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1.
Irrigation of crops in arid regions with marginal water is expanding. Due to economic and environmental issues arising from use of low-quality water, irrigation should follow the actual crop water demands. However, direct measurements of transpiration are scant, and indirect methods are commonly applied; e.g., the Penman–Monteith (PM) equation that integrates physiological and meteorological parameters. In this study, the effects of environmental conditions on canopy resistance and water loss were experimentally characterized, and a model to calculate palm tree evapotranspiration ETc was developed. A novel addition was to integrate water salinity into the model, thus accounting for irrigation water quality as an additional factor. Palm tree ETc was affected by irrigation water salinity, and maximum values were reduced by 25 % in plants irrigated with 4 dS m?1 and by 50 % in the trees irrigated with 8 dS m?1. Results relating the responses of stomata to the environment exhibited an exponential relation between increased light intensities and stomatal conductance, a surprising positive response of stomata to high vapor pressure deficits and a decrease in conductance as water salinity increased. These findings were integrated into a modified ‘Jarvis–PM’ canopy conductance model using only meteorological and water quality inputs. The new approach produced weekly irrigation recommendations based on field water salinity (2.8 dS m?1) and climatic forecasts that led to a 20 % decrease in irrigation water use when compared with current irrigation recommendations.  相似文献   

2.
Granier type sap flow gauges were used to estimate canopy transpiration from a 7-year-old sweet orange (Citrus sinensis L. Osbeck) orchard in Ghana, West Africa. The aim of the study was to use sap flow based transpiration estimates in modelling the stomatal control of water transport under rain-fed and subhumid tropical conditions. Canopy conductance (gc) of the sweet orange was calculated by inverting the Penman–Monteith equation. Both multiple linear regression and a Jarvis-type model, based on a set of environmental control functions, have been used to simulate half-hourly citrus canopy conductance. Both methods could adequately predict bulk stomatal conductance of the orchard and were suitable for use in the Penman–Monteith equation to estimate transpiration rates. In both models, the vapour pressure deficit was the dominant regulator of canopy transpiration as it explained about 80% of the variations in canopy conductance. A simple envelop function of canopy conductance as a function of the solar radiation and vapour pressure deficit was equally suitable for gc prediction. However, the Jarvis formulation provided the best estimation of conductance compared to other models. Validation with separate data sets confirmed the good performance of these models to investigate the response of citrus to changing environmental conditions.  相似文献   

3.
The methodology proposed by the Food and Agriculture Organization (FAO) (Doorenbos, J., Pruitt, W.O., 1977. Crop water requirements. FAO irrigation and drainage. Paper No. 24. FAO, Rome) and updated by Allen et al. (Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO irrigation and drainage. Paper No. 56. FAO, Rome) for calculating crop water requirements is the most extended and accepted method worldwide. This method requires the prior calculation of reference evapotranspiration (ETo). This study evaluates the FAO-56 and American Society of Civil Engineers (ASCE) Penman–Monteith (PM) equations for estimation of hourly ETo under the semiarid conditions of the province of Albacete (Spain). The FAO-56 and ASCE equations (hourly time step) were compared against measured lysimeter ETo values at Albacete for 13 days during the period of April–October 2002 and 16 days during April–October 2003. The average of estimated FAO-56 Penman–Monteith ETo values was equal to the average of measured values. However, the average of estimated ASCE Penman–Monteith values was 4% higher than the average of measured lysimeter ETo values. This method overestimated measured lysimeter ETo values by 0.45 mm h−1.Simple linear regression and error analysis statistics suggest that agreement between both estimation methods and the lysimeter was quite good for the province of Albacete.In this paper, the FAO-56 Penman–Monteith equation for calculating hourly ETo values was more accurate than the ASCE Penman–Monteith method under semiarid weather conditions in Albacete.  相似文献   

