| Initial growth potential and biomass production of field established guayule (Parthenium argentatum Gray.) cultivars | Agenbag, G. A. | 2005 |
Keywordsbiomass production, field trials, growth potential, guayule, Parthenium argentatum AbstractThe initial growth potential and biomass production of four guayule cultivars under dryland conditions were investigated at different localities in South Africa. Growth (plant survival, height, canopy diameter, stem diameter) and biomass (wet and dry mass) were recorded for (1) one-year old plantings established in April 2001 at Elsenburg, Graaff-Reinet and Oudtshoorn, and (2) six-month old plantings established in October 2001 at Bethulie, Glen and Upington. For one year old plantings, significant area x cultivar interactions were observed for plant survival and height, while canopy diameter and stem diameter only differed between areas and cultivars. For six month old plantings interaction between area and cultivar was significant for plant height, but not for plant survival, canopy diameter and stem diameter. There were, however, significant differences in terms of stem- and canopy diameter and dry mass production between production areas. Growth potential and biomass production of guayule was influenced by the availability of water during the growth season. AuthorsAgenbag, G. A., Pieterse, P. J., Bekaardt, C. R. and Reinten, E. M. Year Published2005 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2005.10634706 This article contributed by:
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| Effect of soil tillage, crop rotation and nitrogen application rates on plant-N content of spring wheat (Triticum aestivum L.) in the Swartland wheat-producing area of the Republic of South Africa | Agenbag, G. A. | 2004 |
KeywordsCrop rotation, nitrogen content, N-fertiliser rates, tillage methods AbstractStudies on nitrogen content in spring wheat were conducted during the 2000 and 2001 growing seasons as part of a long-term tillage and crop rotation trial. Four tillage methods were used, namely conventional tillage (CT), tine tillage (TT), minimum tillage (MT) and no-tillage (NT). Crop rotation systems used were continuous wheat (WW) and wheat/lupine/wheat/canola (WLWC). Three rates of nitrogen fertiliser (60, 100 and 140 kg. N ha-1) were applied as sub-plots. Wheat plants were sampled at tillering stage (S1), stem elongation (S2), flag leaf (S3) (2000 growing season only) and anthesis (S4). In general nitrogen content (% of plant component) decreased as the plant reached maturity. Nitrogen content expressed as g plant-1 and kg ha-1 was affected by tillage method in both growing seasons, but the response depended on the amount of precipitation during the growing season. During the low rainfall year, highest N contents were found in the NT treatment. In contrast to this, CT resulted in the highest N content during high rainfall years. Significant differences in total nitrogen content in the plant (g plant-1) due to crop rotation were observed only at the tillering and flag leaf stages. At both stages, plants from the wheat/lupine/wheat/canola system resulted in significantly higher values than those from the monoculture (wheat/wheat) plots. A non-linear increase in the N content of the wheat crop with an increase in the N-application rate from 60 to 140 kg N ha-1 indicated a decrease in N-use efficiency at higher application rates during both years. AuthorsAgenbag, G. A. and Maali, S. H. Year Published2004 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2004.10635059 This article contributed by:
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| Plant water relations and proline accumulation on two cowpea (Vigna unguiculata (L.) Walp.) cultivars as a response to water stress | Agenbag, G. A. | 2004 |
KeywordsCowpea, proline, water stress AbstractCowpeas produced under rainfed conditions of arid and semiarid areas of Sub-Saharan Africa often experience periods of water stress. It is therefore important to identify drought tolerant cultivars of cowpeas and the mechanisms involved in their ability to withstand these conditions. The aim of this study was to evaluate the responses of physiological parameters such as leaf water potential, leaf diffusive resistance, relative water content, leaf proline content and cell membrane stability to water stress and to identify the parameters, which can be used to distinguish between drought tolerant and drought susceptible cowpea cultivars. Water stress was applied from 16 to 30 days after emergence (DAE) to two cowpea cultivar namely Akkerbone Bechuana Wit (AB Wit) and Akkerbone CH 14 (ACH 14) by withholding water to the stressed plants. Well-watered plants were watered regularly to keep the soil moisture content close to or at field water capacity. Water stress increased leaf diffusive resistance (LDR) and proline accumulation and decreased relative water content (RWC) in both cultivars and water potential only in AB Wit. Increases in proline content seemed to correlate more closely to changes in relative water content than changes in water potential. Water potential, relative water content and proline accumulation, therefore, seemed to be useful parameters to distinguish between drought tolerant and drought susceptible cowpea cultivars. AuthorsAgenbag, G. A. and Chiulele, R. M. Year Published2004 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2004.10635032 This article contributed by:
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| The breaking of seed dormancy of guayule (Parthenium argentatum Gray.) by treatment with gibberellic acid and smoke water solution | Agenbag, G. A. | 2004 |
