NIAB - National Institute of Agricultural Botany

Orson's Oracle

Wheat harvest 2017

Posted on 14/07/2017 by Jim Orson

 

It is the time of year when I try to predict the yields of the wheat harvest. Usually I do this in early July but the timings of the blogs have meant that this year it is mid-July. It is going to be an early harvest for many and so we will soon know the true picture. Everything seems to be early in Cambridge this year. I was lifting potatoes on the 1st June and my tomatoes were ready to pick on the 10th July.Wheat harvest

Where wheat crops had established well in the autumn, they came through the winter full of promise. Overall, it was a dry winter and so there was little waterlogging. If anything the winter was perhaps too warm but up to around the first node stage, wheat development is controlled mainly by day length which prevents crops becoming too advanced. The high yielding crop of harvest 2015 also experienced a warm and dry winter. Average temperatures in 2017 were also higher than average from April onwards, which has led to an earlier grain ripening.

Spring 2017 was exceptionally dry. Now I know that high yielding wheat years tend to have dry springs but it can be too dry leading to a reduction in yield potential. This may have been true in some parts of the country this year but the rainfall was so variable as to make it difficult to say which locations were most severely affected by drought. Rain did eventually arrive in May but in some areas there was not enough to alleviate fully the drought pressure.

Sunshine hours tended to be average or above average for every month bar February. There were really no exceptional months during the 2017 harvest year. This is unlike harvest year 2015 when April received far higher than average sunshine hours and solar radiation, particularly in the areas that achieved the very high yields. Overall, June sunshine hours were greater in 2015 than in 2017 except for East Anglia, the South East and parts of Southern Britain.

The final weather feature of note was the extreme heat in mid-June in some of the main arable areas. Temperatures were above 30 centigrade for three consecutive days and the nights were very warm too. This level of heat can cause a permanent reduction in the rate of grain fill as well as shorten the period of grain fill.

The higher than average temperatures may have reduced the period of grain fill by 4-5 days this year. In addition, the warmer weather also reduced the time between the third node stage and flowering when the potential number of grains sites is established. The percentage reductions in the times spent in these development stages may not have been compensated for by the average to above average radiation levels. Hence, in some areas this may have resulted in lower than average levels of intercepted solar radiation during these key stages.

So what are my conclusions? I think that in many parts of the country the wheat yields will do well to be above average. Second wheats seem to have particularly suffered from the lack of rainfall. However, yields in Lincolnshire and further North may be more pleasing. It is a very difficult year to attempt to predict wheat yields and I am by no means confident. So much depends on how the levels of soil moisture affected growth in individual locations. I hope I am wrong and that everyone has a great wheat harvest!

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World wheat record

Posted on 30/06/2017 by Jim Orson

Eric Watson, who has just broken the world wheat record with 16.791 t/ha, stayed with us over the weekend after Cereals. He spoke at a seminar at NIAB on the Friday and we visited farms over the next two days.

I first visited Eric and Maxine in NZ around 20 years ago. It was clear to me then that they could break the world record if they were prepared to go through the bureaucratic process. Their farm has superb soils, their weather (plus irrigation) supports very high yields and their attention to detail is amazing. At that time, Eric was about to take the decision not to have root crops and onions on the farm because of soil damage, either from intensively working the soil or due to trailer traffic.

The soil in the high yielding parts of the farm is 30-40 cm of superb silty loam over around a metre or so of silty clay loam. It is then very gravelly. I am particularly interested in the soil type in terms of the nitrogen dose used for the world record yield. Some people express surprise that they used ‘only’ 258 kg N/Ha applied as urea treated with a urease inhibitor. I think Eric was also surprised because he had used more in previous years but is now convinced that the higher doses may have been inhibiting yield rather than encouraging higher yields.

