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2010

The effect of irrigation and weed competition on yield of a

commercial-scale Solanum centrale (bush tomato) production system:

a preliminary investigation

G El l isG Ol iverA VincentS Raghu

Working Paper

74

The Working Paper Ser ies

The effect of irrigation and weed competition on yield of a commercial-scale Solanum centrale (bush tomato) production system: a preliminary investigation

Gabrielle Ellis

Glen Oliver

Ange Vincent

S. Raghu

Contributing author information

Gabrielle Ellis: Arid Zone Research Institute, Department of Resources, Alice Springs, Northern Territory and Desert Knowledge Cooperative Research Centre (DKCRC), Alice Springs, Northern Territory

Glen Oliver: Arid Zone Research Institute, Department of Resources, Alice Springs, Northern Territory

Ange Vincent: Desert Knowledge Cooperative Research Centre (DKCRC), Alice Springs, Northern Territory

S. Raghu: Arid Zone Research Institute, Department of Resources, Alice Springs, Northern Territory

Desert Knowledge CRC Working Paper #74

Information contained in this publication may be copied or reproduced for study, research, information or educational purposes, subject to inclusion of an acknowledgement of the source.

ISBN: 978 1 74158 168 0 (Web copy)ISSN: 1833-7309 (Web copy)

CitationEllis G, Oliver G, Vincent A and S. Raghu. 2010. The effect of irrigation and weed competition on yield of a commercial-

scale Solanum centrale (bush tomato) production system: a preliminary investigation, DKCRC Working Paper 74, Desert Knowledge CRC, Alice Springs.

The Desert Knowledge Cooperative Research Centre is an unincorporated joint venture with 28 partners whose mission is to develop and disseminate an understanding of sustainable living in remote desert environments, deliver enduring regional economies and livelihoods based on Desert Knowledge, and create the networks to market this knowledge in other desert lands.

Acknowledgements

We acknowledge the Arrernte people, the traditional owners of the land on which this work was done. This project was funded in part by the DKCRC as part of Core Project 2.1: Bush Products. Chansey Paech (Alice Springs Desert Park) assisted with the establishment of the study site. Tim Collins (Alice Springs Desert Park), Geoff Miers and Greening Australia Nursery propagated the seedlings used in this study, and Green Crops, Conservation Volunteers Australia, and inmates from the Alice Springs Correctional Centre assisted with planting of the seedlings. Horticulture staff from Alice Springs Desert Park assisted in the design and installation of the irrigation on the site. Northern Territory Government Department of Resources staff Deb Roberts, Peter Shotton, Darren White and Ben Beumer provided support with site and equipment maintenance. We thank Craig James (DKCRC) for comments on an earlier draft of this manuscript.

The Desert Knowledge CRC receives funding through the Australian Government Cooperative Research Centres Program. The views expressed herein do not necessarily represent the views of Desert Knowledge CRC or its Participants.

For additional information please contactDesert Knowledge CRCPublications OfficerPO Box 3971Alice Springs NT 0871AustraliaTelephone +61 8 8959 6000 Fax +61 8 8959 6048www.desertknowledgecrc.com.au

© Desert Knowledge CRC 2010

Contents Tables ............................................................................................................................................. i Figures........................................................................................................................................... ii Abstract ......................................................................................................................................... 1 Introduction ................................................................................................................................... 1 Materials and methods................................................................................................................... 2

Study site............................................................................................................................. 2 Soil ...................................................................................................................................... 2 Water................................................................................................................................... 3 Plant material ...................................................................................................................... 3 Site preparation ................................................................................................................... 3 Irrigation, planting and harvest ........................................................................................... 3 Trial design and data analysis ............................................................................................. 4

Results ........................................................................................................................................... 5 Discussion ..................................................................................................................................... 7

Does irrigation rate affect yield?......................................................................................... 7 Does irrigation rate affect yield across varieties? ............................................................... 7 Does weed competition affect yield? .................................................................................. 7 Considerations for further research..................................................................................... 8

References ..................................................................................................................................... 9 Appendices – Production notes and observations ....................................................................... 11 Appendix 1: Site characteristics – soil and water quality............................................................ 12 Appendix 2: Pre-harvest phase.................................................................................................... 15 Appendix 3: Harvest phase.......................................................................................................... 18

Hand versus mechanical harvest ....................................................................................... 19 Appendix 4: Post-harvest phase .................................................................................................. 22

Post-harvest handling........................................................................................................ 22

Tables

Table 1: Experimental design for bush tomato (S. centrale) trials at the Arid Zone Research Institute................................................................................................................................. 4

