Agro-Ecosystems最新文献

Stream water samples have been collected from a small (1.6 km²) cultivated catchment in East Devon, UK. Spatial, long term and storm-period nitrate behaviour is described, and attempts are made to model response using a range of statistical techniques for four major gauging stations. These include the main stream and three “representative” subcatchments which reflect variable source areas and include a natural woodland stream, a tile drain and drainage ditch. The variability in partial area contributions from these areas plus the impact of fertiliser application and extreme hydrological conditions are shown to seriously affect the success of modelling procedures.

Rural population density in the Mefou and Lékié divisions is 82 and 102 persons per km², respectively. Food crop growing in the area (annual rainfall approx. 1600 mm, altitude 700 m) is based on shifting cultivation. The main field type is the groundnut field; groundnuts are grown mainly in association with cassava, tannia, maize and plantains. The cropping period covers some 2 years but transition to the succeeding fallow is gradual; harvest of tuber crops and plantains may extend into the fallow period. Duration of the fallow is variable but for many field near dwellings is very short (3–5 years). Shortening of the fallow is the only adjustment to increased cropping intensities.

The system is discussed in relation to the original system, which consisted of a much longer fallow, followed by growing of ngôn (Cucumeropsis mannii) with tubercrops, maize and plantains and thereafter only the groundnut field. Some suggestions for the improvement of the present-day system are presented, including fallow management and use of crop debris as mulch.

We studied the effects of different covers (none, legume and natural) established in different ways (with legumes only: hand-weeded, hand-weeded plus extra fertilizer, and with pre-emergent application of the herbicide Oxyfluorfen at 0.25 kg active ingredient ha⁻¹), on the first 3.5 years' growth and yield of oil palms (Elaeis guineensis Jacq). Legumes were a mixture of Centrosema pubescens and Pueraria phaseoloides. Natural generation consisted mostly of Nephrolepis biserrata and Paspalum conjugatum. Early rates of growth of the palms (as measured by frond area, girth, height, etc.) were greatest in the bare plots and the first yields of fresh fruit bunches were significantly higher than with any other treatment. On the other hand, relative growth rates and net assimilation rates were higher in legume plots (particularly those established with Oxyfluorfen) throughout most of the experimental period. This means that the rate of growth of palms in legume treated plots steadily overtook the rate of growth of those in bare plots. Presumably, these differences resulted from rapid exploitation of soil nutrients by palms in bare plots, and the “banking” of these same nutrients in legume plots.

The results of the detailed survey of Egyptian agriculture made by Napoleon's savants during 1799 and 1800 are analysed to provide estimates of the human and animal work inputs and crop yield outputs of the Egyptian agro-ecosystem before the Nile flood was brought under control. The estimates were found to be internally consistent. In terms of human food production per unit land area, the system was outstanding, exceeding that of western Europe at that time. The food output per unit human labour input was high and the large draft animal population was shown to be an important element in maintaining the fertility of the system. The estimate of human carrying capacity, 4.5 per hectare, was used to calculate the population of Egypt and the estimates were compared with those from historical demographic studies.