Growth of lucerne (Medicago sativa,L.) in response to frequency of irrigation and gypsum application on a heavy clay soil

Summary Effects of weekly (W) and fortnightly (F) irrigation schedules on established stands of lucerne (Medicago sativa L.) grown on gypsum treated (G) and untreated (C) heavy clay soil were investigated. Two irrigations were applied under the fortnightly regime and four under the weekly schedule during a single cutting cycle. Growth and light interception were measured during both the vegetative and mature phases of growth.Leaf expansion, light interception and dry matter production were greater under treatments W _G and W _C, with yield increasing from 3.4 t ha^–1 under the fortnightly schedule to 5.0 t ha-1 with weekly irrigation. Gypsum treatment was effective under the more frequent irrigation schedule. Specific leaf area and the proportion of stem were both increased by treatments W _G and W _C. The responses to irrigation were therefore characteristic of those elicited by a more favourable plant moisture status. Growth was analysed in terms of light interception, the efficiency of utilisation of intercepted light, the proportion of the daily dry matter gain retained by the leaves and leaf expansion. The analysis demonstrated that impaired leaf expansion contributed to a decline of approximately 15% in yield, and that impaired efficiencies of utilisation of intercepted light contributed to losses of approximately 30% under the less frequent irrigation schedule.A comparison of growth rates and efficiencies of energy conversion with published data showed that satisfactory rates of growth and levels of productivity were achieved on the heavy soils of the local region using gypsum treatment and the more frequent irrigation schedule.     

Isohydrodynamic behavior in deficit-irrigated Cabernet Sauvignon and Malbec and its relationship between yield and berry composition

Cabernet Sauvignon and Malbec grapevines were irrigated at 70 or 23 % of estimated crop evapotranspiration throughout berry development over four growing seasons. Stomatal behavior was characterized by relating predawn leaf water potential and mid-morning stomatal conductance to mid-morning leaf water potential. Seasonal average weekly midday leaf water potential was lower in Cabernet Sauvignon than Malbec despite similar irrigation amounts. Both cultivars exhibited anisohydric behavior with midday leaf water potential decreasing linearly with declining predawn leaf water potential (r ² = 0.51) and stomatal conductance (r ² = 0.42). However, both cultivars utilized hydrodynamic mechanisms to maintain a soil-to-leaf water potential gradient of ?0.62 (±0.03) MPa under standard irrigation and ?0.75 (±0.04) MPa under reduced irrigation. Berry fresh weight and titratable acidity decreased, and the concentration of total anthocyanins increased in both cultivars in response to decreases in midday leaf water potential. The slope of regression equations for seasonal mean midday leaf water potential was used to estimate cultivar-specific levels of water stress associated with changes in berry weight and berry composition at fruit maturity.     

Salinity and drought

Summary Water deficit (water stress — WS) and excess salt (salt stress — SS) evoke similar plant responses, yet clear differences have been observed. The effect of the two forms of stress applied consecutively to cotton (Gossypium hirsutum) and pepper (Capsicum annuum) was studied in a growth chamber (29/20°C day/night temperature, 50% RH, 12-h photoperiod) in 2.5-liter containers packed with a silt loam soil.Leaf water potential () under increasing WS [soil water potential decrease from –0.16 to –1.10 MPa] of transpiring cotton and pepper plants declined to lower levels than under equivalent SS. The decline of leaf solute potential ₀ on the other hand, was less under WS than under SS, resulting in reduced turgor potential ( _p ), in contrast with turgor maintenance under SS. Predawn turgor potential of WS plants was maintained at all levels of soil water potential. Transpiration, CO₂ assimilation and light period leaf extension rate were higher under low soil water potential produced by salinity than an equivalent value produced by water deficit.The more severe effect of WS was attributed to incomplete osmotic adjustment — the reduction in solute potential did not keep pace with the reduction in leaf water potential, and to increased root interface resistance in the dry soil.The leaf sap of cotton under WS had a higher proportion of sugars (65%) than electrolytes, compared to SS. When WS was converted to SS and plant solute potential decreased, electrolytes were taken up at the expense of a reduction in the sugar concentration. Water stress and salt stress may have an additive effect in depressing growth. But at equivalent levels, the relative magnitude of the effect of low soil matric potential (WS) on plant growth was twice as great as that of low soil solute potential (SS).     

