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1.
Wheat lines with differing capacities for osmoregulation were grown on a full profile of soil water at sowing in seasons of contrasting evaporative demand. Watered experiments were also included. Across seasons the relative increase in dry weight and yield associated with high osmoregulation was positively correlated with cumulative pan evaporation during the period of most rapid growth before anthesis. In experiments showing the most extreme responses to osmoregulative capacity there was no association with the overall soil water deficit at anthesis or harvest suggesting a direct effect of evaporative demand. This was further confirmed by correlations between vapour pressure deficit and leaf water potential and differences in turgor pressure. Significant differences in turgor were, in turn, associated with significant differences in dry weight. It was therefore concluded that osmoregulative effects on growth were mediated through leaf or shoot responses to leaf water stress rather than through root responses to soil water deficit, and that it was necessary to screen lines specifically for osmoregulation rather than for growth responses to soil water deficit.  相似文献   

2.
The relationship between rate of water loss of Italian ryegrass (Lolium multiflorum) and crop properties, weather conditions and mechanical treatments were studied on a field scale, as was the importance of the variables and their combined effects on influencing the wilting process. Eleven forage-drying experiments were performed between 1992 and 1994 on diploid and tetraploid cultivars cut at different growth stages, ranging from early elongation to flowering, under environmentally variable conditions. The rate of drying was measured until a moisture content of 1 g water g?1 dry matter (DM) (500 g kg?1) was reached, or for a maximum of 2 days by calculating the rate of water loss from two consecutive hourly weights of swath portions placed on trays. Multiple regression analysis was used to correlate the drying rate (k) with crop properties and with meteorological and mechanical treatment variables. The interaction between potential evapotranspiration (ET0) and the moisture content of grass at cutting (Mgrass appeared to be the most important variable, from the twenty-one tested, in influencing K. This variable shows that the same quantity of energy available for evaportaion acts in different ways when the water content of the crop at cutting differs. The rate of water loss is also influenced by the Mgrass itself, surgacae density of the swath, tedding and the weather conditions on the first day of drying. The value of Mgrass at cutting is greatly greatly dependent on crop maturity and ploidy. The tetraploid cultivars, with a higher inital moisture content, lost water more slowly than diploid cultivars did. Because the date of cutting cannot be delayed, owing to the decline in nutrive value, it is helpful to select for cultivars with low moisture contents at cutting, as well as applying mechanical treatment (spreading and tedding), in order to keep the wilting period as short as possible. A validated drying model can be useful for operational purposes to understand the drying process and to assess technological choices for forage drying.  相似文献   

3.

Background  

Stomata respond to vapour pressure deficit (D) – when D increases, stomata begin to close. Closure is the result of a decline in guard cell turgor, but the link between D and turgor is poorly understood. We describe a model for stomatal responses to increasing D based upon cellular water relations. The model also incorporates impacts of increasing levels of water stress upon stomatal responses to increasing D.  相似文献   

4.
Fresh ryegrass and lucerne were macerated and compressed into thin mats over a 4-week period at two yield levels. The mats were left lo dry outside during the day. and inside overnight, and compared with unconditioned crops. Under a low swath yield of 4 t DM ha−1, mats required 0·7-1·4 mm pan evaporation lo reach 70% moisture, suitable for wilted silage, compared with 1·8-3·8 mm pan evaporation for unconditioned crops. On an average non-rainy day. mats were ready to harvest as wilted silage after 2–5 h, whereas the unconditioned crop required between 6 h and 36 h of wilting. With a high swath yield of 8 t DM ha−1, mats required 1·4-3·0 mm pan evaporation to reach 70% moisture compared with 2·4-5·1 mm for unconditioned windrows. Low-yield mats reached 20% moisture, suitable for hay, in 2 d of drying, after 4·5-5·3 mm of pan evaporation. The thickness and cohesion of the mats were measured to assess their sensitivity to mechanical handling. The effect of controlled rainfall on mats was also investigated. Since mat making was most effective in low-yield crops, it could become a useful complement to low-input, extensive forage production. Mat making could eliminate most silage effluent losses; it could re introduce haymaking of ryegrass as a viable system under certain circumstances.  相似文献   

