NIAB - National Institute of Agricultural Botany

Orson's Oracle

Light fantastic

Posted on 30/04/2019 by Jim Orson

During the 1960s there were many films on the telly and at the cinema that were set in California. Looking back they were pretty awful. On the other hand, they were great advertisements for the Californian way of life. One thing that really impressed me in those days was that all their residential garage doors seemed to automatically open. Not to be outdone, we had an automatic opening door fitted to our garage around three years ago.

The big problem is that there is so much rubbish in our garage that we do not have room for one car let alone the two it was designed to accommodate. Matters came to a head a couple of weeks ago when we had a delivery from a builder’s merchant. They were items for some internal changes to our house and had to be stored in the dry. Space had to be made available in the garage and I was sent out to create it.

It was then that I came across a very short Weed Research Organisation report on the role of post-harvest cultivations to encourage the establishment of black-grass seedlings. There is a detailed paper on these trials written by Stephen Moss and presented to the BCPC Congress in 1978.


The cultivations were done in early August and the counts were made in mid-October. The general conclusion was that not doing any cultivation at all was equal or better than shallow cultivations in encouraging black-grass seedlings to establish by mid-October.

The trials were done in the autumns of 1975 and 1976 and the counts show that in some cases thousands of seedlings were established per square metre. It is amazing what black-grass populations could be tolerated in those days when chlorotoluron or isoproturon were providing from a single application 99% control of heads on average in winter wheat or winter barley.

The straw on the plots was removed at harvest and the remaining stubble was not burnt. The prevailing weather was extremely dry, with some rain in late September. At the time these trials were an eye opener for me and ever since I have always encouraged no cultivation at all to be a treatment in stubble management trials. This advice was nearly always ignored!

Before I go any further, I have to emphasise that the number of black-grass seedlings encouraged to establish before drilling may not be a reliable guide to the total loss of viable seed. A truer guide is the number of black-grass seedlings emerging in the immediately following autumn-sown crop.

A few decades after the original work by Stephen Moss, the significance of between-crop management of black-grass has increased, not only because of the development of black-grass resistance to herbicides but also because of the more widespread adoption of shallow tillage. Shallow tillage results in a lower proportion of the black-grass seed buried to below 4-5 cm, the depth below which it will not emerge.

Data recently generated in Northern Europe and also in NIAB TAG trials show that not cultivating stubbles at all can reduce the number of black-grass seedlings, when compared to shallow cultivation(s), in a crop sown later in the same autumn. This is providing that the soil and weather conditions are pretty dry between black-grass seed shed and the drilling date of the subsequent autumn-sown crop. On the other hand, the opposite is true when conditions are moist where stubble cultivations seem to reduce black-grass emergence in a crop sown in the same autumn.

Despite its importance, the advice on stubble cultivation for black-grass control between successive autumn-sown crops has been all over the place in recent years. The extreme recommendations have been not to cultivate at all and the employment of a super heavy roller to really consolidate cultivated ground and produce a tight and fine surface layer of soil.

This variation in advice means that it is worth getting back to basics in order to clarify the situation. The key to optimising the value of stubble management is an understanding of the conditions needed to maximise black-grass germination.

There are three requirements for black-grass germination in the late summer and early autumn: the black-grass seed has to imbibe sufficient water for germination, it has to be exposed to light and it has to be non-dormant. Also, please remember that it needs to be in the top 4-5 cm of soil for it to emerge. This all seems straightforward but there are misleading statements that can lead us astray. These seem to centre on the need for light to enable emergence.

There is no need for the seed to be exposed to light for long periods. Provided that the seed is non-dormant and imbibed, the need for light is minimal. A 1970s scientific paper even suggested that it needed to be only a flash of light. This seems to ring true given the current enthusiasm for not disturbing seedbeds too much in the spring to avoid black-grass emergence. Certainly, a paper published 10 or so years ago suggested that less than five seconds of exposure to light was required. In addition, the light need not be direct sunlight. Pre-harvest, black-grass seed on the soil surface at the bottom of a cereal canopy will get sufficient light for germination as well as seed close to the surface of a relatively coarse seedbed. Hence, no super heavy rollers shutting out the light please!


