Salinity guidelines for irrigation: Case studies from Water Research Commission projects along the Lower Vaal, Riet, Berg and Breede Rivers

A vast number of projects on salinity in irrigated agriculture were funded by the Water Research Commission (WRC) during the past 40 years. However, due to the diversity of the projects it is virtually impossible to cover all  aspects thoroughly in a paper of limited length. Thus this review focuses mainly on projects along the Lower Vaal, Riet, Berg and Breede Rivers in South Africa. The results on the water quality of these rivers indicate that irrigation has led to the deterioration of water sources. There is a direct relationship between river water quality and soils irrigated. Fortunately, effective land-suitability guidelines were developed and applied during the establishment of the major irrigation schemes. This facilitated the management of soils under irrigation. The results from long-term irrigation case studies along the Lower Vaal River and Breede River show that the quality of soils can be improved. The opposite is also true where mismanagement occurred. Research on the salinity threshold of major crops (grapevines, wheat, maize, groundnuts, etc.) confirmed the empiric nature of the guidelines. It is suggested that a more dynamic approach be used for managing salinity under irrigation at farm level, i.e. the use of models. Amongst others, future research should focus on determining the spatial and temporal distribution of salt in irrigated soils.Keywords: crop response, electrical conductivity, sodium adsorption ratio, soil type, water qualit

Prediction of salt balances in irrigated soils along the lower Vaal River, South Africa

In arid and semi-arid regions irrigation tends to degrade soil and water quality through salt accumulation with devastating effects on some crops. This is, according to irrigators, also the case along the lower Vaal River in South Africa. Properly calibrated and tested salinity models could assist the agricultural community in improving salinity management under irrigation.This paper reports on, firstly, salt balances of soils in this region being irrigated for different time periods, and secondly, salt content changes that can be expected as a consequence of future irrigation. Two empirical models, viz. a general and specific salt-balance model were used together with existing water- and soil-quality data to generate such information. The soils selected for this study had been irrigated for periods of between 17 to 53 years. Over these periods addition of salts as a result of farming practices varied between 79 and 280 t·ha-1, with irrigation water being the major contributor. Between 78% to 87% of the salts added to the soils had been leached from the root zone Despite these large amounts of salts that have been removed, certain irrigation practices have promoted the build-up of salts in some of the soils. The freely drained sandy soils irrigated by centre pivot are of particular interest. Poor management of this system can reduce crop yields. On account of inadequate leaching salts are building up to levels that impair the potential evapotranspiration level of maize. Predictions also show that irrigation should rather be withdrawn from soils with poor internal drainage properties, such as the Arcadia soil at Spitskop. In contrast, flood irrigation on certain duplex soils, such as the Valsrivier at Vaalharts, with relatively good internal drainage properties, can improve their quality.Keywords: drained soils, root zone, soil quality, undrained soils, water qualit

Tuberculosis cure rates and the ETR.Net: investigating the quality of reporting treatment outcomes from primary healthcare facilities in Mpumalanga province, South Africa

BACKGROUND : Tuberculosis control programs rely on accurate collection of routine surveillance data to inform program decisions including resource allocation and specific interventions. The electronic TB register (ETR.Net) is dependent on accurate data transcription from both paperbased clinical records and registers at the facilities to report treatment outcome data. The study describes the quality of reporting of TB treatment outcomes from facilities in the Ehlanzeni District, Mpumalanga Province. METHODS : A descriptive crossectional study of primary healthcare facilities in the district for the period 1 January – 31 December 2010 was performed. New smear positive TB cure rate data was obtained from the ETR.Net followed by verification of paperbased clinical records, both TB folders and the TB register, of 20% of all new smear positive cases across the district for correct reporting to the ETR.Net. Facilities were grouped according to high (>70%) and low cure rates (≤ 70%) as well as high (> 20%) and low (≤ 20%) error proportions in reporting. Kappa statistic was used to determine agreement between paperbased record, TB register and ETR.Net. RESULTS : Of the100 facilities (951 patient clinical records), 51(51%) had high cure rates and high error proportions, 14(14%) had a high cure rate and low error proportion whereas 30(30%) had low cure rates and high error proportions and five (5%) had a low cure rate with low error proportion. Fair agreement was observed (Kappa = 0.33) overall and between registers. Of the 473 patient clinical records which indicated cured, 383(81%) was correctly captured onto the ETR.Net, whereas 51(10.8%) was incorrectly captured and 39(8.2%) was not captured at all. Over reporting of treatment success of 12% occurred on the ETR.Net. CONCLUSIONS : The high error proportion in reporting onto the ETR.Net could result in a false sense of improvement in the TB control programme in the Ehlanzeni district.The Desmond Tutu TB Centre, Department of Paediatrics and Child Health, Stellenbosch University, Cape Town, South Africa.http://www.biomedcentral.com/bmchealthservresam2017Medical Microbiolog

