Full Irrigation Plants Research Articles

Measurement and modelling of ABA signalling in potato ( Solanum tuberosum L.) during partial root-zone drying

The objective of this study was to develop a simple mechanistic model to predict the magnitude of ABA signalling ([X-ABA]) of potatoes ( Solanum tuberosum L.) exposed to partial root-zone drying (PRD). Potatoes were grown in pots in a glasshouse with the roots split equally between two soil columns. At tuber initiation stage, plants were subjected to three irrigation treatments: (1) both soil columns were fully irrigated (FI) daily to a volumetric soil water content ( θ) of 18.0%; (2) PRD, in which one soil column was irrigated daily to 18.0% while the other was allowed to dry, and the irrigation was shifted between columns when the θ of the drying soil column had decreased to 7–8%; (3) non-irrigation (NI), where irrigation was withheld after onset of treatments and lasted for 5 days until θ had decreased to 7%. In the PRD plants, the fraction of soil water extraction (FSWE) by the dry roots declined exponentially with declining soil water potential ( Ψ soil-dry); however, after shifting of irrigation, the previously dried roots immediately recovered the full capacity of water uptake. During the first PRD drying cycle, FI plants had the highest stomatal conductance ( g s), and followed by PRD plants and NI plants had the lowest g s. Photosynthesis ( A) was similar for FI and PRD plants, and was significantly lower for the NI plants only on 3–4 days after treatment. In the NI plants, a linear relationship between Ψ soil and [X-ABA] was obtained. Based on these relationships, a simple model predicting [X-ABA] in the PRD plants ([X-ABA] PRD) was developed. Assuming that a constant [X-ABA] of 115 nM (similar to that found in the FI plants) originated from the wet roots; the simulation results indicated that irrigation should be shifted between the two sides when Ψ soil-dry had decreased to ∼−80 kPa, and [X-ABA] PRD had reached a peak of ca. 150 nM. However, the [X-ABA] PRD predicted by the model was significantly lower than the measured value; whilst a simple average of [X-ABA] from the wet and the dry soil columns based on the [X-ABA]– Ψ soil relationship better predicted [X-ABA] PRD.

Nitrogen dynamics in the soil-plant system under deficit and partial root-zone drying irrigation strategies in potatoes

Experiments were conducted in lysimeters with sandy soil under an automatic rain-out shelter to study the effects of subsurface drip irrigation treatments, full irrigation (FI), deficit irrigation (DI) and partial root-zone drying (PRD), on nitrogen (N) dynamics in the soil-plant system of potatoes. In 2005, FI and PRD 2 were investigated, where FI plants received 100% of evaporative demands, while PRD 2 plants received 70% water of FI at each irrigation event after tuber initiation. In 2006, besides FI and PRD 2 treatments, DI and PRD 1 receiving 70% water of FI during the whole season were also studied. Crop N uptake and residual NH 4-N and NO 3-N to a depth of 0–50 cm, at 10 cm intervals were analyzed. For both years, the PRD 2 treatment resulted in 30% water saving and maintained yield as compared with the FI treatment, while when investigated in 2006 only, DI and PRD 1 treatments resulted in significant ( P < 0.05) yield reductions. In 2005, the soil residual N content at harvest was significantly 29% lower with PRD 2 than for FI in the whole root zone; and leaf N concentration for PRD 2 was significantly higher than for FI. In 2006, soil residual N content at harvest was 33% lower with PRD 2 than for FI, which was not significant however. In the late season, reflectance vegetation index and leaf area index for the water saving treatments were higher than for the FI treatment. For both years the PRD 2 treatment had the lowest residual N content in the root zone. We conclude that: (1) of the investigated water saving irrigation strategies (PRD 1 PRD 2, DI) PRD imposed just after tuber initiation until maturity (PRD 2) was the only strategy able to maintain yield; thus, soil drying induced by PRD or DI treatments should be avoided during early growth stages; (2) the PRD and DI treatments improved soil nitrogen availability late in the growing season maintaining top ‘greenness’ to a greater extent, as compared with FI.

