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1.
Summary This study was conducted on the Lagar Distributary of Gugera Branch of Lower Chenab Canal, Punjab, Pakistan. A computer model MISTRAL was adopted for evaluating management options. The study showed that the model can be used as a decision support tool for prioritizing management options. The model suggests that under current physical conditions of this distributary the combination of rotation between the distributaries and along the distributary canals can improve the equity of water discharge. For example, in case of Lagar Distributary the discharge of tail outlets can be increased threefold by introducing rotation between the tail of the distributary and an offtaking minor canal. A small decrease in the discharge of the minor would result from adopting this option. A combination of rotations between this and neighboring distributaries and along the Lagar itself can increase the discharge of tail outlets up to seven times. The results of the model indicate that operational changes can improve the discharge of tail outlets to some extent, but the improvement of physical conditions of the distributary is needed to achieve equity conditions, as specified in the design.  相似文献   

2.
In this study, a regional irrigation schedule optimization method was proposed and applied in Fengqiu County in the North China Plain, which often suffers serious soil water drainage and nitrogen (N) leaching problems caused by excessive irrigation. The irrigation scheduling method was established by integrating the ‘checkbook irrigation method’ into a GIS-coupled soil water and nitrogen management model (WNMM) as an extension. The soil water and crop information required by the checkbook method, and previously collected from field observations, was estimated by the WNMM. By replacing manually observed data with simulated data from WNMM, the application range of the checkbook method could be extended from field scale to regional scale. The WNMM and the checkbook irrigation method were both validated by field experiments in the study region. The irrigation experiment in fluvo–aquic soil showed that the checkbook method had excellent performance; soil water drainage and N leaching were reduced by 83.1 and 85.6%, respectively, when compared with local farmers’ flood irrigation. Using the validated WNMM, the performance of checkbook irrigation in an entire winter wheat and summer maize rotation was also validated: the average soil water drainage and N leaching in four types of soils decreased from 331 to 75 mm year−1 and 47.7 to 9.3 kg ha−1 year−1, respectively; and average irrigation water use efficiency increased from 26.5 to 57.2 kg ha−1 mm−1. The regional irrigation schedule optimization method based on WNMM was applied in Fengqiu County. The results showed a good effect on saving irrigation water, decreasing soil water drainage and then saving agricultural inputs. In a typical meteorological year, it could save >110 mm of irrigation water on average, translating to >7.26 × 107 m3 of agricultural water saved each year within the county. Annual soil water drainage was reduced to <143 mm and N leaching to <27 kg ha−1 in most soils, all of which were significantly lower than local farmers’ flood irrigation. In the mean time, crop yield also had an average increase of 2,890 kg ha−1 when checkbook irrigation was applied.  相似文献   

3.
The cost and scarcity of water is placing increasing pressure on Australian dairy farmers to utilise water for forage production as efficiently as possible. This study aimed to identify perennial forage species with greater water-use efficiency (WUE) than the current dominant species, perennial ryegrass (Lolium perenne L.). Fifteen perennial forage species were investigated under optimum irrigation and two deficit irrigation treatments, over three years at Camden, NSW, on a brown Dermsol in a warm temperate climate. Under optimal irrigation, there was a nearly twofold difference in mean WUEt (total yield/evapotranspiration) between forages, with kikuyu (Pennisetum clandestinum Hochst. ex. chiov.) having the highest (27.3 kg ha−1 mm−1) and birdsfoot trefoil (Lotus corniculatus L.) the lowest (14.8 kg ha−1 mm−1). Kikuyu was also the most water use efficient forage under the extreme deficit irrigation treatment, although its mean WUEt declined by 15% to 23.2 kg ha−1 mm−1, while white clover (Trifolium repens L.) in the same treatment had the largest decline of 44% and the lowest WUEt of only 8.8 kg ha−1 mm−1. In order to maximise WUE for any forage, it is necessary to maximise yield, as there is a strong positive relationship between yield and WUEt.  相似文献   

