NIAB - National Institute of Agricultural Botany

Orson's Oracle

Precision application of nitrogen

Posted on 15/04/2016 by Jim Orson

A few months ago I attended a seminar at which all of the farmers present said that they had abandoned the precision application of nitrogen to wheat. This came as no surprise to me as I am unaware of a strong scientific base to support it. On the contrary, the scientific arguments against it keep strengthening.

One key issue is the way that wheat responds to nitrogen. It is possible to stray from the economic optimum by up to 50 Kg N/ha and have only a minor effect on both yield and margin. This is demonstrated by a slide shown to the HGCA (now AHDB cereals and oilseeds) conference a few years back.

Uncertainty in N rates

Therefore, based on nitrogen response data in individual trials, the economic optimum has to vary very significantly in a field before there are meaningful economic advantages for precision application of nitrogen, provided of course that the average dose is just about right. This overriding basic fact alone explains much of the disenchantment in the precision application of nitrogen to wheat.

Nitrogen trials are carried out in a small part of a field where the level of SMN may not vary much across the trial site. On a field scale SMN levels will vary more significantly and may provide an opportunity for precision application of nitrogen. This approach was tested in a major LINK funded project in the late 1990s. The test fields were divided into a grid and for each section of the grid a SMN measurement was taken and the estimated economic optimum was applied. The result was that the average yield of the grids was no higher than it would have been had the average dose been applied to the entire field.

This is perhaps explained by two factors. First, SMN is not a reliable indicator of soil nitrogen supply and second, SMN has far less influence on the optimum dose than previously supposed. A leading soil scientist told me a few years ago that SMN levels up to 100 Kg N/ha were “merely noise”.

Another possible reason to adopt precision application of nitrogen to wheat could be variations in potential yield across the field. However, yield does not influence the demand for nitrogen fertiliser by as much as suggested in some advisory systems. This is simply because high yielding crops use applied nitrogen and SMN more efficiently. If this is not so, how do you explain plot yields last year of 14 t/ha of wheat being achieved from 220 Kg N/ha in NIAB TAG trials carried out on-long term arable soils receiving no organic amendments? It did seem from these particular trials that additional nitrogen was necessary for plot yields above 14 t/ha.

Finally, there is an argument for spatially applying nitrogen according to the canopy size of wheat. Looking back at the graph at the beginning of this blog, this would typically bring small rewards in yield although it would help ‘even up’ the crop. The reward would be more significant in very variable oil seed rape crops where there is a good relationship between canopy size in the very early spring and the optimum economic dose of applied nitrogen.

You have to understand that the examples I have quoted above for wheat are for feed wheat and I have ignored the critically important issue of the environmental impact of nitrogen. It may be that there is a stronger argument for precision application to milling wheat. However, the understanding of nitrogen nutrition is still relatively rudimentary.

To make progress there needs to be further research at the more basic level. The trouble is that funders are more drawn to projects that offer quick fixes. As far as I can see there are no quick fixes in nitrogen nutrition that will provide the basis for precision application of nitrogen. However, there are those enthusiasts who continue to try to develop a system of precision application of nitrogen that will reap real rewards. I genuinely wish them well whilst reminding them that accurately predicting nitrogen doses for feed wheat to within a few Kg N/ha using the current relatively simplistic recommendation systems is at the moment not possible. The only potential case I can foresee for precision application of nitrogen to feed wheat is perhaps where there are very extreme soil types within a field and/or if there was a way of predicting variations in the efficiency of soil and applied nitrogen use across a field.

Remember, the first rule of precision farming is to assess how much variation there is and then assess whether or not there is an economic advantage in spatially varying an operation in order to correct or minimise it. Good basic and applied science, correctly interpreted, has a significant role to play here.

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Beware of correlations!

Posted on 01/04/2016 by Jim Orson

March is the month of the Cambridge Science Festival and I attended a few lectures. The programme was less plant-orientated this year and one of the major themes was big data.

The lecture I attended on big data and medical science was superb. The lecturer was brilliantly modest, ensuring that his points were understood by the wide-spectrum of knowledge in the audience. Put it this way, even I understood it!

First of all, he undermined some of the bunkum that goes with the term big data. As he said, it is data analysis. The issue is that so much data is now being generated in the medical world that it is becoming ever more challenging to analyse it and extract meaningful messages.

