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Soil and vegetation play a vital role in the global C cycle because C exchange is affected by both. Thus a change in land use may result in either a loss or gain of C in the soil-plant system. This study was conducted in the Weatherley catchment in the northerly Eastern Cape Province, a former grassland area. Approximately half of the 160 ha in the catchment was afforested with three tree species, viz. P. elliottii, P. patula, and E. nitens in 2002. Before afforestation, a baseline study (Le Roux et al., 2005) on soil organic matter was conducted on the areas designated for the above mentioned tree species. Therefore, this study was a continuation of the mentioned study with the aim to quantify the soil and biomass C stocks (in some instances N stocks also) eight years after afforestation. For comparable purposes the same 27 sites studied by Le Roux et al. (2005) were investigated, viz. 25 afforested sites and two control sites. Soil samples were collected in 2010 at various depths from the 27 sites: 0-50, 0-100, 0-150, 0-200, 0-250, 0-300, 0-400, 0- 500, 0-600, 0-700, 0-800, 0-900, 0-1000, 0-1100, and 0-1200 mm and analysed for organic C and total N as organic matter indices. At each site, three sub-samples were taken per depth interval and mixed together to give a composite sample. The procedure was replicated four times at each site. At each of the 27 sites, fallen litter and undergrowth were collected simultaneously with the soil sampling, also in four replicates. After being dried in a glasshouse, the litter was milled and analysed for C and N contents. A year after soil and litter sampling, when trees were eight years old, the height and diameter at breast height of 12 trees were measured at each of the 25 afforested sites. The measured data were used to calculate the utilisable stem volume, and hence the tree C stocks. Afforestation of the former grassland areas influenced soil organic matter in the upper 300 mm layer, resulting in either increases or decreases in soil C stocks, N stocks and C:N ratios. Soil C stocks decreased by 0.9 Mg ha-1 at site 235 (Katsptuit soil with grass) to 23.6 Mg ha-1 at site 232 (Katspruit soil with P. elliottii trees). The rate of decrease ranged between 0.11 and 2.95 Mg C ha-1 yr-1. The soil C stocks increased by 0.9 Mg ha-1 at site 244 (Pinedene soil with P. patula trees) to 11.3 Mg ha-1 at site 242 (Longlands soil with P. patula trees). The rate of increase ranged from 0.11 Mg C ha-1 yr-1 to 1.41 Mg C ha-1 yr-1. Soil C stocks decreased significantly by 5.5 Mg ha-1, 10.0 Mg ha-1, and 12.4 Mg ha-1 for grass, E. nitens, and P. elliottii areas, respectively. Soils under P. patula showed an increase in C stocks of 1.9 Mg ha-1. When soils were grouped according to mapping units, drainage classes or first subsoil (B1 or E1) horizons there was generally a significant decrease in soil C stocks due to afforestation. The soil N stocks to a large extent behaved like the soil C stocks. The aboveground biomass C stocks were obtained by adding the litter C stocks and the tree C stocks together. These aboveground biomass C stocks varied from 3.71 Mg ha-1 at site 209 (Katspruit soil with grass) to 167.2 Mg ha-1 at site 246 (Pinedene soil with E. nitens trees). On average the aboveground biomass C stocks for the 27 sites was 64.9 Mg ha-1. However, aboveground biomass C stocks averaged 69.7 Mg ha-1 for the 25 afforested sites and only 4.8 Mg ha-1 for the two control sites. The aboveground biomass C stocks varied significantly from 4.8 Mg C ha-1 for the grass to 41.2 Mg ha-1 for the P. elliottii and 67.3 Mg ha-1 for the P. patula and 113.2 Mg ha-1 for the E. nitens areas. Based on the soil mapping units, aboveground biomass C stocks varied from 45.6 Mg ha-1 for the C soil group to 83.3 Mg ha-1 for the A soil group. In the drainage class soil group, the aboveground biomass C stocks varied significantly from 44.1 Mg ha-1 for the poorly drained soils to 81.8 Mg ha-1 for the moderately drained soils and 74.4 Mg ha-1 for the freely drained soils. The aboveground biomass C stocks varied significantly from 44.7 Mg ha-1 for the G horizon soils to 86.2 Mg haâ1 for the red apedal B horizon soils. In general, the tree C stocks contributed the greatest portion to the aboveground biomass C stocks, which in turn contributed more to the total C stocks in the catchment. The C (undifferentiated hydromorphic), poorly drained, and G horizon soil groups had the lowest aboveground biomass C stocks because the conditions in these soil groups limited tree growth and hence C sequestration. Total C stocks in the catchment before afforestation were estimated to be 7 209 Mg. After eight years of afforestation C stocks were estimated to be 11 912 Mg. Therefore the trees added 4 702 Mg C to the catchment, at a rate of 588 Mg C yr-1 or 3.67 Mg C ha-1 yr-1. The rate of C sequestration in the afforested areas was 7.74 Mg ha-1 yr-1.