4.
In many water scarce areas, saline water has been included as an important substitutable resource in agricultural irrigation. It would be of practical use to investigate the effect of stage-specific saline irrigation on yield, fruit quality, and other growth responses of greenhouse tomato, to establish a proper irrigation management strategy for tomato production in these regions. Here, saline irrigations (3.33, 8.33, and 16.67 dS m−1 NaCl solution) were applied during four growth stages of greenhouse tomato (L. esculentum Mill. cv. Zhongza No. 9) grown in the North China Plain, respectively. These include flowering and fruit-bearing stage (stage 1), first cluster fruit expanding stage (stage 2), second cluster fruit expanding stage (stage 3), and harvesting stage (stage 4). Compared with the following three stages, yield loss was most remarkable in stage 1 under all three salinity levels. Under irrigation practices using 3.33 dS m−1 saline water in all four stages, 8.33 dS m−1 saline water in latter three stages, and 16.67 dS m−1 saline water in stage 4, yield reduction was not significant while fruit quality was improved. In conclusion, it is feasible to use stage-specific saline irrigation for tomato production in water scarce areas like North China Plain.  相似文献   

5.
Subsurface drip system is the latest method of irrigation. The design of subsurface drip system involves consideration of structure and texture of soil, and crop’s root development pattern. A 3-year experiment was conducted on onion (Allium Cepa L., cv. Creole Red) in a sandy loam soil from October to May in 2002–2003, 2003–2004 and 2004–2005 to study the effect of depth of placement of drip lateral and different levels of irrigation on yield. Tests for uniformity of water application through the system were carried out in December of each year. Three different irrigation levels of 60, 80 and 100% of the crop evapotranspiration and six placement depths of the drip laterals (surface (0), 5, 10, 15, 20 and 30 cm) were maintained in the study. Onion yield was significantly affected by the placement depth of the drip lateral. Maximum yield (25.7 t ha−1) was obtained by applying the 60.7 cm of irrigation water and by placing the drip lateral at 10 cm soil depth. Maximum irrigation water use efficiency (IWUE) (0.55 t ha−1 cm−1) was obtained by placing the drip lateral at 10 cm depth. The greater vertical movement of water in the sandy-loam soil took place because of the predominant role of gravity rather than that of the capillary forces. Therefore, placement of drip lateral at shallow depths is recommended in onion crop to get higher yield.  相似文献   

6.
The influence of a deficit-irrigation (DI) strategy on soil–plant water relations and gas exchange activity was analysed during a 3-year period in mature ‘Lane late’ (Citrus sinensis (L.) Osb.) citrus trees grafted on two different rootstocks, ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tanaka ) and ‘Carrizo’ citrange (C. sinensis L., Osbeck × Poncirus trifoliata L.). Two treatments were applied for each rootstock: a control treatment, irrigated at 100% ETc (crop evapotranspiration) during the entire season, and a DI treatment, irrigated at 100% ETc, except during Phase I (cell division) and Phase III (ripening and harvest) of fruit growth, when complete irrigation cut-off was applied. Under soil water deficit, the seasonal variations of soil water content suggested that ‘Cleopatra’ mandarin had a better root efficiency for soil water extraction than ‘Carrizo’ citrange. Moreover, in all years, trees on ‘Cleopatra’ reached a lower water-stress level (midday xylem water potential values (Ψmd) > −2 MPa), maintaining a better plant water status during the water-stress periods than trees on ‘Carrizo’ (Ψmd < −2 MPa). Similarly, net CO2 assimilation rate (A) was higher in trees on ‘Cleopatra’ during the water-stress periods. In addition, the better plant water status in trees on ‘Cleopatra’ under DI conditions stimulated a greater vegetative growth compared to trees on ‘Carrizo’. From a physiological point of view, ‘Cleopatra’ mandarin was more tolerant of severe water stress (applied in Phases I and III of fruit growth) than ‘Carrizo’ citrange.  相似文献   

