HIGH FLYERS THINK TANK

Innovative technical solutions for water management in Australia

University of Adelaide, 30 October 2006

Group D – Plant and soil sciences
Rapporteur: Dr Marisa Collins

One thing I wanted to start off with is that, in regard to plant and soil sciences, one of the biggest things that we need to think about is actually putting the picture in context. If you look at Australia's stored water use you find that over 70 per cent of the actual stored water is used in irrigated agriculture. Now, 10 per cent of that water is used in urban water use. So if we can make a small 10 per cent saving in irrigated agriculture, we can save a huge amount of water that then can be used for urban water, rural water or environmental flows into rivers and other things like that. So I think that needs to be taken into context when we think about these things, and the sorts of decisions we are going to make regarding water.

We tried to keep to the four breakout topics, and I have loosely arranged what we discussed in those, but they do wander about a little bit because in plant and soil sciences we found it hard at times to keep strictly to these sorts of things.

We opened up with some talk from David Chittleborough's paper this morning on the sorts of things that can be thought about in an agricultural soil and plant sense when you are talking about using water more efficiently, or issues in water management in those sorts of areas. One of the things that David really emphasised was whether we can actually do things to access the stored soil water in the soil.

One of the things that we talked about was changing the soil structure so that that B horizon was utilised and the soil moisture there was accessed by plants. There are huge environmental impacts that you need to think about if you go down that path, particularly in terms of what happens to groundwater, drainage issues, and also salinity issues are quite pertinent. So with the case study that David talked about, where they actually removed the A horizon and then deep-ripped the B horizon – forgive me if that is not entirely correct, but that is the general idea – it is not actually practical in a broader agricultural sense. It requires the removal of a huge amount of soil, which obviously isn't really that practical. So we need to think about ways in which we can use the principles and ideas of this research and apply it in a more practical sense – ways in which we can create some improved soil structure and get access to that soil moisture in the B horizon.

One of the points raised was: can you do a cost-benefit analysis of that sort of thing? How long will it take, and can you get a positive cost-benefit analysis? There are lots of things that you need to take into consideration. One of the other points was: if you do deep-ripping, what sort of impact does it have on soil biology, and can you use improved soil flora and fauna and microbiology to change that B horizon?

One of the end points of all of this discussion about changing the B horizon was that we need more information. So we need more information about how different plant techniques, soil microbe techniques and deep-ripping techniques might be able to help us access that soil moisture. And one of the things that we finished on was: how do you measure the potential gains from these techniques? Is it a path that is worth going down? David's answer to that question was that if you could overcome a modest amount of that soil impenetrability and extract a small amount of the soil moisture from that layer, you could almost double the yield. So I think the end point that our group came to on that particular discussion was that going down this path may be quite a viable solution for us, particularly as we seem to be heading into some dry years and potentially a drier future as well.

There was also quite a bit of talk about the use of nanotechnology: what materials are available to be used, and how expensive are they? There are two pathways that we went down. The first was that in soil there are naturally occurring, highly charged particles which create fine layers within the soil. There was some discussion about whether there are processes that we can carry out or whether there are things that we can add to the soil to help these particles change the B horizon.

We then talked about the potential use of polymers to change this B horizon. At the moment they are used on the surface to change the structure of the clay on the surface of the soil, and they are used very positively in conjunction with fertiliser and other chemical applications on the soil, but there hasn't been any attempt to make them go down.

In terms of using biological agents, you need to create an environment where they will breed. So there was some talk about what sort of things we can do to change that B horizon to create an environment where natural biological flora and fauna will breed and help improve that soil structure and increase the ability of plants to extract moisture out of the soil, which is basically what all of this discussion is focusing around: how can we increase the rate of soil moisture extraction out of the soil, and access that soil moisture?

One of the things that we talked about is that you need to think about the energy tradeoffs. Polymers and other artificial compounds aren't produced in industrial quantities, which means that at the moment they are not a viable option. But in the future they may be, and it is in the technology area where there are potentially some opportunities. And quite a few of these amelioration techniques could be quite expensive.

