Effects Of Agronomic Practices Research Articles

Phytoextraction of Metals from Contaminated Soil: A Review of Plant/Soil/Metal Interaction and Assessment of Pertinent Agronomic Issues

Phytoremediation is an emerging technology that employs the use of higher plants for the cleanup of contaminated environments. Fundamental and applied research have unequivocally demonstrated that selected plant species possess the genetic potential to remove, degrade, metabolize, or immobilize a wide range of contaminants. Despite this tremendous potential, phytoremediation is yet to become a commercial technology. Progress in the field is precluded by limited knowledge of basic plant remedial mechanisms. In addition, the effect of agronomic practices on these mechanisms is poorly understood. Another limitation lies within the very biological nature of this novel approach. For example, potential for phytoremediation depends upon the interaction among soil, contaminants, microbes, and plants. This complex interaction, affected by a variety of factors, such as climatic conditions, soil properties, and site hydro-geology, argues against generalization, and in favor of site-specific phytoremediating practices. Thus, an understanding of the basic plant mechanisms and the effect of agronomic practices on plant/soil/contaminant interaction would allow practitioners to optimize phytoremediation by customizing the process to site-specific conditions.

Myths, models and mitigation of resistance to pesticides.

Resistance to pesticides in arthropod pests is a significant economic, ecological and public health problem. Although extensive research has been conducted on diverse aspects of pesticide resistance and we have learned a great deal during the past 50 years, to some degree the discussion about 'resistance management' has been based on 'myths'. One myth involves the belief that we can manage resistance. I will maintain that we can only attempt to mitigate resistance because resistance is a natural evolutionary response to environmental stresses. As such, resistance will remain an ongoing dilemma in pest management and we can only delay the onset of resistance to pesticides. 'Resistance management' models and tactics have been much discussed but have been tested and deployed in practical pest management programmes with only limited success. Yet the myth persists that better models will provide a 'solution' to the problem. The reality is that success in using mitigation models is limited because these models are applied to inappropriate situations in which the critical genetic, ecological, biological or logistic assumptions cannot be met. It is difficult to predict in advance which model is appropriate to a particular situation; if the model assumptions cannot be met, applying the model sometimes can increase the rate of resistance development rather than slow it down. Are there any solutions? I believe we already have one. Unfortunately, it is not a simple or easy one to deploy. It involves employing effective agronomic practices to develop and maintain a healthy crop, monitoring pest densities, evaluating economic injury levels so that pesticides are applied only when necessary, deploying and conserving biological control agents, using host-plant resistance, cultural controls of the pest, biorational pest controls, and genetic control methods. As a part of a truly multi-tactic strategy, it is crucial to evaluate the effect of pesticides on natural enemies in order to preserve them in the cropping system. Sometimes, pesticide-resistant natural enemies are effective components of this resistance mitigation programme. Another name for this resistance mitigation model is integrated pest management (IPM). This complex model was outlined in some detail nearly 40 years ago by V. M. Stern and colleagues. To deploy the IPM resistance mitigation model, we must admit that pest management and resistance mitigation programmes are not sustainable if based on a single-tactic strategy. Delaying resistance, whether to traditional pesticides or to transgenic plants containing toxin genes from Bacillus thuringiensis, will require that we develop multi-tactic pest management programmes that incorporate all appropriate pest management approaches. Because pesticides are limited resources, and their loss can result in significant social and economic costs, they should be reserved for situations where they are truly needed--as tools to subdue an unexpected pest population outbreak. Effective multi-tactic IPM programmes delay resistance (= mitigation) because the number and rates of pesticide applications will be reduced.

Ridge tillage for corn and soybean production: environmental quality impacts

Tillage practices are needed to increase agronomic stability and productivity while enhancing the environment. Ridge tillage has been demonstrated as an effective agronomic practice; some have described it as a miniature precision agriculture. Environmental impacts have generally been positive but the results vary, depending upon soil and climatic factors. Ridge tillage changes soil temperature and water patterns compared to no-till and full width – moldboard/chisel plowing or disking for primary tillage. These changes lead to an improved soil environment for crop emergence and early growth, because of warmer soil temperatures in cool climates and better water relations in both poorly-drained and moderately well-drained soils. While increased soil water infiltration in the interrow can lead to increased leaching and greater loading of nitrates and herbicides at the bottom of the root zone, controlled studies suggest that ridge tillage with precise agrichemical placement in the ridge can provide a favorable environmental impact. Moreover, the combined herbicide and cultivation for weed control reduces the treated area and overall application for herbicides. Ridge tillage was evaluated at a number of field locations of the Management Systems Evaluation Areas program to assess both agronomic and environmental impacts. A special effort in these ridge tillage evaluations was to trace agrichemical movement from the site of application within the soil and into the surficial aquifer. In most instances, ridge tillage decreased agrichemicals leaching and the negative environmental impact.

