Soil sustainability is a long-term goal. Although physical and chemical properties of soil have been utilized extensively to evaluate soil quality, the application of biological indicators is becoming more important. In order to assess soil quality, soil enzymes and other biological parameters need to be considered. In semi-arid Bethlehem, South Africa, samples were taken at a wheat (Triticum aestivum L.) monoculture trial which was established in 1979 by the Agricultural Research Council-Small Grain Institute. The treatments were: no-tillage (NT), stubble-mulch (SM), and conventional tillage (CT); all paired with chemical weed control, the absence of burning residues, and 40 kg nitrogen ha-1 as limestone ammonium nitrate with single superphosphate as the fertilizer sources. The study period lasted from October 2010 to October 2011 with eight sampling times conducted over this year and two depths sampled (0-5 cm, 5-10 cm). Oat (Avena sativa L.) was growing in the plots from the start of the study until December 2010 when it was harvested. A fallow period then lasted until the planting of wheat in August 2011 which was harvested after the end of the study period. Potential enzyme activities were assayed for β-glucosidase, urease, acid- and alkalinephosphatase, and dehydrogenase at all eight sampling times, along with soil texture, total carbon, total nitrogen, Olsen-extractable phosphorus, and pH. Whole microbial community profiling using BIOLOG EcoPlatesTM was employed at the first sampling time and phospholipid fatty acid (PLFA) analysis for the first, third, and fifth sampling times. It was found that NT and SM had higher values than CT across all enzymes except alkaline phosphatase, which ranked NT higher than both SM and CT. BIOLOG EcoPlatesTM and PLFA showed similar results across tillage treatments. Microbial biomass, estimated from both potential dehydrogenase activities and PLFA values, was higher in NT and SM than in CT. Over the study period the values for all parameters varied but the average ranking of tillage treatments stayed consistent. In comparing the two soil depths, soil quality was easily shown to be higher in NT and SM in the 0-5 cm depth, but often in the 5-10 cm depth the differences faded. Potential acid phosphatase activity was the only measured parameter which was consistently higher in the 5-10 cm depth. If the parameters can be used as an index of soil quality, then it can be accepted that NT has higher quality than CT and often SM has higher quality than CT, but is not at the same level as NT; it can then be recommended that in semi-arid South Africa, NT will enhance soil quality under a monoculture cropping practice.

For each grain production system, there is an optimum row spacing and plant density that optimises the use of available resources, allowing the expression of maximum attainable grain yield in that specific environment. Introduction of the ultra-fast maize hybrids raised the question whether existing guidelines for row spacing and plant density were still applicable. This necessitated the integration of optimum row spacing by plant density to maintain productivity and sustainability the yields with the intention to increase water use efficiency. Field experiments were conducted for two successive cropping seasons (2008/9 to 2009/10) at Kenilworth Experimental Station of the Department of Soil, Crop and Climate Sciences, University of the Free State to evaluate the growth, agronomic performance, phenological development and water use efficiency of an ultra-fast maize hybrid at varying row spacing and plant densities under irrigation. The treatments involved in this study were three row spacings (0.225, 0.45 and 0.90 m) and five plant densities (50 000, 75 000, 100 000, 125 000 and 150 000 plant ha-1). The treatments were arranged in a factorial combination and laid out in a randomized complete block design (RCBD) with four replications. The largest block was used for periodic destructive sampling for growth analysis where a completely randomized design was adopted and replications consisted of five (5) single plants randomly selected. Regarding soil water monitoring, twenty neutron probe access tubes were installed prior to planting in the center of each plot in one of the three blocks of the agronomic study. Soil water content was measured at 0.3 m intervals to a depth of 1.8 m using a calibrated neutron probe. Measurements were made at weekly intervals from planting to crop physiological maturity where the volumetric reading was converted into depth of water per 1.8 m. Seasonal ET (water use) was determined by solving the ET components of the water balance equation. From this water use efficiency was computed as the ratio of total biomass/grain yield to seasonal ET. In each season crop growth, agronomic, phenologic and water use