Search

Global demand for forest products is ever-increasing, creating competition for water between downstream water users and commercial forest producers. Tree production should therefore aim at the effective use of water by producing maximum tree biomass from water used with the least total evaporative losses. A ratio of accumulated biomass to transpiration (T) known as the water use efficiency (WUE) is a common technique used to determine commercial forest plantation productivity. This review argues that WUE does not account for total plantation water use (ET), transpiration efficiency of trees (TE) and harvest index (HI, the tree stemwood, which is the most profitable component of a tree). This research suggests using PWPWOOD which is defined as the maximum amount of wood produced, also referred to as plantation yield (TE × HI) from a given volume of ET (T + canopy interception + soil water evaporation). Improving PWPWOOD requires that TE and HI are increased while ET losses are kept to a minimum. Practical interventions to improve plantation yield (TE and HI) are discussed in detail while techniques to minimise ET are discussed to a lesser extent. PWPWOOD has been shown to be a better measure and found to improve commercial forest plantation productivity as indicated by different case studies presented in this review. [ABSTRACT FROM AUTHOR]

Over the past century, increases in indigenous woody plant species, also known as woody encroachment (WE), has occurred in grasslands and savannas across the globe. While the impact on grassland and savanna composition and productivity has been well studied, little is known of the impacts on the hydrological cycle. WE may increase evapotranspiration (ET) losses, leading to reduced infiltration and ultimately reduced freshwater availability, which is of particular concern in arid and semi-arid areas. The aim of this study was to determine the effect of Colophospermum mopane (mopane) encroachment on ET in a semi-arid savanna located in South Africa. Mopane is widely distributed across southern Africa, and is one of the main encroaching species of the region. Following an assessment of the validity of two surface renewal approaches, SR1 and SRDT, against short eddy covariance campaigns for sensible heat flux estimation, the SR1 approach was used to estimate ET at an experimental woody plant clearing trial from November 2019 to July 2022. For the two drier years of the study, the removal of mopane trees had little effect on ET. However, for the wettest year of the study, the removal of mopane trees decreased ET by 12%, supporting the hypothesis that the conversion from grass dominance to woody dominance can increase ET. Annual ET exceeded annual rainfall in all 3 years, indicating that the vegetation supplements its water use with soil water that has accumulated during previous wet seasons, or that tree roots facilitate hydraulic lift of deep soil water, or groundwater, to depths within the rooting depth of both trees and grasses. Further research is needed to confirm the exact mechanism involved, and the consequences of this for groundwater and streamflow at landscape scales. [ABSTRACT FROM AUTHOR]

Green-mature and turning cherry tomatoes (Solanum lycopersicum L.) of a red ('Cherry Little Wonder') and a yellow ('Goldilocks') cultivar (cv) were illuminated, post-harvest, with either red (118 µmol m–2 s – 1 at 638 nm) or blue LED light (118 µmol m–2 s – 1 at 454 nm) for 48 h and subsequently stored for up to 21 days at room temperature. The effects of the treatments on colour, firmness, sugars and carotenoids were evaluated throughout storage. The light treatments did not have any effect on firmness and mass; however, light exposure, particularly red light, enhanced the a* colour component of the red cv significantly; similarly, colour coordinate b* of the yellow cv, treated at both stages of development, was significantly enhanced by both light treatments, resulting in visually redder and yellower tomatoes, respectively. These effects were more so observed on green-mature than on turning fruit. In addition, the treatments significantly increased lycopene concentrations in the red cv at both ripening stages, and β-carotene concentrations in both, the yellow and red cv treated at the green-mature stage. Total soluble solids (%TSS) also increased significantly following treatment. Findings reported suggest that illuminating tomato fruit with LED lights at the green-mature stage enhances colour development and the concentration of sugars, pigments and other health-related compounds without significantly affecting fruit mass and firmness. [ABSTRACT FROM AUTHOR]