Denitrification and nitrous oxide production in soil fallowed or under alfalfa or grass

Abstract A field study was carried out to assess the effects of agronomic practices and crops on nitrous oxide (N2O) production and denitrification rates. Air‐filled porosity, moisture content, respiration rate, and ammonium (NH4) and nitrate (NO3) concentrations were also measured along with nitrogen (N2) gas production using the static soil core procedure with acetylene (C2H2). Agronomic practices included applications of liquid cattle manure, ammonium sulfate, sucrose, and irrigation water as well as the incorporation of alfalfa. Measurements were made on fallowed soil as well as soils under alfalfa (Medicago sativa L.) and Kentucky bluegrass (Poa pratensis L.). The temporal pattern of N2 gas production was dominated by episodic events caused by manure or sucrose application, or alfalfa incorporation in conjunction with irrigation or rainfall events. Rainfall or irrigation alone did not increase N2 gas production unless following upon a dry period. In wetted soil, the N2O production rate was lower than...

Legume inoculant production and use in East and Southern Africa

Rhizobium inoculation is a cheaper and usually more effective agronomic practice for ensuring an adequate supply of N for legume-based crop and pasture production than the application of fertilizer N. This is particularly important in developing countries in Africa which, due to financial and technological limitations, must otherwise spend scarce foreign currency on foreign imports. We give an account of legume inoculant production, quality control and use in East and Southern Africa, with particular emphasis on Zimbabwe and Kenya.

FARMING AND GROUND BEETLES: EFFECTS OF AGRONOMIC PRACTICE ON POPULATIONS AND COMMUNITY STRUCTURE

AbstractWe studied the effects of agricultural practice on ground beetles, using pitfall traps in field plots and in an uncultivated meadow near Edmonton, Alberta. Ground beetle abundance and species richness were higher in plots operated under an organic farming regime than in those under a chemical regime, but neither crop type [barley (Hordeum vulgare L.), faba bean (Vicia faba L.), barley-pea (Pisum sativum L.) intercrop] nor crop rotation had an effect. Reduced tillage did not significantly change overall carabid activity or species richness but species differed in their response to tillage treatments. The carabid assemblage from an uncultivated field differed conspicuously from assemblages in the crops and fescue. Carabid abundance was highest in the meadow and the fauna was dominated by the exotic species Pterostichus melanarius Illiger. Effects of agronomic practice on carabid assemblages are complex, reflecting the interaction of biological traits of particular species and the combination of agronomic treatments applied.

Using Climatological, Geographical, and Taxonomic Information to Identify Sources of Mature‐Plant Salt Tolerance in Alfalfa

Performance under salinity stress has been improved in elite populations of alfalfa (Medicago sativa L. sensu lato) by mass selection. Use of unimproved germplasm may permit additional gains in salt tolerance or access to unique tolerance mechanisms. Resources would be used more efficiently if germplasm with specific traits could be identified from large collections using taxonomical, climatological, or geographical data. Our objective was to determine whether such information could be used to identify M. sativa accessions in the U.S. plant introduction (PI) collection likely to have improved response to salinity. We evaluated forage yield for three harvests in 630 Pis under saline (80 mMNaCI) and nonsaline irrigation in greenhouse trials. Passport data were used to classify climate (Trewartha's system) at the collection site. No significant differences were found in mean salt tolerance (forage yield with saline irrigation/nonsaline irrigation) among the subspecies of M. sativa sampled extensively (falcata, caerulea, varia, and sativa). Accessions considered either tolerant or with high saline yield (high forage yield with saline irrigation; highest 15.1% of accessions for these traits) were present in all subspecies. Mean salt tolerance and saline yield for accessions, and the proportion of accessions considered tolerant or with high saline yield did not differ between accessions from six basic climate groups (Tropical, Arid, Subtropical, Temperate, Boreal, Highland). An increased proportion of tolerant accessions was found from arid environments where alfalfa is usually grown without irrigation. The effects of agronomic practices seems to represent a major limitation to use of climatological data in identifying germplasm with improved performance under salinity stress.

