Limited Water Supply Conditions Research Articles

Some Weeds Community Percent in Response to Pumice Application on Soil under Water Stress Conditions

A factorial experiment (using RCBD design) with three replications was conducted in 2014 at the University of Tabriz-Iran, in order to determine the effects of pumice application (P1, P2, P3 and P4: control, 30, 60 and 90 tons per ha) on soil and water stress (I1, I2 and I3: 100%, 70% and 50% water requirement calculated from class A pan, respectively) on dominante weeds community percent. Results showed that community percent of weed species changed as a result of water stress and pumice application on soil. Distributions of Chenopodium album and Malva sylvestris were sensitive to water stress but, Amaranthus retroflexus and Solanum nigrum were neutral to water stress. In contrast, Amaranthus retroflexus , Cardaria draba , Setaria viridis , Sisymbrium irio , Xanthium strumarium , Convolvulus arvensis and Salsola rigida distribution were resistant to water stress. Community percent of Chenopodium album as sensitive species to water stress and Salsola rigida as resistance species to water stress positively affected by pumice application especially under water stress condition. Amaranthus retroflexus , Xanthium strumarium and Convolvulus arvensis were positively affected by pumice application under well and limited water supply conditions. In contrast, Cardaria draba , Sisymbrium irio and Solanum nigrum negatively affected by pumice under water stress and it had positive effect on community of these species under well watering conditions. Thus, application of pumice and water stress are two factors which change weed community precent.

Saltgrass, a potential future landscaping plant and a suitable species for desert regions: a review.

Continuous desertification of arable lands mandates use of low quality/ saline water for irrigation, especially in regions experiencing water shortage. Using low quality/ saline water for irrigation imposes more stress on plants that are already under stress in these regions. Thus, a logical solution will be to find a salt/ drought-tolerant plant species that will survive/sustain under such stressful conditions. As the native plants are already growing under such conditions and are adapted to these stresses, they are most suitable for use under these harsh arid environmental conditions. If stress-tolerant species/ genotypes of these native plants are identified, there will be substantial savings in inputs (i.e., water, fertilizers, and agrochemicals) in using them under these stressful conditions. My research studies at the University of Arizona on various native grasses indicate that saltgrass (Distichlis spicata) has a great potential to be used under harsh environmental desert conditions, to combat the desertification processes. The objectives of this review article are to introduce saltgrass, a halophytic plant species, which through my investigations on various salinity and drought-tolerant halophytic plant species has proven to be the most tolerant plant species for recommendation as the potential species for use in arid regions and in areas with saline soils and limited water supply or drought conditions, for sustainable agriculture and for combating desertification. In my various investigations, different saltgrass clones/accessions/genotypes were studied in a greenhouse, to evaluate their growth responses under salinity or drought stress conditions. The grasses were grown vegetatively either hydroponically in culture solution for salt tolerance or in galvanized cans that contained fritted clay for drought tolerance. For salt tolerance, the grasses were grown under four treatments (EC = 6 (control), 20, 34, and 48 dSm-1 salinity stress) with three replications in a randomized complete block (RCB) design experiment. During this period, the shoots were clipped bi-weekly for fresh and dry matter (DM) weight determination. At the last harvest, the roots were also harvested and the DM weights determined. For drought tolerance, the growth responses of the grasses were evaluated under a progressive drought condition for four months in a split plot design experiment with three replications. Shoots were harvested bi-weekly for DM determination. Although growth responses reduced at high salinity levels or as the drought period progressed, all the grasses showed a high degree of salinity/drought tolerance. However, there was a wide range of variations observed in salinity/ drought tolerance among the various clones/accessions/genotypes. The superior salinity/ drought-tolerant plants were identified, which could be recommended for sustainable production under arid regions and combating desertification.