There was also then some discussion relating to when David talked about the plants that bore their roots down into the B horizon. If there could be some genetic engineering of plants that exude compounds from their roots, which is quite possible – phenolics and other secondary metabolites could be used – they could have a potentially positive effect in changing the B horizon and increasing the soil water availability to plants. So I guess the end point was that changing the B horizon definitely has potential.

Under the loose heading of 'Water transport and storage infrastructure, maintenance, engineering', a major issue that kept coming up in regard to irrigated agriculture was that often the water we are applying is saline. That presents a huge problem, and particularly one that is going to increase, the more that we irrigate into the future. Plants are quite good at excluding salt when they uptake water out of the soil, which means that the more you irrigate and the longer the period of time over which it happens, the more the amount of residual salt left in the soil continues to increase. That is quite a big problem, because the more saline the soil gets, the less agricultural productivity you get out of it.

There are current techniques that apply calcium to help ameliorate that problem and help deal with the salt in the soil, but one of the problems at the moment is that liquid calcium, or a calcium solution that could be applied in the dripper with the saline water, would be the best solution to the problem but at the moment the solution is too viscous to actually put through dripper lines. So one of the key areas that we talked about is a way in which calcium can be applied to the soil to help the salinity problem and the long-term salinity effects of using irrigated water, to prevent this long-term build-up of salt. Also, with increasing dry years, you don't get leaching. So when you have a drought year, as we have this year, you get two years' worth of salt building up in the soil. Those sorts of things are very, very pertinent in terms of irrigated agriculture.

Potential solutions in regard to technology that doesn't exist at present but could in the future are making sure that drippers don't irrigate the same spot, which also has a positive benefit in terms of plant root development over a broader area. Can we genetically engineer plants so that they actively uptake sodium chloride in a way that is not bad for the plant? Or can we plant other types of crops, in alternation with irrigated crops, that will help get the salt out of the soil?

With respect to B horizons and genetically engineering plants, can we engineer plants that have deeper root penetration and positive exudates that will help that B horizon? Or do we have to think about things like shifting irrigated agriculture into areas that have more rainfall, so we are applying less irrigated water? There are issues with that, such as engineering crops to cope with tropical conditions. The issues of seasonality and a lack of winter temperatures can be a problem for perennial plants. And soils in northern Australia also present their own challenges.

Getting back to the point where I started: with 70 per cent of stored water used in irrigated agriculture, what can we do to make improvements in the savings of irrigated water? We need to think about growing crops in areas that are most suitable for those types of crops, so that low rainfall crops are grown only in low rainfall areas, et cetera.

One of the other issues raised in terms of grower allocations of water was that water allocations to growers are based on a set megalitre allocation, and if growers make improvements in water use efficiency they then generally just tend to apply the percentage gain to another crop. So instead of having incentives for them to improve in efficiency so their total water use is less, they then go and apply it somewhere else. That is quite a big issue. We didn't really expand on that much further, but it is one of the key issues that came up.

One of the things we did talk about was giving consumers a say on water use efficiency in irrigated agriculture. The idea was that we would get a rating on products for water use efficiency. So people would get a chance to choose. If you were going to buy oranges from different areas, you would get a rating of water use efficiency so growers get a choice about whether they want to go with the product that is more water use efficient or do they want to go with another product. It will be a rating system that is relative to itself: oranges will only be compared with oranges, and rice with rice, that sort of thing. That means you create an environment where there is, in dollar terms, an incentive for the farmer to have good water use efficiency ratings on their agricultural products. We wanted to encourage socially responsible behaviour, based on water use efficiency.

In terms of infrastructure and methods of application – there is potential in the way in which irrigation water is supplied and applied. Such as pipes versus open channels, drips versus sprays. However, one thing that was highlighted was that ways to save water in the agricultural industry often have energy tradeoffs associated with them, and particularly the large level of infrastructure required. It is something that is quite pertinent, and until there is some sort of lead on that, then it is going to be quite difficult to convince growers that they need to change – there is no potential outcome. Or the government needs to help them change to more efficient techniques.

