South African Journal of Plant and Soil - latest Issue
Volumes & issues
Volume 33, Issue 4, 2016
The role of proline and root traits on selection for drought-stress tolerance in soybeans : a reviewSource: South African Journal of Plant and Soil 33, pp 245 –256 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1148786More Less
Drought stress is a major limiting factor in soybean production. It reduces both the yield and its components. This is dependent on the level and occurrence of drought stress with respect to the growth stages of the plants. Breeding for drought stress tolerance can sustainably reduce the impact of drought stress. However, occurrence of drought stress is irregular over locations and seasons, making selection for drought tolerance challenging. Effort is being put into using proline accumulation as a measure to monitor stress tolerance of higher plants. It is evident that proline accumulates with increased drought stress. Genotypic differences exist in proline accumulation among soybean cultivars of different sensitivities to drought stress. There is a positive correlation between stress-induced proline accumulation and drought tolerance. The capacity of root traits to explore spatial domains with limited water and their ability to dynamically respond to soil-water deficit are also being investigated as indicators for drought stress tolerance. Root traits response to available soil water is a heritable trait and genotypic variation is evident in soybeans. This paper reviews the effects of drought stress and advances in the use of proline accumulation and root traits as selection tools for drought tolerance in soybean.
In pursuit of a South African national soil database : potential and pitfalls of combining different soil data setsSource: South African Journal of Plant and Soil 33, pp 257 –264 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1141249More Less
A national soil profile database will be a huge asset to South Africa, enabling improved soil information products to be created. However, numerous practical pitfalls exist in reliably creating such a database. This project aimed to identify such pitfalls, while showing the potential of a larger database. During a 2014 South African Soil Surveyors Organisation (SASSO) workshop in Cathedral Peak, 10 groups of soil surveyors were tasked to describe at least five profiles. The data from the groups were treated as different data sets, which needed to be merged into one SASSO database. Pitfalls to merging the data sets included mis-classification of soils due to incomplete laboratory data, incorrect soil morphology description and incorrect soil description methodology. Furthermore, analysis by different laboratories and methods yielded dissimilar soil property values, while different data dictionaries collected diverse information. However, the enlarged database enabled the creation of a soil map that was more accurate than one created with a smaller, previously collected data set. A minimum set of criteria should accompany all data sets, including the soil surveyor's name, the data collection date, the GPS position, the laboratory where the samples were analysed, and the analysis method with its standard error.
Physical and hydrological properties of peatland substrates from different hydrogenetic wetland types on the aputaland Coastal Plain, South AfricaSource: South African Journal of Plant and Soil 33, pp 265 –278 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1141334More Less
The Maputaland Coastal Plain in KwaZulu-Natal province is home to 60% of all peatlands occurring in South Africa. These ecosystems are increasingly threatened by unsustainable agricultural utilisation, a growing population and climate change. The aim of the study was, therefore, to investigate wetland type characteristic substrates and their physical properties in order to provide more detailed knowledge about the agricultural impact on them. Six study sites were selected and detailed profile descriptions as well as in situ measurements of different physical and hydrological soil parameters were conducted. Soil samples were analysed with laboratory measurements of the saturated hydraulic conductivity, water retention characteristics and hydrophobicity. In addition, the bulk density as well as the organic carbon content were determined. Saturated hydraulic conductivity, hydrophobicity and total water retention capacity were highest for peat derived from wood, which furthermore presented the lowest bulk densities and was found to occur only in channelled and unchannelled valley-bottom wetlands and was absent in interdunal depression wetlands. It was concluded that drainage and clearance of forested valley-bottom wetlands has severe impacts on the physical peat properties. Potential subsidence of low-density peat and consolidation aggravate the danger of flooding and hydrophobicity increases the generation of surface runoff and subsequently the risk of erosion.
