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1.
In this paper, we discuss the effect of elevated CO2 concentration, irrigation and nitrogenous fertilizer application on the growth and yield of spring wheat in semi-arid areas. A field experiment was conducted at the Dingxi Agricultural Experiment Station during 2000–2002. According to the experimental design, the CO2 concentration increased to 14.5, 40 and 54.5 μmol mol−1, respectively, by NH4HCO3 (involving CO2) application, direct application of CO2 gas and combination of fertilizer NH4HCO3 plus CO2 application, which are equal to CO2 concentration of the Earth's atmosphere in the next 5, 15 and 20 years. The fertilizer application was divided into three levels: application of NH3NO3 (250 kg h m−2), NH4HCO3 (500 kg h m−2) and no fertilizer. Irrigation was divided into two levels: with 90 mm irrigation in the growth period and without irrigation. They can be combined as eight treatments. Each treatment was replicated three times. The results showed that elevated CO2 concentration owing to CO2 application leads to remarkable increase in leaf area index (LAI) and shoot biomass, and also generates the higher value of leaf area duration (LAD) that can benefit the photosynthesis in the growth stage and yield increase in crop compared than the no CO2 application treatment. When CO2 concentration elevated by 14.5, 40 and 54.5 μmol mol−1 with irrigation and fertilization, correspondingly, the grain yield increased by 6.3, 13.1 and 19.8%, respectively, whereas without irrigation and fertilization, the grain yield increased by only 4.2% when CO2 concentration increased to 40 μmol mol−1. Meanwhile, irrigation and fertilization can result in larger and deeper root system and have significantly positive influences on higher value of root/shoot (R/S) and water use efficiency. The grain yields in irrigation, irrigation plus NH3NO3 application and irrigation plus application of NH4HCO3 treatments are 73.4, 148.0 and 163.6% higher than that of no-irrigated and no-fertilized treatment, suggesting that both irrigation and fertilizer application contribute to remarkable increase of crop yield. In all treatments, the highest water use efficiency (WUE, 7.24 kg h m−2 mm−1) and grain yield (3286 kg h m−2) consistently occurred in the treatment with 90 mm irrigation plus fertilizer NH4HCO3 and elevated CO2 concentration (54.5 μmol mol−1), suggesting that this combination has an integrated beneficial effect on improving WUE and grain yield of spring wheat. These results may offer help to maintain and increase the crop yields in semi-arid areas.  相似文献   

2.
Plant water status is a key factor impacting crop growth and agricultural water management. Crop water stress may alter canopy temperature, the energy balance, transpiration, photosynthesis, canopy water use efficiency, and crop yield. The objective of this study was to calculate the Crop Water Stress Index (CWSI) from canopy temperature and energy balance measurements and evaluate the utility of CWSI to quantify water stress by comparing CWSI to latent heat and carbon dioxide (CO2) flux measurements over canopies of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.). The experiment was conducted at the Yucheng Integrated Agricultural Experimental Station of the Chinese Academy of Sciences from 2003 to 2005. Latent heat and CO2 fluxes (by eddy covariance), canopy and air temperature, relative humidity, net radiation, wind speed, and soil heat flux were averaged at half-hour intervals. Leaf area index and crop height were measured every 7 days. CWSI was calculated from measured canopy-air temperature differences using the Jackson method. Under high net radiation conditions (greater than 500 W m−2), calculated values of minimum canopy-air temperature differences were similar to previously published empirically determined non-water-stressed baselines. Valid measures of CWSI were only obtained when canopy closure minimized the influence of viewed soil on infrared canopy temperature measurements (leaf area index was greater than 2.5 m2 m−2). Wheat and maize latent heat flux and canopy CO2 flux generally decreased linearly with increases in CWSI when net radiation levels were greater than 300 W m−2. The responses of latent heat flux and CO2 flux to CWSI did not demonstrate a consistent relationship in wheat that would recommend it as a reliable water stress quantification tool. The responses of latent heat flux and CO2 flux to CWSI were more consistent in maize, suggesting that CWSI could be useful in identifying and quantifying water stress conditions when net radiation was greater than 300 W m−2. The results suggest that CWSI calculated by the Jackson method under varying solar radiation and wind speed conditions may be used for irrigation scheduling and agricultural water management of maize in irrigated agricultural regions, such as the North China Plain.  相似文献   