This study was undertaken to derive textural and lumped site-specific calibration equations for Dirk Friedhelm Mercker (DFM) capacitance probes and evaluate the accuracy levels of the developed calibration equations for continuous soil moisture monitoring in three selected soil types. At each site, 9 probes (3 per plot) were installed in 2 m²plots, for continuous soil moisture measurements at 5 different depths (viz. 10, 20, 30, 40 and 60 cm) under dry, moist and wet field conditions. Textural site-specific calibration equations were derived by grouping the same soil textural classes of each site regardless of soil depth, while lumped site-specific calibration equations were derived by grouping all datasets from each site, regardless of soil depth and textural classes. Sensor readings were plotted against gravimetrically measured volumetric soil moisture (θv) for different textural classes as a reference. The coefficient of determination (r²) was used to select the best fit of the regression function. The developed calibration equations were evaluated using an independent dataset. The results indicated that all developed textural and lumped site-specific calibration equations were linear functions, with r² values ranging from 0.96 to 0.99. Relationships between the measured and estimated θv from calibration equations were reasonable at all sites, with r² values greater than 0.91 and root mean square error (RMSE) values ranging from 0.010 to 0.020 m³•m-3. The results also indicated that textural site-specific calibration equations (RMSE < 0.018 m³•m-3) should be given preference over lumped site-specific calibrations (RMSE < 0.020 m³•m-3) to attain more accurate θv measurements. The findings of this study suggest that once DFM capacitance probes are calibrated per site, they can be reliably used for accurate in-situ soil moisture measurements. The developed calibration equations can be applied with caution in other sites with similar soil types to attained reliable in-situ soil moisture measurements. [ABSTRACT FROM AUTHOR]

Long-term gold mining within the Witwatersrand Basin Goldfields has led to the creation of over 200 tailings storage facilities (TSFs) releasing acid mine drainage. Plumes of contaminated shallow groundwater occur downslope of these TSFs. One such area lies adjacent to the Vaal River east of the town of Orkney. Natural vegetation in the riparian soils comprises a mixture of grasslands, reeds and woodlands dominated byVachellia karroo. The Mine Woodlands Project initiated by Witwatersrand University and AngloGold Ashanti is exploring the use of engineered woodlands for hydraulic control of plumes and immobilization of contaminants to protect the wider hydrological resource. To estimate the net increase in evapotranspiration (ET) resulting from various remedial woodlands, ET from existing vegetation types requires quantification. Growing season patterns of ET were measured and modelled in riparian grassland and twoV. karroowoodland sites close to the Vaal River. Two independent estimates of annual ET from these woodland sites (674 and 787 mm) were similar to that from grassland (697 mm) and much less than the 1100–1200 mm reported from some forms of engineered evergreen woodlands established in the vicinity. We conclude that theVachelliawoodlands have low potential for hydraulic control of contaminant plumes. [ABSTRACT FROM PUBLISHER]

Sweet sorghum (Sorghum bicolor (L.) Moench) has been recognized globally as a potential biofuel crop for ethanol production. Sweet sorghum is a drought-tolerant crop that is widely adapted to different environmental growing conditions. The aim of this study was to determine the water use efficiency (utilisable yield per unit amount of water used) of drip-irrigated sweet sorghum (variety Sugargraze) under two different climatic conditions in South Africa. The sweet sorghum trials were conducted at Ukulinga research farm (University of KwaZulu-Natal, Pietermaritzburg) and Hatfield experimental farm (University of Pretoria, Pretoria), South Africa. Field trials were conducted in two successive seasons, viz., 2010/11 and 2011/12. Seasonal water use was estimated using eddy covariance and surface renewal methods. Fresh and dry aboveground biomass yield, stalk yield and stalk Brix % were measured at final harvest. Theoretical ethanol yield was calculated from fresh stalk yield and Brix %. Water use for the two growing seasons was 415 mm at Ukulinga and 398 mm at Hatfield. The ethanol water use efficiency (WUE) values for the sweet sorghum at Ukulinga were 0.27 and 0.60 L.m-3 for 2010/11 and 2011/12 growing seasons, respectively. The ethanol WUE estimate of the sweet sorghum at Hatfield was 0.53 L.m-3 for the 2010/11 season and 0.70 L.m-3 for the 2011/12 growing season. WUE estimates of the sweet sorghum crop were higher for Hatfield compared to Ukulinga research farm. The results from this study showed that the WUE of sweet sorghum was sensitive to plant density. The WUE values confirm that sweet sorghum has high WUE under different climatic conditions. [ABSTRACT FROM AUTHOR]