7.
An on-farm irrigation trial conducted on the upland of Chitwan valley of Nepal evaluated the amount and frequency of irrigation as well as the effect of nitrogen fertilizer and straw mulch applications on the performance of bottle gourd and okra vegetables. The experiment was laid out on split-split-plot design with fertilizer as main-plot factor, frequencies of irrigation as sub-plot factor, and amount of irrigation as sub-sub-plot factor. Data analysis revealed that frequency and amount of irrigation had a significant interaction effect on the number of nodes that emerge before the opening of the first flower in bottle gourd. Likewise, a significant effect of mulching was observed on the number of primary branches (P = 0.05). Number of nodes and primary branches both contributed to higher production of bottle gourd. Results also indicated that frequent application of higher amount of irrigation to bottle gourd could lead to reduced water productivity and suffer from yield losses. In the case of okra, low level of nitrogen application (30 kg N ha−1) with low but daily watering had significantly higher yield (1,365 g plot−1) than from higher level of nitrogen application (90 kg ha−1) (P = 0.01). Interaction effect of all factors was also significant (P = 0.05) on the fruit yield of okra which implied greater value of smaller irrigation to contribute to increased returns to farmers by improving production level of okra in this area of Nepal  相似文献   

8.
A 3-year study was carried out to assess the root biomass production, crop growth rate, yield attributes, canopy temperature and water-yield relationships in Indian mustard grown under combinations of irrigation and nutrient application for revealing the dynamic relationship of crop yield (Y) and seasonal evapotranspiration (ET). Three post-sowing irrigation treatments viz. no irrigation (I 1), one irrigation at flowering (I 2) and two irrigations one each at rosette and flowering stage (I 3), three nutrient treatments viz. no fertilizer or manure (F 1), 100% recommended NPK i.e., 60 kg N, 13.1 kg P and 16.6 kg K ha−1 (F 2) and 100% recommended NPK plus farmyard manure @ 10 Mg ha−1 (F 3) were tested in a split-plot design. Root biomass was significantly greater in I 3 than I 2 and I 1, and in F 3 than F 2 and F 1. The I 3 × F 3, I 2 × F 3 and I 3 × F 2 combinations maintained significantly greater crop growth rate, plant height, yield components, ET and crop yield and better plant water status in terms of canopy temperature, canopy-air temperature difference (CATD) and relative leaf water content (RLWC). Number of siliqua plant−1 and seeds siliqua−1 were the major contributors to the seed yield. Marginal analysis of water production function was used to establish Y–ET relationship. The elasticity of water production (E wp) provides a means to assess relative changes in Y and ET, and gives an indication of improvement of Y due to nutrient application. The ET–Y relationships were linear with marginal water use efficiency (WUEm) of 3.09, 4.23 and 3.95 kg ha−1 mm−1 in F 1, F 2 and F 3, respectively, and the corresponding E wp were 0.63, 0.71 and 0.61. This implies that the scope for improving yield and WUE with 100% NPK was little compared with 100% NPK + farmyard manure. The crop yield was highest in I 3 × F 3 combination, and the similar yield was obtained in I 2 × F 3 and I 3 × F 2 combinations. Application of organic manure along with 100% NPK fertilizers maintained greater crop growth rate, better water relation in plants, yield attributes and saved one post-sowing irrigation.  相似文献   

9.
The increased use of marginal quality water with drip irrigation requires sound fertigation practices that reconcile environmental concerns with viable crop production objectives. We conducted experiments to characterize dynamics and patterns of soil solution within wet bulb formed by drip irrigation. Time-domain reflectometry probes were used to monitor the distribution of potassium nitrate (KNO3) and water distribution from drippers discharging at constant flow rates of 2, 4 and 8 L h−1 in soil-filled containers. Considering results from different profiles, we observed greater solute storage near the dripper decreasing gradually towards the wetting front. About half of the applied KNO3 solution (48%) was stored in the first layer (0–0.10 m) for all experiments, 29% was stored in the next layer (0.10–0.20 m). Comparing different dripper flow rates, we observed higher solution storage for 4 L h−1, with 45, 53 and 47% of applied KNO3 solution accumulating in the first layer (0–0.10 m) for dripper flow rates of 2, 4 and 8 L h−1, respectively. The results suggest that based on the volume and frequency used in this experiment, it would be advantageous to apply small amounts of solution at more frequent intervals to reduce deep percolation losses of applied water and solutes.  相似文献   

