| A family of stochastic models for droughts | Zucchini, W. | 1991 |
KeywordsDrought, rainfall, simulation, stochastic model AbstractThere is no single quantitative definition of a drought; what constitutes a drought depends both on water needs and on storage capabilities. In this paper a family of models is proposed which is sufficiently flexible to cover a range of different situations; the user may select some of the parameters to suit his particular application. The input to the model is a sequence of rainfall values which in turn may be generated by a stochastic model, thus enabling the simulation of a long sequence of rainfall data which allow the user to study the distribution of droughts of any given duration or severity. Several of illustrative examples are given. AuthorsZucchini, W., Adamson, P. T. and McNeill, L. Year Published1991 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1991.10634835 This article contributed by:
|
| Oviposition site preferences by Helicoverpa armigera (Lepidoptera: Noctuidae): effect of season and density on distribution of eggs on plants | Zitsanza, E. S. | 2006 |
KeywordsAfrican bollworm, Helicoverpa armigera, oviposition sites, tomato AbstractIn an attempt to improve field sampling of the African bollworm, Helicoverpa armigera (Hübner), oviposition behaviour of the pest on tomato plants was investigated. From limited studies conducted in the past, variation in oviposition sites preferences by H. armigera is thought to be seasonally related. This phenomenon has been hypothesized as being associated with seasonal variation in leaf nutritional composition. To further our understanding of the oviposition behaviour of the pest, field studies were conducted to determine oviposition site preferences, the effects of season and infestation density on the distribution of eggs on tomato plant parts. Experimental tomato crops were grown on replicated plots in spring (August to November) and in summer (February to April). Oviposition behaviour was determined by weekly sampling for eggs on tomato crops grown during the above seasons. The second and third compound leaves from the terminal bud and flower clusters at the third inter-node were the most preferred egg laying sites. Chi-square tests indicated that significantly higher percentages of eggs (P < 0.01) were laid on flower clusters in summer compared to spring. As infestation densities increased from low to high, significantly higher proportions of eggs (P < 0.01) were deposited on flower clusters but this relationship was only observed during the first year. AuthorsZitsanza, E. S., Giga, D. P. and Knight, J. D. Year Published2006 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2006.10634744 This article contributed by:
|
| Family selection gains for quality traits among South African sugarcane breeding populations | Zhou, MM | 2012 |
Keywordsbroad-sense heritability, covariance parameters, selection gains, sugarcane AbstractIn sugarcane breeding, family selection has been shown to produce larger gains than individual plant selection. During family selection, whole families of seedlings are selected or rejected based on data derived from replicated family plots. The objective of this study was to determine predicted family selection gains and evaluate their implications for variety improvement in terms of quality traits among sugarcane breeding populations of the South African Sugarcane Research Institute's regional breeding programmes. The data was collected from seven breeding populations and analysed using the Statistical Analysis System (SAS). All the quality traits showed highly significant family effects variance components. There were consistent increases in heritability and gains to selection with advancing population series indicating benefits from indirect recurrent selection. Brix % cane, because it costs less to measure, could be used to evaluate within family variability. The B, C, U and F populations produced larger and more consistent selection gains than K, T and S. Recurrent selection could be used to enhance breeding for quality traits. AuthorsZhou, MM and Lichakane, ML Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.743606 This article contributed by:
|
| Simultaneous selection for yield and ratooning ability in sugarcane genotypes using analysis of covariance | Zhou, MM | 2012 |
Keywordsratooning cycles, sugarcane breeding method, Saccharum officinarum L AbstractRatooning ability increases sugarcane production economics by reducing frequency of planting. During sugarcane breeding, indirect selection for pest resistance and direct selection for high ratoon yields increases ratooning ability. The objective of this study was to describe the simultaneous screening of genotypes for yield and ratooning ability in sugarcane breeding trials using analysis of covariance. Data for cane yield (tons ha−1) and stalk population (×103 ha−1) collected from five trials harvested from plant to fourth ratoon crops were analysed using the Statistical Analysis System (SAS). There were significant differences in parameters for yield (intercept) and ratooning ability (slope) among test genotypes indicating potential for simultaneous screening. Comparison of genotypes to a control with known ratooning ability identified higher yield and good ratooning genotypes. Graphical trends identified genotype differences in yield and ratooning ability. The economics of yield and ratooning ability of two varieties was compared providing a mechanism for variety choice at planting. The method described provided statistical tests that would increase genotype selection efficiency for ratooning ability. The decline in yield among genotypes is slowed by the increase in stalk population. AuthorsZhou, MM and Shoko, MD Year Published2012 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2012.717639 This article contributed by:
