Irrigation and Salinity - learning from the past to protect the future.
|What could the fate of the cradle of civilization tell us about modern grapegrowing?|
The grape harvest is concluding around Australia. Almost universally vines have been reaching ripeness earlier than was expected, and in many cases earlier than ever before. In the background it has been officially announced to be the hottest summer in Australia since records began and this heat explains some of the rapid ripening seen.
In many regions summer was very dry and vines heavily reliant on irrigation. And with the reliance on irrigation an ancient curse becomes apparent.
Mesopotamia was known as the cradle of civilization, a bountiful land between two rivers, the Tigris to the north and the Euphrates to the south. The climate was like ours in Southern Australia. Rains were seasonal which meant that the land received good rains in the winter and spring but water was scarce at other times. Farming in the region depended on irrigation drawn from the rivers.
Mashkan-shapir was a typical Mesopotamian city, located about 45km from the Tigris River and connected to the river by a network of canals. They grew grapevines, date palms, olives and flooded fields to grow cereals and run stock.
|Drawing of a Sumerian City State in Mesopotamia.|
Note the use of channels to flood the land.
Despite a flourishing civilization, Mashkan-shapir was abandoned within only 20 years of its settlement. What could have caused this rapid demise?
The Atrahasis Epic, explains: “The black fields become white. That broad plain was choked with salt”.1.
Sodium Chloride from their irrigation water built up in their soil and destroyed the fertility of their farm land. Once the farms went; the city did too.
You might think this is ancient history… Ditto failed Roman irrigation schemes in Tunisia, but you can’t ignore research estimates that suggests that 140 000 ha of land across modern day Victoria is affected.
Technology has changed. Open channels have been replaced by pipes and we now have mechanical or electric pumps. However the basics are the same. We all take water containing salt and apply it to our soil during summer. Our grapevines roots and evaporation remove pure water leaving the salt behind in the top soil. Unless winter rains are sufficient to flush salt away below where plants can access it; topsoil salinity increases.
We face the same fundamental problem as the ancients. Under irrigation soils are becoming increasingly loaded with salt. Plant vigour and yield decreases. What once grew no longer will. Crops are changed until nothing grows. Land is then abandoned.
ARE WE POISONING OUR SOIL?
Driving around some South Australian wine regions, McLaren Vale, the Barossa Valley, Langhorne Creek included, after harvest it is obvious we are not always getting enough rainfall to flush our soils – especially on heavy clay. The visual symptoms of salt uptake are widespread. Salt is building up and we are losing fertility and this is affecting our yields and likely our grape quality.
In many cases where leaf symptoms are not obvious. Other salt signs include vine yields generally decreasing even though the soil has adequate nutrients, wineries are detecting high sodium levels in samples, or vines defoliating after hot weather.
How to we protect our fertility? How do we protect our livelihoods?
UNDERSTANDING THE PROBLEM
Unlike the ancients we understand what is happening. We know salinity is caused by too much salt (sodium chloride) in topsoil reducing the availability of water to plants.
Salinity in topsoil is caused by-
• Poor quality ground water. In most cases from bore water but also from river, mains or recycled water. All of these sources contain some dissolved salt.
• Natural soil salinity that has built up over thousands of years. Areas like the lake shore at Milang in Langhorne Creek, parts of the McLaren Vale Wine Region mainly south of Aldinga or from perched aquifers and old creeklines where water used to drain.
• Undissolved Fertiliser (usually from poorly composted animal manure), or soil amendments like gypsum.
Soil salinity has three main affects-
1. Increasing salt in the soil increases the osmotic pressure. This results in reduced water availability and reduced growth as plants have to work harder to pull up water. Plants handle hot weather poorly further reducing plant health.
2. Some elements or ions, especially Sodium (Na), Chloride (Cl) and Boron (B), are toxic or poisonous to crops in high amounts. They cause burning in plant tissue.
3. High proportions of Sodium in relation to Calcium and Magnesium can adversely affect soil structure, and limit water, air and root movement in the soil. Plants are again limited in their growth.
IDENTIFYING THE PROBLEM
How do you know what to look for?
Symptoms: A general reduction of vigour of your vines with some burnt leaves (photo 1). These vines have slowly declined over several seasons and are now showing symptoms of burnt leaf edges late in the season. Many growers are not recognizing that they have an issue with salt.
|1. Vines with poor canopy and some salt uptake symptoms - 4/3/2013|
|2. Salt symptoms - Pre-flowering (EL-18). Older leaves usually show the symptoms first. Light brown dead patches develop inwards from the leaf margin. This can occur early in the season – as this picture taken at EL-18 Pre Flowering shows.|
|3. Leaf burn mid-summer - McLaren Vale 2012/13. Over the season burnt areas grow rapidly and join together during hot, dry and windy conditions.|
STRATEGIES TO ALLEVIATE SALINITY
• Schedule irrigation applications to ensure adequate leaching of salts.
• For poorly drained soils (especially black, cracking clay “Bay of Biscay”), avoid over-irrigating and creating perched water tables.
• Mound soils with limited drainage or shallow depth.
• Increase soil organic matter. Organic matter helps buffer soil salinity by binding to sodium.
• In the long term plant on saline-resistant rootstocks to minimise the effects of salinity.
• Mulch the under-vine row to reduce surface evaporation and minimise surface salinity.
• Shandy saline water with a less saline source of water (recycled water mixed with bore water etc).
• Reduce the amount of saline water applied to the vines i.e. Partial Rootzone Drying (PRD).
• Take water, soil and tissue tests. Monitor salinity to help make management decisions.
LEARN FROM THE PAST. PLAN FOR THE FUTURE.
I am not trying to be alarmist but rising soil salinity is the main issue that we face in our region. Look at the signs. We have reducing vine vigour, we have reducing yields, we have more symptoms of leaf burn than ever before. It doesn’t matter what grade your vines are if you can’t grow them.
If rising salinity is not addressed all irrigation in low summer rainfall areas runs the risk of going the way of the dead cradle of civilization. We run the risk of reducing the fertility of our soils and the health of our plants, damaging our businesses and not learning from the past.
________________________________References and Links
1. The Social and Environmental Effects of Large Dams: Volume 1. Overview. Wadebridge Ecological Centre, Worthyvale Manor Camelford, Cornwall PL32 9TT, UK, 1984. By Edward Goldsmith and Nicholas Hildyard.
2. Landcare website - http://www.landcare.net.au/files/fieldguidebook/salirr.html