Evaluation of cover crop species for biomass production, weed suppression and maize yields under irrigation in the Eastern Cape Province, South Africa
- Authors: Musunda, Bothwell Zvidzai
- Date: 2010
- Subjects: Cover crops , Biomass energy -- South Africa -- Eastern Cape , No-tillage , Conservation of natural resources -- South Africa -- Eastern Cape , Agriculture -- South Africa -- Eastern Cape , Agricultural systems -- South Africa -- Eastern Cape , Weeds
- Language: English
- Type: Thesis , Masters , MSc Agric (Crop Science)
- Identifier: vital:11867 , http://hdl.handle.net/10353/347 , Cover crops , Biomass energy -- South Africa -- Eastern Cape , No-tillage , Conservation of natural resources -- South Africa -- Eastern Cape , Agriculture -- South Africa -- Eastern Cape , Agricultural systems -- South Africa -- Eastern Cape , Weeds
- Description: Achieving high biomass yields of cover crops has been a challenge to the success of Conservation Agriculture (CA) practices in the Eastern Cape (EC). A study was conducted to evaluate strategies for optimizing cover crop biomass production. Trials were carried out to screen summer and winter cover crops, as well as evaluate intercropping patterns and planting dates for biomass, weed suppression and subsequent maize yield under irrigation. Four summer legume cover crop species were evaluated under a Randomised Complete Block Design (RCBD) design. The cover crops were fertilized with 13.34 kg ha-1 of N, 20 kg ha-1 P and 26.66 kg ha-1 K. In the 2008/09 summer season a maize crop was superimposed on the 2007/08 screening trial under no-till. The crop was fertilized with 60 kg ha-1 of N. An intercropping trial was conducted over two seasons as a way of investigating the best way of incorporating cover crops into farmers cropping systems. This was done bearing in mind the limitation of resources such as land. The trial evaluated 3 factors laid as a 2 x 2 x 3 factorial arranged in a split-plot design. The main factor was cover crop planting date (planting at maize planting or 2 weeks after maize planting). The sub plot factor was intercropping pattern (strip intercropping and between row intercropping). A trial was also conducted to evaluate the effect of planting date (End of April and mid May) and four winter legume cover crop species on cover crop biomass, weed suppression and maize grain yield. The experiment was laid out as a Randomised Complete Block Design (RCBD) replicated 3 times. In the subsequent summer season a maize crop was superimposed on the winter trial to test the residual effects of the cover crop species. Another study was conducted to evaluate winter cereal cover crop species for biomass accumulation, weed suppression and subsequent maize grain yield. The cover crops as well as a weedy fallow control plot treatments were laid out as a Randomised Complete Block Design replicated 3 times. In the subsequent summer season a maize crop was superimposed on the site under no-till to evaluate the residual effect of the cover crops on maize. The results showed sunhemp, cowpea and lablab as the best cover crops with high biomass and weed suppression whilst mucuna was the least. Sunhemp consistently yielded higher cover biomass averaging 11200 kg ha-1 over the two seasons whilst mucuna had a consistently lowest average biomass yield of 4050 kg ha-1. These cover crops were above the critical 6 t ha-1 for effective weed suppression. There was a significant (p<0.01) relationship of cover crop dry weight and weed dry weight in both seasons. Subsequent maize grain yield was significantly higher in the sunhemp plots (64.2 %) than the weedy fallow plot. Mucuna, lablab and cowpea had maize grain yield increases of 16.6%, 33% and 43.2% respectively. Intercropping cover crops at maize planting yielded higher cover crop dry weights than a delay in intercropping cover crops. A delay in intercropping resulted in significantly higher average maize grain yield of 4700 kg ha-1 compared to intercropping at maize planting (3800 kg ha-1) and sole maize (4300 kg ha-1) over the two seasons. Strip intercropping also yielded higher (5000 kg ha- 1) average maize grain yield compared to row intercropping (3600 kg ha-1) and sole maize (4300 kg ha-1). There was a significant (p<0.05) relationship between cover crop dry weight in the 2007/08 season and maize grain yield in the 2008/09 season. Early planting grazing vetch gave the highest biomass yield of 8100 kg ha-1 whilst early planted red clover had the lowest biomass of 635 kg ha-1. Low weed dry weights were also obtained from the early planted grazing vetch as opposed to the other treatments. There was a significant (p<0.001) relationship of cover crop dry weight and weed dry weight. In the subsequent 2008/09 summer season early planted grazing vetch had the highest maize yield of 