In this weeks Web on Wednesday James Quinn talks to CSIRO Research Agronomist Steve Yeates about irrigation interactions with Bollgard II® and Conventional cotton, and the research that is being conducted to investigate the issue.

You have been doing some work over the last couple of seasons in regards to irrigation interactions with cotton.  Can you just give us an outline of what you have been doing?

Most of our work in the last couple of seasons has been looking at whether Bollgard II® high retention plants need a different irrigation schedule than conventional cotton; so whether we really need to change our practices much when we move into Bollgard II®.  We have set up a series of trials to take things a little bit further than a farmer would in terms of stress just to see how the Bollgard II® plant reacts to water stress compared to conventional in a replicated experiment.

You have got a number of trials at Narrabri and in other areas.  Can you give us a run down of where those trials are and what you are actually doing in them?

We have got two trials.  Our major trial is here at ACRI which is a replicated experiment comparing Bollgard II® and conventional cotton with stresses at different growth stages and we have had a couple of trials at “Keytah” (Gwydir Valley) with Andrew Parkes. In the first year, it was a simplified version of what we were doing down here (ACRI) which is just stress at flowering. This year was more what Andrew Parkes wanted to do and fitted in with our objectives. This was comparing Bollgard II® and conventional (in one metre rows) with Bollgard II® in 15 inch rows and for each of these systems we imposed two treatments; one with normal irrigation and another with one less irrigation, so that the watering was stretched between each irrigation to see how the three systems compared.

You have been doing this trial now for a couple of seasons and you are almost through your second season. Can you give us a preliminary idea of how things are going based on one years results?

Yes, mainly on one year, but a little bit of this years work as well.  We are actually picking the last of those trials today. The interesting thing is that the plants are different; conventional plants are tipped out and don’t have a high fruit retention. Bollgard II® plants are not tipped out and they have very high retention so they look different but the Bollgard II® has been amazingly resilient to stress.  It uses about the same amount of moisture as conventional so there really hasn’t been a big differences in rooting depth, not until late in the season (up till cutout) and even when we stress them pretty significantly above 100mm deficits, the Bollgard II® responded very similarly to stress to the conventional.  It is only when we have got the stresses a bit larger than that and post cutout that the Bollgard II® yield was less than the conventional – under stress.  Under full irrigation there wasn’t really much difference.

You just mentioned that there were no great yield differences but what are you seeing in regards to fibre quality? 

Again, I have only got one years results for that and I think we will probably get bigger differences this year because it was hotter and there was more stress.  The 2005 season was a bit more even.  We found that the fibre quality was reduced in the Bollgard II® when we went into pretty significant stress and what I mean by fibre quality is fibre length when we applied moisture stress at about cutout. It was about 120mm deficit so it was pretty stressed. Under those circumstances, the fibre length was reduced in the Bollgard II®.  It was pretty stressed and the micronaire was up as well under that sort of stress.  But other than that, if we had a bit of stress at flowering or a little bit of stress mid flowering, Bollgard II® wasn’t any different to the conventional.  This is all with varieties with a Sicot 71 background.

You just mentioned there wasn’t a lot of difference between the conventional and the Bollgard II® when the stress was applied early.  It seems interesting between the two kinds of systems, one being a high retention system and the other a lower retention system. Could you elaborate more in that regard?

I think with the early stress, both plant types had time to compensate and although there was difference in retention, there was not a big fruit load on either plant yet; they were both only in the early stages of flowering.  By the time we get to cutout, the Bollgard II® cut out earlier than the conventional as it had a much higher fruit load at that stage than the conventional did. The conventional had a greater capacity to compensate and I think that is why the conventional has tolerated the later stress better.

You have mentioned there that as we all know, last year was a kinder season climatically than this year. What are your thoughts to how this will influence the results from this year?

I think this year will test the quality (in particular) a lot more than last year being a lot hotter and the plants going into stress more easily. We have got preliminary data from the ‘Keytah’ trial this year and it indicates that just stretching the irrigation out, cost, quality and yield but I don’t know whether its going to be much different between the three systems yet, we will wait until we get the data but definitely this year with higher insect pressure and the greater stress I think (in terms of yield), the Bollgard II® is going to do better across most of the treatments.  It is a bit of a guess yet as we haven’t picked it but that is how it looks and the quality will be interesting. 

Steve where do you see this research heading?

I am hoping that we will have enough seasonal variation in these last two years that we can get a bit of a feel for how sensitive Bollgard II® is to stress compared to conventional, We can then set some boundaries for growers to know how far they can go.  I don’t think that we have done all of the job yet and are not able to say which is the best irrigation schedule to use or which is the best deficit. That is probably where we will move, putting more focus into fine tuning those deficits and stresses; how much stress and the optimum deficit.

In summary, what do you think are the key points so far in regards to what growers should implement from this sort of work?

I think you have got to look at your plant. Basically Bollgard II® is a conventional plant that sets more fruit, therefore it has got a different leaf area and a different rate of fruit set.  It’s more predictable because of that and you have got to watch that and understand the affect of stress on that fruit load.  It’s going to be more sensitive to stress (probably extreme stress) than conventional and most of the time you are not going to get yourself into trouble.  You can manage it in that situation, for example if you have got to a field that you know you have got to stress and you have got a choice between a Bollgard II® and a conventional field, as long as it is not post cutout you probably you are probably better to stress the conventional field.  I think the quality is a little bit more resilient than we thought (based on one year) but again avoid severe stress. But, is a little bit tougher than we first thought.

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