NIAB - National Institute of Agricultural Botany

Orson's Oracle

Wheat yields revisited

Posted on 08/08/2013 by Jim Orson

I was in the garden on Sunday morning when my mobile rang. The call was from a farmer on the coast of Essex saying that his wheat was yielding well above average and the quality was superb.

What obviously stimulated his call was last week’s blog suggesting that, overall, timely drilled wheat would not yield more than average; ‘overall’ does not mean in every case. In his case it could be that wheat on the east coastal strip did not experience the extreme temperatures in July as in central England.

So I’ve been checking that my prediction was not too ‘Cambridge-centric’. We did seem to miss some rainstorms and we may have experienced more days with very high temperatures in early and mid-July than others. There is now good information to check weather data over the UK on the Met. Office website.

These data show that much of the country was very dry through April to the end of June. The July maps are difficult to interpret as much of the rain fell after grain fill had been completed. However, there were exceptions and North East England (north of the Humber) had a good level of rain in May. The North East also did not have such extreme temperatures as much of central and southern England and so this area may have better than average yields from timely sown wheat. Time will tell.

I also have further information provided by UEA/Weatherquest.  It’s a solar radiation map of the UK which covers a period that approximates to grain fill. This confirms the information that has been appearing on the members’ section of the NIAB TAG website. Much of the country received about average levels of solar radiation during grain fill but there are exceptions with the South Wales coast, the coast of South West England and (wait for it) much of the cereal growing areas north of the Humber receiving above average levels.

They say that when you are in a hole you should stop digging. However, while I stick to what I said in last week’s blog, there might be areas of the country, particularly North East England (north of the Humber) which have better than average yields. Again, only time will tell.

Much of what I said last week was based on the possible impact of high temperatures and/or drought on the grain fill of wheat and I have been ploughing through the scientific literature on the subject. As you can imagine, it is enormously complex. There is general agreement that high temperatures and drought during grain fill can reduce yields but it is not clear what is too high a temperature. 

One detailed paper suggests that the earlier there is heat stress and/or drought stress during grain fill, the greater the impact on yield. In this paper, the heat stress treatment was 28 degrees C during the day and 20 degrees at night compared to 23 during the day and 15 at night. This year the hot weather occurred towards the end of grain fill but in many areas the crops were short of moisture throughout grain fill. This suggests that moisture stress may have a bigger impact on restricting yields than the high July temperatures. Again this suggests that the North East may have higher than average yields.

There are some other interesting pieces of information. One paper concludes that increased night time temperatures have a greater impact on wheat yields than an equivalent increase in day time temperatures. This is of particular interest as night time temperatures during grain fill have been increasing at the NIAB TAG site at Morley for a number of years.

Another paper suggests that when grain fill is restricted by heat, the transport to the developing grain of stem reserves accumulated before anthesis (when the anthers show) becomes more efficient. Varieties introduced over the last few years accumulate more stem reserves than those previously introduced, so this may partly mitigate the possible impact of drought and heat on grain yield this year. Nevertheless, at the moment I am sticking to my guns.   


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Wheat grain fill complete

Posted on 01/08/2013 by Jim Orson

NIAB TAG Network members have had access to a week by week review of potential yield gain during grain fill of winter wheat over the past few months. A brief summary indicated that it was less than average for the first half of grain fill and greater than average for the second half of grain fill. Overall, potential yield gain during grain fill has been about average but with one of the eight centres monitored (Holbeach) being 7-8% higher than average. 

The estimates are based on the observation that potential yield gain during grain fill is directly related to solar radiation intercepted over a period of around 680 day degrees from anthesis (when the anthers are visible). Day degrees in this context are simply the average daily temperature, so an average temperature of 17 degrees C translates into 17 day degrees.

It would be naïve to take these figures at face value. First, high day and night temperatures can restrict grain fill to less than the potential as can a shortage of soil moisture. In addition, some crops are patchy and will not intercept all the solar radiation; late sown crops in particular may not have sufficient grain sites to absorb all the photosynthate. In addition, these same crops may suffer more from dry soil conditions.

This season, over the eight monitored sites, the average potential yield gains during grain fill were close to their medium-term average of just over 10 t/ha. To get a guide to the potential total yield, stem reserves accumulated in the crop before anthesis have to be added. In modern varieties this is around 2 t/ha for typical crops. This suggests that, on average, timely sown wheat crops at these eight sites have a medium-term potential average yield in excess of 12 t/ha.