This study was undertaken to determine the effect of different concentrations of phosphate, ammonium, nitrate, and sulphate as well as that of shading and moisture stress on oil yield and quality of hydroponically grown rose geranium. Five separate trials were conducted during the 2009 and 2010 growing seasons. Different concentrations of phosphate, ammonium, nitrate and sulphate were used in the first four trials, while the last study focused on the effects of shading and moisture stress on rose geranium. The phosphate, nitrate, ammonium and sulphate trials were conducted in a greenhouse at the west campus of the University of the Free State in Bloemfontein, South Africa. Plants were grown for four months using a randomized complete block experimental design. The concentrations of phosphorus evaluated were 0.10, 0.80, 1.50 and 2.20 meq L-1. Ammonium concentrations were 0.00, 0.50, 1.00 and 1.50, nitrate concentrations were 8, 10, 12 and 14 and sulphate concentrations were 0.36, 1.90, 3.44 and 4.98 meq L-1. Foliar drymass and oil yields increased as P concentrations were increased to 2.20 meq L-1. Both, the guaia-6,9-diene content and the citronellol:geraniol (C:G) ratio were better at the high level of phosphate indicating that the best quality oil, as required by the perfume industry is obtained with relatively high phosphate concentrations. Plant growth as measured by the number of branches and biomass production, peaked at 10 to 12 meq L-1 nitrate concentrations. The highest chlorophyll content in the foliage was found at the nitrate concentrations of 10 and 12 meq L-1, where the best oil yield was also produced. At this nitrate level the citronellol:geraniol (C:G) ratio was slightly higher than the upper limit required for good oil quality but the geraniol and citronellylformate contents were within range for top quality oil. Height, biomass, oil yield and chlorophyll content of the leaves were not affected by ammonium, but the concentrations of plant tissue sulphur and nitrogen increased linearly with increasing concentrations of applied ammonium. Rose geranium needs to be grown at a relatively high nitrate concentration (10 to12 meq L-1) to ensure high oil yield. This application falls within the range that is used for most vegetable and ornamental crops under soilless conditions. Ammonium concentrations of up to 1.00 meq L-1 can be used without affecting yield or oil quality of rose geranium. A significant effect of sulphate on branches, height and branch:height (B:H) ratio and foliar dry mass (DM) was observed. The four sulphate concentrations showed a statistically non significant trend on yield. Based on the standards used by the perfume industry the oil of rose geranium was not of a good quality in this trial probably due to the autumn planting time. Shading and moisture stress were used as treatments in a study conducted at the University of the Free State experimental farm during spring and summer. A split plot experimental layout was assigned using 0%, 20%, 40%, 60% and 80% shade treatments allocated to the main plots. The subplots were exposed to moisture stress levels at 0 and -0.15 MPa of osmotic pressure. Rose geranium grew well under a shading of 40%, where plant growth parameters such as foliar fresh mass (FM), foliar dry mass (DM) and the branch:height ratio were increased. Subsequently the best oil yield was obtained at this level. Proline content was high due to excessive solar radiation at 0% shade as well as where moisture stress was induced, however, oil quality was not affected. The number of oil glands cm-2 of leaf area was not significantly affected by shading, but tended to be lower at shading levels higher than 60%. Fresh mass, DM, the ratio of branches to height and oil yield were affected by shading. Proline content gave a clear indication of stress conditions of plants at full radiation as well as moisture stress. Growers are advised to use 40% shading to grow geraniums in summer at radiation levels similar to those found in this study.