Keywordsgibberellic acid, guayule, seed germination, smoke water AbstractGuayule seed exhibits poor germination due to natural dormancy that can last from six- to twelve months after seed-set. In an attempt to stimulate seed germination, four guayule seed lines (AZ101, AZ-3, N565 and 11591) were treated with smoke water as well as gibberellic acid, both separately and in combination. The split-plot analyses of variance showed no significant interaction between cultivar and treatment factors (P = 0.71), but when the time factor was included interaction was highly significant (P < 0.0001), indicating that some treatments influenced the rate of germination. Seeds of cultivar AZ-3 treated with the smoke water-gibberellic acid mixture required the shortest number of days for maximum germination to occur. However, treatment of seeds with gibberellic acid resulted in the highest germination of seeds of all four cultivars. These results showed that guayule seed can be stimulated to germinate faster and better by treatment with gibberellic acid and/or smoke water solutions. AuthorsAgenbag, G. A., Pieterse, P. J., Bekaardt, C. R. and Coetzee, J. H. Year Published2004 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2004.10635033 This article contributed by:
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| Effect of soil tillage, crop rotation and nitrogen application rates on grain yield of spring wheat (Triticum aestivum L.) in the Swartland wheat producing area of the Republic of South Africa | Agenbag, G. A. | 2003 |
KeywordsCrop rotation, grain yield, tillage methods, yield components AbstractStudies on spring wheat yield components were conducted during the 2000 and 2001 growing seasons only, while grain yield responses to tillage, crop rotation and N rates during these years were compared to the mean yield for the years 1992, 1994, 1996 and 1998 at Langgewens Experimental Farm in the Western Cape as part of a long-term tillage and crop rotation trial. Four tillage methods, namely conventional tillage (CT), tine tillage (TT), minimum tillage (MT), and no-tillage (NT) were compared. Crop rotation systems used were continuous wheat (WW) and wheat/lupin/wheat/canola (WLWC). Three rates of N fertilisers (60, 100 and 140 kg N ha−1) were applied. Tillage methods had a significant effect on the number of spikes m−2, spikelets per spike and number of kernels per spike in both the 2000 and 2001 growing seasons. Thousand kernel mass was not significantly affected by different tillage methods in both seasons. Mean grain yield for the years 1992, 1994, 1996 and 1998 did not differ significantly as a result of different tillage methods, but differences due to tillage methods were found in both the 2000 and 2001 growing seasons. Crop rotation had no significant effect on the mentioned yield components. Significantly higher mean yield for the years 1992, 1994, 1996 and 1998 were produced when wheat was rotated with lupins and canola (WLWC) compared to monoculture wheat (WW). Application of different rates of N had no significant effect on the number of spikes m−2, number of spikelets per spike and 1000-kernel mass in both growing seasons. While higher rates of N increased the number of kernels per spike in 2001 growing season, no significant differences were observed between different N rates in the dry season (2000) and the results even indicated a decrease in yield with increasing N rates in 2000. Higher grain yields were obtained by application of higher rates of N fertiliser during the wet season 2001, but significant tillage × crop rotation and tillage × nitrogen interaction for the mean grain yield during the 1992–1998 period indicated that yield responses to tillage were related to soil conditions. AuthorsAgenbag, G. A. and Maali, S. H. Year Published2003 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2003.10634919 This article contributed by:
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| Effect of soil tillage, crop rotation and nitrogen application rates on soil mineral-N levels in the Swartland wheat producing area of South Africa | Agenbag, G. A. | 2003 |
KeywordsConventional tillage, mineral-N, no-tillage, tine tillage AbstractStudies on nitrogen (N) levels in soil were conducted from 1997 to 2000 in a long-term tillage and crop rotation trial, which started in 1976. Three tillage methods namely conventional tillage (CT), tine tillage (TT), and notillage (NT) were compared. Crop rotation systems used were continuous wheat (WW) and wheat/lupin/wheat/canola (WLWC). Three rates of N-fertilisers (60, 100 and 140 kg N ha−1) were applied. All treatments received 60 kg N ha−1 at planting, while the 100 and 140 kg N ha−1 treatments received additional top-dressings of 40 kg N ha−1 at tillering and stem elongation stages respectively. Soil samplings were done at 14-day intervals, starting immediately before planting and continued till harvesting each year. Samplings at planting were done before N-fertiliser was applied and therefore regarded as pre-planting (Pp). The effect of tillage methods on mineral-N was variable and inconsistent among the soil samplings and years. During the four-year-period of this study, higher values of total mineral-N were found with conventional tillage at the pre-planting (Pp) samplings. Crop rotation did not significantly influence total mineral-N, which may be explained by the cultivation of a legume crop (lupins) once every four years only. In general the application of N-fertiliser resulted as expected in an initial increase in the mineral-N content of the soil. However, this was soon followed by a rapid decline as crops start to utilise the added nitrogen, resulting in values of less than 10 mg kg−1 soil during the grain filling stages with application rates of 60 and 100 kg N ha−1. These values may be regarded as deficient for grain yields of 4000 to 5000 kg ha−1. AuthorsAgenbag, G. A. and Maali, S. H. Year Published2003 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2003.10634920 This article contributed by:
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| Bromus diandrus Roth. control with MON 37532 in spring wheat (Triticum aestivum L.). 1. Time of application and dosage rate | Agenbag, G. A. | 1999 |