10.
Equity in the distribution of irrigation water has long been an operational objective for the management of the large canal systems in the north and west of the Indian subcontinent. How well that operational objective continues to be met is the central concern of the research reported in this paper. Detailed studies of canal operations were conducted on three distributaries in the Lower Chenab Canal system in Punjab Province, Pakistan. Mananwala and Lagar Distributaries off-take in the head reach of the Gugera Branch Canal and Pir Mahal Distributary is at the very tail of this Branch. Flow conditions for these distributaries and of selected outlets served by each were measured daily throughout 1988, and data were converted to discharges. These field observations show that discharge variation at the head of distributaries greatly exceeds the original design criteria. The data also indicate that two design assumptions for outlets are no longer valid: continuous full supply water level in the distributary and outlet modular flow conditions. Field measurements confirm that the distribution of surface water among the outlets of all three distributaries is substantially inequitable. Outlets in the channels' head reaches commonly draw 3 to 6 times greater share of total supplies than do tail outlets. Although all three selected distributaries are perennial canals, some outlets remained dry for up to 90% of the total operational days in a year. Finally, evaluation of field data also shows that better operational procedures at the distributary level can substantially improve water supply conditions in the tail reaches.  相似文献   

11.
In turf industry, the ability of a cultivar to use less water is an important consideration, especially where rainfall and irrigation water are insufficient. Knowledge of turf grass water-use patterns is therefore important for developing efficient water management practices and also for selection of drought-resistant cultivars. We evaluated the soil water‐use patterns of tall fescue and hybrid bluegrasses cultivars irrigated at different rates. Field experiments were conducted at the Turfgrass Research Facility, Auburn University, AL, in 2005 and 2006. Two tall fescue (Festuca arundinacea Schreb.) cultivars (‘Kentucky 31’ and ‘Green Keeper’) and four hybrid bluegrass (Poa pratensis L. × Poa arachnifera Torr.) cultivars, viz., HB 129 [‘Thermal Blue’], HB 130 (Experimental line), HB 328 (Experimental line) and HB 329 [‘Dura Blue’] were included in this study. Plots were irrigated based on the potential evapotranspiration, viz., 100% ET, 80% ET and 60% ET replacements. Tensiometers were installed at 0.075, 0.15 and 0.30 m depths, and their readings used to calculate the matric head, water content and water-use values. Turf color quality was determined from turf canopy digital images. Analysis of variance (ANOVA) for a random complete block design (RCBD) was conducted for available water, water-use and turf color quality values. Hybrid bluegrasses revealed significantly (P = 0.05) higher turf color indices compared to the tall fescue cultivars, but there was no indication of differential responses to irrigation among cultivars. Based on water-use data, hybrid bluegrass cultivars revealed significantly (P = 0.05) lower water-use compared to tall fescue cultivars.  相似文献   

12.
The response of sunflower (Helianthus annuus L.) to 14 irrigation treatments in a sub-humid environment (Bursa, Turkey) was studied in the field for two seasons. A rainfed (non-irrigated) treatment as the control and 13 irrigation treatments with full and 12 different deficit irrigations were applied to the hybrid Sanbro (Novartis Seed Company) planted on clay soil, at three critical development stages: heading (H), flowering (F) and milk ripening (M). The yield increased with irrigation water amount, and the highest seed yield (3.95 t ha−1) and oil yield (1.78 t ha−1) were obtained from the HFM treatment (full irrigation at three stages); 82.9 and 85.4% increases, respectively, compared to the control. Evapotranspiration (ET) increased with increased amounts of irrigation water supplied. The highest seasonal ET (average of 652 mm) was estimated at the HFM treatment. Additionally, yield response factor (k y) was separately calculated for each, two and total growth stages, and k y was found to be 0.8382, 0.9159 (the highest value) and 0.7708 (the lowest value) for the total growing season, heading, and flowering-milk ripening combination stages, respectively. It is concluded that HFM irrigation is the best choice for maximum yield under the local conditions, but these irrigation schemes must be re-considered in areas where water resources are more limited. In the case of more restricted irrigation, the limitation of irrigation water at the flowering period should be avoided; as the highest water use efficiency (WUE) (7.80 kg ha−1 mm−1) and irrigation water use efficiency (IWUE) (10.19 kg ha−1 mm−1) were obtained from the F treatment.  相似文献   