5.
Five experiments were conducted to determine the effect of pre-harvest treatment with steam or formic acid on the moisture concentration (MC) in crops of lucerne, two varieties of perennial ryegrass, tall fescue and Italian ryegrass. In each experiment, plots were treated with a mixture of hot gases and steam (S) or sprayed with an aqueous solution of formic acid (F). In the tall fescue experiment the F treatment was applied to the cut swath but in all other instances the F and S treatments were applied to the swards before cutting and the MC changes after treatment compared with those in untreated cut swaths (W 1). Twenty-four hours after initial treatment all S plots, and those F plots other than tall fescue, were cut and the subsequent water loss compared with that from (i) untreated material cut at the same time (W 2) and (ii) the W 1 plots cut the previous day. In all five experiments the change in the MC of the S plots was similar to that of the W 1 plots both before and after cutting. The reduction in the MC of the F plots before cutting was less than that of the S and W 1 plots, and in three of the five experiments water loss from cut F plots was apparently restricted in comparison with that from untreated cut material (W2). Neither desiccant treatment showed great promise as a pre-treatment to cutting for hay making although formic acid may have limited value when a crop is to be harvested directly for silage or artificial dehydration. In an appendix, the efficacy of using accumulated vapour pressure deficit as a basis for comparing the water loss from the untreated cut crops drying under different conditions is demonstrated.  相似文献   

6.
An apparatus is described which enables excised pieces of plant material lo be weighed al frequent intervals as they dry in controlled conditions of temperature, humidity and air-speed. The effect of removing the epidermis on the drying rate of red clover ( Trifolium pratense ) leaflets, leaf petioles and stems is examined. Initially this treatment caused a very large increase in the drying rate of leaflets. Although the effect declined as water content fell, leaflets from which the epidermis had been removed still dried more rapidly than the controls at a water content equivalent to 50% of the dry weight. Removing the epidermis had a greater effect on the drying rate of leaf petioles and stems at low water contents than it did on the drying rate of leaflets.
Slow drying at low water contents is a major factor responsible for the undesirably long periods for which hay may lie in the field. Slow drying occurs even though swath microclimate becomes more favourable for drying as water content falls. The results presented here suggest that treatments which reduce cuticular resistance have the potential to reduce field drying time.  相似文献   

7.
《Field Crops Research》1995,41(3):179-188
Maize and bean were grown under varying levels of nitrogen fertilizer, plant population, and irrigation at Kiboko, Kenya in the short rains 1990, 1991, 1992 and the long rains 1991. The production of dry matter was not affected significantly by any treatment, because treatments only had a small impact on the balance between evaporation and transpiration. In all seasons the greatest loss of water from the profile was through direct evaporation from the soil surface. Transpiration was always less than 25% of rainfall. The ratio of transpiration (T) to evapotranspiration (E + T) was small (0.23), but increased from 0.15 to 0.40 as rainfall increased from 158 mm in the long rains 1991 to 470 mm in the short rains 1992. Treatments had little impact on the balance between transpiration and evaporation from the soil surface. The average transpiration efficiencies for maize and bean were 89 and 29 kg shoot dry matter ha−1 mm−1, respectively. For each crop there was a 60% change in transpiration efficiency between the short and the long rain season which could be accounted for by differences in saturation vapour pressure deficit.  相似文献   

8.
An investigation has been made with the object of establishing a satisfactory drying method for use in determining the dry weight of air-dry herbage. In one experiment, drying was carried out at various temperatures over P2O5 and also at a sustained high vacuum: in a second experiment, oven drying was carried out at atmospheric pressure at various temperatures and for various periods.
Decomposition has been found to occur at comparatively low temperatures while, on the other hand, the intensity with which some of the moisture is held suggests that it may not all be removed at "safe" temperatures, even at very low vapour pressures.
The best technique that can be suggested at the present time is drying over P2O5 at 40°C. For less accurate results oven-drying at atmospheric pressure at 80°C for 16 hours is proposed.  相似文献   