4.
In order to assess the effect of soil water deficit (SWD) during fruit development and ripening, on yield and quality of processing tomato under deficit irrigation in the Mediterranean climate, an open-field experiment was carried out in two sites differing from soil and climatic characteristics, in Sicily, South Italy. Six irrigation treatments were studied: no irrigation following plant establishment (NI); 100% (F = full) or 50% (D = deficit) ETc restoration with long-season irrigation (L) or short-season irrigation up to 1st fruit set (S); and long-season irrigation with 100% ETc restoration up to beginning of flowering, then 50% ETc restoration (LFD). The greatest effect of increasing SWD was the rise in fruit firmness, total solids and soluble solids (SS). A negative trend in response to increasing SWD was observed for fruit yield and size. Tough yield and SS were negatively correlated, the final SS yield under the LD regime was close to that of LF, and 47% water was saved. However, SS seems to be more environmental sensitive than SWD, since it varied more between sites than within site. The variations between sites in fruit quality response to deficit irrigation demonstrate that not only SWD but also soil and climatic characteristics influence the quality traits of the crop.  相似文献   

5.
Satellite remote sensed data on canopy biophysical properties, ground data and agro-meteorological information were combined to estimate evapotranspiration (ET) fluxes of orange orchards using a modified Penman–Monteith equation. The study was carried out during the irrigation season 2004 in an irrigation district, cover for about 95% with orange groves, of 1550 ha located in eastern Sicily (Italy). The spatial pattern in ET-fluxes have been analysed using IKONOS high-resolution satellite and hyper-spectral ground data acquired and processed for the study-area. The remote estimates of ET-fluxes varied between 1.3 and 5.7 mm/day, with a daily average value of about 4.2 mm, showing a good agreement with crop ET values determined as residual of soil water balance of selected ground control sites. Crop coefficient estimates ranged between 0.22 and 1.08 showing positive correlations with percentages of ground cover (Cg) increasing from 30 to 80% ground shading and with LAI values. By comparing ET estimates with water volumes supplied in each sub-district of the study-area, the performance indicator “IP” was evaluated, allowing to rank the conditions of un-fulfilment of crop water requirements by public and private water distribution systems. Generally, out of 29 sub-districts, 14 had “IP” values less than 50%, revealing a sub-optimal water supply for the study-area.  相似文献   

6.
We studied the suitability of empirical crop water stress index (CWSI) averaged over daylight hours (CWSId) for continuous monitoring of water status in apple trees. The relationships between a midday CWSI (CWSIm) and the CWSId and stem water potential (ψ stem), and soil water deficit (SWD) were investigated. The treatments were: (1) non-stressed where the soil water was close to field capacity and (2) mildly stressed where SWD fluctuated between 0 and a maximum allowable depletion (MAD of 50 %). The linear relationship between canopy and air temperature difference (ΔT) and air vapor pressure deficit (VPD) averaged over daylight hours resulted in a non-water-stressed baseline (NWSBL) with higher correlation (?T = ?0.97 VPD – 0.46, R 2 = 0.78, p < 0.001) compared with the conventional midday approach (?T = ?0.59 VPD – 0.67, R 2 = 0.51, p < 0.001). Wind speed and solar radiation showed no significant effect on the daylight NWSBL. There was no statistically meaningful relationship between midday ψ stem and CWSIm. The CWSId agreed well with SWD (R 2 = 0.70, p < 0.001), while the correlation between SWD and CWSIm was substantially weaker (R 2 = 0.38, p = 0.033). The CWSId exhibited high sensitivity to mild variations in the soil water content, suggesting it as a promising indicator of water availability in the root zone. The CWSId is stable under transitional weather conditions as it reflects the daily activity of an apple crop.  相似文献   

