NIAB - National Institute of Agricultural Botany

Orson's Oracle

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.

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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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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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