Mount Edgecombe Research Articles

Reproduction of Marphysa sanguinea Annelida, Polychaeta (Eunicidae), at Mount Edgecombe, Plymouth, near the type locality in Southwest England

Abstract The reproductive cycle of Marphysa sanguinea is described for a population at Mount Edgecombe, Plymouth, near the type location in Southwest England, using a data set obtained previously (October 1999 to September 2000). The species is iteroparous without schizogamy, spawning prior to October 1999 and during a short breeding season in 2000 from end August through September. The sexes are separate with a sex ratio of 1:1. Mature oocytes and spawned eggs are 215 μm in diameter and spermatozoa of the ectaqua sperm type. Mature gametes of both sexes are discharged through paired coelomoducts, and the diploid chromosome number is 28. Proliferation of new coelomic gametes from paired gonads began within a month of spawning and continued for 8–9 months but ovulation was suppressed in June and July. Attempts to undertake fertilisation using spawned oocytes and active spermatozoa were unsuccessful. The size of discharged oocytes suggests a short pelagic larval duration of a few days. This is the first publication about the reproduction of this species, and our results suggest that M. sanguinea is restricted to intertidal areas in SW England, NW France and southern North Sea. The highly synchronised pattern of reproduction observed is not compatible with a quasi-cosmopolitan species range indicating that this species has been mistakenly reported from around the world. Future studies of the genus should combine rigorous taxonomy with observations of reproduction to facilitate comparison among Marphysa spp.

Temperature trends for coastal and adjacent higher lying interior regions of KwaZulu-Natal, South Africa

Temperature trends for KwaZulu-Natal (KZN), South Africa, are investigated for the period 1930–2015, with the intention to test whether interior regions (within ~ 100 km of the coast) are warming faster than coastal regions, given oceanic moderating effects along the coast. This is achieved through analyzing instrumental temperature records from the coastal station of Mount Edgecombe, and adjacent interior stations of Cedara and Emerald Dale. The modified Mann-Kendall test is used to determine annual and seasonal mean temperature ( $$ \overline{T} $$ ), maximum temperature (Tmax), and minimum temperature (Tmin) trends for the period 1930–2015, and for the most recent few decades. For annual Tmax, a significant increasing trend (0.07 °C/decade) is recorded at the coast, whereas adjacent interior stations record no trend. Annual Tmin record significant warming at all stations, with warming rates over the interior being double that recorded at the coast for the period 1930–2015. For seasonal Tmin over the interior, significant warming rates are recorded: 0.21 °C/decade (summer), 0.22 °C/decade (autumn), 0.20 °C/decade (winter), and 0.15 °C/decade (spring). Seasonal Tmin warming over the coast were also significant: 0.16 °C/decade (summer), 0.08 °C/decade (autumn), 0.06 °C/decade (winter), and 0.12 °C/decade (spring). Thus, higher lying interior regions are warming at considerably greater magnitudes compared to adjacent coastal areas, mainly due to Tmin warming trends. For the period 1930–2015, record positive annual Tmax anomalies are reported for 2015 at Mount Edgecombe (mean anomaly = 1.6 °C), Cedara (mean anomaly = 1.7 °C), and Emerald Dale (mean anomaly = 2.0 °C).

Predicting genotypic differences in irrigated sugarcane yield using the Canegro model and independent trait parameter estimates

