NIAB - National Institute of Agricultural Botany

Orson's Oracle


Posted on 06/08/2012 by Jim Orson

Initially, Mrs Orson and I were disappointed to get tickets for only one of ouJess Ennisr three carefully chosen athletics sessions at the Olympics. However, it soon became clear that we were lucky to get any at all. This luck was compounded by the fact that the tickets were for the night that Team GB won three athletic gold medals. It was an extremely noisy, dramatic and unforgettable experience. The media described it as historic. That’s perhaps a bit strong but it was truly exceptional. How lucky we were!

Also exceptional was the rainfall for the three months from mid-April to mid-July. When I started to think about its implications on the nitrogen status of crops and soil, I asked Rothamsted Research for a view. I think I’ve said before that the behaviour of nitrogen in the soil is fiendishly difficult, even impossible, to grasp but Rothamsted has been researching this subject since 1843 and know more than anyone else.

The (very rapid) response is intriguing and I should like to thank Keith Goulding and Andy Whitmore for their help. I should also point out that neither has been at Rothamsted since 1843, but Keith has been there since 1974!

The possible scenarios I had in mind were that excessive rain may have caused leaching of applied nitrogen; the rain-induced lush growth may have increased potential nitrogen uptake; the constant moist state of the soil may have resulted in more nitrogen being released (increased mineralisation); or that waterlogging may have caused losses through denitrification.

In today’s context, the latter has serious connotations. In anaerobic (e.g. waterlogged) conditions, bacteria convert nitrates and nitrites in the soil to nitrous oxide gas. During this process the main gas produced is nitrogen, which is inert, but a lot of nitrous oxide is also produced. This is a greenhouse gas 300 times more potent than carbon dioxide. So not only do we lose the major plant nutrient through this process but also the greenhouse gas output from cropping increases significantly.

The Rothamsted team kindly ran one of their models to see what the implications of the wet weather could be in the context of their own rainfall data and for winter wheat grown on their flinty silty clay loam. The results may surprise some. Leaching losses were only marginally higher this year at Rothamsted.

This sounds surprising but please remember that when it started to rain in mid-April the soil under winter cereals was very dry to depth. There needed to be a lot of rainfall in excess of transpiration losses before the drains actually ran. Even then, the applied nitrogen had to move a long way before it got into the drains.

The model also shows that crops had a reduced nitrogen status this year. Personally, I was surprised that I didn’t see winter cereal crops looking very short of nitrogen but on the other hand, they were not quite so dark green this year.

The main cause of any nitrogen loss since 1st March on a clay loam soil at Rothamsted was calculated to be denitrification; up to around 40 kg/ha of nitrogen could have been lost through this process. To put this into context, the same model suggests that the loss due to denitrification for the same time period last year was just 0.1 kg/ha of nitrogen.

Perhaps this exceptional spring represented the worst case scenario for this process and should be treated as a ‘one-off’? Soils were wet at a time when all the bag nitrogen had just been applied and also they were warm(ish), so bacterial activity was high. Logically, denitrification losses may have been lower on better natural draining soils and even higher on very heavy clays. Conversely, leaching losses may have been more significant on better natural draining soils.

This Rothamsted model also suggests that the soils were so waterlogged that there was insufficient oxygen for root growth. Perhaps this wasn’t so critical this year as the crops didn’t suffer any subsequent drought stress but it may have meant that the ability of the crop to scavenge nitrogen at depth was inhibited.

My next question to Rothamsted was what does this all mean for soil nitrogen levels this autumn?

The answer was that there are too many ‘ifs’ and ‘buts’ to be definitive two months in advance. However, it seems logical to me that there will not be a lot of nitrogen kicking around.

The problem with nitrogen is that logic does not always apply. To return to simpler subjects: it is certain that in two months time our ears will still be ringing from the crowd noise during Mo Farah’s last and glorious lap of the Olympic 10,000 metres final. Truly exceptional!

