| Particulate organic matter, soil texture and mineralogy relations in some Eastern Cape ecotopes in South Africa | Wakindiki, IIC | 2012 |
Keywordsclay, primary minerals, quartz, soil organic matter AbstractContrasting reports have been given on the relationships between soil texture, mineralogy and particulate organic matter (POM). The objective of this study was to determine the effects of soil texture and mineralogy on aggregate POM in several ecotopes in the Eastern Cape province of South Africa. Soil from the surface 0–20 cm was collected from 14 ecotopes. Particulate organic matter was fractionated into litter POM, coarse POM and fine POM. Isolation of the POM fraction was done by dispersing the soil in 5 g l-1 sodium hexametaphosphate and passing the dispersed soil samples through a 0.053 mm sieve. Both total soil organic matter (SOM) and the POM in each fraction were determined using the weight loss on ignition procedure. Most ecotopes were either sandy loam or sandy clay loam and primary minerals especially quartz dominated the soil mineralogy. The clay content was significantly related to the total SOM (r = 0.78), hematite (r = 0.83) and quartz (r = -0.74). The results suggest that in soils that are dominated by primary minerals such as quartz, the clay content, rather than the clay plus silt content, is a better indicator of fine POM and total SOM. AuthorsWakindiki, IIC and Nciizah, AD Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.688882 This article contributed by:
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| Effect of tillage systems and nitrogen application rates on selected physical and biological properties of a clay loam soil in KwaZulu-Natal, South Africa | Taylor, TS | 2012 |
Keywordsbulk density, cellulolytic activity, hydrolytic activity, limestone ammonium nitrate, penetration resistance, soil water retention AbstractThe effects of agricultural management practices on soil physical and biological parameters provide fundamental information for assessing sustainability. Tillage (annual conventional tillage and no-till) and nitrogen fertiliser (limestone ammonium nitrate at rates of 0, 100 and 200 kg N ha−1) were evaluated for their effects on bulk density, water retention characteristics, saturated hydraulic conductivity, soil penetration resistance and microbiological activity (hydrolytic and cellulolytic) on a clay loam soil (Typic Haplustox) at a field experiment initiated in 2003 and planted to dryland maize. Tillage regime and nitrogen application rate significantly (p < 0.05) affected soil physical properties and microbial activity in the 0–5 cm layer. Under no-till the saturated water content and saturated hydraulic conductivity were significantly lower than under annual conventional tillage while plant available water was greater under no-till. Penetration resistance, bulk density and microbial activity were greater under no-till than annual conventional tillage. At 200 kg N ha−1 microbial activity, bulk density, water retention and saturated hydraulic conductivity were significantly lower than at the lower rates of application, especially under no-till. These results indicate that no-till improved soil physical properties and suggest there is a need to re-evaluate the sustainability of using high rates of nitrogen to increase maize yields, especially under a no-till system. AuthorsTaylor, TS, Titshall, LW, Hughes, JC and Thibaud, GR Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.689663 This article contributed by:
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| Optimum replications and crop-years for sugarcane genotype trials at Dwangwa Sugar Estate in Malawi | Zhou, MM | 2012 |
Keywordsbroad-sense heritability, discriminating ability, genotype by environment interaction, variance components AbstractThe ability to detect significant differences among genotypes in trials depends on the variance associated with the means. Dwangwa Sugar Estate, Malawi, imports genotypes from the South African Sugarcane Research Institute (SASRI) to test for possible commercial release. The objective of this study was to determine the optimum number of replications and crop-years required for adequate discriminating ability for yield and quality parameters. Data for yield (cane and sugar) and quality (estimable recoverable crystal [ERC %] and fibre %) were collected from two trial series. Each trial had eight replications and was harvested in the plant and four ratoon crops. The data were analysed using the MIXED procedure of the Statistical Analysis System (SAS) to estimate the variance components used to calculate broad-sense heritabilities (BSH). The optimum number of replications and crop-years was modeled using BSH. Yield traits produced more significant variance components for genotype by environment interaction (G×E) than quality traits. Quality traits produced larger BSH than yield traits. Four replications and harvesting in the plant and three ratoon crops provided adequate discriminating ability among genotypes. The resources saved by reducing replications could be used to plant more trials on different soil types to exploit or minimise G×E. AuthorsZhou, MM, Chihana, A and Parfitt, RC Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.690231 This article contributed by:
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| Sugarcane cultivar x time of harvest interactions in South Africa | Ramburan, S. | 2011 |