7500 kg ha-1 which was 56.3 % more than the weedy fallow plot had 4800 kg ha-1. The weedy fallow plot also had high weed infestation than the cover crop plots. There were significant (p<0.01) relationships between cover crop dry weight and maize grain yield, winter weed dry weight and maize grain yield and summer weed dry weight and maize grain yield. The results also showed triticale (13900 kg ha-1) as the best winter cover crop for biomass production. Italian ryegrass (6500 kg ha-1) produced the least amount of biomass. In The subsequent maize crop white oats gave highest maize grain yield (6369 kg ha-1) which was 33 % more than the weedy fallow plot (4784 kg ha- 1). There were also significant (p< 0.01) relationships of maize grain yield and winter weed dry weight, maize grain yield and summer growing weeds. The various studies demonstrated that there is opportunity for high biomass production under small scale farmers irrigated conditions using cover crops both in winter and summer. Best bet cover crops were sunhemp, cowpea and lablab for summer and triticale, white oats, barley, Italian ryegrass and grazing vetch for winter. Cover crops can also be incorporated into farmers cropping systems as sole crops or intercrops within the maize based cropping systems. Strip intercropping can be used by farmers as a way of introducing cover crops. Critical to achievement of high biomass is the time of planting cover crops with high biomass when planting is done early. A 2 week delay in strip intercropping cover crop into maize can be used as a way of incorporating cover crops into farmers cropping systems with minimal maize yield reduction.
- Full Text:
- Date Issued: 2010
- Authors: Musunda, Bothwell Zvidzai
- Date: 2010
- Subjects: Cover crops , Biomass energy -- South Africa -- Eastern Cape , No-tillage , Conservation of natural resources -- South Africa -- Eastern Cape , Agriculture -- South Africa -- Eastern Cape , Agricultural systems -- South Africa -- Eastern Cape , Weeds
- Language: English
- Type: Thesis , Masters , MSc Agric (Crop Science)
- Identifier: vital:11867 , http://hdl.handle.net/10353/347 , Cover crops , Biomass energy -- South Africa -- Eastern Cape , No-tillage , Conservation of natural resources -- South Africa -- Eastern Cape , Agriculture -- South Africa -- Eastern Cape , Agricultural systems -- South Africa -- Eastern Cape , Weeds
- Description: Achieving high biomass yields of cover crops has been a challenge to the success of Conservation Agriculture (CA) practices in the Eastern Cape (EC). A study was conducted to evaluate strategies for optimizing cover crop biomass production. Trials were carried out to screen summer and winter cover crops, as well as evaluate intercropping patterns and planting dates for biomass, weed suppression and subsequent maize yield under irrigation. Four summer legume cover crop species were evaluated under a Randomised Complete Block Design (RCBD) design. The cover crops were fertilized with 13.34 kg ha-1 of N, 20 kg ha-1 P and 26.66 kg ha-1 K. In the 2008/09 summer season a maize crop was superimposed on the 2007/08 screening trial under no-till. The crop was fertilized with 60 kg ha-1 of N. An intercropping trial was conducted over two seasons as a way of investigating the best way of incorporating cover crops into farmers cropping systems. This was done bearing in mind the limitation of resources such as land. The trial evaluated 3 factors laid as a 2 x 2 x 3 factorial arranged in a split-plot design. The main factor was cover crop planting date (planting at maize planting or 2 weeks after maize planting). The sub plot factor was intercropping pattern (strip intercropping and between row intercropping). A trial was also conducted to evaluate the effect of planting date (End of April and mid May) and four winter legume cover crop species on cover crop biomass, weed suppression and maize grain yield. The experiment was laid out as a Randomised Complete Block Design (RCBD) replicated 3 times. In the subsequent summer season a maize crop was superimposed on the winter trial to test the residual effects of the cover crop species. Another study was conducted to evaluate winter cereal cover crop species for biomass accumulation, weed suppression and subsequent maize grain yield. The cover crops as well as a weedy fallow control plot treatments were laid out as a Randomised Complete Block Design replicated 3 times. In the subsequent summer season a maize crop was superimposed on the site under no-till to evaluate the residual effect of the cover crops on maize. The results showed sunhemp, cowpea and lablab as the best cover crops with high biomass and weed suppression whilst mucuna was the least. Sunhemp consistently yielded higher cover biomass averaging 11200 kg ha-1 over the two seasons whilst mucuna had a