Table A2.1: Insect pests observed on bush tomato site at AZRI................................................. 15 Table A2.2: Weeds observed on bush tomato production site at AZRI ...................................... 16 Table A3.1: Summary of relative advantages and disadvantages of hand vs. mechanical

harvest of bush tomato ....................................................................................................... 20

i

Figures

Figure 1: Aerial photograph of bush tomato trial site at the Arid Zone Research Institute .......... 3 Figure 2: Box plots depicting the effect of irrigation (L/h) on bush tomato yield (dry

weight; g) in Trial 1 ............................................................................................................. 5 Figure 3: Box plots showing the effect of irrigation (L/h) on bush tomato yield (dry weight;

g) across the three different varieties ................................................................................... 6 Figure 4: Box plots of the effect of weed competition on yield (dry weight; g) of bush

tomato varieties; (A) Amberlindum and (B) Napperby ....................................................... 6 Figure A3.1: Bush tomato plant with fruit at various stages of ripeness..................................... 18 Figure A3.2: (A) Hege harvester showing green bag placed over chute to collect waste

material............................................................................................................................... 19 Figure A3.2: (B) Bush tomato plot after Hege harvester had cut rows in both directions .......... 19 Figure A3.3: (A) Material collected in hopper............................................................................ 20 Figure A3.3: (B) Close-up of material, comprising stem, berries and seeds............................... 20 Figure A3.4: (A) Zig-Zag Seed Aspirator used to clean harvested material ............................... 21 Figure A3.4: (B) Close up of material collected in hopper that was fed into the seed cleaner ... 21 Figure A3.4: (C) Berries and waste material separated once it had been through the zigzag

seed cleaner ........................................................................................................................ 21 Figure A3.4: (D) Cleaned berries being sieved to remove waste material in a 34 mm sieve...... 21 Figure A4.1: (A–C) Washing ...................................................................................................... 22 Figure A4.1: (D) sub-drying of harvested bush tomato fruit....................................................... 22 Figure A4.1: (E) the resultant ochre-coloured sun-dried fruit..................................................... 22

ii

Desert Knowledge CRC Working Paper 74: Gabrielle Ellis

Abstract

Research was undertaken to gain a preliminary understanding of the horticultural potential of Solanum centrale L. (bush tomato) in central Australia to support the unpredictable supply of wild-harvested product. Specifically, the effects of irrigation (1L/h, 2L/h and 3L/h) and of weed competition (presence, absence) on the performance/yield of three geographic varieties of bush tomato (sourced from Amberlindum, Napperby and Utopia) were evaluated. Yield of plants irrigated at 2L/h was greater than those at 1L/h but did not differ from those irrigated at 3L/h, suggesting that there is a threshold at which irrigation is optimal. While there was considerable variability in form and yield of the three different cultivars, there was no statistical difference between the three varieties of bush tomato in terms of yield under varying rates of irrigation. Unsurprisingly, weed competition had a significant effect on yield of bush tomato, with plants growing with weeds having 15% of the yield of those grown in the absence of weeds. These results suggest that the potential for bush tomato production on a commercial scale requires several follow-up questions that need investigation. Significant questions that need to be addressed prior to horticultural production include careful characterisation of bush tomato genotypes, understanding the interactions of these genotypes with the production environments (i.e. phenotypic plasticity), the development of sustainable production systems (e.g. optimal irrigation rates, mechanical harvesting) and the integration of horticultural production goals with the goals of Aboriginal economic development.

Introduction

Solanum centrale L., also known as the desert raisin and bush tomato, is an arid zone plant typically restricted to the desert habitats of central Australia (Latz 1995, Purdie et al. 1982). The fruit of the plant is edible and turns from green to yellow when ripe and dry on the bush until it reaches a reddish ochre colour (CSIRO 2008, Low 1991). The fruit has been described as exhibiting intense, earthy caramel flavours, balanced by fruit sugars (Robins & Ryder 2004). Dried fruit is predominantly used as a dried ground spice, in the manufacture of dipping sauces, chutneys and relishes as well as a seasoning for meats (Cleary et al. 2008).

Increased uptake of S. centrale (‘bush tomato’ hereafter) fruit into the food manufacturing and food-service industry has lead to increased demand for a reliable source of high quality fruit (Robins & Ryder 2004). Current demand for bush tomato fruit has been largely met by small groups and individuals gathering produce in desert regions of Australia as the produce becomes available (Alyawarr speakers from Ampilatwatja et al. 2009, Walsh & Douglas in prep.). Harvests from the wild can be unreliable as crops are seasonal and subject to considerable year-to-year variation (Cleary et al. 2008, Miers 2004, Morse 2005).

