Potency of some nematicides for controlling nematodes and improving banana production in the southern region of Oman (Dhofar)

Abstract

An established banana field was treated by applying three compounds, fenamiphos, isazofos and carbofuran, to the soil around each mat. The tested compounds were found to reduce significantly soil and root nematode populations. The production cycle of the nematocide treatments was 24 days faster than that of the untreated control. Application of the above chemicals enhanced to the total production of banana. Carbofuran may be ranked top of these nematocides, followed by isazofos. Application of 2 g a.i. of carbofuran three times at intervals of 4 months, yielded 2.66 tonnes per acre more than that of the control.     

Electron Microscopy in Biology

Abstract

Farmer surveys were conducted in the Yaqui Valley, Sonora, Mexico during 1983 and 1985 to investigate the relationship between agronomic practices used by the farmers and the incidence of Karnal bunt (Tilletia indica) disease of wheat. The variables investigated included soil type, land preparation, origin of seed, irrigation, nitrogen fertilizer, weed control and crop rotations. None of these variables were found to have a significant influence on the disease. This indicates that although management practices may have some effect on the incidence of the disease they are not the primary factor. The coincidence of rainfall and/or high humidity at flowering time appears to be of more importance than agronomic practices.     

Soil Microbial Biomass Under the Canopy of Coastal Sand Dune Shrubs

Coastal sand dunes are affected by seasonal fluctuations in salinity due to seawater spray and precipitation. Salinity was found to be very high in summer soil samples and was about 15-20 times lower in the preceding rainy winter. High microbial biomass values of 234.6 and 173.1 mugC g-1 dry soil were found under Artemisia monosperma and Retama raetam, respectively, even at elevated salinity. The metabolic quotient for CO2, which may serve as an indicator for changes in microbial diversity or environmental stress, was unexpectedly high (58.5 and 48.8 mug mg-1 d-1 under A. monosperma and R. raetam, respectively) in low-saline samples from the winter when compared to the summer (a maximal value of 20 mug mg-1 d-1), probably indicating a shift in community structure. It may be concluded that even under hostile conditions in poor sandy soils and with high salinity the presence of perennial shrubs creates favorable niches for microorganisms and affects their activity.     

Long-Term Crop Rotation Effects on Organic Carbon,Nitrogen, and Phosphorus in Haplustoll Soil Fractions

Soil organic matter (SOM) or carbon (SOC) consists of a number of fractions (which can be separated by granulometric wet sieving) having different properties among them. Information on fraction nutrient distribution and long-term crop rotations is lacking for semiarid environments. The objective of this research was to study the agronomic effects on soil OC, N, and P fractions. The humified OC was the largest and least variable fraction of the SOC. Soil under continuous mixed pasture had higher OC contents than under annually tilled treatments. Similarly, soil total nitrogen under the cropped treatments decreased from 1.7 g N kg-¹ in noncultivated soils (reference plots) to 1.0, 0.7 an 0.7 g N kg-¹ under mixed pasture, pasture-crop, and wheat-crop respectively, in the fine soil fraction. The reference plots also showed significantly lower levels of organic phosphorus (P o ) in comparison to the other treatment (from 67.1 w g P o g-¹ to greater than 100 w g P o g-¹ in the fine fraction of the treatments and years). The noncultivated soil showed larger values of P o and inorganic P in the large-size granulometric fraction (0.1-2 mm) than in the soil fine fraction (0-01 mm). However, the rotation treatments had greater concentrations of P in the fine fraction. The P o from the coarse fraction appears to be the most labile and sensitive fraction to tillage and environmental conditions, and may be closely related to P availability.     

A Method for Baiting Corticium rolfsii and of Estimating the Sclerotial Population in Soil

Abstract

The use of tissue blocks of Xanthosoma sagittifolim for baiting Corticium rolfsii from soil is described. The baiting technique has been found efficient for gross estimation of the viable sclerotial content of air-dried soil. The results obtained by this method compare well with those determined by the sieving technique of Rodriguez-Kabana et al.     