consistently lowest average biomass yield of 4050 kg ha-1. These cover crops were above the critical 6 t ha-1 for effective weed suppression. There was a significant (p<0.01) relationship of cover crop dry weight and weed dry weight in both seasons. Subsequent maize grain yield was significantly higher in the sunhemp plots (64.2 %) than the weedy fallow plot. Mucuna, lablab and cowpea had maize grain yield increases of 16.6%, 33% and 43.2% respectively. Intercropping cover crops at maize planting yielded higher cover crop dry weights than a delay in intercropping cover crops. A delay in intercropping resulted in significantly higher average maize grain yield of 4700 kg ha-1 compared to intercropping at maize planting (3800 kg ha-1) and sole maize (4300 kg ha-1) over the two seasons. Strip intercropping also yielded higher (5000 kg ha- 1) average maize grain yield compared to row intercropping (3600 kg ha-1) and sole maize (4300 kg ha-1). There was a significant (p<0.05) relationship between cover crop dry weight in the 2007/08 season and maize grain yield in the 2008/09 season. Early planting grazing vetch gave the highest biomass yield of 8100 kg ha-1 whilst early planted red clover had the lowest biomass of 635 kg ha-1. Low weed dry weights were also obtained from the early planted grazing vetch as opposed to the other treatments. There was a significant (p<0.001) relationship of cover crop dry weight and weed dry weight. In the subsequent 2008/09 summer season early planted grazing vetch had the highest maize yield of 7500 kg ha-1 which was 56.3 % more than the weedy fallow plot had 4800 kg ha-1. The weedy fallow plot also had high weed infestation than the cover crop plots. There were significant (p<0.01) relationships between cover crop dry weight and maize grain yield, winter weed dry weight and maize grain yield and summer weed dry weight and maize grain yield. The results also showed triticale (13900 kg ha-1) as the best winter cover crop for biomass production. Italian ryegrass (6500 kg ha-1) produced the least amount of biomass. In The subsequent maize crop white oats gave highest maize grain yield (6369 kg ha-1) which was 33 % more than the weedy fallow plot (4784 kg ha- 1). There were also significant (p< 0.01) relationships of maize grain yield and winter weed dry weight, maize grain yield and summer growing weeds. The various studies demonstrated that there is opportunity for high biomass production under small scale farmers irrigated conditions using cover crops both in winter and summer. Best bet cover crops were sunhemp, cowpea and lablab for summer and triticale, white oats, barley, Italian ryegrass and grazing vetch for winter. Cover crops can also be incorporated into farmers cropping systems as sole crops or intercrops within the maize based cropping systems. Strip intercropping can be used by farmers as a way of introducing cover crops. Critical to achievement of high biomass is the time of planting cover crops with high biomass when planting is done early. A 2 week delay in strip intercropping cover crop into maize can be used as a way of incorporating cover crops into farmers cropping systems with minimal maize yield reduction.
- Full Text:
- Date Issued: 2010
The Rhodes BioSURE process and the use of sustainability indicators in the development of biological mine water treatment
- Authors: Neba, Alphonsus
- Date: 2007
- Subjects: Acid mine drainage Water -- Purification -- Biological treatment Mine water Mine water -- Purification Sewage -- Purification
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3984 , http://hdl.handle.net/10962/d1004043
- Description: Polluted waters, arising from extensive past and ongoing mining operations in South Africa, pose serious environmental threats to the limited fresh water resource. The long time periods, of decades to centuries, over which decanting mine waters may be expected to flow raises additional concerns about the sustainability of these resources. Responses to the problem have thus increasingly been directed towards the long-term sustainability of mine water treatment technologies (MWTT) as a critical indicator in both their research and development, and application. Bioprocess treatments have been considered in this regard and, among these, the Rhodes BioSURE Process has been investigated in preliminary studies using complex organic carbon wastes as the carbon source and electron donor for the central sulphate reduction unit operation. Although both the mining industry and the related statutory/regulatory authority in South Africa share public commitment to sustainability in the treatment of mine waters, no systematic mechanism has emerged to enable the application of sustainability thinking as a guiding principle in the selection and application of MWTTs, nor in the research and