Effects of stage of growth,irrigation frequency and gypsum treatment on CO2 exchange of lucerne (Medicago sativa L.) grown on a heavy clay soil

Summary Effects of weekly (W) and fortnightly (F) irrigation schedules on CO₂ assimilation by lucerne grown on untreated (C) and gypsum-ameliorated (G) heavy clay soil were investigated. Leaf area limited rates of assimilation during the initial stages of regrowth, but rates of up to 9 g CO₂ m^–2 h^–1 were measured once full ground cover was achieved after approximately two weeks. High rates were maintained until the fifth week of regrowth (one week after full flower), after which there was a marked decline.During the fourth week of regrowth, afternoon rates of canopy photosynthesis under less frequent irrigation were less than those measured at similar irradiance during the morning. This was evidenced as hysteresis in the light response curves and was apparent in all treatment during the final stages of the experiment.For the first five weeks of regrowth, daytime integrals of photosynthesis were directly related to the amount of light intercepted by the crops. The mean efficiency of utilisation of light in CO₂ assimilation was 6.2 g CO₂ MJ^–1 in all treatments apart from that on untreated soil under the fortnightly irrigation regime (treatment F_C). Its mean efficiency was 5.1 g CO₂ MJ^–1. The amounts of CO₂ assimilated exceeded the growth and respiratory requirements of the above-ground components of the crops, and it was estimated that 25% and 40% of the assimilated carbon was partitioned to and retained in the roots and crowns of the weekly and fortnightly irrigated crops, respectively.Results are appraised in terms of the response of lucerne to moisture deficits. Implications for above-ground dry matter production are also discussed.     

Relationship between root uptake-weighted mean soil water salinity and total leaf water potentials of alfalfa

Summary Alfalfa was grown in five laboratory soil columns and irrigated at a fixed average amount per day. One column received tapwater at 6-day intervals; the others saline water (h _o=–12 m) at intervals of 4, 6, 8, and 12 days. The alfalfa was harvested at 24-day intervals. The resulting widely varying distributions of soil water content, pressure potential and osmotic potential were measured in detail. From these data variously weighted mean soil water potentials were calculated and correlated with measured total leaf water potentials. This indicated that in the moist, saline soil columns the alfalfa plants tended to maximize the root uptake-weighted mean total soil water potential and, since the pressure potentials were generally high compared with the osmotic potentials, also the uptake-weighted mean osmotic soil water potential (minimize the uptake-weighted mean salinity). For the drier nonsaline soil column the leaf water potentials were much lower than expected from the soil water retention function. This was attributed to dominant resistance for water flow through the soil and across the soil-root interface.     

Osmotic adjustment of sugar beets in response to soil salinity and its influence on stomatal conductance,growth and yield

Sugar beets were grown in tanks filled with loam and clay, and were irrigated with waters of three different levels of salinity. Osmotic adjustment was determined by analyzing the pressure-volume curves at three growth stages. Sugar beets showed osmotic adjustment in two ways: with their phenological development and towards salinity. Owing to the latter adjustment sugar beets are able to maintain the turgor potential at the same value for lower values of the leaf water potential, to maintain stomatal conductance and photosynthesis and finally their production under severe water stress.Salinity affected the pre-dawn leaf water potential, stomatal conductance and evapotranspiration on both soils, but leaf area and yield only on loam.Soil texture affected stomatal conductance, evapotranspiration, leaf area and yield. As the latter was about 35% lower on clay, whereas the evapotranspiration decreased 10 to 15%, the water use efficiency was about 25% lower on clay compared with loam.     

Influence of water stress on kiwifruit growth

Summary An irrigation experiment was conducted on young kiwifruit vines over two seasons to examine effects of water stress on fruit development. Vines were grown outdoors in a sandy, rooting medium enclosed within a polythene-lined trench with removable surface covers to enable strict control of the water supply. Measurements of fruit growth, leaf water potential, and stomatal conductance were made throughout the season in conjunction with periods of water stress imposed at different times, and for varying durations. Fruit development was very responsive to water stress with mean fruit size per vine at harvest varying from 60 to 130 cm³ as a result of various stress treatments. Fruit expansion ceased when predawn leaf water potentials fell below –0.1 MPa. Upon rewatering, leaf turgor was regained within 24 h even after severe, prolonged stress. Any turgor loss associated with fruit softening was quickly made up, and thereafter fruit growth continued at the same rate concurrently exhibited on continuously well-watered vines. Suggesting that stomatal conductance did not follow the rapid recovery of leaf water potentials and fruit expansion may be more closely linked to water supply than to the concurrent rate of photosynthesis. Despite the large range in mean fruit size, the shape of the fruit size distribution at harvest was not affected by water stress and it is concluded that harvest yields can be adequately modelled by assuming a normal distribution with a fixed standard deviation.     