Hydrogen generation from deliquescence of ammonia borane using Ni–Co/r-GO catalyst

Hydrogen generation from the catalyzed deliquescence/hydrolysis of ammonia borane (AB) using the Ni–Co catalyst supported on the graphene oxide (Ni–Co/r-GO catalyst) under the conditions of limited water supply was studied with the molar feed ratio of water to ammonia borane (denoted as H2O/AB) at 2.02, 3.97 and 5.93, respectively. The conversion efficiency of ammonia borane to hydrogen was estimated both from the cumulative volume of the hydrogen gas generated and the conversion of boron chemistry in the hydrolysates analyzed by the solid-state 11B NMR. The conversion efficiency of ammonia borane could reach nearly 100% under excess water dosage, that is, H2O/AB = 3.97 and 5.93. Notably, the hydrogen storage capacity could reach as high as 6.5 wt.% in the case with H2O/AB = 2.02. The hydrolysates of ammonia borane in the presence of Ni–Co/r-GO catalyst were mainly the mixture of boric acid and metaborate according to XRD, FT-IR and solid-state 11B NMR analyses.

Equitable Water Distribution in Main Irrigation Canals with Constrained Water Supply

In this study a novel configuration of the Water Level Difference Error method is introduced to speed up the error sharing in the context of Model Predictive Control (MPC). The potential application of the controller is examined. The main objective of this controller is fair distribution of water between upstream and downstream users in main canals suffering from water shortages. The scheme uses the Integrator-Delay (ID) model for canal pool responses in a model predictive controller. The designed controller is tested on an accurate simulation model of a large canal system, using four test scenarios. The scenarios suffer from limited water supply conditions that are imposed by a limitation on the canal inflow. The results show fast reactions in equitable sharing of water level deviations from target throughout the canal. Since, all the pools are involved in optimally managing the water shortage, significant improvements in operational performance of the canal are achieved. In addition, the operational performance of the designed controller is remarkably improved by applying a new strategy of target-bands instead of target-levels in the canal pools as it increases the flexibility of the controller in making appropriate decisions.

English

A study was conducted during the 2009-2010 summer growing season to determine the effects of varying irrigation frequencies and NPK application rate on biomass yield and partitioning to fractions of Cucumis africanus. The experiment was laid out in a split-plot design arrangement and replicated three times. Three irrigation frequencies, namely, 2, 4 and 6 days interval, were the main plots and sub-plot treatments were application rates of three NPK fertilizer levels combined in a ratio 3:2:1and a control treatment of 0 Kg NPK ha-1. Total and plant fraction biomass yield were higher in the four day irrigation frequencies and 120-80-40 kg NPK ha-1 fertilizer rate treatment combination. In conclusion, the results indicate that the plant can produce adequately under conditions of limited water supply provided there are supplemental nutrients available. Key words: Irrigation frequency, biomass yield, root/shoot ratio, ethnobotanicals.

Influence of field re-ponding pattern and plant spacing on rice root–shoot characteristics, yield, and water productivity of two modern cultivars under SRI management in Indian Mollisols

A 2-year field experiment was conducted during the wet seasons (July–October) of 2008 and 2009 on a Typic Hapludoll Mollisol in Indo-Gangetic Plains Region (IGPR) to: (i) investigate the effects of field water re-ponding intervals and plant spacing on the growth, yield, and water productivity (WP) of two rice cultivars under system of rice intensification (SRI) management, and (ii) assess comparative performance of SRI versus ‘best management practices’(BMP) of rice cultivation. This experiment was designed with 14 treatments, 12 under SRI, and 2 BMP (controls). SRI treatments comprised of 3 irrigation regimes viz, irrigation at 1, 3, and 5 day(s) after disappearance of ponded water (DADPW), 2 plant spacings (20 × 20, 25 × 25 cm), and 2 rice cultivars (Pant Dhan 4 and Hybrid 6444). Two BMP (control) treatments comprised of standard cultivation recommendations for flooding and spacing. The experiment was laid-out in a factorial randomized complete block design with three replications. Statistical analysis of data revealed significant variations in root–shoot characteristics and rice yield under SRI between years, reflecting different rainfall patterns. During 2009, a low rainfall year, the panicle numbers m−2, dry root weight m−2, root volume m−2, filled spikelet number panicle−1, and filled spikelet weight panicle−1 were significantly higher, which resulted in a rice grain yield enhancement by 5.1 % over 2008, when there was unusually heavy rainfall. Climate × irrigation regime interaction revealed a non-significant influence of irrigation regimes on growth and yield during 2008, whereas in 2009, irrigation at 1 DADPW and 3 DADPW increased grain yield by 12.8 and 8 %, respectively over 5 DADPW. Better root–zone soil moisture regimes, balancing water, and oxygen availability were responsible for higher yields under irrigation at 1 and 3 DADPW. In 2008, soil moisture content (SMC) in 0–15 cm layer was 91, 86, and 82 % of field capacity (FC) at panicle initiation, and 88, 80, and 77 % at panicle emergence stage when irrigation was at 1, 3, and 5 DADPW, respectively; the lower layers (15–30, 30–45 cm) retained their SMC between 87 and 94 % of FC at both stages. During 2009, SMC in all the three layers at both stages was more than 85 % of FC when irrigating at 1 DADPW, and a little more than 70 % for the 0–15 cm layer and >80 % for the other two layers when irrigation was done at 3 DADPW. SMC dropped to below 60 % of FC in the 0–15 cm layer and remained between 67 and 77 % of FC in the other two layers, with lower yield resulting when irrigations were applied at 5 DADPW. However, WP was the highest with irrigation at 5 DADPW (38.5 kg ha cm−1). Wider plant spacing (25 × 25 cm) resulted in generally and significantly higher grain yield and WP. On an average, SRI (6.1 t ha−1) resulted in yield advantage of 0.9 t ha−1 over BMP (5.2 t ha−1). Overall, it is inferred that in SRI, wider planting (25 × 25 cm) with field re-ponding at 3 DADPW if there is adequate water availability and at 5 DADPW under limited water supply conditions, may lead to higher rice yields and WP in sub-humid tarai Mollisols of IGPR and comparable agro-climatic conditions in Indian sub-continent.