3.
Atmospheric CO2 enrichment may bring different effects on plant growth and evapotranspiration if plants are under N and water deficient conditions. In this study, spring wheat (Triticum aestivum L.) was grown in pots at two atmospheric CO2 concentrations (ambient and elevated), two levels of soil moisture (well-watered and droughted to 45–60% of field capacity) and five nitrogen (N) fertilization treatments (0, 112.5, 225.0, 337.5, 450.0 kg hm−2) in growth chambers. Leaf growth, leaf area, and tiller increment were largely a function of N application and water supply. Elevated CO2 increased 23–45% in leaf area only with the N-added treatments 55 days after sowing. Elevated CO2 also reduced stomatal conductance more in droughted treatments (−51%) than in well-watered treatments (−41%), and more with zero N application (−60%) than with the adequate N (−35 to 44%). Evapotranspiration (ET) was also reduced by CO2 enrichment in a similar way. Our results showed that the CO2-enrichment-induced decrease in transpiration almost compensated for the increase in ET brought by the higher leaf area under adequate N and water supply, such that ET was similar for control and CO2-enriched plants. Under reduced N and water supply, CO2 enrichment had limited effect on either leaf growth or ET.  相似文献   

4.
The aim of the present investigation was to simulate the uptake concentrations (weights of ion per volume of water absorbed) of Na+ and Cl− in hydroponic tomato crops as a function of the NaCl concentration in the root zone. An empirical model was calibrated and validated, which can be incorporated into on-line operating decision support systems aimed at optimizing the nutrient supply and minimizing the discharge of drainage solution in tomato crops grown in closed-cycle hydroponic systems. Three experiments were conducted, of which one was carried out to calibrate the model using irrigation water with NaCl concentration ranging from 0 to 14.7 mol m−3 while the other two experiments were commissioned to validate the model within either a low (0.5-2 mol m−3) or a high (1.2-12 mol m−3) concentration range. The model could successfully predict the uptake concentration of Na+, but Cl− could not be simulated by this model at external Cl− concentrations lower than 10 mol m−3. The results indicate that Na+ is excluded actively and effectively by the tested tomato cultivar even at low external Na+ concentrations, while Cl− is readily taken up at low concentrations, particularly during the initial growing stages. Due to the efficient exclusion of Na+ by tomato, the Na+ concentration in the root environment increased rapidly to extremely high levels even when the Na+ concentration in the irrigation water was relatively low. These results indicate that tomato genotypes characterized by high salt-exclusion efficiency, require irrigation water with a very low NaCl concentration, if they are grown in closed hydroponic systems and the drainage water is not flushed periodically. To maintain Na+ at levels lower than 19 mol m−3 in the root zone of the tomato hybrid ‘Formula’ in closed hydroponics, a maximum acceptable Na+ concentration of 0.53 mol m−3 was estimated for the irrigation water.  相似文献   

5.
Borkhar district is located in an arid to semi-arid region in Iran and regularly faces widespread drought. Given current water scarcity, the limited available water should be used as efficient and productive as possible. To explore on-farm strategies which result in higher economic gains and water productivity (WP), a physically based agrohydrological model, Soil Water Atmosphere Plant (SWAP), was calibrated and validated using intensive measured data at eight selected farmer fields (wheat, fodder maize, sunflower and sugar beet) in the Borkhar district, Iran during the agricultural year 2004-2005. The WP values for the main crops were computed using the SWAP simulated water balance components, i.e. transpiration T, evapotranspiration ET, irrigation I, and the marketable yield YM in terms in terms of YMT−1, YM ET−1 and YM I−1.The average WP, expressed as $ T−1 (US $ m−3) was 0.19 for wheat, 0.5 for fodder maize, 0.06 for sunflower and 0.38 for sugar beet. This indicated that fodder maize provides the highest economic benefit in the Borkhar irrigation district. Soil evaporation caused the average WP values, expressed as YM ET−1 (kg m−3), to be significantly lower than the average WP, expressed as YMT−1, i.e. about 27% for wheat, 11% for fodder maize, 12% for sunflower and 0.18 for sugar beet. Furthermore, due to percolation from root zone and stored moisture content in the root zone, the average WP values, expressed as YMI−1 (kg m−3), had a 24-42% reduction as compared with WP, expressed as YM ET−1.The results indicated that during the limited water supply period, on-farm strategies like deficit irrigation scheduling and reduction of the cultivated area can result in higher economic gains. Improved irrigation practices in terms of irrigation timing and amount, increased WP in terms of YMI−1 (kg m−3) by a factor of 1.5 for wheat and maize, 1.3 for sunflower and 1.1 for sugar beet. Under water shortage conditions, reduction of the cultivated area yielded higher water productivity values as compared to deficit irrigation.  相似文献   

