Agro-Ecosystems最新文献

Shifting agriculture locally known as jhum is the predominant form of agriculture used by the local tribe of the north-eastern hill region of India. There is also some valley rice cultivation and terrace cultivation. The structure and some functional aspects of these three agro-ecosystem types are discussed and compared. The 30 year jhum cycle has the advantage over the 10 or 5 year cycle apart from higher yields, in that the monetary output/input ratio under a 30 year jhum cycle is comparatively favourable. Further, the 30 year jhum cycle is advantageous over terrace cultivation as the latter needs heavy inputs of fertilizers. The main advantage of settled valley cultivation is the raising of crops consistent in yield year after year from the same site.

An analysis of the energy inputs and outputs for conuco agriculture (i.e., shifting cultivation) and a comparison of productivity between conuco crops and successional vegetation was undertaken near the town of San Carlos de Rio Negro in southern Venezuela.

The main crop, yuca (Manihot esculenta, Crantz), yielded (m.t. = metric tonnes) 4.31 m.t. ha⁻¹ wet weight in year one; production declined to 2.81 m.t. ha⁻¹ in the second year. The infertile soils of the region are the major cause of these low yields.

Although relatively unproductive, conuco agriculture is much more energy efficient than mechanized agriculture. The ratio of energy output, in the form of processed food, to energy input in the form of human labor, averaged 13.9:1 over two cropping periods. Slightly more energy was devoted to field activities than to processing activities.

The conuco crops were more productive than the adjacent succession site vegetation (532 vs. 109 g m⁻² dry weight) during the first year after cutting and burning; but in the second year the successional vegetation was more than twice as productive as the conuco crops (1446 vs. 529 g m⁻² dry weight). This difference in second year production was attributable to greater resource allocation to leaves and longer leaf retention time for the successional vegetation.

China's agro-ecosystem is circumscribed by two critical environmental constraints; relative shortage of arable land and frequent regional lack or surplus of moisture. Intensive cropping and intricate water controls were developed over the centuries to deal with these constraints, and they remain the cornerstone of China's farming today. Human and animal labor continues to be an essential input, as are large quantities of organic fertilizers. Reliance on biomass fuels will also stay high for the foreseeable future. Farming modernization has brought the greatest advances to water control (both irrigation and drainage) and nitrogenous fertilizer production. However, widespread shortages and qualitative deficiences of modern inputs will not be easily eradicated. Total food output during the past three decades just kept pace with the population growth and the one-sided stress on grain production led to insufficient supply of edible oils, fruits and above all, animal foods. Overall use of external energy subsidies (direct and indirect use of fossil fuels and hydro-electricity) is still rather moderate but bold modernization plans for the 1980's would raise it substantially, thus lowering the currently high output/input ratio. Whatever the actual pace of modernization, careful attention to China's deteriorating environment will be critical. Land losses and soil degradation, erosion, deforestation and pollution are assuming alarming proportions and the long-range development of China's farming in balance with its protected environment is finally being recognized as the precondition of sustainable success.

Diurnal and seasonal changes of the concentration of eight inorganic ions (NO₃, NO₂, NH₄, PO₄, K, Na, Ca, Mg) in stream water were investigated at four study sites in the rural landscape of the Kakioka Basin, Japan. Study sites included two woodlands and two croplands with rural and urban settlements. The diversification of land use from woodlands and croplands to settlements enhanced ionic concentrations in the stream water. Monthly variations were significant in all the eight ions. The number of ions showing significant diurnal variations increased with the increase of human activities in the drainage basin. Principal component analysis was used to characterize the difference in water quality between study sites and the seasonal and diurnal patterns of fluctuation.