The wild harvest of bush tomato fruit in 2000–01 was estimated to be 8–10 tonne, fetching a price of $15–$20/kg (Robins & Ryder 2004). The effect of ongoing drought on reduced wild harvest supply resulted in an increase in price of bush tomato fruit to $35–$50/kg for the 2007–08 harvest. Total volume of fruit from both wild harvest and cultivated supply for this period was estimated to be ~600 kilograms (Juleigh Robins, Director – Robins Foods, pers. comm. 5 June 2009). Increased awareness of bush tomato has elevated its demand and price, and collectively these factors have resulted in increased interest from various groups wishing to establish small-scale commercial plantings of bush tomato and other bush foods (Miers 2004, Robins & Ryder 2004). The demand for bush tomato and the variability of wild harvest has lead to limited exploratory cultivation under irrigation in several

The effect of irrigation and weed competition on yield of a commercial-scale Desert Knowledge CRC 1 Solanum centrale (bush tomato) production system: a preliminary investigation


areas outside of central Australia, notably in South Australia in the Yorke Peninsula to Riverland regions, and Murray Bridge and Ceduna. Production has also been tried in the cooler areas of South Australia with little success (CSIRO 2008). Since bush tomato requires dry, sunny and warm conditions for optimal plant health and to ripen and dry fruit, it is unlikely to be suitable for cooler or wetter areas, unless adapted varieties become available (Hele 2006).

Initial research conducted by the Desert Knowledge Cooperative Research Centre (DKCRC) resulted in the establishment of a number of small-scale plots (<100 m2) to explore basic aspects of plant biology and potential yield. Transitioning from small research plots to large-scale horticulture is required for the commercial food industry to establish and grow. However, it is a substantial step to take a plant from the wild and use it in horticulture in only a few generations. While it is easy in the short term to establish any plant on a reliable water supply, many attributes of its phenology (flowering and fruiting cycles) may be unfavourable for horticulture, and behaviour under these circumstances may depart from observed wild patterns in unexpected ways.

In order to gain a preliminary understanding of the horticultural potential of bush tomato in central Australia, this study investigates the effect of (a) irrigation rates, (b) origin of plant material (‘variety’ hereafter), and (c) weed competition, on bush tomato yield.

Materials and methods

Study site

The study site was situated on the Frank McEllister Horticulture Block at the Arid Zone Research Institute (AZRI; 23º46’07”S 133º53’21”E) located south of Alice Springs on the South Stuart Highway. The site consisted of two plots: A1 (50 m x70 m) and A2 (50 m x 40 m), lying east–west with the rows running north–south; the two plots were separated by a permanent bed of asparagus (Figure 1).

Soil

In January 2007, a composite soil sample was collected from each plot. The samples were obtained by sampling multiple random locations within each plot to a depth of 30 cm. The samples were sent to Australian Perry Agricultural Laboratory (Adelaide) and tested for Total Exchange Capacity, Organic Matter, Anions, Cations and Base Elements (Appendix 1). Both A1 and A2 were found to have excessive levels of Potassium (A1: 1516 kg/ha; A2: 1763 kg/ha) and Phosphorus (A1: 366 kg/ha; A2: 563 kg/ha). Both plots were low in Nitrogen (A1: 44 kg/ha; A2: 48 kg/ha) and colloidal organic matter (A1: 1.20%; A2: 1.40%). Given the high level of both potassium and phosphorus salts, fertiliser regimes were not included as treatments in this study.

2 Desert Knowledge CRC The effect of irrigation and weed competition on yield of a commercial-scale Solanum centrale (bush tomato) production system: a preliminary investigation


Figure 1: Aerial photograph of bush tomato trial site at the Arid Zone Research Institute

Water

Ground water for irrigation was sourced from bore RN16958, with RN144438 available as a back-up. A chemical analysis conducted in March 2007 revealed that the water had a high salt content; electrical conductivity (EC) of RN16958 and RN144438 were 2400µScm-1 and 2350 µScm-1 respectively (Appendix 1). The pH of the water was marginally alkaline (7.5–7.9) and the water was high in calcium carbonate (638–736 mg/L).

Plant material

Three local nurseries, Alice Springs Desert Park, Geoff Miers Garden Solutions and Greening Australia, were commissioned to propagate seedlings for the trial. Approximately 11,000 seedlings were germinated from seed sourced from three geographical sources (varieties): Napperby, Amberlindum and Utopia. Plants exhibited variation in morphology both within and between varieties.

Site preparation

Site preparation included the spraying of Roundup® (Scotts Australia Pty Ltd., Baulkham Hills, NSW) to knock down weeds in situ (Appendix 2). Areas A1 and A2 were ploughed with a disk plough to break up the soil surface and to plough in weeds 10 days after knockdown. Rabbit-proof fences were installed around the study site to minimise risks to seedlings after planting.

Irrigation, planting and harvest

Non-pressure compensated 17 mm inline sub-surface drip irrigation lines were installed in rows 1.5 m apart. To examine the effect of different irrigation rates, three lines were used to deliver water at different rates. The lines used were:

• Netafim Typhoon Super 80, drip spacing 30 cm, delivering 1 L/hour • Netafim Dripline 2000, drip spacing 30 cm, delivering 2 L/hour • Netafim Dripline 2000, drip spacing 30 cm, delivering 3 L/hour



Irrigation on both A1 and A2 was a closed loop design to ensure adequate pressure was maintained. The system was run from three separate stations on an automated controller. Seedlings were planted manually in April 2007 above each sub-surface irrigation line at 300 mm intervals in a zigzag pattern either side of the buried drip line. The plants were watered for two hours per week during April–May and August–September, and twice weekly for two hours at a time during October–March. Plants were not irrigated during the cooler parts of the year (June–July). Plants were hand harvested from November 2007 to April 2008, and both hand and machine-harvested from May to October 2008 to quantify yield.