The abiotic stress response and adaptation of triticale — A review

After a decade of genetic manipulation and improvement, triticale stand out as a crop of high biomass and grain yield potential which generally surpass that of wheat. Its high productivity is most likely derived from high rates of carbon assimilation linked to stomatal physiology and probably low respiration rate. Being a derivative of rye, triticale has always been assumed to be relatively resistant to abiotic stress. The last review of triticale adaptation to abiotic stress as published by Jessop (1996) pointed at its general and specific fitness to harsh growing conditions. This review as based on additional data published in the last 20 years indicates that triticale retain good to excellent adaptation to conditions of limited water supply and problem soils which involve salinity, low pH, defined mineral toxicities and deficiencies and waterlogging. Despite the understandable expectations, freezing tolerance of triticale was not found to be up to the level of rye. The freezing tolerance of the rye complement in triticale is inhibited by unknown factors on the wheat parent genome. Any given triticale cultivar or selection cannot be taken a priori as being stress resistant. Research has repeatedly shown that triticale presented large genetic diversity for abiotic stress resistance and most likely this diversity has not yet been fully explored due to the very limited research and the small studied sample of the potential triticale germplasm. Triticale is a valuable stress tolerant cereal on its own accord and a potential genetic resource for breeding winter and spring cereals. Because of its high productivity and resilience it might become as important as wheat or better on a global scale if its grain technological quality will be improved to the level of wheat.

Particle film technology: A supplemental tool to save water

This paper aims to evaluate kaolin application as an effective tool for controlling stomatal conductance (gs) and transpiration rate (E), in order to enhance tolerance to water stress and salinity and to improve water productivity. Five experiments were carried out under open field conditions in Southern Italy in order to evaluate the effect of kaolin application on the physiological responses of well watered bean and Clementine, tomato under three salinity levels and two irrigation regimes and to try to overcome the vegetables’ transplant shock under two irrigation regimes.Kaolin reduced crop evapotranspiration in bean by 13% and increased photosynthetic water productivity (pWP) and yield water productivity (yWP) by 20 and 9.8%, respectively. In Clementine kaolin reduced E by 26.2% and increased pWP by 30.5%.In tomato kaolin improved the water status of the plant, and reduced gs, net photosynthesis (A) and E under low salinity or well watered conditions. By contrast, under salt stress or drought, kaolin was effective in limiting the reduction in A and reducing leaf temperature (Tl). This increased pWP by 25.3 and 33.1%, respectively, in well watered and water stressed tomato, and by 9.2 and 24.9%, respectively, in the non saline and high saline treatment.Kaolin proved effective in limiting transplant shock under conditions of limited water supply, increasing dry biomass growth rate and biomass water productivity (bWP) by 18.4 and 19%, respectively.Kaolin can be efficiently utilized as an antitranspirant to alleviate the effects of drought and salinity, to reduce transplant shock and to save water in dry regions.