And so, on the basis that prolonged exposure to light is not important, the focus has to move to what is the best situation for freshly shed seed to become imbibed in a dry autumn. It may well be on the soil surface rather than after a cultivation that results in an extremely dry seedbed. Embedded in the soil surface amongst the trash from the crop (chaff and chopped straw) may provide a moister environment for the seed because of dews and any light showers.

I could get more techie on this issue and perhaps I am in danger of over-simplifying because there is a myriad of individual circumstances. For instance, where there is no freshly shed seed, all the viable black-grass seed will be in the soil and so cultivation is needed, even in dry conditions, to expose them to light. In this circumstance it is best to produce the final(ish) seedbed as soon as possible in order that the black-grass seed likely to produce plants after drilling (i.e. those in the top 4-5cm of soil at drilling) is given the opportunity to germinate and emerge before drilling.

More consideration is required where freshly shed seed is the main target. In very dry conditions, delaying shallow cultivations until there is more moisture around may be optimal. Re-cultivating may be needed to expose seed that was dormant when the previous shallow cultivation(s) was carried out, should that cultivation have created a very fine seedbed and blocked out the light.

So it all becomes a rather complicated judgement on not only the best way to encourage freshly shed seed to germinate but also to take into account the relative numbers of seeds shed in previous years that are likely to be in the top 5 cm of the final seedbed for the immediately following autumn-sown crop.

I know that I have given the same views in a very recent blog but I thought it worthwhile repeating the message with an explanation as to why the approach to ‘stale seedbeds’ should vary according to black-grass seed depth at harvest and to weather conditions. In addition, I accept that there is more to life that optimising the reduction in viable black-grass seeds between crops.

Volunteer cereals and sterile brome need to be buried under a shallow layer of soil to optimise germination. Also, many farmers on heavy soils cultivate to 15-20 cm depth and press the soil immediately after harvest in order that the soil surface layers have time to ‘weather’ and do much of the seedbed preparation. Trials show that in moist conditions this approach results in less black-grass in the immediately following autumn-sown crop when compared to leaving the soil undisturbed until just before drilling.

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Read this before leaf tissue testing for micronutrients

Posted on 26/02/2019 by Jim Orson

The great Gordon Banks is dead. I regularly sat behind the goal at Leicester City’s Filbert Street ground in the very early 1960’s and witnessed his sublime skills. The fulsome tributes reflect that he was blessed with a true richness of talent which, through hard work, he was able to express on the football pitch.

There are often other attributes people need in order that they can exploit their talents to the full. Like Gordon Banks, it may simply be hard work but for others, it may also be identifying the right opportunity, if and when it comes along. I was thinking about this the other day whilst preparing for a talk. It is clear that the UK is blessed with a climate and mineral rich soils that can support high yields but we were only able to express this potential once effective crop protection evolved. Now, we regularly feature in the world’s top three or four countries for wheat yield/ha. This success has come at the cost of criticism or indeed hostility towards the methods we have adopted. Despite this, hard scientific evidence clearly shows that if we are to increase food production at a rate to reflect our own growing population then high yield farming is essential to make space for nature.

As I said earlier, there are always those wishing to criticise conventional farming. All kinds of lurid tales are thrown at the industry. The common accusation on the website is that conventional farming is stripping our soils of the essential minerals for growth and for the health of the consumer. The evidence from Rothamsted for wheat in a paper written over ten years ago is that the soil content of micronutrients had not changed over 160 years of the Broadbalk experiment but higher yields have diluted the content of some minerals in the harvested grain.

