Heat shield for vegies
From the May 2007 edition of Agriculture Today.
A team of vegetable growers at Griffith has found a solution to hostile summer growing conditions that could change the way vegetable crops are grown in inland Australia.
Tony and Frank Catazariti, and John and Anthony Vitucci of Nericon, are in their second year of production using a shade structure to protect what is essentially a field-grown vegetable crop.
The shade modifies the environment to enable otherwise unsuitable crops to grow successfully.
Suppliers of the shade structure, Envirotech, contributed several years of research to determine the best combination of colour and density of shade cloth on the roof to modify sunlight penetration, and on the sides to moderate wind speed.
Having proven the system works, the company and growers are confident the amortised cost of the shade cloth will make the technology viable to a wider market.
According to Tony, the structure has provided an opportunity to grow a much sought-after product, which growers using conventional systems find hard to produce in mid-summer.
The structure is housing a one hectare crop of mini capsicums this season, and sits alongside John’s melon and grape crops.
Buried drip irrigation and plastic mulch is used on the beds, while the slender plants have been trellised to prevent breakage and support the prolific load of fruit on the bushes.
“Normally these minicaps are supplied from Queensland in winter, with the other summer supplier being a glasshouse operation,” Tony said.
“We’ve been able to grow ours in the field, keeping our costs down, and creating a good working environment for our pickers.”
Tony admits there has been a lot of trial and error with adapting to the new growing system.
“We’ve had to be very conscious that we have created a favourable environment for pests, so we regularly check the crop for thrips, as we are concerned about the spread of virus diseases.
“In our first year when we grew seedless watermelons, we discovered water use is much lower under the shade and plastic mulch.
“We over-irrigated as a result, but still only used a fraction of the water we normally use to grow a crop.”
More effective use of the farm’s water allocation was a major factor in the eventual decision to erect the shade structure.
“With the minicaps, we have used around four megalitres per hectare, which is good considering the productivity, and the fact we had virtually no rain during the season,” Tony said.
“A gypsum block logger, installed to record soil moisture levels, has been an enormous help in more accurately managing water to meet the crop needs.
“We take a reading every couple of days, and a graph on the screen lets us make a decision on the spot.
“It has improved our understanding of what is going on under the beds.”
Tony said the team, coming from a broadacre vegetable background, believes it’s been worth the effort, as they are being rewarded now with excellent packouts of a high value crop from a fairly small block.
Soil moisture key to science under shade
A combination of factors makes protected cropping viable, despite added costs.
Reductions in sunlight intensity, windspeed, evaporative losses from the plant and soil surface as well as small increases in humidity surrounding the plant, when added together, provide a more favourable environment for plant growth.
In general, photosynthetic activity is unaffected by shading in most plant species, but there are changes in leaf area and stem elongation due to the altered light intensity.
Leaf surface temperatures will also be moderated, but the effects under this particular system have not been measured.
Water management is critical, as excess water can lead to diseases such as pythium and phytophthora, particularly when the plants are young.
Reduced evapo-transpiration losses because of the shade and plastic mulch means the crop can be easily overwatered, leaving the soil saturated, and reducing soil oxygen content; this is damaging to plant roots.
That’s why use of soil moisture monitoring is so important.
Contact Mark Hickey, National Vegetable Industry Centre, Yanco, (02) 6951 2611.