He warned that correlations in data do not mean causation. The well known example he quoted was the close link between ice cream sales and shark attacks in Australia. This is simply explained by the fact that there are more people in the sea on the hot days when ice cream sales are high. Hence, stopping ice cream sales will not prevent shark attacks.

Another example I can remember was when someone found a correlation between the fall in sparrow numbers in the UK and the rise in lead-free petrol sales. This amazingly lead to suggestions that there should be an investigation into the environmental impact of the additives in lead-free petrol but that proposal soon ran out of gas (pun intended).

In the medical world, there is a real danger of correlations leading to false conclusions that may impact on the lives of many people and so much of the lecture was based on this issue. There are some similarities in arable agriculture.

During the 1970s it was fashionable to say that high wheat yields were correlated with crops that had a high above-ground biomass at harvest. When you think about it, it is stating the b******* obvious. At harvest much of the biomass is in the grain and the rest is in the remaining above ground plant matter, notably straw. The two are related. Varieties tend to have a consistent harvest index, which is the proportion of total above-ground dry matter that is in the grain. Hence, inevitably high yields must be associated with high levels of biomass.

The correlation between wheat grain yield and high biomass crops was the basis of the Schleswig-Holstein system. This attempted to have a high biomass throughout the life of the crop, starting with high seed-rates and continuing with encouraging high growth rates from early spring onwards. Also in the 1970s there was another approach called the Laloux system. This stemmed from research by the then Professor of Agronomy at the University of Gembloux in Belgium. This was based on modest seed rates (roughly what we use now) and a more measured programme of feeding and protecting the crop in the spring and early summer. I did trials comparing the two approaches and the Laloux system consistently outyielded the Schleswig-Holstein system. The striking observation of the trials was that by harvest the two systems gave similar looking crops. Obviously the weather intervened and influenced final tiller numbers and biomass.

In the event, the then best UK practice was equal to or superior to the Laloux system. This was partly due to the fact that the Laloux system relied on late nitrogen applications. These are relevant to Belgium because of the regular incidence of thunderstorms in late May and June but not to the UK where it may be as dry as toast at that time of year.

Hence, whilst there is an obvious correlation between wheat biomass at harvest and wheat yield, it may not necessarily be pointing a way towards growing higher yielding crops. Obviously, things would be different if there was a correlation between yield and wheat biomass at a far earlier growth stage.

Last year proved that good standard UK practice can result in very high levels of biomass and yields provided that the weather is with us. Therefore, the approach must surely be to ensure that crops are able to take advantage of such conditions in order to achieve high levels of biomass at harvest without spending a shed load of money.

By the way, Gembloux is a very small town. I have visited the superb Department of Agronomy of the Agricultural University a few times and on occasions my wife came along too. The first time I suggested she looked around the town and we would meet up for lunch. I think it took her less than an hour to ‘do’ the town but the salads in the restaurant at the gates of the University made up for that.

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Preventing broad-leaved weed resistance is a priority

Posted on 17/03/2016 by Jim Orson

The EU referendum debate is getting quite emotive. It is almost a carbon copy of the Scottish independence debate. There are those who support an improving status quo who are saying it would be a mistake to rock the boat and there are those who say that real progress will only be made if we are independent. The problem is that really no one knows what the future will hold and so the argument is between ‘project fear’ and ‘project faith’. It is sometimes easier for the ‘project faith’ lobby to be positive, an example being SNP’s assertion in the debate on Scottish independence that Scotland would reap huge rewards from North Sea oil. However, events conspired to show that this forecast was a little hollow.

In one or two aspects at least, the future of pesticides looks a little more certain. Resistance and registration issues will continue to increase. However, the full implications of both are not certain.

Unlike with fungicide and insecticide resistance, individual farmers can largely dictate the future of herbicide resistance on their own farms. Hence, they need to think about this issue with great care and, as I have said before, adopt a change in mindset. No longer should a low level infestation of weeds showing above a crop go un-rogued. This applies mainly to grass weeds but broad-leaved weeds such as charlock should also be removed if at all possible. In other countries there is herbicide resistance in charlock and its near relatives and it poses a huge problem in parts of Australia.