Striga seed avoidance by deep planting and no-tillage in sorghum and maize

The possibility of reducing Striga hermonthica (Del.) Benth. parasitism in severely infested fields, by means of deep planting - thereby reducing the root length in the upper layers of the soil where Striga seeds are predominantly found - was tested in field trials with maize and sorghum in western Kenya. Sorghum seeds were planted in Striga-infested fields approximately 2.5 cm deep in the soil or at the bottom of conically-shaped plant holes (15-20 cm deep). Depth of plant holes for maize varied from 0 to 30 cm, in un-tilled soil. Deep planting in un-tilled soil gave higher (up to double) grain yields, compared with standard planting in tilled soil. Parasite emergence was related negatively to planting depth of maize (p< 0.05). Deep planting in tilled soil gave 74% more sorghumgrain yield relative to standard planting. In this treatment Striga seed production was not reduced but in un-tilled fields with deeply planted sorghum Striga seed production was completely suppressed. Therefore, a combination of zero-tillage and deep planting seems to be the most effective treatment. The probable mechanism causing these results is avoidance of Striga seed by the host root system, resulting in a delay in the onset of Striga attachment and the formation of smaller numbers of attachments.     

Inconspicuous restraint of rice seedling growth by root-infecting fungi in soil of a rice paddy field

 Rice seedling growth, estimated by plant height and root development and discoloration, was better in pasteurized soil than in unpasteurized soil obtained from a flooded rice field. Rice seedlings also grew better in sterilized soil modified by adding roots harvested from the pasteurized soil than in soil modified by adding roots harvested from the unpasteurized soil. The results demonstrate that seedling growth in the rice field soil was inhibited by soil microorganisms, even though no typical symptoms such as seedling blight or damping-off appeared. Pythium aristosporum is suggested to be involved in the inhibition. Thus, it appears that inconspicuous restraint of rice seedling growth could occur in soils of rice paddy fields. Received: May 20, 2002 / Accepted: October 16, 2002 Acknowledgments The authors thank Dr. T. Ichitani, former professor at Osaka Prefectural University, for providing an isolate of Pythium aristosporum for comparison, and Mr. Mitsuaki Sato of Akita Prefectural College of Agriculture for technical assistance.     

Sorghum-cowpea Intercropping: An Effective Technique Against Runoff and Soil Erosion in the Sahel (Saria,Burkina Faso)

In the Central Plateau of Burkina Faso, runoff on bare soil amounts to 40% of annual rainfall and soil losses reach 4 to 8 Mg ha-¹ a-¹, despite slopes of under 3%. Several studies have shown that mulching the soil surface can reduce runoff by over 60%. However, the scarcity of straw and the incompatibility of mulching with mechanical soil preparation have prevented the large-scale adoption of the technique. The study conducted in Saria village where annual rainfall is 800 mm,set out to evaluate the efficacy of sorghum-cowpea intercropping in reducing runoff and erosion. The study design comprised five plots set up so as to recover runoff and transported solids, on a Ferric lixisol with a slope of 0.7%. Three years results showed that sorghum-cowpea intercropping reduces runoff by 20-30% compared to a sorghum monoculture and by 45-55% compared to a cowpea monoculture. Soil loss is also reduced with intercropping by at least a half compared to sorghumand cowpea monoculture. Moreover, it transpired that sorghum-cowpea intercropping is also beneficial in agricultural production terms, since the grain yield of the intercropped plots was double that obtained with sorghumor cowpea monocultures. The better crop production can be an asset for the widespread use of this technique in the country. An evaluation of the advantages of the legume in terms of nitrogen supplies to the cereal (N 2 symbiotic fixation) and of added soil OM will be useful in improving the cost-effectiveness of such a technique.     

Estimation of Loss in Wheat Yield Due to the Cerealcyst Nematode Heterodera avenae

Abstract

The cereal cyst nematode, Heterodera avenae Wollenweber, 1924, occurs worldwide including India where it causes ‘molya’ disease of wheat and barley. Wheat yield losses due to the nematode were estimated during 1974-76 at a few villages in Mohindergarh district, Haryana, India, by applying dichloropropane-dichloropropene mixture and dibromochloropropane singly or in combination as soil f umigants. In light soil the cereal cyst nematode infestation at 4/5 eggs and larvae/g soil approximated the economic threshold level. However, depending on the initial population density of H. avenae and other field conditions, such as soil type, moisture, soil condition, chemical application method, chemical application time etc., the increase in yield of wheat cv. Kalyan Sona ranged from 8 to 49% at nematode infestation levels of about 6 to 13 eggs and larvae/g soil when treated with these nematicides.     

Effect of coffee pulp on Trichoderma spp. in Kenyan tea soils

Abstract

Six organic amendments and one soil sterilant (Basamid) were screened at different rates to a given amount of soil, for their efficiency to enhance the population of Trichoderma spp. Coffee pulp significantly (P = 0.01) enhanced the population of Trichoderma spp. in the soil compared to other amendments. The enhancement was rate‐dependent with 16 and 22 g carbon giving the optimum population. The Trichoderma species enhanced included T. koningii, T. harzianum and T. longibrachiatum. The implications of these results in relation to biological control of soil‐borne plant pathogens are discussed.     

