Phesheya Dlamini - Academia.edu (original) (raw)

Papers by Phesheya Dlamini

Grasslands occupy about 40% of the world’s land sur face and store approximately 10% of the globa... more Grasslands occupy about 40% of the world’s land sur face and store approximately 10% of the global soil organic carbon (SOC) stock. This SO C pool, in which a larger proportion (ca 60-70%) is held in the topsoil (0-0.3 m), is st rongly influenced by grassland management. Despite this, it is not yet fully under stood how grassland soils respond to degradation, particularly for the different environ mental conditions found globally. The objective of this review was to elucidate the impac t of grassland degradation on changes in SOC stocks and the main environmental controls, wor ld ide. A comprehensive metaanalysis was conducted using 29 studies with 630 so il pr files from 131 temperate, subtropical and semi-arid sites, to compare SOC stocks in the topsoil of non-degraded and degraded grassland soils. Grassland degradation sig nificantly reduced SOC stocks by 16% in dry climates (<600 mm) compared to 8% in wet cli mates (>1000 mm). The depletion of SOC stock induced by degradat...

Frontiers in Microbiology

Sustainability

Sub-Saharan Africa (SSA) is experiencing an increase in food insecurity, which is fueled by both ... more Sub-Saharan Africa (SSA) is experiencing an increase in food insecurity, which is fueled by both high population growth and low agricultural productivity. Smallholder farmers are seriously affected by low soil fertility, land degradation, and poor agronomic management practices that reduce crop productivity. Therefore, there is a huge need for reliable soil information to support agricultural decision-making in smallholder farms to ensure sustainable agricultural production. However, most studies focused on land capability and soil suitability do not consider the spatial variability of soils and their inherent properties. The main objectives of this study were (1) to survey, classify and characterise soils at Makuleke farm in order to derive and map the land capability classes and (2) to quantify the physical and chemical properties of the soils in order to derive and map the suitability classes. A field survey and classification of soils led by transect walks complemented by auger ...

Heliyon, 2020

For adequate mitigation and adaptation measures, it is essential to have detailed analysis of dro... more For adequate mitigation and adaptation measures, it is essential to have detailed analysis of droughts patterns. This study determined the i) occurrence and severity of droughts ii) drought recurrence frequencies and iii) drought trends across different agro-ecological zones in the Kingdom of Eswatini for the period 1981 to 2018. A Standardised Precipitation Index (SPI) computed from long-term precipitation data measured from six meteorological stations was used to determine drought occurrence and severity. Python software (Version 3.6) was applied on the SPI values to predict the recurrence of drought events over time in years. The SPI showed that in the Highveld, 42% of the droughts were moderate, 32% were severe and the remaining 26%, which all occurred post 1980 were extreme (SPI-2.34 to-2.82). The Middleveld had an even proportion of drought categories (29-35%). The Lowveld recorded 62% of moderate, 8% severe and 30% extreme droughts of which 70% occurred post 2000. Moderate droughts were found to recur every 4-5 years while extreme droughts are expected every 13-21 years. These findings are essential for mitigation and adaptation measures geared towards the adverse effects of droughts.

Ecological Indicators, 2019

Although tree transpiration (T) studies across multiple spatial scales have been conducted, the s... more Although tree transpiration (T) studies across multiple spatial scales have been conducted, the synthesis of the driving factors of tree water use, especially for a variety of species under different climatic conditions has not yet been made. This paper analyses T data from 94 published studies conducted in various sites between 1970 and 2016, representing 196 data points to seek relations between morphological traits; tree height (H), diameter at breast height (DBH) and environmental factors; mean annual precipitation (MAP), mean annual temperature (MAT) and altitude (Z) on whole tree water use for 130 species of trees. Techniques used in the studies for T measurement were also analysed. Log transformed T (ln T) varied between 0 and 7.1 L day −1. Univariate correlation and regression analysis revealed that ln T was positively and significantly correlated with H (Spearman correlation coefficient (r s) = 0.55) and DBH (r s = 0.62) at P < 0.1. A weak positive correlation was found between ln T and MAP (r s = 0.16) at P < 0.1. The results further showed that during the study period (1970-2016), 82% of the studies used thermodynamic methods to measure T, in particular thermal heat dissipation probes were used by 60% of the studies, while 21% reported use of heat pulse velocity. The results contribute to a better understanding of T in forest ecosystems, and the factors of control to inform global scale modelling and ecosystem management. Thermodynamic methods, especially thermal heat dissipation probes and heat pulse velocity are the most prevalent techniques used for whole tree T measurement.

