Brent Clothier

Natural and induced cadmium-accumulation in poplar and willow: implications for phytoremediation.

Potentially poplars and willows may be used for the in situ decontamination of soils polluted with Cd, such as pasturelands fertilised with Cd-rich superphosphate fertiliser. Poplar (Kawa and Argyle) and willow (Tangoio) clones were grown in soils containing a range (0.6–60.6 μg g−1 dry soil) of Cd concentrations. The willow clone accumulated significantly more Cd (9–167 μg g−1 dry matter) than the two poplar clones (6–75 μg g−1), which themselves were not significantly different. Poplar trees (Beaupré) sampled in situ from a contaminated site near the town of Auby, Northern France, were also found to accumulate significant quantities (up to 209 μg g−1) of Cd. The addition of chelating agents (0.5 and 2 g kg−1 EDTA, 0.5 g kg−1 DTPA and 0.5 g kg−1NTA) to poplar (Kawa) clones caused a temporary increase in uptake of Cd. However, two of the chelating agents (2 g kg−1 EDTA and 0.5 g kg−1 NTA) also resulted in a significant reduction in growth, as well as abscission of leaves. If the results obtained in these pot experiments can be realised in the field, then a single crop of willows could remove over 100 years worth of fertiliser-induced Cd contamination from pasturelands.

Root water uptake by kiwifruit vines following partial wetting of the root zone

Rates of sap flow and root-water uptake by two 7-year old kiwifruit vines (Acinidia deliciosa) were studied in an orchard with the aim of determining the ability of the vines to alter their spatial pattern of root-water uptake following differential wetting of the root zone. Time-domain reflectometry (TDR) was used to monitor changes in the soils volumetric water content, π. The heat-pulse technique was used to monitor sap flow not only in the stem but also in several large roots to see how root flow responded with local changes in soil water availability. Prior to irrigation there was a broad correspondence between the pattern of water uptake and the distribution of root-length density. However, following irrigation, we observed a preferential uptake of water from the wetter parts of the soil and a corresponding decline in water uptake from the drier parts of the soil. Observations of root uptake by TDR following irrigation also revealed the inordinate activity of near-surface roots. The vine would preferentially draw upon near-surface water if it were available. Kiwifruit vines are able to shift rapidly their pattern of uptake, in a matter of days, away from drier parts of the root zone and begin to extract water preferentially from those regions where it is more freely available. Upon full wetting of the root zone, previously inactive roots in the dry soil of the root zone were quickly able to recover their activity. Indeed their activity following rewatering was found to be greater than it had been prior to the period of soil dryness. A rapid flush of new root growth is considered to be the mechanism that leads to this enhanced activity.

Roots : The big movers of water and chemical in soil

Root water uptake and the dynamic availability of water to plants is a phenomenon that tends to be overlooked by soil scientists, despite the often dominant role of roots as a sink for water in the soil. Water taken up by roots is vital for plant growth and the productive management of soils. In

Transpiration and root water uptake by olive trees

While the cultivated olive tree (Olea europaea L.) is known to be sclerophyllous and effective at tolerating drought, little is known of its short-term water-use dynamics for most studies have been based on longer-term, water-balance information. We present here, for the first time, heat-pulse measurements of the sap flux measured not only within the semi-trunk of an olive tree, but also within a root excavated close to the stump. One tree in the olive grove near Seville in Spain had regularly received basin irrigation during the summer, whereas the other, growing on this deep silt loam, had been without water for over 3 months. Following a flood irrigation of 730 L to a dyked area around the tree, the regularly-irrigated olive maintained a transpiration rate of 1.65 mm3 mm−2 d−1, on a leaf area basis, for only 3 days following the irrigation. This rate was maintained for a total consumption of 110 L. It then began again to limit its rate of water use with transpiration falling below that predicted for well-watered conditions by the Penman-Monteith equation. The flow of sap in the near-surface root dropped concomitantly. Meanwhile the unirrigated tree was using water at just 0.78 mm d−1. Yet following an irrigation of 870 L it only lifted its consumption to 1.12 mm d−1, on a leaf area basis. Neither did it recover its leaf water potential following this wetting because of an inability to refill cavitated vessels. These data again show olive to be a parsimonious and cautious consumer of soil water.

