Country Gal, the other "villain" is rice, and it does seem to me as a layman that anything requiring that level of water shouldn't be grown in a dry country like Australia. However, I heard Graham Blight http://www.google.com.au/search?sourceid=navclient&ie=UTF-8&rls=GGLG,GGLG:2005-33,GGLG:en&q=graham+blight on radio yesterday suggesting that rice is the most efficient converter of water into carbohydrate.

If that's true, and I'd love someone to give me some information on that, then growing rice probably isn't a stupid thing to do at all.

Is there a comparable efficiency argument about cotton?

Billie, I don't have a problem with Cubby having 25% of the Queensland allocation (if that is what it is), because they presumably had to buy it from someone else who put less value on the water. If Cubby goes broke or scales down (and you'd have to wonder about how it is travelling given its dam is all but empty), then that water will presumably be purchased by someone else.

http://www.ancid.org.au/pdf/mildura_pdfs/DriversinWaterValue/NihalJayawardane_ancid.pdf

The tables in this research paper show a comparison of the efficiencies of various food crops, both in yields and water usage. Rice is on the higher end of the water usage scale, and uses much more irrigation water, but this is because it has to be grown in areas of Australia that are winter-rain based. The winter rain (and snow melt) is collected and then used in the irrigation of these summer crops. Evaporation rates are higher as the crop is a summer crop, and thus more heat = more evaporation. However, rice is a very high yield crop and thus despite its high mg/ha count, its tonne/ml count is quite reasonable. Whats more the soils in the vast majority of the rice growing areas are more suited to rice growing than other types of crops.In the above paper it shows that barley is a very efficient water user. However barley needs a certain type of soil to perform well, as does rice.

There are no water-carb production details for cotton, as it is a fibre crop, not a food crop. Cotton is pretty unique in that it has no commercial cropped competitor (its competitors are wool and nylon - grazed and manufactured). Cotton is a crop that has more than one use. The fibre itself is used for clothing, the seed (seperated from the fibre at harvest) is used for cottonseed oil (cooking) and cottonseed meal (stock feed) and the plant remains are ploughed back in as compost to improve soil nutrients and structure

As for water use, cotton is a desert plant. However to produce well it needs a regular water supply. Its does better under irrigation methods than grown in wet climates. This is because too much moisture in the plant structure and around the plant leads to boll rot (the boll is the part of the plant holding the cotton). When boll rot occurs the cotton is rotten and yield destroyed. Cotton grown in argentina (for example) faces this problem of boll rot. They have enough rainfall to grow the crop without irrigation, but lose a large percentage to rot, particularly if the rain falls at the wrong time of the season (when the bolls are developing). Northern NSW and southern QLD are good cotton growing areas, as they have the daily heat requirements to eoncourage good growth, and whilst they are subject to summer storms (which helps reduce irrigation requirements), the storms are not often enough ro large enough to give a large risk of boll rot. The soils of these areas are also well suited to cotton requirements.

Therein lies the difficulty in farming in australia. We have very few areas where we have all 3 requirements (soil, climate and water). So the solution so far has been to find the right soil and climate for a particular crop and try to get the water to where it is needed.

I dont think that the answer is to stop farming here. Climate change may be happening and may end up having a huge effect on farming in this country. I am suspect of this though, as I grew up in a rice growing area where rising water tables were the evil of the day. Now we find that perhaps too much effort has gone into trying to lower these water tables, with the result that the land is drying out too much. Science at the moment is doing a pretty big backflip on this one, and on other environmental issues.