There is also a need to exploit the weaknesses of already resistant weeds. I was reminded of this the other day when I received an email from a Western Australian farmer who had read one of my recent blogs on managing black-grass between crops. He described a machine that crushes the seed of their extremely herbicide resistant rye-grass (Lolium rigidum) as it comes over the back of the combine. This approach has the ability to kill 50% of the viable seed that has been set in the harvested crop.

black-grassUnfortunately, black-grass seed is shed before harvest but it has other weaknesses which can be exploited. I will not go over, yet again, the cultural measures that can be used to reduce populations except to say that its major weaknesses are that it cannot emerge from depths greater than 5 cm and that it is very much an autumn germinator. Rye-grass (Lolium multiflorum) is also autumn germinating and vulnerable to burial below 5 cm.

Wild-oats (Avena fatua) has fewer weak spots that can be exposed by changes in cultivation and time of sowing. It is both autumn and spring germinating and can emerge from greater depths, perhaps up to 15 cm. Its greatest weakness is that it shows above crops and hence is vulnerable to hand-roguing. There are a handful of populations that now show quite frightening levels of herbicide resistance and I am sure that it is advisable to reduce all populations to levels where they can be rogued if necessary.

The other forms of herbicide resistance in UK arable crops are common poppy, common chickweed and scentless maywPoppieseed resistance to the ALS mode of action of the sulfonylureas and one or two other herbicides. In Spain, poppies have developed resistance to a range of modes of action. I have been trying to think of the weaknesses in their growth cycle that can be exploited by cultural control measures. Unfortunately, I cannot think of any other than either killing the crop, adopting grass leys in the rotation or mechanical weed control.

Hence, although herbicide resistant annual grass weeds get the headlines, it is the herbicide resistant broad-leaved weeds that could eventually have the greatest impact on our arable systems. So please ensure that there is a herbicide resistance strategy adopted on each arable farm, which generally means rotating herbicide modes of action. There is a temptation to use more sulfonylureas for broad-leaved control as more spring barley and wheat is grown on farms that have herbicide resistant black-grass. This should be tempered by a sound anti-resistance policy, partly because the future of some alternative modes of action is uncertain.

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Silencing scientists?

Posted on 04/03/2016 by Jim Orson

In the last couple of weeks I have been viewing the lights of Cambridge from the top of the Gog Magog hills (well they pass for hills in Cambridgeshire). To explain, I drive over the hills whilst returning home from my golf club.

There are now two levels or layers of lights. The lower layer comprises the normal lights of a city: houses, flats, streetlights etc. The upper layer comprises red lights that mark the top of the large cranes on the many construction sites in and around the City. I do not know how many cranes there are but the effect of their lights at night is quite striking. Some have likened the skyline to that of Dubai during its rapid expansion.

I have often wondered what it must be like to operate such cranes. However, I will never find out because I am a wimp when it comes to heights. The overviews of the City must be great but of course to see the precise detail of a specific location you have to be at ground level.

I am becoming increasingly concerned that the views of those who work at the ground level of science and who know the nuances and details of the subject are becoming more and more pushed aside by those who have just an overview of the issues. This is a worrying trend and one which shows signs of getting worse.

Last year there was a missive from the Cabinet Office demanding that all civil servants (many scientists are civil servants) must seek prior permission from a minister to speak to the media. This feels like a restraint on scientists engaging pro-actively with topical controversies such as badger culling and gene editing. I realise that ministers have scientific commitbadgertees in order to inform decisions but there are, inevitably, many expert scientists who are excluded from this process.

There is now further concern that UK scientists may be prevented from arguing for changes in national legislation or policy if research grants are not exempted from a government ban on the use of public funds for political lobbying. This ban was announced in February and will be introduced in May. This prohibition could impact on University and Research Station staff who are receiving support from public funds. Much agricultural research is publically funded by the BBSRC (Biotechnology and Biological Sciences Research Council). Does this mean that these scientists will not be able to take part in public debates on scientific issues relating to policy or to respond to public consultations in their areas of expertise?

At the moment there is confusion on this issue and the government department responsible seems unable to provide clarification. This has prompted a petition which many scientists are signing. I sincerely hope that it is not the government’s intention to gag scientific opinion and that clarification will protect the right of scientists to make their informed opinions widely known.

Without such clarification life for scientists will become very difficult because ‘lobbying’ is not easily defined. Nor is it easy to define a policy issue. For example, some scientists have commented that a recent paper stating that ‘organic’ milk is more nutritious for consumers is flawed. The paper compares ‘organic’ milk from grass-fed cows with ‘conventional’ milk. The flaw is that the comparison should have been between ‘conventional’ milk from grass-fed cows and ‘organic’ milk from grass-fed cows. It has been known for some time that grass-fed cows produce more nutritious milk: even I knew this!

