Browsing by Author "Rietz, Diana Nicolle."

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The effects of burning or mulching of harvest residues on selected soil properties in a Eucalyptus plantation in Northern KwaZulu-Natal.
(2014) Madikizela, Siphamandla.; Hughes, Jeffrey Colin.; Titshall, Louis William.; Rietz, Diana Nicolle.; Podwojewski, Pascal.
The sustainable management of commercial forest resources is required to ensure long-term soil fertility and the productivity of later rotations; this includes soil nutrient retention and the protection of soil structure. A major factor in the protection of soil structure is the distribution of soil organic carbon (SOC) and nutrients, as well as the stability of soil aggregates. These are influenced by forest harvest residue management practices such as the removal, displacement on the soil surface, or burning of residues. Soil aggregate stability is an important soil property that gives a reliable estimation of the ability of soils to respond to external forces such as rainfall, wind, and land management. The objectives of the study were to investigate the effect of forestry residue management methods on selected soil properties and their effect on soil structural stability under the previous stump-line and in the current inter-row. The results obtained from the study will contribute to understanding the effects of forest harvest residue management on some soil properties. The study site was near Paulpietersburg, northern KwaZulu-Natal, South Africa. A trial was established by the Institute for Commercial Forestry Research (ICFR) in 2010 to investigate the effect of tree harvest residue management, soil compaction and its amelioration through ripping, on the growth of Eucalyptus dunnii grown on a Magwa soil form. This trial has a factorial treatment design and consists of three soil disturbance treatments (no compaction, compaction, and compaction with amelioration) and two residue management practices (burning and residue mulching), with four replicates (24 treatment plots). The effect of burning and mulching harvest residue on selected soil properties and soil aggregation in relation to other soil properties was studied two years after the treatments were established. For the purposes of the present study, the no-compaction treatment and both residue management treatments (burning and mulching) were used (eight plots). Bulk samples, 192 in total, were collected from each of the eight plots, from both the current inter-row and the old stump-line, at a depth of 0 to 0.1 m and 0.1 to 0.2 m using a spade. Samples were air dried and sieved to collect soil aggregates between 2 and 8.5 mm for soil aggregate stability determinations by determination of the mean weight diameter (MWD). Some of the bulk sample was analysed for SOC, pH, exchangeable bases (Ca2+, Mg2+, K+, and Na+), and particle size distribution. Statistical analyses were carried out using Genstat and the results were regarded as significant if p < 0.05 (or 5%). Residue management had no significant (p ≥ 0.05) effect on exchangeable Mg2+, K+, and Na+, soil pH, exchangeable acidity, effective cation exchange capacity and texture. There was, however, a significant effect of residue management on SOC and exchangeable Ca2 Ca2+. Under the mulched plot treatment, SOC at the 0 to 0.1 m depth was significantly higher in soils when compared to the burned plot treatment. Under the burned plot treatment, exchangeable Ca2+ concentrations were significantly higher than the mulched treatment. Furthermore, under the burned plot treatment; exchangeable Ca2+ and Mg2+ concentrations were significantly higher in the 0 to 0.1 m depth than at the 0.1 to 0.2 m depth. Neither residue management strategy had any significant effect on MWD. However, there was a significant effect on MWD relating to soil depth and sampling position. Under both treatments, the MWD was higher at 0 to 0.1 m than at the 0.1 to 0.2 m depth, in both inter-row and stump-line samples. The average MWD of 2.45 mm (with a standard error of 0.04) and values that ranged between 0.8 and 3.5 mm was indicative of stable aggregates. Thus, surprisingly, no significant correlation was found between SOC and MWD. However, it was concluded that changes in residue management may alter SOC, thus impacting on the productivity of the soil. Furthermore, it was suggested that soil aggregate stability was driven by exchangeable Ca2+ and Mg2+.
Effects of irrigation-induced salinity and sodicity on soil chemical and microbial properties and sugarcane yield.
(2001) Rietz, Diana Nicolle.; Haynes, Richard John.