Rootzone processes and the efficient use of irrigation water

Abstract The need for more-efficient agricultural use of irrigation water arises out of increased competition for water resources, and the greater pressure on irrigation practices to be environmentally friendly. In this review for the 25th Jubilee volume of Agricultural Water Management we focus on three rootzone processes that determine water-use efficiency in irrigation. Firstly, we discuss the role of macropores in preferentially-transporting irrigation water to depth during infiltration under both sprinkler and flood systems. It is suggested that more-uniform entry of irrigation water into the rootzone will result either by matching the sprinkler rate to the soils matrix hydraulic conductivity, or by modifying the soil-surfaces macroporosity prior to flood irrigation. Secondly, the environmentally-deleterious leaching of chemicals by irrigation is shown to be reduced if the applied fertilizer is first washed into dry soil by a small amount of water. This first pulse of water is drawn by capillarity into the soils microporosity, and it carries with it the dissolved fertilizer which becomes resident there. These nutrients are then available for plant uptake, yet less prone to susbsequent leaching by heavy rains. Meanwhile, initially-resident solutes in the dry soil, such as salts, will be more-effectively displaced by the infiltrating irrigation water. Finally, our time domain reflectometry (TDR) observations of the changing soil water content in the rootzone of a kiwifruit vine, and our direct measurements of sap flow within individual roots, both reveal that plants can rapidly change their spatial pattern of water uptake in response to the application of irrigation water. The prime uptake role of near-surface roots is highlighted. Consideration of all three of these rootzone processes reinforces the claim that more- efficient and environmentally-sustainable water management will arise through higher-frequency applications of smaller amounts of irrigation. Key words: Rootzone process; Water-use efficiency; Macropore: Sprinkler and flood systems *Corresponding author. 0378-3774/94/

The breakdown of water repellency and solute transport through a hydrophobic soil

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Plant uptake and leaching of copper during EDTA-enhanced phytoremediation of repacked and undisturbed soil

Unsaturated infiltration into the Ramiha silt loam, an Andic Dystrochrept, follows the classic pattern. A rapid drop-off from a high flow rate, seemingly induced by capillary attraction, appears followed by an apparent steady-flow maintained by gravity at around 0.5 μm s−1. Beyond 100 min, however, the infiltration rate climbs nearly linearly to exceed 4 μm s−1 as the soils water repellency breaks down. This is only evident after a period that might exceed the observers attention span. The hydrophobicity in this case could be due to one, or a combination, of the many unusual characteristics of this soil—its low bulk density (0.8 Mg m−3), its strongly aggregated nature, the presence of mycorrhizal fungi, its high organic matter content (16.5%), or the presence of allophanic clay (4%). Our measurements of infiltration into undisturbed cores of Ramiha silt loam were made with disc permeameters set at the unsaturated pressure head of h0=−40mm. The permeameters contained a solution of electrolytic tracer (KBr) so that we could observe solute transport in this soil. Vertical three-wire rods for Time Domain Reflectometry (TDR) measurement were inserted directly through the base plate of the permeameter so that we could continuously monitor the soils changing water content and resident concentration of electrolyte. The TDR measurements revealed the transient behaviour of fingered preferential flow into this soil during the breakdown of hydrophobicity. At the conclusion of the experiment, the soil cores were sectioned to permit measurement of the profiles in the resident concentration of the invading chemical. Near the surface, at the conclusion of the experiment, the resident concentration of bromide was found to be exactly that of the invading solution. So, despite the initial water repellency of the soil, the infiltrating bromide solution was subsequently able to invade the entire pore space—once the hydrophobicity had dissipated. Classic theory would then seem capable of describing solute transport after the effects of water repellency had faded.