Climate Risk Management, 2017

Engineering infrastructures such as stormwater drains and bridges are commonly designed using the... more Engineering infrastructures such as stormwater drains and bridges are commonly designed using the concept of Intensity-Duration-Frequency (IDF) curves, which assume that the occurrence of precipitation patterns and distributions are spatially similar within the drainage area and remain unchanged throughout the lifespan of the infrastructures (stationary). Based on the premise that climate change will alter the spatial and temporal variability of precipitation patterns, inaccuracy in the estimation of IDF curves may occur. As such, prior to developing IDF curves, it is crucial to analyse trends of annual precipitation maxima. The objective of this study was to estimate the precipitation intensities and their uncertainties (lower and upper limits) for durations of 0.125, 0.25, 0.5, 1, 2, 4, and 6 h and return periods of 2, 10, 25, 50 and 100 years in the Ghaap plateau, Northern Cape Province, South Africa using the Generalized Extreme Value (GEV) distribution. The annual precipitation maxima were extracted from long-term (1918-2014) precipitation data for four meteorological stations (Postmasburg, Douglas, Kuruman and Groblershoop) sourced from the South African Weather Services (SAWS). On average, the estimated extreme precipitation intensities for the plateau ranged from 4.2 mm/h for 6 h storm duration to 55.8 mm/h for 0.125 h at 2 years return period. At 100 year return period, the intensity ranged from 13.3 mm/h for 6 h duration to 175.5 mm/h for the duration of 0.125 h. The lower limit of uncertainty ranged from 11.7% at 2 years return period to 26% at 100 year return period, and from 12.8% to 58.4% for the upper limit for the respective return periods. This methodology can be integrated into policy formulation for the design of stormwater and flood management infrastructures in the Ghaap plateau, where mining is the main economic activity.

Soil Research, 2017

Partitioning of evapotranspiration (ET) into its components of evaporation (E) and transpiration ... more Partitioning of evapotranspiration (ET) into its components of evaporation (E) and transpiration (T) is difficult, yet important for managing unproductive and productive water losses under irrigated agriculture. A lysimeter experiment (Expt 1) was conducted on sandy Clovelly and sandy loam Bainsvlei soils in Bloemfontein, South Africa where plastic sheet and dolerite gravel mulches were applied to lysimeters to determine to what extent they restricted E from the soil surface compared with a bare soil control. No crops were grown in the lysimeters for Expt 1. Gravel mulch on Clovelly-filled lysimeters reduced E by 33% and by 41% for Bainsvlei-filled lysimeters compared with bare soil. Based on these results, lysimeter Expt 2 was undertaken on gravel mulched and unmulched bare soil lysimeters to assess the effectiveness of gravel mulch in partitioning ET into E and T using the Tanner and Sinclair (1983) method embedded in the soil water balance. In Expt 2, canola (Brassica napus L.) w...

Agronomy Journal, 2017

The study was performed to investigate the effect of water stress and duration of water stress at... more The study was performed to investigate the effect of water stress and duration of water stress at different growth stages on yield and yield components of glasshouse grown malt barley (Hordeum vulgare L.). The crop was grown for two seasons on lysimeters, and was subjected to water stress at different growth stages (Late tillering, Flag leaf, Anthesis, and Milk/Dough) from the beginning until the end of each growth stage. Yield and yield components focused on were number of plants per pot (NP), tillers without ear (TWE), full ears (FE), empty ears (EE), mass of grains of 10 ears, total biomass per pot (TBPP) and total grain per pot (TGPP). Irrespective of season, results show that water stress during different growth stages did not significantly affect NP and EE but had a significant effect on TWE and FE. Total grain per pot produced due to the effect of water stress at Anthesis (105.110 and 29.860 g) and Milk/Dough (100.350 and 51.680 g) growth stages were lower than that of the well-watered (177.570 and 99.310 g) for both seasons. Relative yield due to the effect of water stress confirmed that more yield will be lost per day if the crop experiences stress at Anthesis than other growth stages. This present an opportunity for improved management of irrigation scheduling for malt barley to maximize the period and level of irrigation water applications. Proper deficit irrigation during the Late tillering stage will help save water and reduce irrigation cost without significantly affecting grain yield.