These average yields have unfortunately never been achieved in practice; this shows that there are always limitations that prevent such yields from accumulating. The question is whether this year we have had more limitations than usual. I consider that the answer to this is, unfortunately, “yes”. 

The very hot days and nights in July, coupled with very dry soils in many areas, must have taken a higher toll on potential yield gains than in an ‘average’ year. So overall, I’m predicting no better than average yields on timely sown wheat crops. The hot weather and moisture stress would have had an even higher negative impact on late sown crops. I hope that I am wrong and would be delighted to eat humble pie.

I’ve been thinking around the subject of the impact of solar radiation on potential yield gains during grain fill. As I said earlier, it depends on how much radiation can be packed into a grain fill duration of 680 day degrees, which is typically 6 weeks. So the size of potential yield gain is dependent on the average energy from the sun per day degree. As an example, at one site this year the potential yield gain during grain fill was on average 15.3 kg/ha/day degree.wheat harvest

However, there were good days and bad days. The 6th June was a great day with lots of solar radiation but relatively cool temperatures. The potential yield gain per day degree on that day was 32.7 kg/ha. This was unfortunately before grain fill started but if every day was like the 6th June, during grain fill the total potential yield gain would be 22.2 t/ha. In contrast, 23rd July was hot but cloudy and the potential yield gain on that day was a measly 6.5 kg/ha/day degree. Out of interest, the potential yield gains on those hot and sunny days in mid-July were between 15 and 20 kg/ha/day degree and on the cool and cloudy days in mid-June they were between 10-15 kg/ha/day degree. By using this information we can develop a ‘feel’ for good and bad days for grain fill, provided that we still remember it next June!

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Posted on 24/07/2013 by Jim Orson

The temperature outside is 32°C.  What a contrast to last year.  The climate scientists now say that we will have to get used to variations in the weather that are accentuated by the increased carbon dioxide concentrations in the atmosphere.   These extremes have a huge impact on those businesses that rely on the weather, be it ice cream manufacturers, seaside hotels or farming.  There is a double whammy for some branches of agriculture because both demand and supply are influenced by the weather.  For instance, demand for salads is higher this summer than last but the market for summer cabbage, cauliflowers and calabrese has collapsed.

There is much talk about what arable farmers should do in order to minimise the impact of such extreme weather events on their businesses.  The word ‘resilience’ is used frequently and there are at least three technical issues.

November 2012 floodsFirstly, the cropping system should not be too dependent on one specific and limited weather ‘window’.  There are lots of examples of this but perhaps one has been particularly obvious over the last few years.  It is now essential for many farmers to spray the pre- or early post-emergence winter wheat herbicides for the control of black-grass onto a moist seedbed.  When this does not happen, the levels of control can be very low.   This can be disastrous in terms of yield where there is the potential for a high number of black-grass plants to establish.  A more resilient system would not have the potential for high numbers of black-grass.  This is easier said than done but it is the concept behind the NIAB TAG “Low Seedbank Farming” philosophy.

Secondly, the level of equipment and labour available should be sufficient to exploit fully the appropriate weather windows when they do occur.  I realise that this has to be balanced against costs but the NIAB TAG co-ordinated and Defra/HGCA funded ‘yield plateau’ study contains data that show that those farmers achieving the highest yields and financial margins have higher than average labour and machinery costs per ha.

Finally, cultivations and soil management have to be tip-top.  This includes maintaining effective drainage systems, ensuring that water can move to the drains without major impediment, maximising the ability of the soil to store water and enabling roots of a well established crop to extract the maximum amount of soil moisture.  Everyone knows that this is a huge subject and it is increasingly the topic under discussion with farmers and their advisers.

One part of the soil management issue is water infiltration rate.   Low infiltration rates mean the reduced ability of the soil to ‘take in’ water, which can be critically important when trying to store in the soil the maximum amount of limited rainfall in a dry summer.  Low infiltration rates also result in a higher likelihood of surface ponding, run-off and erosion.

