NIAB - National Institute of Agricultural Botany

Orson's Oracle

Wheat seed rates

Posted on 08/09/2017 by Jim Orson

In my most recent blog I suggested that the industry needs more research on stubble management for black-grass control. However, that comes with the caveat that such research will illuminate rather than confuse. There has been an example of research causing confusion on another current issue. At the end of the last century the industry was content that seed rates for winter wheat was a done deal. NIAB TAG had been doing research for years and had achieved, what we thought, robust guidelines.

Then in 2000, AHDB published a project report on winter wheat seed rates. It suggested that the typical recommended optimum plant numbers at the time, including those recommended by NIAB TAG, were far, far too high and huge cost savings could be made on seed. Understandably NIAB TAG staff sat down and read the AHDB report very carefully to see if we had missed a trick.

It soon became clear that we had misgivings about the report. First of all the choice of treatments broke the common sense rule I was taught in my first statistics lecture at University. The key message from the lecturer on choice of treatments was to ensure that there should be adequate coverage of the likely or assumed optimum values: it is a common sense approach to help ensure a clearer identification of the actual optimum. He was keen on common sense throughout the course of lectures. He emphasised that there is always the danger that getting too pre-occupied with statistical techniques can cause a drift away from reality.

The seed rates tested in the AHDB project were 20, 40, 80, 160, 320 and 640 seeds/m2. Hence, there were no treatments between 160 and 320 seeds/m2 (roughly 80 and 160 kg/ha) and also between 320 and 640 seeds/m2 (roughly 160 and 320 kg/ha). I was told that this was a true scientific approach but having poor coverage of the typical recommended seed rates of the day worried me. The average results of the project are shown in the first graph below. The horizontal axis shows the plant/m2 established after the increasing seed rates tested and the vertical axis shows the resulting yields.

Another concern was that using what was said to be the best line fit, known in the trade as a linear plus exponential function, resulted in a straight line between the 160 seeds/m2 and 640 seeds/m2 treatments, i.e. the seed rates producing the three highest plant populations in the graph below. This worried me even more because the straight line meant that the economic optimum seed rate had to be below 160 seeds/m2, or if it sloped upwards sufficiently for the additional yield to more than pay for the additional seed, above 640 seeds/m2 (see the High Mowthorpe results in the second diagram below). Hence, in the analysis of these trials there could be no chance of an economic optimum seed rate lying between 160 and 640 seeds/m2 i.e. the seed rates commonly used at the time. Our review of the AHDB project report resulted in NIAB TAG continuing to recommend the optimum plant populations suggested by its own trials.

AHDB report

And so the years went by. Then in 2011 there was a Defra science report on artificially imposed slug damage and its likely impact on seed rates. The same seed rates were used as in the AHDB report. The results of the seed rate treatments were not published in the same way. As I said earlier, in the AHDB report the horizontal axis is plant population and in the Defra report it is seed rate (see graph below). This is unfortunate.

The statistical analysis of results was similar but not quite the same as that used in the AHDB report. On the whole it appears that the economic optimum seed rates, where ‘slug damage’was not imposed, were far higher than those implied in the AHDB report. There were 5 instances in 28 trials where the straight line inclined upwards sufficiently to have optimum seed rates above 640 seeds/m2 e.g. High Mowthorpe in the graph below. There were only three instances where optimum seed rates were between 320 and 640 seeds/m2. The Rosemaund line in the graph below had an optimum seed rate of 174 seed/m2. There was a huge variation in economic optimum seed rates between sites and years and no clear conclusion could be made from the results. The question has to be asked: was this due to natural variation or due to the choice of seed rate treatments and the analysis of the results? Again, I am very uncomfortable with the information provided.

DEFRA graph

I have said many times that being a slave to statistical approaches and ignoring common sense can create difficulties in interpreting results in order to produce reliable guidance for farmers. I am delighted that 50 years ago I learnt something from my statistics course at University that is and will remain very relevant! Another continuing relevance is that wheat is a very adaptable crop and plants/m2, within a reasonable range of the optimum appropriate to the date of drilling, will give about the same financial margins. This is just as well with the variation in establishment that can occur in practice.

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Stubble management: where is the research?

Posted on 24/08/2017 by Jim Orson

I would not blame anyone for being totally confused about how to treat stubbles this autumn in order to minimise black-grass in future crops. I have read three separate articles on this subject in the farming press over the last few weeks which have intended to inform us. Unhelpfully, there seem to be three approaches being simultaneously suggested, sometimes within the same article! Some contributors are suggesting leaving the stubble undisturbed and allowing the black-grass seed to emerge. Then there is the very opposite advice being proffered. The stubble needs to be cultivated as soon as possible in order to get the black-grass seed to chit.

