NIAB - National Institute of Agricultural Botany

Orson's Oracle

Return of the rain

Posted on 02/05/2012 by Jim Orson

Right up to 28 April (last Saturday) the rainfall in Cambridge was below the monthly average. Then over Saturday and Sunday we had nearly 25 mm of rain. This means that at last we’ve had a month where rain has exceeded the monthly average.Raining

Much to the surprise of my wife, I decided to play golf on Sunday afternoon. The course was quite busy because the wind and the temperature were very acceptable. Underfoot the soil wasn’t soggy, because the course is built on shallow chalk.

I was playing a doctor who expressed surprise on how well the course walked. This led to a discussion on rain, soil moisture deficit and transpiration. At first, he couldn’t understand why it is most unlikely that summer rainfall will not recharge the watertables. I explained that in the summer the transpiration losses can be around 25 mm a week, and so it needs rainfall consistently above that figure to get water moving down the profile.

There has been sufficient rainfall locally for some drains to start running and, of course, tramlines are very wet. This can mean only one thing - pesticides in watercourses. In the West Midlands, where there was more rain earlier in the month, pesticides are appearing in feeder streams to reservoirs at levels above those specified in the good old Drinking Water Directive.

The usual suspects for this time of year are being recorded; clopyralid and the hormone herbicides mecoprop and MCPA. Fortunately, water companies are prepared to treat raw water in order to reduce pesticides in tap water to below the levels specified in the legislation.

These herbicides currently appearing in water are not effectively taken out of water by activated charcoal filters. This is because they are relatively water soluble and activated carbon is more effective on the more water insoluble herbicides, the classic one being isoproturon. But, the hormone herbicides are more effectively removed by the other process adopted to reduce pesticides in water - passing ozone through the water which oxidises chemicals in the water and breaks them down.

Unfortunately, clopyralid is one of two major pesticides detected in water that can get through both processes relatively unscathed. Metaldehyde is the other one. As they cannot be removed from water, their levels have to be reduced in raw water to below the threshold specified in the Drinking Water Directive. At the doses commonly used, this presents a particular challenge to metaldehyde, hence the importance of the Pelletwise campaign.

The problem is that all herbicides can occur in water at very high levels for a short time after a significant rain, particularly if the soil is already wet and the water treatment works cannot cope with these spikes of concentrations. This is where grass buffer zones to reduce immediate run off of surface water, particularly from tramlines, are particularly useful.

There is a great fear that the Water Framework Directive, which includes the Drinking Water Directive, will eventually result in the withdrawal of some key herbicides. Many now consider that these fears are over-egged. The Water Framework Directive says that the position of pesticides in water should not get worse, with the implication that an indication of the situation getting worse would be water companies installing additional facilities to remove pesticides.Winter cereal spraying

So the future may not be so bleak, provided that each and every farmer adopts sensible practice, both for filling and cleaning out sprayers as well as for the spraying operation itself. Identifying fields with a high risk of run-off and only spraying them when the risk is low is also an essential step.

Buffering watercourses with sufficiently wide grass strips is required in most cases. These strips are only as good as the weakest point and so they shouldn’t have breaks in them. Most breaks are where vehicles enter the field, but check to see if they are sufficiently wide and robust by walking them during periods of heavy rain to see if there is a breach from run-off.

The weather over the last few years has shown that we can get periods of very wet and very dry weather. Should this type of variable weather become even more exaggerated then there is the prospect that water companies may not be able to cope with pesticides in water with their current facilities. This really could spell trouble unless the farming industry reacts promptly to the situation.

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Pesticide resistance? Darwin rules OK

Posted on 23/04/2012 by Jim Orson

There was a time when considerable effort was spent trying to convince independent advisers and researchers that low doses cause pesticide resistance. There wasn’t much scientific rigour in the argument; apparently target organisms ‘got used to’ low doses and that was the start of resistance development.

That argument never struck a cord with me. My first experience of resistance was with powdery mildew to Bayleton (triadimefon), in the late 1970s/early 1980s after only a few years of use. We knew from trials that a quarter dose initially controlled the disease in the field, and most growers Charles Darwinat the time were using doses well above this. So, resistance wasn’t a result of incomplete control.

The science on the causes of resistance has been transformed by biotechnology. Typically, target site resistance is caused by genetic mutations that block the activity of pesticides at the single site of action. Enhanced metabolism is often caused by the over-expression (hyperactivity) of gene(s) that in susceptible target organisms would only result in the slow breakdown of the pesticide.