Yield and vegetative growth as related to plant water potential of cotton irrigated with a moving sprinkler system at different frequencies and wetting depths

Summary Seed-cotton yield, yield components and vegetative growth were determined under different irrigation frequencies and wetting depths with a self-propelled moving-irrigation-system (MSIS) in 1986 and 1987. Irrigation timing was determined in both years by pre-irrigation, mid-day plant water potential (_w). The amount of water to be applied was determined by measuring the soil moisture deficit. In 1987, the effect of a change from one irrigation frequency and wetting depth to another at mid-flowering was also examined. Linear responses of relative seed-cotton yield to the amount of evapotranspiration (ET) were found for both years with similar slopes but different intercepts. Significant positive regressions were obtained between pre-irrigation plant _w and relative seed-cotton yield, and vegetative growth during the linear growth stage. Seed-cotton yield was affected by both wetting depth and pre-irrigation plant _w. The deeper the irrigation the higher was the seed-cotton yield for each pre-irrigation plant _w. Irrigation frequencies which maintained plant _w above -1.5 MPa during vegetative growth, flowering and boll-filling resulted in maximum production. The boll filling stage appeared to be a very sensitive one, as boll weight was found to be the main yield component responding to irrigation treatments. At a wetting depth of 120 cm, higher seed-cotton yields were obtained than at a more shallow wetting. Different irrigation managements resulted in different turgor potentials (_t) mainly during mid-day. Both leaf water vapour conductance and net assimilation rate were sensitive to leaf _w.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagon, Israel, No. 2903-E, 1990 series. Research was supported by the U.S.-Israel Binational Agric. Res. and Develop. Fund.     

Influence of irrigation on leaf water relations and dry matter production in coconut palms

Summary The effect of different frequencies of irrigation on the leaf water relations and dry matter production of the West Coast Tall coconut palms (Cocos nucifera L.) was studied during two growing seasons. Irrigation was applied in amounts of 60 mm at a ratio of irrigation water to cumulative pan evaporation (I/E) of 1.0, 0.75, 0.50 and 0.0. Measurements were made of stomatal resistance, leaf water potential and epicuticular wax content, and vegetative and reproductive dry matter production. Irrigation treatments resulted in a four-to five-fold increase in the soil water deficit at I/E ratios of 0.5 and 0.0 as compared to 1.0. Coconut palms experienced severe moisture stress at an irrigation level of 0.50, resulting in a greater stomatal resistance (111%) and epicuticular wax content (32%) and reduced transpiration rate (10%), leaf water potential (68%), and reproductive dry matter production (22%), compared with well watered palms. Based on the relationship between the soil water deficit and the stomatal resistance, the critical soil water deficit for irrigation scheduling was deduced to be 110 mm. However vegetative dry matter production was reduced at much lower soil water deficits than this value.     

Response of tomatoes,a crop of indeterminate growth,to soil salinity

Tomatoes were grown in tanks filled with loam and clay, and were irrigated with waters of three different levels of salinity. Osmotic adjustment was determined by analysing the pressure–volume curves at four growth stages. Owing to the osmotic adjustment, tomatoes are able to maintain the turgor potential and the stomatal conductance at the same value for the lower values of the leaf-water potential. Salinity affected the pre-dawn leaf-water potential, stomatal conductance, evapotranspiration, leaf area and fruit yield on both soils. Soil texture only affected the fruit yield. The evapotranspiration showed a moderate decrease, owing to the small decrease in leaf area and the effect of osmotic adjustment on the stomatal conductance, whereas the fruit yield decreased strongly. The tomato plant apparently favours under saline conditions, the growth of foliage at the expense of fruit formation.     