7.
A field experiment was conducted for 3 years to evaluate the effect of deficit irrigation under different soil management practices on biomass production, grain yield, yield components and water productivity of spring wheat (Triticum estivum L.). Soil management practices consisted of tillage (conventional and deep tillage) and Farmyard manure (0 and 10 t ha?1 FYM). Line source sprinkler laterals were used to generate one full- (ETm) and four deficit irrigation treatments that were 88, 75, 62 and 46 % of ETm, and designated as ETd1, ETd2, ETd3, and ETd4. Deep tillage significantly enhanced grain yield (14–18 %) and water productivity (1.27–1.34 kg m?3) over conventional tillage. Similarly, application of FYM at 10 t ha?1 significantly improved grain yield (10–13 %) and water productivity (1.25–1.31 kg m?3) in comparison with no FYM. Grain yield response to irrigation varied significantly (5,281–2,704 kg ha?1) due to differences in soil water contents. Water productivity varied from 1.05 to 1.34 kg m?3, among the treatments in 3 years. The interactive effect of irrigation × tillage practices and irrigation × FYM on grain yield was significant. Yield performance proved that deficit irrigation (ETd2) subjected to 75 % soil water deficit had the smallest yield decline with significant water saving would be the most appropriate irrigation level for wheat production in arid regions.  相似文献   

8.
Relationship between plant water stress and soil water depletion (SWD) is not investigated thoroughly for irrigated pecans of southern New Mexico. In this study, transient soil water contents, rootzone SWD, and midday stem water potential (SWP) were monitored in mature pecan orchards in sandy loam (Site 1) and silty clay loam (Site 2) soils near Las Cruces, New Mexico. Corresponding to transient variations of soil water content at different depths, daily SWD varied with soil depth but not spatially. The SWD within the rootzone (0–80 cm) was higher in the shallow depths (0–40 cm) where root length density (RLD) was also higher than in the deeper depths (40–80 cm). The SWD at Site 1 was higher compared to Site 2 due to the higher clay content of the latter. The SWD patterns at outside the tree driplines were similar to those under-canopy locations because of similar RLD at the shallow depths. At both pecan orchards, differences in SWP at 2.5, 4.5, and 7.6 m tree heights were evident particularly 10–14 days after irrigation. This was due to the stress caused by decreasing soil water contents at different depths, which were generally significantly correlated with SWP. Midday air temperature was as useful as midday atmospheric vapor pressure deficit for interpreting SWP. Combined influence of soil water content (0–40 cm) and air temperature on midday SWP was significant at both orchards, which can be used as an adjunct for the clear interpretation of SWP to help refine irrigation scheduling.  相似文献   

9.
Maize (Zea mays L.) is an important food crop for irrigated regions in the world. Its growth and production may be estimated by different crop models in which various relationships between growth and environmental parameters are used. For simulation of maize growth and grain yield, a simulation model was developed (Maize Simulation Model, MSM). Dynamic flow of water, nitrogen (N) movement, and heat flow through the soil were simulated in unsteady state conditions by numerical analysis in soil depth of 0–1.8 m. Hourly potential evapotranspiration [ETp(t)] for maize field was estimated directly by Penman–Monteith method. Hourly potential evaporation [Ep(t)] was estimated based on ETp(t) and canopy shadow projection. Actual evaporation of soil surface was estimated based on its potential value, relative humidity of air, water pressure head and temperature at soil surface layer. Actual transpiration (Ta(t)) was estimated based on soil water content and root distribution at each soil layer. Hourly N uptake by plant was simulated by N mass flow and diffusion processes. Hourly top dry matter production (HDMAj + 1, where j is number of hours after planting) was estimated by hourly corrected intercepted radiation (RSLTj + 1) by plant leaves [determined from leaf area index (LAIj + 1)] with air temperature, the maximum and minimum plant top N concentration and the amounts of nitrogen uptake. The value of LAIj + 1 at each hour was estimated by the accumulated top dry matter production at previous hour using an empirical equation. Maize grain yield was estimated by a relationship between harvest index and seasonal plant top dry matter production. The model was calibrated using data obtained under field conditions by a line source sprinkler irrigation. When the values of water and nitrogen application were optimum, grain yield (moisture content of 15.5%) was 16.2 Mg ha−1. Model was validated using two independent experimental data obtained from other experiments in the Badjgah (Fars province). The experimental results validated the proposed simulation model fairly well.  相似文献   