|
| 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:
|
| Seasonal and varietal effects on tiller population development of sugarcane (Saccharum Officinarum L.) | Zhou, M.M. | 2011 |
KeywordsPeak tiller population, thermal time per tiller, tiller survival rate, final tiller population, tiller survival rate AbstractAbstract Tillers carry leaves, determine leaf area index and indirectly influence the amount of photosynthetically active radiation (PAR) intercepted by the sugarcane canopy. Tillers develop into stalks, the sink for the products of photosynthesis. The objective of this study was to investigate the effects of seasons and varieties on tiller population development trends and parameters using different varieties (ZN6, ZN7, N14 and NCo376). Three replicated experiments were established in early (March), mid (July) and late (October) seasons at Zimbabwe Sugar Association Experiment Station. The tiller population development parameters were determined in each plot and the data were analysed for seasonal and varietal effects using the mixed procedure of SAS. The tiller development parameters investigated were: peak tiller population (PTP), final tiller population (FTP), thermal time to peak tiller population (TTTP), thermal time per tiller (TTPT) and tiller survival rate (TSR). The order of importance of the parameters was season > variety > variety x season. The study suggested the presence of genotype by environment (GxE) interaction for PTP. The cane yield of the varieties significantly (P mid > late season. AuthorsZhou, M.M. and Shoko, M.D. Year Published2011 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2011.10640007 This article contributed by:
|
| Soil water variability in the Weatherley grassland catchment, South Africa: II. Soil water content | Zere, TB | 2009 |
KeywordsHydropedology, model, soil water, water saturation AbstractAbstract Soil water content is a major factor that affects the hydrological response of a hillslope or catchment. It is therefore important to have reliable soil water content data to estimate catchment water yield. Daily soil water content (θ) data was calculated based on weekly measured and other data for the Weatherley grassland catchment in South Africa. A modelling procedure, based on the soil water balance equation and the interpretation of the physical properties of soils was used to calculate daily θ for all 28 sites for the six-year period. A statistical model performance indicated that the mean index of agreement was 0.88, root mean square error (RMSE) was 6.8 mm water per 300 mm soil and mean unsystematic RMSE to total RMSE was 93%. These results indicated that the calculated soil water contents agreed well with the measured values and could therefore be used with reasonable confidence to fill data gaps. The proposed procedure therefore affords the possibility to increase the resolution of irregular measured soil water content data. This would significantly advance the usability of such data, because the influence of rainfall events on soil water content is frequently missed by manual soil water content measurements. AuthorsZere, TB, Hensley, M and Huyssteen, CW
van Year Published2009 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2009.10639952 This article contributed by:
|
| Potassium nitrate and urea sprays affect flowering and yields of ‘Tommy Atkins’ (Mangifera indica) mango in Ethiopia | Yeshitela, T. | 2005 |
Keywordsflowering, fruiting, mango, potassium nitrate, urea AbstractThe effects of leaf applications of potassium nitrate (KNO3), alone and in combination with urea at different concentrations on flowering, fruit set and fruit quality of Tommy Atkins' mango grown in the rift valley of Ethiopia were evaluated. The trees were characterised by erratic flowering, continuous and high intensity of vegetative growth as well as irregular bearing. Uniform trees were selected for a randomised complete block design experiment with three replications and three trees per plot. Spraying was conducted initially on the immature postharvest flushes and then repeated after the flushes had matured and had dark green leaves. Potassium nitrate concentrations especially in combination with urea (5 litre solution of 4% KNO3+0.5 g urea tree−1 and 5 litres of 4% KNO3+I g urea tree−1) produced better results for most of the flowering and yield parameters. There was a non-significant difference for the qualitative parameters between the treated and non-treated trees. The supplementation of nitrogen through the spraying of KNO3 and urea is believed to be the reason for the observed greater flowering and yield results of the sprayed relative to the unsprayed trees. AuthorsYeshitela, T., Robbertse, P. J. and Stassen, P.