The effects of irrigation-induced salinity and/or sodicity on sugarcane yield, and two growth parameters, namely stalk height and number of nodes per stalk , were investigated on a sugarcane estate in the Zimbabwean lowveld. The effects of soil salinity and/or sodicity on the size, activity and metabolic efficiency of the soil microbial community was also studied. Furrow-irrigated fields which had a gradient in soil salinity and/or sodicity which increased from the upper to lower ends of the fields were selected for this study. This gradient was recognized by decreasing sugarcane growth down from the upper to the lower ends and the appearance of salt on the soil surface at the lower ends of fields. Sugarcane growth was classified as either dead, poor, satisfactory or good; and soil samples (0-0 .15 m, 0.15-0 .3 m, 0.3-0 .6 m and 0.6-0.9 m) were taken from each of these areas. Soils from under adjacent areas of undisturbed veld were also sampled. Sugarcane growth and yields in micro-plots of the various areas of the fields were measured. Foliar samples of sugarcane were taken at 22 weeks of age and analysed for nutrient content. Soil salinity and sodicity were quantified by measuring pH(water), electrical conductivity (ECe) and cation content of saturation paste extracts and the exchangeable cation content. From this information, the sodium adsorption ratio (SARe)and exchangeable sodium percentage (ESP) were also calculated. The calcareous, vertic soils in the study area under undisturbed veld were found to have high pH values (8 to 9.5), very high exchangeable Ca and Mg concentrations and there was evidence of accumulation of soluble salts in the surface 0.15 m. Under sugarcane production, irrigation induced salinity and sodicity had developed. Under poor and dead sugarcane, high values for ECe, SARe, and ESP were generally encountered in the surface 0-0 .3 m of the profile. In addition, the pH values under sugarcane were often between 9 and 10 particularly in profiles where sugarcane grew poorly or had died. As expected, pH was positively related to ESP and SARe, but negatively related to ECe. Measurements of aggregate stability by wet sieving, the Emerson dispersion test and the Loveday dispersion score all showed that soils from the study sited tended to disperse and that dispersion was most apparent where high ESP and SARe values occurred in association with elevated pH values and relatively low ECe values. These measurements confirmed observations at the sites of low infiltration rates and restricted drainage particularly on the lower ends of fields where sugarcane had died. In addition to the above measurements it was also observed that there was a rise in the watertable under furrow irrigation and that the watertable was nearest to the surface at the lower ends of the fields. In some cases the watertable was observed to be only 0.2 to 0.3 m from the surface. Thus, death of roots due to anaerobic conditions could be occurring to a greater extent at the lower ends of the fields. Another consequence of the high watertable was that these vertic soils were observed to remain in a permanently swollen state. This limits air and water movement in the soil profile as such soils need to be allowed to dry out and crack regularly so that macroporosity can be restored. Sugarcane yield, stalk height and number of nodes per stalk were not significantly related to ECe. Sugarcane yields were, however, significantly correlated with ESP and pH while stalk height and number of nodes were negatively correlated with ESP, SARe and pH. These results suggested that sodicity was a more limiting factor for sugarcane growth than salinity. Foliar analysis of leaf tissue did not reveal substantial differences in macro- or micro-nutrient content between good and poorly-growing sugarcane. It was concluded that the gradient of decreasing sugarcane growth down the furrow-irrigated fields, with crop death at the lower ends, was the result of a combination of factors. That is, the watertable had risen due to over-irrigation and it was nearer the surface at the lower ends of the fields. Due to capillary rise of salts, this resulted in sodic and sometimes saline-sodic conditions in the surface soil. These conditions could limit plant growth through ion toxicities, plant water stress and inhibition of root growth and function and physiological processes. These would be induced by the high pH and high salt, Na and HC03- concentrations in soil solution. Poor physical conditions associated with sodicity and the continually swollen state of the soils presumably limited infiltration and aeration in the surface soil, and probably restricted root growth. In addition, it is likely that the high watertable limited effective crop rooting depth to about 0.2 m at the lower ends of the fields. The net result was that sugarcane died at the lower ends. A negative effect of soil salinity and/or sodicity was also observed on the soil microbial population. Significant negative correlations were obtained with ECe SARe and ESP with microbial biomass C and microbial activity (as measured by FDA hydrolytic activity or arginine ammonification rate). The activity of enzymes involved in C (P-glucosidase), P (phosphatase) and S (arylsulfatase) mineralization and potential nitrogen mineralization (as determined by aerobic incubation) were also negatively correlated with these factors, with the exception of arylsulfatase activity and ESP. All the above mentioned microbial population measures were also positively correlated with soil organic C content, besides potential nitrogen mineralization. The metabolic quotient, which provides an indication of stress and efficiency of the microbial community, increased considerably with increasing salinity and sodicity and decreased with soil organic C. Thus, increasing salinity and/or sodicity resulted in a smaller, more stressed, less efficient microbial community, while the turnover rate and cycling of C, N, P and S also decreased. It was concluded that salt affected soil not only causes a decline in sugarcane yield through raising the concentration of soluble salts in soil solution, but also has a detrimental effect on microbial activity and on mineralization of soil organic C, N, Sand P.