13.
Performance of tomato when irrigated with sodic waters particularly under drip irrigation is not well known. A field experiment was conducted for 3 years to study the response of tomato crop to sodic water irrigation on a sandy loam soil. Irrigation waters having 0, 5 and 10 mmolc L−1 residual sodium carbonate (RSC) were applied through drip and furrow irrigation to two tomato cultivars, Edkawi (a salt tolerant cultivar) and Punjab Chhuhara (PC). High RSC of irrigation water significantly increased soil pH, ECe and exchangeable sodium percentage progressively; the increases were higher in furrow compared to drip irrigation. Effect of high RSC on increasing bulk density and decreasing infiltration rate of soil was also pronounced in furrow-irrigated plots. Higher soil moisture and lower salinity near the plant was maintained under drip irrigation than under furrow irrigation. Performance of the two cultivars was significantly different; pooled over 2002–03 and 2003–04 seasons, PC yielded 38.8 and 30.0 Mg ha−1 and Edkawi yielded 31.8 and 22.9 Mg ha−1 under drip and furrow irrigation, respectively. At RSC10, cultivar PC produced 38 and 46% higher fruit yield than cultivar Edkawi under drip and furrow irrigation, respectively. Reduction in fruit yield at higher RSC was due to lower fruit weight under drip irrigation and due to reduced fruit number as well as fruit weight under furrow irrigation. Decrease in fruit weight was more pronounced in cultivar Edkawi than in cultivar PC. Increase in RSC lowered quality of the fruits except the ascorbic acid content. High RSC under drip irrigation, in general, had lesser deteriorating effect on the fruit quality particularly for cultivar PC than under furrow irrigation. For obtaining high tomato yield and better-quality fruits using high RSC sodic waters, drip irrigation should be preferred over furrow irrigation. Better performance of local cultivar PC compared to Edkawi at medium and high RSC suggests that cultivars categorized as tolerant to salinity should be evaluated in the sodic environment particularly when irrigated with high RSC sodic waters.  相似文献   

14.
A drip-irrigation module was developed and included in an ecosystem model and tested on two independent datasets, spring and autumn, on field-grown tomato. Simulated soil evaporation correlated well with measurements for spring (2.62 mm d−1 compared to 2.60 mm d−1). Changes in soil water content were less well portrayed by the model (spring r 2 = 0.27; autumn r 2 = 0.45). More independent data is needed for further model testing in combination with developments of the spatial representation of below-ground variables. In a fresh-water drip-irrigated system, about 30% of the incoming water was transpired, 40% was lost as non-productive evaporative flows, and the remainder left the system as surface runoff or drainage. Simulations showed that saline water irrigation (6 dS m−1) caused reduced transpiration, which led to higher drainage and soil evaporation, compared with fresh water. Covering the soil with plastic mulch resulted in an increase in yield and transpiration. Finally, two different drip-irrigation discharge rates (0.2 and 2.5 l h−1) were compared; however the simulations indicated that the discharge rate did not have any impact on the partitioning of the incoming water to the system. The model proved to be a useful tool for evaluating the importance of specific management options.
Louise KarlbergEmail:
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15.
A study was conducted to determine the relationship between midday measurements of vine water status and daily water use of grapevines measured with a weighing lysimeter. Water applications to the vines were terminated on August 24th for 9 days and again on September 14th for 22 days. Daily water use of the vines in the lysimeter (ETLYS) was approximately 40 L vine−1 (5.3 mm) prior to turning the pump off, and it decreased to 22.3 L vine−1 by September 2nd. Pre-dawn leaf water potential (ΨPD) and midday Ψl on August 24th were −0.075 and −0.76 MPa, respectively, with midday Ψl decreasing to −1.28 MPa on September 2nd. Leaf g s decreased from ~500 to ~200 mmol m−2 s−1 during the two dry-down periods. Midday measurements of g s and Ψl were significantly correlated with one another (r = 0.96) and both with ETLYS/ETo (r = ~0.9). The decreases in Ψl, g s, and ETLYS/ETo in this study were also a linear function of the decrease in volumetric soil water content. The results indicate that even modest water stress can greatly reduce grapevine water use and that short-term measures of vine water status taken at midday are a reflection of daily grapevine water use.  相似文献   