Trial design and data analysis

In Trial 1 we investigated the effects of three levels of irrigation on the yield of the Napperby variety of bush tomato; while Trial 2 was a comparative study of the effects of same three levels of irrigation on the yield of three varieties of bush tomato. In Trial 3 we compared the performance of two varieties of bush tomato in the presence/absence of weed competition and varying irrigation rates; weeding was regularly done by hand. Yield was recorded per row for Trials 1 and 3, and was recorded at the plot level for Trial 2.

Data from Trial 1 were analysed as a mixed-model ANOVA (randomised complete block design) with block as a random factor and irrigation as a fixed factor. Trial 2 was analysed as 2-way fixed factorial ANOVA with variety and irrigation as factors. For Trial 3, the data were analysed as a 3-way fixed factorial ANOVA with variety, irrigation and weed competition as factors. Where significant treatment effects were detected, a Tukey’s HSD test was used to carry out posthoc pairwise comparisons of means.

Table 1: Experimental design for bush tomato (S. centrale) trials at the Arid Zone Research Institute outlining treatments within each plot

Trial No. [Plot (Rows)]*

Factors/Treatments (levels)

Replication Response variables

1 [A1 (2–46)]

Irrigation (3) • 1 L/h • 2 L/h • 3 L/h Block (5)

3 rows (115–155 plants) of Napperby per irrigation type within each block

Dry weight of harvested berries

2 [A2.1 (48–56)]

Variety (3) • Napperby • Amberlindum • Utopia Irrigation (3) • 1 L/h • 2 L/h • 3 L/h

9 replicate plots (40 plants each)


3 [A2.2 (59–70)]

Variety (2) • Napperby • Amberlindum Irrigation (3) • 1 L/h • 2 L/h • 3 L/h Weed competition (2) • Present • Absent

2 replicate rows at the level of the interaction term


*Buffer rows (bush tomato variety): 1 (Napperby); 47 (Napperby); 57–58 (Napperby); 71 (Amberlindum); 72 (Napperby)



Results

There was a significant effect of block on yield of bush tomato (F4,38=7.82, P<0.001) in Trial 1, but the differences in yield in relation to irrigation were consistent between blocks as evident from the absence of an interaction effect. Yield varied significantly in relation to irrigation level (F2,38=3.22, P=0.05), with the yield being significantly greater in the 2 L/h treatment (2359.00±392.43 g; mean±SE) than the I L/h treatment (1121.13±350.98 g) (Figure 2). The yield from 3L/h treatment was 1955.07±578.23 g and was not statistically different from either the 1 L/h or the 2 L/h treatments.

Figure 2: Box plots depicting the effect of irrigation (L/h) on bush tomato yield (dry weight; g) in Trial 1 The box represents the interquartile range and the line within the box indicates the median. Whiskers represent the range and symbols mark the outliers. Boxes with the same letter are not statistically different at P=0.05.



Figure 3: Box plots showing the effect of irrigation (L/h) on bush tomato yield (dry weight; g) across the three different varieties The box represents the interquartile range and the line within the box indicates the median. Whiskers represent the range and symbols mark the outliers.

The yield of the three bush tomato varieties (Amberlindum, Napperby, Utopia) in Trial 2 did not differ from each other under any of the irrigation rates (Figure 3).

The presence of weeds significantly affected the yield of both Amerlindum and Napperby bush tomato varieties in Trial 3, consistently across all irrigation rates (F1,12 = 44.19; P<0.001). The yield of plants growing in competition with weeds (206.25±112.19 g) (mean±SE) was less than a fifth of those growing without weed competition (1375.42±170.59 g) (Figure 4).

Figure 4: Box plots of the effect of weed competition on yield (dry weight; g) of bush tomato varieties; (A) Amberlindum and (B) Napperby The box represents the interquartile range and the line within the box indicates the median. Whiskers represent the range and symbols mark the outliers. Boxes with the same letter are not statistically different at P=0.05.



Discussion

Does irrigation rate affect yield?

The rate of irrigation was found to have a significant effect on yield. The results indicate that at the trial site at AZRI, 2 L/h was the optimal rate of irrigation in terms of bush tomato yield. The yield of bush tomato was significantly greater in the 2 L/h treatment than the 1 L/h treatment. However, the yield obtained from bush tomato irrigated at 3 L/h was not found to be significantly greater than the 2 L/h treatment. This suggests that there is a threshold level above which irrigation had no further effect on yield in the system.