Water shortage and quality of fleshy fruits--making the most of the unavoidable.

Extreme climatic events, including drought, are predicted to increase in intensity, frequency, and geographic extent as a consequence of global climate change. In general, to grow crops successfully in the future, growers will need to adapt to less available water and to take better advantage of the positive effects of drought. Fortunately, there are positive effects associated with drought. Drought stimulates the secondary metabolism, thereby potentially increasing plant defences and the concentrations of compounds involved in plant quality, particularly taste and health benefits. The role of drought on the production of secondary metabolites is of paramount importance for fruit crops. However, to manage crops effectively under conditions of limited water supply, for example by applying deficit irrigation, growers must consider not only the impact of drought on productivity but also on how plants manage the primary and secondary metabolisms. This question is obviously complex because during water deficit, trade-offs among productivity, defence, and quality depend upon the intensity, duration, and repetition of events of water deficit. The stage of plant development during the period of water deficit is also crucial, as are the effects of other stressors. In addition, growers must rely on relevant indicators of water status, i.e. parameters involved in the relevant metabolic processes, including those affecting quality. Although many reports on the effects of drought on plant function and crop productivity have been published, these issues have not been reviewed thus far. Here, we provide an up-to-date review of current knowledge of the effects of different forms of drought on fruit quality relative to the primary and secondary metabolisms and their interactions. We also review conventional and less conventional indicators of water status that could be used for monitoring purposes, such as volatile compounds. We focus on fruit crops owing to the importance of secondary metabolism in fruit quality and the importance of fruits in the human diet. The issue of defence is also briefly discussed.

Water-deficit stress effects on pistil biochemistry and leaf physiology in cotton (Gossypium hirsutum, L.)

Flowering in cotton (Gossypium hirsutum L.) is a sensitive stage to water-deficit stress, but the effects on metabolism are not well understood. The objective of this study was to monitor gas exchange responses of cotton plants under conditions of limited water supply and evaluate the effects on the carbohydrate concentrations and glutathione reductase levels in the cotton flower. Growth chamber experiments were conducted in 2008 and 2009, with normal day/night conditions of 32/24°C and optimum quantities of Hoagland's nutrient solution applied until flowering. Treatments were imposed at flowering and consisted of control (Control), where optimum quantities of water were applied, and water stress (WS) where 50% of optimum quantity of water was supplied. Water-deficit stress resulted in a significant decrease in leaf stomatal conductance. Leaf photosynthetic and respiration rates were similarly decreased compared to the control. Ovary and style water potential of water-stressed leaves were significantly higher compared to the water potential of water stressed leaves, indicating that cotton flowers are fairly resistant to changes in the water status of the plant. However, carbohydrate concentrations of water-stressed pistils (ovary and style) were significantly increased compared to the control and a similar pattern was observed in the levels of glutathione reductase of water-stressed pistils. In conclusion, water-deficit stress during flowering resulted in significant decreases in leaf gas exchange functions as well as leaf water potential. Cotton pistils appeared to be less sensitive since they were able to maintain water potential similar to the control under limited water supply and increase glutathione reductase levels. However, pistil carbohydrate metabolism was significantly affected resulting in accumulation of both hexose and sucrose indicating a perturbation in sucrose cleaving and hexose utilizing enzymes that could potentially have as a consequence a decrease in fertilization and seed set efficiency.

Seed priming improves irrigation water use efficiency, yield, and yield components of late-sown wheat under limited water conditions

A randomized complete block design field study with split plot arrangements was conducted during 2006-2007 and 2007-2008 at the Agronomic Research Station in Khanewal, Pakistan, to evaluate if seed priming could improve grain yield and water use efficiency of late-sown wheat under limited water supply conditions. Seeds of cultivar Inqlab-91 received one of the following treatments: they were soaked in aerated distilled water for 12 or 24 h (hydropriming), layered between moist gunny bags for 12 or 24 h (matriconditioning), soaked in tap water for 12 h (on-farm priming), or hydroprimed for 12 h and then kept at -20 °C for 12 h (hydropriming + chilling). Crops were subjected to 5 irrigation regimes in which irrigation was applied equivalent to 120%, 100%, 80%, 60%, or 40% of evapotranspiration (ETo). Seed priming treatments reduced the mean emergence time and promoted germination, early canopy development, and tillering in comparison to the untreated control. The number of fertile tillers, plant height, 1000-grain weight, and grain and biological yield were also increased by different priming techniques. On-farm priming and hydropriming for 12 h gave higher grain and biological yields and higher harvest index than other priming treatments. Seed priming increased the irrigation water use efficiency (IWUE) of all irrigation regimes. Grain yields were linearly increased at 100% ETo while maximum IWUE was achieved at 80% ETo. Results suggest that the use of either on-farm priming or hydropriming of seeds for 12 h can be helpful in improving grain yields in late-sown wheat under both optimum as well as limited water conditions.