9.
The rates of drying of cut perennial ryegrass (Lolium perenne L.) herbage over short periods of time were measured in four experiments in a controlled environment room. Standard weights of 33·7 g grass dry matter (DM) were placed in half the area of wire‐mesh trays (0·5 m long × 0·3 m wide × 0·07 m high with 11‐mm‐square mesh) which, so as to simulate conditions in a swath, were supported on wooden frames within dark plastic boxes 25 mm above 35‐mm‐thick wet sponges. The trays of grass in the controlled environment room were weighed hourly for 7 h, drying rate being assessed by the change in grass fresh weight. Light was supplied from 400‐W mercury vapour lamps, while an air conditioning unit within the controlled environment room allowed control of vapour pressure deficit (VPD). Only one particular VPD could be created on any one day and resource limitations restricted the study to one replicate per day. The first experiment correlated drying rates under the mercury vapour lamps with drying rates in the open air under sunshine over 3 d. This work showed that a distance of 200 mm between the tray and lamps equated to 1081 W m–2, 400 mm to 432 W m–2 and 600 mm to 281 W m–2. Experiment 2, conducted with previously frozen grass, was a 4 × 4 factorial design with light intensity and VPD as factors. The third experiment (Experiment 3) compared the drying rate of freshly cut grass with grass that had previously been frozen in a 2 × 2 × 2 factorial design with the two grasses, two light intensities and two wind speeds as factors. The final experiment (Experiment 4) was a 3 × 2 × 2 factorial design with light intensity, VPD and wind speed as factors. A wind of approximately 3 m s–1 was simulated using a 22‐mm, 30 W fan set in a fixed position 600 mm from each tray plus grass. Fresh grass was cut each morning of the experiment. There were six replicates of each treatment. The effect of the three radiation intensities on grass DM concentration in Experiment 2 was highly significant (P < 0·001). VPD had less effect (P < 0·05). Results from Experiment 3 showed that previously frozen material dried much more rapidly than fresh grass and as a result would not simulate actual grass drying in the field. Consequently in Experiment 2 fresh grass was used as opposed to previously frozen material. In Experiment 4, light intensity had the greatest influence on grass drying followed by VPD and wind speed. However, the influence of wind speed was variable. A wind speed of ≈3 m s–1 increased the rate of water loss from grass with a low initial DM concentration (<160 g kg–1) receiving low levels of solar radiation (281 W m–2), while at higher initial DM concentrations (>210 g kg–1) and higher solar radiation levels (432 W m–2) the effect of wind was to slow grass drying. The results from Experiments 2 and 4 also indicated that high levels of either wind (3 m s–1) or VPD (>6 mbars), when associated with low levels of solar radiation, resulted in large increases in grass DM concentration. However, these extreme weather conditions are unlikely to occur in practice.  相似文献   

10.
This study presents a theoretical and experimental investigation of the process of drying of fabrics on a continuously moving flat plate. A mathematical model is developed for heat and mass transfer analysis of fabric in the impingement dryers. For simplicity, it is assumed that during the drying period of the fabric has porous media and on the drying surface the vapour pressure of the evaporating liquid remains at a quasi-saturated value corresponding to the temperature of the liquid. Using the model, the calculated transient fabric temperatures in the impingement dryers agree well with the experimental results.  相似文献   

11.
This experiment was done on the three potato cultivars [Agria (susceptible), Satina (semi-tolerant) and Ceaser (tolerant to water deficit)] and three irrigation treatments (after 30 mm evaporation from basin class A, after 60 mm evaporation + spraying by Potassium Humate, and after 60 mm evaporation from basin class A) for two locations in 2007. Experimental design was Split Plot with three replications. Potassium Humate spraying (250 mL ha(-1)) were done in three stages of emergence, before tuberization and during tuberization period. Combined analysis of variance showed that there were significant differences between locations, cultivars, irrigation treatments and location x cultivars interaction as effect on tuber yield. Comparison of means for irrigation treatments showed that spraying by Potassium Humate in stress condition induced increasing of tuber yield. Spraying by Potassium Humate in water deficit condition increased tuber yield up to 11.01 ton ha(-1). Ceaser had the highest tuber yield. It had higher tolerance to water deficit as well. Ceaser had a high potential in control and severe stress. Decrease in yield of Ceaser after 60 mm evaporation + spraying by Potassium Humate and after 60 mm evaporation from basin class A, relative to control (after 30 mm evaporation from basin class A) was 1.03 and 13.08 ton ha(-1) but for Satina was 7.83 and 16.61 ton ha(-1), respectively. Satina had the lowest Environmental Variance, Environmental Variance Coefficient, Finlay and Wilkinson's and Eberhart and Russell's model and was the most stable cultivar. Lin and Binns parameter showed that Ceaser and Satina were the most stable cultivars. Results of GMP, STI and MSTI were very considerable and Ceaser and Satina had a high yield in water stress and control conditions.  相似文献   