The record breaking crop followed after a two year break from cereals and the previous crop was beetroot for seed. The soil mineral nitrogen (SMN) was 109 kg N/ha which firmly puts the field in nitrogen index 4 in the new RB 209. Soil tests indicated that the level of mineralisable N was 40 kg N/ha, although such analyses may not be very accurate.

I think that in RB 209 the soil type would be classified as a deep silt. In this case it recommends 100 kg N/ha for an 8 t/ha crop and 200 kg N/ha for a 13 t/ha. There are no yield adjusted recommendations above 13 t/ha but if the same rule of an extra 20 kg N/ha is applied for every tonne above 8 t/ha then a 16.8 t/ha should receive 280 kg N/ha. The crop would receive 245-255 kg N/ha using the NIAB TAG recommendations. Of course we do not know the actual optimum for the world record crop but its protein content was around 11%, suggesting that the dose was approximately correct. It is comforting that these two UK systems recommend similar levels of nitrogen to the approach adopted in New Zealand to produce the record yield. Perhaps we are making some progress at last.

In the world record crop, the total nitrogen removed in the grain was 319 kg/ha. This suggests that the combined amount in the grain and the straw was over 400 kg N/ha. Once again this demonstrates that in high yielding crops the efficiency of use of applied N and SMN is well above average and also that net nitrogen mineralisation can often exceed that estimated. All this helps to explain why using average data in a balance sheet of nitrogen supply and requirement for potentially very high yielding crops often recommends far too high nitrogen doses. Hence, previous experience in field trials still provides the most reliable guide to recommended nitrogen doses; albeit, this is an admission of our failure to understand sufficiently soil processes.

Finally, food for thought… The yield map of the world record crop shows that there were significant parts of the field approaching 20 t/ha. The lower yielding parts of the field tended to be in straight lines showing the impact of the tramlines and/or the wheelings of the linear boom irrigator. The NIAB TAG guidelines take such yield variation into account and assume that significant areas of a ‘X’ t/ha crop will have yields of ‘X+2’ t/ha. The other thing to take from the yield map is that there is more to come!

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Is plant resistance a free lunch?

Posted on 16/06/2017 by Jim Orson

There is often a perception that plant resistance to pests or diseases is a bit of a free lunch. Instead of paying for a pesticide the plant will look after itself. In general, this is not true. The presence of resistance genes can result in a yield drag either in the absence of a challenge from an insect pest/disease and/or when challenged by an insect/disease.

This issue became clearer at the turn of the century because of advances in genomics and NIAB TAG had quite an internal debate in 2004 on the cost of plant resistance. In that year, there were very high numbers of orange wheat blossom midge which resulted in responses to insecticides in trials of up to 2.75 t/ha in susceptible wheat varieties. Counts in the unsprayed plots showed that the resistant varieties were almost clean of larvae and yet they still had significant responses to insecticides of around 1.25 t/ha. There were very low levels of aphids in that year and so it was postulated that the response of the resistant varieties could have been due to the insecticides reducing the energy expended by the crop in fighting off the very high numbers of blossom midge larvae.

Recent research partly funded by the AHDB shows that there are yield penalties associated with septoria, yellow rust and brown rust resistance genes in wheat. Losses from an individual resistance gene to an individual disease could amount to 0.3 to 1.0 t/ha in the absence of disease challenge. The researchers muse that total losses could be higher where a number of resistance genes are introduced to provide resistance to a range of diseases but do not offer any proof that this may happen. Reassuringly, stacking of individual genes against septoria does not significantly increase yield losses and not all rust resistance genes exhibit a yield cost in the absence of disease. The latter provides plant breeders with some options of incorporating genes without detriment to yield.

Is there any way forward or will disease or pest resistance in crops always be associated with yield losses? A letter to a recent edition of the Nature magazine suggests that there may be a way out of this conundrum, at least for disease resistance. It seems that researchers have identified a genetic approach whereby a resistance gene is ‘switched on’ only when the plant is under challenge from disease. They have managed to engineer this for both the laboratory test plant of thale cress (Arabidopsis thaliana) and rice. So there may be a free lunch after all.

