NIAB - National Institute of Agricultural Botany

Orson's Oracle

How to get high wheat yields with nitrogen

Posted on 07/01/2017 by Jim Orson

One of our daughters had a weird dream over Christmas. Apparently, I went missing for six months and was eventually found on a golf course. When asked why I had not returned home earlier I simply replied that I was having a bad round. Obviously, at least one of our daughters thinks that I have fixations. Golf is probably one and another is definitely looking at how data can provide guidance to farmers.

I have recently been looking at datasets of nitrogen trials on winter wheat. This is a risky exercise because of the variable nature of results and the way optimum doses are calculated. Imposing any assumption on the shape of the response can influence the results and maybe mask the true answer. However, using the conventional methods, which may not be correct for some individual trials, the datasets I have examined allow me to have a more informed deduction as to how to get high wheat yields with nitrogen. It seems that the way to get high nitrogen-fertilised yields is to get high yields in the absence of applied nitrogen. In general, the higher the unfertilised yields, the higher the fertilised yields. I think that most farmers either know or suspect this to be the case. Good crop and soil management and favourable weather conditions are the key, with nitrogen providing the icing on the cake.

In these databases, for every extra tonne of nitrogen-fertilised yield/ha there is a contribution of at least half a tonne from the yield without applied nitrogen. One very large database suggests that for every tonne of nitrogen-fertilised grain/ha, two thirds of a tonne comes from the yield without nitrogen. These observations have a surprisingly high level of statistical validity for nitrogen trials. The associations explain to me why the additional amount of nitrogen required for very high yields in field trials is less than would logically be expected.

I have to say that the contribution of yields without nitrogen to increasing fertilised yields vindicates the nitrogen recommendations for feed wheat, based on field trials, provided to NIAB TAG members over the last ten years or so. These recommendations ignore Soil Mineral Nitrogen (SMN) levels if below 100 kg N/ha (i.e. nitrogen indices 0-3 in the current version of RB209) and only suggest applying relatively small amounts of additional nitrogen to a realistic base dressing when field yields are expected to exceed 10-11 t/ha. This is in contrast to the current version of RB 209 where the recommended doses decrease significantly between nitrogen indices 0-3. The reason why SMN can normally be ignored at these levels of SMN is because potential yields tend to increase with more available soil nitrogen: therefore the crop can economically use it and the additional nitrogen applied over and above the reduced doses recommended in current RB 209 for nitrogen indices 2-3. This is a rather neat self-correcting system. It appears to explain why there is, on average, no real difference in the economic optimum nitrogen dose in field trials carried out in situations where SMN is anywhere below or around 100 kg N/ha.

The conclusion of this piece is to reinforce my usual plea that we should be more cognisant of what field trials are telling us, despite their associated frustrations and errors. Now that I have got that off my chest I must return to the golf course.

Best wishes for 2017 (and don’t overdo the nitrogen).

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2016 wheat yields – a post mortem

Posted on 17/12/2016 by Jim Orson

Back in July I forecast average wheat yields, with some areas having yields on the disappointing side of average whilst the far North perhaps having above average yields. Well, as they say on Strictly “the results are now in”. The Defra estimated yields are in the following slide. I have included national yields for England and Scotland as well as two English regions of interest.

                 Jim Orson NIAB TAG blog - wheat yields

Yields in all regions of England were around average suggesting that my concern over lack of June sunshine leading to slightly lower than average yields in some areas may have been slightly over-egged. This may be because I wrote the blog in the first few days of July and then the first half of July turned out to be relatively sunny. Also, my contention that the very North of England might experience better yields than average turned out to be slightly optimistic although some very acceptable yields were reported. Scotland did have a good year. The yields in Yorkshire and Humberside came back down to average after the outstanding yields of 2015. Yields in the eastern region were actually lower in 2015 than 2014 due to the dry early summer last year.

Perhaps I was over-influenced by the June sunshine data, as shown below. There are one or two comments worth making. Sunshine hours are not directly related to the amount of radiation that drives potential yields and the graphic is for sunshine hours in relation to the average and not absolute values.