Abstract Crop models have the potential to support plant breeding by predicting genotype response to environmental factors, and identifying desirable genetic traits for improved crop performance. The study tested whether the Canegro sugarcane model can predict genotypic differences in stalk dry mass (SDM) yields observed in field trials using independently derived genetic trait information. Other objectives included the estimation of three trait parameters (TP) for selected genotypes, and assessing their role in determining genotypic differences in SDM yields. Phenotyping was conducted in a well-watered pot trial at Mount Edgecombe, South Africa comprising 14 genotypes. Gross photosynthate produced per unit of intercepted photosynthetically active radiation under ideal conditions (PARCEo) was estimated from leaf level photosynthetic efficiency (A) and stomatal conductance (gs). Thermal time from shoot emergence to the start of stalk elongation (CHUPIBASE) was estimated from measurements of leaf number. Maximum fraction of aerial dry biomass growth partitioned to stalks (STKPFMAX) was estimated from the measured stalk fraction of aerial biomass at harvest. Values of PARCEo (A) and PARCEo (gs) differed significantly between genotypes with a range of 47% and 67% of the mean, respectively. CHUPIBASE values also differed significantly between genotypes and showed a range of 23% of the mean. STKPFMAX values did not differ significantly between genotypes and showed the least variation with a range of 17% of the mean. The Canegro model predicted SDM yields and rankings well (r = 0.90**) for nine genotypes grown in well-watered field trials at Pongola, South Africa, using these independent estimates of PARCEo (A), CHUPIBASE and STKPFMAX values. The overestimation of the observed genotypic range in SDM yields were corrected by dynamically scaling leaf level photosynthetic efficiency using fractional sunlit leaf area. The reliable prediction of genotype performance was mostly ascribed to the impact of PARCEo. The extent of genetic variation in PARCEo found in the relatively small number of genotypes for well-watered crops, suggest that sugarcane improvement could be enhanced by screening breeding populations for high values of this trait. The study provided proof of concept that realistic sugarcane models could be used for identifying key traits (in this case PARCEo) and their ideal values (in this case as high as possible), and therefore could be used to assist in defining sugarcane breeding targets.

Water relations of two contrasting sugarcane genotypes

High-fibre sugarcane (energy-cane) cultivars have generated a lot of interest as candidates for bio-fuel production in marginal areas, especially when cellulosic ethanol is also considered. However, a better understanding is required of how much water would be used during cultivation and of their response to drought in terms of water relations. The aim of the study was to investigate the water relations of a high-fibre sugarcane hybrid (Saccharum spp F1 hybrid, 04G0073, referred to as G73) under well watered and drought stress conditions, and compare it with that of a traditional sugarcane cultivar (Saccharum spp, cultivar N19). This would help with a better understanding of the underlying physiology of differences in water use and drought response between high-fibre and traditional sugarcane. The trial consisted of four plots which were planted in a rainshelter facility at Mount Edgecombe, South Africa in October 2011. Two plots received adequate water for the duration of the trial (well-watered treatments), while the other two received no water after 10 February 2012 (water stress treatments), except for the unintended intrusion of water into the root zone on 3 March 2012. The experiment ended on 7 May 2012. Volumetric soil water content was measured with a neutron water meter and daily sap flow was recorded using the non-intrusive heat-balance method. Leaf water potential (ψL) was measured periodically with a pressure chamber, while stomatal conductance was measured periodically with a LiCor 6400. The study has shown that the heat balance method (constant heat source) of measuring sap flow velocity is a suitable technique for estimating transpiration rate in sugarcane. Transpiration rates of well-watered G73 were higher (11%) than that of well-watered N19, presumably due to a higher green leaf area index (GLAI) (6%). There was no evidence to suggest that parameters for calculating maximum evapotranspiration using the Penman-Monteith or FAO method need to be adjusted for high-fibre varieties. Transpiration rates of N19 were reduced sooner and at higher levels of soil water status, than that of G73, as water stress levels increased. G73 had the ability to maintain higher stomatal conductance (gs) than N19 at the same soil water status level, even though leaf water potential was similar between the genotypes. Higher transpiration rates of stressed G73 plants facilitated extended extraction of water from a drying soil profile, which could be a detrimental trait in marginal areas where long dry spells are common. Reduced rates of transpiration and water extraction from the soil profile through stomatal control could be a desirable trait for survival and optimal biomass production in marginal areas. G73 had higher biomass yield (12%) and WUE (10%) under well-watered conditions compared with N19 but water stress reduced both yield and WUE of G73 by 44% and 24%, respectively. The data obtained from the current study will be used for deriving crop parameters for sugarcane crop models with regards to energy-cane genotypes and may be useful in identifying marginal areas suitable for energy-cane cultivation.

Modelling water uptake, growth and sucrose accumulation of sugarcane subjected to water stress