12.
The effects of seven agricultural adjuvants and two polymeric drift retardants on the distribution of spray were compared with water applied through a multiple nozzle boom. Similarly, the effects on droplet spectra from a single XR80004VS nozzle operating at 276 kPa (40 p.s.i.) were compared. Except for two adjuvants, swath pattern relative to water was significantly altered. With one exception, droplet spectra parameters relative to water were shifted to both smaller and larger frequency distributions. The polymers, whether sprayed alone or in mixture, had the greatest effect on swath pattern. The polymers sprayed alone had the greatest effect on droplet spectra, but the mixtures gave a more variable response. Swath patterns and droplet spectra derived using water are not, therefore, representative when spraying pesticides with adjuvants. Dynamic surface tension (DST) and viscosity at high shear rates were measured for all spray solutions. Analysis to determine the feasibility of predicting quality of swath pattern and various spray spectra parameters (e.g. VMD, NMD) showed that the interaction between the two physicochemical parameters and the results of atomization are complex. DST and viscosity were poor predictors when applied to the mixtures of polymers and conventional adjuvants tested.  相似文献   

13.
Summary Leaf stomatal resistance varies considerably in response to changes in environmental conditions. Understanding cultivar differences in the response of stomata to these conditions is important for effectively simulating water-use and growth. In this study the stomatal resistance of three field grown potato (Solanum tuberosum L.) cultivars Atlantic. Monona and Norchip was observed in response to photosynthetic photon flux density, leaf to air vapour pressure difference and root zone available soil water. Substantial variation in stomatal resistance was accounted for by functions of the environmental variables for both Monona and Norchip. The explained variation for Atlantic was considerably less. Light saturation occurred near 500 μmol m−2 s−1. Increasing stomatal resistance above 1000 μmol m−2s−1 was also observed but is likely an artifact of stomatal closure on days in which mid-day leaf water potentials dropped below critical levels. Although the leaf presumably insufficient to obtain substantial effects. The soil water status was partially linked to the average 1000 h to 1500 h stomatal resistance on clear, sunny days. Significant differences were observed among the cultivars in the response of stomata to changes in the available soil water.  相似文献   

14.
Weight losses of potatoes during storage were closely related to the product of average water vapor pressure deficit of the air between the tubers and the duration of storage in weeks. Shortly after harvest, the water loss per cm2 skin area per hour per mm Hg VPD was five to seven times as high as later in the storage period. Temperature, through its influence on respiration did not appreciably affect weight loss, but had in several cases a clear effect on specific gravity. In those cases the relations between specific gravity and either weight loss or the product of storage duration and VPD were close only if the influence of storage temperature was eliminated.  相似文献   

15.
Appropriate benchmarking is essential for evaluating the efficiency with which crops use water and for identifying constraints, other than water, to crop yield. No benchmark exists for sunflower. Boundary and simulation analyses were used to quantify the water productivity of sunflower crops grown in the Western Pampas (semiarid central Argentina). The approach involved the use of a large database (n = 169) collected in farmers’ fields over a period of 4 years, and the application of a crop simulation model in combination with actual weather and soil data. Using field data, an upper bound of 8 kg grain ha−1 mm−1 for water productivity, with an apparent seasonal soil evaporation of 75 mm, was defined. Seasonal water supply exceeded maximum expected seasonal crop requirements (ca. 630 mm) for many crops, and a majority of crops with <630 mm of available water during the season had water productivities considerably lower than the upper bound. The field data-based upper bound was indistinguishable from that obtained using yields for a set of 47 simulations using observed initial values for soil water and nitrogen profiles. Simulation confirmed the main features of the boundary-analysis applied to field data, and many simulated crops had yields that fell below the boundary function, even when simulated yield was plotted against simulated seasonal evapotranspiration or transpiration. Long-term (33-year) simulation analyses for two sites showed that most sunflower crops in the area are subjected to episodes of transient and unavoidable water stress after floral initiation. High levels of available soil water at sowing moderate, but in most years do not eliminate, these exposures to water stress. Yield gaps with respect to the boundary function were associated with deficient or excessive rainfall during grain filling, and other, non-water related, factors such as inadequate crop nutrition, biotic stresses, low photothermal quotients during the interval close to anthesis, and lodging. A grain yield/seasonal evapotranspiration plot for a large (n = 154) data set from experiments conducted by others in five separate environments suggests that the boundary function found for the Western Pampas is broadly applicable. Sunflower water productivity, corrected for oil-synthesis costs and seasonal vapour pressure deficit differences, approximates that of winter cereals grown in Mediterranean environments.  相似文献   