It is now very clear to me that measuring total radiation is not an entirely accurate approach to measuring yield potential, even when water supply is not limited. Not all the spectrum of total radiation is used for photosynthesis. Photosynthetic active radiation would provide a more accurate estimate of yield potential than total radiation. Photosynthetically active radiation, often abbreviated to PAR, defines the spectral range (wave band) of solar radiation from 400 to 700 nanometres within which photosynthetic organisms are able to photosynthesise.

Jim Orson NIAB TAG blog - June 2016 sunshine duration

There is a limit to the amount of radiation that plants can process in a day. This is often around 60% of that which occurs on the very brightest of June days. It is far better to have radiation spread out evenly over a month than have the vast majority concentrated into a few days of the month. An outstanding feature of the record wheat year of 2015 was that nearly every day from March to mid-July had a few hours of sunshine and this resulted in a better exploitation of the energy received.

Compared with harvest 2015, with its mild and dry winter and spring, an exceptionally sunny April and a few hours sunshine nearly every day in the late spring and early summer, 2016 had less overall radiation during the spring and summer, a very wet winter and early spring and a cold April. When you take all this into account, the yields of 2016 held up well.

I wish you all a great Christmas and New Year.

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Peak Wheat

Posted on 02/12/2016 by Jim Orson

The Soil Association was making a huge fuss over ‘Peak Oil’ around the new Millennium. Subsequently, new technology has resulted in the fears of an oil shortage evaporating. The reason for highlighting Peak Oil was that the Soil Association appeared to believe that conventional agriculture is more vulnerable to energy prices than organic agriculture. This may have been good PR at the time for the organic industry but the fact is that organic agriculture is possibly more vulnerable to energy shortages and price. Herbicides and fungicides produce huge yield benefits from relatively little energy use which may more than counteract the high amounts of energy that are needed for nitrogen fertiliser production.

Until recently the Soil Association was making ‘Peak Phosphate’ a feature in its campaigns and on its website. It was stated that we have only around another 30 years of phosphate in reserve. It is true that the mining companies have approximately 30 years of declared reserves in their accounts but the US Geological Survey estimates that there are at least 1,500 years of phosphate reserves to meet current demand. Peak Phosphate was to publicise the organic movement acting responsibly by recycling nutrients. Another PR exercise which is not borne out by the facts. Conventional farmers also recycle nutrients, possibly to the same extent, but are admittedly not so dependent on this source of plant nutrition when achieving significantly higher yields/ha.

Jim Orson - Peak Wheat - NIAB blogI think it is my turn to introduce a Peak, in this case Peak Wheat. Has the UK passed its Peak Wheat production? We produced 17.2 million tonnes in the 2008 harvest year; a combination of planting more than 2 million hectares of wheat and of what was then a record average yield/ha. In 2014 and again in 2015, we surpassed the record average yield/ha set in 2008 but the 5-10% lower area of the crop resulted in a total production of around 16.5 million tonnes.

The smaller area of wheat production in recent years can be attributed to a number of factors which now include herbicide resistance in black-grass. Effective and relatively cheap weed control makes it more likely that rotational and crop management restraints can be eased thus allowing farmers to maximise the area and potential of the most profitable crops. Take that away and there is a necessity to take the traditional rotational restraints more seriously. In this case, herbicide resistance in black-grass means less autumn-sown crops and also a higher proportion of later autumn-sown wheat. All this results in a smaller heap of wheat unless the yield potential of wheat increases very significantly.

Then there is also the issue of how agriculture will be supported in the future. It seems to me that there may be less overall support and perhaps a greater proportion of that support will be devoted to environmental enhancement. This may mean less crop production in parts of the country where yields are average or below, particularly where there is also an intractable black-grass problem. In these circumstances the temptation may be to restrict the area of crop production to the highest yielding parts of fields or farms and to increase the area devoted to environmental enhancement.