10.
In the Gezira irrigation scheme in central Sudan, serious symptoms of water waste have been identified in the last two decades, especially in sorghum and groundnut fields. To quantify losses, water-use efficiencies and related parameters were obtained for these two food crops under the traditional attended daytime water application and the newly evolved unattended continuous watering method. In this on-farm research, the neutron scattering method was used to determine the actual soil water deficits of the two crops. A simple Penman equation was used for approximating reference crop evapotranspiration and evaporation losses from standing water and wet soil surface. An updated approach using the Penman-Monteith equation was additionally applied. The study revealed wastage of irrigation water in both irrigation methods but at different rates and also differently for each crop. In the attended field, the average seasonal over-irrigation, which is the difference between average application depth Q and average soil moisture deficit SWD, was observed to range between 0.4 and 1.5 of SWD (0.3 and 0.6 of Q) and the corresponding values in the unattended field were 0.6 and 3.2 of SWD (0.4 and 0.8 of Q). Higher values are shown by the groundnut subplots, which crop also suffers from excess water, and by the drier year as well as in the unattended fields. A first approximation is given, still including readily available water at harvest, of minimum water requirements in attended watering for maximum yields. In the drier year, when more irrigation water was applied, an amount equal to 30-50% of these minimum water requirements was lost in evaporation from standing water/wet surface, which is the main unproductive water. More frequent land levelling aiming at minimum standing water in better attended irrigation and farm management (e.g. weeding) are priority measures proposed. The quantitative on-farm water waste determinations represent the innovative content of this paper. Knowing precisely how large the problem is and being able to quantify its components will contribute much to the arguments of those who wish to take the proposed measures.  相似文献   

11.
Camelina sativa (L.) Crantz is a promising, biodiesel-producing oilseed that could potentially be implemented as a low-input alternative crop for production in the arid southwestern USA. However, little is known about camelina’s water use, irrigation management, and agronomic characteristics in this arid environment. Camelina experiments were conducted for 2 years (January to May in 2008 and 2010) in Maricopa, Arizona, to evaluate the effectiveness of previously developed heat unit and remote sensing basal crop coefficient (K cb ) methods for predicting camelina crop evapotranspiration (ET) and irrigation scheduling. Besides K cb methods, additional treatment factors included two different irrigation scheduling soil water depletion (SWD) levels (45 and 65 %) and two levels of seasonal N applications within a randomized complete block design with 4 blocks. Soil water content measurements taken in all treatment plots and applied in soil water balance calculations were used to evaluate the predicted ET. The heat-unit K cb method was updated and validated during the second experiment to predict ET to within 12–13 % of the ET calculated by the soil water balance. The remote sensing K cb method predicted ET within 7–10 % of the soil water balance. Seasonal ET from the soil water balance was significantly greater for the remote sensing than heat-unit K cb method and significantly greater for the 45 than 65 % SWD level. However, final seed yield means, which varied from 1,500 to 1,640 kg ha?1 for treatments, were not significantly different between treatments or years. Seed oil contents averaged 45 % in both years. Seed yield was found to be linearly related to seasonal ET with maximum yield occurring at about 470–490 mm of seasonal ET. Differences in camelina seed yields due to seasonal N applications (69–144 kg N ha?1 over the 2 years) were not significant. Further investigations are needed to characterize camelina yield response over a wider range of irrigation and N inputs.  相似文献   