Effects of agronomic practices on free fatty acid levels in the oil of Ontario-grown spring canola

Spring canola (Brassica napus) seed grown in Ontario frequently exhibits elevated levels of free fatty acids (FFA) in the oil. The objective of this study was to determine the effects of various agronomic practices on FFA levels. Several field experiments were conducted in 1989 and 1990, and one experiment was conducted in 1987. FFA levels in the oil were higher in 1989 than in 1990. Two cultivars, Kristina and Global, were included in most experiments. The cultivar Kristina exhibited consistently lower FFA levels than the cultivar Global, averaging 42% less over years and treatments. Global averaged 1.31 and 0.62% FFA in 1989 and 1990, respectively. Decreasing seeding rates raised FFA levels in both cultivars in 1989 and in Global in 1990. Increasing rates of nitrogen (N) fertilizer increased FFA in Global in 1989. The removal of drought stress by irrigation during seed filling decreased FFA in Global by 46% in 1989. A combination of high N, low seeding rates, and no irrigation increased FFA in both cultivars in 1990. Delays in planting date resulted in higher FFA in 1987. The effect of these agronomic practices on yield and seed oil concentration were also reported. Applications of potassium or boron fertilizers did not affect FFA, nor did weekly applications of the fungicide, benomyl, or dosing plants with elevated levels of atmospheric ozone. The problem of elevated FFA can be diminished by avoiding excessively high nitrogen fertilizer rates and low seeding rates and by selection of low-FFA cultivars. Key words: Canola, free fatty acids, irrigation, ozone, planting date, oil content

A review of the effects of various agronomic practices on cereal stem borer populations

Abstract The effects of agronomic practices such as sanitation and alternate hosts, tillage and mulching, time of planting, multiple and intensive cropping, rotations, spacing, intercropping, use of fertilizers and irrigation on pest populations are reviewed, with special reference to cereal stem borers. The disadvantages of chemical control of stem borers are discussed. It is concluded that agronomic practices have some potential for reducing populations of many pest species and of increasing those of beneficial ones. The effects of cultural methods are complex, and attention is drawn to the many areas of study requiring further investigation and the need for an interdisciplinary approach.

Silicon uptake by wheat and its relation to grain yield and water use

The silicon content in wheat in South Australia was measured in 46 experiments over four seasons. The percentage silicon, silicon uptake and its distribution in the plant tops varied greatly. The maximum uptake was 2.4 per cent of the dry matter production, but high yields were obtained with a lesser percentage than this. Of the total silicon uptake, 16-48 per cent was found in the glumes. The correlations between grain yield and silicon, either in the glumes or in the plant, were generally poor. There were significant relationships between water use and silicon. The relationship with silicon uptake in the tops was best and accounted for 77 per cent of the variation in water use but silicon analyses were not a satisfactory measure of water use efficiency. The effect of agronomic practices on the relationships is discussed.

Studies on the effect of the nutrient status of sugar-cane on the fecundity of Saccharosydne saccharivora (Westw.) (Hom., Delphacidae)

An account is given of glasshouse experiments in Jamaica to determine the effects of agronomic practice on the fecundity of the sugar-cane pest Saccharosydne saccharivora (Westw.). Eggs (up to one egg per ovariole per day) develop throughout adult life. On young vigorous plant cane the pre-oviposition period was 5·3 days; egg production was highest during the first six days of the oviposition period and declined markedly after 12 days. Mean daily egg production per female over 12 days was taken as an index of fecundity.The effects of fertiliser application (ammonium sulphate and potassium chloride), wet and dry water regimes, variety (B41227, B42231 and B4362) and crop cycle (plant and ratoon cane), all at different stages of crop development, were observed in four series of experiments involving 1 000 female S. saccharivora. Potassium (K2O) and phosphorus (P2O5) per cent lamina dry matter varied comparatively little, but nitrogen content declined with the age of the plant, increased with application of ammonium sulphate, and was unaffected by crop cycle or variety. Egg production was highest on young cane (up to a mean of 12·0 eggs per female per day), but declined on older cane; it increased with the application of ammonium sulphate but was unaffected by potassium chloride. A direct linear correlation between egg production and the nitrogen content of the leaf (r2 = 0·69, 0·81, 0·52 and 0·69 in series I–IV, respectively) suggested a causal relationship. The pre-oviposition period lengthened and the proportion of females failing to lay any eggs increased in the absence of fertiliser and with increasing plant age. Variation in leaf nitrogen under field conditions could affect egg production.

A second report on the effect of agronomic practices on the incidence of rhizoctonia and scab of potatoes

The results obtained in three rotation experiments in New York State in 1939, confirm the report made in 1938. They are as follows: More potato tubers bore sclerotia ofRhisoctonia where potatoes were grown continuously than where they were grown in longer rotations. Where potatoes were grown continuously, the largest percentage of tubers were affected withRhizoctonia where they were grown without commercial fertilizer, manure or cover crop. The addition of fertilizing material in any of these forms reduced the percentage of tubers affected, and the greatest reduction was secured on plots where all of these fertilizing materials Were used together. At the only location where the pH of the soil was such as to favor scab, the largest amount occurred on plots which received no fertilizer, manure or cover crop. At the other locations small increases in scab occurred on plots Which had been previously limed for clover. The largest increases were obtained on plots which received both manure and lime. Manure alone has caused a small increase at Malone.