The response of sap flow in apple roots to localised irrigation

EDTA-enhanced phytoremediation of copper contaminated soil was evaluated. Up to 740 μg g−1 of Na2H2 EDTA in solution was added to repacked soil columns, and intact cores of a sandy loam of volcanic origin, that was growing Agrostis tenuis. The soil contained up to 400 μg g−1 of copper due to a history of fungicide spraying. EDTA application increased the herbage copper concentration of the grass growing in repacked soil from 30 to 300 μg g−1, but the same application to an intact core only brought about an increase from 10 to 60 μg g−1. More copper accumulated in the herbage when the EDTA was applied in numerous small doses than in just one or two larger amounts. Calculation of the concentration of copper in the water taken up by the grass revealed this to be two orders of magnitude lower than that in the soil solution. As a result of the EDTA applications, about 100 times more copper was leached than was taken up by the herbage. This means that a strategy for managing leaching losses needs to be part of any plan for EDTA-enhanced phytoremediation.

Responses of ‘Petopride’ processing tomato to partial rootzone drying at different phenological stages

Abstract The oft-touted reason for the efficiency of drip irrigation is that roots can preferentially take up water from localised zones of water availability. Here we provide definitive evidence of this phenomenon. The heat-pulse technique was used to monitor rates of sap flow in the stem and in two large surface roots of a 14 year old apple tree (Malus domestica Borkh. cv. Braeburn). The aim was to determine the ability of an apple tree to modify its pattern of root water uptake in response to local changes in soil water content. We monitored the water status of the soil close to the instrumented roots by using time domain reflectometry (TDR) to measure the soils volumetric water content, θ, and by using ceramic-tipped tensiometers to measure the soils matric pressure head, h. A variation in soil water content surrounding the two roots was achieved by supplying a single localised irrigation to just one root, while the other root remained unwatered. Sap flow in the wetted root increased straight away by 50% following this drip irrigation which wetted the soil over a zone of approximately 0.6 m in diameter and 0.25 m in depth. Sap flow in the wetted root remained elevated for a period of about 10 days, that is until most of the irrigation water had been consumed. A comparative study of localised and uniform irrigation was then made. Following irrigation over the full root zone no further change in sap flow in the previously wetted root was observed when referenced to the corresponding sap flow measured in the stem of the apple tree. However sap flow in the previously dry root responded to subsequent irrigations by increasing its flow rate by almost 50%. These results show that apple roots have the capacity to transfer water from local wet areas at much higher rates than normally occurs when the entire root zone is supplied with water. They are also able to shift rapidly their pattern of uptake and begin to extract water preferentially from those regions where it is more freely available. Such an ability supports the use of drip irrigation for the efficient use of scarce water resources. We conclude that the soil-to-root pathway represents a major resistance to water uptake by apple, even at the relatively high soil water pressure heads developed during parts of this experiment, during which the tree was not even under any stress.

Cadmium accumulation by willow clones used for soil conservation, stock fodder, and phytoremediation

Partial rootzone drying (PRD) is a water-saving irrigation practice which involves watering only part of the rhizosphere at each irrigation with the complement left to dry to a pre-determined level. The effect of PRD, applied at different phenological stages, on yield, fruit growth, and quality of the processing tomato cv. ‘Petopride’ was studied in this experiment. The treatments were: daily full irrigation (FI) on both sides of the root system considered as the control, and PRD treatments applied at three phenological stages. These were: during the vegetative stage until the first truss was observed (PRDVS–FT), from the first truss to fruit set (PRDFT–FS), and from fruit set to harvest (PRDFS–H). In some occasions, leaf xylem water potential was lower in each PRD period than in FI. Number of fruits, total fresh and dry weight of fruit per plant, harvest index, and fruit growth were lower in PRDFT–FS and PRDFS–H plants than in FI and PRDVS–FT plants. However, irrigation water use efficiency, on a dry weight basis, was the same among the treatments. For PRDFT–FS and PRDFS–H treatments, mean fresh weight of fruit and fruit water content were reduced and dry matter concentration of cortex and total soluble solids concentration of fruit increased compared with FI and PRDVS–FT treatments. Incidence of blossom-end rot was the same among PRDVS–FT, PRDFS–FH, and FI fruit, but it was higher in PRDFT–FS fruit. Fruit skin colour was the same among treatments. Total dry weight of fruit per plant decreased by 23% for PRDFT–FS and by 20% for PRDFS–H relative to FI. Fruit quality improvement in PRDFS–H could compensate for the reduction in total dry weight of fruit where water is expensive for tomato production. But an economical analysis would be needed to substantiate this. PRD from the first truss to fruit set is not recommended because of the high incidence of blossom-end rot.