16.
Potato (Solanum tuberosum L.) is particularly sensitive to soil water potential below ?50 to ?60 J kg?1 during tuber development. Soil water must also be carefully monitored to irrigate efficiently and to minimize nitrate leaching associated with over-irrigation. Water distribution in and below potato hills during and following sprinkler irrigation was monitored using granular matrix sensors (Watermark Model 200, Irrometer Co., Riverside, CA) placed in 0.10 m × 0.15 m cross-sectional grids down to 0.6-m depth below the soil surface. Each grid consisted of 26 sensors. Sensor electrical resistance had been calibrated to soil water potential. During one test, soil water potential was intentionally lowered to levels drier than ideal for potato to emphasize soil wetting and drying patterns. Over the 26 locations in the grids, the soil water potential averaged ?33 J kg?1 over a six week period, with sprinkler irrigations evenly rewetting the upper 0.2 m of the hill. On average, the driest locations were the top of the hill, directly under the hill, and below the furrow with wheel track compaction. Ideal sensor locations for monitoring soil water status and scheduling irrigations are offset 0.15 m from the center of the hill and 0.1 to 0.2 m deep. Sensors installed in silt loam soil responded within four hours to wetting and within 12 hours to drying, the shortest increments of time measured.  相似文献   

17.
通过对云南橡胶园植胶土壤和橡胶树叶片微量元素含量进行测定和分析，初步拟出云南橡胶树叶片微量元素养分含量的适宜范围，其中铜12．00～13．50mg／kg，锌30．00～40．00mg／kg，铁110．00～170．00mg／kg，锰350．00～600．00mg／kg，硼18．00～35.00mg／kg和钼0．05～0．20mg／kg；同时根据云南胶因微量元素营养水平，建议对不同土壤类型的胶园开展施用钼肥和硼肥的试验研究。  相似文献   

18.
A large-scale sealed system for freeze-drying herbage is described. It utilizes the principle of sorption drying and is dependent upon the vapour pressure differential (VPD) between the herbage and the silica gel drying agent. Ice sublimes to vapour from the sample in a system operating at approximately – 10°C and the vapour is adsorbed by silica gel in an air stream recycled by a blower; equal masses (up to 50 kg each) of wet herbage and silica gel are used. The system is simple to construct and is relatively inexpensive.
Approximately eight days drying time are needed to reduce moisture content from 90 to 10%. Twenty-four different species or cultivars of both temperate and tropical grasses and legumes sampled at several stages of maturity have been dried in the system. When snap-frozen herbage is freeze-dried by this process the physical and chemical changes that otherwise occur when herbage is harvested and prepared for evaluation can be reduced and sufficient material can be obtained to permit animal feeding studies as well as chemical analyses.  相似文献   

19.
Inflorescence-bearing tillers of Italian ryegrass (Lolium multiflorum cv. RvP) were dried in controlled temperature, relative humidity and air speed conditions chosen to be within the range likely to occur in a hay swath drying in the field. After drying for increasing intervals the tillers were separated into inflorescence, exposed flowering stem, leaf-laminae, leaf-sheath and flowering stem enclosed by leaf-sheath and the drying rates of these components in addition to that of whole tillers were measured. There were large differences in drying rate between components, but the differences were similar over the range of drying conditions employed. The drying rate of the inflorescence as well as that of stem enclosed by leaf-sheath was found to be very low and that of leaf-laminae and leaf-sheath very high.  相似文献   

20.
In order to estimate soil evaporation from saline soil in arid area, a maximum surface temperature (MST) model was applied to Hetao Irrigation District (HID). The model was developed based on energy balance and sinusoidal function of surface soil temperature. Evaporation and surface temperature of drying soil columns and surface temperature of natural field were observed in each 1-h interval in daytime (from September 10 to 19, 2010) in a saline land in HID. The results indicated that the estimated evaporation shows a similar trend and in good agreement with the observed values. To quantitatively evaluate the performance of the model, some statistic parameters were calculated as well. These statistics could also indicate that the observed values perform similar trend to the estimated values. It is concluded that the MST model could be applied to estimate soil evaporation from saline land. The proposed method is hopeful to estimate soil evaporation over large scale area using only surface temperature available from the satellite image while assigning an effective exchange coefficient (c h ).  相似文献   

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