A realistic total cost of growing a hectare of wheat is around £950-£1,000/ha, which at current prices means that a yield of around 8 tonnes/ha is required to make a profit. Our 5 year rolling average yield is about 7.9 t/ha: food for thought. It is also worth pointing out that winter wheat and winter oilseed rape are the only two crops that many farmers can grow which will turn a profit without support from the Government.

All this sounds gloomy but there are scenarios that will mean we have not passed Peak Wheat. Plant breeding breakthroughs are now more likely with the accumulating knowledge of the genetic makeup of the crop and the new breeding techniques that are currently being used or being developed. There is also the possibility that wheat prices may reach a higher plateau as a result of an increasing world population and increasing climate uncertainty. Finally, an effective black-grass herbicide in wheat or herbicide-tolerant crops may be around the corner. Would I bet my shirt on these happening in the short to medium term? ……. perhaps not.

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Isoproturon – the great soil improver

Posted on 18/11/2016 by Jim Orson

We live in the Trumpington ward of Cambridge. Since the US election there has been a debate amongst some residents about the Trump in Trumpington. A local LibDem councillor has been very concerned and has changed his Twitter handle because it contained the dreaded word Trump.

Trumpington is expanding at an enormous rate and the land where the famous Plant Breeding Institute (PBI) once stood is now being gradually covered with houses. I looked at the name of some of the new streets. They invoke memories of varieties past; Proctor, Rialto, Bead, Consort, Piper, Avalon, Charger, Kestrel, Osprey and Hereward. Many of these had the handle Maris. This was because the PBI entrance was on Maris Lane. Incidentally, I came across Mrs Maris’ grave recently when helping to give the churchyard a bit of a spruce up.

The other variety that appears as a street name is Huntsman. Its introduction helped to start the surge towards greater wheat yields in the 1970s. I started in the National Agricultural Advisory Service (the predecessor of ADAS) in 1969 and one of my first jobs was to sow a winter wheat trial in South Essex. It was the first year that Maris Huntsman was in the NIAB Recommended List trials and my scores showed that it was visually very disappointing over the winter. However, the harvest demonstrated its true value.

There were many other significant introductions to the industry during the 1970s; for instance, chlorotoluron and isoproturon came on the market in 1971. In the early years, chlorotoluron was the more effective black-grass killer but it was more vulnerable to herbicide resistance and isoproturon came to the fore in the 1980s.

Sprayer  - NIAB imageIt is easy to overlook what these herbicides achieved. My personal experience was that the longer-term arable soils had terrible structure in the late 1960s and 1970s as a result of intensive late-autumn and spring-cropping. At the same time the Government commissioned the Strutt report ‘Modern Farming and the Soil ‘. This was published in 1970/71 and described the parlous state of our longer-term arable soils. Effective grass weed control not only resulted in a huge increase in autumn sowing, with its attendant advantages of plant cover and an effective root system during the winter, but also their sowing dates were brought forward to a time when typically soils were drier and less susceptible to damage. This all resulted in a huge improvement in soil structure and helped to set the scene for a near doubling of winter wheat yields between 1976 and 1984.

Bringing forward autumn sowing dates also meant a larger crop going into the winter with the advantages that it entails: more plant cover over-winter and a larger root system. Now that we are seeing a retreat from autumn cropping and a return to later autumn sowing dates, we have to remember these lessons from recent history. There is evidence that these lessons have been learnt because of the current enthusiasm for cover crops prior to spring crops.

I have been debating with colleagues as to whether a cover crop followed by a spring cereal is as beneficial as an early-sown winter crop. Typically the objective of a cover crop is to produce more green material in the autumn than is achieved with a winter cereal crop sown at optimum seed rates for grain yield. In addition, it has been suggested (but not, as far as I know, proven) that it may be advantageous for the soil biomass of fungi and bacteria that the cover crop is an entirely different type of plant from the following spring crop and also from other crops that appear in the rotation.

A major issue on the heavy clays is that cover crop management is not easy, particularly the transition between the cover crop and the sowing of the spring crop because there can be a delay in the soil surface layers drying out in spring. I am sure that the inventiveness of the industry will come up with some practical solutions. My experience in the early 1970s suggests that these solutions will be very beneficial in helping to retain the structure of heavy soils where black-grass control necessitates spring cropping. However, it would more straight-forward and profitable to be able to chemically control black-grass in early autumn-sown crops!