Effect of cultivar, season and locality on lipid content and fatty acid composition of cactus pear seed oilSource: South African Journal of Plant and Soil 33, pp 279 –228 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1141335More Less
Opuntia ficus-indica (cactus pear) seeds are rich in linoleic acid and have beneficial properties for nutritional, industrial and pharmaceutical purposes. The total lipid content and fatty acid composition depends on various factors, including cultivar, degree of maturity, climate, harvesting season as well as agricultural practices. The aim of this study was to conduct a comprehensive seed oil quality analysis by investigating variation among cultivars across locations over two seasons. Seed oil content and fatty acid content, as well as the ratios thereof, differed among cultivars, seasons and locations. Cultivar x location x season interactions were significant for oil content. Levels of oleic acid (C18:1c9) were significantly influenced by the cultivar x location interaction. Mono-unsaturated fatty acid content was significantly influenced by cultivar x location and location x season interactions. Oil content was significantly correlated with levels of palmitic acid (C16:0), stearic acid (C18:0) and oleic acid. The cultivars 'Van As', 'Turpin', 'Roedtan' and 'Meyers' showed good associations with oil content and C18:1c9, while Bloemfontein was the most stable location.
Quantification of primary salinity, sodicity and alkalinity in South African soils using climate regionsSource: South African Journal of Plant and Soil 33, pp 289 –296 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1147089More Less
No reliable primarily salinity, sodicity and alkalinity information is available for South Africa, nor are there monitoring programs in place to track the salt-affected status of South African soils. Such information is, however, needed for various agricultural and environmental studies on a provincial and national scale. Natural geological, hydrological, geomorphological and pedological processes lead to the development of most salt-affected soils. The aim of the study was therefore to determine the baseline salinity, sodicity and alkalinity of South African soils as related to selected climatic parameters. Soil analyses from the Agricultural Research Council-Institute for Soil, Climate and Water (ARC-ISCW) soil survey database were used in this study. Data from the ARC-ISCW and the South African Weather Service weather stations with a recording period of five years or more were used to determine temperature, rainfall and evaporation statistics. The aridity index (precipitation/evaporation) was used to express aridity. No clear relationship was observed between rainfall, evaporation, and aridity and salt accumulation on a national scale and other factors, such as geology, position in the landscape and previous climatic conditions, should also be accounted for. The relationship between climate and salt-affected soils was difficult to determine, probably because of the paleoclimate differing from the present climate. Thus, not all salt-affected soils showed predictable associations with present-day climate.
Effect of integrated soil bunds on key soil properties and soil carbon stock in semi-arid areas of northern EthiopiaSource: South African Journal of Plant and Soil 33, pp 297 –302 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1148788More Less
Land degradation is a serious global problem. To reclaim degraded land, many soil bunds have been implemented. However, their effectiveness has not been studied in all regions of Ethiopia. The objective of this study was to investigate the effect of soil bunds integrated with tree fodder species on selected soil properties and carbon stock in semi-arid areas of northern Ethiopia. Twenty-seven composite soil samples were collected from 20 cm depth. The soil parameters texture, soil organic matter (SOM), total nitrogen (TN), pH, cation exchange capacity (CEC),available phosphorus (Av.P) and available potassium (Av.K) were analysed. Statistical analyses were performed using one-way ANOVA and mean comparisons were made using Tukey's honestly significant difference test. Mean values of SOM (2.13%, 1.47% and 0.85%), CEC (150.42, 100.58 and 80.68 cmol kg-1 soil), TN (0.2, 0.14 and 0.08%),Av.P (7.08, 6.03 and 4.36 ppm), Av.K (1.52, 1.34 and 1.27 cmol kg-1 soil), soil carbon stock (SCS; 12.48, 10.47 and4.7 t ha-1) and soil bulk density (BD; 1.35, 1.43 and 1.44 g m-3) were recorded in soil bunds integrated with foragespecies (ISB), soil bunds alone (SB) and non-conserved cultivated land (NC), respectively. The BD, SOM, CEC,TN and SCS showed a significant difference among the three cropland treatments and Av.P showed a significant difference only between (ISB and SB) and NC. The pH showed no significant differences and Av.K showed no significant difference between SB and NC. The findings indicate that integrating soil bunds with forage species was a better option to improve soil properties than soil bunds alone.