efficiency parameters were measured and the collected data were combined over seasons after carrying the homogeneity test of variances. Growth parameters, agronomic traits, phenology and water use efficiency of maize reacted differently to row spacing and plant density and the combination thereof. In general a slow increase in growth parameters during establishment was followed by an exponential increase during the vegetative phase. At the reproductive phase growth ceased following the onset of flowering. Photosynthetic efficiency (NAR) and CGR, averaged over row spacing, were highest at a plant density of 100 000 plants ha-1 at all growth phases. Reducing row spacing from 0.45 to 0.225 m and a plant density below or above 100 000 plants ha-1 showed LAI outside the optimum with respect to NAR for optimum seed yield. Row spacing, plant density and its interaction affected yield and yield components of maize significantly. Narrowing rows from 0.45 to 0.225 m and plant densities above 100 000 plants ha-1 as main or interaction effects led to the formation of smaller ears, a shorter ear length and diameter, low seed mass, favored plant lodging and development of barren plants with an obvious negative impact on grain yield. On other hand, plant densities below 100 000 plants ha-1 were insufficient to utilise growth-influencing factors optimally. Thus, growth analysis provided an opportunity to monitor the main effects and interaction effects of row spacing and plant density on crop growth at different growth and development phases. Row spacing and plant density combinations affected the phenological development of maize. Increasing row spacing from 0.225 to 0.90 m relatively prolonged the number of days to anthesis and silking. Regarding anthesis-silking interval (ASI), the lowest plant density had the shortest ASI while the higher plant densities had relatively longer ASI. Wide row spacing coupled with low plant density increased the number of days to physiological maturity and vice versa. Row spacing and plant density and their interaction affected water use efficiency of maize. Highest water use was observed at a plant density of 125 000 plants ha-1. Biomass WUE was highest at a row spacing of 0.45 m with a plant density of 125 000 plants ha-1 while the highest grain yield WUE recorded was at a row spacing of 0.45 m with a plant density of 100 000 plants ha-1. The overall combined effect of row spacing and plant density revealed that a combination of 0.45 or 0.90 m with 100 000 plants ha-1 to be the optimum for the selected ultra-fast maize hybrid under irrigation.

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Amaranthus (Amaranthus spp) and pearl millet (Pennisetum glaucum [L.] R. Br.) are drought tolerant crops with much potential that has not been well exploited as they can be cultivated under semi-arid climatic conditions. This study was carried out to characterize their water use and model their growth and yield in response to water. Experiments were carried out under a field line source sprinkler irrigation system for both crops for two seasons, as well as in a greenhouse with a pot experiment for amaranthus and in the lysimeter facility for pearl millet studies, each for one growth cycle. One genotype of amaranthus (Amaranthus crentus ex Arusha) and two lines of pearl millet (GCI 17, improved line and Monyaloti, local variety) were used in the trials with these crops in a semi-arid area near Bloemfontein, South Africa. The influence of water application on growth of amaranthus was contrary to the expectation that fully irrigated plants will perform better than the plants receiving less water. Fully irrigated plants produced shorter plants with less leaves and branches. However, irrigation improved the plant height in both lines of the pearl millet. A large amount of irrigation resulted in taller plants for both lines while the shortest plants were found in the rainfed plots. Another millet crop parameter that was affected by irrigation was flower emergence. Flower emergence was earlier in irrigated plots of both lines of pearl millet and during the two seasons. In both lines of pearl millet, irrigation increased leaf area index and biomass accumulation during both seasons. The two crops were able to exhibit the ability to tolerate water stress with different coping mechanisms and this influenced their water uptake and invariably also water use. Amaranthus was able to manage water stress in rainfed plots through the closure of stomata in the field and during the pot trials. Stomatal closure reduces water loss as a response to water deficit in the soil-crop-atmosphere continuum. Daily water use of amaranthus ranged from 1.2 to 6.5 mm day-1 while the seasonal water use was 437 mm for the first season and 482 mm for the second season. Higher water use in the second