The Impact of Land Degradation on the Quality of Soils in a South African Communal Rangeland

Grassland productivity of communal rangelands is limited by land degradation, which leads to nutrient depletion, soil fertility decline and overall soil quality. However, little is known as to what the soil quality threshold is for different degradation intensities. To address this, we selected a 0.05 m surface soil layer of a communal rangeland site in Drakensburg, South Africa, exhibiting a degradation gradient varying from heavily degraded (0–5%, grass aerial cover), moderately degraded (25–50%) and non-degraded (75–100%) grasslands, to evaluate the effects of land degradation on soil aggregate stability, compaction, bulk density and texture. Results indicate that land degradation decreased soil aggregate stability by 47%, increased soil compaction by 42% and increased soil bulk density by 12%, and these were accompanied by a pattern of lower sand and almost two times greater clay content in heavily degraded grassland compared with non-degraded grassland. Ultimately, this decline in the soil quality of the communal rangeland has serious implications for the ecosystem services and functions it provides, such as storing water, carbon sequestration and nutrient cycling. We recommend the protection and improvement of grass vegetation because of its dense sward characteristics, which intercept raindrop energy, slow surface runoff and increase the structural stability of the soil to minimize and prevent degradation in rangelands

Utilisation of Intrinsic and Extrinsic Soil Information to Derive Soil Nutrient Management Zones for Banana Production in a Smallholder Farm

In South Africa (SA), smallholder farmers contribute significantly to food production and play an essential role in the nation’s food and nutritional security. However, there is a lack of basic understanding of the spatial variability of soil nutrients and their controlling factors in these smallholdings, which subsequently hinders their agricultural production. In this work, we assessed the spatial variability and structure of key soil nutrients required by banana fruit, identified their factors of control, and delineated management zones in a smallholder farm. We used a regular grid (50 m × 50 m) to collect a total of 27 composite samples from the 0–30 cm depth interval and analysed for soil physicochemical properties. Our classical statistics results indicated that phosphorus (P), potassium (K), calcium (Ca) and zinc (Zn) varied highly, while magnesium (Mg) and total nitrogen (TN) varied moderately across the plantation. On the other hand, geostatistics revealed that P and K were strongly spatially dependent (implying a good structure), while Mg and Zn were moderately spatially dependent (indicating a moderate structure) across the banana plantation. Soil Ca and TN contents were found to be weakly spatially dependent (meaning there was no structure) across the farm. The spatial prediction maps showed that P, Mg and Zn contents were high in the northeast part (underlain by Valsrivier) and low in the northwest part (underlain by Westleigh) of the banana plantation farm. Similarly, K and Ca were low in the northwest part (underlain by Westleigh), but they were high in the south to southwest portion (underlain by Glenrosa) of the farm. Soil TN was high in the west part (underlain by Westleigh) and low in the east-northeast part (underlain by Valsrivier) across the plantation. Three management zones (MZs) were delineated for soil P, K and Ca, while for other nutrients (Mg, Zn and TN), two MZs were delineated. The results of this study provide baseline information for site-specific management of fertilisers to supplement soil nutrients in the field to improve banana productivity

Potential of grassland rehabilitation through high density-short duration grazing to sequester atmospheric carbon

International audienc

Overgrazing decreases soil organic carbon stocks the most under dry climates and low soil pH: A meta-analysis shows

International audienc

Land degradation impact on soil organic carbon and nitrogen stocks of sub-tropical humid grasslands in South Africa

International audienc

Characterisation and Effects of Different Levels of Water Stress at Different Growth Stages in Malt Barley under Water-Limited Conditions

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 of tillering, flag leaf, and milk/dough growth stages, which represent severe water stress, plant available water (PAW) was below 35%, 56%, 14%, and 36%, respectively. LWP responded in accordance to depletion of soil water during the growing season, with the lowest recorded value to −5.5 MPa at the end of the milk/dough growth stage in the first season. Results also show that inducing water stress resulted in high variability of T and SC for both seasons. In the second season, plants severely stressed during the anthesis growth stage recorded the least total grains per pot (TGPP), with 29.86 g of grains. The study suggests that malt barley should be prevented from experiencing severe water stress during the anthesis and milk/dough stages for optimum malt barley production. Quantification of stress into different levels will enable the evaluation of the impact of different levels of stress on the development, growth, and yield of barley