KeywordsAMMI, environmental covariate, G x E, time of harvest AbstractThe adaptability of new sugarcane (Saccharum spp.) cultivars to time of harvest (TOH), and reasons for yield variability between harvest times are currently unclear in South Africa. The objectives of this study were to evaluate the adaptability of commercial cultivars to TOH and to identify environmental factors responsible for differential cultivar responses. Two field trials consisting of the same set of seven commercial cultivars were established on adjacent fields and harvested either early (April/May) or late (October/November) in the season for six ratoons. Climatic data were summarized within individual growth stages (establishment, elongation, and ripening) and used to create environmental covariates for thermal time (TT), rainfall (RAIN), radiation (RAD), and a water stress index (WSI). Additive main effects and multiplicative interaction (AMMI) analysis, principal components analysis (PCA), factorial regression, and covariate-effect biplot analysis were used to analyse and interpret the genotype x environment (G x E) interaction for three commercial variables. The G x E interactions were significant (P<0.001) for all three variables. The AMMI biplots showed distinct separations between environments, and characterized cultivars according to their adaptability to early (NCo376, N36, N35, N29) and late (N27, N19, N17) harvesting. PCA and factorial regression identified RAD and TT as significant environmental covariates affecting TOH, while WSI and RAIN had insignificant effects. The covariate-effect biplot identified correlations between plant population and early harvests, while stalk mass was correlated to late harvests. These findings will inform selection strategies and future interpretive studies involving sugarcane G x E interactions. AuthorsRamburan, S. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640016 This article contributed by:
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| Preliminary evaluation of soil-residual herbicides for the control of silver-leaf bitter apple (Solanum elaeagnifolium Cav.) | Viljoen, B.D. | 2011 |
KeywordsChemical control, noxious weed, satansbos, silverleaf nightshade AbstractSolanum elaeagnifolium Cav., commonly known as silver-leaf bitter apple, silverleaf nightshade or “satansbos”, has become one of the most important emerging weeds in South Africa, with the potential to spread throughout some of the major crop growing areas of the country. Consequently, it has been declared a weed of national importance. Previous research revealed the difficulty in killing the extensive root system when using foliar applied herbicides. The small leaf area for herbicide absorption relative to the large root system and apparent inability to translocate sufficient herbicide beyond the root crown are believed to be some of the main reasons for the poor levels of control achieved. Since herbicides capable of being absorbed by the roots may be more effective, a study was undertaken to evaluate a range of soil-residual herbicides in the hope of improving control. While imazapyr 250 g −1 SL applied at 8 1 ha−1initially caused the most significant reduction in weed population levels, it was ultimately tebuthiuron 500 g −1 SC and a bromacil/tebuthiuron mixture 250/250 g −1 SC applied at 32! ha−1 that sustained the best long-term control. However, the high cost and long soil residual nature of these products would seriously limit their application value in cropping areas and sensitive habitats. Nonetheless, they may be useful for controlling isolated dense patches on fallow land and along roadsides, away from desirable vegetation, steep slopes or watercourses. The registration holders of these products are encouraged to conduct further evaluations using lower rates, as well as combining these products with foliar applied herbicides, to reduce costs and potential environmental impacts if used in sensitive habitats. AuthorsViljoen, B.D., Stoltsz, C.W. and Rijst, M.
van der Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640017 This article contributed by:
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| Sampling variation in the quantification of fumonisins in maize samples | van Rensburg, B.
Janse | 2011 |
KeywordsELISA, Fusarium, HPLC, replications, sub-sample size AbstractFumonisins produced by F. verticillioides and F. proliferatum cause mycotoxicoses in horses, swine and rats and have been associated with oesophageal cancer in humans. Accurate measurement of mycotoxins is essential for determining the safety of grain and their products for consumption. Four sources of variation were studied, namely sub-sample size, variation within a single maize sub-sample, number of replicates and toxin detection techniques used by independent laboratories. Variation in detected fumonisin levels within a single maize sample was high using the 25 g sub-samples proposed in the Neogen Veratox protocols. A 250 g sub-sample significantly reduced variation in fumonisin levels of samples. An incremental increase in sample size also improved the number of positive samples recorded. Increasing the number of replicates using the recommended sub-sample size (25 g) did notreduce variation except when the sample had high fumonisin levels. Improved accuracy was recorded when a 250 g sub-sample was used in conjunction with increased replicates. Data from laboratory analyses indicated that ELISA reactions (Agricultural Research Council – Grain Crops Institute) correlated significantly with HPLC results of the Medical Research Council (MRC), but neither of these correlated with results from an independent laboratory. Concentrations determined using ELISA were consistently higher than those from the HPLC (MRC) technique. Quantification technique, sample size, replicate number and laboratory where analyses are conducted, appear to be important sources of variation for quantification of fumonisins. Authorsvan Rensburg, B.
