NIAB - National Institute of Agricultural Botany

Orson's Oracle

Climate and rotation

Posted on 13/08/2014 by Jim Orson

My final pre-harvest prediction of wheat yields was superseded by the actual harvest! As expected, yields are exceptionally high in some areas. The reported variable yields must in part be explained by the variation in June rainfall, which was a result of localised storms rather than frontal rain. Solar radiation in June and July was well above average and temperatures were not too high until the very end of ripening.

It was on a recent and beautiful sunny Sunday morning that I noticed that my neighbour’s leylandii hedge appeared to be dying. The Cambridge Council tree officer was kind enough to visit and said it was due to the high number of aphids that had survived the exceptionally warm winter. Apparently, this is the worst year in living memory for such damage. So, my neighbour and I have sprayed thrice with a legal neonicitinoid, but there may be lasting damage to the hedge.

Is this a result of a warming climate? There are other clues in our garden. For instance, this is also the first year that I have had to spray my zonal pelargoniums (geraniums) against rust. From a personal point of view, after a shower my hair now dries three or four time more quickly than when I was a teenager, but my wife diplomatically points out that there could possibly be less of it.

The mild winter has had its impact on UK agriculture. The challenge from yellow rust in wheat has been exceptionally high. The only compensation is that there appears to be no resistance in yellow rust to the major groups of fungicide used on wheat. The mild winter and early drilling may also have contributed to the difficulty in controlling triazole-resistant septoria in wheat. All this has resulted in more flexible and expensive fungicide programmes, banging a further nail in the coffin of the old (T0), T1, T2 and T3 approach.

One problem with the exceptionally mild winter was that there was little or no frost tilth present on the heavy soils when the spring crops were sown. This problem was magnified by the fact that it was extremely wet in the early spring and, in many areas, when it eventually turned dry there was little further rain in the following two months to support crop establishment. In the ‘old days’ this could have been disastrous because the seedbed cultivations would have dried out the soil resulting in poor and slow crop germination. In fact, this is what happened in some cases this year when a combi-drill was used. However, where the crops were established into autumn cultivated land with a single-pass disc or with a disc direct drill the germination, establishment and initial growth was superb despite the very dry March and April.

This experience is great in order to convince those farmers who are knee deep in black-grass to consider adopting spring cereals in order to break its life cycle. Possibly one of the reasons for their reluctance is the memory of trying to establish a spring cereal crop in conditions similar to this year. The thing is that equipment has changed dramatically since they may last have tried to do it, and now we have better machines for the job. These make spring-sown cereals a much more resilient and sustainable cultural control option. I must admit that I am not a ‘tyre-kicker’ and this is perhaps the full extent of my knowledge on drills, but I think that I have made my point.

Talking of difficulties with drilling and crop establishment, we’ve just had a visit from a NZ farmer who reports the trauma they have recently been going through whilst trying to establish autumn-sown cereals and small-seeded crops.

They have had exceptionally wet and dull conditions for months. Lack of sun resulted in disappointing wheat yields and the rain meant a difficult and delayed harvest. In the main area on the Canterbury Plains, especially on heavy soils, there have been few small-seeded seed crops and winter wheat crops established in their autumn. Some crops that were sown have failed. The only realistic option for many farmers in this part of the world is now spring barley.  

It is their worst late summer and autumn for arable farming in living memory and confirms that we are not the only ones who suffer from prolonged periods of extreme weather.  Such events plus that of pesticide resistance and pesticide withdrawals mean that farming and the supply industries must adjust to a more flexible approach.  In the UK, sowing spring crops on heavy soil is now part of that desired flexibility. The old certainties seem to be disappearing.

NZ Canterbury Plain - autumn drilling 2014

June on the Canterbury Plains in New Zealand. This is a time of year when fields should be green with vegetable seed crops, grass seed crops or winter wheat. The grass margins provide a firm base for the passage of linear boom irrigation equipment along the field (when needed!!!).

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Black-grass, the year of the double whammy

Posted on 22/07/2014 by Jim Orson

Our garden and allotment are now in full production and currently we do not have to buy any vegetables. This weekend we ate our first tomatoes and the first aubergines are a few days away. We really enjoy gardening but over the years I have often considered whether producing our own vegetables is economically worthwhile. This is particularly so when my wife has to struggle with a dirty and misshapen parsnip when the local corner store (Waitrose) can provide washed and perfectly shaped roots!