A combination of measurement and modelling was used to find a pragmatic solution to estimate the annual total evaporation (ET) from the rare and indigenous Nkazana Peat Swamp Forest (PSF) on the east coast of Southern Africa to improve the water balance estimates within the area. Total evaporation was measured during three window periods (between seven and nine days each) using an eddy covariance (EC) system on a telescopic mast above the forest canopy. Sapflow of an understory and an emergent tree was measured using a low maintenance heat pulse velocity system for an entire hydrological year (October 2009 to September 2010). An empirical model was derived, describing the relationship between the observed ET of the Nkazana PSF measured during two of the window periods (R = 0.92 and 0.90) which, overlapped with sapflow measurements, thereby providing hourly estimates of predicted ET of the Nkazana PSF for a year, totalling 1125 mm (while rainfall was 650 mm). In building the empirical model, it was found that including the understory tree sapflow provided no benefit to the model performance. In addition, the observed emergent tree sapflow relationship with observed ET between the two field campaigns was consistent and could be represented by a single empirical model (R = 0.90; RMSE = 0.08 mm). During the window periods of EC measurement, no single meteorological variable was found to describe the Nkazana PSF ET satisfactorily. However, in terms of evaporation models, the hourly FAO56 Penman-Monteith equation best described the observed ET from EC during the August 2009 (R² = 0.75), November 2009 (R² = 0.85) and March 2010 (R = 0.76) field campaigns, compared to the Priestley-Taylor model (R² = 0.54, 0.74 and 0.62 during the respective field campaigns). From the empirical model of ET and the FAO56 Penman-Monteith equation, a monthly crop factor (Kc) was derived for the Nkazana PSF providing a method of estimating long-term swamp forest ET from meteorological data. The monthly crop factor indicated two distinct periods. From February to May, it was between 1.2 and 1.4 compared with June to January, when the crop factor was 0.8 to 1.0. The derived monthly Kc values were verified as [ABSTRACT FROM AUTHOR]

Total evaporation ( ET) is one of the major components of the water budget of a wetland. Very little research has been conducted on the loss of water to the atmosphere from different wetland vegetation types occurring in southern Africa. This study on the ET of taro (locally known as madumbe) and sedge within the Mbongolwane wetland was conducted to assess the potential impact of madumbe cultivation on the hydrology of the wetland. Sugarcane planted on the contributing catchment outside the wetland was the other crop examined. Two field campaigns were conducted in November 2009 and January 2010 during the growing season of the madumbe crop to quantify ET rates in the Mbongolwane wetland and from sugar cane in the surrounding catchment. ET was measured over two vegetation types in the wetland, namely: madumbe ( Colocasia esculenta); sedge ( Cyperus latifolius) with some reeds ( Phragmites australis); and sugarcane in adjacent terrestrial areas. ET from the madumbes ranged from 1.0 to 6.0 mm day−1. The daily average ET rates in November 2009 were 3.5 and 4.9 mm for the madumbe and sedge sites, respectively, and 4.0 mm for sugarcane grown in the catchment. The daily average ET rates in January 2010 were 3.3 and 3.7 mm for the madumbes and sedge sites, respectively, and 2.4 mm for the sugarcane site. The daily ET was therefore lower at the madumbe site in November 2009 and in January 2010 compared to the sedge site. An average crop factor of 0.6 was obtained from this study during the growth stage of the madumbes. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]