluorescens strain through a soil microcosm.

Vertical soil microcosms flushed with groundwater were used to study the influence of water movement on survival and transport of a genetically engineered Pseudomonas fluorescens C5t strain through a loamy sand and a loam soil. Transport of cells introduced into the top 1 cm of the vertical soil microcosms was dependent on the flow rate of water and the number of times microcosms were flushed with groundwater. The presence of wheat roots growing downward in the microcosms contributed only slightly to the movement of P. fluorescens C5t cells to lower soil regions of the loamy sand microcosms, but enhanced downward transport in the loam microcosms. Furthermore, the introduced P. fluorescens C5t cells were detected in the effluent water samples even after three flushes of groundwater and 10 days of incubation. As evidenced by a comparison of counts from immunofluorescence and selective plating, nonculturable C5t cells occurred in day 10 soil and percolated water samples, primarily of the loamy sand microcosms. Vertical soil microcosms that use water movement may be useful in studying the survival and transport of genetically engineered bacteria in soil under a variety of conditions prior to field testing.     

Transport of a genetically engineered Pseudomonas fluorescens strain through a soil microcosm

Vertical soil microcosms flushed with groundwater were used to study the influence of water movement on survival and transport of a genetically engineered Pseudomonas fluorescens C5t strain through a loamy sand and a loam soil. Transport of cells introduced into the top 1 cm of the vertical soil microcosms was dependent on the flow rate of water and the number of times microcosms were flushed with groundwater. The presence of wheat roots growing downward in the microcosms contributed only slightly to the movement of P. fluorescens C5t cells to lower soil regions of the loamy sand microcosms, but enhanced downward transport in the loam microcosms. Furthermore, the introduced P. fluorescens C5t cells were detected in the effluent water samples even after three flushes of groundwater and 10 days of incubation. As evidenced by a comparison of counts from immunofluorescence and selective plating, nonculturable C5t cells occurred in day 10 soil and percolated water samples, primarily of the loamy sand microcosms. Vertical soil microcosms that use water movement may be useful in studying the survival and transport of genetically engineered bacteria in soil under a variety of conditions prior to field testing.     

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.     

Distribution of entomopathogenic nematodes in Southern Cameroon

A first survey of entomopathogenic nematodes (EPN) was conducted in three agro-ecological zones of Southern Cameroon in 2007 and 2008. Entomopathogenic nematodes were recovered from 26 of 251 soil samples (10.4%). Three species, Heterorhabditis baujardi, Steinernema sp. A and Steinernema sp. B were found. The two steinernematids were considered unidentified species. Among the positive samples, 23 samples contained only H. baujardi (88.5%), two contained Steinernema sp. A co-occurring with H. baujardi (7.7%), and one sample contained Steinernema sp. B (3.9%). H. baujardi was frequent in forest and fruit crop (cocoa and oil palm plantations). Steinernema sp. A was found in a tree plantation of teak, Steinernema sp. B in a forest habitat. Nematodes were mostly present in acidic soils with pH ranging from 3.7 to 7.0. The highest EPN presence was recorded in sandy loam, sandy clay loam, sandy clay and clay soils. EPNs were not recovered in sand, loamy sand and clay loam soils. Using principal component analysis for elucidating the major variation patterns among sampling sites, four factors explaining for 73.64% of the overall variance were extracted. Factors were a combination of geographical (latitude, longitude, altitude), soil (pH, contents of sand, silt and clay, organic carbon, texture), and moisture (wilting point, field capacity) parameters as well as climatic parameters (mean annual rainfall, mean air temperature). Logistic regression and redundancy analyses (RDA) revealed that soil pH, longitude, available water and altitude were associated with presence and absence of EPN. Both logistic regression and RDA indicated that, increasing soil pH and longitude, associated with decreasing altitude, led to higher percentages of samples containing entomopathogenic nematodes.     

Soil fungistasis: role of the microbial nutrient sink and of fungistatic substances in two soils.