It is with this in mind that I recently studied the price of vegetables in the local corner store whilst sipping my free coffee. After a while I came to the conclusion that it was worth growing the basics such as potatoes, lettuce, onions, shallots, leeks, parsnips, broad, French and runner beans, butternut squash and courgettes. However, things like tomatoes, aubergines, peppers and chillies are our loss leaders particularly when we have to take into account one of our daughters or a neighbour having to water the greenhouse when we are away. I even have to hand-pollinate the aubergines with a paint brush and yet you can buy a large and perfect example for around 70p.

This is a microcosm of world trade in food. Grow what you are best at and import the rest. UK heavy land farmers can grow wheat competitively because of high potential yields. However, to exploit this potential we have to apply a high level of inputs.

Perhaps I am biased but it was the introduction of herbicides such as isoproturon that set the foundation for exploiting this high yield potential. Not only did it allow us to grow more wheat on the land most suited to its production but also to use non-inversion tillage and to sow earlier. Early sowing has three advantages; it enables a longer drilling window (so spreading machinery costs), in many cases it results in a higher yield potential and it also helps to ensure that the operation is carried out in good soil conditions.

Black-grassIt cannot have escaped anyone’s notice that this foundation for exploiting our potential for wheat production is now being undermined by herbicide resistance in black-grass. The industry has no option but to take this on board. No longer do farmers believe that high herbicide use and a minimum of cultural measures will overcome the problems they are encountering. There is a realisation that two or even three years of spring cropping (plus herbicide use) may be required to get some populations under control.

Amongst all the gloom, it is worth bearing in mind that this year we may have suffered a bit of a double whammy with black-grass populations. The epically cold and wet summer of 2012 resulted in high levels of dormancy and a very significant proportion of the black-grass seed shed in that year would not have germinated until the autumn of 2013. The summer of 2013 was conducive to low dormancy which meant that a very high proportion of the black-grass seed shed last year would also germinate last autumn. This helps to explain the rather unbelievably high numbers of black-grass that emerged after early drilling last autumn.

We are not alone in having pesticide resistance challenging the most economic production methods developed when the pesticides were working effectively. I have mentioned before that in Ireland, which has the highest average wheat yields in the world, there is caution in sowing a very high proportion of wheat in the rotation because of the danger of fungicide-resistant septoria dramatically reducing yields. In Australia, the measures required to control herbicide resistant rye-grass (Lolium rigidum) have had an enormous impact on rotations. A visiting Australian consultant told me at the weekend that the attention to detail required has made them better farmers. I am sure the same will be true for black-grass control in the UK but try telling that to the bank manager.

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It’s not every year that…

Posted on 14/07/2014 by Jim Orson

Tour de France in Essex 2014It’s not every year that you can walk ten minutes down to the end of your street and see the Tour de France go by. It is really a spectacle. We were lucky enough to see all the first three stages as one of our daughters lives in a part of Yorkshire that’s very close to where the first two stages passed. I must admit there appeared to be more enthusiasm in Yorkshire during the build up for Le Tour, but the citizens of Cambridge did turn up in huge numbers to see the start of the third stage. We went down to the centre of Cambridge early on the morning of the start and I heard an announcer say that France was the host country of the Tour de France. I guess we all say something daft on occasions.

It’s also not every year that has good conditions for the control of perennial broad-leaved weeds with pre-harvest glyphosate, but they do come round far more regularly than the Tour de France visiting Cambridge. This year in many parts of the country we’ve had sufficient moisture to encourage the active weed growth that is so necessary for good control with glyphosate.

The pre-harvest recommendation, announced in 1981, played a critical role in the development of UK farming systems during the last couple of decades of the last century. Before then, we had to wait until the couch and other perennial weeds grew to a sufficient size after harvest. This delayed cultivations and in many cases there was never enough growth of perennial broad-leaved weeds for effective control. In some years an early frost removed the green growth of creeping thistle.