Irrigation with brackish water under desert conditions II. Physiological and yield response of maize (Zea mays) to continuous irrigation with brackish water and to alternating brackish-fresh-brackish water irrigation

The physiological behavior and yield response of maize under irrigation with saline water was studied in the laboratory and in the field. In the laboratory, the germination rate decreased only when the electrical conductivity (EC) of the substrate solution was above 17 dS/m. The osmotic potential of germinating maize seedlings decreased in proportion to the decrease in osmotic potential of the substrate.In the field, two maize cultivars (a field maize and a sweet maize) were irrigated alternately with saline (11 days from sowing), fresh (21 days from emergence), and saline (from day 33 to harvest) water and compared with maize irrigated with saline water continuously throughout the season. Four levels of irrigation water salinity were used (EC_i = 1.2, 4.5, 7.0 and 10.5 dS/m).In the field no osmotic adjustment by the leaf sheaths of plants in response to salinity was observed. The osmotic potential of corn leaf sheaths (π) decreased with ontogeny in all treatments. The midday leaf water potential (ψ_L) in maize irrigated with 10.5 dS/m water was 0.75 MPa lower than in plants irrigated with 1.2 dS/m water.In the continuous treatment grain yield was reduced significantly with each increase in salt concentration, and the relationship between relative yield (y) and EC_i could be expressed as y = 100?8.7 (EC_i-0.84). With alternating irrigation and 7.0 dS/m treatment the grain yield was the same as in the low EC treatment (6.98 kg/m²).     

Simulation of possible adaptive mechanisms in crops subjected to water stress

Summary The dynamics of stress development in crops involves a decrease in turgor potential of leaves which causes decreases in leaf expansion, photosynthesis, and transpiration. A study was conducted to evaluate the effectiveness of three possible adaptive mechanisms in maintaining turgor potential and growth. These mechanisms — osmotic adjustment, increased root growth, and increased stomatal resistance at full turgor — were examined by a simulation experiment using a dynamic model of the soil-crop-atmospheric system. Osmotic adjustment was found to be ineffective in maintaining turgor for crops grown in a sandy soil because of the rapid development of stress. When a ten-day drying cycle was simulated for a clay soil, cumulative transpiration, photosynthesis and growth were increased by osmotic adjustment, indicating an improved ability of the crop to maintain turgor under the simulated conditions for the clay soil. increased stomatal resistance was ineffective for the simulated conditions because of a concomitant decrease in photosynthetic rate. Increased soil volume occupied by roots was found to be the most effective adaptive mechanism for maintaining turgor, transpiration, photosynthesis and growth of crops in both soil types.Contribution from Department of Agricultural Engineering, Institute of Food and Agricultural Sciences, University of Florida. Supported in part by Grant No. FL-AGO-1911 Cooperative Research, United States Department of Agriculture. Florida Agricultural Experiment Station Journal No. 2657     

Online-monitoring of tree water stress in a hedgerow olive orchard using the leaf patch clamp pressure probe

The need for sophisticated irrigation strategies in fruit tree orchards has led to an increasing interest in reliable and robust sensor technology that allows automatic and continuous recording of the water stress of trees under field conditions. In this work we have evaluated the potential of the leaf patch clamp pressure (LPCP) probe for monitoring water stress in a 4-year-old ‘Arbequina’ hedgerow olive orchard with 1667 trees ha⁻¹. The leaf patch output pressure (P_p) measured by the LPCP probe is inversely correlated with the leaf turgor pressure (>50 kPa). Measurements of P_p were made over the entire irrigation season of 2010 (April to November) on control trees, irrigated up to 100% of the crop water needs (ET_c), and on trees under two regulated deficit irrigation (RDI) strategies. The 60RDI trees received 59.2% of ET_c and the 30RDI trees received 29.4% of ET_c. In the case of the RDI trees the irrigation amounts were particularly low during July and August, when the trees are less sensitive to water stress. At severe water stress levels (values of stem water potential dropped below ca. −1.70 MPa; turgor pressure < 50 kPa) half-inversed or completely inversed diurnal P_p curves were observed. Reason for these phenomena is the accumulation of air in the leaves. These phenomena were reversible. Normal diurnal P_p profiles were recorded within a few days after rewatering, the number depending on the level of water stress previously reached. This indicates re-establishment of turgescence of the leaf cells. Crucial information about severe water stress was derived from the inversed diurnal P_p curves. In addition P_p values measured on representative trees of all treatments were compared with balancing pressure (P_b) values recorded with a pressure chamber on leaves taken from the same trees or neighbored trees exposed to the same irrigation strategies. Concomitant diurnal P_b measurements were performed in June and September, i.e. before and after the period of great water stress subjected to RDI trees. Results showed close relationships between P_p and P_b, suggesting that the pressure chamber measures relative turgor pressure changes as the LPCP probe. Therefore the probe seems to be an advantageous alternative to the pressure chamber for monitoring tree water status in hedgerow olive tree orchards.     

The influence of soil water potential on the flowering pattern,pod set and yield of snap beans (Phaseolus vulgaris L.)