6.
In the spring-summer season of 2005 and 2006, we explored the influence of three fertigation strategies (A-C) on the water and nitrogen use efficiency of semi-closed rockwool culture of greenhouse tomato conducted using saline water (NaCl concentration of 9.5 mol m−3). The strategies under comparison were the following: (A) crop water uptake was compensated by refilling the mixing tank with nutrient solution at full strength (with the concentrations of macronutrients equal or close to the corresponding mean uptake concentrations as determined in previous studies) and the recirculating nutrient solution was flushed out whenever its electrical conductivity (EC) surpassed 4.5 dS m−1 due to the accumulation of NaCl; (B) the refill nutrient solution had a variable EC in order to maintain a target value of 3.0 dS m−1; due to the progressive accumulation of NaCl, the EC and macronutrient concentrations of the refill nutrient solution tended to decrease with time, thus resulting in a progressive nutrient depletion in the recycling water till N-NO3− content dropped below 1.0 mol m−3, when the nutrient solution was replaced; (C) likewise Strategy A, but when EC reached 4.5 dS m−1, crop water uptake was compensated with fresh water only in order to reduce N-NO3− concentration below 1.0 mol m−3 before discharge. In 2005 an open (free-drain) system (Strategy D), where the plants were irrigated with full-strength nutrient solution without drainage water recycling, was also tested in order to verify the possible influence of NaCl accumulation and/or nutrient depletion in the root zone on crop performance. In the semi-closed systems conducted following strategies A, B or C, the nutrient solution was replaced, respectively, 10, 14 and 7 times in 2005, and in 19, 24 and 14 times in 2006, when the cultivation lasted 167 days instead of 84 days in 2005. In both years, there were no important differences in fruit yield and quality among the strategies under investigation. Strategy C produced the best results in terms of water use and drainage, while Strategy B was the most efficient procedure with regard to nitrogen use. In contrast to strategies A and D, the application of strategies B and C minimized nitrogen emissions and also resulted in N-NO3− concentrations in the effluents that were invariably lower than the limit (approximately 1.42 mol m−3) imposed to the N-NO3− concentration of wastewater discharged into surface water by the current legislation associated to the implementation of European Nitrate Directive in Italy.  相似文献   

7.
Silicon absorption by crops in the form of silicic acid confers efficient utilization of available irrigation water by minimizing transpiration losses. In present study, silicon and irrigation effects on sorghum growth dynamics and drought tolerance mechanism were evaluated during 2007-2008. Two sorghum cultivars: PARCSS2 and Johar1 were treated with two levels of silicon (Si0 = control and Si200 = 200 ml l−1 of potassium silicate per kg of soil) and irrigation (W0 = control, crop lower limit and W40 = 40 mm of water, crop upper limit). The results depicted that silicon absorption led to increased leaf water potential, growth, transpiration, net photosynthetic rate and decreased shoot to root ratio in sorghum cultivars compared to control treatment. It can be concluded that synergistic effect of silicon fertilization with ample irrigation may improve the crop stand under drought and biotic stresses.  相似文献   

8.
Crop yield responses to climate change in the Huang-Huai-Hai Plain of China   总被引：3，自引：0，他引：3  
Global climate change may impact grain production as atmospheric conditions and water supply change, particularly intensive cropping, such as double wheat-maize systems. The effects of climate change on grain production of a winter wheat-summer maize cropping system were investigated, corresponding to the temperature rising 2 and 5 °C, precipitation increasing and decreasing by 15% and 30%, and atmospheric CO2 enriching to 500 and 700 ppmv. The study focused on two typical counties in the Huang-Huai-Hai (3H) Plain (covering most of the North China Plain), Botou in the north and Huaiyuan in the south, considering irrigated and rain-fed conditions, respectively. Climate change scenarios, derived from available ensemble outputs from general circulation models and the historical trend from 1996 to 2004, were used as atmospheric forcing to a bio-geo-physically process-based dynamic crop model, Vegetation Interface Processes (VIP). VIP simulates full coupling between photosynthesis and stomatal conductance, and other energy and water transfer processes. The projected crop yields are significantly different from the baseline yield, with the minimum, mean (±standardized deviation, SD) and maximum changes being −46%, −10.3 ± 20.3%, and 49%, respectively. The overall yield reduction of −18.5 ± 22.8% for a 5 °C increase is significantly greater than −2.3 ± 13.2% for a 2 °C increase. The negative effect of temperature rise on crop yield is partially mitigated by CO2 fertilization. The response of a C3 crop (wheat) to the temperature rise is significantly more sensitive to CO2 fertilization and less negative than the response of C4 (maize), implying a challenge to the present double wheat-maize systems. Increased precipitation significantly mitigated the loss and increased the projected gain of crop yield. Conversely, decreased precipitation significantly exacerbated the loss and reduced the projected gain of crop yield. Irrigation helps to mitigate the decreased crop yield, but CO2 enrichment blurs the role of irrigation. The crops in the wetter southern 3H Plain (Huaiyuan) are significantly more sensitive to climate change than crops in the drier north (Botou). Thus CO2 fertilization effects might be greater under drier conditions. The study provides suggestions for climate change adaptation and sound water resources management in the 3H Plain.  相似文献   