Irrigation is a precondition for stable crop production in arid areas. Excessive irrigation can waterlog plants and damage crop health, resulting in a reduction in fruit quality and yield. Furthermore over-irrigation wastes water and energy, both of which have economic and environmental consequences for any production system. Long-term effects of over-irrigation can include degradation of the soil, nutrient leaching and associated increases in fertiliser requirements, as well as contamination of the water table (Giddings 2004, Qassim & Ashcroft 2006, Vlek et al. 2008). The water used in this study had a high salt content (EC of 2400µS cm-1). The productivity observed of irrigated bush tomatoes validates earlier anecdotal observations of this species’ tolerance to saline water (Robins & Ryder 2004). A low water requirement and tolerance of high salt loads are desirable traits for crops reliant on ground water in the arid zones of central Australia. Specific investigations of the effect of salinity and water quality on yield and plant water-use efficiency would further refine our understanding of optimal irrigation requirements for bush tomato.

Does irrigation rate affect yield across varieties?

Irrigation rate did not significantly affect yield across varieties. The absence of an effect of irrigation on yield across varieties may be due to an inadequate definition of variety in terms of the underlying genotypes of bush tomato. It was expected that morphological characteristics would be similar for plants sampled from a location, but this was not found to be the case. Differences were observed in leaf shape and colour, abundance of spines, growth habit, flower colour, and in the shape, size and yield of fruit both across and within varieties. This is not altogether surprising, given that similar patterns have been recorded in previous investigations of geographical varieties of bush tomato (Collins 2002). Careful characterisation of different genotypes of bush tomato and the implications of genotype-by-environment interactions (i.e. phenotypic plasticity) on plant traits and associated yield is required as part of subsequent investigations on optimising irrigation.

Does weed competition affect yield?

Unsurprisingly, the presence of weed competition has a negative effect on the yield of bush tomato. The presence of weeds was found to affect yield across both Amberlindum and Napperby bush tomato varieties across all three irrigation rates. Yield of bush tomato growing in competition with weeds was reduced to 15% of bush tomato growing without weed competition. Caustic weed (Euphorbia drummondii Boiss., Euphorbiaceae) was the principal competitor, forming a green impenetrable carpet that smothered bush tomato plants, resulting in plant mortality and reducing yield at the plot level. To ensure optimum yield in any future commercial production of bush tomato, management of weed competition is essential.



Considerations for further research

While this preliminary study specifically investigated the role of irrigation and weed competition on bush tomato yield, several key areas were identified for future investigations. The variability in bush tomato morphology and yield within what we labelled a variety suggests that careful characterisation of genotypes is an urgent need. Subsequent investigations of phenotypic plasticity will also help separate the effects of genotype and environment in the productivity of this species.

From a production system perspective, future studies need to consider changes in yield of bush tomato with age, to determine if treating this species as an ‘annual’ in a production sense would be more profitable than harvesting from the same individuals across multiple seasons. The efficiency of harvesting method is another aspect that needs careful consideration, paying particular attention to optimising harvest machinery for bush tomato harvest. Cursory investigations comparing hand- versus machine-harvesting in this study suggested that while machine harvesting was quicker in terms of harvesting the fruit from the plant, machine-harvested fruit required multiple post-harvest cleaning steps (Appendix 3: Table A3.1). Therefore, based on the machinery available at present, hand-harvesting may be more efficient (Appendix 3). Design of machinery that could incorporate cleaning of the harvested biomass to extract just the desired end-product (the fruit) would be an important step in this regard. A more rigorous cost-benefit analysis around harvesting methods and technology would help optimise this process for commercial production.

Future research into horticultural production systems needs to investigate the compatibility of commercial-scale activities (e.g. automated irrigation systems, mechanical harvesting) (Ahmed & Johnson 2000) with the wild-harvest industry and the developmental aspirations of Aboriginal participants to ensure benefits obtained from commercial production of bush tomato flow to Aboriginal people living in arid zones of Australia (Miers 2004, Morse 2005, Alyawarr speakers from Ampilatwatja et al. 2009).



References

Ahmed AK and Johnson KA. 2000. Horticultural development of Australian native edible plants. Australian Journal of Botany, 48:417–426.

Alywarr speakers from Ampilatwatja, Walsh F and Douglas J. 2009. Angka Akatyerr-akert: A Desert raisin report. Desert Knowledge CRC, Alice Springs..

Cleary J, McGregor M, Bryecson K and James C. 2008. 'Development of a value-driven bush foods industry chain that rewards Aboriginal people.' XXI International Grassland Congress and VIII International Rangeland Congress, Hohhot, Inner Mongolia, China, 29 June – 5 July 2008. http://www.desertknowledgecrc.com.au/publications/downloads/DKCRC_Development-of-a-Value-Driven-bush-foods-industry-chain-that-rewards-Aboriginal-people.pdf

Collins C. 2002. ‘A study into the domestication of Solanum centrale, Australian bush tomato’. University of Adelaide, Department of Horticulture, Viticulture and Oenology, Waite campus, unpublished PhD thesis.