Water stress affects the rate of water uptake, biomass accumulation and structural growth of sugarcane differently and, consequently, alters the partitioning of assimilate to sucrose storage. The CANEGRO sugarcane model is unable to accurately simulate the subtle rate changes in the source and sink processes during the progression of water stress during dry spells, with subsequent poor prediction of sucrose yields. The aim of this study was to test eight different water balance models by comparing simulated and experimentally determined rates of water uptake (WU), carbon assimilation (CAR), plant extension (PER) and sucrose accumulation (SA). Data from two experiments conducted in a rainshelter at Mount Edgecombe, South Africa were used: in the 2002/03 trial, WU, CAR, PER, SA were monitored over a 40-day period starting with 5-month-old well-watered sugarcane, which then received either adequate or no water (Experiment A). The 1998/99 trial was conducted under similar conditions, but with the stress treatment imposed at 3 months after planting (Experiment B). The approaches to modelling WU evaluated ranged from a simple approach based primarily on whole profile soil water content to relatively complex approaches taking account of layer specific soil water retention and root density. Results show that the fraction of available soil water at which soil water supply started limiting WU varied from 0.129 in Experiment A to 0.307 in Experiment B. The difference is ascribed to a difference in evaporative demand at that time. PER (sink activity) responded to water stress much sooner (14 days) and at much higher fractional soil water contents (0.81 compared with 0.14 in Experiment A) than CAR (source activity). SA was enhanced marginally in Experiment A and markedly in Experiment B due to mild water stress, presumably due to the differential impacts of water stress on source and sink activity. Severe water stress led to a cessation of sucrose accumulation. Increased modelling complexity did not necessarily result in better predictions of WU for these experiments. All models except CANESIM predicted the onset of reduced WU uptake to within 3 days of estimated actual onset. Simple models simulated a more gradual decline in WU with increasing stress levels than complex models, and mimicked actual decline closer. BEWAB was chosen as the most appropriate WU model for inclusion in CANEGRO because of its more gradual extraction of water as stress progresses. All models simulated smaller time differences between the onset of reduced sink activity and source activity than was observed. The best WU models in this respect were BEWAB and CANESIM. Using the BEWAB WU model also resulted in better simulations of CAR and PER. However, all models, except the CANESIM model, underestimated the early impact of water stress on PER. All models performed surprisingly well to simulate subtle changes in SA due to mild water stress. The BEWAB WU model with an adjusted water stress impact equation produced the best predictions of SA. It is recommended that the appropriate changes be made to the CANEGRO model and then to thoroughly re-validate yield predictions for many different cropping situations.

Sugarcane response to row spacing-induced competition for light

Information about crop response to row spacing (RS) in sugarcane is often contradictory and there is a lack of understanding of competition for light. This study aimed to gain a better understanding of how competition for light affects leaf and tiller development, radiation capture and conversion to biomass, and its partitioning between leaves and stalks. A first ratoon crop of cultivar NCo376 was started on 29 August 2003 (when the plant crop was cut back) at Mount Edgecombe, South Africa (29°42′18.4″S, 31°02′48.5″E, 105 m). A wagon wheel design was used with RS ranging from 0.36 m to 2.66 m and the crop received adequate water and nutrients. Radiation interception was measured within cane rows (FI INTRA) and across cane rows (FI INTER). FI INTRA was not affected by RS and maximum FI INTRA (defined as the first value above 0.9) was reached simultaneously for all RS. The progression of FI INTER differed substantially between the different RS. Maximum green leaf number was attained when FI INTRA reached 90% and coincided with the occurrence of peak tiller density. Thereafter there was a gradual decline in green leaf number caused by intra-row competition for light. As soon as FI INTER exceeded a value of 90%, there was a drastic reduction in green leaf number due to a sharp acceleration in leaf senescence rate induced by inter-row competition for light. Inter-row competition had an effect on aboveground biomass accumulation of RS of less than 1.37 m from before the first sampling at 730 °Cd (base temperature of 16 °C). For RS of 1.73 m the competition effect commenced sometime between the first and second sampling (at 948 °Cd). There appeared to be no inter-row competition effect for RS of 2.15 m and more. Radiation use efficiency seemed unaffected by RS (average value of 1.50 g MJ −1), although the increase in biomass yield (22% per metre reduction in RS) could not be fully explained by a concurrent increase in intercepted radiation (source size—18% per metre reduction in RS). Sink size (stalk density) responded more to a decrease in RS than source size (intercepted radiation) and the latter became insufficient to fill the sink to capacity when row spacing was less than 1.37 m. Conversely, sink size appeared to be the limiting factor for wider RS as evidenced by a similar mass per stalk for different RS. The stalk partition fraction of biomass increments was unaffected by row spacing, although the start of stalk growth was delayed with decreasing RS in terms of the threshold biomass required for stalk partitioning to commence. This resulted in lower final stalk fractions for narrower RS. The information obtained in this study enabled important new insights into underlying mechanisms of row spacing-induced competition effects on sugarcane growth and development. It should be useful for improving crop models’ ability to predict crop response to row spacing more accurately and in a more functional manner. The improved understanding could highlight avenues for effective crop improvement (e.g. ideal canopy development sub-traits) and crop management (e.g. weed and water management).