This suggests that typically it is high selection pressure (high doses, particularly if regularly repeated) that leads to the most rapid increase in resistance, as only the most resistant target organisms will survive a high dose. Provided these survivors have roughly the same fitness as the susceptible organisms to compete and multiply then they will slowly dominate the population - following the principles of evolution, first described by Charles Darwin.

[You will have noticed that I’ve extensively used the word ‘typically’ so far in this blog. This is because over the years I have learnt that whilst simple principles apply in the vast majority of occurrences of resistance, there may be some exceptions...]

So far, so good.Resistant blackgrass

Then recently I read some scientific papers suggesting that low, rather than high, doses were causing resistance to weeds in Australia. My first thought was ‘how dare these colonials challenge our cherished Darwin’ - so when I visited earlier this year I disputed their conclusions.

It was easily resolved - the argument was that low doses led to higher numbers of weeds that had a level of resistance. However, there was an acceptance that high doses may result in a more rapid increase in resistance, so it became an argument about populations and the resistance development rate.

In the UK we have experience of statements saying that less effective treatment caused more resistance. It is said that it was the spring application of ‘fops’ and ‘dims’ that caused more resistance in black-grass than autumn applications.

Autumn applications typically (that word again) gave more effective control and so only the most resistant black-grass survived. This would, as a consequence, lead to a more rapid increase in resistance. Despite resistance increasing more slowly as a result of spring applications, after several years it may still have increased to the same maximum level as that from winter applications. However, being the less effective timing also meant that there would be a lot more black-grass plants present - hence the assertion that the spring timing caused more resistance that the autumn timing.

In practical agriculture the rate of development of resistance and populations is perhaps a rather pedantic argument. Nobody intentionally uses doses that will provide inadequate control. If lower than recommended doses are used, which is rare for black-grass, they should be at an appropriate dose to provide sufficient control in both the current and future crops.

Hence, Darwin still rules OK! However, there are apparently many in the US Republican Party who still disagree!

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Technology with a future

Posted on 15/04/2012 by Jim Orson

On Easter Sunday we sang the hymn ‘Now the green blade riseth from the buried grain’. My mind wandered away from the service and to how fortunate we are in the UK to have both the weather and the soils that can sustain good crops of grain. Of course the hymn book, from an agricultural point of view, gets really revved up for harvest festival. There are hymns that convey the labour and planning that lie behind producing a crop and the age-old worry about the weather. ‘Hopes of sun and rain’ is from a hymn written by John Arlott, who is more remembered for Test Match Special (if you are old enough) than for anything else.

When you look at an atlas (or on Google Earth!) it is surprising to see that we farm at a more northern latitude than the Canadian prairies - noted for vicious winters and hot summers. Yet we have relatively mild winters and summers. So why are we so successful at growing wheat?Growing wheat

The explanation is clear; we have a maritime climate warmed by the Gulf Stream. In fact, look at the countries with the highest wheat yields - they are all islands that benefit from the moderating effects of the surrounding seas.

The Republic of Ireland has the highest average wheat yields in the world, followed by New Zealand; I believe the UK is in third place. New Zealand is capable of extraordinarily high yields, but these can often be achieved only with irrigation at the end of the season.

The reason for this very high yield potential is that, despite having the same number of days during grain fill (flowering to maximum yield at around 35% moisture content) as the UK, NZ accumulates yield at a rate about a third higher than ours.

My calculations suggest that, on average, the UK accumulates wheat yields at a rate of 0.23 t/ha a day during grain fill whilst in New Zealand the rate is 0.30 t/ha. This is because the Canterbury Plain is on the same latitude south as the very south of France is north. So, despite having the same temperatures as East Anglia during grain fill, their solar radiation is much higher.

It’s not only the weather but our soils that have in the past provided us with such a great advantage. They are relatively young and have not been leached of nutrients as have the very old soils in some other parts of the world. This meant that during the development of agriculture, when there was little or no knowledge of plant nutrition, we had a natural advantage.

Of course it is important that we exploit our natural advantages. Pesticides and plant nutrients have enabled us to tap much of that potential. But, we now seem to have reached the point where any further yield increases are incredibly hard to achieve. Not only that but some of the technologies that enabled us to exploit these natural advantages are under pressure because of pesticide resistance and/or from regulation.

What we need is more technology, and not less, if we are to play the role in food production that society now increasingly recognises as essential.