Sensitivity of conidia of Cochliobolus victoriae to fungistasis decreased markedly following incubation on moist sand for at least 1 h. Germination was greater on Conover loam or on sand being leached with water than on an alkaline clay loam soil known to produce a volatile fungistatic substance. Evolution of 14CO2 began within 3 min after [14C]glucose was applied to the soils; the rate of 14CO2 evolution was faster with Conover loam. Germination of Thielaviopsis basicola conidia per unit of glucose remaining in agar discs initially containing 0-1% glucose, was lower for discs incubated on the clay loam soil than on Conover loam, and was greatest on a bed of sand undergoing aqueous leaching. Germination of ascospores of Neurospora tetrasperma and conidia of C. victoriae was suppressed on discs of washed, Purified Agar or polyacrylamide gel incubated on or over the clay loam soil, but no suppression resulted when discs were incubated on Conover loam. Extensive aeration of either soil did not remove its fungistatic effect. Fungistasis in Conover loam appears to be caused primarily by nutrient deprivation, whereas volatile fungistatic substances may play a major role in the clay loam soil.     

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana carpocapsae (Nematoda: Steinernematidae)

The vertical migration of N. carpocapsae infective juveniles applied to the soil surface or introduced 14 cm below the soil surface was studied in four different soil types (pure silica sand, coarse sandy loam, silty clay loam, and clay). The percentage of juveniles able to migrate and infect wax moth pupae placed in the soil decreased as the percentage of clay and silt increased. Most nematodes placed on the soil surface remained within 2 cm of the surface, but some penetrated to a depth of 10 cm in pure silica sand and coarse sandy loam to infect pupae. Some pupae at the same depth were also infected with nematodes in silty clay loam soil. In pure silica sand and coarse sandy loam, nematodes introduced 14 cm below the soil surface were able to infect wax moth pupae located between 4 and 24 cm. Movement was least in clay soil and limited in silty clay loam. Nematodes showed a tendency to disperse upwards from the point of application. In all cases the number of migrating nematodes was greatest when wax moth pupae were present.     

Feeding inhibition and mortality in Reticulitermes flavipes (Isoptera: Rhinotermitidae) after exposure to imidacloprid-treated soils

Feeding inhibition and mortality of Reticulitermes flavipes (Kollar) exposed to sand, sandy loam, loam, and silty clay loam soils treated with several concentrations of imidacloprid were studied using bioassay techniques under laboratory conditions. Termite workers stopped feeding after exposure to treated soils. Differences in feeding reduction varied among the soil types. Based on the magnitude of the F-statistics, the effect of imidacloprid on the reduction of termite feeding was greatest in sand followed by sandy loam, loam, and silty clay loam soils. Soil properties such as organic matter content, silt and clay proportions, pH, and cation exchange capacity were suggested to affect the bioavailability of imidacloprid. Similar soil effects on mortality were observed in termites continuously exposed to treated soil for 21 d. In three of four soils tested, susceptibility to imidacloprid was not affected by the source of the termites tested.     

Salt uptake and salt tolerance by sunflower

Summary A normally grown crop of sunflower on red sandy loam soils was found to remove considerable quantities of chloride and sodium. On heavy clay soils with saline patches sunflower plants removed large quantities of sodium followed by chloride and sulphate. In view of its salt tolerance, it is suggested that intercropping or rotation with sunflower might help reduce soil salinity and improve soil conditions where salinity problems are coming up especially in heavy clay soils with low permeability. re]19720711     

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana glaseri (Nematoda: Steinernematidae)

The vertical migration of infective juveniles of Neoaplectana glaseri applied to the soil surface or introduced 16 cm below the soil surface was studied in pure silica sand, coarse sandy loam, silty clay loam, and clay. The number of juveniles that migrated and infected wax moth pupae placed in the soil decreased as the proportion of clay and silt increased. The majority of nematodes moved downwards 2-6 cm from the surface, but some penetrated to a depth of 14 cm in pure silica sand and coarse sandy loam. In pure silica sand and coarse sandy loam, nematodes introduced 16 cm below the soil surface were able to infect wax moth pupae located at depths of 0-4 cm and 28-32 cm. Nematodes showed a greater tendency to disperse downwards from the point of application. Movement of the nematode was least in clay soil and limited in silty clay loam soil. The number of migrating nematodes was greatest when wax moth pupae were present.     

Quantification of soil-to-plant transport of recombinant nucleopolyhedrovirus: effects of soil type and moisture, air currents, and precipitation.