Simulation of sugarcane residue decomposition and aboveground growth

Due to the worldwide increase in demand for biofuels, the area cultivated with sugarcane is expected to increase. For environmental and economic reasons, an increasing proportion of the areas are being harvested without burning, leaving the residues on the soil surface. This periodical input of residues affects soil physical, chemical and biological properties, as well as plant growth and nutrition. Modeling can be a useful tool in the study of the complex interactions between the climate, residue quality, and the biological factors controlling plant growth and residue decomposition. The approach taken in this work was to parameterize the CENTURY model for the sugarcane crop, to simulate the temporal dynamics of aboveground phytomass and litter decomposition, and to validate the model through field experiment data. When studying aboveground growth, burned and unburned harvest systems were compared, as well as the effect of mineral fertilizer and organic residue applications. The simulations were performed with data from experiments with different durations, from 12 months to 60 years, in Goiana, Timbauba and Pradopolis, Brazil; Harwood, Mackay and Tully, Australia; and Mount Edgecombe, South Africa. The differentiation of two pools in the litter, with different decomposition rates, was found to be a relevant factor in the simulations made. Originally, the model had a basically unlimited layer of mulch directly available for decomposition, 5,000 g m−2. Through a parameter optimization process, the thickness of the mulch layer closer to the soil, more vulnerable to decomposition, was set as 110 g m−2. By changing the layer of mulch at any given time available for decomposition, the sugarcane residues decomposition simulations where close to measured values (R 2 = 0.93), contributing to making the CENTURY model a tool for the study of sugarcane litter decomposition patterns. The CENTURY model accurately simulated aboveground carbon stalk values (R 2 = 0.76), considering burned and unburned harvest systems, plots with and without nitrogen fertilizer and organic amendment applications, in different climates and soil conditions.

Simulation of Soil Carbon Dynamics under Sugarcane with the CENTURY Model

Currently there is a trend for the expansion of the area cropped with sugarcane (Saccharum officinarum L.), driven by an increase in the world demand for biofuels, due to economical, environmental, and geopolitical issues. Although sugarcane is traditionally harvested by burning dried leaves and tops, the unburned, mechanized harvest has been progressively adopted. The use of process based models is useful in understanding the effects of plant litter in soil C dynamics. The objective of this work was to use the CENTURY model in evaluating the effect of sugarcane residue management in the temporal dynamics of soil C. The approach taken in this work was to parameterize the CENTURY model for the sugarcane crop, to simulate the temporal dynamics of soil C, validating the model through field experiment data, and finally to make predictions in the long term regarding soil C. The main focus of this work was the comparison of soil C stocks between the burned and unburned litter management systems, but the effect of mineral fertilizer and organic residue applications were also evaluated. The simulations were performed with data from experiments with different durations, from 1 to 60 yr, in Goiana and Timbaúba, Pernambuco, and Pradópolis, São Paulo, all in Brazil; and Mount Edgecombe, Kwazulu‐Natal, South Africa. It was possible to simulate the temporal dynamics of soil C (R2 = 0.89). The predictions made with the model revealed that there is, in the long term, a trend for higher soil C stocks with the unburned management. This increase is conditioned by factors such as climate, soil texture, time of adoption of the unburned system, and N fertilizer management.

A novel method to determine larval mandibular wear of the African stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae)