There are still those who argue that we should have less technology and we should return to more ‘natural’ methods. I cannot agree with this and that's why I was a bit upset by a recent letter to Farmer’s Weekly regarding the GM wheat trial at Rothamsted Research. The letter questioned why a milling spring wTrojan Room Coffee Potheat, a relatively minor crop in the UK, was being used, and that no-one would use the flour produced.

The letter is missing the point. Rothamsted Research is a scientific institution and this is an experiment into what may, or may not, be possible. To stop science’s quest for knowledge on such arguments is an attempt to stop the clock. It goes to show the lack of coherence in the objections to GM. Surely, even if you are against multinationals allegedly taking the easy options, such as herbicide tolerance, to make profits from GM, why object to a scientific study of the possibilities it may offer?

It is widely acknowledged that we are still in the early stages of using biotech to improve crops and so today’s commercial products should not be used to damn the technology. I live in Cambridge, the birthplace of internet usage. It was in the University’s computer lab where a picture of a coffee pot, the Trojan Room Coffee Pot, could be accessed on all the VDUs to see if it was sufficiently full to make the foot journey to replenish cups/mugs worthwhile. That surely is a technology without a future.

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Lost in translation

Posted on 05/04/2012 by Jim Orson

Being semi-retired has it advantages. During the recent warm and sunny weather we took off to London for the day. The morning was spent looking around part of the British Museum and for the afternoon we got last minute tickets for the matinee of a stage show. This was followed by a walk round St. James’s Park and dinner. A good day with good company (my wife checks my blogs for English and so I have to say that).

Rosetta stone
The three languages on the rosetta stone

At the British museum we saw the famous Rosetta Stone. Just to remind you, it was the key to the decipherment of Egyptian hieroglyphs. The inscription on the Rosetta Stone is a decree passed by a council of priests. It is the same script in three languages, in hieroglyphic (suitable for a priestly decree), demotic (the native script used for daily purposes) and Greek (the language of the administration). This enabled the literal translation of hieroglyphics into their Greek equivalent and consequently into modern day language.

Another aspect of working part-time is to keep up-to-date and so I was listening to the Archers omnibus edition the following Sunday. The Rosetta Stone was mentioned in the context of enabling the truth to be deciphered. Bizarrely, this got me thinking about nitrogen recommendations for crops.

Nitrogen processes in the soil are fiendishly complex and Rothamsted is still researching the subject, despite nearly 170 years of endeavour. That is not meant to be a criticism but a way of demonstrating the complexity of the subject. Leonardo da Vinci wrote 500 years ago that ‘we know more about the movement of celestial bodies than about the soil underfoot’. Even today we would say ‘he was not wrong’.

No doubt there are variations in the soil processes between and within fields and perhaps within individual square metres of fields. So how do we get nitrogen doses correct with this type of background? The task is made even more demanding because weather after application will affect the amount of bag nitrogen required.

The reality is that recommended doses are often a long way off the mark. So the task in hand is to minimise these errors. The key is how should we do it? What is the equivalent to the Rosetta Stone for nitrogen application?

As many of you know, despite the complexity of nitrogen use in the soil and by the crop, many current recommendation systems are based on a simple model. The model is that Soil Mineral Nitrogen is used by the crop at 100% efficiency and fertiliser nitrogen is used at 60% efficiency. This sounds a bit odd to many: why the difference in efficiency, surely nitrogen is nitrogen?

I think the basis for the assumed difference in efficiency goes back to a time when there was more potential for mineralisable nitrogen in the soil. This was because arable land typically had a recent history of grassland and/or regular use of organic manures. One way to take this into account was to assume a high uptake of the measured Soil Mineral Nitrogen to ensure that there was an allowance for a significant amount of net mineralisable nitrogen during the season.

However, this is not now the typical situation. The vast majority of arable fields have no recent history of grassland or organic manure use. NIAB TAG trials over the last ten years suggest that the efficiency of use of Soil Mineral Nitrogen by wheat is way below 100% in long term arable soils where organic manures have not been used. As I have previously reported, in Australia, where the majority of nitrogen for the crop is from the soil, they assume an efficiency of uptake of 40-50%.