You have to remember that there were many more couch and perennial broad-leaved weed infestations around when glyphosate was introduced. It was really the pre-harvest recommendation that did for these weeds. I’m often asked whether herbicides have been so efficient that they have destroyed their own market by eradicating all their target weeds. The only example I can think of is that perennial weed populations have dramatically been reduced by glyphosate and are no longer a common occurrence.

Pre-harvest glyphosateThe main reasons for the application of pre-harvest glyphosate nowadays seem to be general weed control rather than perennial weed control and to ‘aid harvest’ of weed free crops. I do have problems with the latter because all the independent trials I have seen suggest that the application does not bring forward the wheat harvest but it can bring forward the spring barley harvest by a day or so.

The claim for glyphosate ‘evening-up’ the ripening of wheat can be precarious. Pre-harvest glyphosate application can start when the bulk moisture content of the grain is 30%. In a very variably ripening crop a significant proportion of the wheat may not be fully ripe and continuing to put on weight despite the average bulk grain moisture being 30%. Hence, the application of glyphosate may not only reduce the yield but also, glyphosate residues in the grain may be increased.

This is not a theoretical notion; there is trial data recording yield decreases in such situations. Hence, pre-harvest application should start only where the bulk grain moisture content in the latest part of the field is at or below 30% and at this moisture content, as I said earlier, application will not bring forward the wheat harvest.

I’m also not sure whether the pre-harvest application to a weed free crop will make harvesting any easier. All the trials I’ve seen suggest that such applications don’t reduce the moisture content of the straw by the time that the grain is sufficiently dry to harvest. I suppose that it may be an advantage regarding the moisture content of the straw a couple of weeks or so after application but trial data also suggests that treated straw can become wetter than untreated straw where the harvest is significantly delayed by rain. This is logical because the treated straw may be degrading more quickly and therefore is more likely to absorb moisture.

So whilst I recognise the huge contribution that glyphosate makes to modern cropping systems there is always a need to question whether each application will produce the desired results.

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2014 wheat yields

Posted on 07/07/2014 by Jim Orson

The end of June is around halfway through grain fill of winter wheat and for the last couple of years I have had a stab at predicting the yields of the coming harvest at this stage. In 2012, I predicted below average yields, based on well below average levels of solar radiation, not just during the first half of grain fill but also in May as well. What I did not take into account was the negative impact of waterlogging during May and/or June which was very significant, particularly in parts of the Midlands.

In 2013, I predicted fairly average yields because of average radiation levels during grain fill and over the previous month and also because of the dryish soil conditions in many parts of the country. I did however predict higher than average yields for timely sown wheat in parts of Lincolnshire and further North because this part of the country received more than average radiation levels and some parts had some useful rains at the right time.

I must admit that I have less data available than in previous years for an early prediction this year but where crops have been kept weed and disease free, the yield potential looks very good. Like the good years of 1984 and 2008, we generally had a dry April but had good rains in May. Sunshine levels and limited radiation data suggest that whilst May was a bit below average, the conditions for grain fill have been better than average. In addition, we have had warm but not really hot weather, particularly during flowering. If I wanted to be picky, I would have liked the nights during grain fill to have been a little cooler so that the crop respired less of the weight it put on during the day.

There are many magnificent looking crops around and the wetter than average May has enabled them to sustain high tiller counts. I suppose the only downside was the exceptional wet winter which would have shaved-off some yield potential. Trials in very large containers (lysimeters) suggest that summer waterlogging is far more damaging to yield than winter waterlogging but the latter can have some affect.

There is still some time to go before the crop has finished putting on weight this year but it is interesting that the very high temperatures we experienced in the second and third weeks of July last year did not appear to be very damaging to yield. Not that I am saying we are almost there; in 2008, the very wet harvest compromised yields although on average they were still the highest we have achieved.

Therefore there are very solid grounds for optimism. I hope that in three weeks time I will be able to confirm this with some more accurate data than that I have available at the moment. As I have said many times before, the fundamental driver for yield potential is solar radiation. It is now clear to me that I have previously underestimated the value of good levels of solar radiation before the start of grain fill.

Wherever possible it is important that solar radiation rather than sunlight hours is measured. This is because an hour of sunlight at dawn does not provide the same level of potential energy to the crop as an hour of sunlight when the sun is at its highest. To be even more precise, only the wavelengths of radiation that the plant uses in photosynthesis should be measured (Photosynthetically Active Radiation).