The African stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae), is the most significant indigenous pest on sugarcane in South Africa (Atkinson 1980; Conlong 2001). Currently, crop management and cultivar resistance in sugarcane remain the most widely accepted control methods for E. saccharina in South Africa (Nuss & Atkinson 1983; Keeping 2006). Following emergence, E. saccharina larvae graze up and down the sugarcane stalk or disperse onto dead leaf sheaths for several days until old enough and, presumably, with sufficiently strong mandibles to bore into the plant (Leslie 1993). As young larvae use their mandibles to chew through the sugarcane stalk, abrasion of the mandibles’ chewing surface is inevitable and could ultimately reduce feeding efficiency. It is recognized that fertilization with silicon (Si) can enhance the resistance of plants to insect attack, including that of sugarcane to E. saccharina (Keeping & Meyer 2002, 2006; Kvedaras et al. 2007). Testing the effects of this treatment highlighted a need to measure the extent of wear on larval mandibles. While there have been studies that have reported wear of chewing mouthparts of insects, they have either failed to describe the method (Djamin & Pathak 1967), used a method which can only be applied to mandibles of the same size (Raupp 1985) or have not accounted for differences in mandibular size between individuals (Kokko et al. 1993). The objective of this study was to develop an accurate and repeatable method to measure the mandibular wear experienced by E. saccharina larvae fed on commercial sugarcane. It is anticipated that the method will be useful in quantifying mandibular wear in other adult and larval chewing insects. A method is described that uses a simple image analysis technique to determine the loss of feature on the chewing edge of the mandible. Ten third instar E. saccharina larvae were randomly sampled from commercial sugarcane cultivars N26 and N11 grown at the South African Sugarcane Research Institute (SASRI), Mount Edgecombe, KwaZulu-Natal. Larvae were placed directly into 70 % alcohol until required. Prior to analysis, the larvae were removed from the alcohol, allowed to air dry for 10 min and their heads removed under a light microscope. The labrum was removed and using a fine tipped dissecting needle, the mandibles were carefully pried apart to avoid chipping and air-dried for 1 h. The heads were mounted with their mandibles in a horizontal position using black, double-sided carbon tape (12 mm × 20 m, Structure Probe Inc., West Chester, U.S.A.), on standard aluminium scanning electron microscopy (SEM) stubs. Debris on the mandibles was removed using a fine dissection needle and a fine camel hair brush. The specimens were gold coated for 3.5 min (approx. 6 nanometres thickness) using a gold sputtercoater (Polaron E5100 coating unit and E5500 film thickness moniter, Polaron Equipment Limited, Watford Hertfordshire, U.K.). Specimens were viewed using a scanning electron microscope (Leo 1450 Scanning Electron Microscope, Cambridge, U.S.A.) and the images captured digitally. Each mandible has two scissorial teeth and a proximal tooth, the mola. The degree of wear of a mandible was quantified using an algorithm to obtain a mean square error (MSE), as follows. The (x,y) coordinates (x = horizontal, y = vertical) of the pixels in the digital image that represent the chewing edge of the mandible, from the distal to the proximal convex protrusion (distal scissorial teeth and mola tooth) (Fig. 1), were subjected to linear regression. As the chewing edge of each mandible is carefully orientated under a microscope in a vertical direction, the deviation in the X-axis is the most relevant measurement, hence the best-fitting straight line is calculated as:

The response of sugarcane canopy development to water stress

Water stress is a common occurrence in dryland crop production, including sugarcane production. A good understanding of how crops respond to water stress is a prerequisite for choosing the best cultivar and management practices to optimally exploit natural resources. One aspect of sugarcane growth and development that has not been investigated thoroughly is how canopy development is affected by water stress. The aim of this study was to gain a better understanding of the effect of water stress on various canopy development processes and interception of radiation. An experiment was conducted on a rainshelter facility at Mount Edgecombe, South Africa. The crop was planted and grown to four months age under optimal conditions. Subsequently, water was withheld from one half of the experiment for a period of 42 days. Soil water content for the stressed plots decreased from a field capacity of 26% at the start of drying to 15% on day 15 and a permanent wilting point of 10.5% at approximately day 40. Shoot and leaf development and interception of radiation were measured and related to soil water content, leaf water potential and stomatal conductance. Leaf senescence responded the most to drying (220% increase in leaf senescence rate as RSWC dropped from 0.7 to 0.3), followed by leaf appearance (96% decrease) and shoot senescence (113% increase for N22 and no response for NCo376). Cultivar NCo376 was able to maintain canopy development processes longer under conditions of increasing water stress than N22, at least initially. This was evidenced by lower rates of shoot senescence and leaf senescence (initially). NCo376 also maintained high stomatal conductance and leaf water potentials for longer during the drying process and at lower soil water content values than N22. The information obtained in this study should assist in simulating canopy responses in a more mechanistic way.