Why is this important? The assumption of 100% efficiency of Soil Mineral Nitrogen and 60% efficiency of bag nitrogen results in a reduced recommendation of around 1.67 kg/ha (100 divided by 60) of bag nitrogen for every additional kg/ha of nitrogen in the soil. Hence, if the efficiency of Soil Mineral Nitrogen is in fact significantly less than 100% then there is a danger of recommending sub-optimal levels of bag nitrogen. This is particularly relevant for long term arable soils with nitrogen indices of 2 and above in RB 209 and where there is no recent history of organic manures. This includes wheat after oilseed rape.

As I am a rather pragmatic part-time agronomist I consider that actual trial results, with all their shortcomings, are the Rosetta Stone for nitrogen recommendations. These indicate that nitrogen recommendations for wheat after oilseed rape in the current edition of RB 209 are still too low. Hence, I believe that the simple assumptions adopted in many recommendation systems have led to something being lost in translation.

By the way, I really do not see the Archers as being at the cutting edge of agriculture but what are the chances of building the super-dairy at Ambridge? In such a politically correct programme I suspect the chances are zero!

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White on white

Posted on 30/03/2012 by Jim Orson

On MondWinter cereal sprayingay 2nd June 1975 it snowed in Suffolk. By the end of the week the temperatures were around 250C and remained so for weeks. The subsequent dry winter meant that there was still a significant soil moisture deficit at the end of February. The following summer of 1976 was hot and dry and there was no meaningful rainfall until September. Naturally, once it started to rain it didn’t know how to stop.

This was a real problem to those with irrigated potatoes. They were worth £300/tonne (remember this was 1976) and the land was too wet for the harvesters. Luckily, that autumn/winter was also mild and so they were harvested eventually.

The biggest problem then was the potential tax bill. In my opinion, much money was wasted on unnecessary expenditure in an effort to reduce it. Perhaps today more sophisticated ways of avoiding taxes would be adopted. But, I’m not going there!

So farming in extreme weather conditions is not new. However, we seem to have recently been experiencing more prolonged periods of rain…or drought…or high or low temperatures. Until it happened this year, who would’ve thought that there could be active brown rust in wheat around Newcastle in March?

How do we manage crops in such variable weather conditions?

With fixed costs, it’s important that such variation is borne in mind, and minimising labour and machinery for the fabled ‘average’ season will obviously not be the best strategy.

With our input management there are many issues to discuss on the requirement, timing and amount of individual inputs in addition to the overall strategy. For instance, seed rates can influence moisture loss from the crop, particularly if there is a dry winter. This may be critical if there is a dry ripening period. I remember seeing a winter wheat seed rate trial in New Zealand where the higher seed rate plots had ‘hayed off’ because of associated higher moisture losses at earlier stages of growth. On the other hand, reasonable seed rates are required to compete with herbicide resistant black-grass and to minimise the impact of tiller loss during a dry spring.

Last year we got yield responses to chlormequat use in winter wheat. This was because chlormequat increased the number of potential grain sites by reducing the loss of grain sites in the very dry spring. The increased yields came from the great grain fill conditions experienced in June and July which enabled these additional grain sites to be filled.

But it could have gone the other way. More grain sites than considered wise by the untreated crop at, and shortly after, the time of the application of chlormequat would have resulted in more ‘tail corn’ and lower harvested yields should the dry conditions have continued into June and July.

Perhaps my most sobering experience of the impact of drought on crop inputs was in 1976. Over the previous winter I, as a lowly ADAS district adviser, had had heated discussions with soil scientists on the optimum dose of applied N for wheat.

This was the time when yields were beginning to rise rapidly and I was convinced that the then recommendation of 125 kg N/ha was too low. However, I didn’t win the argument and recommendations for 1976 stayed the same. I had to be content with the knowledge that there were plenty of N trials in the ground and they would prove me right!

However, it was so dry that the optima in nearly all these trials were zero applied N. Presumably, the additional moisture loss from the extra green area created by applied nitrogen negated the value of its ability to trap more solar radiation. You must remember that we were then talking of yields of 4-5 t/ha.

One unexpected result from last year was that urea and ammonium nitrate applied during the extremely dry spring produced the same wheat yields. It seems that significant ammonia losses from urea will not occur until moisture starts to affect the integrity of the applied material. So losses can be minimal when applied in extremely dry conditions provided that there is sufficient rain when the drought breaks to quickly ‘wash’ the urea into the soil.

Conclusion: adjusting inputs to take into account more variable weather conditions is fraught with difficulty. It comes down to risk management based on experience, good information sources and sound science.

By the way, the reason why I remember the snow in June 1975? I was playing in a golf tournament at the time. For the less informed, you play golf with a white ball.

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