12.
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   

13.
A 2 years field study was conducted to develop crop coefficients for field-grown tomato (Lycopersicon esculentum Mill.), a major irrigated crop in the Jordan Valley, under drip irrigation system with black plastic mulch. The area of the study field was 1.5 ha surrounded by many similar tomato fields. Actual crop evapotranspiration (ETC) was measured using eddy covariance technique which distinguishes this study from other previous studies conducted in the Jordan Valley that relied on the old indirect approach for ETC estimation based on the soil water balance.Grass reference evapotranspiration (ETO) was determined by using the FAO Penman–Monteith method utilizing the agrometeorological parameters measured at the study site. The crop coefficient (KC) was determined as the ratio of ETC to ETO. The tomato crop coefficients were determined following the FAO crop coefficient model. The average crop coefficient during the midseason growth stage (KC mid) was 0.82 which is far below the adjusted FAO crop coefficient of 1.19 by about 31%. Also, the late season crop coefficient (KC end) was much lower than the adjusted FAO crop coefficient of 0.76 by about 40%. Moreover, the weighted average crop coefficient over the entire growing season (KC GS) was 0.69, which is about 36% lower than the FAO corresponding value. In fact, the low KC values obtained reflect the effect of practicing both localized drip irrigation and plastic mulch covering. This study showed that there is a big difference between the reported FAO crop coefficients and the one measured in the filed using a precise approach. These exact updated values of crop coefficients will enhance future estimation of crop water requirements and hence irrigation management of tomato crop which is the major irrigated crop in the Jordan Valley.  相似文献   

14.
Evaluation of crop water stress index for LEPA irrigated corn   总被引：6，自引：0，他引：6  
This study was designed to evaluate the crop water stress index (CWSI) for low-energy precision application (LEPA) irrigated corn (Zea mays L.) grown on slowly-permeable Pullman clay loam soil (fine, mixed, Torrertic Paleustoll) during the 1992 growing season at Bushland, Tex. The effects of six different irrigation levels (100%, 80%, 60%, 40%, 20%, and 0% replenishment of soil water depleted from the 1.5-m soil profile depth) on corn yields and the resulting CWSI were investigated. Irrigations were applied in 25 mm increments to maintain the soil water in the 100% treatment within 60–80% of the “plant extractable soil water” using LEPA technology, which wets alternate furrows only. The 1992 growing season was slightly wetter than normal. Thus, irrigation water use was less than normal, but the corn dry matter and grain yield were still significantly increased by irrigation. The yield, water use, and water use efficiency of fully irrigated corn were 1.246 kg/m2, 786 mm, and 1.34 kg/m3, respectively. CWSI was calculated from measurements of infrared canopy temperatures, ambient air temperatures, and vapor pressure deficit values for the six irrigation levels. A “non-water-stressed baseline” equation for corn was developed using the diurnal infrared canopy temperature measurements as T c–T a = 1.06–2.56 VPD, where T c was the canopy temperature (°C), Ta was the air temperature (°C) and VPD was the vapor pressure deficit (kPa). Trends in CWSI values were consistent with the soil water contents induced by the deficit irrigations. Both the dry matter and grain yields decreased with increased soil water deficit. Minimal yield reductions were observed at a threshold CWSI value of 0.33 or less for corn. The CWSI was useful for evaluating crop water stress in corn and should be a valuable tool to assist irrigation decision making together with soil water measurements and/or evapotranspiration models. Received: 19 May 1998  相似文献   

15.
Four different levels of drip fertigated irrigation equivalent to 100, 75, 50 and 25% of crop evapotranspiration (ETc), based on Penman–Monteith (PM) method, were tested for their effect on crop growth, crop yield, and water productivity. Tomato (Lycopersicon esculentum, Troy 489 variety) plants were grown in a poly-net greenhouse. Results were compared with the open cultivation system as a control. Two modes of irrigation application namely continuous and intermittent were used. The distribution uniformity, emitter flow rate and pressure head were used to evaluate the performance of drip irrigation system with emitters of 2, 4, 6, and 8 l/h discharge. The results revealed that the optimum water requirement for the Troy 489 variety of tomato is around 75% of the ETc. Based on this, the actual irrigation water for tomato crop in tropical greenhouse could be recommended between 4.1 and 5.6 mm day−1 or equivalent to 0.3–0.4 l plant−1 day−1. Statistically, the effect of depth of water application on the crop growth, yield and irrigation water productivity was significant, while the irrigation mode did not show any effect on the crop performance. Drip irrigation at 75% of ETc provided the maximum crop yields and irrigation water productivity. Based on the observed climatic data inside the greenhouse, the calculated ETc matched the 75–80% of the ETc computed with the climatic parameters observed in the open environment. The distribution uniformity dropped from 93.4 to 90.6%. The emitter flow rate was also dropped by about 5–10% over the experimental period. This is due to clogging caused by minerals of fertilizer and algae in the emitters. It was recommended that the cleaning of irrigation equipments (pipe and emitter) should be done at least once during the entire cultivation period.  相似文献   