The effect of crop start date, crop class and cultivar on sugarcane canopy development and radiation interception

The two components of sucrose yield are the biomass and the sucrose fraction thereof. Increasing one or both of these will increase yield. Biomass could be increased by maximizing radiation interception or the efficiency of its use in photosynthesis, or both. In this paper we investigated the effect of crop start date (planting or ratooning date), crop class (plant or ratoon) and cultivar on canopy development and interception of radiation. A better understanding of this interaction may point the way to more effective crop improvement and husbandry strategies that could enhance radiation interception. A brief review of the literature and available sugarcane simulations revealed where there is a lack of sufficient understanding of canopy development processes in sugarcane. Some of the information is contradictory, while some of the modelling concepts do not reflect the current status of knowledge adequately. Fractional interception of photosynthetic active radiation (FI PAR), and leaf and shoot development was measured on well-watered crops harvested at 12 months in June and December at Mount Edgecombe, South Africa. Results showed that start date had a significant impact on radiation intercepted. Seasonal mean FI PAR for a June ratoon was 80% of that of a ratoon starting in December. The cultivar effect was less than the start date effect, the largest difference being 13% between cultivars NCo376 and CP66/1043 for the June start. Leaf appearance rates were similar for different crop classes and start dates. Leaf size distribution up the stalk depended on start date and sequence of shoot appearance (shoot rank order). The dynamic nature of leaf size profiles could be explained by source–sink concepts and the dependence of leaf area on temperature. Shoot appearance rate was directly related to the density of buds present in the ground. This explained the difference in shoot appearance rate between crop classes and row spacing. Peak shoot population density occurred at a thermal-time (base 16 °C) of 600 °C d. Evidence presented here shows that radiation interception of unstressed crops could be increased significantly by adjusting planting density to optimally match the cultivar and crop start date, at least in theory. Increases of between 10 and 15% could be expected when cultivar and planting density is optimally matched with starting date. The main shortcomings of models are (1) the separation of leaf and shoot phenology from biomass dynamics and (2) inadequate representation of intra-stool shoot variation.

Organic matter accumulation and fertilizer-induced acidification interact to affect soil microbial and enzyme activity on a long-term sugarcane management experiment

The effects of crop residue management and fertilizer applications on the size and activity of the microbial community and the activity of exocellular enzymes involved in mineralization of C, N, P and S were examined on a long-term (60 years) field trial under sugarcane situated at Mount Edgecombe, South Africa. Treatments at the site included pre-harvest burning with harvest residues removed (B), burning with harvest residues (unburnt tops) left on the soil surface (Bt) and green cane harvesting with retention of a trash blanket (T). Plots were either fertilized annually with N, P and K or unfertilized. The size and activity of the microbial community and the activity of soil enzymes assayed increased with increasing inputs of crop residues (B < Bt < T) and this effect was evident to a depth of 30 cm. The metabolic quotient was decreased by inputs of both crop residues and fertilizers. Annual fertilizer additions did not affect basal respiration, increased fluorescein diacetate (FDA) hydrolysis rate and acid phosphatase, invertase and protease activities and decreased arginine ammonification rate and dehydrogenase, alkaline phosphatase, arylsulphatase and histidase activities. These effects were attributed to an interaction between the positive effect of fertilizer in increasing the size of the microbial biomass and the negative effect of fertilizer-N-induced soil acidification on microbial activity and on the activity of exocellular enzymes. Such results demonstrate the importance of using a range of measurements of microbial and enzyme activity when determining the effects of management on soil microbial and biochemical properties.

A new method of simulating dry matter partitioning in the Canegro sugarcane model

Crop simulation modelling is widely accepted as a useful tool for research and management purposes in agriculture, also in sugar industries worldwide. Successful model application depends on accurate predictions of stalk and sucrose yield. The literature shows that the simulation of dry matter partitioning in sugarcane models “such as the Canegro model” could be improved by using source-sink concepts. This should lead to a better understanding of the processes involved and could lead to improved predictions of sucrose yield. With these aims in mind a new dry matter partitioning model was developed and incorporated into the Canegro model, and tested against independent experimental data. In the proposed model, daily partitioning of assimilate between roots and aerial parts is simulated as a non-linear function of total biomass. A constant fraction of aerial dry mass is partitioned to stalk when thermal time since emergence exceeds a given value. The rate of dry matter partitioning to stalk is regarded as the source strength. Partitioning of stalk dry matter is regulated by sink capacity and the source to sink ratio. Sink capacity is dictated by current growing conditions, current stalk mass and varietal characteristics. The sucrose accumulation component of the model is based on a framework of sucrose distribution within stalks as it is affected by temperature and water stress. Values of model parameters for cultivar NCo376 were determined from the literature and by model calibration on data from an experiment conducted at Mount Edgecombe, South Africa. The new and old method of simulating dry matter partitioning was compared to observations from 24 NCo376 crops grown at Umhlanga, La Mercy and Pongola, South Africa. The new method performed better than the old method in all respects. The RMSE of aerial dry mass, stalk dry mass and sucrose mass predictions was 6.94, 5.48 and 2.6 t/ha respectively. These values compare favourably with other models in the literature. The results show that the new method is sufficiently robust to accurately predict aerial dry mass, stalk yield and sucrose yield for a wide range of conditions. It is also capable of simulating subtle changes in partitioning associated with shifts in temperature and water stress conditions. It provides a good platform for further refinement of sugarcane dry matter partitioning such as the inclusion of chemical ripener, nitrogen and variety effects.