The criticism of this paper is perhaps just scientific opinion rather than lobbying. However, organic production could be seen by some as part of government policy. Hence, the uncertainties of the boundaries between scientific opinion and lobbying would inevitably inhibit scientific comment and progress should the lobbying by scientists receiving public funds be banned. Let’s hope further clarification from government will prove that this concern is a storm in a teacup.

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Hard science vs. field observation

Posted on 19/02/2016 by Jim Orson

I attended the BCPC Pests and Beneficials review this week. It concentrated on flea beetle control in oilseed rape and I came away depressed about the prospects for the crop in some parts of the country unless the neonicitinoids are reintroduced or an alternative and at least equally effective seed dressing is introduced. I am sure that there will be press reports on some of the papers delivered at the review.

However, there are likely to be no press reports on a fascinating paper that included the issue of bias in scientific reports. Those that regularly read my blogs know that I have been tub-thumping on this issue and asking for more transparent systems of science reporting. During the delivery of this particular paper my mind wandered to some of the practices that we have adopted in arable agriculture without a scintilla of good scientific study.

The prime example is stubble cultivations to encourage the emergence of black-grass. Now I am sorry that I have to mention black-grass once again but this example demonstrates my concerns that a practice can be adopted with next to no science and where field observations are biased towards thinking that a practice is actually working.

Many years ago I addressed a large audience of agronomists on the control of black-grass and questioned whether the then widespread practice of cultivating stubbles to up to 20 cms depth immediately after harvest with something akin to a Simba Solo was significantly contributing to black-grass control. I was met with a wall of silent disbelief. I was told that black-grass emerges where this practice is adopted and it can be killed with glyphosate before sowing the following autumn sown crop, so it must be contributing to the control of the weed.

This approach was originally sold on the basis that it would make long-term black-grass control in non-plough tillage as effective as where the soil was ploughed. There was little or no evidence for this and what ‘evidence’ I saw was incomplete and unconvincing. However, everyone seemed to believe it was a valuable approach and I assume that it did not benefit my reputation by having the temerity to question this new dawn.

Now we know that this practice of so-called ‘stale seedbeds’ did little to increase the technical sustainability of black-grass control and I am sure resistance built up more quickly where the plough was abandoned.

The time between harvest and the establishment of the following crop needs to be a key time to try to maximise the loss of viable black-grass seed; yet, it is absolutely amazing that there has been no thorough scientific study of the best way to maximise such losses in the range of circumstances that are likely to occur. All we have are a series of un-coordinated field trials with incomplete sets of treatments and observations. Field trials can help but these should be based on the knowledge gained from thorough mini-plot or laboratory studies that establish the principles of maximising the loss of viable black-grass seed.

There are some data in the AHDB Cereals and Oilseeds (what a mouthful) Project Report 381. I have tabulated the data and it seems that there was consistently more black-grass emergence between autumn-sown wheat crops when there was no soil disturbance at all, when compared to using a Solo to a depth of 15cm immediately after harvest. In years when there was good soil moisture status from harvest onwards, this additional emergence between autumn-sown crops resulted in less black-grass in the following wheat crop. However, in dry autumns the opposite was true. Despite little or no black-grass emergence where the stubble was cultivated to 15 cm depth in dry condition, there was less black-grass in the following winter wheat crop than where direct drilling was adopted. This is hard to explain and, very significantly, it questions whether the level of black-grass emergence between crops is a reliable guide to viable seed loss. I have a theory or two but hard facts are required.

Needless to say, in the trials covered by this report, ploughing was the most effective cultivation method in containing black-grass numbers.

This snippet of data only results in highlighting more unknowns. The critical question must be is black-grass emergence between autumn-sown crops a reliable way of estimating the loss of viable black-grass seed? In addition, we need to know how soil moisture as well as the age, dormancy and depth of black-grass seed influence the efficiency of the various approaches to stimulate viable black-grass seed loss.

No amount of un-informed field trials or abstract field observations will provide a robust answer to these questions. Rather than continue an unproductive debate that has gone on for far too long, we need to have some very closely monitored mini-plots and laboratory studies, where the impact of position, age and dormancy of black-grass seed as well as soil moisture status can be monitored. Even a small step in this direction will help to provide some foundation for more informed field testing of approaches that are much more likely to optimise the management of the soil between crops in order to maximise the loss of viable black-grass seed. It would be a huge prize for the industry.


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