We think it is important from an agricultural perspective to allocate water into environmental flow. We discussed several things: wetlands, and particularly coastal aquifers and the importance, where salt water was flowing into those situations, of keeping a check on salinity problems in irrigated systems, because it is something that most growers aren't all that aware of – they haven't thought about it all that much – and also maintaining river flows.

We also spent a bit of time talking about the impact that climate change will have on irrigated agriculture. One thing that has come out of one of the latest reports on climate change is that in southern Australia the summer and winter rainfall will decrease significantly, but particularly the winter rainfall. If you consider where Australia's major agricultural areas are, that is going to have a huge impact on the future of agricultural Australia, and water availability in those areas.

We think that there is a need for a more coordinated management of water resources, to regulate both quality and quantity of water. We talked about quality quite a bit, because it is a big issue when you are irrigating and applying that water to food and other crops. We talked about issues to do with recycled and recharged water, the seasonality, additional heat impacts from climate change, and environmental allocations.

Risk management: we discussed this in terms of agricultural water use, risks relating to things like reducing runoff and drainage in coastal systems, and what if there is an impact on the water in the soil as a result of this. We talked about groundwater diffusing, and how much soil water needs to remain in the soil without changing soil structure and causing degradation. It was suggested by David Chittleborough that only a small amount needs to remain in the soil, so there is the potential, in tapping into that soil water, for an increase there.

Risks associated with improving precision irrigation: I have already mentioned the effect of salinity in precision irrigation. The other thing is that you also get compaction under dripper lines. So there are soil property and soil salinity issues for improving precision irrigation.

Also in relation to risk management: we talked earlier on about genetically modifying organisms so they suit different areas better, so if you have a low-rainfall area you genetically engineer a wheat variety that is suited to that sort of rainfall pattern. But the problem is that with these sorts of crops you often have a tradeoff with yield – with increased drought tolerance there often comes a lower yield. That is something that we thought was a risk. The other thing is that although there are targets to meet the different rainfall requirements and crops that are suitable for different areas, at the moment the germ plasms aren't available.

The second issue we talked about was that if you could engineer a crop so drought tolerance was switched on when needed but remained dormant if the year was wet, that would be of significant advantage in terms of trying to manage that risk.

Also, salinity management has a very positive effect on improving water extraction. As David showed in his paper, if you can manage salinity properly, the wilting point is a lot lower so your plant doesn't need to work as hard to extract soil moisture out of the soil.

Discussion

Question (Stuart Minchin) – This is probably more for David. I have been mulling over this soil water thing for the last hour or so, and I am not sure about this. The water in soil is a dynamic store, in that it gets used and replaced. Sucking it all out will give you a one-off gain; you have then got to refill it with irrigation. So what we are really talking about is crop efficiency and yield improvement, as opposed to water saving.

The question I have relates to who keeps the savings from the water. If we get better efficiency in the crops it doesn't mean more water. It just means that the person that does it first gets the benefit of utilising their full entitlement to create yield, and the users that are relying on the inefficiency of that farmer for flow downstream go without their water, whether it be the environment as a user or other users. So I am interested in whether we can't treat the soil water as a thing to mine, because it has to be replaced every year and that takes water that was previously used for other things. It is a closed system. We may get better yield and better efficiency for the water that we use, but we have got to be careful that in doing so we are not taking water away from downstream users who rely on that inefficiency at the moment.

David Chittleborough – What has exercised our minds as a nation, I suppose, for the last decade or so is the problem of seepage salinity: the issue of leaky agriculture where water goes through the soil as a result of lack of use of winter rainfall, and therefore either in situ or along the B horizon the water passes down to low-lying areas and causes a problem with salinity. So one of the environmental aspects of this modification that we hope we could do with soils is that we would actually capture more of that water, use it in place and therefore prevent that off-site impact which is so manifest in other parts of southern Australia.