Agro-Ecosystems最新文献

A practical approach for the inclusion of environmental factors in land-use planning is presented. The Jalapa region, an area of 4750 km² which embraces a diversity of ecological conditions, is used to illustrate the approach. Data were gathered from aerial photographs, a survey of maize fields and interviews of farmers concerning their cultivation practices.

After devising a climatic and geomorphological system of land classification, 33 land types were identified, described and inventoried; 58 land-use systems were identified and described. The descriptions were structured to predict the income, employment, costs, food production, agricultural chemical inputs and erosion that could be expected for each land-use system on each land type. This information was used to devise a multi-objective land-use game for planners. Users of the game may set priorities on their planning objectives, specify the amounts of agricultural services available, and see the effects these have on optimal allocation of the available land of each type among the different possible uses, as well as how well the objectives are satisfied by the allocation.

By shifting objective priorities and varying infrastructure levels, the game user may examine the trade-offs among planning goals and among possible avenues of investment or other management interventions. A study of the environmental cost of producing increasing amounts of food for a growing population in the Jalapa region illustrates the game's usefulness, and actual land allocations in the Jalapa region are compared with optimal allocations under different priorities. The carrying capacity of the region is examined from this point of view, giving particular attention to the demands that increasingly urban habits of consumption may place on the land and to the role properly directed technology can play in increasing carrying capacity without causing environmental damage.

Plants of two important crops of India, wheat (cultivar N-4) and gram (cultivar H-355) were dusted with 2, 4 and 6 g m⁻² day⁻¹ of fly ash for 45 days. Both crops showed an increase in the height of the plants, dry weight, and chlorophyll and carotenoid content. The higher dusting rates affected the photosynthetic pigment contents.

The relationship between rodent control, decline in damage and resultant increase in production in twelve vegetable crops was studied in fields (2000 ha) in eight villages near Jodhpur. The rodent damage to various vegetable crops ranged from 4.1–19.9%, the average being 8.7%. A reduction of 92.5% of the rodent population corresponded with a 91.9% reduction in damage. On average, this increased the production of vegetable crops to 11.7 quintals (q) ha⁻¹ (7% ha⁻¹). The cost benefit ratio was 1:900. The paper also discusses the migration of rodents to crop fields from surrounding non-agricultural land and vice versa and replacement of rodent species after control operations.

Intensification of land use by shifting Maya agriculturists in Belize, Central America, has led to a decline in soil fertility and crop yields. Examination of eleven nutrients in crop plants and soil, and changes in nutrient levels with the length of the cropping period, indicated that phosphorus was the limiting factor for plant growth. Physical analyses of the soil and visual evidence suggested that erosion is a contributing factor to declining soil quality. A variety of solutions to the infertility problem are discussed.

The growth and species structure of vegetation in relation to the proximity of termite (M. michaelseni) mounds was studied in a semi-arid savannah ecosystem during 1978–1980. The dry matter yield in the termite-modified area at 1–10 m distance from mounds was significantly greater (P < 0.01) than that in the area beyond 22 m which is relatively unaffected by the termites. Themeda triandra and Digitaria scalarum, dominant grass species of the area, were totally absent in the 1–10 m zone around the mound. The major species in the immediate vicinity of the mound were Pennisetum stramineum and Cynodon dactylon, the latter was a dominant species (over 90%) within the 0–10 m zone and entirely absent beyond 15 m from the mound. The number of grass species increased from 2–3 species around the mound to 6–7 species in the area apparently beyond the influence of the mound. High concentration of nutrients and favourable water availability, together with good drainage, appeared to be the major causes of increased biomass and different species composition of vegetation around the mound.