Improving irrigated agriculture in the Fergana Valley, Uzbekistan.

摘要

Water scarcity and severe environmental degradation are causing water managers in Central Asia to reevaluate irrigation water use. The objective of this research was to investigate cropping systems that could improve food security in rural areas of the Fergana Valley of Uzbekistan given the constraints of limited water, increasing salinization of land resources and a rigid state order system which requires farmers to produce cotton and wheat. Growing short season food legumes after winter wheat harvest using alternate furrow and regulated deficit irrigation is proposed.;The different response of the two legumes to regulated deficit irrigation and alternate furrow irrigation is explained by examining components of the plant-soil-water system. Both strategies resulted in water savings and reduced crop evaporative consumption, with larger reductions in green gram than common bean. Severely stressed common bean extracted more water at 60 cm than non-stressed plants, whereas severely stressed green gram used less water at all depths. Transpiration rates were generally lower in green gram than common bean and decreased in both crops as soil water deficit increased. However, after irrigation, common bean's water use was higher than the non-stressed treatments while green gram's transpiration rate only increased slightly from the before-irrigation value: Collectively, these results suggest alternate furrow irrigation and deficit irrigation are appropriate methods to increase WUE, allowing application of less irrigation water, particularly, for green gram production. Use of the FAO's water stress coefficient in predicting evapotranspiration under water limiting conditions appears to over-predict water use for green gram and could lead to over-irrigation.;A greenhouse study was conducted to assess how these crops will respond to soil salinity when produced in the gypsiferous soils of the region. The study evaluated various growth components of common bean and green gram irrigated with deficit irrigation in soils with and without gypsum and at three levels of soil salinity. Results showed that biomass and leaf area were decreased by approximately 20% for both crops, as ECe increased from 2.8 dSm-1 to 7.5 dSm-1. Yields were higher at all salinities for green gram than in common bean. However, relative yield reductions with increasing salinity were greater for green gram (43%) compared to common bean (19--31%). The presence of gypsum enabled both crops to maintain reasonable yield at ECe values which would be lethal in soils dominated by other salts.;The CROPGRO model was modified to include a salinity response function. An iterative process was used to modify the CROPGRO code for root water uptake in an approach very similar to the empirical reduction functions found in hydrological models. This approach has been evaluated in the literature as largely superior to the approach found in the current CROPGRO model under conditions of soil salinity. A qualitative analysis of the model indicated the model performed as expected under a range of atmospheric, irrigation and crop tolerance scenarios. Model simulations compared very favourably to results obtained in the greenhouse for yield and seasonal ET with values of the Willmott agreement index (i) of 0.98 for both variables evaluated at different levels of salinity and deficit irrigation (a value of 1.0 indicates perfect agreement). Final biomass predictions were less satisfactory, though the modified model performed as well as the original model. The modified model was successfully tested with field data, on common bean from an experiment in the Fergana Valley (i of 0.75 for ET and 0.74 for final yield), though the sensitivity of the model to a soil fertility function and relative nodule number made it difficult to assess the model performance.;Increasing water use efficiency (WUE) associated with crop production is a way for arid and semi-arid areas to increase their agricultural production where there is little or no prospect for expansion of water resources. The WUE of common bean (phaseolus vulgaris) and green gram ( vigna radiata) irrigated with deficit and alternate furrow irrigation was evaluated in a field experiment in the Fergana Valley. The results indicate the WUE for both commercial yield and biomass were approximately twice as high for green gram as common bean. Conversely, the water use efficiency for root biomass in common bean (0.15 kg m-3) was slightly higher than green gram (0.13 kg m-3). WUE increased in green gram when deficit irrigation or alternate furrow irrigation were practiced, whereas it remained constant in common bean for all treatment combinations.