Plants

Malt barley is typically grown in dryland conditions in South Africa. It is an important grain af... more Malt barley is typically grown in dryland conditions in South Africa. It is an important grain after wheat, but little is known about its water requirements and, most importantly, how it responds to water stress. Determining when water stress sets in and how malt barley responds to water deficit during its growing season is crucial for improved management of crop water requirements. The objectives of this study were to evaluate the response of transpiration (T), stomatal conductance (SC), and leaf water potential (LWP) to water stress for different growth stages of malt barley and to characterise water stress to different levels (mild, moderate, and severe). This was achieved by monitoring the water stress indicators (soil- and plant based) under greenhouse conditions in well-watered and water-stressed lysimeters over two seasons. Water stress was characterised into different levels with the aid of soil water content ‘breaking points’ procedure. During the first season, at the end o...

Agriculture, Ecosystems & Environment, 2016

Geoderma, 2014

Abstract Land degradation is recognized as a main environmental problem that adversely depletes s... more Abstract Land degradation is recognized as a main environmental problem that adversely depletes soil organic carbon (SOC) and nitrogen (SON) stocks, which in turn directly affects soils, their fertility, productivity and overall quality. While it is expanding worldwide at rapid pace, quantitative information on the impact of land degradation on the depletion of SOC and SON stocks remains largely unavailable, limiting the ability to predict the impacts of land management on the C losses to the atmosphere and associated global warming. The main objective of this study was to evaluate the consequences of a decrease in grass aerial cover on SOC and SON stocks. A degraded grassland showing an aerial cover gradient from 100% (Cov100, corresponding to a non-degraded grassland) to 50–75% (Cov75), 25–50% (Cov50) and 0–5% (Cov5, corresponding to a heavily degraded grassland), was selected in South Africa. Soil samples were collected in the 0.05 m soil layer at 48 locations along the aerial cover gradient and were subsequently separated into the clay + silt (2–20 μm) and sand (20–2000 μm) fractions, prior to total C and N analysis (n = 288). The decline in grass aerial cover from 100% to 0–5% had a significant ( P − 2 for SOC and 0.074 kg m − 2 for SON, which corresponded to depletion rates of 89 and 76%, respectively. Furthermore, both the C:N ratio and the proportion of SOC and SON in the silt + clay fraction declined with grass aerial cover, which was indicative of a preferential loss of not easily decomposable organic matter. The staggering decline in SOC and SON stocks raises concerns about the ability of these acidic sandy loam soils to sustain their main ecosystem functions. The associated decrease in chemical elements (e.g., Ca by a maximum of 67%; Mn, 77%; Cu, 66%; and Zn, 82%) was finally used to discuss the mechanisms at stake in land degradation and the associated stock depletion of SOC and SON stocks, a prerequisite to land rehabilitation and stock replenishment.

Agriculture, Ecosystems & Environment, 2015

Surface organic carbon enrichment to explain greater CO2 emissions from short-term no-tilled soils.