development undertaking. This study undertook the development of a Sustainability Indicator Framework in order to provide a systematic basis for the incorporation of sustainability objectives in MWTT bioprocess development, and specifically to use this framework as an input to the investigation of the scaleup development of the Rhodes BioSURE Process. In the development of the MWTT Sustainability Indicator Framework, an initial survey of industry thinking in this area was undertaken and, based on these outcomes, a detailed questionnaire methodology was developed in order to identify and quantify critical sustainability indicators. These included analysis of environmental, economic, social and technical indicators used in sustainability accounting practice in the industry. Statutory/regulatory sustainability targets in the same categories were derived from State of the Environment Reports (SoER) from Provincial authorities where mining is undertaken in South Africa. A synthesis of industry and SoER values was derived from weighted averages and the Sustainability Indicator Framework based on these outcomes. A Conceptual Decision-Support System, to guide the selection and development of MWTTs, was proposed and also based on these results. In the development of the Rhodes BioSURE Process the use of primary sludge (PS) had been investigated as a potential complex carbon and electron donor source. In this regard the utility operator, and sewage treatment process infrastructure, was identified as potentially meeting aspects of the sustainability objectives identified for MWTT application development. Both the Sustainability Indicator Framework and the Conceptual Decision-Support System provided inputs in the formulation of the experimental programme relating to the scale-up development of the Rhodes BioSURE Process. Based on these outcomes, a series of single- and multi-stage reactor configuration, optimisation and enzymology studies were undertaken at bench-, pilot- and technical-scale operations. These units were operated at hydraulic retention times (HRT) ranging between 22 to 72 hours and at chemical oxygen demand to sulphate ratios (COD:SO[subscript 4]) ranging between 1:1 to 2:1. Studies undertaken in fed-batch, bench-scale reactors confirmed the preliminary feasibility of using established sewage treatment infrastructure as a replacement for novel reactor configurations that had been used in the initial studies. The results further indicated that the hydrolysis of PS occurred at different rates under biosulphidogenic conditions in the different reactor configurations investigated. Scale-up of these findings in multi-stage pilot- (7.4m[superscript 3]) and technical-scale plants (680m[superscript 3]) showed comparable performances between the unit operations in terms of SO[subscript 4] and COD removal. These results indicated no apparent advantages in the uncoupling of hydrolysis and sulphate reduction in separate unit operations as had been suggested in previous studies. Scale-down/scale-up studies were undertaken in a continuously fed single-stage reactor configuration and showed that the process could be effectively operated in this way. Previous proposals that chemical and biological gradients established in the sludge bed of the Recycling Sludge Bed Reactor (RSBR) exercised an influence on the rates of substrate hydrolysis were investigated and the relative activity of α- and β-glucosidase and protease enzymes was measured. Results provided additional support for this hypothesis and it was shown that enzyme assay may also provide a useful tool in process development and monitoring studies. While sulphide recovery, following the sulphate reduction step in the BioSURE Process, was not investigated as a component of this study, the treatment of final effluent or waste spills was identified as an important sustainability requirement given the toxicity of sulphide to human and ecosystem environments. A conventional trickle filter reactor system was evaluated for this purpose and showed close to 100% oxidation to sulphate in a short contact time operating regime. Although residual COD removal was low at ~20% of influent, it is considered that high rate recycle biofilter operation could achieve the COD discharge standard of 75 mg/l. The results of the above studies provided inputs into the design, construction and commissioning of the first full-scale commercial application of the Rhodes BioSURE Process for mine wastewater treatment using sewage sludge as the carbon and electron donor source. An adjacent mine and sewage works have been linked by pipeline and an operational capacity of 10 Ml/day water treated has been established with sulphate reduced from ~1300mg/l to <200mg/l. These developments constitute a novel contribution in the mine waste water treatment field.