16.
Summary Concurrent diurnal measurements of water potential, osmotic potential and conductance were made on leaves of lucerne grown under weekly (W) and fortnightly (F) irrigation on gypsum-treated (G) and untreated soil (C). Measurements were made throughout the period of vegetative growth.Leaf water potentials were lower both at dawn and in the afternoon under fortnightly as compared to weekly irrigation. Gypsum application led to a slower decline in water potential under fortnightly irrigation, although the effect was small compared with more frequent irrigation. Stomatal conductance was reduced under treatments FG and FC during the later stages of vegetative growth, coinciding with leaf water potentials of less than c. –1.6 MPa.The relationship between leaf water potential and turgor potential changed with time such that positive turgor was maintained as leaf water potential declined. Turgor maintenance was achieved through a decrease in leaf osmotic potential. These data suggest that lucerne is capable of osmotic adjustment.Stomatal conductance declined rapidly below a leaf turgor potential of c. 0.1 MPa. It is hypothesised that osmotic adjustment enabled stomatal adjustment, which contributed to continued assimilation despite increasing soil moisture deficits.  相似文献   

17.
Interaction of water and nitrogen on maize grown for silage   总被引：3，自引：0，他引：3  
Water scarcity and environmental pollution due to excessive nitrogen (N) applications are important environmental concerns. The Varamin region, which is located in the central part of Iran, is one of the locations where farmers apply 250-350 kg N ha−1 for silage maize without any concerns with respect to the available water for irrigation. The objective of this study was to quantify the response of the silage maize (Zea mays L.) to variable irrigation and N fertilizer applications under arid and semi-arid conditions and to determine the optimum amount of N fertilizer as a function of irrigation. The maize Hybrid 704 single-cross was planted on 3 August 2003 and on 25 June 2004. The experimental treatments consisted of three N rates (0, 150, and 200 kg N ha−1) and four levels of irrigation, including two deficit irrigation levels 0.70 SWD (soil water depletion) and 0.85 SWD, a full-irrigation level (1.0 SWD) and an over-irrigation level (1.13 SWD). Twelve treatments were arranged in a strip-plot design in a randomized complete block with three replicates. Gravimetric soil samples were collected in 2003 and a neutron probe was used in 2004 to measure soil water content. Leaf area index, total aboveground biomass (TB), plant height, stem diameter, and leaf, stem, and ear dry weight were measured during the growing seasons and at final harvest. Total aboveground biomass was affected by irrigation (P < 0.0001) during both years and was also affected by N fertilizer in 2003 (P = 0.0001) and 2004 (P < 0.0001). However, there was no irrigation and N fertilizer interaction for both years (P > 0.5). Total aboveground biomass and biomass of the crop components increased as a function of the amount of water and N applied. For each of the irrigation levels, there was an associated optimum amount of N, which increased as the amount of irrigation water that was applied increased. Among the four irrigation levels that were studied, 0.85 SWD was the optimum level of irrigation for the conditions at the experimental site. The results also indicated that an increase in N applications is not a good strategy to compensate for a decrease of TB under drought stress conditions. We concluded that the effect of N fertilizer on TB depends on the availability of water in the soil, and that the amount of N fertilizer applied should be decreased under drought stress conditions. Further research will combine these results with a crop simulation model to help optimize nitrogen and water management for silage maize.  相似文献   