Physics and Chemistry of the Earth, Parts A/B/C, 2012

ABSTRACT Digital Soil Mapping (DSM) is widely used in the environmental sciences because of its a... more ABSTRACT Digital Soil Mapping (DSM) is widely used in the environmental sciences because of its accuracy and efficiency in producing soil maps compared to the traditional soil mapping. Numerous studies have investigated how the sampling density and the interpolation process of data points affect the prediction quality. While, the interpolation process is straight forward for primary attributes such as soil gravimetric water content (θg) and soil bulk density (ρb), the DSM of volumetric water content (θv), the product of θg by ρb, may either involve direct interpolations of θv (approach 1) or independent interpolation of ρb and θg data points and subsequent multiplication of ρb and θg maps (approach 2). The main objective of this study was to compare the accuracy of these two mapping approaches for θv. A 23 ha grassland catchment in KwaZulu-Natal, South Africa was selected for this study. A total of 317 data points were randomly selected and sampled during the dry season in the topsoil (0-0.05 m) for θg by ρb estimation. Data points were interpolated following approaches 1 and 2, and using inverse distance weighting with 3 or 12 neighboring points (IDW3; IDW12), regular spline with tension (RST) and ordinary kriging (OK). Based on an independent validation set of 70 data points, OK was the best interpolator for ρb (mean absolute error, MAE of 0.081 g cm-3), while θg was best estimated using IDW12 (MAE = 1.697%) and θv by IDW3 (MAE = 1.814%). It was found that approach 1 underestimated θv. Approach 2 tended to overestimate θv, but reduced the prediction bias by an average of 37% and only improved the prediction accuracy by 1.3% compared to approach 1. Such a great benefit of approach 2 (i.e., the subsequent multiplication of interpolated maps of primary variables) was unexpected considering that a higher sampling density (˜14 data point ha-1 in the present study) tends to minimize the differences between interpolations techniques and approaches. In the context of much lower sampling densities, as generally encountered in environmental studies, one can thus expect approach 2 to yield significantly greater accuracy than approach 1. This approach 2 seems promising and can be further tested for DSM of other secondary variables.

Geoderma, 2010

One of the most important challenges of digital soil mapping is the development of methods that a... more One of the most important challenges of digital soil mapping is the development of methods that allow the characterisation of large areas with a high-resolution. Surface soils, forming the largest pool of terrestrial organic carbon, may be able to sequester atmospheric carbon and thus mitigate climate change. However, this remains controversial, largely due to insufficient information on SOC stocks worldwide. One reason for this is the generally limited number of available data points, especially when large areas are considered, while another reason lies on the accuracy of interpolation techniques used for SOC mapping. The study was performed in Laos, a 230,566 km 2 area mostly forested and with steep slopes, and where soil data from 2806 pits is available. Our objective was to estimate SOC stocks to a depth of 1 m over the whole country while improving regional digital soil mapping (RDSM). SOC mapping by using purely spatial approaches of ordinary kriging (OK), inverse distance weighting (IDW) and regularized spline with tension (RST) was compared with the use of additional information on relief, climate and soils through co-kriging (OCK). The generation and validation data sets were composed of 2665 and 141 data points respectively. Overall, OCK using a multiple correlation with elevation above sea level, compound topographic index, mean slope gradient, average annual rainfall, and soil clay content (R 2 = 0.42; P level b 0.001) as covariate, yielded the most accurate predictions (19.7 kg C m − 2 with standard error of ± 3.2 kg C m − 2 ; and 4.54 ± 0.74 billion tons of SOC for Laos). The pure interpolation techniques were less accurate with 4.51 ± 1.02 billion tons of SOC for OK and 4.88 ± 0.94 billion tons of SOC for RST. Besides providing nationwide estimates of SOC stocks these results indicate that using collectively soil punctual information on SOC stocks and their interrelationships with controlling factors which are easy to gather might be an efficient way to improve RDSM.

Agricultural Water Management, 2011

Gully erosion is one of the main causes of soil loss in drylands. Understanding the dominant mech... more Gully erosion is one of the main causes of soil loss in drylands. Understanding the dominant mechanisms of erosion is important to achieve effective erosion control, thus in this study our main objective was to quantify the mechanisms involved in gully bank retreat as a result of three processes, falling of entire soil aggregates, transport of soil material by splash and by water running along gully banks (runoff), during rainfall events. The study was conducted in the sloping lands of the KwaZulu-Natal province, a region that is highly affected by gully erosion. Artificial rain was applied at 60 mm h −1 for 45 min at the vertical wall of a gully bank typical to the area. The splash material was collected by using a network of 0.045 m 2 buckets. The sediments in the running water were assessed by sampling the runoff collected from a microplot inserted within the base of the bank, and collecting the fallen aggregates after the rainfall simulation was complete. Results indicated that the overall erosion for the simulation was 721 g m −2 h −1. Runoff erosion proved to be the dominant mechanism and amounted to 450 g m −2 h −1 , followed by splash and fall down of aggregates (about 170 g m −2 h −1). Gully bank retreat occurred at a rate of 0.55 mm h −1 and assuming that the soil bulk density is 1.3 g cm −3 , this corresponds to a retreat of 8.8 mm y −1. Extrapolations to the watershed level, where about 500 m 2 of gully bank are observed per hectare, would lead to an erosion rate of 4.8 t ha −1 y −1. These limited results based on a simulated storm show that the three main mechanisms (runoff, splash and fall down of aggregates) are responsible for the retreat of gully banks and that to mitigate gully erosion, appropriate measures are required to control all three mechanisms. Further research studies are needed to confirm and to scale up, both in time and space, as these data are obtained at one location and from a single artificial storm.