16.
The continuous flow furrow irrigation (COFFI), surge flow furrow irrigation (SUFFI), cutback flow furrow irrigation (CUFFI), variable alternate flow furrow irrigation (VAFFI), and tail water reuse system furrow (TWRSF) techniques with the same inflow rate of 0.072 m3 min−1 were compared in relation to the cotton yield and water use efficiency at a 3-year field study conducted on cotton (Gossypium spp.) in the Southeastern Anatolia Project (GAP) area of Turkey. Yields revealed significant statistical differences between the furrow management techniques (P < 0.05). The maximum yield was obtained from the COFFI treatment (2,630 and 2,920 kg ha−1) in the first 2 years, and from SUFFI and CUFFI treatments (3,690 and 3,780 kg ha−1, respectively) in the last year. There were significant yield reductions, which varied from 10 to 35% in TWRSF and from 11 to 19% in VAFFI treatments although 43 and 28% more water was applied to the TWRSF than to CUFFI and SUFFI treatments, respectively. The average total water use efficiencies (WUEET) varied from 4.14 (VAFFI) to 2.59 (COFFI). The corresponding values were 0.37 and 0.36 kg ha−1 m−3 for CUFFI and SUFFI, respectively. The average irrigation water use efficiency (WUEIR) for CUFFI and SUFFI treatments were 0.30 and 0.23 kg ha−1 m−3, respectively.  相似文献   

17.
Irrigation with effluents can detrimentally affect soil physical and chemical properties and impact plant growth and development. Excessive irrigation can leach salts from the root zone; which can be accomplished by precipitation in some areas. This study was conducted to examine the effect of applications of Kraft pulp mill effluent (KPME) with and without distilled water (DW) to simulate precipitation would have on soil chemical properties and growth of hybrid poplar (Populus deltoides × P. petrowskyana L. cv. Walker). Distilled water (DW), KPME, and a 50% combination (v/v; COMB) of DW and KPME were applied at rates of 6 and 9 mm day−1. COMB resulted in heights, biomasses, and leaf areas that were greater than those for KPME and comparable to those for DW. Diluted KPME treatments (i.e., COMB) still significantly increased soil electrical conductivity and sodium adsorption ratio compared to DW. Leachate collected from KPME 9 mm day−1 had concentrations of HCO3 −, SO4 2−, Cl−, Ca2+, K+, and Mg2+ comparable to those collected from COMB 9 mm day−1, but Na+ concentrations were three times higher in KPME than COMB 9 mm day−1. Results indicate that precipitation or additional irrigation water could potentially provide the leaching necessary to prevent salt accumulation within the rooting zone; however, irrigating with saline or sodic effluents requires careful management.  相似文献   

18.
Prediction of plant water status is necessary for the judicious application of regulated deficit irrigation. CropSyst, a generic crop growth model that is applicable to fruit trees, was used to forecast plant water potential for irrigation management recommendations in a pear orchard. Plant water potential is predicted along with tree transpiration using Ohm’s law analogy. The parameters of the model were adjusted by using field measured data on a lysimeter-grown pear tree. After adjustment, and using the same lysimeter data, a satisfactory agreement was found between simulated and measured tree transpiration, light interception, and stem water potential. Model simulations were also performed for other independent field data. These corresponded to eight different conditions of a deficit-irrigated field experiment in a pear orchard. Each condition differed in soil texture, time of irrigation cut-off, crop load, and tree leaf area. Deficit irrigation was managed first by withholding irrigation until reaching a threshold in midday stem water potential of −1.5 MPa. Subsequently, irrigation was applied at fixed proportions of full irrigation requirements. Simulations with CropSyst were used as decision support system that could work independently of stem water potential measurements. Simulations in all eight sites were satisfactory at providing adequate time without irrigation during the first part of the deficit period. A highly significant relationship (r 2  = 0.71) between predicted and measured stem water potentials was found for a simulation period of 40 days. Simulations for longer periods (i.e. 74 days) decreased the r 2 to 0.61, and for this reason after resuming irrigation, slight deviations were found for the average stem water potential in two out of five sites. In conclusion, CropSyst produced relevant information for managing deficit irrigation in simulation periods shorter than 40 days.  相似文献   