The contributors to these articles suggest that glyphosate should be used on multiple occasions to kill off the emerged black-grass but perversely also suggest that the farmer must think about the possibility of glyphosate resistance. Using cultivations to kill off small emerged black-grass is not mentioned as a possibility, although I do accept glyphosate must be used immediately before or very soon after drilling.

The third school of thought is that ‘it all depends’. I am firmly in this camp because that is what the data suggest. NIAB TAG staff regularly read trial reports from throughout Northern Europe and analyse the published data. It is a cheap way of supplementing our research for our membership. Trials can often have specific objectives and the authors of the reports regularly do not glean all the messages from the data. It is through this means that we came across data that provide a strong steer on how best to treat stubbles to maximise black-grass seed loss. Please note the emphasis on seed losses rather than simplistically encouraging seeds to germinate; one conclusion of this broad reading is that maximising losses, both those that occur through germination and those which are less visible, should be the goal.

The conclusions are pretty straightforward. When the soil is tinder dry, as it was last year, it is best to leave the stubbles undisturbed in order to minimise black-grass emerging in the following crop. In such conditions more viable black-grass seeds are lost from undisturbed stubbles than when shallow cultivations are adopted. This may be because the undisturbed soil surface structure seems to result in more black-grass seed germination in the stubble in dry conditions. It is also obviously the case that there are some natural losses from the soil surface. Shallow cultivations straight after harvest are more likely to provide an environment for seed survival in very dry conditions.

Around 15 years ago The Morley Agricultural Foundation funded a PhD on seed losses of different grass weed species from the soil surface. The conclusions suggest that nearly all seed from the major grass weed species are lost from the soil surface in the autumn and over-winter but some may be taken into the surface layers of the soil by earthworms. This study may, I emphasise may, have found the first evidence that birds predate black-grass seed from the soil surface during the winter.

The higher rate of black-grass seed losses in undisturbed stubble in very dry conditions rather goes against those who subscribe to the assertion that non-soil disturbance results in less black-grass germination than when the soil surface is cultivated. I have to stress that this is more relevant to spring sowing when some black-grass seeds need the stimulus of cultivation in order to germinate.

The opposite is true in moist or wet conditions. Incorporating the seed into a shallow seedbed straight after harvest results in less black-grass emerging in the following crop. This is hardly surprising when you think about it.

I have other gripes concerning these press articles! They mention weeds other than black-grass in their introductions and then, without any notice, specifically discuss black-grass. This only adds to the muddle.

Highlighting the present muddle means that I have to be absolutely clear;
• The effectiveness of different cultivation strategies post-harvest depends entirely on the context and, although there is work to be done in this area. The total losses of freshly shed seed seem to be maximised in dry conditions by leaving them undisturbed on the soil surface. In wetter conditions, however, some shallow, superficial cultivation immediately post-harvest to encourage black-grass seeds to germinate appears to be a more effective strategy.
• As an overall comment on the whole topic of post-harvest cultivations, there needs to be a focus on the totality of seed losses during this period and not just losses through germination.

My greatest gripe is that there is no publically available specific research on this issue. Unfortunately it is not headline stuff and does not promise to revolutionise arable production in one project. However, three years of NIAB TAG member-funded research suggests that a better understanding of this area of the biology of black-grass is critical to improving practical management on farm. That is what research is about: not the glamour of a quick fix promised breakthrough but of slowly and painstakingly producing better options for farmers. Instead, we have chaos and confusion.

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Why is life like a Dulux colour chart in monochrome?

Posted on 16/08/2017 by Andrew Watson

I am a simple man. I like things to be black and white. Day follows night, e=mc2 and Game of Thrones is on at 9pm on a Monday. A book titled 50 Shades of Grey sounds like a nightmare read to me.

Take Brexit. A black and white decision was made, like it or not, but we appear to be entering a decade of greyness. Whether hard or soft, I think it will definitely be a lemon Brexit - slightly firm on the outside, soft in the middle, leaves a sour taste in mouth and why-o-why would you to chew on it in the first place?

Agricultural regulations, which I’ve been involved with for 25 years, are the ultimate grey. The ‘Ministry’ (which I’m always reminded of when I see Gringotts Bank in Harry Potter), put out definitive black and white rules on a subject and this is what the farmer has to do.