Geoderma, 2016

World Resources Institute (2000), a relative increase of carbon (C) stocks in world soils by 0.4%... more World Resources Institute (2000), a relative increase of carbon (C) stocks in world soils by 0.4% per year would be sufficient to compensate all anthropogenic greenhouse gas emissions. Several land management practices such as the suppression of tillage in agroecosystems and livestock exclusion in grasslands had initially been thought to store more carbon into the soil, but recent research puts this into question. In a context where finding effective C sequestration methods is urgent, the main objective of this study was to assess the ability of an innovative grassland management practice based on high density and short duration (HDSD) grazing to sequester atmospheric C into soils. The study was performed in a degraded communal rangeland in South Africa where soil organic C (SOC) depletion ranged from 5 to 95% depending on the degradation level, which varied from non-degraded (ND; with grass above ground coverage, Cov of 100%), degraded (D1; 50 b Cov b 75%), D2 (25 b Cov b 50%) and HD (highly degraded: Cov b 5%). The ability of HDSD (1200 cows ha −1 for 3 days a year) to replenish SOC stocks was compared to four commonly used strategies: (1) livestock exclosure (E); (2) livestock exclosure with topsoil tillage (ET); (3) livestock exclosure with NPK fertilization (2:3:3, 22 at 0.2 t ha −1) (EF); (4) annual burning (AB); all treatments being compared to traditional free grazing control. A total of 540 soil samples were collected in the 0-0.05 m soil layer for all treatments and degradation intensities. After two years, topsoil SOC stocks were significantly increased under EF and HDSD, by an average of 33.4 ± 0.5 and 12.4 ± 2.1 g C m 2 y −1 , respectively. In contrast, AB reduced SOC stocks by 3.6 ± 3.0 g C m 2 y −1 , while the impact of E and ET was not significant at P b 0.05. HDSD replenished SOC stocks the most at D1 and D2 (6.7 and 7.4% y −1) and this was explained by grass recovery, i.e. a significant increase in soil surface coverage by grass and grass production. HDSD is cost-effective, and thus has great potential to be widely adopted by smallholder farmers.

Physics and Chemistry of the Earth, Parts A/B/C

With drought expected to increase in frequency and severity as a result of climate change, drough... more With drought expected to increase in frequency and severity as a result of climate change, drought and rainfall variability assessments at interannual time scales using long-term rainfall data are necessary to develop drought mitigation strategies and planning measures, especially in semi-arid and arid environments where drought impact is expected to be adverse. The objective of this study was to determine the occurrence and severity of droughts and interannual rainfall variability trends in the Ghaap plateau, Northern Cape Province, South Africa. This study was based on long-term rainfall data for three meteorological stations (Postmasburg, Douglas and Groblershoop) from 1918 to 2014, sourced from the South African Weather Services (SAWS). Calculation of the Standardized Precipitation Index (SPI) showed that more droughts occurred since the 1990s; these droughts were all moderately dry with SPI values ranging between −1.03 and −1.46, except for the 1992 drought at Groblershoop which was severe. The longest drought duration on record in the study area was 2 years. Fitting of the long-term rainfall data to a non-parametric spline smoother revealed that the total annual rainfall, number of rainfall days and extreme rainfall events were essentially stable. The total annual rainfall, however, followed a secular pattern of fluctuations over the years.