season was attributed to higher atmospheric evaporative demand recorded during the second amaranthus growing season compared to the first. It was observed that while water application can increase the production of amaranthus, it should also not be too much or it could have a detrimental effect on biomass production of the crop. This conclusion is due to the fact that the lowest irrigated plots produced higher fresh and dry mass of amaranthus during both seasons while production in the fully irrigated plots was low for the two seasons. The response of pearl millet to water deficit stress was to lower the leaf water potential (more negative) and also gradually decrease the leaf stomatal conductance. Pearl millet demonstrated a response to the water stress condition by closing of the stomata as leaf water potential declined (towards more negative) so as to conserve water and prevent water loss. This minimized water loss through transpiration when the soil water available is limited. The crop adjusted to severe water stress conditions by maintaining a leaf water potential that keeps the leaf turgid in order to avoid wilting when the stomata closes so as to prevent excessive water loss. The daily evapotranspiration of the two lines of pearl millet for the two seasons were between 2 and 8 mm day-1 for the first season and 1 and 6 mm day-1 for the second season. The difference could also be attributed to a higher atmospheric evaporative demand in the first pearl millet growing season than the second season. Overall, the improved (GCI 17) and the local variety (Monyaloti) of pearl millet had water use of 309 and 414 mm in 2008/2009 season. The water use for the two lines was higher in the 2009/2010 season with GCI 17 having water use of 401 mm and Monyaloti 457 mm which was probably due to high availability of water. High soil water content coupled with a higher amount of rainfall in the second season than the first season could be the reason for difference of the water use of the two lines of pearl millet for the two seasons. However, the water use of the plants of the two lines of pearl millet from the rainfed plots and water stressed treatments showed that the crop was able to reduce water use under water stress conditions as a coping mechanism and hereby increase water use efficiency of the crop. With the aid of the data from the field experiment, greenhouse and lysimeter trials, calibration and validation of AquaCrop crop model was performed successfully for both crops. Simulation of biomass production and cumulative evapotranspiration of both crops were performed adequately. The good performance in simulating these crop parameters were illustrated with a high index of agreement that was higher than 0.9 except for 2 cases of CC excluding the soil water comparisons. However, it was observed that more effort is needed to accurately simulate early canopy cover in amaranthus and also the soil water content and depletion patterns for both crops. Following successful validation, the model was also applied to predict the performance of both crops under a range of proposed planting dates and choice of varieties in pearl millet as possible adaptation strategies under two climate change scenarios. The model was able to predict the production of the two crops under predicted climate change for the period between the year 2046 and 2065 and the most appropriate adaptation strategy as a recommendation is to delay planting for two months until the first half of January for both crops under the two future climate change scenarios (A2 and B1). In conclusion, the two crops under investigation can adjust to water limited conditions but through different mechanisms. Amaranthus can avoid water stress through restricting growth, while the pearl millet crop escapes water stress through speedy completion of growth stages before the water stress condition sets in. It was also revealed that there are possibilities of cultivating these crops in central South Africa. However, more studies should be carried out on the effect of interaction of nutrient and irrigation on amaranthus production to reveal the reasons for the unexpected response of amaranthus to water application. Studies on root development of the two crops are hereby recommended to aid in accurate simulation of water balance of the two crops in the field situations. The calibration and validation of AquaCrop for these two crops can also be improved by using datasets of more varieties or genotypes of the crops and from other agro-ecological regions. In general, underutilised crops provide means of food security and source of income for farmers. Due to the fact that they are drought tolerant, they require minimum amount of input which is a desirable quality for low resource farmers and can be used as alternative crops in semi-arid areas.