In-field assessment of soil pH and mineralization of phosphorus and potassium following the application of composted winery solid waste in sandy loam Ferric Luvisol

Special attention on the plant nutrients mineralization rates is often required when organic fertilizers are used on croplands. This study described the patterns of phosphorus (P) and exchangeable potassium (K) released from winery solid waste (WSW) compost in sandy loam soil. Treatments consisted of equivalent rates of 0, 5, 10, 20 and 40 t ha-1 of compost-soil mixture in Ziplock bags buried on the field at 30 cm soil depth. Destructive sampling of treatments was conducted at 0, 7, 21, 42, 63, 84, 105 and 126 days after incubation (DAI) for laboratory analysis. The 40 t ha-1rate resulted in up to a 9.5% increase in soil pH while the contents of net mineralized P and K measured were significantly affected by compost rate and incubation period interaction. Over the 126 days of the incubation period that runs across summer and winter seasons, mineralized P ranged from -62 to 86 mg kg-1 whereas mineralized K varied between 41 and  2047 mg kg-1. Cumulative mineralized P and K contents ranged from 62 to 207 mg kg-1 and 1272 to 9206 mg kg-1, respectively with the highest amount obtained at the 40 t ha-1 compost rate. The high net P and K mineralized contents suggest that WSW compost may act as a P and K source. However, cautious use of WSW compost as a soil amendment is recommended to mitigate the potential risks of soil pH increases and other unintended consequences such as toxicity, nutrient imbalance, and possible P and K antagonistic effects.Keywords: Compost; Nutrient mineralization; Phyto-toxicity; Soil amendment

In-field assessment of soil pH and mineralization of phosphorus and potassium following the application of composted winery solid waste in sandy loam Ferric Luvisol

Special attention on the plant nutrients mineralization rates is often required when organic fertilizers are used on croplands. This study described the patterns of phosphorus (P) and exchangeable potassium (K) released from winery solid waste (WSW) compost in sandy loam soil. Treatments consisted of equivalent rates of 0, 5, 10, 20 and 40 t ha-1 of compost-soil mixture in Ziplock bags buried on the field at 30 cm soil depth. Destructive sampling of treatments was conducted at 0, 7, 21, 42, 63, 84, 105 and 126 days after incubation (DAI) for laboratory analysis. The 40 t ha-1rate resulted in up to a 9.5% increase in soil pH while the contents of net mineralized P and K measured were significantly affected by compost rate and incubation period interaction. Over the 126 days of the incubation period that runs across summer and winter seasons, mineralized P ranged from -62 to 86 mg kg-1 whereas mineralized K varied between 41 and  2047 mg kg-1. Cumulative mineralized P and K contents ranged from 62 to 207 mg kg-1 and 1272 to 9206 mg kg-1, respectively with the highest amount obtained at the 40 t ha-1 compost rate. The high net P and K mineralized contents suggest that WSW compost may act as a P and K source. However, cautious use of WSW compost as a soil amendment is recommended to mitigate the potential risks of soil pH increases and other unintended consequences such as toxicity, nutrient imbalance, and possible P and K antagonistic effects.Keywords: Compost; Nutrient mineralization; Phyto-toxicity; Soil amendment

Seasonal dynamics of soil CO2 emissions from different semi-arid land-use systems

ABSTRACTSoil carbon dioxide (CO2) fluxes are a critical component in understanding carbon sequestration. In sub-Saharan Africa, empirically measured CO2 emissions data from diverse land-use systems is limited. Soil CO2 emission rates were measured in the Limpopo Province, South Africa for 12 months at two-week intervals in natural systems (forest and shrubland) and commercially managed orchards (avocado and citrus) to establish seasonal dynamics of soil CO2 emissions across these land-use systems. The results showed a variation in emission rates with the variation depending on the season. In the spring and winter, soil CO2 emission rates in citrus were four times higher than in the shrubland due to higher moisture levels. However, in the summer season, the forest emission rates were 40% higher than in citrus due to higher soil organic carbon content. Organic carbon stocks were higher in the forest (1.19 kg/m2) compared to the other land uses. This study revealed differences in soil CO2 emission rates among land-use systems, with the cumulative amount of CO2 emitted over a 12-month period following the order: forest (39.3 tons/ha) > citrus (36.1 tons/ha) > shrubland (28.1 tons/ha) > avocado (26.9 tons/ha). Thus, understanding the emission patterns from various ecosystems can inform strategies for mitigating greenhouse gas emissions