Cotton Seed Distributors - Web on Wednesday

Mike Bange, Principal Research Scientist, CSIRO and CRC, discusses the implications of waterlogging in cotton crops.

Mike, obviously a lot of the valleys, particularly the southern valleys, the Namoi and the Gwydir have had a pretty severe waterlogging event in terms of flooding and heavy rain. Can you explain actually what happens when cotton crops are waterlogged?

Well it’s pretty straightforward Rob, but I think basically what happens is that your soil goes beyond full capacity or stays at full capacity. It is completely saturated and you get a lack of oxygen in the soil. Because you get that lack of oxygen in the soil and roots need oxygen to function you basically get poor root growth, nutrient uptake is impaired and overall plant growth is impaired because of that.

And the impact of that on cotton yields. Could you maybe run through what you’d expect from this event and if there were any more waterlogging events?

Basically the overall impact of what waterlogging does is slow the growth of the crop down or stops the growth completely and takes away the opportunity of producing more fruit in sites, so you get a reduction in nodes as a result of reduction of fruiting nodes, you get a reduction on fruit in sites and consequently your total boll number is down when you get to the end of the season. But there are opportunities for compensation in a sense that if your season length is long enough you will be able to keep putting that fruit on it and compensate for it much a kin to any fruit damage or something like that. But yes it reduces yield simply because you get a reduction in fruit number.

Some of the work that Arthur Hodgson did many years ago actually did have a formula or a guideline on how much yield loss occurs.

Yes, with Arthur’s work he showed in the system and at that time I think it was the early 80’s, on the research farm here at Narrabri showed that after 48 hours of inundation he was measuring the oxygen levels in the soil and he used that as an indicator of waterlogging.

He showed after 48 hours for each day of waterlogging that you would get, you’d get a reduction in about 0.2 of a bale per day and that was back in the 80’s but some recent work that we’ve been doing probably in the last 5 year here looking at waterlogging trials we are able to show that even up to 72 hours of inundation in normal hills and furrows that we actually weren’t getting impacts of waterlogging and what that was highlighting was that probably since the work that Arthur had done we have improved things like soil compaction; we’ve reduced soil compaction, we’ve leveled our fields, we manage our water much better and those sort of things so it provides really good insurance against, it showed that if you do all those things right it basically gives you a lot of insurance against waterlogging in the first place.

And some of that recent research that was done. Are there any other findings with regard to waterlogging?

One of the other key findings was obviously that hill height thing. We actually compared knocking the hills down first as normal hill heights and we showed that that’s when we got waterlogging after 72 hours was when we knocked the hills down, which showed that waterlogging early in crop growth around first square and then square end had much more of a consequence on the total growth than say after flowering or mid flowering, which is something to think about if you are putting in place strategies for trying to protect against waterlogging. It’s much more important earlier on than later on. I suppose that’s probably one of the other the key messages that came out of it.

So if you can just outline those things that people can do preventably to reduce the chance of waterlogging. Would you just go through those for us?

The first obvious one is your field design, your layout of your field, your slope, management of your tail water and those sort of things to get it off. Obviously having good, well-formed beds is great insurance. Good nutrition, healthy growth before you have the waterlogging. If you’re monitoring the weather and you can see that there’s going to be some cloudy conditions coupled with the possible high rainfall you can actually have a go at putting some folia applications of nitrogen on or iron chelates on. But basically I suppose really the major thing is to have your field laid out properly, good irrigation practices and things like that to really have good insurance against waterlogging.

So now I guess people have had the situation where they have had waterlogging. Is there anything you can do after or are there any management strategies after the waterlogging that they could do to improve the crops prospects?

The way I think about it is that you look at where you are in terms of monitoring your crop again and see where you are. You possible could use some folia fertilizers and those sort of things to nurture it if it needs nitrogen. If you have already got one of the consequences of waterlogging is you get de-nitrification from the soil, so if you’re getting a run down of nitrogen and the plant needs more then look at some strategies to give it a bit more. Put in some iron chelates on, can actually help get rid of the iron deficiency that can come about. But I sort of think just monitor it as you would a normal crop and just take into account your season length, what you would consider a season length. I’ve recently seen some cotton while I was in the States that was severely waterlogged earlier on and produced some of the best yields but they had a long season to make up for it. So you can actually still grow a good crop but you just have to take your season length into account and that’s no different from any other crop I suppose.

There are some fields obviously around that have been very, very severely waterlogged to the point where they have been under water for several days. Any ideas on what the prospects for those are?

I’d say if the water was dirty and running across the cotton it has probably damaged the plant. As a consequence of the damage you’ve probably let a lot of microbes in and the things are probably going to die anyway but just again I’d say monitor it and see if there’s any potential or regrowth coming as a result of that it’s going to be well behind. I don’t think we have any real formula for the plants that might look like that but keep an eye on it and just see whether it would recover. But the other aspect of it is if the water was sitting there on the field not moving and started to warm up there’s probably a high probability that you’ve got a lot of disease effecting the plant.

Further Information:  Robert Eveleigh, John Marshall, Craig McDonald or David Kelly