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Wheat yield prediction for 2012

Posted on 30/07/2012 by Jim Orson

A couple of weeks ago I summarised the weather conditions for the first half of wheat grain fill. There is a strong link between solar radiation received during this period and final yield. However, there are other factors at play, such as whether the crop has a sufficient ‘sink’ for the products of photosynthesis during grain fill, is there sufficient green leaf to absorb the radiation, and while the crop is not short of water whether the nights are so warm that the crop respires much of the gains of the day.

Hence, I am not so naïve as to believe that yield can be accurately predicted based on solar radiation intercepted by the crop during grain fill. For instance, we had great conditions for grain fill in 2011 but the wheat crops in the areas of the early summer drought had insufficient ‘sink’ (in this case lack of grain sites) to use all of the products of photosynthesis.

At first hand there appears to be no danger of lack of potential grain sites or an ‘overall’ sink in 2012. On the other hand fusarium in the ear may be affecting the final number of viable grain sites and high levels of septoria have resulted in less green area on the final three leaves.

On average there are about 660 day degrees (some studies have concluded a little longer) between flowering and maximum dry matter yield. This means that on average grain fill takes 42 days. I’ve assumed this year that this lasted from 10th June to 21st July inclusive for the following analysis. Whilst doing this, I recognise that this year has been cooler than average and so grain fill will take two or three days longer than usual.Ear of wheat

The data, kindly provided by Stephen Dorling of the University of East Anglia, comes from the two weather stations mentioned in my previous blog on the subject; Watnall in Nottinghamshire and Wattisham near the Suffolk Coast.

For those 42 days the radiation was about the same as in 2007, a relatively poor yielding year. We had sufficient rain in June and July in 2007 and so there was no great shortage of moisture during grain fill. However, we’ve had cooler nights in 2012 than in 2007 but crops were cleaner in 2007.

The big difference is that in 2007 we had a spring drought. There was no real significant rain in many areas for around six weeks from mid-late March. April was exceptionally warm and the crops were potentially on fire with brown rust. However, the crops did not suffer from the drought as much as they did last year.

So, where does that leave us? Some farmers are expecting tremendous yields this year. I’m not so sure; there are too many potential downsides. Hence, if I was to stick my neck out I would say that yields are not going to exceed the recent averages achieved. I hope that I’m wrong but if I’m correct - at least the prices are not too bad!

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Lovely crumbly soil

Posted on 23/07/2012 by Jim Orson

To sell or to incorporate straw is a debate that’s been slowly hotting up over the last few years. The heightened interest was caused initially by the dramatic increase in the cost of phosphate and potash. This year a shortage of good forage is enlivening the debate, and there is also a call by some excellent black-grass growers to enable some straw and stubble to be burnt in an effort to keep the weed under control.

Let’s deal with the last point first. Stephen Moss of Rothamsted Research says that straw burning, on average, controls around 40% of freshly shed black-grass seed, and it can be as high as 70%. That sounds impressive but it only partially lifts the pressure on herbicides. Perhaps of equal importance, the survivors can be stimulated to germinate. Hence, there is little doubt that straw burning would contribute to keeping black-grass under control, but it is likely that it wouldn’t make a hopeless situation manageable without the adoption of other cultural measures.Straw burning

Much of the debate on whether to bale or to incorporate straw centres around the possible delays caused by baling and carting which is likely to be more significant during a wet harvest, alongside the value of straw as a provider of plant nutrients. The additional field traffic, much of it out of tramlines, from equipment that may be fitted with road tyres could cause localised soil structure problems.

There is also the value of straw as a means of increasing soil organic matter, which has been the subject of a long term experiment at Morley. We started in 1983 comparing straw burning, baling and incorporation. However, over the past 20 years we’ve been investigating the value of straw produced from a range of nitrogen doses, ranging from 0 to 250 kg/ha, applied to continuous wheat. Obviously the plots receiving the highest doses of nitrogen have produced the most straw.

After around 20 years the organic matter is around 1.7% in the plots receiving the highest N doses and 1.55% in the plots receiving no N. It doesn’t sound a lot and some would say that, based on these data, the value of straw for increasing soil organic matter isn’t that significant. However, simple tests on the soil suggest that there’s a remarkable difference in the aggregate stability of the soil. In practice, this means that the soil is much more resilient to cultivations and rainfall and also, it may be easier to prepare a seedbed.