9.
Wheat is the most important cereal crop in the semi-arid eastern Mediterranean region that includes northern Syria. Knowledge of wheat root depth and the vertical distribution during the winter growing season is needed for sound scheduling of irrigation and efficient use of water. This article reports evaluation of root development for three winter-grown bread (Triticum aestivum L.) and durum (Triticum turgidum L.) wheat under four soil water regimes (rainfed and full irrigation with two intermediate levels of 33 and 66% of full irrigation). Roots were sampled by soil coring to a depth of 0.75 m at four occasions during 2005-2006 growing season. Two distinct phases of root development were identified, a rapid downward penetration from emergence to end tillering phase, followed by a substantial root mass growth along the profile from tillering to mid-stem-elongation phase. Roots were detected as deep as 0.75 m during the initial rapid penetration, yet only 29% of the total seasonal root mass was developed. This downward penetration rate averaged 7 mm d−1 and produced 10.8 kg ha−1 d−1 of root dry-biomass. The bulging of root mass from tillering to mid-stem-elongation coincided with vigorous shoot growth, doubling root dry-biomass at a rate of 52 kg ha−1 d−1, compared to the seasonal root growth rate of 18.3 kg ha−1 d−1. A second-degree equation described the total root dry-biomass as a function of days after emergence (r2 = 0.85), whereas a simpler equation predicted it as a function of cumulative growing degree days (r2 = 0.85). The final grain yield was a strong function of irrigation regimes, varying from 3.0 to 6.5 t ha−1, but showed no correlation with root biomass which remained similar as soil water regimes changed. This observation must be viewed with care as it lacks statistical evidence. Results showed 90% of root mass at first irrigation (15 April) confined in the top 0.60-0.75 m soil in bread wheat. Presence of shallow restricting soil layers limited root depth of durum wheat to 0.45 m, yet total seasonal root mass and grain yield were comparable with non-restricted bread wheat. Most root growth occurred during the cool rainy season and prior to the late irrigation season. The root sampling is short of rigorous, but results complement the limited field data in literature collectively suggesting that irrigation following the rainy season may best be scheduled assuming a well developed root zone as deep as the effective soil depth within the top meter of soil.  相似文献   

10.
Corn crop response under managing different irrigation and salinity levels   总被引：1，自引：0，他引：1  
Non-uniformity of water distribution under irrigation system creates both deficit and surplus irrigation areas. Water salinity can be hazard on crop production; however, there is little information on the interaction of irrigation and salinity conditions on corn (Zea Mays) growth and production. This study evaluated the effect of salinity and irrigation levels on growth and yield of corn grown in the arid area of Egypt. A field experiment was conducted using corn grown in northern Egypt at Quesina, Menofia in 2009 summer season to evaluate amount of water applied, salinity hazard and their interactions. Three salinity levels and five irrigation treatments were arranged in a randomized split-plot design with salinity treatments as main plots and irrigation rates within salinity treatments. Salinity treatments were to apply fresh water (0.89 dS m−1), saline water (4.73 dS m−1), or mixing fresh plus saline water (2.81 dS m−1). Irrigation treatments were a ratio of crop evapotranspiration (ET) as: 0.6ET, 0.8ET, 1.0ET, 1.2ET, and 1.4ET. In well-watered conditions (1.0ET), seasonal water usable by corn was 453, 423, and 380 mm for 0.89EC, 2.81EC and 4.73EC over the 122-day growing season, respectively. Soil salt accumulation was significantly increased by either irrigation salinity increase or amount decrease. But, soil infiltration was significantly decreased by either salinity level or its interaction with irrigation amount. Leaf temperature, transpiration rate, and stomata resistance were significantly affected by both irrigation and salinity levels with interaction. Leaf area index, harvest index, and yield were the greatest when fresh and adequate irrigation was applied. Grain yield was significantly affected in a linear relationship (r2 ≥ 0.95) by either irrigation or salinity conditions with no interaction. An optimal irrigation scheduling was statistically developed based on crop response for a given salinity level to extrapolate data from the small experiment (uniform condition) to big field (non-uniformity condition) under the experiment constraints.  相似文献   