J.C. Year Published2005 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2005.10634676 This article contributed by:
|
| Changes in inorganic phosphorus following incubation of some Zambian soils | Yerokun, O. A. | 2005 |
KeywordsAlfisol, inorganic phosphorus, laboratory incubation, Ultisol, Zambia AbstractPhosphorus (P) deficiency is a major problem of many Zambian soils and annual applications of the recommended 60 kg P2O5 ha−1 (26 kg−1 ha−1) do not seem to reverse this trend. In order to better understand the dynamics of P in some of these soils, a laboratory incubation study was done to determine the changes in inorganic soil P when fertilizer application is made. Two P rates, 0 and 13 mg P kg−1 (0 and 60 kg P2O5ha−1, respectively) were applied to one Alfisol (Chakunkula series) and two Ultisols (Misamfu Red and Mufulira series) which were incubated for 14, 28, 56 and 100 days. Extractable Bray-1 P, acid extractable Ca-P and non-occluded Al+Fe-P were determined. Addition of soluble P to these soils increased extractable Bray-1 P levels, although the contribution of organic P was important. As the time of contact between soil and fertilizer increased, extractable Bray-1 P levels decreased. The soil with more Fe and Al concentrations showed lower extractable Bray-1 P levels, indicating the probable role of these colloids in P retention. Following an initial decreasing trend in Al+Fe-P levels, this fraction increased at 100 days of incubation, pointing to this as the pathway for P transformation in the soils. Acid extractable Ca-P showed better correlations with extractable Bray-1 P, but the amounts of P in this fraction were generally lower than those of the non-occluded Al+Fe-P fraction. It was concluded that non-occluded Al+Fe-P is an important store for P in the soils included in this study, therefore the extractable Bray-1 P test method in use may need to be modified to better capture this pool. AuthorsYerokun, O. A., Kumoyo, K. and Damaseke, M. I. Year Published2005 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2005.10634698 This article contributed by:
|
| Response of maize to ammonium nitrate, urea and cogranulated urea-urea phosphate | Yerokun, O. A. | 1997 |
KeywordsMaize yield, cogranulated urea-urea phosphate, ammonium nitrate, nitrogen fertilizers, ammonia volatilization AbstractUrea fertilizers may lose N by ammonia volatilization when applied in the field. In order to reduce this loss, modified urea compounds are being used. Not all of them reduce ammonia loss and improve crop yields. A field study was conducted to evaluate the comparative advantage of cogranulated urea-urea phosphate (340 g N kg−1, 73 g P kg−1) over urea (460 g N kg−1) and ammonium nitrate (350 g N kg−1) when supplied as nitrogen fertilizers to maize. The fertilizer granules were applied at rates of 67, 134 and 202 kg N ha−1, as surface-broadcast or soil-incorporated treatments. Fertilizer application increased crop yields and nitrogen uptake, but the sources were not significantly different from each other. Increasing nitrogen supply up to 134 kg N ha−1 improved maize yield and nitrogen uptake. Incorporating the fertilizer with the soil was not better than surface application. The data available suggest that maize responded to cogranulated urea-urea phosphate, urea and ammonium nitrate similarly. AuthorsYerokun, O. A. Year Published1997 PublicationSouth African Journal of Plant and Soil Locations- Lower Michigan, USA (42.6501, -84.5288)
- Vryburg, Northwest (-26.95, 24.7333)
- Virginia, Freestate (-27.9831, 26.7208)
- Hennemann, Freestate (-27.9667, 27.0333)
- Ottosdal, Northwest (-26.8, 26.0)
- Koppies, Freestate (-27.2333, 27.5833)
- Tweespruit, Freestate (-29.1856, 27.0289)
- Harrismith, Freestate (-28.2833, 29.1333)
- Warden, Freestate (-27.85, 28.9667)
- Bloemfontein, Freestate (-29.1213, 26.2128)
- Brandfort, Freestate (-28.7, 26.4667)
- Boshof, Freestate (-28.55, 25.2333)
- Hoopstad, Freestate (-27.8333, 25.9167)
- Wesselsbron, Freestate (-27.85, 26.3667)
- Petrusburg, Freestate (-29.1167, 25.4167)
- Warmbad, Limpopo (-24.8833, 28.2833)
- Middelburg, Mpumalanga (-25.7639, 29.4577)
- Bethal, Mpumalanga (-26.45, 29.45)
- Delmas, Mpumalanga (-26.15, 28.6833)
- Morgenzon, Mpumalanga (-26.7331, 29.6153)
- Charl Cilliers, Mpumalanga (-26.6667, 29.1833)
DOI10.1080/02571862.1997.10635083 This article contributed by:
|