Summary The effect of the soil water potential on pod yield of snap beans grown with a series of irrigation frequencies was studied over two seasons. The treatments were to furrow-irrigate either weekly or fortnightly during the preflowering period, and each treatment then received weekly or fortnightly irrigations to harvest. These treatments were compared with trickle irrigation applied daily in the first season and every second day in the second season. The irrigation frequencies during the pre-flowering period did not influence the pod yield. However, in the second season plants given the trickle irrigation treatment produced more early flowers and set pods earlier than those in the other treatments. Consequently the pods were harvested three days earlier from plants on this treatment.Pod yield was determined by the irrigation treatments applied after flowering. The highest yield was similar in each season (16.7 t ha^–1) and was produced under trickle irrigation. Fortnightly irrigations during the pod-fill phase reduced yield by 56% in the first season and 41% in the second season when compared with trickle irrigation. The pod yield was reduced by 0.5 t ha^–1 each day the soil water potential at 30 cm depth was less than –50 kPa. This relationship accounted for about 77% of the variation in pod yield.     

Sap flow in the stem of water stressed soybean and maize plants

Summary Water stress was imposed upon soybean [Glyxine max (L.) Merr. cv. Williams] and maize [Zea mays (L.) cv. Pioneer 3377] plants grown under controlled-environment conditions during a growing period of several irrigation cycles. Transpiration rates of individual plants were measured with a calibrated heat-pulse method and correlated to the rate of water loss obtained from successive weighings of the pots containing irrigated or water-stressed plants. Transpiration rate was reduced in the stressed plants of both species, but the reduction was not linear with decreasing soil matric potential. Transpiration rates declined rapidly at high soil matric potential, and dropped more slowly as the soil dried. Although measured transpiration rate declined by nearly 30% following a reduction of soil matric potential to -0.1 MPa, differences in leaf water potential and CO₂ assimilation rate were small and less than the sensitivity of the measurement techniques used. Total system resistance to water flow increased as the soil dried.     

Yield and water use efficiency of cauliflower under varying irrigation frequencies and water application methods in Lower Gangetic Plain of India

A field study (1999-2000 to 2001-2002) was carried out to optimize the irrigation frequency and suitable water application methods for cauliflower with a view to increase curd yield (CY) and water use efficiency (WUE). Check Basin (CB), Each Furrow (EF) and Alternate Furrow (AF) methods were tested with three irrigation frequencies depending on the attainment of soil matric potential (Ψ_m) value at 0.2 m depth as: −0.03 MPa (F₁), −0.05 MPa (F₂) and −0.07 MPa (F₃). Maximum CY was recorded under F₁ and decreased by 10.4 and 31.4%, respectively under F₂ and F₃ frequencies. In contrast, WUE decreased by 9.3% from F₃ to F₁. Highest CY and WUE obtained under CB followed by EF and AF methods. Furrow application methods saved 12-24% irrigation water over CB method. Maximum soil water stress coefficient (K_s) recorded at curd development stage in comparison to other stages. Both seasonal evapotranspiration (ET_a) and yield-moisture stress index (Kys) recorded positive linear relationships with CY. Present study shows a crop response factor of 0.822 for cauliflower. In this region, cauliflower should be irrigated with check basin method at an interval of 8-10 days.     

Plant response to the soil water reserve: Consequences of the root system environment

Summary The ability of water balance models based on the concept of Transpirable Soil Water to predict the occurrence of water stress and the need for irrigation was tested for several environmental conditions of the root system, to determine in which conditions errors are likely to be appreciable. The response of evapotranspiration, stomatal conductance and leaf water potential to soil water reserve was studied under three conditions: (i) in pots with maize plants, (ii) in the field with deep soil and the root system placed in favourable conditions, with wheat during a dry year and with maize during four years with contrasting climate, (iii) in the field, with soil compaction which disturbed the maize root system, decreasing its efficiency for water uptake, during four year. (i) In the pot experiment, where the volume of the Transpirable Soil Water (TSW) is well defined, the responses followed the hypothesis of water balance models. (ii) The soil depletion was higher than the calculated TSW during two dry years in the field, because of an appreciable contribution of the non-rooted soil layers to the water balance. As a consequence, evapotranspiration, stomatal conductance and predawn water potential did not decrease over the whole range of soil water reserve. Grain yield was no lower in those years than in the wet years, in spite of the fact that the soil water reserve was depleted. Thus, a water balance based on the TSW would have underestimated in these conditions the ability of plants to withdraw soil water, overestimating the necessity of irrigation. Predawn water potential gave, on the contrary, indications consistent with the responses of the stomatal conductance and the net CO₂ assimilation. (iii) The water uptake by plants would have been overestimated in the case of compacted soil. Stomatal conductance was low even for high levels of the soil water reserve, except if the densely rooted top 0.1 m layer of soil was rewatered by irrigation. Water stress could not have been diagnosed in this case from indications of soil water potential or of pre-dawn water potential. These data confirm that some knowledge of the environmental conditions of the root system is necessary to determine if errors made using water balance models are likely to be appreciable, and to know if they lead to an underestimation or overestimation of the risk of water stress.     