19.
A subsurface drip irrigation study with cotton used canopy temperature to determine signals for irrigation control during 2002–2004. Timing of irrigation applications was controlled by the biologically identified optimal temperature interactive console (BIOTIC) protocol, which used stress time (ST) and a crop-specific optimum temperature to indicate water stress. ST was the cumulative daily time quantity when cotton canopy temperature exceeded 28°C. STs between 5.5 and 8.5 h in 1 h increments were irrigation signal criteria, which produced different irrigation regimes. This investigation examined the association among ST, daily average canopy temperature (T c), canopy and air temperature difference (T c−T a), and the relative crop water stress index (RCWSI) including their relationship with lint yield. Number of irrigation signals decreased linearly with ST at the rate of −10.2 and −8.7 irrigations per 1 h increase of ST in 2003 and 2004. There were significant curvilinear relationships between ST and the average daily stress on days with irrigation signals and for days without irrigation signals across years. The percentage of positive daily (T c−T a) values increased with ST level. ST and T c were positively related in all irrigation signal treatments with 5.5 and 6.5 h being significant in 2003 and 2004. Yield declined at the rate of 343 kg lint/ha for each 1 h increase of ST for days with irrigation signals. ST, mathematically the most simple of the canopy temperature-based parameters, provided the most consistent estimate of crop water stress and correlation with lint yield. The power of ST to characterize water stress effects on crop productivity evolves from being an integrated value of time while canopy temperature exceeds a physiologically based threshold value.
D. F. WanjuraEmail: Phone: +1-806-7235241Fax: +1-806-7235272
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20.
Agricultural nonpoint-source pollution is the leading cause of water-quality degeneration of rivers and groundwater. In this context, the coast of Granada province (SE Spain) is economically an important area for the subtropical fruit cultivation. This intensively irrigated agriculture often uses excessive fertilizers, resulting to water pollution. Therefore, a 2-year experiment was conducted using drainage lysimeters to determine the potential risk of nutrient pollution in mango (Mangifera indica L. cv. Osteen) and cherimoya (Annona cherimola Mill. cv. Fino de Jete) orchards. These lysimeters were used to estimate the nutrient budgeting for each crop. NO3-N, NH4-N, PO4-P and K losses according to lysimeters were, respectively, 55.1, 12.4, 3.7, and 0.6 for mango and 61.8, 17.8, 4.9, and 0.5 kg ha−1 yr−1, for cherimoya. NO3, concentrations in the leachates ranged from 1.8 to 44.3 mg L−1, and from 23.0 to 51.0 mg L−1, for mango and cherimoya, respectively, in some cases exceeding the limits for safe drinking water. PO4 also exceeded the permitted concentrations related to eutrophication of water, ranging from 0.07 to 0.5 mg L−1 and from 0.12 to 0.68 mg L−1 from mango and cherimoya lysimeters, respectively. With respect to the nutrient balance, N, P, and K removed by cherimoya fruits was 76.4, 5.5, and 22.6 kg ha−1 yr−1, and for mango fruits 30.2, 3.3 and 27.8 kg ha−1 yr−1, respectively. Nutrient losses in the leachates were surprisingly low, considering total N, P, and K applied during the year, in mango lysimeters 3.8, 0.11, and 12.6%, and in cherimoya lysimeters 7.7, 0.23 and 16.0%, respectively, indicating a potential soil accumulation and eventual loss risk, especially during torrential rains. Crop coefficient (Kc) values of mango trees varied within ranges of 0.35–0.67, 0.55–0.89, and 0.39–0.80 at flowering, fruit set, and fruit growth, respectively. Kc values for cherimoya trees had ranges of 0.58–0.67, 0.61–0.68, and 0.43–0.62 at flowering, fruit set and fruit growth, respectively. In this study, the Kc values of mango and cherimoya were significantly correlated to julian days. Therefore, the estimated WUE in the mango and cherimoya orchards reached 21.2 and 14.0 kg ha−1 mm−1, respectively. Thus, this study highlights the urgency to establish the optimal use of fertilizers and irrigation water with respect to crop requirements, to preserve surface-water and groundwater quality, thereby achieving more sustainable agriculture in orchard terraces.  相似文献   

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