Food production in semi-arid areas principally depends on the availability of water. Consequently, improving rainwater productivity and modifying the available energy for unproductive water losses is an important and necessary step towards promoting rainfed agriculture in dryland farming. It has been convincingly argued that water management strategies on rainfed semi-arid areas, including in-field rainwater harvesting (IRWH) deserve considerable attention. However, integrated studies of water and energy balance on the IRWH technique in particular in optimizing runoff to basin area ratio and mulching levels (ML) was not comprehensively appraised. Therefore, in this thesis, the two main research questions concern: (i) what is the optimal runoff to basin area ratio to sustain maize crop yield? and (ii) how do the microclimatic conditions change under wide and narrow runoff strip length (RSL)? Field experiments were conducted (2007/08 and 2008/9) on the Kenilworth Bainsvlei ecotope, associated with high evaporative demand of 2294 mm per annum and relatively low and erratic rainfall (528 155.6 mm). Topographically the area had a gentle slope (< 1%) with reddish brown in colour (Amalia family) a fine sandy loam texture soil, thus was classified as a Bainsvlei form. The soil is regarded as very suitable for dryland agriculture, because it is deep (2000 mm) and drains freely in the top and the upper sub-soil. So the study was performed by quantifying and evaluating the soil-crop-atmosphere parameters. In the first part of the thesis, the soil water balance components and different efficiency parameters were assessed. In the second part of the thesis, the micrometeorological variable profiles within and above the maize canopy for the heat and water vapour exchange processes were characterized. Furthermore, comparison of available energy for evapotranspiration (ET) was evaluated for both wide and narrow runoff strips through the quantification of energy balance components. A multiple regression model was developed to predict in-field runoff by combining the effects of rainfall event characteristics and surface treatments. From the results of runoff-rainfall (RR) ratio a lower efficiency was observed from full mulch covered wide runoff strip length (RSL-3) i.e. only about 4% of the rainfall, while the highest mean RR was about 27% from bare, narrow RSL- 1. From the estimation of rainfall canopy interception (RCI) it was revealed that the highest interception was in the range of 4.5% to 9.0% of the precipitation. The RCI capacity of a maize field under IRWH reached a plateau at about 0.5 â 0.6 mm for narrow RSL and 1.0 â 1.1 mm for wide that would be evaporated eventually from the canopy. Furthermore the cumulative Es (ΣEs) was evaluated as influenced by both mulch (âdry-mulchâ) and shading (âgreen-mulchâ) effects. Thus, the proportion of water loss by Es from seasonal rainfall is about 62%, 64% and 66% in the bare treatments and as low as 28%, 30% and 32% for full mulch cover treatments under full shade, (FC), partial canopy shaded (PC) and unshaded (UC) respectively. This implies that, reduction of runoff and evaporation losses through surface treatments can promote improved water use efficiency, of the stored available water in the root zone and thus, enhance yield. The final grain yield decreased slightly as an order of increasing the length of the runoff strip. The performance of the harvest index (HI) was slightly variable among the treatments due to more water for yield being collected from bare plots than mulch covered plots. The higher mulch conserves much water by suppressing the soil evaporation. In expressing grain yield per unit ET (WUEET) and transpiration, Ev (WPEv) the RSL-2 m and RSL-1.5 m at lower mulch cover showed significant higher values than RSL-1 and RSL-3 treatments. However, the transpiring water for yield and unproductive evaporation losses more under IRWH should be evaluated in terms of micrometeorological profile characterization and available energy. With regard to micrometeorological variables, the growth stage had a strong effect on the vertical profiles of climatic variables. In wide runoff strips lapse conditions extended from lowest measurement level (LP) to the upper middle section (MU) of the canopy and inversion was apparent at the top layer (UP) of the canopy. The reason for the extension of temperature inversion into the upper part of the wide RSL canopy was as a result of higher air movements compared to narrow strips. From this result it was confirmed that the effect of wind on water vapour removal decreased downward from wind flow within the canopy. This had an influence on the resistance of the boundary layer and canopy and soil surface resistance. This is a clear indication that wide strips supply more drying power to respond to evaporative demand of the atmosphere compared to narrow strips. From the measurement of profiles within and above the canopy, it was suggested that, the presence of local advection in the wide runoff strips of IRWH could be a common phenomenon causing variations in water vapour removal under the heterogeneous nature of IRWH tillage system. Thus, profile characteristics within and above a plant canopy are playing a great role in determining the vapour pressure deficit and consequently, can explain the ET rate. Therefore based on micrometeorological measurements, results indicated that the latent heat (LE) was dominant and higher in wide compared to narrow runoff strips (RSL) under both dry and wet conditions. However, sensible heat (Hs) showed lower values on wide runoff strips during wet conditions due to the advective effect of the runoff area. Thus, the wide runoff strip with a higher basin leaf area ratio (BLAR) of 2.43 had higher ET and used more energy in evaporating water than the narrow runoff with a lower BLAR of 1.42. Wide runoff strips converted the higher available energy more efficiently into a higher biomass production. During wet days, the wide RSL used more than 70% of the available energy for evapotranspiration, while the narrow RSL response to the available energy (63%) was stronger during dry compared to wet days. In general the wide and narrow RSL used the available water and energy differently during dry and wet conditions under IRWH system. From this experiment finding, important implications were described such as better yield obtained from narrow RSL-1, however RSL-1.5 and 2 m with minimum mulch cover gave higher water productivity compared to narrow RSL-1 and wide RSL-3. On the other hand when quantifying and evaluating the cause behind the effect of available energy, the wide RSL converted available energy more efficiently into higher biomass production than the narrow RSL. Therefore, this challenge should be addressed on the basis of an integrated approach to water and energy resources in order to develop comprehensive management strategies. Furthermore, for improved rainwater use management strategies, it is recommended to link an integrated approach of water and energy resources with crop growth simulation models. The application of the crop models could be important by incorporating a range of planting dates and densities along with the selection of surface treatment management strategies

No description available.

