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by David Peasley and Chris Rolfe

August 2003

RIRDC Publication No 03/094 RIRDC Project No: DPH-1A

Executive Summary

Background
Consistent high yields and high bean quality are essential to the viability of the coffee industry in Australia. The sub-tropic region of Eastern Australia produces distinctive cup quality and superior bean size that is readily marketable throughout the world.

Rainfall variability and distribution make irrigation essential to producing this quality coffee consistently. In the sub-tropics, coffee is susceptible to over bearing and subsequent die back. Water stress and inadequate nutrition predispose trees to this die back affecting yields and bean quality.

Current suitable coffee growing areas are located in environmentally sensitive areas close to rapid urban and lifestyle expansion and the future of the industry will be determined by its low impact on this environment. The industry must produce hard evidence that it can use water efficiently and any diversions from the catchment will be kept to a minimum.

Water entitlements are now limited in NSW and the cost of water set to escalate through water trading.

It is imperative that a cost benefit analysis on the return per megalitre of water be carried out to provide investors in this industry with a dollar value of water that will provide an acceptable return on investment.

This publication examines how efficient use of irigation can assist the coffee industry to achieve quality production with minimum environmental impact. It looks at the optimum water requirements and likely returns/Megalitre to grow coffee in the sub-tropics and establishes design criteria for irrigation and storage systems.

Methodology
In 1998, two sites were selected in northern NSW, one near the coast at Newrybar with mature trees that had not been irrigated since establishment and the other a new planting at Nimbin , away from the maritime influence, where summer and winter temperature ranges were higher and on a different soil type. The trees on the second site were drip irrigated from planting.

Trees at both sites were K7 variety from Kenya selected for its drought tolerance, its performance in local field trials and used extensively in current plantings in northern NSW. The tree spacings were 0.9 metres x 3.75 metres providing a density of 2963 trees/ha.

Both sites were laid out to three treatments. The first a non irrigated treatment (T1), the second irrigating to maintain a low stress level on the trees (T2) and the third treatment irrigating when a medium stress is induced on the trees (T3). The soil moisture at both sites was monitored by EnviroSCAN equipment with sensors at several depths to fully explore the fibrous root system.

Automatic weather stations were installed at both sites to collect temperature, rainfall, humidity, wind and solar radiation data to calculate the daily evaporation rates. The irrigation was carried out with a single line of pressure compensated dripline applying about 7 – 7.5 mm/hour.

Irrigation, flowering and yield and quality assessment data was collected to compare treatments and determine water requirements, irrigation system design criteria and management techniques.

Results
The rainfall recorded, irrigation applied and irrigation requirements for each of the treatments over the period of the project are shown in Tables 1, 2, and 3. The drip irrigation system only applies water to 19% of the plantation area wetting a strip 700 mm wide in a row spacing of 3.75 metres. In 1999 there was 2994 mm of rainfall over 195 days and irrigation was not required for either treatment.



Irrigation and storage requirements
Depending on the availability and cost of securing a water supply, even in a dry year (eg 2002), water requirements will vary between 1.23 (medium stress) and 4.11 megalitres/hectare (low stress) plus an allowance for seepage and evaporation in the case of an on farm storage.

If the water supply is a creek, river or a ground water supply then the daily extraction rate using a single dripline would be between 127,000 and 151,000 litres/ha/day in the month of highest usage.

Design criteria
The highest monthly irrigation application occurred in January 2000. Treatment T2 was 234 mm and T3 was 197 mm. These figures represent 31 and 26 hours of monthly irrigation per block.

Crop coefficient (kc) The monthly crop factors have been averages for the two irrigation treatments and are shown in Table 4.


Plant water use
From the data generated by the hourly readings of the EnviroSCAN capacitance soil moisture sensors, coffee trees extract between 70% and 93% of their water requirements from the top 300 mm depth of soil. This is even during periods of moisture stress in non-irrigated trees. Irrigation operation should only allow sufficient time to replenish the top 300 – 400 mm of the soil profile.

Yield response to irrigation
Yield data from the years 2000 – 2002 measured in tonnes of cherry/ha have been compared for each treatment and the details are shown in table 5.


Within these three years, there was a significant variation in the yields of cherry, but consistently treatment 2 was higher than treatment 3, which was always higher than treatment 1. The additional yield from the two irrigated treatments in tonnes of cherry/ha is shown table 6.



The value of the additional yield/ha at $8.15/kg dry green bean is shown in Table 7.


   If water is the limiting factor then the additional tonnes/ML might be more applicable. This reverses the treatments so that although treatment 3 has a reduced yield when compared to treatment 2 it uses much less irrigation water, so the yield per megalitre is greater. The results are shown in Table 8.



To fully evaluate the cost of providing additional on farm storage or constructing a bore to add groundwater supplies to improve the water security, the additional returns/ML at $8.15/kg DGB are shown in Table 9.


Bean quality
Bean size and cupping quality were compared for each year that irrigation was applied.

Bean size Year 2000 showed an 18% increase in size 18 bean for both the irrigation treatments when compared to the non irrigated treatment. In 2002 the comparison in bean size difference was insignificant.

Cupping quality Over the period of the project an independent professional panel blind tasted each harvest. There was no significant difference in the cupping quality between the treatments.

Typical results as per the 2002 harvest as assessed under internationally recognised SCAA cupping form were:

• The non irrigated scored 69 –“low acidity and mild smoky flavour and thin body”
• The low stress irrigated treatment scored 73 –“ dull bakey aroma, nice acidity, sour, green apple flavour”
• The medium stress irrigated treatment scored 75.5 – “ faint but sweet aroma, juicy, citrus flavour.


Ok body.”

Irrigation management
Unlike the climate of North Queensland coffee producing area, with its defined dry season which is favourable for managing flowering, rainfall events at both sites during the trial period showed conclusively that a defined dry season with little or no rainfall couldn’t be relied upon in the subtropics.

As a consequence flowering cannot be manipulated with irrigation in this region. A publication “Best Management Guidelines for Irrigation of Coffee in the Sub-Tropics” is currently being prepared.

Drip irrigation of the trees at each site only provided water to between 19% and 21% of the total plantation area of the trees. The bulk of the roots are under water stress in a similar way to the nonirrigated treatments and flower blossoming was only triggered by rainfall, regardless of the water status of a small proportion of the root area. This means that irrigation to keep the trees healthy during crop development and ripening will have little effect on the blossoming pattern for next year’s crop.

To achieve maximum yield irrigation should be available throughout the year and water provided when soil moisture in the top 300 – 400 mm profile reaches 50% of the readily available water supply for this section of the profile.

If water is limited then trees can be dried out to 100% of the readily available water supply in the top 300 – 400 mm of the soil profile with some reduction in yield but no change in quality or bean size.

Single row driplines with dripper spacings that provide a continuous wetted strip along the row with either 1.6 or 2.3 litre/hour dripper discharge will allow the trees to extract sufficient water to meet their requirements.

As coffee trees in full sun are gross feeders’ fertigation is strongly recommended to provide adequate nutrition throughout the growing season to also assist in greater stomatal opening to provide additional photosynthesis. Even during ‘the wet season’ fertiliser can still be applied at higher concentrations in short irrigations to meet nutritional needs and minimise any nutrient leaching caused by excessive rainfall events.