Over the previous 100 years or so, this lack of a fall in the soil content of some micronutrients may have been due to partly their industrial emissions. These emissions are now rapidly falling, which suggests that there is perhaps a need to monitor soil content in the medium to long term. The graph, based on Defra data, is taken from AHDB Project Report 518. It reminds me of the reduction in sulphur emissions we saw two or three decades ago. This Rothamsted led project report published five years ago concluded that levels of copper and zinc in the soil may have fallen slightly over the previous 25 years but to such a small extent that it had no practical significance. So levels in the soil may be changing but very, very slowly.

The same project investigated the value to winter wheat of two foliar spray applications of copper, zinc or manganese on sites where deficiencies are most likely to occur i.e. organic and/or sandy soils with a high pH where organic amendments containing these micronutrients are not applied. There were five field sites a year in the three year project. Despite the sites being located on soils most likely to have a deficiency, there was only one statistically significant yield increase with the application of copper and one with zinc in the 15 trials.

There has subsequently been a huge argument over these results. The basis of the debate is whether or not some slight yield ‘increases’ were real or were just a reflection of the natural variation within an individual site. The problem is that micronutrient sprays are reasonably cheap and the level of yield response required for an economic treatment can be below what can be assessed as statistically significant.

I have been looking through the data from these 15 trials and have come to the conclusion that the two statistically significant yield increases were the only true responses to the micronutrient sprays. My reason for saying this is that the two sites had levels of zinc or copper in the soil and grain at deficiency levels. However, leaf tissue analysis of samples collected in the spring, at the time recommended by the commercial partners in the project, was pretty hopeless in predicting deficiency. Just look at the histogram for the ‘yield responses’ to zinc at each of the 15 sites. Above each ‘yield response’ column are the results of the leaf tissue analysis in milligrams/kilogram and the numbers in red denote ‘deficiency’. Enough said, except to point out that the site which gave the statistically significant response (starred) had satisfactory levels in the leaf tissue at the time of sampling but soil and grain analysis showed that this site would have been likely to respond to a spray treatment.

Overall, leaf tissue analysis suggested a deficiency of either zinc or copper in seven of the fifteen sites; four for zinc and three for copper but all but one of these sites did not respond to treatment. The high and statistically significant response to copper on one site was predicted by leaf tissue analysis but there were very similar levels in the leaf tissue at two other sites that did not respond at all. Grain and soil analysis show that this was a deficient site.

When you really think about it, the unacceptable ability of leaf tissue analysis to identify responsive sites to micronutrient sprays is not surprising. A leaf tissue test in the spring is a mere snapshot of the micronutrient content in a constantly changing crop whilst soil analysis and grain analysis reflect copper and zinc availability for the whole season.

In my opinion, this AHDB project clearly shows that only soil and grain analyses are good identifiers of sites that are most likely to respond to a micronutrient treatment. On the other hand, leaf tissue analysis is far more likely to miss responsive sites to sprays and result in a lot of money wasted on false recommendations to spray. Make sure that the soil or grain analysis is done using the correct laboratory technique and also ensure that the correct standards are used to indicate deficiency. I have to say that my conclusions on the (lack of) value of leaf tissue testing are not new. It says as much on page 26 of section 4 of RB 209.

An exception when using soil analysis as a predictor of deficiency is manganese. It only indicates the soluble manganese at the time of sampling, not what will happen later. Luckily, even in the presence of mild deficiency symptoms, experiments have suggested that there is no yield response to a manganese spray but the crop can look awful. In the short term, a mild deficiency may result in a floppy and more disease ridden crop canopy that may be more susceptible to damage from pesticides.

I have also learnt from the AHDB project that, in contrast to manganese, yield responses to the application of zinc and copper can occur in the absence of deficiency symptoms. Hence, particularly in view of falling levels of atmospheric deposition, it is worth monitoring, say once in every four or five years, levels in grain or soil in situations where deficiencies are most likely to occur. It may be that grain analysis is the preferred option for long term monitoring, provided of course that micronutrient sprays were not applied to the sampled crop. This is because grain analysis has a better chance than soil sampling of achieving a truly representative sample of a field.