Africa’s drylands in a changing world: Challenges for wildlife conservation under climate and land-use changes in the Greater Etosha Landscape

Proclaimed in 1907, Etosha National Park in northern Namibia is an iconic dryland system with a rich history of wildlife conservation and research. A recent research symposium on wildlife conservation in the Greater Etosha Landscape (GEL) highlighted increased concern of how intensification of global change will affect wildlife conservation based on participant responses to a questionnaire. The GEL includes Etosha and surrounding areas, the latter divided by a veteri nary fence into large, private farms to the south and communal areas of residential and farming land to the north. Here, we leverage our knowledge of this ecosystem to provide insight into the broader challenges facing wildlife conservation in this vulnerable dryland environment. We first look backward, summarizing the history of wildlife conservation and research trends in the GEL based on a literature review, providing a broad-scale understanding of the socioecological pro cesses that drive dryland system dynamics. We then look forward, focusing on eight key areas of challenge and opportunity for this ecosystem: climate change, water availability and quality, vegetation and fire management, adaptability of wildlife populations, disease risk, human wildlife conflict, wildlife crime, and human dimensions of wildlife conservation. Using this model system, we summarize key lessons and identify critical threats highlighting future research needs to support wildlife management. Research in the GEL has followed a trajectory seen elsewhere reflecting an increase in complexity and integration across biological scales over time. Yet, despite these trends, a gap exists between the scope of recent research efforts and the needs of wildlife conservation to adapt to climate and land-use changes. Given the complex nature of climate change, in addition to locally existing system stressors, a framework of forward-thinking adaptive management to address these challenges, supported by integrative and multidisciplinary research could be beneficial. One critical area for growth is to better integrate research and wildlife management across land-use types. Such efforts have the potential to support wildlife conservation efforts and human development goals, while building resilience against the impacts of climate change. While our conclusions reflect the specifics of the GEL ecosystem, they have direct relevance for other African dryland systems impacted by global change

Clinical standards for drug-susceptible TB in children and adolescents.

BACKGROUND: These clinical standards aim to provide guidance for diagnosis, treatment, and management of drug-susceptible TB in children and adolescents.METHODS: Fifty-two global experts in paediatric TB participated in a Delphi consensus process. After eight rounds of revisions, 51/52 (98%) participants endorsed the final document.RESULTS: Eight standards were identified: Standard 1, Age and developmental stage are critical considerations in the assessment and management of TB; Standard 2, Children and adolescents with symptoms and signs of TB disease should undergo prompt evaluation, and diagnosis and treatment initiation should not depend on microbiological confirmation; Standard 3, Treatment initiation is particularly urgent in children and adolescents with presumptive TB meningitis and disseminated (miliary) TB; Standard 4, Children and adolescents should be treated with an appropriate weight-based regimen; Standard 5, Treating TB infection (TBI) is important to prevent disease; Standard 6, Children and adolescents should receive home-based/community-based treatment support whenever possible; Standard 7, Children, adolescents, and their families should be provided age-appropriate support to optimise engagement in care and clinical outcomes; and Standard 8, Case reporting and contact tracing should be conducted for each child and adolescent.CONCLUSION: These consensus-based clinical standards, which should be adapted to local contexts, will improve the care of children and adolescents affected by TB

The logic of kinetic regulation in the thioredoxin system

<p>Abstract</p> <p>Background</p> <p>The thioredoxin system consisting of NADP(H), thioredoxin reductase and thioredoxin provides reducing equivalents to a large and diverse array of cellular processes. Despite a great deal of information on the kinetics of individual thioredoxin-dependent reactions, the kinetic regulation of this system as an integrated whole is not known. We address this by using kinetic modeling to identify and describe kinetic behavioral motifs found within the system.</p> <p>Results</p> <p>Analysis of a realistic computational model of the <it>Escherichia coli </it>thioredoxin system revealed several modes of kinetic regulation in the system. In keeping with published findings, the model showed that thioredoxin-dependent reactions were adaptable (i.e. changes to the thioredoxin system affected the kinetic profiles of these reactions). Further and in contrast to other systems-level descriptions, analysis of the model showed that apparently unrelated thioredoxin oxidation reactions can affect each other via their combined effects on the thioredoxin redox cycle. However, the scale of these effects depended on the kinetics of the individual thioredoxin oxidation reactions with some reactions more sensitive to changes in the thioredoxin cycle and others, such as the Tpx-dependent reduction of hydrogen peroxide, less sensitive to these changes. The coupling of the thioredoxin and Tpx redox cycles also allowed for ultrasensitive changes in the thioredoxin concentration in response to changes in the thioredoxin reductase concentration. We were able to describe the kinetic mechanisms underlying these behaviors precisely with analytical solutions and core models.</p> <p>Conclusions</p> <p>Using kinetic modeling we have revealed the logic that underlies the functional organization and kinetic behavior of the thioredoxin system. The thioredoxin redox cycle and associated reactions allows for a system that is adaptable, interconnected and able to display differential sensitivities to changes in this redox cycle. This work provides a theoretical, systems-biological basis for an experimental analysis of the thioredoxin system and its associated reactions.</p