Soil Properties Required by Some Southern Africa Fruit Trees as Assessed by Discriminant Analysis

Some indigenous fruit trees, in the drylands of southern Africa are worthy of interest because of their adaptation to environmental conditions prohibitive for traditional crops. Their fruits or their derivatives are traditionally used as an additional income by rural population, but little information is available about the properties of the soils that support their growth, although this information is necessary if the trees are subjected to sustainable domestication. Several soil properties are, however, to be considered as a whole and discriminant analysis provides a helpful tool to individuate the best conditions for the tree growth. Thirty-five soil samples were taken in areas where the trees naturally grow and produce, and the analytical data of the surface layer were used to relate soil properties to tree species. Four groups of trees were well separated using two discriminant functions that takes into account both the fertility characteristics (pH, organic C, N, texture, and properties of the exchange complex) and the Fe contents and distribution among the oxide forms. The discriminant functions allow a very acceptable reclassification of the data (more than 80% of cases correctly reclassified) and the classification coefficients were used to build an empirical equation that may help to identify the most suitable tree to be introduced at a new site.     

Phospholipid Fatty Acid (PLFA) Composition and Its Dynamics in a Desert Soil System

The effect of environmental conditions, and especially soil water content, on microbial community structure was quantified during a 15-month sampling period (1994-1995) in a Negev Desert soil system by determination of phospholipid fatty acids (PLFAs). Two rainy seasons were observed during the study period: (1) the rainy season of 1993-1994, with a total rainfall of 58mm, and (2) the rainy season of 1994-1995, with a total of 140mm, which is 55% more than the multiannual average. Soil samples collected from the 0-10cm layer exhibited changes in soil moisture and PLFA composition. Palmitic acid (nC16:0) was found to be the most common acid, with a maximum abundance found in May 1994 (27.2%). Oleic acid (C18:1 omega 9) was found to be the second highest in abundance, with high levels in January 1994 (14%), decreasing gradually to 1.3% of total ion current in January 1995. This decrease was interpreted as being caused by abiotic factors affecting the microbial community, resulting in fatty acid profile and lipid abundance. Other acids were found to be present in relatively small amounts. The iC17:1 omega 9 and C18:2 omega 8, 11 were found among the major PLFAs during the study period. The data obtained in this study were found to be similar to data obtained in soils of temperate climates, in spite of the hypothesis that the total PLFAs of the desert soil microbes are triggered and depend on soil water availability. This can afford special data interpretation of the viable biomass of the soil microbes and their metabolic status.     

Soil Fertility Variability and Constraints on Village Scale Transects in Northern Burkina Faso

Soil variability has a profound impact on crop yields in low-input agriculture. The objectives of this study were to examine soil fertility variability and to identify potential soil constraints relating to farmers' conditions for agricultural production in the Sahelian zone of northern Burkina Faso. Surface soil (0-20 cm) and subsoil (20-100 cm) were sampled from 25 pedons on village-scale transects embracing three genetic soil units: two generations of sandy dune soils showing incipient development; a complex unit of clayey pediplain soils with duplex properties showing both alkaline and acid subsoil reaction; and hydromorphic, clayey valley bottom soils. Particle size distribution, pH, electrical conductivity, cation exchange capacity, exchangeable base cations and acidity, soluble base cations, organic carbon, nitrogen, total and available phosphorus, moisture constants, and bulk density were determined. Contents of organic carbon, total nitrogen, total and available phosphorus,and exchangeable potassium are low in all soils and are presumably major constraints.The sodium influenced clayey soils show high absolute variability; properties that vary are subsoil clay (5.8-38.5%), pH (5.8-10.0), cation exchange capacity (4.49-24.81 cmolc kg1), exchangeable sodium percentage (0-26), as well as electrical conductivity, structure, consistency, and available water holding capacity. The sandy soils are homogeneous and not as acid as elsewhere in the Sahel, presumably due to a dust influx. The soil fertility is generally low but highly variable, implying that constraints within production units may consist of multiple com binations of adverse chemical and physical properties, conceptually consistent with the low and variable millet yields. The variability also implies that soil character ization depends on the design of soil sampling, that average values are of doubtful use, that application of chemical fertilizers will produce very different results, and that there is no general scheme for correcting soil fertility. The application of lives tock manure will continue to be the best strategy for sustaining soil productivity.     

