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Sarah Hood, Sustainable Irrigation Systems St George, explains ways that growers have improved furrow irrigation techniques, saving water and irrigating better.

I am talking with Sarah Hood from Sustainable Irrigations Systems at St. George.  Sarah work's with their clients to improve their efficiency of furrow irrigation.  Sarah can you give us a rundown of the sort of program that you go through when a grower comes to you to improve their furrow optimisation?

With furrow irrigation optimization, what you are trying to do is managing all the variables when you are irrigating so that you put in the amount of water that is required to be put in and no more or no less.  So what we need to do is we need to measure or observe the variables which are impacting upon how much water is going in to the profile.  Those variables are your flow rate through the siphon which we know is from the siphon size and the head in the ditch and the number of siphons can impact on how much water is actually entering the furrow.  Water quality is another one with increasing salinity you will get more infiltration in a certain amount of time.  So you probably need to take into account measure your water quality just to be sure that it is not impacting on your infiltration.  Soil type which includes the soil type obviously, its condition and its history and what I mean by condition is whether or not it has just had rain on it, its moisture content, sealing and history – has it just been cultivated or not.  Then you would measure the slope of the field and the length and those two variables, slope and length as you may well expect to sort of fix but once you go through the process of measuring all the variables and trying to optimise them, you might have very good economic reason to consider whether or not those variables are fixed.  So when we are doing furrow irrigation optimisation we measure and observe those variables then we put them all together to see how it is impacting upon the infiltration and then we run a program to optimise the infiltration or how much water is entering the root zone.

So, you have got a program, a computer program you put all those variables into and it spits out what the current practice is and does it also tell you what the impact of various changes to each of those variables will be.

It does.  So you put all those variables into the program which is called SIMOD the Surface Irrigation Modelling Program and it will model the current practice and what I mean by that is it will tell you how much entered the field, how much ran off and how much infiltrated the furrow.  Now depending upon how much infiltrated the furrow, you may well be happy, it might be very close to what you wanted.  For example it you are after 80mls you might have put 90mls in there or 85mls and you might have done it quite uniformly down the paddock.  But if its say 1.2 megs or 120mls that you have put in then you might consider doing something about it.  Then what you do is you start to change some of those variables in the program and see what sort of impact its going to have on the irrigation before you actually change them in the field.  And then we go out and that the exciting bit – we go out and start mucking around with the changes in the field and we are seeing how they stack up and seeing that we can actually make some real gains.

So how do farmers change some of those variables in the field?

Well initially, the easiest thing to do is cut the syphons off so that’s the first thing that they usually go for is to minimise the time that the waters actually in the furrow.  Because what we see is that the longer the waters ponded on the furrow, the more opportunity it has to infiltrate.  So the first thing that people do is that they usually cut down how long that they run their syphons for and get a few more shifts in the day and then the other thing that generally happens is that the flow rate has to increase and sometimes that means that they have got to run more syphons like two syphons every second row or sometimes it might mean they might go to a completely different syphon size.

And what other things have you seen people change the design of fields?

Yes, I have seen run lengths halve, yes halve like if you have got 1000 over a 1000 metre run or they might come back to 600 metres with quite significant economical gains in yield and water use making it quite a viable option.  I have also seen people using different strategies to improve their infiltration.  Say if they got a soil that crusts or doesn’t take in water as easily they might want to improve the infiltration so they don’t have to put so much water our there and they don’t have to recycle so much water.  So the things that they might use there are polyacrylamides or they might use standing wheat stubble.

What sort of benefits have you seen growers get out of using some of this technology and making changes based on it?

Early season I have seen massive reductions in water use and in fact I think that’s the biggest area.  It’s the biggest opportunity for saving water as early season, your pre-irrigation your water up and your first couple of irrigations and in those I have seen 20 – 50ml or .2 - .5 a mega hectare less water used to water up the field or pre-irrigate a field.  Later season I see 10 – 20mls less or .1 - .2 a meg less and over a whole season this usually amounts to anywhere between 15 and 30% water. 

Some people would see these success stories of some growers and choose to adopt some of the changes that they have made.  Can you just stress how important it is that people just adopt what someone else has done but also look at their own system and see what changes they need to make for their farm?

It is so critical to have and to measure on your farm those variables and see how they are interacting together to come up with the infiltration characteristic of your paddock and its going to be different.  It is going to be different with different run lengths, it’s going to be different with different slopes, it is going to be different with different soil types.  And if you see somebody over the road doing two syphons and you go and do it and you wonder why it didn’t work, it’s probably because one of those things wasn’t the same as your paddock.

Further Information:  David Kelly