11.
Soil soluble phosphorus (P) transport with root-phosphorus-uptake (RPU) is a critical process for plant growth, cycling of P in soil-plant systems and environment protection. However, modeling soil soluble P transport is extremely challenging because it is difficult to measure the RPU distribution directly, especially in the field. In this study, an inverse method, which was utilized successfully to estimate the root-water-uptake (RWU) rate distribution by Zuo and Zhang (2002) and the source-sink term in the nitrate (NO−3-N) transport equation by Shi et al. (2007), was applied to estimate the RPU rate distribution and analyze soil soluble P transport in the soil-plant systems. A soil column experiment (Exp. 1) and a field experiment (Exp. 2), respectively with winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) growth, were carried out to observe the dynamics of soil water and soluble P. Based on the experimental data in Exp. 1, the average RWU and RPU rate distributions during different irrigation periods were estimated using the inverse method. The relative errors of the total P extracted by wheat between the estimated and measured values during all periods were less than 10%. The estimated RPU rate distribution during the period of 10.5-15.5 days after planting (DAP) was used to optimize the dimensionless RPU factor δ to establish the RPU model (δ = 1.31), which helped to calculate the RPU rate distributions during other periods (from 16.5 to 57.5 DAP) in Exp. 1. The calculated RPU rate distributions were compared well with the estimated profiles by the inverse method, and the root mean squared error between them was less than 0.00005 mg cm−3 d−1. Correspondingly, the calculated total P extracted by winter wheat was also comparable with the measured value, with the relative error less than 10%. Similarly, the procedures were employed for summer maize in Exp. 2. The estimated (using the inverse method) and calculated (through the RPU model with δ = 1.38) RPU rate distributions were in good agreement with the root mean squared error as less as 0.000031 mg cm−3 d−1. According to the established RPU models (δ = 1.31 and 1.38 for Exps. 1 and 2, respectively), the distributions of soil water content and soluble P concentration were simulated, and compared well with the measured profiles, with the maximum root mean squared error of 0.0088 cm3 cm−3 and 0.0066 mg cm−3 in Exp. 1, and 0.023 cm3 cm−3 and 0.0015 mg cm−3 in Exp. 2, respectively. The inverse method should be effective and applicable for estimating the RPU rate distribution, establishing the RPU model and analyzing soil soluble P transport in soil-plant systems, either in laboratory or in the field.  相似文献   

12.
Olive tree (Olea europaea L.) is commonly grown under environmental conditions characterised by water deficit, high temperatures and irradiance levels typical of Mediterranean semi-arid regions. Measurement of gas exchange, chlorophyll content, chlorophyll fluorescence and photoinhibition was carried out on two-year-old olive trees (cv. ‘Coratina’) subjected to a 21-day period of water deficit followed by 23 days of rewatering. At the beginning of the experiment, plants were divided in to two groups and subjected to different light regimes: exposed plants (EP) under a mean photosynthetically active radiation (PAR) at mid-day of 1800 μmol m−2 s−1 and shaded plants (SP) under a mean PAR of 1200 μmol m−2 s−1. The effect of drought and high irradiance levels caused a reduction of gas exchange and photosystem 2 (PSII) efficiency, in terms of quantum yield of PSII (ΦPSII) both in EP and SP. Shading conditions allowed plants to maintain a high photosynthetic activity at low values of stomatal conductance, whereas in EP the reductions in photosynthetic efficiency and intrinsic water efficiency were due to non-stomatal components of photosynthesis. The decrease in photosynthetic activity and the increase of photoinhibition under drought were more marked in EP than in SP. Full sunlight caused in EP a higher non-photochemical quenching, whereas SP showed a better photochemical efficiency. The information here obtained can be important to understand the mechanisms by which olive plants can minimize photoinhibition when subjected to simultaneous abiotic stresses.  相似文献   