Assessment of variable application rates of biological amendment substances on establishment and growth characteristics of maize plants

Good plant establishment and excellent vigour constitute essential  pre-requisites for successful grain production. The sowing of good viable seeds could contribute to increased productivity and ultimately lead to minimal seed cost and high return on investment. These are however dependent on such factors as the possible effects of pre- and post-seed sowing soil amendments. Hence, a greenhouse experiment was  conducted in 2008 to assess the effects of variable rates (50, 75 and 100% of the recommended rates) of industrial manufactured biological amendment substances (IMBAS) (Biozone, Crop care, Gromor, Growmax, K-humate, Lanbac, Molcast, Montys and Promis) on the establishment and growth characteristics of maize seedlings. Inorganic NPK fertilizer and unamended control treatments were included as standards. Results obtained revealed a significant IMBAS as well as IMBAS x rates interaction effects on plant height, number of leaves, total biomass and leaf area. The percent plant emergence in K-humate, Montys and Promis treatments at 50% recommended rate were significantly decreased relative to the standard treatments. Application of most of the IMBAS at 100% of the recommended rate generally decreased plant establishment and phenological characteristics of maize. The study underpins the relevance of in-depth and accurate agronomic evaluation of industrially manufactured growth enhancement materials prior to recommendation for use by farmers.Keywords: Industrial manufactured biological amendment substances, maize phenology, plant vigour, seedling emergence, soil amendment

Relationships between agronomic and environmental phosphorus analyses of selected soils

Phosphorus (P) is an essential nutrient in crop production and is therefore typically applied as phosphatic fertilisers.&nbsp; This can induce soil P concentrations that may contribute to freshwater eutrophication.&nbsp; Soil P tests developed from a water pollution protection perspective are unlike those developed for agronomic purposes and are also not easily adapted to routine analyses.&nbsp; The aim with this study was therefore to establish whether the values of P extracted from a range of soils by various agronomic and environmental P determination methods are related or not.&nbsp; Topsoil samples were collected from virgin soils in central South Africa and treated with KH2PO4 to induce different P concentrations and then incubated for 3 months, while subjected to various wetting and drying cycles.&nbsp; The samples were then analysed for P using the extractants of Bray 1, citric acid, ISFEI, Olsen, and Truog, commonly employed to establish the agronomic P status of soils.&nbsp; Environmental P status was determined with calcium chloride (CaCl2) and ammonium oxalate (DPSox) extractants.&nbsp; Generally good relationships were found between CaCl2 and ISFEI (R2 = 0.72), between DPSox and Truog (R2 = 0.79), and between DPSox and citric acid (R2 = 0.82).&nbsp; Agronomic P soil tests therefore have the potential to be used in regulating application of phosphatic fertilisers to ensure optimum crop yields, while simultaneously limiting freshwater pollution.&nbsp; Further field studies are, however, recommended to determine threshold values from an environmental point of view

Canola (Brassica napus L.) water use indicators as affected by sustained deficit irrigation and plant density in central Free State, South Africa

In South Africa canola (Brassica napus L.) is cultivated in rotation with wheat under winter rainfall in the Western Cape Province, primarily for seed to make oil. Expansion of the crop to the other 8 provinces is proposed to reduce shortages of locally produced plant oils. At the same time, canola can serve as a rotational crop for wheat in these summer rainfall provinces. In central Free State, information on evapotranspiration and various water use indicators for canola as influenced by sustained deficit irrigation and plant density is lacking. An experiment with a line source sprinkler irrigation system was therefore conducted, comprising of full irrigation as a control with 4 sustained deficit irrigation levels (mean reduction in irrigation depth per event of 67%, 52%, 34% and 19%) and 5 plant densities (25, 50, 75, 100 and 125 plants‧m−2). Mean seasonal maximum evapotranspiration amounted to 429 mm across plant densities. Plant density did not significantly influence seasonal evapotranspiration. Reducing the irrigation depth per event by more than 20% decreased seasonal evapotranspiration by a mean 3.5 mm per percentage increase in irrigation depth. A maximum biomass water productivity of 22 kg‧ha−1‧mm−1 was measured with full irrigation and a plant density of 75 plants‧m−2. Seed water productivity amounted to a high of 11 kg‧ha−1‧mm−1 with full irrigation and a plant density of 25 plants‧m−2. A percentage reduction in irrigation depth and increase in plant density above 25 plants‧m−2 will reduce seed water productivity by 0.071 and 0.033 kg‧ha−1‧mm−1, respectively. Sustained deficit irrigation increased water use efficiency by a mean 0.5% per percentage reduction in irrigation depth per event