Agro-Ecosystems最新文献

An examination of support energy use within the major systems of animal production shows that substantial outputs occur as heat and excreta and, if these could be utilised, overall energetic efficiencies could be greatly changed.

The main justification for energy accounting as more relebant than financial accounting in the longer term rests on the probability that the price of energy will rise more than the price of other resources.

Whilst there are substantial differences between the support energy costs of production for different products, the differences between intensive and extensive systems producing the same product are not enormous. The more intensive systems tend to use more support energy, but also produce more product per unit of other resources, and their support energy costs tend to represent a higher proportion of total costs.

The background contamination of wheat grains and straw with residues of DDT and HCH has been observed in all the samples collected at maturity from Punjab, India during April, 1979. The mean levels of DDT residues were 0.03 and 0.05 mg kg⁻¹ in wheat grains and straw, respectively, while the corresponding levels of HCH were 0.04 and 0.06 mg kg⁻¹,. respectively. This contamination has been ascribed to the ubiquitousness of these insecticides in the environment rather than to their deliberate usage.

Domesticated animals can adjust to the effects of modern production practices by employing neural and hormonal response mechanisms. Such mechanisms may have biological costs that appear as reduced growth or productivity and a decline in antibody activity. However, there exists within most domestic species genetic variation for adaptivity so that selection for reduced responsiveness to physical and behavioral stressors is possible.

A growing number of agricultural scientists, environmentalists, government officials, farmers, and both urban and rural laymen, have become increasingly alarmed over the potential vulnerability of the energy-intensive systems of food and fiber production which now characterize U.S. agriculture. During the past 40 years, conventional agriculture has become increasingly dependent upon petroleum-based, chemically-synthesized fertilizers and pesticides to supply plant nutrients and for crop protection. Certainly these energy-intensive technologies have contributed greatly to the U.S.'s agricultural productivity. However, sharply escalating production costs associated with the increasing cost and uncertain availability of energy, i.e. fuel and fertilizers, have generated considerable interest in less expensive and more environmentally compatible production alternatives such as organic farming. The apparent decline in soil productivity throughout the U.S. from excessive soil erosion, nutrient runoff, and loss of soil organic matter; the impairment of environmental quality from sedimentation and pollution of natural waters by agricultural chemicals; and, the potential hazards to human and animal health and food safety from heavy use of pesticides, have also stimulated interest in organic farming systems of food production. This article describes and analyzes the agronomic and socioeconomic character of organic farming in the U.S. and assesses its future potential contribution to the overall system of food and fiber production in this country and abroad. Clearly, a number of factors, such as future research and education programs, public policies, and the cost and availability of conventional farm production inputs, will greatly influence the rate at which organic farming technologies and management practices are adopted. However, current trends and circumstances indicate that organic farming systems will play an increasingly important role in both U.S. and world agriculture.

Dissolved nutrients were monitored bi-weekly in stream water draining 14 upland watersheds in Oregon's Coast Range after spraying with 2,4,5-T + 2,4-D, clearcut harvesting and slash burning. Anion generation and leaching were primarily studied. The nitrate concentrations fell and the bicarbonate concentrations rose during summer low-flows from treated watersheds without detectable increases in loss of macronutrients (N, Ca, Mg, K, Na). The stream water concentrations of bicarbonate (the most prevalent anion) related to watershed orientation and the degree of devegetation. Nitrate concentrations appeared to be correlated positively with watershed drainage rates. Studies with incubated soils and field sampling of soil solution indicate that denitrification probably minimizes nitrate loss from saturated soils during frequent winter to spring storm periods.

The behaviour of the iron chelates and sodium salts of EDTA, DTPA and EDDHA in calcareous (iron deficient) and alluvial (border-line iron deficient) soils and their effectiveness during plant growth were studied. The effectiveness of the iron chelates in maintaining soluble iron and in supplying barley with iron was in the order Fe-EDTA < Fe-DTPA < Fe-EDDHA. Replacement of iron by other cations in Fe-EDTA and Fe-DTPA, rather than adsorption of iron chelate by the soil, was the main factor influencing their effectiveness. The equilibrium of Fe-EDTA with soils was dominated by competition between iron and calcium, whereas that of Fe-DTPA was dominated by iron being in competition with manganese initially and with calcium, zinc and copper afterwards. The relative dominance of the chelate of the competing cation varied with soil type. Fe-EDDHA was neither adsorbed nor was its iron fixed by the soil to any great extent.

The sodium salt of DTPA and EDDHA continually dissolved native soil iron but increased soluble manganese only temporarily. Dissolution of native zinc and copper was least with EDTA and EDDHA and most with DTPA. The sodium salts of the chelating agents were as effective as the iron chelates in supplying barley with iron in the alluvial soil, which was marginally deficient, whereas they were much less effective in the calcareous soil, where iron supply is a greater problem.

Soil surface arthropod populations in conventional tillage (CT) and no-tillage (NT) sorghum and adjacent old field (OF) were compared using pitfall trap captures. Overall diversity ($\text{H}$) and similarity quotients (QS) between systems were calculated for each of seven 24-h sampling periods throughout the season. Diversity of the soil surface arthropods was greater in NT than either CT or OF. Although each system was distinct (any two of the systems had less than 30% of their species in common), NT was most similar to OF and least similar to CT during a period of drought and after heading of the sorghum. Percentages of individuals and species represented by spiders were similar in NT (30 and 15%) and OF (22 and 17%); percentages were substantially less in CT (11 and 8%). Yields (biomass of sorghum) in CT and NT were not significantly different despite the generally predicted higher pest populations in NT in the absence of insecticides. Leaf area grazed by insects was greater in CT (28%) than in NT (12%).