Evaluation of Variety, Cropping Pattern and Plant Density on Growth and Yield Production of Grain Sorghum -Cowpea under Limited Water Supply Condition Growth, yield and yield component characters of Sorghum

Evaluation of Variety, Cropping Pattern and Plant Density on Growth and Yield Production of Grain Sorghum -Cowpea under Limited Water Supply Condition Growth, yield and yield component characters of Sorghum

Evaluation of Variety, Cropping Pattern and Plant Density on Growth and Yield Production of Grain Sorghum -Cowpea under Limited Water Supply Condition Growth, yield and yield component characters of Sorghum

An intercropping experiment of sorghum/cowpea intercrops was carried out in summer season of 2009 and 2010 at Agricultural and Research Station, College of Food Science and Agriculture, King Saud University. The main objective of the study was to evaluate the growth and yield potential of sorghum/cowpea intercrops over sole cropping pattern. The experiments included 18 treatments three sorghum varieties, i.e., two semi dwarfs (Pioneer and S-1007) and a tall one local variety (Shahlaa), theses varieties were planted in two cropping patterns as solid culture at the densities of 200, 300 and 400 10 3 plants/hectare for semi dwarfs varieties, whereas tall variety at 160,240 and 320 10 3 plants/hectare. These densities for the three varieties are equal to 100, 150 and 200 % of the solid recommended culture .The intercropping was alternating two rows of grain sorghum with other rows of cowpea (2 & 2) pattern. The data obtained indicated that sorghum plants, when intercropped with cowpea, exhibited greater potentiality and recorded higher values of most of the studied criteria viz., plant height, number of leaves per plant, stem diameter, leaf area, dry matter accumulation and grain yield /plant .Grain yield per hectare was lower in intercropping pattern than solid pattern. The increase in grain yield per plant and plant density could not compensate the decrease of the area occupied by the crop under solid culture.

Approach to assess infrared thermal imaging of almond trees under water-stress conditions

Approach to assess infrared thermal imaging of almond trees under water-stress conditions. Abstract - Introduction. Optimising agricultural water use implies the combination of physiological, technological and engineering techniques, especially those for continuously monitoring the water status of plants subjected to deficit irrigation. A methodology to estimate water stress of young almond trees from thermal images was developed based on assessing the physiological status of almond crops under limited water-supply conditions. Materials and methods. Two irrigation treatments were tested during the maximum evapotranspirative demand period (214th to the 243rd day of the year) in an experimental almond (Prunus dulcis (Mill) D.A. Webb, cv. Guara) orchard: a low-frequency deficit irrigation (LFDI) treatment, irrigated according to the plant-water status, and a fully irrigated treatment (C100) at 100% of crop evapotranspiration. Daily canopy temperature at midday (TC) was measured with an infrared camera, together with standard measurements of stem-water potential (ΨStem) and stomatal conductance (gS). The time course of these parameters and their relationships were analysed. Results and discus- sion. The time course of the parameters studied showed highly significant correlations among the diffe- rentials of canopy-air temperature (ΔT), ΨStem and gS. The methodological protocol for analysing thermal images allowed a time saving in processing information and additionally offered the possibility of estima- ting the ΨStem and gS values. Conclusion. Our results confirm that infrared thermography is a suitable technique for assessing the crop-water status and can be used as an important step towards automated plant-water stress management in almond orchards.