CSIRO. 2008. Australian Native Foods, Plant Profiles, Bush Tomatoes, viewed 27 November 2008, <http:www.cse.csiro.au/research/nativefoods/crops/bushtomatoes.htm>

CSIRO. 2005. Australian Insect Common Names (AICN). Version 1.52. Last updated 16 May 2005. CSIRO. http://www.ento.csiro.au/aicn/

DEC (Department of Environment and Conservation). no date. FloraBase: the Western Australian Flora. Western Australian Herbarium. DEC, Government of Western Australia. http://florabase.calm.wa.gov.au/

Giddings J. 2004. Series 3: Irrigation management-scheduling. Waterwise on the Farm-Fact Sheet. NSW Department of Primary Industries, viewed 30 November 2008, <http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0003/165099/scheduling.pdf >

Hele A. 2006. Bush tomato, Desert raisin production. Fact sheet no. 8/03. Primary Industries and Resources South Australia (PIRSA).

Latz PK. 1995. Bushfires and Bushtucker – Aboriginal plants use in Central Australia, Institute for Aboriginal Development Press, Alice Springs.

Low T. 1991. Wild food plants of Australia. Angus and Robertson Publishers, Sydney.

Miers G. 2004. Cultivation and sustainable wild harvest of Bushfoods by Aboriginal Communities in Central Australia, RIRDC Research report No. W03/124. Rural Industries Research and Development Corporation, Canberra.

Morse J. 2005. Bush Resources: Opportunities for Aboriginal Enterprise in Central Australia, DKCRC Research Report 2, Desert Knowledge CRC, Alice Springs.

Purdie RW, Symon DE and Haegi L. 1982. Solanaceae. In: Flora of Australia, vol. 29. Robertson R, Briggs BG, Eichler H, Pedley L, Ross JH, Symon DE, Wilson PG, McCusker A and George AS (Eds.) Australian Government Publishing Service, Canberra.


http://www.desertknowledgecrc.com.au/publications/downloads/DKCRC_Development-of-a-Value-Driven-bush-foods-industry-chain-that-rewards-Aboriginal-people.pdf

http://www.desertknowledgecrc.com.au/publications/downloads/DKCRC_Development-of-a-Value-Driven-bush-foods-industry-chain-that-rewards-Aboriginal-people.pdf

http://www.ento.csiro.au/aicn/

http://florabase.calm.wa.gov.au/

http://florabase.calm.wa.gov.au/


Qassim A and Ashcroft B. 2006. Irrigation scheduling for vegetable crops, State of Victoria, Department of Primary Industries Agriculture Notes AGO787. State of Victoria, Department of Primary Industries, Tatura, Australia.

Robins J and Ryder M. 2004. Bush tomato. In The New Industries Crop Handbook: Native Foods, Salvin S, Bourke M and Byrne T (Eds.), Rural Industries Research and Development Corporation, Canberra.

Vlek PLG, Hillel D and Braimoh AK. 2008. Soil degradation under irrigation. In Land Use and Soil Resources. Braimoh AK and Vlek PLG (Eds.) Springer, Germany.

Walsh F and Douglas J. in prep. Aboriginal harvesters who sell bush foods and seeds from Central Australia for food and revegetation markets. Desert Knowledge Cooperative Research Centre, Alice Springs.



Appendices – Production notes and observations

Gabrielle Ellis1,2 and Ange Vincent2

1Arid Zone Research Institute, Department of Resources, Alice Springs, Northern Territory

2Desert Knowledge Cooperative Research Centre, Alice Springs, Northern Territory

Further to gathering quantitative information on the primary objectives outlined in the report, qualitative information was also gathered to identify high-yielding plant material, identify potential pests and weeds, explore feasibility of mechanical harvest opportunities, and document harvest and post-harvest handling and storage protocols. The following appendices contain notes and observations that were considered of significance to commercial-scale production of bush tomato. Information is presented under categories related to the production timelines: e.g. site characteristics (soil and water quality prior to planting of crop), pre-harvest phase, harvest phase, and post-harvest phase.



Appendix 1: Site characteristics – soil and water quality


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Appendix 2: Pre-harvest phase

The following are the pests (Table A2.1) and weeds (Table A2.2) identified at the study site at AZRI that could potentially affect a bush tomato production system in central Australia.

Table A2.1: Insect pests observed on bush tomato site at AZRI Scientific name Bemisia tabaci (Gennadius) Common names Silverleaf Whitefly, Poinsettia Whitefly, Cotton Whitefly Photo: Scott Bauer USDA, Agricultural Research Service

Scientific name Nysius vinitor Bergroth Scientific name Rutherglen Bug Photo: Nanet Pagsanjan, Department of Resources, Northern Territory Government

Scientific name Aphis craccivora Kock Common name Cowpea Aphid Photo: Nanet Pagsanjan, Department of Resources, Northern Territory Government

Common names sources CSIRO 2005

Other insects observed were lady bugs, native bees and ants. Ants were present in large numbers and appeared to be attracted to a clear, sticky exudate that formed on some fruits. Despite some insects being present in large numbers, none caused any discernable damage to the plants in the AZRI plot. Consequently no chemical control was deemed necessary.