KeywordsBromus diandrus, Roth, control, MON 37532, spring wheat. AbstractMON 37532 (sulfosulfuron) is a new herbicide for the selective control of grasses and annual broadleaf weeds in wheat (Triticum aestivum L.). In this glasshouse study done in 2-litre pots filled with coarse sand, the product was evaluated for the selective control of Bromus diandrus Roth, in spring wheat. Dosage rates of MON 37532 varying between 0 and 45 g a.i ha-1 plus 0.25% of the surfactant, Agral 90, were applied at the 1-, 2-, 3- and 4-leaf stage of the weed plants. Although efficient control (> 85%) was only achieved when weeds were sprayed at the 1 -leaf stage, leaf growth of all B. diandrus plants ceased within 5 days after spraying, irrespective of time of spraying. Leaf area and dry mass determinations done at 6 weeks after spraying in this study confirmed that even if sprayed at the 4-leaf stage, MON 37532 stops B. diandrus from further growth and competition with the wheat plants. Higher dosage rates may be needed when sprayed at later growth stages. Growth of the spring wheat cultivar, SST 55, used in this study was not affected by the herbicide. AuthorsAgenbag, G. A. and Crous, R. Year Published1999 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1999.10634995 This article contributed by:
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| Bromus diandrus Roth. control with MON 37532 in spring wheat (Triticum aestivum L.). 2. Effect of relative weed density and time of spraying | Agenbag, G. A. | 1999 |
KeywordsBromus diandrus Roth. control, MON 37532, weed density, spring wheat AbstractBromus diandrus Roth, is one of the most troublesome weeds in spring wheat crops of the western Cape wheat producing area of the Republic of South Africa and Australia. The selective control of this weed in wheat crops may, in future, be possible with MON 37532 (sulfosulfuron) a new herbicide developed by Monsanto SA. The effect of the relative density of B. diandrus in a wheat crop on the efficacy of this herbicide sprayed at either the 2- or6-leaf stage of the weed was studied in a pot experiment in a temperature-controlled glasshouse. A density of 3 plants pot-1 (170 plants rrr-2) was used for the wheat crop, while that of B. diandrus varied between 0 and 10 plants pot-1 (565 plants -2). At early applications (2-leaf stage), efficacy of MON 37532 improved with higher densities of B. diandrus. This was possibly due to stress conditions created by higher weed densities. This tendency was less evident when MON 37532 was applied at the 6-leaf stage. Reduced susceptibility in the older plants and less efficient wetting of weeds in pots with high weed densities were probably the reason for reduced percentage control when plants were sprayed at this stage. AuthorsAgenbag, G. A. and Crous, R. Year Published1999 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1999.10634996 This article contributed by:
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| Quality response of spring wheat cultivars to post-anthesis water stress intensity | Agenbag, G. A. | 1995 |
KeywordsQuality, spring wheat, water stress AbstractThe effect of different intensities of water stress imposed during the first three weeks of grain filling were determined on the protein content, protein composition and bread volume of three spring wheat cultivars. Water stress was induced by watering the plants with a nutrient solution containing 0%, 15% and 22.5% polyethylene glycol (PEG 6000). Water stress generally decreased the protein content and bread volume by decreasing the production of the reserve proteins, gliadin and glutenin. The lower PEG-concentration had a more pronounced effect than the higher concentration, because the effect of the higher concentration on the production of protein, relative to non-protein components, was less than that of the lower PEG concentration. In this study cultivars did not differ in their response to different intensities of water stress. AuthorsAgenbag, G. A. and de Villiers, O. T. Year Published1995 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1995.10634335 This article contributed by:
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| Physiological response of spring wheat cultivars to post-anthesis water stress intensity | Agenbag, G. A. | 1995 |
KeywordsPhysiological response, water stress, wheat, yield AbstractWheat crops produced under dryland conditions in the winter rainfall belt of South Africa are often subjected to water stress. To study the effect of water stress on the spring wheat cultivars Nantes, Palmiet and SST 66, an experiment was conducted in a glasshouse at a 15°/10°C (day/night) temperature. Three intensities of water stress (0% PEG = unstressed; 15% PEG = low stress intensity and 22.5% PEG = high stress intensity) were imposed with polyethylene glycol (PEG) 6000 during the period of anthesis to milk stage in the three spring wheat cultivars. Water stress increased leaf diffusive resistance (LDR) and decreased the relative water content (RWC) of all three cultivars. Although plants were rehydrated after milk stage was reached, leaf senescence was hastened and the kernel-filling period shortened. These effects increased with increasing stress intensities. The low stress intensity (15% PEG) did not affect grain yield, but plants subjected to the high stress intensity (22.5% PEG) had significantly smaller kernels and a 37.5% lower grain yield. Although cultivars differed in their response to stress treatments for some parameters, these differences were too small and inconsistent to be recommended for use in breeding programmes for drought tolerant cultivars. AuthorsAgenbag, G. A. and de Villiers, O. T. Year Published1995 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1995.10634330 This article contributed by:
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