But it’s not black and white. It’s like producing a Dulux colour chart in monochrome; endless shades of grey as the rules are interpreted at a practical level, by the experts, on farm.

Look at the Nitrate Vulnerable Zones (NVZ) rules which were so vague that the farm inspectors at that time, The Environment Agency, would publish periodic semi-practical interpretations to make the rules less grey. Like it or not, at least it provided more clarity - more black and whiteness. Then independent farm inspectors came along and interpreted the rules further, and often completely differently, on an individual farm. Back to grey again.

Pesticide rules are so “grey” that it can be difficult for a farmer or advisor to interpret them correctly. Which of the numerous buffer zones applies and where does the buffer start? What water volume or spray nozzle can I use? What are the definitive legal requirements for using this pesticide product?

As some of you know, I’ve spent over a year developing the definitive black and white database of pesticide products. ActivSmart, a NIAB Digital service launched at this year’s Cereals Event, puts all the grey pesticide rules and product data into one place in sharp, defined colour. It allows users to easily compare the defined attributes of similar pesticide products; with up to 26 black and white facts on each of the 2,300 plus approved products on the database. It provides clarity; from active ingredient to maximum total dose, from arthropod buffer zone requirements to a document library. ActivSmart is the perfect project for me as I get to replace shades of grey with black and white.

However, despite ActivSmart (with all modesty) being by far the most comprehensive, up-to-date but still simple, pesticide comparison tool, there is still a nagging greyness for a small percentage of the data.

Let me give you an example. In 2017, a new buffer was very quietly introduced by the UK Chemicals Regulation Division (CRD). This 5 or 10 m ‘non-target plant’ buffer around the outside of the field currently only affects five of the 41 products containing the active ingredient clomazone currently approved in the UK (yet more unnecessary greyness). However, CRD has published two authorisations for three of the five products. One authorisation has no new buffer but the other has the buffer clearly defined. In 2017, both these legal documents are valid. As a result the manufacturers can pick which authorisation to follow, and are not required to put the new buffer requirement on the product label in 2017 so they haven’t.

Clomazone is very toxic to many plant species and there is a history of legal disputes relating to drift damage onto neighbouring crops. It is one of very few products that must be applied as a coarse spray. I have concerns about how this grey area between CRD authorisations and product labels, both of which are legal documents, could potentially be viewed by a court of law should a serious legal dispute occur.

So, to finish, can I make a plea for more decisions to be made? Around the world and increasingly in the UK, no-one, even if they have the power to do so, wants to put their head above the parapet and say this is how it will be. Personally, it gets to the point that I almost don’t care what the black and white decision is but, please, please, make it and give us all a less grey world.

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What makes rotations tick?

Posted on 14/08/2017 by Jim Orson

I have written before on Salle Farms in North Norfolk and their experience of introducing a seven year rotation around the turn of the century. It replaced a variety of short intensive rotations that were employed in different parts of the estate. The crop that seems, in particular, to benefit in terms of yield comparisons with both national and regional performance is winter wheat. This is now grown either two times in the seven years or three times depending on the date of the sugar beet harvest.

Some of the increase in yield may be due to reduced levels of black-grass but I do not think this explains everything. Hence, the magnitude of the relative improvement in wheat yield compared to other crops was a bit of a mystery to me until someone sent me a paper from the Journal of Ecology. This may start to provide a basis for an explanation.

The paper reports on an investigation into how soil biota may over time influence changes in plant species on uncropped land. I found the paper challenging to read but there was some clear guidance as to how soil fungi and bacteria may influence the relative growth rates of different plant groups. One of the main conclusions was that wild grass species are particularly reduced in growth when grown in soil that is inoculated with the biota extracted from soil that has previously just grown the same species. Hence, winter wheat may not grow so well in soil where wheat has been recently grown due to the soil biota that it encourages or the loss of organisms that are inhibited. In addition, the paper also reports that grass growth (and so perhaps wheat growth) is better when the soil contains a greater variety of soil biota left after growing a range of crops.

I have always been led to believe that the reduction in yield of wheat in wheat intensive rotations is by no means all due to take-all and it seems that the rest of the reduction could be due to other unidentified soil biota.

The overall conclusion of the study is that all the plant groups studied grow better in soil that has just previously grown other species because of less net negative effects of soil biota (in grasses) or because of more net positive soil biota effects. This may provide a more scientific basis to crop rotations and indicates that increasing the number of species grown in a rotation, perhaps including cover crops, may be better for the growth of all crop plant types.