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Nitrogen recommendations – it's very complicated

Posted on 04/11/2016 by Jim Orson

I wrote a blog in April (Precision application of nitrogen) on why I thought that experiments and field experience over the past 10-20 years have not shown a significant benefit in the spatial application of nitrogen in winter wheat. The recent publication of the AHDB project ‘Automating nitrogen fertiliser for cereals (Auto-N)’ has strengthened the argument that this approach to nitrogen fertilisation has little or no economic advantage.

The authors of the report seem to accept that the simplistic models that are currently used to predict nitrogen requirement do not take into account the unpredictability of nitrogen uptake by the crop, in this case winter wheat. In many cases there are interactions between the components used to predict optimum nitrogen requirement. For instance the authors highlight a possible negative correlation between soil nitrogen supply (SNS) and fertiliser recovery. Where SNS is high there is sometimes a lower recovery of fertiliser nitrogen by the crop.


However, despite the failure to define an approach that will make the spatial application of nitrogen pay in winter wheat, the report is full of data. I love data, but there is far too much for me to absorb. There are, though, some standout pieces of information and interpretation by the authors.

Highlighted in the project summary is the statement that high SNS is associated with high yields. We are familiar with the term SNS; in current recommendation systems it is the sum of Soil Mineral Nitrogen (SMN) in the spring,plus the amount of nitrogen in the crop at that time, plus an estimate of usable net mineralisable nitrogen released by the soil. However, in the report it has a different meaning: it is the amount of nitrogen in the crop at harvest in the plots that did not receive nitrogen, hence it is Harvested SNS. The interesting observation that high Harvested SNS is associated with high yields is only useful if it is predictable. Unfortunately it may not be; in this project the relationship between SMN and Harvested SNS was tenuous.

Other data collected in this project suggest that there is not a strong association between grain yield and nitrogen requirement. This confirms previous field and experimental evidence that very high yields can be achieved with moderate levels of nitrogen. In this project, plot yields in excess of 13 t/ha were achieved with 240 kg N/ha in a field which had modest levels of SMN. Last year, in a NIAB TAG experiment in a field with typical levels of SMN, treatment yields in excess of 14 t/ha were achieved with 220 kg N/ha before additional nitrogen was required to enable even higher yields. However, please remember that spot yields in excess of 14 t/ha can occur in fields averaging 10-12 t/ha.

To quote the report ‘the lack of a strong relationship between yield and nitrogen requirement raises some important questions’. The most important question is how yield expectation can be incorporated into future nitrogen recommendation systems. My view for feed wheats is that nitrogen doses should not be increased until field yields above 10-12 t/ha are expected. For field yields above this level any increase in nitrogen recommendation should be modest.

Any new recommendation system cannot continue to adopt the principle that each kg of SMN is equivalent to a kg of SNS. Continued adherence to this principle explains why RB 209 has too large a change between soil nitrogen indices in recommended doses for feed wheat.

AHDB has funded two large projects that patently show that each kg of SMN changes SNS by only up to half a kg. Reviews of field experiments and the Auto N project also indicate the surprising lack of influence of SMN levels below about 100 kg/ha on the economic optimum dose of nitrogen for feed wheat.

All this is perhaps summed up by this statement in the report: ‘However, the large and somewhat unexplained variation in measured N requirements means that any prediction system will inevitably produce errors and improvement over the standard recommendation system (or even a standard figure of, say, 200 kg N/ha) is likely to be relatively modest’. I think that the 200 kg N/ha quoted was in the context that a kg of nitrogen was five times more expensive that a kg of wheat.

I suppose that the only comfort is that errors of up to 50 kg N/ha either side of the optimum dose has a relatively small effect on the margin over nitrogen costs. Please remember that the doses of nitrogen quoted in this report are relevant to feed wheats rather than milling wheats.

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