Soil organic matter content and quality: effects of fertilizer applications, burning and trash retention on a long-term sugarcane experiment in South Africa

The effects of crop residue management and fertilizer applications on soil organic matter (SOM) content and labile soil organic fractions were examined on a long-term (59 years) field trial under sugarcane situated at Mount Edgecombe, South Africa. Treatments at the site included pre-harvest burning with harvest residues removed (Bto), burning with harvest residues left at the soil surface (Bt) and green cane harvesting with retention of a trash blanket (T). Plots are either fertilized annually with N, P and K or unfertilized. Soil organic matter content in the surface 10 cm increased with increasing inputs of crop residues (Bto<Bt<T) and with annual fertilizer applications. There were no significant treatment effects on organic C or total N content below 10 cm but for microbial biomass C and N, readily mineralizable C and N, K 2SO 4-extractable and light fraction C, treatment effects were evident in the 10–20 and 20–30 cm layers. Changes in soil N content were more marked than those for organic C and, as a result, the C-to-N ratios of total SOM, the readily mineralizable fraction and the microbial biomass were all decreased by both increasing crop residue returns and fertilizer additions. By contrast, both crop residue and fertilizer inputs increased the microbial quotient since microbial biomass C was increased to a greater extent than total soil organic C. The results demonstrate that greater inputs of organic matter due to either increased returns of above-ground crop residues or increased deposition due to higher yields (induced by annual fertilizer applications) cause a proportionately greater increase in the size of labile pools of organic matter than in the total organic matter content.

An Improved Syringe Holder for the Hewlett Packard 7671A Autosampler

Journal Article An Improved Syringe Holder for the Hewlett Packard 7671A Autosampler Get access K.J. Schäffler K.J. Schäffler Huletts Sugar Limited, Research & Development Division, Mount Edgecombe, Natal, South Africa Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Chromatographic Science, Volume 14, Issue 10, October 1976, Page 498, https://doi.org/10.1093/chromsci/14.10.498 Published: 01 October 1976 Article history Received: 27 October 1975 Published: 01 October 1976

The Zia System of Soil Classification

Soil Science Society of America JournalVolume 10, Issue C p. 326-327 Miscellaneous Paper The Zia System of Soil Classification† B. E. Beater, B. E. BeaterSearch for more papers by this author B. E. Beater, B. E. BeaterSearch for more papers by this author First published: 01 January 1946 https://doi.org/10.2136/sssaj1946.03615995001000C00055x † Contribution from Soils Laboratory, Experiment Station, South African Sugar Association, Mount Edgecombe, Natal, South Africa. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume10, IssueC1946Pages 326-327 RelatedInformation

INDIAN CANES IN SOUTH AFRICA

On my way down the East-coast of Africa I visited the experiment station of the South African Sugar Association at Mount Edgecombe. and I thus had an opportunity of learning something about the re search work heing done on sugarcane in the Union. In the course of my stay at Durban I also saw, in a general way. the agricultural condi- tions prevailing in the main sugar-cane growing area in Natal.. It will be remembered that the Uba cane, which is the only variety grown on any scale in South Africa, was imported some years ago from Northern India, and my visit was of interest in providing an opportunity of seeing the conditions under which this Indian cane has become acclimatised and grown almost to the exclusion of all others. Recently a number of Coimbatore seedlings, which are closely related to the class of cane to which Uha belongs. have been under trial, one of which has already been released for cultivation, and although it is rather early to say how far these seedlings are likely to replace Uba. there is every reason to believe that the work at Coimbatore will be of great value to the industry in South Africa.