Living With Limited Water, Part II: Dynamics of Leaf Rolling, Leaf Water Homeostasis and Water Economy by Hybrid Rice*

Change in leaf form or shape has often been enumerated as a potential means of reducing transpiration by plants experiencing water deficit. Because leaf rolling is the first and foremost visible physiological response to water deficit in rice plant, its dynamic nature and impact on leaf water homeostasis and water conservation were studied in hybrid rice (Oryza sativa L.) in depth. Marked diurnal fluctuations were observed in leaf rolling behavior over short as well as extended periods of time during the drying cycle. Leaves were found unrolled (open) during early and late hours of the day in watered plants, whereas stressed plants exhibited partial rolling (score >3) even in the morning, followed by complete rolling at noon (score 5). The rolling of leaves of watered plants fluctuated within a very narrow range (between score 1 to 2) throughout 20 days of drying cycle, whereas stressed plants, although they did not differ from control plants during the first 5 days of stress, displayed wide fluctuations thereafter, culminating into complete rolling (score 5) with no further diurnal variations in space and time. The pattern of changes in leaf water potential closely followed leaf rolling behavior. Examination of leaves by naked eye and hand lens revealed two distinct textures of surfaces in a given leaf blade, i.e. smooth or ridged, located opposite to each other on either side of the midrib. Quite often, the ridged portion rolled first, followed by the smooth one rolling over the former during the drying cycle as the water potential of the ridged portion was less by 0.48 MPa than the smooth portion at the completion of leaf rolling (score 5). Similarly, the water potential of the apical half portion of the leaf blade was less by 0.41 MPa in comparison with the basal half. In the main, two types of leaf rolling were observed: one was classified as acropetal, which consisted of helical and non-helical rolling, and the other was non-acropetal, characterized by either the ridged portion bending first or ridged and smooth portions bending almost simultaneously. Leaf rolling in etiolated leaves was quicker by 14 min than the green ones; however, darkness delayed the rolling (score 5) of green leaves by 32 min. The rate of transpiration decreased by 52% in manually rolled, excised turgid leaves, which reversed back to the initial rate of water loss once the leaves were unrolled (open). In the absence of water supply to the excised leaves, the spontaneously rolled leaves exhibited 87% water saving (only 13% loss in fresh weight) against 68% saving (32% loss) by leaves mechanically prevented from rolling, suggesting its important role in leaf water homeostasis and water economy during limited-water supply conditions. The findings carry biotechnological applications that may further provide important information for the design of strategies for future engineering of an improved external plant defense system against drought with increased water-use-efficiency in hybrid and super hybrid rice.

An overview of models of stomatal conductance at the leaf level

Stomata play a key role in plant adaptation to changing environmental conditions as they control both water losses and CO(2) uptake. Particularly, in the context of global change, simulations of the consequences of drought on crop plants are needed to design more efficient and water-saving cropping systems. However, most of the models of stomatal conductance (g(s)) developed at the leaf level link g(s) to environmental factors or net photosynthesis (A(net)), but do not include satisfactorily the effects of drought, impairing our capacity to simulate plant functioning in conditions of limited water supply. The objective of this review was to draw an up-to-date picture of the g(s) models, from the empirical to the process-based ones, along with their mechanistic or deterministic bases. It focuses on models capable to account for multiple environmental influences with emphasis on drought conditions. We examine how models that have been proposed for well-watered conditions can be combined with those specifically designed to deal with drought conditions. Ideas for future improvements of g(s) models are discussed: the issue of co-regulation of g(s) and A(net); the roles of CO(2), absissic acid and H(2)O(2); and finally, how to better address the new challenges arising from the issue of global change.

Effect of different drip irrigation regimes on sugar beet (Beta vulgaris L.) yield, quality and water use efficiency in Middle Anatolian, Turkey

Agricultural production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant plant varieties or water management for arid and semi-arid areas under water shortage conditions. A field study was conducted to determine effects of seasonal deficit irrigation on plant root yield, quality and water use efficiency (WUE) of sugar beet for a 2-year period in the semi-arid region. Irrigations were applied when approximately 50–55% of the usable soil moisture was consumed in the effective rooting depth at the full irrigation (FI) treatment. In deficit irrigation treatments, irrigations were applied at the rates of 75, 50 and 25% of full irrigation treatment on the same day. Irrigation water was applied by a drip irrigation system. Increasing water deficits resulted in a relatively lower root and white sugar yields. The linear relationship between evapotranspiration and root yield was obtained. Similarly, WUE was the highest in DI25 irrigation conditions and the lowest in full irrigation conditions. According to the averaged values of 2 years, yield response factor (ky) was 0.93 for sugar beet. Sugar beet root quality parameters were influenced by drip irrigation levels in both years. The results revealed that irrigation of sugar beet with drip irrigation method at 75% level (DI25) had significant benefits in terms of saved irrigation water and large WUE, indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25% saving of irrigation water (DI25) caused 6.1% reduction in the net income.