Significantly more occlusion bodies (OB) of DuPont viral construct HzSNPV-LqhIT2, expressing a scorpion toxin, were transported by artificial rainfall to cotton plants from sandy soil (70:15:15 sand-silt-clay) than from silt (15:70:15) and significantly more from silt than from clay (15:15:70). The amounts transported by 5 versus 50 mm of precipitation were the same, and transport was zero when there was no precipitation. In treatments that included precipitation, the mean number of viable OB transported to entire, 25- to 35-cm-tall cotton plants ranged from 56 (clay soil, 5 mm of rain) to 226 (sandy soil, 50 mm of rain) OB/plant. In a second experiment, viral transport increased with increasing wind velocity (0, 16, and 31 km/h) and was greater in dry (-1.0 bar of matric potential) than in moist (-0.5 bar) soil. Wind transport was greater for virus in a clay soil than in silt or sand. Only 3.3 x 10(-7) (clay soil, 5 mm rain) to 1.3 x 10(-6) (sandy soil, 50 mm rain) of the OB in surrounding soil in experiment 1 or 1.1 x 10(-7) (-0.5 bar sandy soil, 16-km/h wind) to 1.3 x 10(-6) (-1.0 bar clay soil, 31-km/h wind) in experiment 2 were transported by rainfall or wind to cotton plants. This reduces the risk of environmental release of a recombinant nucleopolyhedrovirus (NPV), because only a very small proportion of recombinant virus in the soil reservoir is transported to vegetation, where it can be ingested by and replicate in new host insects.     

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.     

MOVEMENT OF EELWORMS

The optimum crumb sizes for movement of potato-root eelworm larvae in a sandy loam, a heavy clay and a peat soil were 150–250 and 250–400 μ. Mobility was very similar in clay and sandy loam, in both of which there was an optimum suction for movement. In the peat, however, mobility increased with suction and no optimum suction was established. Larvae may be able to move in peat at high suctions because friction between the larvae and the peat crumbs is less than between clay or sand crumbs. Larvae moved to the wet end of a moisture gradient in sand, the number increasing with the steepness of the gradient. The rate of spread of larvae in sand 150–250 μ diameter varied between 2 and 3 cm. a day, depending on suction. As pore size increases, any upward movement in a moisture gradient is opposed by falling under gravity. Larvae do not respond to a moisture gradient or fall under gravity in sand where the width of the pore approximates to the diameter of the larva. The presence of host roots also counteracted the response to a moisture gradient; the degree of orientation to the roots increased with the time the roots were in the sand. Direct observation on larvae, newly emerged from cysts, in the presence of host plant roots, suggests that larvae orientate themselves at a distance from the root and do not reach the root by random movement. Many of the movements of eelworms are explicable by considering the relationship between pore size, eelworm diameter and water distribution, and a diagram relates movement and various soil factors.     

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.     

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.     

Population Increase of Pratylenchus hexincisus on Corn as Related to Soil Temperature and Type

Population increase of Pratylenchus hexincisus on corn was tested over 3 months at 15, 20, 25, and 30 C in Marshall silt loam, Clarion silt loam, Buckner coarse sand, and Haig silty clay loam soils. The optimum temperature for increase was 30 C in all soils. The nematode population was significantly larger in Buckner coarse sand than in other soil types at 50 C. The recovered P. hexincisus populations equaled or exceeded initial inoculum levels at the two higher temperatures in Marshall silt loam and Haig silty clay loam and at 30 C in Clarion silt loam and Buckner coarse sand. P. hexincisus required 32,400 heat units in Haig silty clay loam and more than 40,000 heat units in the three other soil types to reach a level that is known to cause significant height and biomass reduction in corn under controlled condition.     

Movement of nitrate,chloride, and potassium in a sandy loam soll

Summary This study was conducted to measure the movement of nitrogen, chloride, and potassium in a sandy loam soil under field conditions and with controlled sprinkle irrigation. After 62.5 mm of water was applied, soil nitrate measurements indicated 67 per cent of the applied N fertilizer was lost from the upper 105 cm of the soil profile. Following a cumulative irrigation of 112.5 mm of water, 82 per cent of the applied N was lost. Since the chloride movement and redistribution was almost identical to the nitrate movement pattern, it would seem plausible that most of the nitrates were lost from the upper part of the soil by leaching. The potassium movement involved the redistribution of exchangeable K from the 0–8 cm soil zone into the 8–15 cm zone and with some buildup of K occurring in the 15–30 cm soil layer. re]19741126 rv]19751111     

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.