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Wheat yields 2018

Posted on 03/01/2019 by Jim Orson

The summer of 2018 is clearly summed up by the autumnal picture of a banana tree in Clare College gardens, just down river from our house in Cambridge. It was hot and also it was very dry from late April onwards. In the UK, dry summers are often associated with high wheat yields but in my blog, written in early July (blog posted on 13 July), I suggested that it might perhaps prove too dry in 2018 and that wheat yields could be significantly down on average. The Defra statistics, released just before Christmas, show that yields were down by around 6% in the UK and 5% in England (see Table), when compared to the average yield for the previous five years.

So how good was my prediction? I suppose it all depends on what is meant by ‘significant’. I must admit that I was pleasantly surprised by the overall yields but some farms in the very driest parts of the country were well down. In East Anglia much depended on the amount of rain that fell in the last week of May. The West Midland regional yield was down by 9% compared to the average of the previous five harvests. The late spring and summer was particularly hot and dry in that region and the lighter soils, in particular, must have suffered.

In Scotland and the North West of England yields were down by around 18-20%. Unlike the rest of England, the establishment conditions in these areas were far from ideal and the growing conditions during the winter and early spring were hostile to plant growth. As a result the wheat crop was poorly developed when the drought conditions occurred.

As one would expect, second wheats were often particularly low in yield. In this rotational situation one would normally expect antagonistic soil biota to reduce root growth and hence restrict access to soil water during the prevailing extremely dry conditions.


Perhaps I can tentatively congratulate myself on my prediction if a reduction in average yield of 6% can be called ‘significant’. On the other hand, it may be that I have again over-estimated the impact of dry conditions on final yields. As I have said in previous blogs, solar radiation is typically above average in dry summers and this can more than compensate for a moderate lack of moisture. However, this year was so hot and dry that the very high levels of solar radiation could not compensate for the impact of high soil moisture deficits and for the much shorter period of grain fill that occurred as a result of the high average temperatures.

As I mentioned in my previous blog, the drought in the summer of 2018 was less severe than in 1976 when I was seeing crops showing drought symptoms as early as the end of April. In contrast, at that time of year in 2018 the soil moisture deficits were low or non-existent. This may explain why UK average wheat yields were down by 12% in 1976 rather than the 6% of this year. So, it could have been worse! Overall we must be very thankful that our wheat yields are so resilient from year to year.


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Looking back to the future

Posted on 24/08/2018 by Jim Orson

I have been motivated to emerge from blogging retirement by the latest AHDB Project Report on applied nitrogen (N) doses for feed winter wheat. As regular readers of my blogs know, I have a ‘thing’ about the subject. This is because field trials data do not support some of the underlining principles that have been used to develop the recommendations in RB 209. I eventually wrote papers on the subject in 2010 and 2012 (referred to in the AHDB report) and came to the conclusion that on mineral long-term arable soils, where little or no organic amendments are used, using a fixed dose of N produces economic margins at least equal to those using RB 209 as a guide. The field trials data indicate that only when Soil Mineral Nitrogen (SMN) levels exceed around 100 kg N/ha, equivalent to N index 4 and above, is there a consistent need to contemplate reducing doses of applied N.

The papers I wrote were met by a howl of outrage by many soil scientists. It seemed that I had committed heresy. However, their field trials data said the same as NIAB TAG’s. Some soil scientists insisted that the scientific literature backed the approaches taken by RB 209, particularly the influence of measured SMN on recommendations. I had already read the papers they quoted and knew that these actually concluded the opposite by detailing the lack of influence of measured SMN on the optimum economic dose of N for feed winter wheat.

Let me acknowledge that I was not the first to suggest a fixed dose of N for feed winter wheat. During the 1980s, the then newly available measurement of SMN and also the first attempts to estimate Soil Nitrogen Supply (SNS = SMN plus nitrogen in the crop in early spring plus an allowance for N net mineralisation of the soil) were being tested by ADAS for their possible role in N recommendations. A range of tactics employed in Northern Europe was tested. However, in 1987 ADAS reported that using a fixed rate of N gave as good or better prediction of the optimum economic dose than using measured SMN or SNS or an N index system as the basis of a recommendation.