Water relations and yield of lysimeter-grown strawberries under limited irrigation

Abstract The effects of partial root-zone drying (PRD), as compared to deficit irrigation (DI) and full irrigation (FI), on strawberry (cv. Honeoye) berry yield, yield components and irrigation water use efficiency (WUE I ) were investigated in a field lysimeter under an automatic rain-out shelter. The irrigation treatments were imposed from the beginning of flowering to the end of fruit maturity. In FI the whole root zone was irrigated every second day to field capacity viz. volumetric soil water content ( θ ) of 20%; while in DI and PRD 60% water of FI was irrigated to either the whole or one-half of the root system, respectively, at each irrigation event. In PRD, irrigation was shifted from one side to the other side of the plants when θ of the drying side had decreased to 8–11%. Compared to FI plants, leaf water potential was significantly lower in DI and PRD plants in 3 out of 10 measurement occasions, while stomatal conductance was similar among the three treatments. Leaf area, fresh berry yield (FY), individual berry fresh weight, berry water content, and berry dry weight (DW) were significantly lower in DI and PRD plants than those of FI plants; whereas the total number of berry per plant was similar among treatments. Compared with FI, the DI and PRD treatments saved 40% of irrigation water, and this led to a 28 and 50% increase of WUE I based on berry FY and DW, respectively, for both DI and PRD. Conclusively, under the conditions of this study PRD had no advantage compared to DI in terms of berry yield and WUE I . DI and PRD similarly decreased berry yield and yield components and thus cannot be recommended under similar conditions.

Effects of partial root-zone drying on yield, tuber size and water use efficiency in potato under field conditions

Water resources are limited for irrigation worldwide; therefore, there is a need for water-saving irrigation practices to be explored. Partial root-zone drying (PRD) is a new water-saving irrigation strategy being tested in many crop species. Experiments were conducted in potato ( Solanum tuberosum L. cv. Folva) under open field conditions in 2004 and under a mobile rainout shelter in 2005. Two subsurface irrigation treatments were studied: full irrigation (FI) receiving 100% of evaporative demands, 50.1 and 201 mm of irrigation water in the 2 years, to keep it close to field capacity; and PRD, which received 21.7 and 140 mm of irrigation in 2004 and 2005 respectively. Due to rain in 2004, the PRD treatment was imposed over a short period only during the late tuber filling and maturing stages. In 2005, the PRD treatment was imposed during the whole period of tuber filling and tuber maturation. The PRD treatment was shifted from one side to the other side of potato plants every 5–10 days. Especially in 2005 it was apparent that stomatal conductance was generally lower in the PRD than in the FI plants, whereas leaf water potential tended to be lower in only a few instances. During the treatment period, plants were harvested five times, and no significant difference was found between the treatments in leaf area index, top dry mass and tuber yield. At final harvest, tubers were graded based on size into four classes C 1–C 4, of which the yield of the important marketable class (C 2) was significantly higher (20%) in the PRD than in the FI treatment. Compared with FI, the PRD treatment saved 30% of irrigation water while maintaining tuber yield, leading to a 61% increase of irrigation water use efficiency. The limited data of 2004 support these results. In summary, PRD is a promising water-saving irrigation strategy for potato production in areas with limited water resources.

Effects of deficit irrigation (DI) and partial root drying (PRD) on gas exchange, biomass partitioning, and water use efficiency in potato

