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The

Report

SR67: Windbreaks

Increasing Crop Growth on the Atherton Tablelands

The full report

This is a summary of an unpublished RIRDC final report ‘The effect of windbreaks on crop growth in the Atherton Tablelands of north Queensland ’ (DAQ-147A)by Dr Amanda Snell (phone 07 40915 200,fax 07 4091 5211, email snella@dpi.gov.au) and Simon Brooks of the Queensland Forest Research Institute (Department of Primary Industries – Forestry).

Research conducted on the Atherton Tablelands has found that trees grown as windbreaks can increase peanut and potato yields,leading to increased farm revenue.

The researchers say that given the environmental benefits associated with trees and the potential for yield increases in a range of crops,windbreaks would be a sensible investment for farmers in the region.

The windy tablelands

The Atherton Tablelands constitute one of the main agricultural production regions in Queensland.They are subject to strong winds throughout the year,yet prior to this study little quantitative research on the effects of windbreaks on crops had been carried out there.

Windbreaks offer a range of potential benefits: they can increase soil and air temperatures, improve plant water relations and irrigation effi- ciency and reduce pest and disease problems. They may also extend the growing season for sheltered paddocks,resulting in increased crop development,earlier crop maturity and market advantage.If managed appropriately,the trees in a windbreak might also be harvested for their timber products.

But there are costs.The trees in a windbreak occupy space that might otherwise be used for crop production.And they can compete for resources – light,,water and nutrients – with crops,thereby reducing crop yields.Such nega- tive effects may explain widespread scepticism amongst Atherton farmers about the value of windbreaks – a scepticism that this study might help to dispel.

The Atherton study

The study was initiated with funding from the RIRDC/LWRRDC/FWPRDC Joint Venture Agroforestry Program in 1994.It involved several scientists at the Queensland Forest Research Institute (Department of Primary Industries – Forestry))including Dan Sun,Geoff Dickinson,Amanda Snell and Simon Brooks;the latter two saw the project through to completion and wrote the final report.

The project,part of a nationally coordinated Joint Venture research program on windbreaks, aimed to quantify the effects of windbreaks on the three most common crops in the region: peanuts,potatoes and maize.It also aimed to determine the manner in which any possible windbreak effect was achieved:was it by reduc- ing the physical damage inflicted by wind on crops,or by influencing crop water balance?

The research was conducted over a four-year period on the adjoining properties of the Serra brothers.It involved the establishment and mon- itoring of crop performance at various distances from the windbreaks.These consisted of trees of various species and heights growing in two,three or four rows oriented in either a north-south or east-west direction to counteract the region ’s prevailing winds.

Potatoes

Figure 1 illustrates the effect of a windbreak on potato yields in the period 1995 –97.It shows that yield is low close to the windbreak, increases in a region beyond the windbreak,and then declines again as the influence of the wind- break diminishes.

The study found that windbreaks increased potato yield significantly at a distance of 3 –8 windbreak heights from the windbreak.Most of this increase was probably due to a reduction in the amount and severity of wind damage to potato leaves (see Figure 2).Drought stress is known to adversely affect potato yield,but the crops in this study were irrigated,so water was probably not a limiting factor.

Yield benefits varied between years.For example, an overall increase in potato yield of 4.8% was achieved in the ‘sheltered’ portion of the paddock in 1994;modelling showed that this amounted to an increase of about 1.8 tonnes per hectare – from 37.5 tonnes per hectare in unsheltered sites to 39.3 tonnes per hectare in protected areas.In 1996,the percentage increase achieved in the sheltered part of the paddock was 2.5%,rising from 48.6 tonnes per hectare in the unsheltered part to 49.8 tonnes per hectare in the protected area.

Figure 1:Potato yield versus distance from windbreak (log normal regression)



Peanuts

It was a similar story for peanuts,although pro- tection from water stress may have played a more prominent role.In the 1998 season,for example,peanut yield increased by an average of about 11.9%in the portion of the paddock between 1 and 40 windbreak heights from the windbreak compared to that portion of the paddock beyond the influence of the windbreak. The researchers attributed productivity gains to decreased leaf damage,coupled with decreased water stress in the early part of the peanut crop growth stage.

Maize

Although significant differences existed between maize grain yields at different distances from the windbreak in some plots in some years,there was no clear trend in this study.Similarly,there was no clear trend in final maize plant height across the paddock.In fact,the only noticeable trend was that maize leaf damage due to wind increased significantly as the effect of the wind- break diminished – although this had no meas-- urable effect on yield.

Figure 2: Potato leaf damage at different distances from the windbreak.


 

Why is maize different?

Why should windbreaks have a marked effect on the yields of peanuts and potatoes,but none on maize?According to the researchers,this might be due to differences in plant physiology between C 3 (potato and peanut)and C 4 (maize) plants.C 4 plants use the Hatch-Slack photo- synthetic pathway,which allows greater water use efficiency and greater maximum assimilation rates than does the C 3 pathway.The researchers speculated that given this greater efficiency, levels of leaf damage to maize away from the influence of the windbreak were insufficient to cause lower productivity.

Economic analysis

The researchers also conducted a cost-benefit analysis for a potato/maize rotation (with pota- toes grown in winter and maize in summer), using a model developed with data from one of the paddocks used in the study.This was 165 m wide and 750 m long;along its eastern boundary it had one three-row,9-metre high,165 m long windbreak.

The model outputs summarised in Table 1 suggest that the financial benefits provided by the windbreak were considerable,even allowing for the loss of cropping area and the nil response of maize to the presence of the windbreak.These benefits were calculated to be $335 per hectare per year,summing to $4,150 for the entire paddock.As the windbreak grows in height, yield increases in potatoes should extend over a greater proportion of the paddock,with addi- tional financial benefits.Similarly,if a second windbreak were established about halfway up the paddock,the area under protection would increase.Modelled returns for a second,three- row,north-south windbreak located 375 m west of the first windbreak provided a net increase in return of $670 per hectare,or $8,288 for the entire paddock.

Additionally,windbreaks can be managed for timber production,thereby providing additional revenue to the farmer.This could offset the costs of establishing and maintaining the windbreaks (which were not included in the above analysis). The researchers also noted anecdotal evidence that pest control may benefit from the presence of windbreaks.For example,one of the farmers involved in the study reported that the fungicide used to control diseases in peanuts appeared to be more effective on plants grown closer to the windbreak,where there may be less spray drift and a greater effectiveness due to better plant coverage.The researchers called for studies into the pest control benefits of windbreaks on the Atherton Tablelands.

Table 1:Cost-benefit analysis for growing maize and potatoes in rotation on one paddock,with a windbreak on the eastern side.



Model data is from the 1997 potato harvest.
Calculations for gross margin returns are based on figures supplied by DPI Notes Agdex 111/821 (Dryland Maize)and Agdex 262/851 (Atlantic Potatoes)costs and returns for the Atherton Tablelands.These notes also carry a disclaimer stating Information contained in this publication is provided as general advice only.For application to specific circumstances, professional advice should be sought.The Department of Primary Industries,Queensland,has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication.Readers should ensure that they make appropriate enquiries to determine whether new information is available on the particular subject matter.
 

Conclusion

The results of this study suggest that the incorporation of windbreaks into maize/peanut/ potato farming systems on the Atherton Tablelands would be profitable to the farmer. Such benefits may extend to other crops: orchardists,for example,may also expect improved fruit quality,and possibly yield,from the establishment of well-located windbreaks.

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Last updated: 17 December 1999 Copyright © RIRDC
http://www.rirdc.gov.au/pub/shortreps/sr67.htm