Factors affecting the economic benefits of sprinkler uniformity and their implications for irrigation water use

Adoption of more uniform sprinkler systems involves a trade off between increased capital expenditure on equipment and the benefits associated with reduced water application when application is uniform. An empirical analysis of the economics of lettuce production, grown using sprinkler systems under the windy conditions of the Swan Coastal plain in Western Australia is presented, where the yield response to water exhibits eventual declining marginal productivity. A range of sprinkler designs that have been field-tested for performance were examined. The optimal per-crop water application for the least efficient system was up to double the application rate of the most efficient system. However, the economic analysis demonstrates that there are clear incentives for adopting more water-efficient systems despite the higher capital cost, because of the yield depressing effect of over-watering. Sensitivity analysis demonstrates substantially poorer incentives for improving irrigation efficiency when yield relationships follow a Mitscherlich functional form.

Developing a methodology for identifying,mapping and potentially monitoring the distribution of general farming system types in Vietnam’s northern mountain region

This study tests a method to identify and map the spatial distribution of general farming system types in five districts of the northern mountain region (NMR) of Vietnam. Over the last 50 years the NMR has suffered from a large loss of forest cover, often blamed on the swidden farming systems that are found in the mountains. As a result different programs have been put forward to change local land use practices: to decrease the amount of swidden land, “sedentarize” farmers responsible for practicing swidden agriculture, and introduce new farming systems. However, some researchers have identified one type of swidden farming system, composite swiddening, as ecologically more stable, causing little net deforestation and less environmental degradation than other farming systems in the NMR. To date no study has identified how widespread this or other types of farming systems are in the NMR. This study makes use of geographic data for five districts in the NMR within a GIS, combined with field checking, to characterize, identify and map the spatial distribution of the general farming system types, including composite swiddening, by commune for these districts. The results of the mapping indicate that there are few communes where a single farming system type is found. As these districts are spread over five provinces, the results reinforce the view that in Vietnam’s NMR, farming system types vary down to below the commune level. An 80% agreement between the results shown on the map and field checking resulted from an examination of 19 communes in the districts mapped. A comparison was done of 2000 data to 1992 data for one district. An analysis of the communes’ farming systems for 1992 and for 2000 indicate that permanent agriculture farming systems of both rice paddy agriculture and permanent upland agriculture are appearing and replacing swiddening systems.     

Effect of modern irrigation methods on growth and energy production of sweet sorghum (var. Keller) on a dry year in Central Greece

The subject of this project is to estimate the growth and productivity of sweet sorghum [Sorghum bicolor (L.)] var. Keller, under two different irrigation methods – the conventional surface drip method (two treatments) and the subsurface drip method – in a dry year in Central Greece, as an energy crop for the production of bio-ethanol. A field experiment was carried out on the experimental farm of the University of Thessaly during 2005, comprising of a completely randomized block design with four treatments in four blocks, including control (non-irrigated). In the treatments of surface drip method the evapotranspiration needs were satisfied by using full (100% ETm) and supplement (80% ETm) irrigation doses, while in the treatments of subsurface drip method only supplement irrigation water was used (80% ETm) with the aim of more efficient water conservation. Irrigation was fully automated, and application depths were determined, using a class A open evaporation pan for matching the evapotranspiration needs. The growth of the crop was measured by means of plant height and leaf area index, which were determined periodically throughout the growing period. Fresh and dry biomass productions were measured over six harvests covering the entire growth and production process of cultivation. The results of the first year demonstrated a clear superiority of the subsurface drip method on plant heights, leaf area index and total fresh and dry biomass production compared with the surface drip method for equal values of irrigation water. Maximum yield was attained by mid-September, before crop maturation, something which should be taken into consideration when choosing the best harvesting time of the crop. After late September, large negative growth rates were recorded, resulting in an appreciable drop in the final fresh and dry matter yield.