Let us look at a couple of quotes from the latest AHDB report:

“Little relation between soil mineral N or grain yield and N optimum was observed.” The lack of relationship between measured SMN and N optimum is nothing new and the relationship between grain yield and N optimum has always been rather tenuous.

“….. in long-term arable situations with high yields where N requirements were expected to be similar, it was difficult to improve on recommendations beyond RB209 (or a single average N rate).” The last caveat is extremely important and reflects the following table from the report which shows that adopting a single fixed rate of N in all the trials was as cost effective as using RB 209. This very important conclusion is not mentioned in the abstract of the project report.

Comparison of different approaches to deciding N fertiliser rates

Using average results from previous trials on mineral long-term arable soils with little or no organic amendments, the single standard rates in the table are predictable and this approach has been the basis of NIAB TAG recommendations for the past few years. Please remember that field yields tend to be lower than plot yields because of lower yielding headlands etc.

It is worth highlighting that the basis of the RB 209 recommendations in the report was the Field Assessment Method. This is based on previous cropping. The approach based on measured SNS is now only being advocated where very high levels may be expected. The lack of a relationship between measured SMN and optimum doses in this report underscores the advice in RB 209 on which method to adopt.

I have often mused why measured SMN or SNS has so little influence on applied N requirement for feed winter wheat. There are some possible explanations. First of all, the efficiency of use of every extra Kg/ha of SMN or SNS above a threshold (i.e. the marginal efficiency) of around 40-50 kg N/ha (N index 0) is far less than the 100% assumed in RB 209. In this newly reported AHDB project this marginal efficiency of use of SNS was less than 50% when no applied N was used. Secondly, higher levels of SNS are often a reflection of good moisture retentive soils and/or a ‘better’ rotation and/or a more healthy soil, resulting in higher yields and consequently a higher N demand by the crop. This could largely offset the need to reduce N doses with increasing measured SNS levels until they become very high. Analysis of an extensive trials database suggests that there may be more than a grain of truth in this theory but the statistical analysis is not convincing. A third, and less techy possible explanation, is that measuring SMN, estimating SNS and also identifying an economic optimum dose are not precise exercises. There may well be other possible explanations. It could be that it is a combination of several factors that explain the lack of influence of measured SNS on optimum economic doses of N for feed winter wheat.

Another quote from the report is “Grain protein cannot therefore be used as an entirely reliable indicator for N management.” This is slightly at odds with the advice in RB 209 which suggests that “Farm nitrogen strategies for wheat can be assessed periodically using information on grain protein concentration.” Perhaps this statement in RB 209 is too dogmatic when it is clear that the AHDB original project report on this approach included caveats on using protein as a guide to optimised N management.

RB 209 recommendations remain based on some underlining principles with which I disagree. However, its recommendations have now been adjusted to reflect the average results of field trials. Does this mean that we have all the answers on N nutrition of feed winter wheat? We certainly do not. The project again demonstrates that there is a huge unexplained variation in the actual optimum economic doses between fields, farms and years. The report does emphasise that there can be an error around the optimum economic dose of plus or minus 50 Kg of applied N/ha without affecting too much the financial margin over fertiliser costs. However, there remain an uncomfortably high proportion of trials where the error in predicting the optimum is outside this range. As AHDB (HGCA) project report 73 (1993) concludes “current recommendation systems are similarly poor because they fail to identify fields with aberrant responses to N”. The 1987 ADAS paper I quoted earlier said that “measurements of SMN have shown promise where small optima are suspected [i.e. very high SMN levels]”. To be perfectly honest we are now back to exactly the same situation we were 25-30 years ago despite a huge investment in research on the subject in the intervening years. It is truly looking back to help define the future research needs of this very important subject.