I have used the word ‘engineer’ and whether such an approach can be achieved by more conventional means is beyond my area of understanding. However, the title of the letter ‘uORF-mediated translation allows engineered plant disease resistance without fitness costs’ suggests that some form of genetic engineering may be key. This is another example where the green blob’s built-in objection to any form of genetic engineering may come back to bite them. Surely, if such a process meets realistic registration requirements then only a fool would object?

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Science under pressure

Posted on 02/06/2017 by Jim Orson

My wife and I regularly go to the British Library. It is close to Kings Cross railway station and is a delightful way of starting a day out in London. There is always a small exhibition in its main vestibule and the subjects change on a regular basis. Last time we visited, it was on Victorian entertainment. It is clear that science lectures were then considered a good night out and the populace was very willing to pay for the experience.

Not a lot of people know this but the popularity of scientific lectures in the early 19th century resulted in Albemarle Street in Piccadilly becoming the first one-way street in the world in order to improve traffic flow. The decision was taken after a series of lectures by Humphry Davy (of miners’ safety lamp fame) at the Royal Institution caused horrendous queues of horse-drawn carriages bringing in the eager audience.

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The Royal Institution in one-way Albemarle Street, Piccadilly

Science was certainly making great strides and each discovery was celebrated. There was a less well known lecturer, Professor E V Gardner, who appears to have been very popular in the late 19th century. I have tried to find out more about him but there is little on the internet other than that he had his own college and he also worked for another institution. Outside his lectures he was drawn into a debate about using aluminium compounds to whiten bread. In 1873 he wrote a letter to the press stating “It is curious to observe how, in hurried exercise of judgement, even technical journalists are capable of publishing most gross mistakes”. Unfortunately this is still a familiar theme. By the way, aluminium compounds as bread additives were banned in 1875.

Science remained a subject over which the populace enthused for another century. Last autumn the harvest festival at our local church included a hymn written in 1968 with the following lines; “Praise God for harvest of science and skill, the urge to discover, create and fulfil: for dreams and invention that promise to gain a future more hopeful, a world more humane”. It was written in the early days of the green revolution which has resulted in a more humane world, with the numbers of undernourished people in the world steadily falling since the early 1990s.

Now science, in relation to agricultural progress, is viewed in a different light. There is a widespread cynicism; witness the row over the safety of glyphosate. So when did it go wrong? Autumn 1997 was a watershed. A letter to Nature was published saying that BSE in cattle could be transmitted to other species. This was following on from well intentioned denials by politicians that such a thing could not happen. It was in fact a misinterpretation of the scientific advice at the time, which was that transmission across species was unlikely but could not be completely ruled out.

This event seemed to break the popular belief in the UK that scientific endeavour was necessarily a force for good in order to meet the future challenges for food production. Ever since, science in relation to food safety and production has been under intense scrutiny.

There is a need to improve the credibility of science, particularly so-called popular science . One essential element is to make the peer review system more robust. This present weakness has been targeted by the green blob who have funded ‘popular research’ and published it in ‘peer reviewed’ journals. Many of these papers, when subject to wider scrutiny, have been torn to shreds and some have had to be withdrawn.

A way forward is to do something that was suggested at the Cambridge Science Festival a few years back. Papers are peer reviewed and the resulting drafts are published on the internet for at least a few months for wider scrutiny. Only after such an exercise should a final version of the paper be published. Such a process should also be adopted for project reports funded by public and levy money, which generally have a less rigorous review process. The internet opens up the possibility for more stringent review systems and we should use it.

There also needs to be better scientific communication with the public. I have just been leafing through the details of those appearing in this year’s Latitude festival in Suffolk. In addition to singers and groups that I have or have not heard of, there was a list of scientists who will be appearing but not singing! This Wellcome Trust initiative has been part of the festival for the last few years and, according to independent analysis, has been effective and well received. We need more of this. Remarkably, it is a return to the Victorian age when people paid to hear the latest in scientific progress. Why not? The science being done today, particularly in the biosciences, is no less exciting or transformative.