Janse, Flett, B.C., Mc Laren, N.W. and Mc Donald, A.H. Year Published2011 PublicationSouth African Journal of Plant and Soil Locations- Hartbeesfontein, North West, South Africa (-26.7649, 26.4253)
- Derby, North West, South Africa (-25.9086, 27.0374)
- Sannieshof, North West, South Africa (-26.5333, 25.8)
- Ventersdorp, North West, South Africa (-26.3167, 26.8167)
- Bronkhorstspruit, Pretoria, Gauteng, South Africa (-25.805, 28.7464)
DOI10.1080/02571862.2011.10640018 This article contributed by:
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| Comparative performance of tomato cultivars cultivated in two hydroponic production systems | Maboko, M.M. | 2011 |
KeywordsClosed hydroponic system, fruit cracking, open hydroponic system, marketable yield AbstractCultivar selection for different hydroponic production systems is an important management decision, potentially impacting the tomato grower’s profitability. Knowledge on the performance of tomato cultivars, in specific hydroponic systems (open-bag and closed system) under South African conditions, is still very limited. The performance of four cultivars was evaluated in an open and a closed hydroponic (gravel-film technique) system. The commonly grown cultivars evaluated in each of the two hydroponic systems were ‘FA593’, ‘Malory’, ‘Miramar’ and ‘FiveOFive’. For each experiment a randomized complete block design was used with four replicates. Total, marketable and unmarketable yields, as well as internal fruit quality characteristics (total soluble solids (°Brix) and pH) were determined. Although no significant differences in total yield could be established - neither in the open nor in the closed hydroponic system - differences in marketable yield were observed. ‘Miramar’ and ‘Five-OFive’ produced the highest marketable yield in the closed system; the high unmarketable yield of ‘FA593’ and ‘Malory’ in the closed hydroponic system could be attributed to the high number of cracked fruit due to their inherent larger fruit size. There were no significant differences in °Brix between cultivars in the closed system. Cultivar ‘FiveOFive’, ‘FA593’ and ‘Miramar’ produced higher marketable yields than cultivar ‘Malory’ when grown in the open-bag system. ‘Malory’ and ‘FA593’ produced the highest number of fruit exhibiting fruit cracking in the open bag system. In the open system, only cultivar ‘Malory’ had a higher °Brix than ‘Miramar’ and ‘FiveOFive’. The most promising cultivars for local hydroponic tomato production, with regard to yield and quality, were identified as ‘Miramar’ and ‘FiveOFive’, with ‘FA593’ performing equally in the open system only. Further studies need to be undertaken on economical comparison of the two production systems. AuthorsMaboko, M.M., Du Plooy, C.P. and Bertling, I. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640019 This article contributed by:
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| Growth regulator manipulation of apple bud dormancy progressions under conditions of inadequate winter chilling | Allderman, L.A. | 2011 |
Keywordscytokinin, abscisic acid, Malus x domestica Borkh, rest, South Africa AbstractElgin (34°S, 19°E; 305 m.a.s.l.), typical of South African apple growing regions, accumulates 745 Utah Chill Units (CU) p.a. The chilling requirement of ‘Golden Delicious’ apple (Malus xdomesf/ca Borkh.) is c.a. 1100 CU. Consequently, the chilling requirement is not satisfied and delayed foliation is common. The aim of this study was to use plant growth regulators (PGR’s) to manipulate the progression of dormancy in order to reduce the chilling requirement of ‘Golden Delicious’ shoots in mature commercial orchards. A trial was conducted in a commercial orchard in Elgin during the winters of 2004, 2006 and 2007. To advance the onset of dormancy, 250 mg −1 abscisic acid (ABA) was sprayed several times during April and May of 2004 and 2006. To induce a shallower state of dormancy, cytokinins were applied during April and May of 2006 and 2007. Benzyl adenine (BA) was applied at concentrations between 250 and 1000 mg −1 and forchorfenuron (CPPU) at 15 mg −1. Progression of dormancy was assessed by harvesting shoots every 2–3 weeks from initial spray date until commercial rest breaking agents were applied in the orchard. The time interval for 50% of the shoots to exhibit budburst under controlled conditions was used as a parameter for depth of dormancy. Although shoots were sprayed on c.a. the same calendar dates each year and before any significant CU had accumulated, the physiological state of the buds at application varied from shallow to deep dormancy depending on the season. Therefore calendar dates were not a good criteria for spray applications and CU accumulation was not a prerequisite for the onset of dormancy. PGR’s altered the dormancy progression of ‘Golden Delicious’ shoots. However, their efficacy was dependant on the dormancy status of the buds at the time of application. Furthermore, the effect was not sustainable. The trees appeared to “normalize” after a short period of time and consequently the PGRs had no effect on the dormancy release or budburst the following spring. AuthorsAllderman, L.A., Steyn, W.J. and Cook, N.C. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640020 This article contributed by:
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| Non-uptake of silicon and variable nematode species relationships between different levels of this element in sugarcane | Berry, S.D. | 2011 |
KeywordsFly ash, Helicotylenchus, Pratylenchus, Si, Sugarcane by-products AbstractSilicon (Si) is known to alleviate biotic and abiotic stresses in many crops. Much of the research on the biotic influence of Si has dealt with insects and fungi, with no proper studies on the effect of Si on plant-parasitic nematodes. To investigate this effect, a replicated field trial was planted with sugarcane in KwaZulu-Natal, comparing Si carriers, bagasse, filtercake and fly ash, added either by themselves or in combination with condensed molasses stillage (CMS), thume, CMS alone and aldicarb (a synthetic nematicide) to untreated plots. Applying the Si carriers to the soil was not always sufficient to increase levels of Si in the sugarcane leaves. Uptake of Si by sugarcane required a particular chemical balance in the soil, which was not found uniformly in this field. As a consequence,the addition of Si carriers, per se, had no effect on the nematode community. However, a comparison between Si-rich and Si-poor plots, selected independently of the treatments, showed that total numbers of plant-parasitic nematodes and numbers of Pratylenchus zeae and Helicotylenchus dihystera in the soil were significantly lower in plots where foliar Si levels were higher. The same trend was true for the number of P. zeae in the roots, but the difference was not significant. Multivariate analysis showed that while numbers of some of the nematodes in the soil were depressed in the higher Si plots, numbers of the more damaging nematodes were unaffected. As a result there was still a potential risk in the long term for damage to the crop caused by these nematodes. AuthorsBerry, S.D., Spaull, V.W., Ramouthar, P.V. and Cadet, P. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640021 This article contributed by:
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| The effect of degree and duration of water saturation on selected redox indicators: pe, Fe2+ and Mn2+ | Smith, K. | 2011 |
KeywordsIron, manganese, reduction, saturation, yellow-brown apedal B horizon AbstractIt was previously hypothesised that reduction in the soil will set in at 70% water saturation (S0.7). This study aimed to determine the effect of different degrees and durations of water saturation on reduction in soil. Reduction was measured as a decrease in soil oxidisability (pe) and an increase in soluble iron (Fe2+). A yellow brown apedal B horizon from profile 234 in the Weatherley catchment was used in this study. Soil cores were packed to a bulk density of 1.6 Mg m−3 and saturated to S0.6 (60% of the pores saturated with water), S0.7 (70% of the pores saturated with water), S0.8 (80% of the pores saturated with water), and S0.9 (90% of the pores saturated with water). Analyses started three days after water saturation. Samples were analysed every 3.5 days for the first three months and then once a week for another month. The experiment was terminated after 121 days. There was a good correlation between an increase in degree of water saturation and pe (R2=0.95), Mn2+ (R2=0.99) and Fe2+ (R2=0.99) concentration. The tendency was for pe, pH, Fe2+, and Mn2+ to remain relatively stable at S0.6 and to increase in variability as the water saturation increased, with most variability observed at S0.9. The change in redox activity took place between the S0.7 and S0.8 treatments. For this particular soil the highest rate of reduction took place in the S0.9 treatment. AuthorsSmith, K. and van Huyssteen, C.W. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640022 This article contributed by:
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