Diseases in Reduced Cultivation and Direct Drilling Systems1

Mould board ploughing, long the foundation of arable agriculture, has been replaced on many British farms by reduced cultivation systems not involving the inversion of the soil. There is also an increasing interest in direct drilling into untilled soil. The change to such techniques may be expected to influence the incidence of certain cereal diseases. Increases in Rhynchosporium secalis (Oud.) Davis and Septoria spp. have been noted in non-plough situations where infected debris is left on the soil surface. Effects on other diseases are more complex and may be mediated through the effects of cultivation technique on time of sowing, crop establishment, weed control, pest incidence and other factors including the physical nutritional and microbiological characteristics of the soil.     

Global Assessment of Human-Induced Soil Degradation

Soil is a valuable natural resource that in the short - term is nonrenewable and is difficult to reclaim when degraded. The use of soils on a sustainable basis requires that their capability to withstand the demands upon them is not exceeded. Those people concerned with conservation should be aware of the vital importance of soil for maintaining food supplies for an increasing world population. Increasing demands place a greater strain upon the soil. If the demands become too great, the soil becomes degraded. As soil is the basis of all terrestrial ecosystems, a degraded soil means lower fertility, reduced biodiversity, and human poverty. To provide basic information on soil degradation worldwide, a survey of soil loss through erosion, physical deterioration, and chemical pollution was made. Digital databases are not available to hold information necessary to monitor and combat soil degrada tion at global and national scales. Soil degradation is recognized as a serious and widespread problem, so in September 1987 the International Soil Reference and Information Centre was commissioned to make a survey for a map at a scale of 1:10,000,000 entitled "Global Assessment of Human - Induced Soil Degradation" (GLASOD). Until it was published in 1990, there was no uniformly collected body of information on soil degradation worldwide. The GLASOD survey provides basic data on the world distribution and intensity of erosional, chemical, and physical types of degradation. The original purpose of GLASOD was to provide factual information, to replace sweeping statements about soil and land degradation, and to raise awareness of policy makers and governments for the continuing need for soil conservation. The GLASOD survey also enables comparisons to be drawn between degraded soils of different continents, and the methodology used can be a basis upon which plans for restoration of degraded lands can be based.     

Weed Control Work in Progress at the University of the West Indies - Part 3

Abstract

Results of replicated trials in dry beans and groundnuts showed that weeds could reduce yields by 5–50%. Certain herbicide treatments significantly increased or decreased seed number/pod and 100-seed weight. Two trials, one a maize herbicide trial, studied soil persistence of a number of herbicides. Preliminary experience with glyphosate is summarised and work on the control of Drymaria cordata is described.     

Fourteenth International Congress of Entomology,Canberra, August 22–30, 1972

Abstract

An experimental herbicide, AC 92,553 has been developed by Cyanamid International to control most annual grasses and several small-seeded broad-leaved weeds, applied either pre- or post-seeding on a wide range of crops. The influence of soil and weather conditions on the effectiveness of the herbicide are discussed. Suggested combinations with other herbicides and rates of application are given. The results of toxicity studies are summarised.     

Insect Repellents

Abstract

Many countries in the Arabian Peninsular are anxious to develop fully their limited agricultural resources. A knowledge of plant diseases and nematodes which attack their crops is essential before this is achieved. A survey of these in The Sultanate of Oman shows that soil-borne pathogens predominate and that the damage they cause is exacerbated by soil conditions. Nevertheless, some important pathogens are absent and hopefully their introduction to the relatively new agricultural areas in this part of the world can be prevented.     

Microbiotic Crust Influence on Unsaturated Hydraulic Conductivity

Microbiotic crusts occur extensively in rangeland soils . Developed by filaments of cyanobacteria and algae , and thalli of lichen and moss entanglement of soil particles , they create a physical discontinuity in the surface profile with greater concen trations of clay , silt , and potentially hydrophobic organic matter. These conditions potentially contribute to variability in soil hydrology of arid land and should be considered in the development of hydrologic and erosion models. However, there is limited manipulative research examining the functional relationships between soil and microbiotic crusts . We investigated the influence of cyanobacterial-dominated microbiotic crust on measured hydraulic conductivity (K) in a sandy loam soil at a southeastern Utah site . Using a tension infiltrometer , we determined K under three surface treatments: undisturbed , chemically killed (representing dead microphytes within the crust), and removed (scalped) microbiotic crusts. We applied treatments to spatially interspersed intact surface soils within shrub interspaces . Microbiotic crusts at this site and in this stage of successional development had no discernible influence on K. This finding supports results from research conducted in a variety of soils from sandy to silt dominated with a range of microbiotic development . Because this research was site and time specific , and because the role of microbiotic crusts in the environment continues to be debated , additional research is warranted to deter mine how stage of development of microbiotic crust influences soil hydrology .