Can a difference of 0.15% in organic matter be that significant? Perhaps, but in my opinion there may be another significant factor - microbes! Incorporating organic materials, including straw, on an annual basis increases the soil biomass, which is made up of soil bacteria and soil fungi. These produce enzymes whose activity results in the production of substances that help to bind soil particles together into more stable aggregates.

There is a host of scientific evidence to support the value of an increase in soil biomass, as well as the practical experience of arable farmers when we first returned to straw incorporation in the early 1990s after years of burning. After only a couple of years, farmers reported that the land was much easier to work which was attributed to increases in soil organic matter. However, the organic matter difference would have been minute after just a couple of years of straw incorporation. The ‘workability’ must have been due to something else that can build up more rapidly than soil organic matter which I believe must have been soil microbial biomass.

Unfortunately, the increase in soil biomass from the incorporation of a crop residue lasts only around 18 months, so it has to be a regular practice to maximise its value. I’m not sure how persistent the effects are from incorporating organic manures. However, you know who to thank if you don’t have access to organic manures but you regularly incorporate your crop residues and the soil is in good condition. Soil organic matter is not everything.

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Past, present and future of KT

Posted on 13/07/2012 by Jim Orson

Despite the weather forecast we attended the first day, and sadly the only day, of the Great Yorkshire Show. It was crowded and the weather held until mid-afternoon, and in that rain-break I briefly read about the conclusions of the Defra Green Food Project. So, for me, the day provided a link between the past, present and future.

Many county, including the Yorkshire, and local agricultural societies were established in the 1830-40s; the Royal Agricultural Society of England in 1838 and Rothamsted in 1843. This was a time of greater domestic demand for food from an increasingly urbanised society - but before the steam engine had enabled the opening up of the Ukraine and the prairies and the cheap international transport of agricultural produce.KT in practice at NIAB in 1922 - discussing the impact of drought on potato trials

However, internal communications were rapidly improving through better roads and the establishment of railways. So there was an emphasis on and a reward for domestic food production. Improved communications not only meant more efficient transport of produce but also that farmers could get together more regularly to discuss the latest techniques.

It was really the start of what we now call knowledge transfer (KT), with the agricultural societies and shows playing a key role.

It was also a time of great technical innovation, particularly the understanding of soil nutrients, increased mechanisation and installation of field drainage. Coke of Holkham established better farm practices based on the Norfolk Four Course Rotation which was developed by ‘Turnip’ Townshend on the nearby Raynham Estates.

‘Turnip’ was perhaps the first great agronomist; he worked out how to crop all the land without having to resort to fallows and used the invention of perhaps the first great ‘tyre kicker’, Jethro Tull, in order to drill cereals and turnips in rows. This made it easier to weed crops and soon the horse hoe was introduced.

Coke established model farms, i.e. demonstration units, and open days, and farmers flocked to attend. As always, attendance was bolstered by the offer of a free lunch - nothing changes.

However, Coke complained that his ideas only spread by a mile a year, so KT was a problem even in those days and is a salutary lesson for those still seeking the ‘Holy Grail’ of KT. Some of the issues of KT were evident from Coke’s efforts. His system was great for the light soils of north Norfolk but perhaps less pertinent to heavy soils. I can imagine a couple of heavy land farmers kicking the soil at Holkham and saying it was not for them, but what a great lunch!

The reality is that there is no single ‘one-fits-all’ approach to KT; all that can be hoped for is that it is appropriate, timely and well co-ordinated. Each farmer and adviser is different and requires knowledge packaged in different ways. Some take more cognisance than others of what other farmers are doing; some are more risk-takers than others etc.

Researchers have been known to complain about poor KT preventing their pet projects from being adopted without thinking either about the risks involved or about the ease of management. Sadly, some researchers only present current findings in such a way as to try to secure further funding - farmers and advisers are very good at spotting that behaviour. Indeed, many of those responsible for KT in the past have underestimated the farmer’s and adviser’s ability to judge what they are seeing, reading or hearing and to assess if it is appropriate for their own businesses.