Author Sheunesu RuwanzaSource: South African Journal of Plant and Soil 33, pp 303 –308 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1155765More Less
Lantana camara is an invasive plant in South Africa with a wide range of impacts. This study assessed the impact of L. camara invasion on the soil seed bank. The study asked the question, does species density and diversity of soil seed banks differ between L. camara invaded and uninvaded sites? The study was conducted over a 10-month period under greenhouse conditions using soils collected from five L. camara invaded and uninvaded sites that were located between Port Alfred and East London in the Eastern Cape province of South Africa. The study measured species density, diversity and identified seedlings that germinated in trays containing soils from invaded and uninvaded sites. Species density and diversity were lower in L. camara invaded sites compared with uninvaded sites, an indication that L. camara invasion has the potential to deplete the soil seed bank of other species. The study concluded that L. camara invasion reduces the soil seed bank community composition and structure.
Variations on soil carbon dioxide flux with land-use type and selected soil properties in the hardveld of BotswanaSource: South African Journal of Plant and Soil 33, pp 309 –916 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1161091More Less
The dynamics of carbon dioxide (CO2) flux in the hardveld regions of Botswana are poorly understood, with previous studies having concentrated on sandveld and pan environments. In particular, soil organic carbon (SOC) has a positive influence on CO2 emissions to the atmosphere. To examine the effects on soil CO2 flux of land use,namely conventional tillage, horticultural and grazing land uses, measurements were carried out in sites having similar climatic conditions. To enhance the understanding of soil carbon dynamics in these typical land uses, an investigation on the influence of soil pH, moisture content, organic carbon and temperature on CO2 flux rates was carried out. The results showed a relatively stronger dependence of CO2 flux rates on soil temperature for conventional tillage (R 2 = 0.71) and grazing (R 2 = 0.56) compared with horticultural land use (R 2 = 0.05). High SOC content in the grazing and horticultural land uses was due to increased oxidation of organic matter following soil disturbance. High organic matter turnover was probably from animal wastes and plant decomposition. Similarly, a decrease in CO2 flux with pH in the conventional tillage and grazing land uses suggests there is clear potential for these land uses to become carbon sources depending on the acidity of the soil.
Tillage and crop rotation effects on carbon sequestration and aggregate stability in two contrasting soils at the Zanyokwe Irrigation Scheme, Eastern Cape province, South AfricaSource: South African Journal of Plant and Soil 33, pp 317 –324 (2016) http://dx.doi.org/http://dx.doi.org/10.1080/02571862.2016.1163424More Less
Intensive tillage and monocropping have adversely affected the quality of soils in South Africa through accelerated loss of soil organic matter. Two clay loam soils, a Bonheim at Burnshill and a Shortlands at Lenye, at the Zanyokwe Irrigation Scheme in the Eastern Cape province were used to evaluate the short-term effects of tillage and croprotations on carbon sequestration and aggregate stability under sprinkler-irrigated crop production. A split-plot arrangement of treatments in a randomised complete block design was used with tillage as the main plots and croprotations as subplots. Conventional tillage (CT) was compared to no-till (NT) under maize-fallow-maize (MFM), maize- wheat-maize (MWM) and maize-oat-maize (MOM) rotations. Carbon sequestration was monitored by measuring changes in soil organic carbon (SOC) and the stability index (SI) was used for monitoring aggregate stability. No-till had inconsistent effects on SOC relative to CT but resulted in improved soil SI on both soils, especially on the Shortlands soil. The MOM rotation enhanced SOC relative to the MWM and MFM rotations on both the Bonheim and Shortlands soils. Across tillage practices, the MOM rotation significantly increased the soil aggregate SI compared with the MWM and MFM rotations on the Shortlands and to a lesser extent on the Bonheim soils. Scanning electron microscopy revealed that soil aggregates under MOM had dense organic coatings and bridges compared with the MFM rotation, indicating the positive effect of carbon sequestration on aggregate stability. Generally, the results indicated that, in the short term, cover crops, especially oats, have greater influence on SOC accumulation and aggregate stability than tillage, irrespective of soil type.