Agriculture and Environment最新文献

A model has been used to estimate the losses of N by leaching from arable soils throughout England and Wales during winter and spring. It is predicted that the extent to which autumn residues of nitrate are leached by winter rains varies considerably from year to year and from site to site, and that this variation will cause much bigger differences in the N fertilizer requirements of deep-rooted crops than of shallow-rooted ones. It is estimated that an average of about 42% of the N applied as fertilizer is leached from arable soils in England and Wales each year. However, the resulting increase in the average nitrate concentration in the drainage water is estimated to exceed 11.3 μg N/ml only in the Eastern region. Spring leaching of freshly-applied N fertilizer is likely to be generally small, and will have little effect on the N fertilizer requirements of deep-rooted crops, but may affect those of shallow-rooted crops in the west.

Year-round irrigation and multiple cropping with paddy as a dominant crop in the monsoon months have given rise to an increase in the incidence of malaria over an 18-year period in the Mahi-Kadana Irrigation Project in Gujarat State, India. Further man-made disturbances such as over-irrigation, and lack of drainage have also compounded the problem. The remedies, apart from the conventional control and prevention measures, are better water management practices and continuous monitoring of the projects by an inter-disciplinary team which should include a public health administrator.

Earth worms (Lumbricus terrestris) were exposed under laboratory conditions to aldrin, endrin, DDE, parathion and carbaryl in seven different concentrations ranging from 1.5 to 150 μg/g of bedding. Results showed that earthworms were able to tolerate doses of up to 14 μg/g of bedding.without significant mortalities. However, some behavioral and physical symptoms such as “withdrawal responses” and discoloration of the skin were noted in animals where non-lethal dosages were employed. Aldrin and endrin gave an LD₅₀ of approximately 45 μg/g, DDE gave an LD₅₀ of 46 μg/g, parathion showed an LD₅₀ of 34 μg/g and carbaryl which gave an LD₅₀ of 28 μg/g showed the most lethal effect of all insecticides tested.

Soil conservation policy and the resultant programs of soil conservation may be viewed as efforts of planned change. A major reason for the failure of conservation programs is the assumptions or criteria upon which conservation policy is based that limit the amount of flexibility for application of programs to unusual or unanticipated situations. The assumptions relate to (1) the economic rationality of men, (2) the homogeneous distribution of knowledge and information across a population of farmers, and (3) the indivualism of the farmer in his decision-making and action. These assumptions have serious implications upon a farmer's capacity to implement and maintain conservation practices.

The relationship between existing and proposed soil conservation policies and the structure of agriculture are examined, with consideration of these assumptions and the capacity for change. Data on farmer preferences for alternative conservation policies are then examined to determine differential effect by farm structure. Results indicate a definite relationship between farm structure, capacity for change and policy preference.

Damson-hop aphid, Phorodon humuli, is the major insect pest of English hops and has developed marked resistance to many organophosphates (OPs), and lower levels of resistance to other OPs, carbamates and endosulfan used as foliar sprays. Current control methods rest heavily on the systemic OP mephosfolan applied as a soil drench. After the persistent aphidical action of an early-season (May) soil drench of mephosfolan has declined, insect predators, particularly Anthocoris nemoralis and A. nemorum, can usually contribute greatly to control for the remainder of the season, especially within the hop cones. Means of suppressing aphids in July/August with minimum harm to predators are essential for a commercially feasible system of integrated control; possible methods of achieving this are discussed.