Wildfires are a natural phenomenon that strongly impacts the environment. Many terrestrial ecosystems depend on fire to maintain their ecological equilibrium and biodiversity, but new destructive fire patterns, often associated with land management practices and rapid climate change, have been degrading soil and water resources, increasing erosion by wind, precipitation and floods, decreasing biodiversity and contributing to desertification. Furthermore, pyrogenic emissions from biomass burning are an important source of atmospheric pollution and they impact the radiative balance of the troposphere, strongly contributing to the greenhouse effect. The objective of this research was to investigate the impact of climate variability on geographic, ecological, seasonal and inter-annual distributions of fires and correspondent pyrogenic emissions, across a variety of ecosystems. With this purpose, 10 years of world, monthly, 1°x1° gridded data, from the Global Fire Emissions Database, were compared with land-cover data, from the Goddard Institute of Space Studies, and with weather data, from the European Centre for Medium Range Weather Forecasting, the Global Precipitation Climatology Centre and the Global Hydrology Resource Centre. Overall, the climate parameters significantly correlated with carbon emissions were air and soil temperature, air and soil humidity, rainfall, wind speed and lightning density during the fire season, and also precipitation and snow cover up to 6 months before the fire season. Good statistical quantitative models of carbon emissions (correlations above 70%, and up to 95%, between estimated and predicted values, with residuals normally distributed) using humidity, temperature or lagged rainfall as predictors, were found almost exclusively in tropical grasslands, shrublands and woodlands, especially in Africa, where fire behaviour was more regular. In boreal and temperate forests and woodlands, where fire patterns were irregular and fire returning periods were larger, there were not enough fires, in 10 years of data, to obtain useful predictive statistical models. The fire models presented here, together with the quantitative statistical relationships found between climate and fire patterns, in different land ecosystems, are apt to be used in predictive climate models, land management, fire risk assessment and mitigation of climate change.

The climate is changing and the rate of this change is expected to increase. In the 20th century global surface temperatures rose by 0.6 (±0.2) K. Based on current model predictions, and economic forecasts, global temperature increases of 1.4 to 5.8 K are expected over the period 1990 – 2100. One of the main drivers for this temperature increase is the build up of CO2 in the atmosphere which has been increasing since pre-industrial times. Pre-industrial concentrations of CO2 were bounded between 180 ppm and 300 ppm, however the current concentrations of 380 ppm are far in excess of these bounds. Further more, forecasts indicates that a further doubling in the next century is a distinct possibility. However making predictions about the future climate is difficult. Predicting the trajectory that the climate will take uses assumptions of economic growth, technological advances and ecological and physical processes. If we are to make informed decisions regarding the future of the planet, we have to account not only for future anthropogenic emissions and land use, but we also have to identify the response of the Earth system. By its very nature the Earth is immensely complex; processes, interactions and feedbacks exist which operate on vastly different spatial and temporal scales. Each of these processes has an associated level of uncertainty. This uncertainty propagates through models and the processes and feedbacks they simulate. One of our jobs as environmental scientists is to quantify and then reduce these uncertainties. Consequently it is critical to quantify the interactions of the land-surface and the atmosphere. The role of the land-surface is critical to the response of the Earth’s climate. All general circulation models and regional scale models need representations of the land-surface. A lot of the work concerning the land-surface aims to determine the land-surface partitioning of energy, the evapotranspiration of water and if the land-surface is a sink or a source of CO2. To do achieve this we need to understand (1) the underlying processes governing the response of the land-surface, (2) the response of these processes to perturbations from climate change and humans, (3) the temporal and spatial heterogeneity in these processes, and (4) the feedbacks that land-surface processes have with the climate. In this thesis I use a coupled atmosphere-biosphere model to show current understanding of the carbon, water and energy dynamics of the biosphere and the atmosphere to be consistent with both PBL and stand-based measurements. I then use the CAB model to investigate the strength of different feedbacks between the atmosphere and biosphere. Finally the model is then used in a Monte Carlo Bayesian inversion scheme to invert atmospheric measurements to infer information about surface parameters.

