Farm crops

Carbon. Most of the Earth s supply of carbon is stored in carbonate rocks in the Hthosphere. Normally the circulation rate for Hthospheric carbon is slow compared with that of carbon between the atmosphere and biosphere. The carbon cycle has received much attention in recent years as a result of research into the possible relation between increased atmospheric carbon dioxide concentration, most of which is produced by combustion of fossil fuel, and the "greenhouse effect," or global warming. Extensive research has been done on the rate at which carbon dioxide might be converted to cellulose and other photosyntheticaHy produced organic compounds by various forms of natural and cultivated plants. Estimates also have been made of the rate at which carbon dioxide is released to soil under optimum conditions by various kinds of plant cover, such as temperature-zone deciduous forests, cultivated farm crops, prairie grassland, and desert vegetation. 

MAFF/SOAFD Pesticide Usage Survey Group, Arable Farm Crops in Great Britain 1994, 1995. Water Research Council, Atmospheric Sources of PoUntion. Inputs of Trace Organics to Surface Waters, R D Report No. 20, Water Research Council, 1995. 

Neher DA, Olson RA (1999) Nematode communities in soils of four farm cropping management systems. Pedobiologia 43 430-438... 

Prof Peter von Fragstein und Niemsdorff, Department of Organic Farming Cropping Systems, University of Kassel, Nordbahnhofstr, la, Witzenhausen 37213, Germany. Tel +49 5542 981567, Fax +49 5542 981568,... 

Conventional breeders often think that organic farmers require an absolute disease resistance, but in many cases tolerance or partial resistance can be sufficient. Organic farmers are used to searching for ways to reduce risks by an array of solutions at different levels (farm, crop, variety) and also adopt such a strategy in their search for appropriate combinations of supporting variety characteristics. There are different variety characteristics that support yield and yield stability through optimal plant health (Table 5.2). Plant health can be defined as a result of the following components ... 

If farm crops are harvested from the land rather than left to decay, the soil becomes deficient in this important element. The nitrogen is removed in the harvested crops rather than remaining as the plants decay. In addition, nitrates can be washed from the soil by the action of rain (leaching). For the soil to remain fertile for the next crop, the nitrates need to be replaced. The natural process is by decay or by the action of lightning on atmospheric nitrogen. Without the decay, however, the latter process is not efficient enough to produce nitrates on the scale required. 

As a consequence of the very rough surface of a coniferous canopy (which in no way approaches a plane structure) thermal fluxes from these surfaces are relatively small ie. forest canopy surfaces are relatively cooler than the surfaces of farm crops (18). The spire like structure of the crown result in daytime temperature gradients immediately above the canopy surface which are small and wind speed gradients which are relatively large. It should he anticipated that buoyant (free convective) eddies generated by vertical temperature gradients will be relatively unimportant and that wind speed gradients will provide the major source of eddy currents. 

Insect pests of farm crops are difficult to control when necessary activities such as tillage weeding irrigation and harvesting increase the pest population and decrease the numbers of its natural enemies. 

R. P. Davis, M. R. Thomas, D. G. Garthwaite and H. M. Bowen, Pesticide Usage Survey Report 108 Arable Farm Crops in Great Britain, MAFF, London, 1992. 

The various fungicides have either specific or broad spectrum efficacy. These can be deployed for either prophylactic or curative action. Beyond the farm crops and horticulture, maintenance of turf and lawns free of insects and weeds, and the preservation of natural and agricultural forestry are significant markets for insecticides and herbicides. 

This reaction is important to agriculture because ammonia is used widely as a source of nitrogen for fertilizing corn and other farm crops. The photo on the opposite page shows ammonia being knifed into the soil. 

Organic Mercury. Case report studies suggest that dermal exposure to methylmercury or phenylmercury in humans can cause rashes and blisters on the skin (Hunter et al. 1940 Morris 1960). A 33-year-old male worker exposed to methylmercury nitrate dust for 2 years developed bums and blisters on his forearm (Hunter et al. 1940). These effects healed within 9 days. Sensitivity to phenylmercuric salts is shown by individuals who developed itchy, pruritic, papular eruptions or rashes on their skin following acute dermal exposure (Morris 1960). A 54-year-old woman with a family history of atopy was found to display erythema (at 30 minutes postexposure) and urticaria (at 60 minutes) when treated topically with a 0.01% solution of phenylmercuric acetate (Torresani et al. 1993). This positive reaction was associated with aggravation of facial edema and an attack of bronchospasm. The woman, who was a farmer, was believed to have been previously exposed to phenylmercuric acetate during contact with pesticides and herbicides used on farm crops. 

Utilization of farm crops. Hearings, Eighty-first Congress, 1949-51. 

Sly, J.M.A. Arable farm crops and grass 1982. Preliminary Report of Pesticide Usage England and Wales No. 35. Ministry of Agriculture, Fisheries and Food London, 30pp, 1984. 

Visit a garden supply store to see what chemicals are being sold for use around the home. Look up the chemicals in the Merck Index and other suitable sources to see what they are and what their toxici-ties are. Include Scott s four-step lawn care program in the survey. If possible compare the levels of application to those recommended by your local agricultural extension agent for use on farm crops. 

On cultivated soils located on hilly or rolling landscapes, water erosion can reduce soil fertility and productivity to such an extent during periods of 25 years or less that cultivation is no longer profitable. Such erosion occurred on millions of acres in the East, Southeast, and even in many Midwest and Western soils. In many areas practically none of the original topsoil now remains. It is only the availability in recent years of abundant fertilizers that has made possible the use of many of these severely-eroded soils for general farm crops (see Chapter 26). Other soils that were originally very shallow are now classed as marginal and suitable only for pasture and forests. 

Carbon sequestration is the capture and storage of carbon that would otherwise be emitted or remain in the atmosphere. Terrestrial ecosystems, which consist of vegetation and soils containing microbial and invertebrate communities, sequester CO2 directly from the atmosphere. The terrestrial ecosystem is essentially a huge natural biological scrubber for CO2 from all sources of fossil fuel emission, such as automobiles, power plants, and industrial facilities. Terrestrial ecosystems (forests, vegetation, soils, farm crops, pastures, tundras, and wetlands) have a net carbon accumulation of about one-fourth of the amount emitted to the atmosphere from fossil fuels. 

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