Well, that’s dealt with the past and perhaps a bit of the present. So what of the future? The Green Food Project is all about how increasing productivity can be balanced with improving the environment i.e. sustainable intensification. Now there’s a challenge for KT!

However, the authors fully acknowledge the future role of farmers and advisers in this process and have used the term Knowledge Exchange rather than KT. Other parts of the report suggest that as our climate gets warmer we may be growing more exotic crops such as chickpeas. I hope they’re easier to harvest than field peas or a year such as this will sort them out.

Our personal links with the past and future at the Great Yorkshire Show were reflected in our purchases. My wife bought me a liquorish whirl; a good and now traditional product of Yorkshire. I bought some rather nice olives; a new crop for the UK?

Finally, in this blog I may have overplayed the role of the UK in the development of farming systems. I say this because I was made aware of a salutary lesson a few years ago when visiting a research farm in a part of Australia well endowed with rainfall but not having the ability to get the water away from the fields. So they started to grow wheat on raised beds to increase the ‘freeboard’ for the cereal roots. A young researcher told me that she was excitedly explaining this new approach to some Chinese agronomists who quietly explained that they’d been doing the same for the past 1,500 years.

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This year’s wheat yields will be...?

Posted on 06/07/2012 by Jim Orson

I am sorry for the delay in writing this blog. Last weekend we met up with one of our daughters and her family. I think it was our 7-month old grand-daughter who gave me the sickness bug. Let’s say it was not the most successful of weekends away.

Despite feeling rotten (as only a man can) I managed to keep in touch with Steve Dorling of the University of East Anglia by e-mail. The reason for this communication was that on average (there are lots of assumptions in this blog, so beware) the end of June is halfway through grain fill of wheat. Steve had kindly offered to update me on the solar radiation and temperatures during this period (June 10th – 30th). You may remember that I talked of the importance of these two factors on grain fill in my blog ‘A late winner’ a couple of weeks ago.Wheat grain

Well, thanks to Steve, I now have the data for this first half of grain fill from two centres, at Wattisham in Suffolk and Watnall in Nottinghamshire, over the past 10 years.

I’ve compared this data with the regional wheat yields over the same period - my first observation is that in every year, except 2010, there has been typically 10-20% more radiation at Wattisham, near Ipswich, than at Watnall. Not only that - there is less year to year variation at Wattisham.

Steve explained that in the summer there is typically less convection and less cloud development the nearer you are to the coast due to cooler air temperatures; as I write, the sea temperature in the North Sea is still only 15°C!

This may partly explain why the Suffolk Hanslope clay soils yield more wheat than the Cambridgeshire Hanslope soils. Or perhaps that’s insulting the superb agronomic skills of the Suffolk farmer!

The second observation is that the good yielding years appear to have a minimum of average radiation for the site and below average temperatures at night. I emphasise that I’m only talking currently about the first half of grain fill and perhaps I can prepare a blog at the end of grain fill to give a more complete story.

The exception was 2011 - which seemed to have superb grain fill conditions with higher than average radiation and low temperatures at night, but below average yields. I think we all know what happened here - the early spring drought took its toll on the number of potential grain sites.

One of my first blogs a few months ago explained why we got yield responses to chlormequat in the absence of lodging in 2011. This plant growth regulator ensured that more grain sites survived that drought and this resulted in a yield benefit because the grain fill conditions were so good.

So what of 2012? Well, radiation so far at Wattisham has been just less than average for the site. However, radiation at Watnall has been very low, nearly as low as in 2007 (the time of the Hull floods). And, whereas night temperatures at Watnall were high in 2007 they have been low in 2012. Similarly, night temperatures have been low in Wattisham in 2012.

This seems to suggest that conditions for grain fill up to the end of June have been OK at Wattisham, but not good at Watnall. This is providing all things are equal. However, can all things be equal in a year when we have seen a huge challenge from BYDV, lorry loads of black-grass and fungicides only being able to damp down rather than control diseases?

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