Effects of irrigation regimes on the yield and water use of strawberry

Summary Strawberry plants (Fragaria x annanasa D. cv Chandler) were grown in field plots and in drainage lysimeters under controlled soil moisture regimes. Four irrigation treatments were established by watering the plants when soil water potential reached -0.01, -0.03,-0.05 and -0.07 MPa. The maximum yield was attained at -0.01 MPa soil water potential. Differences in yield were caused by both changes in the number of fruits per plant and in the fresh weight per fruit. Yield reductions were associated with reductions in total assimilation rate resulting from the decreased assimilatory surface area in plants irrigated at lower soil water potentials. The crop water production function calculated on a fruit fresh weight basis resulted in a yield response factor (K _y) of 1.01.     

Leaf permeability as an index of water relations,CO2 uptake and yield of irrigated wheat

Summary An irrigation experiment was conducted on wheat in the northern Negev, Israel. The growing season rainfall was 198 mm; six irrigation treatments, ranging from 0 to 320 mm were applied at different stages of growth. The grain yields ranged from 1.20 to 5.84 t/ha. Stomatal aperture was evaluated by leaf permeability, as measured with a fast-reading viscous flow porometer. Other indices of soil-plant water status measured were: soil moisture with a neutron probe; leaf water potential with a pressure chamber; CO₂ uptake with a ¹⁴CO₂-pulse apparatus; and leaf water saturation deficit.For the penultimate and flag leaves, midday leaf permeability was highly correlated with the soil moisture in the upper 60-cm layer. CO₂-uptake, however, remained constantly high (ca. 0.8 mg m^–2s^–1 = 29 mg dm^–2h^–1) throughout a wide range of leaf permeability, from 10 down to 2 porometer units (p. u.); below this value, it decreased linearly with leaf permeability. Therefore, the value of 2 p. u. was tentatively regarded as a critical value for judging the critical values of the other indices studied; these were estimated to be: leaf water potential, –1.57 MPa = –15.7 bars; leaf saturation deficit, 18,8% and soilmoisture, 12.6% representing a 83% depletion of the available moisture in the Gilat soil. The grain yield was highly negatively correlated with the duration of period when the soil moisture was below these critical values. The use of the porometer method for evaluating water stress is discussed.     

Influence of irrigation rate on the rehydration of olive tree plantlets

The scarcity of water for use in agriculture - a consequence of its use in other areas - has made deficit irrigation common on irrigated farmland. Regulated deficit irrigation involves scheduling periodic cycles of water stress over the growing season that result in no (or only a very slight) reduction in yield. The complete recovery of plant water status is, however, necessary if losses are to be minimised. In this work, cv. Picual olive plants, grown in pots in Ciudad Real (Spain), were withheld irrigation for 26 days, and then subjected to one of three different irrigation rates during the recovery period. Two treatments were designed to provide rapid recovery but had different soil moisture targets: T1 involved irrigation to field capacity, and T2 replaced half of the water consumed during the drought period. The third treatment, T3, allowed rehydration to field capacity but at a lower irrigation rate than in either T1 or T2; the pots only reached this soil moisture level after 2 weeks. Compared to a fully irrigated control, the delay in recovery between leaf conductance and mid-day stem water potential was shorter in T1 and T2 (just 1 day) than in T3 (11 days). The T2 plants showed a trend towards lower stem water potentials compared to the controls, while the T3 plants showed a trend towards lower leaf conductance. In all treatments the recovery of water potential was very fast—less than 5 days. The differences in the recovery of leaf conductance and mid-day stem water potential are probably related to root flow. Varying irrigation rates could provide a new means of controlling - and even reducing - the intensity and length of water stress during the recovery period. Measuring the water potential alone during this period may not provide an accurate picture of plant water relations.