Hence, I will try to improve my data sources for a final prediction over the next two to three weeks during which I hope the weather remains conducive to good yields. Here’s hoping that the wheat price will improve too.

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They think it’s all over….

Posted on 28/06/2014 by Jim Orson

Until the World Cup it has been a good footballing year for me. As a lifetime supporter of Leicester City, I was over the moon this spring because an amazing unbeaten run culminated in their promotion to the Premiership as champions of the Championship. Not only that, but I watched with a mixture of fear and excitement as the mighty U’s (for the few who do not know – Cambridge United) climbed to the top of the FA Conference Premier League at Christmas and then hung on for second place. A trip to Wembley was necessary to see them grab promotion to the Football League. This was their second Wembley appearance of the season as a few weeks previously, one of my daughters and I also watched them win the FA Vase (the equivalent to the FA Cup for non-league clubs). The photo shows them on their victory parade through the city at the end of the season.

Cambridge United victory parade 2014

Cambridge United victory parade 2014 2








Then came the World Cup; so near and yet so far. Naturally I remember the 1966 World Cup final win over Germany although I did not watch it on TV. Believe it or not, I was playing cricket for the local farmers’ team. However, we did have a radio behind each set of stumps and really lived the drama. In many ways it was perhaps a better experience than watching it on TV.

This got me thinking about how competitive we were in the world wheat yield stakes in 1966. So I looked it up and with increasing excitement found that our average yield that year of 3.86 t/ha was higher than Germany (of course!), Ireland (the current country with the highest average yields), New Zealand and France. At the last moment I thought I should check some other likely candidates and I am afraid that Denmark spoilt the story, with an average yield of 4.27 t/ha. It is sobering that their current yields are being compromised by significant nitrogen restrictions.

There is much current excitement about ‘breaking the yield ceiling’. It’s a bit like the World Cup; we spend hour upon hour planning the strategy and tactics only for the weather to prove too strong an opposition. We get so close but it is either not wet enough in the summer (e.g. 2013) or too wet and dull in the summer (e.g. 2012) for us to claim victory. Sometimes we lose in extra time. 2008 was our record year for average yields and it could have been so much better had it not been for the extremely wet harvest. That year I heard over and over again from farmers who said that they were half-way through harvesting a field when the weather broke and when they recommenced a fortnight later, the yields in the remainder of the field were a tonne/ha less.  As one Essex farmer sagely told me recently, wheat has only to look good once and that is when it is feeding into the combine i.e. it is not over until it is over.

There are some amazingly good looking wheat crops at the moment. With the right combination of sunshine and rain there could possibly be some bumper yields around. The recipe for very high yields is well known, the crop needs to intercept high levels of solar radiation and not run short of moisture. High temperatures during grain fill, particularly around and just after flowering, will reduce the yield potential.

There is a need to maintain a green wheat canopy until the end of grain fill. This is not the same as saying that a green crop canopy should be maintained for as long as possible. There is evidence in scientific literature that clearly shows that the relationship which exists between maintaining a green canopy and yield has a time limit (measured in day degrees) which is around the time of the end of grain fill.  

Extending a significant green canopy beyond that time does not further increase yields. Additionally, it does not have to be a full canopy at the end of grain fill, field experiments carried out at the University of Reading just over ten years ago suggest that by around the end of grain fill the majority of the flag leaf can be senesced and maximum yields can be achieved. Whilst I accept that such a canopy at the end of grain fill could possibly be insufficient for a record yield, it is clear that the canopy needs to be kept green but perhaps the rider ‘for as long as possible’ may be the route to some unnecessary expenditure.

It is interesting to note that whilst barley can be very different to wheat a recent HGCA project report shows that light interception by the canopy of spring barley must only be protected for approximately the first 75% of grain fill in order to maximise yield; a period of three to five weeks from 50% ear emergence depending on the site and year.  After that period, yield is insensitive to major reductions in light interception (e.g. caused by leaf diseases) probably because grain filling can be completed using dry matter from storage reserves.

So please remember, as always, do not get carried away with dogma but look at the results of field experiments and do not try to maintain the green canopy at all costs. Green is not necessarily the new gold.

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