Another conclusion in the paper is that the growth of plant species that tend to first infest bare soil, which have high root length and low colonisation from arbuscular mycorrhizal fungi (AMF), particularly suffers when they are grown in soil inoculated with the biota that they encourage. Oilseed rape fits this description and this may explain the NIAB TAG results that show that yields decrease as the intensity of its cropping increases. This latter research does identify two species of soil biota that are associated with intensive rape cultivation and may be the cause of the yield reduction. It is not clear whether this is because of direct effects via the crop roots or because they out compete other more favourable species.

                        Impact of rotational intensity

A recent review of the role of AMF and the impacts of agricultural management highlights the very negative effects of intensive soil disturbance and fertilisation on AMF. The review states that the fundamental principle of crop rotations is to exert a control function that prevents particular AMF from dominating the soil matrix. The review explains that continuous wheat favours the selection and proliferation of less co-operative and more aggressive AMF species. These are likely to enact behaviour similar to parasitism. Hence, at least in some circumstances, there can be ‘bad’ AMF species as well as ‘good’ AMF species. It goes on to say that this effect can be toned down by ‘break crops’, such as Brassicae (e.g. oilseed rape) or legumes. Brassicae are non-mycorrhizal crops which act as inhibitors of the dominant AMF species proliferation and legumes are AMF dependent crops which favour the overall propagation of AMF communities.

Complicated isn’t it?! New laboratory techniques are revolutionising research into soil biota and so I hope that we are now on the cusp of a better understanding of how crop rotations tick.

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The anatomy of high yielding crops

Posted on 28/07/2017 by Jim Orson

A few years ago NIAB TAG and FAR had a joint trial series on maximising wheat yields in England and NZ. FAR is the Foundation for Arable Research, the levy board in NZ responsible for cereals and a range of other crops.

The same varieties were grown in both countries. These were the highest yielding in each of the respective variety lists. High yielding sites were chosen and the intensity of use of crop inputs investigated. The components of yield, i.e. ear number, grains/ear and grain weight, were among the factors recorded.

The years in which the trials were held were not conducive to record yields but plot yields of up to 17 t/ha were recorded. The trials in NZ had more grains/m2 with higher ear numbers/m2 but the number of grains/ear was less than in England. Their higher yields were due partly to an increase in grains/m2 and, at least as significant, was that their thousand grain weights were superior. I cannot provide the precise results because the NIAB TAG membership paid for the English trials.

This example again shows that wheat is a wonderfully flexible crop. This flexibility comes in useful in a number of ways and shows why we can achieve reasonably good yields from year to year despite the variability in weather.

The question is why do they tend to have higher ear numbers and less grains/ear in NZ? I think we have to assume that this is an effect from weather and perhaps the following graph of average temperatures offers some explanation. I have shifted the monthly averages for Christchurch on the South Island of NZ by six months to allow for an easier comparison.

Jim Orson blog 200

As you can see, NZ has a warmer winter, spring and early summer. This, along with their higher levels of solar radiation, perhaps encourages robust tillering and tiller survival, resulting in more ears/m2. The late autumn and early winter for their 2017 crop was particularly warm, which may have helped Eric Watson establish a sound base to his world beating crop. Similarly, the high yielding UK crop in 2015 followed a mild winter.

The main period when grain numbers are determined, between the third node stage and flowering, is likely to be shorter in NZ because of their warmer conditions. The impact of this shorter period may be offset by higher levels of solar radiation and so the warmer conditions may not contribute to a lower number of grains/ears. It may simply be that their lower grains/ear is due to the increased competition as a result of higher numbers of ears/m2. Should competition be the explanation then this may well be a barrier to even higher yields.

Temperatures in NZ and England are more comparable during the period of grain fill when, logically, the higher levels of solar radiation in NZ result in higher thousand grain weights.

This explanation of the difference in the components of yield in NZ and England sounds very plausible. However, I have learnt over the years that seemingly logical explanations may distract from greater truths and the search for answers should ideally reach beyond simple analyses.

Unfortunately, despite being in different hemispheres, the harvests in NZ and the UK have overlapped this year. The weather in NZ has been very wet in recent months and some farmers are still trying to harvest their grain maize. Our own harvest is also being frustrated by rain and I hope that there will be a more promising weather forecast by the time this blog is on the NIAB website.

There is more on NZ crop production in my blog posted on 3 March 2017. 

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