Now, back to my retirement. There has been sufficient rain for me to sow cover crops on my allotment. I am hoping that the spring oats that I liberated from a farmer’s grain store last year are still viable.

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Wheat yields 2018

Posted on 13/07/2018 by Jim Orson

The very hot and dry weather continues. My galvanised watering can was much used in 1976 and the same can is now starting to leak in 2018. Perhaps I should buy a new one but I suspect that there may be a run on them. The watering can was bought in 1974 (ish) at the same time as a galvanised wheel barrow. The latter had to go to the dump only a handful of years ago. Time moves on!

The current weather conditions perhaps mean that there is no need to write a blog on predicting the 2018 wheat yields. The easiest years to predict relative wheat yields are those with extreme weather. The horrifically wet and dull summer of 2012 resulted in me predicting lower than average yields. What I did not take into account was the additional impact of waterlogging during the critical stages of grain filling. In areas which received the most rainfall this resulted in exceptionally low yields on the clay soils. Subsequent reading of the scientific literature indicates that waterlogging in the middle of the winter has some impact on wheat yields but its effect is very significantly greater during grain fill. The widespread waterlogging in March and early April this year must have had some impact on potential yields.

The most difficult years for prediction are those where the spring and summer weather is drier than average but not exceptionally dry and hot. Lack of rain usually means that solar radiation levels are higher than average. We really do not have sufficient understanding of the processes to predict yields accurately. The impact of soil moisture availability is hard to assess as is the efficiency of use of solar radiation. The latter varies according to several factors (

February and March were cold this year. In addition, March was generally very wet and it was really not until mid-April at the earliest that we witnessed good growth. This is in contrast to the high wheat yielding years of 2014 and 2015 which had dry and warm springs. The lack of solar radiation in April means that perhaps stem reserves, which are used to supplement grain fill, are this year lower than usual. The warmer than average weather during April and May means that the crops shot through the critical growth stages during which potential grain numbers are established and stem reserves continue to accumulate. So the signs were not positive even before the wheat crops experienced the hot and dry June.

Many people of my age look back at the hot and dry summer of 1976! This was a different type of year. It followed the hot and dry summer of 1975 and the 1975/76 winter was dry. It was so dry that, without any hindrance from the weather, I deep dug our front garden in Essex in order to get rid of a couple of skips of builder’s rubble. This is when my relatively new galvanised wheelbarrow came into its own! The spring of 1976 was very dry and I was seeing patches of drought stressed winter barleys on gravelly land in April. The only realistic summer rain in Essex fell on 21 June. It may be that the relatively dry winter meant that the crops were well rooted at the beginning of spring growth but of course at there was less moisture in the soil at this time than there was this year.

I have perhaps overestimated the impact of dry weather on yields in previous years but it seems obvious to me that wheat yields in the main arable areas of England must be well below average this year mainly, but certainly not solely, because of lack of moisture and the consistently high temperatures in late June and early July. Wheat prefers temperatures around 20 C, is not keen on 25 C, dislikes 30 C and positively hates 35 C. Higher temperatures not only have a direct effect on growth but also shorten the length of grain fill. This year the length of grain fill might be reduced from a typical 42 days to around 32-35 days in the main arable areas of England.

Hence, the cold February and March, a wet March, the higher than average temperatures in April and May and the very hot and dry June/early July do suggest very disappointing wheat yields this year where these weather conditions have prevailed. A hot ‘finish’ is associated with higher proteins and so, provided specific weights are OK, quality may be good. However, I think that I should finish with the caveat that when many grass crops mature under hot conditions, the dormancy of the seed is reduced. This is true of black-grass, wild-oats and cereals. Hence, rain before harvest could have a larger than average impact on Hagberg’s this year. It may well be worth starting an already early wheat even earlier should rain be forecast. 

Photo:  Many Australian farmers have suggested that galvanised steel is the most significant technical introduction in the development of their farms. This photo was taken was taken in a barn right next to the Murray River in the very north of South Australia. Makes you proud!

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