Table A2.2: Weeds observed on bush tomato production site at AZRI Scientific name Acetosa vesicaria (L.) A.Love Common names Bladder Dock Ruby Dock Rose Dock

Botanical name Calotis hispidula (F. Muell) F. Muell Common names Bindy Eye Bogon Flea

Botanical name Cenchrus ciliaris L. Common name Buffel Grass

Botanical name Euphorbia drummondii Boiss. Common name Caustic Weed



Botanical name Salsola tragus L. Common name Russian Thistle Tumbleweed

Photos: Ange Vincent (DKCRC)

Botanical names sources DEC n.d.

Acknowledgements

Brian Thistleton and Coral Allan (Department of Resources, Northern Territory Government) assisted with identification of insects and weeds respectively.



Appendix 3: Harvest phase

Under irrigation, bush tomato produced flowers and fruits at the study site from September through to early June. Inflorescences consisted of 1–6 flowers and were found to vary in colour from bright purple to a soft mauve. On occasion, bush tomato individuals produced white flowers; plants with white flowers produced little or no fruit.

Fruit size, shape and colour were found to vary substantially across the trial plot both within and between varieties. Size ranged from 6 mm to 20 mm. Fruit shape was found to range from spherical to obovoid. Some fruit exhibited an acuminate shape, having a pointed end. Fruit colour ranged from bright yellow to an opaque cream. All fruit turned an ochre colour upon drying. The majority of plants exhibited a sprawling habit. Others exhibited an upright habit. Plants with a sprawling habit tended to bear more fruit. The weight of fruit, which dry and remain on the plant, contributes to plants becoming more prostrate over time. The tendency for mature fruit to remain attached resulted in many plants having new flowers at the growing tip and several fruit in various stages of ripeness and dryness down the length of the stem (Figure A3.1).

Figure A3.1: Bush tomato plant with fruit at various stages of ripeness Photo: Ange Vincent, DKCRC

During the trial fruit was hand harvested from November through to May. From the fruiting and flowering patterns observed, it is thought that harvesting, either by hand or machine, would be best conducted in late May or early June before the first frost event. Frost causes the bush tomato to arrest growth, and in some cases severe frost causes death of the aboveground tissues. Plants then shoot clonally from extensive underground root systems between late August and early September. Fruit that is hand-harvested earlier in the growing season at the yellow stage of ripeness require drying, as the major use of bush tomato is as a dried, ground spice. The average reduction in weight of harvested product after sun drying was calculated to be in the range of 30–40% during the course of the trial. Although a delayed harvest may mean some losses from fruit drop, the cost savings due to a single harvest and minimal post-harvest handling far outweigh the benefits obtained from continuous hand harvest during a growing season.



Hand versus mechanical harvest

Hand harvest resulted in minimal losses. Fruit that dropped from the plant could be retrieved by the picker. Green fruit could be left on the bush to ripen and be picked at a later time. The calyx of bush tomato clings strongly to the fruit and can be difficult to remove. However, pickers developed a technique where the calyx was removed as the picking process occurred. Hand harvest, however, had the disadvantages of being physically demanding. Plants are low to the ground, prickly and often covered with biting ants. Further to this, hand picking is slow; an inexperienced picker can take up to three hours to harvest 1 kg of fruit; this could be reduced to 2 h/kg by experienced pickers.

To assess whether bush tomato is harvestable mechanically, plots were harvested with a 1972 Hege Plot Combine Harvester in 2008, and a 1992 Kingaroy Engineering Works Trial Plot Harvester in 2009 (Figure A3.2). Machine harvesting was significantly faster than hand harvesting in terms of the removal of plant biomass.

(A) (B)

Figure A3.2: (A) Hege harvester showing green bag placed over chute to collect waste material Figure A3.2: (B) Bush tomato plot after Hege harvester had cut rows in both directions Photo: Ange Vincent, DKCRC

Machine harvesting, however, did have some disadvantages (Table A3.1). Separation of fruit from leaf and stem by the mechanical harvester was poor (Figure A3.3). Additional hand cleaning and sorting with an air column seed cleaner was required to separate berries from the leaf and stem material, as well as any unripe berries collected in the harvester’s hopper. Hand removal of the calyx from the berries was also required. Further to this, much of the fruit was chipped or cracked. This was evident through the amount of seed visible in the product collected in the hopper (see Figures A3.3A and A3.3B). Drought-stressing the plants (through reduction in irrigation duration) for 1–2 months prior to mechanical harvest reduced clogging of the harvester. This is likely due to a reduction in water content of the plant material going through the harvester. Having drier plant material going through the harvester also appeared to reduce the amount of unwanted plant material in the hopper.