18.
The applicability of commercially available remote sensing instrumentation was evaluated for site-specific management of abiotic and biotic stress on cotton (Gossypium hirsutum L.) grown under a center pivot low energy precision application (LEPA) irrigation system. This study was conducted in a field where three irrigation regimes (100%, 75%, and 50% ETc) were imposed on areas of Phymatotrichum (root rot) with the specific objectives to (1) examine commercial remote sensing instrumentation for locating areas showing biotic and abiotic stress symptomology in a cotton field, (2) compare data obtained from commercial aerial infrared photography to that collected by infrared transducers (IRTs) mounted on a center pivot, (3) evaluate canopy temperature changes between irrigation regimes and their relationship to lint yield with IRTs and/or IR photography, and (4) explore the use of deficit irrigation and the use of crop coefficients for irrigation scheduling. Pivot-mounted IRTs and an IR camera were able to differentiate water stress among irrigation regimes. The IR camera distinguished between biotic (root rot) and abiotic (drought) stress with the assistance of groundtruthing. The 50% ETc regime had significantly higher canopy temperatures than the other two regimes, which was reflected in significantly lower lint yields when compared to the 75% and 100% ETc regimes. Deficit irrigation down to 75% ETc had no impact on lint yield, indicating that water savings were possible without reducing yield.  相似文献   

19.
Pomegranate (Punica granatum L.) is a deciduous fruit tree native of central Asia included in the so-called group of minor fruit tree species, not widely grown but of some importance in the south east of Spain. Fruit consumption interest is due to the organoleptic characteristics and to the beneficial effects on health. Pomegranate tree are considered as a culture tolerant to soil water deficit. However, very little is known about pomegranate orchard water management. The objective of this work was to characterize, for the first time in P. granatum, water relations aspects of applied significance for irrigation scheduling. Trees under different irrigation regimes were used and midday stem water potential (Ψstem) and midday leaf gas exchange were periodically measured over the course of an entire season. During spring and autumn, Ψstem did not show significant differences between irrigation treatments while there were considerable differences in leaf photosynthesis and stomatal conductance, suggesting a near-isohydric behaviour of pomegranate trees. This might explain why the signal intensity of Ψstem was lower than those of gas exchange indicators during the experimental period. Thus, leaf photosynthesis rates and stomatal conductance might have a greater potential for irrigation scheduling of pomegranate trees than Ψstem measured at solar noon.  相似文献   

20.
The Penman–Monteith (P–M) model with a variable surface canopy resistance (rc) was evaluated to estimate latent heat flux (LE) or crop evapotranspiration (ET) over a furrow-irrigated tomato crop under different soil water status and atmospheric conditions. The hourly values of rc were computed as a function of environmental variables (air temperature, vapor pressure deficit, net radiation, and soil heat flux) and a normalized soil water factor (F), which varies between 0 (wilting point, θWP) and 1 (field capacity, θFC). The Food and Agricultural Organization (FAO-56) method was also evaluated to calculate daily ET based on the reference evapotranspiration, crop coefficient and water stress coefficient. The performance of the P–M model and FAO-56 method were evaluated using LE values obtained from the Bowen ratio system. On a 20 min time interval, the P–M model estimated daytime variation of LE with a standard error of the estimate (SEE) of 46 Wm−2 and an absolute relative error (ARE) of 3.6%. Thus, daily performance of the P–M model was good under soil water content ranging from 118 to 83 mm (θFC and θWP being 125 and 69 mm, respectively) and LAI ranging from 1.3 to 3.0. For this validation period, the calculated values of rc and F ranged between 20 and 114 s m−1 and between 0.87 and 0.25, respectively. In this case, the P–M model was able to predict daily ET with a SEE of 0.44 mm h−1 (1.1 MJ m−2 d−1) and an ARE of 3.9%. Furthermore, the FAO-PM model computed daily ET with SEE and ARE values of 1.1 mm h−1 (2.8 MJ m−2 d−1) and 5.2%, respectively.  相似文献   

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