Cosmas Parwada

Soil properties influencing erodibility of soils in the Ntabelanga area, Eastern Cape Province, South Africa

ABSTRACT Soil erosion has serious off-site impacts caused by increased mobilization of sediment and delivery to water bodies causing siltation and pollution. To evaluate factors influencing soil erodibility at a proposed dam site, 21 soil samples collected were characterized. The soils were analyzed for soil organic carbon (SOC), exchangeable bases, exchangeable acidity, pH, electrical conductivities, mean weight diameter and soil particles’ size distribution. Cation exchange capacity, exchangeable sodium percentage, sodium adsorption ratio, dispersion ratio (DR), clay flocculation index (CFI), clay dispersion ratio (CDR) and Ca:Mg ratio were then calculated. Soil erodibility (K-factor) estimates were determined using SOC content and surface soil properties. Soil loss rates by splashing were determined under rainfall simulations at 360 mmh−1 rainfall intensity. Soil loss was correlated to the measured chemical and physical soil properties. There were variations in soil form properties and erodibility indices showing influence on soil loss. The average soil erodibility and SOC values were 0.0734 t MJ−1 mm−1 and 0.81%, respectively. SOC decreased with depth and soil loss increased with a decrease in SOC content. SOC significantly influenced soil loss, CDR, CFI and DR (P < .05). The soil loss rate was 5.60 t/ha per 8 minute rainstorm of 360 mmh−1. Addition of organic matter stabilize the soils against erosion.

The nature of soil erosion and possible conservation strategies in Ntabelanga area, Eastern Cape Province, South Africa

ABSTRACT Soil erosion is a major land degradation problem in South Africa (SA) that has economic, social and environmental implications due to both on-site and off-site effects. High rates of soil erosion by water are causing rapid sedimentation of water bodies, ultimately leading to water crisis in SA. Lots of financial and human resources are channelled towards controlling of soil erosion but unfortunately with little success. The level of soil erosion in a particular area is governed by the site properties. Therefore, it is inappropriate to generalize data on soil erosion at a large-scale spatial context. The literature on soil erosion in SA classifies Eastern Cape Province as a high-erosion-potential area using data collected at a large-scale spatial context. Collecting soil erosion data at a large spatial scale ignores site-specific properties that could influence soil erosion and has resulted in failure of many traditional soil erosion control measures applied in the province. Moreover, scientific principles underlying the processes and mechanisms of soil erosion in highly erodible soils are missing in SA. This review was to find effective soil erosion control measures by having an insight on what happens during soil erosion and how soil erosion occurs in Ntabelanga. The literature suggested that erosion in Ntabelanga could be influenced by both the erosivity and erodibility factors though the erodibility factors being more influential. Soil permeability contrast between the horizons could be influencing the rate and nature of soil erosion. To mitigate the impact of soil erosion in Ntabelanga, efforts should aim to improve the vertical flow capacity in the B horizon. Clay spreading, clay delving, addition of gypsum, deep ploughing and mulching could aid the water permeability problems of the subsurface horizons. However for effective soil management and control option, detailed studies of specific site properties are needed. The generated information can assist in formulating soil erosion policies and erosion control strategies in the Ntabelanga area and SA at large.

Effects of litter source on the dynamics of particulate organic matter fractions and rates of macroaggregate turnover in different soil horizons: Stabilization of intraparticulate organic matter

Soil texture influences the transformation of soil organic matter (SOM), and depletion and reduction in the number of macroaggregates. However, the extent of changes in SOM in response to its quality and mechanisms of stabilization in different types of soil texture is unclear. We evaluated changes in SOM during a 30‐week incubation experiment using seven soils mixed with two sources of litter; Vachellia karroo (Hayne) Banfi & Galasso leaf and Zea mays L. stover. We hypothesized that changes in intraparticulate organic matter (iPOM) are influenced by litter quality • soil type • time interactions, which affect rates of turnover of macroaggregates. A completely randomized design was used in arranging soil jars in the incubator. Free light fractions and coarse and fine iPOM within macroaggregates (>250 μm) decreased exponentially from week 1 to 30 and were significantly (P < 0.05) affected by litter source • soil horizon • time interactions. Trends of changes in fine iPOM fractions were the same in macroaggregates and microaggregates (P < 0.05). The greatest changes in POM fractions occurred 8 weeks after litter incorporation. Both V. karroo leaf and Z. mays stover stabilized macroaggregates during the first 8 weeks after incubation; thereafter they lost their influence. Therefore, we needed to reapply fresh litter after this period. Changes in iPOM fractions and macroaggregate turnover were specific to a soil type, suggesting that different sources of litter have different stabilizing effects in macroaggregates. Soil macroaggregate stabilization and changes in iPOM could be used as indicators to apply more appropriate management practices for soil protection or productivity. HIGHLIGHTS: Does the source of organic matter affect transformation rates of different intraparticulate organic matter in the soil? Degradation of organic matter into very fine particulate matter also increases the rate of turnover of macroaggregates. Soil type • litter source interactions greatly influenced the rate of transformation from coarse to fine intraparticulate fractions. Effects of litter quality on dynamics of POM fractions in aggregates and macroaggregate turnover were horizon specific.