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Spray drift and pesticide legislation

Posted on 19/05/2017 by Jim Orson

A couple of blogs ago I discussed some of the issues around aquatic buffer zones. I promised to mention spray application in a future blog. Well, the future starts here.

One issue that spray specialists keep banging on about is boom height. Lifting the boom so that nozzle tips are 20 cm above the typical recommended height of 50 cm can double spray drift. Why is spray drift so sensitive to boom height?

Drift from all types of nozzles can be minimised by ensuring that the tips of the nozzles are as low as possible above the target to provide good spray coverage. This is 50 cm for 110 degree nozzles at a half metre spacing. In addition, spray pressures should not be above around 3 bar for conventional flat fan nozzles.

Data produced from experiments in the wind tunnel of the Silsoe Spray Application Unit emphasise the considerable influence on spray drift of the height of the tip of the nozzle. Increasing it by 20 cm (8 inches) can double the drift from a conventional standard flat fan nozzle and the increase from extended range/variable pressure flat fan nozzles is even greater. These latter nozzles produce higher levels of drift than conventional flat fan nozzles when operating at 3 bar.

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The question frequently posed is why such a small increase in the height of the tip of the nozzle can increase drift risk so dramatically? The answer is clearly demonstrated in the photograph taken at the Silsoe Spray Application Unit. This shows that drift largely emanates from a zone a distance below the nozzle.

The actual distances involved will depend on many variables, such as nozzle type and size, wind speed, forward speed and spray pressure. However, in simple terms, where the tips of the nozzles are 50 cm above the target and the zone where most of the drift originates is 20 cm above the target, then increasing the height of tip of the nozzle by 20 cm can more than double the size of this zone.

There is a simple explanation as to why drift largely emanates from spray fan nozzles at a distance from the tip of the nozzle: the spray liquid leaves the nozzle under pressure and at a high velocity and entrains (draws in) air as it travels.

The influences of both spray pressure and air entrainment fade as the spray droplets move away from the flat fan nozzle and eventually the droplets fall solely by gravity if the boom is far too high. By the time they get to just above the target, the droplets are moving slower and are the most vulnerable to drift. Smaller droplets lose their momentum more quickly and so not only is the ‘driftable zone’ wider for fine quality sprays from flat fan nozzles but also the smaller droplets are more ‘driftable’.

There are calls for CRD to adopt four star nozzles in order that aquatic buffer strips can be reduced in width. The current three star nozzles reduce drift by 75% compared to a standard 11003 nozzle working at 3 bar pressure. Some ‘smaller droplet’ air induction nozzles meet this target but often at slow forward speeds and pressures which may mean some compromises in efficacy. Even when working at 3 bar they have a few issues with efficacy e.g. small weeds with foliage applied herbicides and, anecdotally, on potato blight. One way of reducing spray drift by 90% or even 95% is to use even coarser nozzles but this will result in further compromises with efficacy because of poor spray retention on leaves and/or spray distribution, particularly on small targets and even, perhaps, on the soil surface.

There are ways in which such drift reduction is possible and which largely or completely retain efficacy but it may require a radical overhaul of the vast majority of sprayers currently on farms. Air assistance is one option. With conventional boom sprayers, achieving a 90% drift reduction and the good and uniform spray distribution necessary for some targets may mean a reduction in boom height. Some sprayer manufacturers now offer 25 cm nozzle spacings as an option aimed at drift control with the recommendation that the boom is operated 25 cm above the target. Boom suspension then needs to be very good with effective height sensors and probably some articulation.

There is a long way to go on the issue of aquatic buffer zones and spray application. This topic deserves to be higher up on the agenda of the future of farming in the UK.

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