Stochastic efficiency analysis of deficit irrigation with standard risk aversion

The main objective of this research was to develop an expected utility optimisation model to economically evaluate deficit irrigation within a multi-crop setting while taking into account the increasing production risk of deficit irrigation. The dynamic problem of optimising water use between multiple crops within a whole-farm setting when intraseasonal water supply may be limited was approximated by the inclusion of multiple irrigation schedules into the optimisation model. The SAPWAT model (South African Plant WATer) was further developed to quantify crop yield variability of deficit irrigation while taking the non-uniformity of irrigation applications into account. Stochastic budgeting procedures were used to generate appropriately correlated matrixes of gross margins necessary to incorporate risk into the water use optimisation model. Special care was taken to represent risk aversion consistently between the alternatives through the use of a new procedure to standardise values of absolute risk aversion. The model was applied to study the impact of increasing levels of risk aversion on the profitability of deficit irrigation under limited water supply conditions. The main conclusion from the analyses was that although deficit irrigation was stochastically more efficient than full irrigation under limited water supply conditions, irrigation farmers would not willingly choose to conserve water through deficit irrigation and would be expected to be compensated to do so. Deficit irrigation would not save water if the water that was saved through deficit irrigation were used to plant larger areas to increase the overall profitability of the strategy. Standard risk aversion was used to explain the simultaneous increasing and decreasing relationship between the utility weighted premiums and increasing levels of absolute risk aversion and was shown to be more consistent than when constant absolute risk aversion was assumed.

Modelling the economic tradeoffs between allocating water for crop production or leaching for salinity management

Salinisation threatens the sustainability of irrigation agriculture and needs to be managed through leaching practices. Under conditions of water scarcity a tradeoff exists between allocating water for salinity management and production. Currently no model in South Africa is able to model explicitly the impact of salinity management through leaching on the economic efficiency of irrigation farming, taking the opportunity cost of water under limited water supply conditions into consideration. The main objective of this paper is to develop a robust non-linear optimisation model that is able to determine endogenously the impact of declining irrigation water quality on the economic efficiency of irrigation farming. A data envelopment framework was used to integrate recently developed soil water salinity crop-yield production functions and leaching functions to model the complex interactions involved in water allocation decisions. Results showed that it is profitable to reduce the area irrigated under limited water supply conditions in order to release water for leaching purposes. When more water, but still a limited amount of water, is allocated to the farmer, his willingness to pay for water will increase if irrigation water deteriorates. Thus, the conclusion is that leaching is profitable irrespective of the water supply conditions.Keywords: salinity, leaching, economics, trade-off, non-linear optimisation, data envelopment analysis

Effects of drought stress and subsequent rewatering on photosynthetic and respiratory pathways in Nicotiana sylvestris wild type and the mitochondrial complex I-deficient CMSII mutant.

The interaction of photosynthesis and respiration has been studied in vivo under conditions of limited water supply and after consecutive rewatering. The role of the alternative (valt) and cytochrome (vcyt) pathways on drought stress-induced suppression of photosynthesis and during photosynthetic recovery was examined in the Nicotiana sylvestris wild type (WT) and the complex I-deficient CMSII mutant. Although photosynthetic traits, including net photosynthesis (AN), stomatal (gs) and mesophyll conductances (gm), as well as respiration (vcyt and valt) differed between well-watered CMSII and WT, similar reductions of AN, gs, and gm were observed during severe drought stress. However, total respiration (Vt) remained slightly higher in CMSII due to the still increased vcyt (to match ATP demand). valt and maximum carboxylation rates remained almost unaltered in both genotypes, while in CMSII, changes in photosynthetic light harvesting (i.e. Chl a/b ratio) were detected. In both genotypes, photosynthesis and respiration were restored after 2 d of rewatering, predominantly limited by a delayed stomatal response. Despite complex I dysfunction and hence altered redox balance, the CMSII mutant seems to be able to adjust its photosynthetic machinery during and after drought stress to reduce photo-oxidation and to maintain the cell redox state and the ATP level.