Table A3.1: Summary of relative advantages and disadvantages of hand vs. mechanical harvest of bush tomato Hand harvest Machine harvest Advantages

• Reduced losses of fruit at harvest • Low/no non-fruit material in harvested

material • Ability to sort fruit based on quality as picked

Advantages

• Quick • Reduced labour costs for harvesting

Disadvantages

• Time consuming • High likelihood of pickers getting attacked by

ants that are typically abundant on the plant • Physically demanding • Expensive to pay pickers

Disadvantages

• Some berries chipped or cracked resulting in reduced yield

• Berries require separating from leaf and stem material

• Berries require hand cleaning to remove calyx

• Green fruits must be removed by hand • Additional hand cleaning and sorting is

time consuming • Additional costs for post-harvest cleaning

and sorting, and/or potential cost of seed-cleaning machinery

(B) (A)

Figure A3.3: (A) Material collected in hopper Figure A3.3: (B) Close-up of material, comprising stem, berries and seeds Green unripe fruit are also evident.

Photo: Ange Vincent, DKCRC

Hand cleaning and sorting of harvested material could potentially negate the time savings of mechanical harvest. Harvested material was cleaned by putting it through the Zig-Zag Seed Aspirator (Selecta Machinefabriek BV, Netherlands) (Figure A3.4). This sped up the process, but calyx material remained attached and required hand removal. The model of seed aspirator used was designed for small sample sizes. Only 500 grams of berry and waste material could be put through the machine at any one time, although larger capacity machines capable of better cleaning are commercially available (See http://www.selectamachines.com; http://www.kimseed.com.au). After going through the aspirator, larger material still needed to be picked out by hand and then the final product hand sieved to get rid of foreign seed material.



Figure A3.4: (A) Zig-Zag Seed Aspirator used to clean harvested material Figure A3.4: (B) Close up of material collected in hopper that was fed into the seed cleaner Figure A3.4: (C) Berries and waste material separated once it had been through the zigzag seed cleaner Figure A3.4: (D) Cleaned berries being sieved to remove waste material in a 34 mm sieve Photos: Gabrielle Ellis

In order to develop a large-scale production system for bush tomato, mechanical solutions to harvest and cleaning must be identified. To ensure that the crop is threshed properly, the berries cleared of debris and that all of the berries entering the harvester reach the hopper, the setting of the concave clearance, fan speed and sieve size is critical. A combine harvester fitted with a flex head that can flex over ground contours and pick up plant material close to the ground may eradicate the need to identify plants with an upright habit and limit fruit left on the ground. Trialling a combine harvester that is fitted with de-awning plates may address the problem of calyx material remaining attached to berries. De-awning plates are fitted to the concave in the harvester and provide additional friction to assist in the removal of difficult-to-remove plant material from grains. Whether this could also work for bush tomato requires further investigation.

Another aspect of mechanical harvest that warrants further investigation is whether it could be used manipulate yield. When the plot was mechanically harvested and cut to the ground, bush tomato plants responded with a flush of growth. Whether the timing of harvest could be manipulated to produce two crops a year requires further investigation. Further to this, yield would need to be measured to evaluate whether two harvests per year produce a greater yield than a single annual harvest.



Appendix 4: Post-harvest phase

Post-harvest handling

Green or unripe bush tomatoes contain a solanine, which if ingested in large quantities can be poisonous, and in smaller doses can cause gastric upset in humans. For this reason, it is important that green berries, which dry to a black colour, not be included in the harvested product. The picked fruit must be as free as possible from all leaf, stem, calyx and foreign materials. For current market demand, bush tomato must be dried prior to sale. Fruit that has too high a moisture content will not be accepted by buyers and is more prone to spoil during storage. Sun drying is the most cost effective way to dry fresh yellow fruit to the dried product, which turns ochre in colour.

After picking, the fruit was hand cleaned to remove any foreign material and then washed in lukewarm water for several minutes to remove residue and any ants and/or dirt attached to the fruit. The fruit was drained and spread onto mesh racks to dry (Figure A4.1). Approximately 30–40% weight loss occurred during the drying process. Dry fruit should be firm and not soft when squeezed between the forefinger and thumb. Sun-drying fruit to a firm state took 2–5 days.

Figure A4.1: (A–C) Washing of harvested fruit Figure A4.1: (D) Sun-drying of harvested fruit Figure A4.1: (E) The resultant ochre-coloured, sun-dried fruit Photos: Ange Vincent, DKCRC

Fruit picked late in the season had dried on the bush, and did not require preliminary drying. The dried fruit was also washed in lukewarm water (Figure A4.1). Dried fruit quickly re-hydrated, taking up water and becoming soft. Hence it was important to wash fruit quickly, preferably for less than two minutes to minimise re-hydration. Fruit collected late in the season (especially after rain events) was found to have a greater amount of dirt adhered to the fruit: as much as 1–2% of total weight prior to washing. After washing, the fruit was drained and spread onto mesh racks to dry. It took 3–6 hours for the fruit to dry back to a firm state after washing.


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