Water Use Efficiency Levels Research Articles

Ecophysiological Responses of two Xerophytes Atraphaxis fruescens and Elaeagnus angustifolia to the Change of Groundwater Depth in Arid II. Leaf Photosynhesis and Photosynthetic Response to Light and Temperature

The eco physiological responses of dominant trees (Atraphaxis frutescens and Elaeagnus angustifolia) to ground water availability were investigated in a controlled environment at the Plant Transpiration Consume Water Observation Station in Minqin Desert Botanical Garden, Gansu province. In this experiment, the depths of groundwater(DGW)were designed as 1.4m, 2.4m and 3.4m. In each treatment, the two desert species were transplanted to the observation sites with different DGW after growing naturally for 3 or 4 years. The results showed that: 1) the changes of DGW resulted in the significant changes of net photosynthetic rate (Pn), the transpiration rate(E), stomatal conductance(Gs), leaf contents of chlorophyll a(Chl a), chlorophyll b(Chl b) and the total chlorophyll(Chl a+Chl b), the ratio of Chl a and Chl b(Chl a/Chl b), the quantum yield efficiency and the CO_(2) carboxylation efficiency; 2) although these two desert species were well adapted to the water stress environment at 3.4m DGW, their adaptive strategies were different.In response to the water stress environment. A. frutescens reduced its photosynthetic rate and maintained the level of water use efficiency, while E. angustifolia largely decreased the transpiration rate and thus increased the water use efficiency;3) in different DGW, the optimal temperature of photosynthesis in these two desert species did not change significantly, but the net photosynthetic rate under the optimal temperature range declined markedly. Since E.angustifolia is a nitrogen fixation species, further studies are needed to verify whether or not the differences of drought adaptation between these two species are related to the nitrogen fixation.

A preliminary study of the responsiveness to seasonal atmospheric and rainfall patterns of wash woodland species in the arid Richtersveld

Seasonal carbon and water relations were compared among seven tree or shrub wash woodland species in the winter rainfall desert of the Richtersveld National Park, South Africa. Plants were generally aseasonal with respect to gas exchange, but responsive to rainfall events with respect to water relations and phenology. Relatively narrow annual ranges in potential evapotranspiration due to the maritime influence could explain why these plants respond more to fluctuations in water acquisition potential than to evaporative demand. Two species were summer-deciduous, but one of them (Ozoroa concolor) responded to aseasonal summer rainfall by leafing out and flowering. These two species had high shoot xylem water potentials when in leaf. All other species were sclerophyllous evergreens with low water potentials, particularly the shallow-rooted shrub Zygophyllum prismatocarpum, and Boscia albitrunca which may have a different rooting pattern to the other phreatophytes. The latter species was also unique due to its high leaf nitrogen contents, photosynthetic rates and stomatal conductances, despite very low leaf water potentials. Leaf stable carbon isotope composition C13δC) varied between species (−22 to −27‰), but was lower than the mean for arid regions worldwide. The values indicated moderately high levels of water use efficiency, but a less conservative strategy in two species, including Boscia albitrunca. The affinities of these species to summer rainfall biomes, their apparent decline in the western arid regions in recent geological history following aridification, and their absence southwards in the winter rainfall regions, suggest that these wash species rely on sporadic summer rainfall events to some extent. They may be at risk if predicted increases in temperature and changes in rainfall patterns alter their effective moisture availability.

Economic factors and opportunities as determinants of water use efficiency in agriculture

A consequence of water scarcity is that it has enhanced research and development aimed at increasing water use efficiency in irrigated agriculture. Although biological, genetic, and technological achievements may induce potential high levels of water use efficiency, actual observed values may be much smaller. This paper distinguishes between potential and actual water use efficiency measures, and discusses factors and opportunities that may affect actual water use efficiency in irrigated agriculture. These include economic forces, environmental effects, and institutional arrangements, each of which may affect water use decisions at field, farm, regional, and national levels. The paper develops a scheme to generally address differences between private and social considerations that determine water use efficiency decisions. Using this scheme, several examples from California and Israel are provided to support the arguments. The paper concludes that the concept of water use efficiency is much broader than its definition: yield per water applied or transpired. Moreover, determination of water use efficiency levels in irrigated agriculture is a complex issue that requires interdisciplinary considerations.

ECONOMIC EVALUATION OF ON‐FARM WATER MANAGEMENT PROJECTS1

ABSTRACT: During the last three decades, developing countries have invested enormous amounts of resources (running into billions of dollars) in the development of large surface irrigation systems. Investment funds were largely spent on the development of the main systems such as dams, canals and distributaries. Very little attention and resources have been spent on the development of below‐the‐outlet subsystems, in spite of very low levels of water use efficiency due to lack of proper land leveling, high water losses in field channels, and skewed distribution of available water among farmers served by individual water courses. This state of affairs has resulted in a lack of confidence on the part of most farmers in the reliability of surface irrigation systems to deliver water on time and in adequate quantities which, in turn, has resulted in farmers using below optimum levels of all other complementary inputs except labor. Realizing the importance of improving water use efficiency, both the domestic governments and donor agencies are increasingly paying serious attention to these problems. On‐Farm Water Management (OFWM) as a strategy to improve water use efficiency and consequently agricultural production in many developing countries has been currently receiving very wide and vigorous consideration among economists, water management experts, policymakers, and donor agencies. A judicious use of the newly allocated funds of OFWM projects obviously needs proper evaluation procedures so that money could be allocated for the most deserving purposes and projects. In particular, recently, private profitability calculations due to public investments in OFWM activities have received attention from economists and decision makers in developing countries’governments and in donor agencies are very much interested in knowing the impacts of their investments in OFWM activities on farmers’income and welfare. However, the evaluation procedures commonly used in empirical studies, using a production function approach, seem to be at variance and sometimes inconsistent with proper comparative‐static procedures. Thus, the primary objective of this paper is to develop consistent procedures for evaluating the impacts created by OFWM investments on farmers’income and resource use. In this context, the paper examines the critical relationship between the market price of the agricultural output and production function parameters which are affected by the OFWM investments.