13.
The highly weathered, low-carbon, intensively cropped, drought-prone Coastal Plain soils of Georgia are susceptible to runoff and soil loss, especially at certain times of the year when soil water contents are elevated. We quantified the effects of antecedent water content (AWC) on runoff (R) and sediment (E) losses from two loamy sands managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems. Two AWC treatments were evaluated: field moist (FM) and pre-wet (PW), created with and without post pesticide application irrigations (∼12 mm of water added with the rainfall simulated over 30 min) for incorporation. Treatments (5) evaluated were: CT + FM, CT + PW, ST + FM, ST + PW, and NT + PW. Field plots, each 2-m × -3 m, were established on each treatment. Each 6-m2 field plot received simulated rainfall at a variable rainfall intensity (Iv) pattern for 70 min (site 1) or a constant rainfall intensity (Ic) pattern for 60 min (site 2; Ic = 50.8 mm h−1). Adding ∼12 mm of water as herbicide incorporation increased AWCs of the 0-2 (3-9-fold) and 2-15 (23-117%) cm soil depths of PW plots compared to existing field moist soil conditions. Increase in AWC increased R (as much as 60%) and maximum R rates (as much as 62%), and decreased E (at least 59%) and maximum E rates (as much as 2.1-fold) for corresponding tillage treatments. Compared to CT plots, ST and NT plots decreased R (at least 2.6-fold) and maximum R rates (as much as 3-fold), and decreased E (at least 2.7-fold) and maximum E rates (at least 3.2-fold). Runoff curves for pre-wetted CT and ST plots were always higher than corresponding FM curves, whereas E curves for field moist CT and ST plots were always higher than corresponding PW curves. Changes in AWC and tillage affected detachment and transport processes controlling runoff and sediment yields. A more accurate measure of rainfall partitioning and detachment and transport processes affecting R and E losses was obtained when commonly occurring field conditions (increased AWC with irrigation; Iv pattern derived from natural rainfall; commonly used tillage systems) were created and evaluated.  相似文献   

14.
Agriculture is a big consumer of fresh water in competition with other sectors of the society. Within the EU-project SAFIR new water-saving irrigation strategies were developed based on pot, semi-field and field experiments with potatoes (Solanum tuberosum L.), fresh tomatoes (Lycopersicon esculentum Mill.) and processing tomatoes as model plants. From the pot and semi-field experiments an ABA production model was developed for potatoes to optimize the ABA signalling; this was obtained by modelling the optimal level of soil drying for ABA production before re-irrigation in a crop growth model. The field irrigation guidelines were developed under temperate (Denmark), Mediterranean (Greece, Italy) and continental (Serbia, China) climatic conditions during summer. The field investigations on processing tomatoes were undertaken only in the Po valley (North Italy) on fine, textured soil. The investigations from several studies showed that gradual soil drying imposed by deficit irrigation (DI) or partial root zone drying irrigation (PRD) induced hydraulic and chemical signals from the root system resulting in partial stomatal closure, an increase in photosynthetic water use efficiency, and a slight reduction in top vegetative growth. Further PRD increased N-mineralization significantly beyond that from DI, causing a stay-green effect late in the growing season. In field potato and tomato experiments the water-saving irrigation strategies DI and PRD were able to save about 20-30% of the water used in fully irrigated plants. PRD increased marketable yield in potatoes significantly by 15% due to improved tuber size distribution. PRD increased antioxidant content significantly by approximately 10% in both potatoes and fresh tomatoes. Under a high temperature regime, full irrigation (FI) should be undertaken, as was clear from field observations in tomatoes. For tomatoes full irrigation should be undertaken for cooling effects when the night/day average temperature >26.5 °C or when air temperature >40 °C to avoid flower-dropping. The temperature threshold for potatoes is not clear. From three-year field drip irrigation experiments we found that under the establishment phase, both potatoes and tomatoes should be fully irrigated; however, during the later phases deficit irrigation might be applied as outlined below without causing significant yield reduction:
•
Potatoes
°
After the end of tuber initiation, DI or PRD is applied at 70% of FI. During the last 14 days of the growth period, DI or PRD is applied at 50% of FI.
•
Fresh tomatoes
°
From the moment the 1st truce is developed, DI is applied at 85-80% of FI for two weeks. In the middle period, DI or PRD is applied at 70% of FI. During the last 14 days of the growth period, DI or PRD is applied at 50% of FI.
•
Processing tomatoes
°
From transplanting to fruit setting at 4th-5th cluster, the PRD and DI threshold for re-irrigation is when the plant-available soil water content (ASWC) equals 0.7 (soil water potential, Ψsoil = −90 kPa). During the late fruit development/ripening stage, 10% of red fruits, the threshold for re-irrigation for DI is when ASWC = 0.5 (Ψsoil = −185 kPa) and for PRD when ASWC (dry side) = 0.4 (Ψsoil, dry side = −270 kPa).
The findings during the SAFIR project might be used as a framework for implementing water-saving deficit irrigation under different local soil and climatic conditions.  相似文献   