This work has contributed to the understanding of dominant runoff generation at the large catchment scale and to the understanding of the relationships between landscape properties and hydrological behaviour. The developed models were used to estimate the climate change impact on the hydrology in the study catchment. A multivariate geochemical tracer survey was carried out in North Esk catchment in north east Scotland. A generic typology was developed using multivariate statistical methods to characterise the hydrochemical tracer response. Upland headwater runoff was dominant downstream in winter and provided significant flows during base flow periods in summer. These insights were complemented by a conjunctive analysis of long-term river flow data and a one year stable isotope survey. Integrative metrics of transit times, hydrometric responses, and catchment characteristics were explored for relationships at the large catchment scale. The evaluation that the associated soils and bedrocks, themselves controlling the flow path distribution, have a strong influence on the integrated hydrological catchment response. The empirically-based understanding of dominant runoff generation processes in the North Esk uplands and lowlands were used in a stepwise rainfall-runoff model development. Tracers were directly incorporated to reduce structural and parameter uncertainty. The integration of tracers helped reduce parameter uncertainty. These tracer-aided models increased confidence for using them to explore the effects of environmental change. Climate change impacts in the catchment where explored by forcing the models with projected climate change forcing from the UK Climate Projections 2009. The results revealed landscape-specific changes in the hydrological response with increased summer drought risk in the lowlands and diminishing snow influence and increased winter floods in the uplands. The spatial integration mediated the extremes observed in the subcatchments.

Adaptation to past changes in the climate of Britain may be indicative of the way in which society will respond to future climate change. The long run costs associated with climate change are, once full adaptation has occurred, not obviously detrimental. Furthermore even if the frequency of 'extreme events' such as floods and storms increases it is not apparent that these will necessarily be as detrimental to society as they currently might seem since society in effect chooses its exposure to extreme events. Some extreme events such as hard frosts are likely to decrease in frequency. The thesis uses the theory of hedonic prices to examine the role of climate variables in explaining differences in average residential land prices and wage rates relating to 127 English and Welsh counties, Scottish regions, metropolitan areas and London boroughs. Substantial evidence is found in favour of the hypothesis that compensating land price differentials exist for climate variables. An alternative approach to estimating amenity values is to argue that households respond in part to differing levels of environmental amenities by altering their patterns of consumption. This phenomenon can be given a 'Household Production Function' interpretation. Given the assumption of 'demand dependency' between climate variables and marketed commodities it is possible to determine the amenity value of climate change from market data. Using cross country data for 60 countries the analysis points unambiguously to the existence of a 'climatic optimum'. The hedonic technique can also be used as a means of determining the value to British agriculture of a marginal change in climate. In the hedonic approach sale price differentials between land characterised by different climates is given an interpretation in terms of underlying productivity differences. Data characterising over 400 separate transactions in farmland is analysed and the value of marginal changes in climatic variables computed. The analysis suggests that the financial value of climate variables to farmers could in some cases be quite high and also that changes in seasonal patterns and the frequency of 'extreme events' are quite important. The impact of climate change on the chosen destinations of British tourists is also investigated. Destinations are characterised in terms of various 'attractors' including climate variables, travel costs and accommodation costs. Together these variables are used to explain the observed pattern of overseas travel in terms of a model based on the precept of utility maximisation. This approach permits the changes in consumer surplus following climate change to be predicted and effectively identifies the 'optimal' climate for generating tourism. It is argued that British tourists are likely to experience a large gain in welfare in the sense that the attributes of nearby (low cost) locations improve following climate change. Finally, information on marginal willingness to pay for climatic amenities is combined with predictions concerning the scale and direction of possible climate change over Britain in order to provide a money measure of the welfare impact of such changes. Because households appear to prefer a climate characterised by much higher temperatures than currently prevail over Britain households reap large gains from climate change.