In crop production phosphorus (P) is an essential nutrient for crop growth, and hence P fertilization is necessary to achieve optimum yields. However, this can induces in soil a P concentration which may contributes to eutrophication of fresh water bodies. Soil P tests are therefore considered very useful in setting threshold values important for both agronomic and environmental management purposes. Soil P tests developed from a water pollution protection point unlike agronomic P tests are not easily adapted for use on a routine basis because they are not considered, for this purpose, and this could make agronomic P tests more practical for routine environmental P assessment also. Determination of appropriate agronomic P tests for this purpose however, involves evaluating the potential use of the tests for environmental purposes. Hence, the objective of this study was to review the current methods used to determine the agronomic and environmental P status of soils, and to establish whether P extracted from a range of soils by various agronomic and/or environmental P determination methods are related or not. Soil samples from the orthic A horison were collected in three cropping areas in the Free State province, namely Jacobsdal, Bloemfontein, and Ficksburg. These samples were treated with K2HPO4 to induce different phosphorus concentration levels and then incubated at room temperature for three months. During incubation the samples were subjected to several wetting and drying cycles to ensure that the applied phosphorus equilibrated. The samples were then analysed for P using the extractants of Olsen, Bray 1, Truog, ISFEI and citric acid commonly employed for routine analysis to establish the agronomic P status of soils. In order to establish the environmental P status of the soils, the samples were analysed for using the extractants calcium chloride (CaCl2) and ammonium oxalate [(NH4)2C2O4.H2O]. The latter was used to calculate the degree of phosphorus saturation (DPSox). The results showed significant relationships among agronomic P tests when data of individual soils were analysed separately (r2=0.65-0.99) and, when data of all soils from a sampling area were pooled (r2=0.52-0.87). All the relationships were significant for the Ficksburg soils (r2â¥0.55) and for the Bloemfontein soils (r2â¥0.82) but not for the Jacobsdal soils. For the latter soils the Truog-P correlations with Olsen-P (r2=0.44), Bray 1-P (r2=0.42) and ISFEI-P (r2=0.35) were not significant, probably due to that they are calcareous. Significant relationships were also obtained for P extracted by the environmental P tests when regression analysis was done for each individual soil (r2â¥0.80). However, when data of soils from a sampling area were pooled significant relationships were obtained for Bloemfontein soils (r2=0.92) and Ficksburg soils (r2=0.56) while Jacbosdal soils (r2=0.33) showed an insignificant relationship. Pooling data of all soils from the three sampling areas also resulted with a lower correlation coefficient (r2=0.40) implying a poor relationship between the environmental P tests. The correlation between P extracted by the agronomic tests and CaCl2-P showed positive relationships (r2 â¥0.57) except in a few instances. Truog-P and citric acid-P showed a poor correlation with CaCl2-P when the Jacobsdal soilsâ data were pooled (r2=0.22 and 0.35 respectively). Pooling of all soilsâ data resulted also in a poor correlation between CaCl2-P and Truog âP (r2= 0.28). The DPSox correlated significantly with the extractable P of all agronomic tests when the individual soilâs data were analysed separately (r2 â¥0.73). However, when data of all soils from a sampling areas were pooled for regression analysis, all relationships were significant for the Bloemfontein soils (r2 â¥0.70), but not for the Jacobsdal soils, and Ficksburg soils. Pooling data of all soils from the three sites resulted with a positive relationship between DPSox and the extractable P of all agronomic tests (r2 â¥0.50), except ISFEI (r2 â¥0.45). The threshold values estimated for agronomic tests with regression equations from CaCl2-P DPSox threshold values varied greatly between individual soils and even the soils groups of a sampling area. The threshold values for all soils when based on CaCl2 implied that if the extractable P status of cropped soils are maintained at optimum levels for Bray 1, Truog, ISFEI and citric acid the soils may be a threat to water pollution. The opposite is true with the estimated threshold values when based on DPSox. The results therefore showed that agronomic tests can be used also for environmental management of P although only the Olsen test showed the potential for developing a single threshold value for all soils.