15.
Free-drainage or “open” substrate system used for vegetable production in greenhouses is associated with appreciable NO3− leaching losses and drainage volumes. Simulation models of crop N uptake, N leaching, water use and drainage of crops in these systems will be useful for crop and water resource management, and environmental assessment. This work (i) modified the TOMGRO model to simulate N uptake for tomato grown in greenhouses in SE Spain, (ii) modified the PrHo model to simulate transpiration of tomato grown in substrate and (iii) developed an aggregated model combining TOMGRO and PrHo to calculate N uptake concentrations and drainage NO3− concentration. The component models simulate NO3−-N leached by subtracting simulated N uptake from measured applied N, and drainage by subtracting simulated transpiration from measured irrigation. Three tomato crops grown sequentially in free-draining rock wool in a plastic greenhouse were used for calibration and validation. Measured daily transpiration was determined by the water balance method from daily measurements of irrigation and drainage. Measured N uptake was determined by N balance, using data of volumes and of concentrations of NO3− and NH4+ in applied nutrient solution and drainage. Accuracy of the two modified component models and aggregated model was assessed by comparing simulated to measured values using linear regression analysis, comparison of slope and intercept values of regression equations, and root mean squared error (RMSE) values. For the three crops, the modified TOMGRO provided accurate simulations of cumulative crop N uptake, (RMSE = 6.4, 1.9 and 2.6% of total N uptake) and NO3−-N leached (RMSE = 11.0, 10.3, and 6.1% of total NO3−-N leached). The modified PrHo provided accurate simulation of cumulative transpiration (RMSE = 4.3, 1.7 and 2.4% of total transpiration) and cumulative drainage (RMSE = 13.8, 6.9, 7.4% of total drainage). For the four cumulative parameters, slopes and intercepts of the linear regressions were mostly not statistically significant (P < 0.05) from one and zero, respectively, and coefficient of determination (r2) values were 0.96-0.98. Simulated values of total drainage volumes for the three crops were +21, +1 and −13% of measured total drainage volumes. The aggregated TOMGRO-PrHo model generally provided accurate simulation of crop N uptake concentration after 30-40 days of transplanting, with an average RMSE of approximately 2 mmol L−1. Simulated values of average NO3− concentration in drainage, obtained with the aggregated model, were −7, +18 and +31% of measured values.  相似文献   

16.
Quantification of the interactive effects of nitrogen (N) and water on nitrate (NO3) loss provides an important insight for more effective N and water management. The goal of this study was to evaluate the effect of different irrigation and nitrogen fertilizer levels on nitrate-nitrogen (NO3-N) leaching in a silage maize field. The experiment included four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil moisture depletion, SMD) and three N fertilization levels (0, 142, and 189 kg N ha−1), with three replications. Ceramic suction cups were used to extract soil solution at 30 and 60 cm soil depths for all 36 experimental plots. Soil NO3-N content of 0-30 and 30-60-cm layers were evaluated at planting and harvest maturity. Total N uptake (NU) by the crop was also determined. Maximum NO3-N leaching out of the 60-cm soil layer was 8.43 kg N ha−1, for the 142 kg N ha−1 and over irrigation (1.13 SMD) treatment. The minimum and maximum seasonal average NO3 concentration at the 60 cm depth was 46 and 138 mg l−1, respectively. Based on our findings, it is possible to control NO3 leaching out of the root zone during the growing season with a proper combination of irrigation and fertilizer management.  相似文献   

17.
Root respiration was measured in vivo by infrared gas analysis of complete root systems in drought-sensitive (Longchun 8139-2) and drought-tolerant (Dingxi 24) spring wheat (Triticum aestivum) cultivars. Plants were grown in sand culture for 3 weeks under the following regimes: (a) water sufficiency, (b) moderate drought stress or (c) severe drought stress. The aim was to study the acclimation to drought stress in terms of changes in root growth, root respiration and energy requirement for water uptake. Drought stress increased the root:shoot ratio of both varieties. Roots of water-sufficient treatments respired 4.03 and 2.87 mg glucose h−1 g−1 in Longchun 8139-2 and Dingxi 24, respectively. However, severe drought stress enhanced root respiration of Longchun 8139-2 and Dingxi 24 to 6.52 and 3.01 mg glucose h−1 g−1, respectively. Compared with water-sufficient plants, drought-sensitive spring wheat (Longchun 8139-2) used a relatively higher amount of glucose to absorb water in drought stress treatment, especially in severe drought stress. The drought-resistant spring wheat Dingxi 24 used lower amount of glucose to absorb water in drought stress conditions, relative to drought-sensitive plants. In the arid and semi-arid region of the Losses Plateau, drought-resistant wheat species have many advantages over drought-sensitive species.  相似文献   