The effects of compaction and residue management on soil properties and growth of Eucalyptus grandis at two sites in KwaZulu-Natal, South Africa.
(2010) Rietz, Diana Nicolle.; Hughes, Jeffrey Colin.; Smith, Colin William.
Concerns have been raised over the long-term site productivity (LTSP) of short rotation plantation forests, such as those of Eucalyptus, in South Africa. This is because diminished productivity of long rotation plantations overseas has been found to be generally due to decreases in soil porosity and organic matter. Since soil porosity and organic matter in plantations are mainly affected by soil compaction by harvesting machinery and residue management, the more frequent harvesting of short rotation plantations are of particular concern. Therefore the effects of soil compaction and residue management on soil properties at two sites, one a low organic carbon, sandy soil (Rattray), the other a high organic carbon, clay soil (Shafton) were investigated. The potential of early E. grandis productivity as an indicator of changes in soil properties at these sites was also evaluated. Three different levels of compaction (low, moderate and high) were applied to the sites by three methods of timber extraction, i.e. manual, logger and forwarder loaded by a logger, respectively. Three types of residue management, i.e. broadcast, windrow and residue removal were also applied. A factorial treatment design was used to ensure a resource-efficient study that allowed separation of main and interaction effects. Various soil physical and chemical properties were measured at intervals from before treatment implementation, until approximately 44, and 38 months after treatment implementation at Rattray and Shafton, respectively. Trees were planted at a commercial espacement at both trials, and their growth monitored over the same time period. In addition, to accelerate early growth, negate silvicultural variation, and determine changes in stand productivity with treatments, a portion of the treatment plots were planted at a very high density and harvested when these trees reached canopy closure at about six months of age. Moderate and high compaction treatments at both sites resulted in significant increases in penetrometer soil strength, and often in bulk density. Increasing residue retention decreased the compaction effects of machinery and, generally, increased the total quantity of nutrients contained in residues and soil. Changes in soil bulk density and organic matter as a result of the treatments in turn affected soil water characteristics, generally decreasing plant available water capacity with increasing compaction intensity and residue removal. Tree growth measurements showed that at both sites, tree productivity was negatively affected at some point by increasing compaction. In contrast, residue management only significantly affected tree growth at Shafton, initially increasing and later decreasing growth with residue removal. These variations in tree growth over time in response to treatments are most likely a result of changes in tree characteristics that occurred with age. In addition, trees did not always reflect changes in soil properties that may affect LTSP, most likely because these soil properties had not yet reached levels that would affect tree growth. It was therefore concluded that early tree growth is not always a good indicator of changes in LTSP, and that soil properties are a more reliable indicator. Plantation management practices that lead to soil compaction and residue removals will negatively impact LTSP in South Africa. However, variable responses of the two soils indicate that soils vary in their sensitivity to compaction and residue management. This therefore needs to be quantified across a range of major soil types in the South African forestry industry.