- Full Text:
- Date Issued: 2007
- Authors: Neba, Alphonsus
- Date: 2007
- Subjects: Acid mine drainage Water -- Purification -- Biological treatment Mine water Mine water -- Purification Sewage -- Purification
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3984 , http://hdl.handle.net/10962/d1004043
- Description: Polluted waters, arising from extensive past and ongoing mining operations in South Africa, pose serious environmental threats to the limited fresh water resource. The long time periods, of decades to centuries, over which decanting mine waters may be expected to flow raises additional concerns about the sustainability of these resources. Responses to the problem have thus increasingly been directed towards the long-term sustainability of mine water treatment technologies (MWTT) as a critical indicator in both their research and development, and application. Bioprocess treatments have been considered in this regard and, among these, the Rhodes BioSURE Process has been investigated in preliminary studies using complex organic carbon wastes as the carbon source and electron donor for the central sulphate reduction unit operation. Although both the mining industry and the related statutory/regulatory authority in South Africa share public commitment to sustainability in the treatment of mine waters, no systematic mechanism has emerged to enable the application of sustainability thinking as a guiding principle in the selection and application of MWTTs, nor in the research and development undertaking. This study undertook the development of a Sustainability Indicator Framework in order to provide a systematic basis for the incorporation of sustainability objectives in MWTT bioprocess development, and specifically to use this framework as an input to the investigation of the scaleup development of the Rhodes BioSURE Process. In the development of the MWTT Sustainability Indicator Framework, an initial survey of industry thinking in this area was undertaken and, based on these outcomes, a detailed questionnaire methodology was developed in order to identify and quantify critical sustainability indicators. These included analysis of environmental, economic, social and technical indicators used in sustainability accounting practice in the industry. Statutory/regulatory sustainability targets in the same categories were derived from State of the Environment Reports (SoER) from Provincial authorities where mining is undertaken in South Africa. A synthesis of industry and SoER values was derived from weighted averages and the Sustainability Indicator Framework based on these outcomes. A Conceptual Decision-Support System, to guide the selection and development of MWTTs, was proposed and also based on these results. In the development of the Rhodes BioSURE Process the use of primary sludge (PS) had been investigated as a potential complex carbon and electron donor source. In this regard the utility operator, and sewage treatment process infrastructure, was identified as potentially meeting aspects of the sustainability objectives identified for MWTT application development. Both the Sustainability Indicator Framework and the Conceptual Decision-Support System provided inputs in the formulation of the experimental programme relating to the scale-up development of the Rhodes BioSURE Process. Based on these outcomes, a series of single- and multi-stage reactor configuration, optimisation and enzymology studies were undertaken at bench-, pilot- and technical-scale operations. These units were operated at hydraulic retention times (HRT) ranging between 22 to 72 hours and at chemical oxygen demand to sulphate ratios (COD:SO[subscript 4]) ranging between 1:1 to 2:1. Studies undertaken in fed-batch, bench-scale reactors confirmed the preliminary feasibility of using established sewage treatment infrastructure as a replacement for novel reactor configurations that had been used in the initial studies. The results further indicated that the hydrolysis of PS occurred at different rates under biosulphidogenic conditions in the different reactor configurations investigated. Scale-up of these findings in multi-stage pilot- (7.4m[superscript 3]) and technical-scale plants (680m[superscript 3]) showed comparable performances between the unit operations in terms of SO[subscript 4] and COD removal. These results indicated no apparent advantages in the uncoupling of hydrolysis and sulphate reduction in separate unit operations as had been suggested in previous studies. Scale-down/scale-up studies were undertaken in a continuously fed single-stage reactor configuration and showed that the process could be effectively operated in this way. Previous proposals that chemical and biological gradients established in the sludge bed of the Recycling Sludge Bed Reactor (RSBR) exercised an influence on the rates of substrate hydrolysis were investigated and the relative activity of α- and β-glucosidase and protease enzymes was measured. Results provided additional support for this hypothesis and it was shown that enzyme assay may also provide a useful tool in process development and monitoring studies. While sulphide recovery, following the sulphate reduction step in the BioSURE Process, was not investigated as a component of this study, the treatment of final effluent or waste spills was identified as an important sustainability requirement given the toxicity of sulphide to human and ecosystem environments. A conventional trickle filter reactor system was evaluated for this purpose and showed close to 100% oxidation to sulphate in a short contact time operating regime. Although residual COD removal was low at ~20% of influent, it is considered that high rate recycle biofilter operation could achieve the COD discharge standard of 75 mg/l. The results of the above studies provided inputs into the design, construction and commissioning of the first full-scale commercial application of the Rhodes BioSURE Process for mine wastewater treatment using sewage sludge as the carbon and electron donor source. An adjacent mine and sewage works have been linked by pipeline and an operational capacity of 10 Ml/day water treated has been established with sulphate reduced from ~1300mg/l to <200mg/l. These developments constitute a novel contribution in the mine waste water treatment field.
- Full Text:
- Date Issued: 2007
- «
- ‹
- 1
- ›
- »