18.
Actual measurements of water uptake and use, and the effect of water quality considerations on evapotranspiration (ET), are indispensable for understanding root zone processes and for the development of predictive plant growth models. The driving hypothesis of this research was that root zone stress response mechanisms in perennial fruit tree crops is dynamic and dependent on tree maturity and reproductive capability. This was tested by investigating long-term ET, biomass production and fruit yield in date palms (Phoenix dactylifera L., cv. Medjool) under conditions of salinity. Elevated salinity levels in the soil solution were maintained for 6 years in large weighing-drainage lysimeters by irrigation with water having electrical conductivity (EC) of 1.8, 4, 8 and 12 dS m−1. Salinity acted dynamically with a long-term consequence of increasing relative negative response to water consumption and plant growth that may be explained either as an accumulated effect or increasing sensitivity. Sensitivity to salinity stabilized at the highest measured levels after the trees matured and began producing fruit. Date palms were found to be much less tolerant to salinity than expected based on previous literature. Trees irrigated with low salinity (EC = 1.8 dS m−1) water were almost twice the size (based on ET and growth rates) than trees irrigated with EC = 4 dS m−1 water after 5 years. Fruit production of the larger trees was 35-50% greater than for the smaller, salt affected, trees. Long term irrigation with very high EC of irrigation water (8 and 12 dS m−1) was found to be commercially impractical as growth and yield were severely reduced. The results raise questions regarding the nature of mechanisms for salinity tolerance in date palms, indicate incentives to irrigate dates with higher rather than lower quality water, and present a particular challenge for modelers to correctly choose salinity response functions for dates as well as other perennial crops.  相似文献   

19.
Nigellone (dithymoquinone) is the main active constituent of volatile oil of black cumin (Nigella sativa) seeds. It is presently used in traditional medicines, for culinary as ornamentals, and is also considered for its abundant nectar secretion. While black cumin, investigated recently (for the oil, essential oil, and other biologically active constituents of their seeds) the effects of deficit irrigation on seeds Nigellone content produced on gypsifereous soils are not known. Randomized complete block design experiments were conducted with three replications and four irrigation treatments on soils with five different gypsum contents over two growing seasons (2008-2009 and 2009-2010). These experiments aim to monitor and quantify water stress and Nigellone volatile oil content of black cumin as a function of crop water stress index and soil gypsum content. The soil gypsum content treatments were 60.0 (G1), 137.6 (G2), 275.2 (G3), 314.2 (G4) and 486.0 (G5) g kg−1. Three irrigation treatments were based on replenishing the 0.60 m deep root zone to field capacity when the maximum allowable depletion (MAD) of the available soil water holding capacity of 25% (I1), 50% (I2) and 75% (I3) were maintained in the crop experiments. A dryland treatment (fully stressed, I4) was also included. The lower (non-stressed) and upper (stressed) baselines were measured to calculate crop water stress index. The crop water stress index behaved as expected, dropping to near zero following an irrigation and increasing gradually as black cumin plants depleted soil water reserves. The seasonal mean values of crop water stress index for the irrigation treatments; I1, I2, and I3 were increased from 0.189, 0.287, 0.380 to 0.239, 0.366, 0.467, respectively when the soil gypsum content increased from 60.0 to 486.0 g kg−1. The highest Nigellone volatile oil content of black cumin seeds was obtained for G1I1 treatment (5.1 g kg−1) while the lowest content (3.5 g kg−1) was obtained for G5I1 treatment. Equations that can be used to predict the Nigellone volatile oil content of black cumin seeds were developed for the three irrigation schedules of different maximum allowable depletion of available soil water holding capacity using the relationships between the Nigellone volatile oil content and the seasonal mean crop water stress index for different soil gypsum contents. The relationships between black cumin seed yield, Nigellone volatile oil content and seasonal mean crop water stress index values were primarily linear. These relations can be used to predict the yield of black cumin seeds, seeds Nigellone volatile oil content, and irrigation timing in soils with different soil gypsum contents. Thus, the obtained data will be beneficial for further research.  相似文献   

20.
Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm3 cm−3, 0.59 Mg ha−1, 2.05 Mg ha−1, and 0.19 kg m−3, respectively, for wheat; and 0.027 cm3 cm−3, 0.71 Mg ha−1, 1.51 Mg ha−1 and 0.35 kg m−3, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.  相似文献   

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