The effect of ‘partial root drying’ (PRD) compared with other irrigation strategies, viz. full irrigation (FI) and deficit irrigation (DI), on morphological and physiological characteristics of potato (Solanum tuberosum L. cv. Folva) were investigated at tuber initiation stage. Potatoes were grown in pots with roots split equally between two soil columns. In FI, the whole root system was irrigated at 100% of evapotranspiration (ETfull); in DI 50% of ETfull was irrigated to the whole root system; in PRD 50% of ETfull was irrigated to one soil column while the other was allowed to dry, and irrigation was shifted when 80–85% of plant available water in the dry side had been used. Midday leaf water potential was similar for all treatments at 9 days after onset of treatments (DAT), while it was significantly lower in PRD than in FI and DI plants at 21 DAT. Photosynthesis, stomatal conductance, and transpiration were generally greater in FI plants. Compared to FI, both DI and PRD significantly decreased leaf area and biomass. DI decreased biomass allocation to leaves and stems while increasing it into roots and tubers. PRD increased biomass allocation to roots. ET under PRD was ca. 80% of DI and FI until six DAT, thereafter ET of DI and PRD was similar and was significantly less than that of FI. Water use of DI and PRD plants was 37% less than that of FI. Water use efficiency (WUE) and transpiration efficiency were similar for PRD and FI plants, and were significantly less than those of DI plants. Conclusively, given the same amount (50% of ETfull) of irrigation, PRD has no advantages compared to DI in terms of biomass production and WUE in potato at tuber initiation stage.

Transpiration characteristics of banana leaves (cultivar ‘Williams’) in response to progressive depletion of available soil moisture

Young parent-crop banana plants (cultivar ‘Williams’) were subjected to two soil moisture potential (SMP) regimes, namely, continuous field capacity and progressive depletion of total available soil moisture (TAM). Experiments were conducted in a fibreglass tunnel under mild or enhanced conditions of vapour pressure deficit (VPD), and also in the field during summer. Transpiration rates, stomatal resistance, photosynthetically-active radiation and leaf temperature were measured simultaneously with a steady-state porometer, according to a developed technique which minimised natural sources of error. Under mild conditions of VPD (± 5 hPa) plants responded slowly to soil drying, and at a SMP of −82 kPa, transpiration was reduced by 27% compared to fully-irrigated plants. Under enhanced VPD (15–20 hPa), plants responded rapidly to soil drying, and at a SMP of −75 kPa transpiration was reduced by 73%. In the field, reduction of transpiration in response to SMP at high VPD followed a similar pattern to the covered experiment. At a SMP of −46 kPa the reduction in transpiration rate was 41% in the late afternoon at high VPD, but the following morning transpiration rates of the two treatments were similar due to lower VPD and overnight re-establishment of turgor. At −525 kPa SMP, reduction of transpiration was 70% and plants could not regain turgor overnight. Stomatal conductance seemed more sensitive to water stress than transpiration, but leaf temperature only differentiated advanced levels of stress (± 2°C difference between stressed and non-stressed leaves). These results hold important implications for irrigation scheduling of bananas. Initiation of stress occurred at a SMP of around −20 to −25 kPa which occurred at a 20% depletion of TAM, thus necessitating a summer irrigation frequency of daily or every 2 days.

Photosynthesis of cotton plants exposed to elevated levels of carbon dioxide in the field

The cotton (Gossypium hirsutum L.) plant responds to a doubling of atmospheric CO2 with almost doubled yield. Gas exchange of leaves was monitored to discover the photosynthetic basis of this large response. Plants were grown in the field in open-top chambers with ambient (nominally 350 μl/l) or enriched (nominally either 500 or 650 μl/l) concentrations of atmospheric CO2. During most of the season, in fully-irrigated plants the relationship between assimilation (A) and intercellular CO2 concentration (ci) was almost linear over an extremely wide range of ci. CO2 enrichment did not alter this relationship or diminish photosynthetic capacity (despite accumulation of starch to very high levels) until very late in the season, when temperature was somewhat lower than at midseason. Stomatal conductance at midseason was very high and insensitive to CO2, leading to estimates of ci above 85% of atmospheric CO2 concentration in both ambient and enriched chambers. Water stress caused A to show a saturation response with respect to ci, and it increased stomatal closure in response to CO2 enrichment. In fully-irrigated plants CO2 enrichment to 650 μl/l increased A more than 70%, but in water-stressed plants enrichment increased A only about 52%. The non-saturating response of A to ci, the failure of CO2 enrichment to decrease photosynthetic capacity for most of the season, and the ability of the leaves to maintain very high ci, form in part the basis for the very large response to CO2 enrichment.