Increasing soil organic matter is a way of increasing infiltration rates.   However, increasing soil organic matter levels is not easy due to the limited amounts of organic materials (soil amendments) available.   I suspect that incorporating rather than removing straw or other crop residues will also increase infiltration rates due to the resulting increased levels of soil fungal biomass.  I have written before about soil fungal biomass being a part-surrogate for soil organic matter.  The problem is that increased levels of soil fungal biomass from the incorporation of a soil amendment are typically only short lived, lasting up to 18 months.   Hence, there needs to be annual incorporation of residues to maintain levels.   

For several years The Morley Agricultural Foundation has been funding a series of experiments investigating resilience of cropping systems.   It has to be commended on its foresight.  One experiment is investigating how long the positive impacts of applying different soil amendments persist.  A surprising result was that only paper crumble appreciably increased infiltration rates in the second cropping year after application.  Possibly, this suggests that the initial impact of a single application of a soil amendment on infiltration rate is in part due to increasing soil fungal biomass levels.   A proportion of the paper crumble maintained its integrity into the second year which may have continued to help to keep the soil ‘open’ as well as to continue to be a food source for the soil fungal biomass.   This is limited data but if it is repeated then we will have to start to re-think how best to use manures to increase the resilience of cropping systems.

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Apocalypse postponed

Posted on 17/07/2013 by Jim Orson

We will all be doomed if the latest GM trial goes ahead.

That’s what we’ve heard over the years from the eco-zealots. They’ve said on each occasion that ‘once the genie is out of the bottle there will be no going back’ and eco-meltdown is inevitable.

Well life seems to go on, despite these prophesies. No harm has resulted from the many GM trials held in the UK over the past couple of decades. Around 10% of the world’s crops are now GM and no adverse environmental or health issues have been recorded. This still doesn’t stop the now few from repeating the mantra of disaster whenever a trial in the UK is proposed.

I say the ‘now few’ because significantly less than 100 UK citizens turned up at last year’s ‘day of action’ to protest against the wheat trial at Rothamsted. They were supplemented by aroblackgrassund the same number from France. As far as I’m aware, no similar event has been planned for this year.

Protesters have increasingly adopted apocalyptic language over the last few years to make their case. For example, two or three years ago we had only 36 months to save the world from climate change. I assume that this type of language is deemed to be an effective way of catching our attention. It may not be rational or based on facts but it makes the headlines.

However, it’s now clear that the press has become very guarded about such statements. The sorry tale of sensationalising the false claims that the MMR vaccine is linked to autism lays heavily on the press’s conscience. This is why recent ‘scientific’ papers aimed at undermining glyphosate have not been reported. Rather than repeat these claims parrot fashion, the press now looks carefully at the provenance of these ‘scientific’ papers and takes advice from other scientists. Slowly but surely apocalyptic language is being replaced by rational debate.

I’m no stranger to such language having used it myself about black-grass over the past few years. It has become clear over this time that systems that are comprised only of early drilled winter wheat and winter oilseed-rape are indeed doomed. The inconvenient truth is that we cannot rely on herbicides alone and that some form of cultural control is required.

But again, life goes on. I recently visited the farm where we first identified high levels of herbicide resistance in black-grass in 1984. Despite this discovery, the farm still grows continuous wheat. Atlantis has come and gone and the struggle with the weed has become a white knuckle ride.

The cultural control measures that have NOT been adopted are ploughing (the soil is London Clay) or spring cropping. The cultural control measure that HAS been adopted is extremely late drilling. It is important that more than one flush of the weed is controlled with glyphosate before drilling is contemplated. There is still more black-grass than I would like to see but it isn’t out of control.

Luckily the farm is in the driest part of the country and in some recent years a significant area has been drilled ‘on the frost’. Naturally the drilling operation is fast and efficient and the operators are skilled and dedicated. Whilst the average low rainfall helps to facilitate late drilling it can also reduce the yield potential of late drilled crops. In addition, wet autumns can have a huge impact unless there is sufficient frost to enable winter drilling.

So whilst black-grass has wreaked a huge cost, mainly due to lost yield potential, the farm is not ‘doomed’. Similarly, those who have adopted a proportion of spring sown rather than winter sown cereals over the last few years have been pleasantly surprised by the returns they have received.

Each farm is different but there are a range of cultural control options that can be considered. Rather than just thinking ‘we’re doomed’, it’s important to recognise that the system may well be ‘doomed’ but the farm is not. For many, this is the time to sit down and work out the best strategy.

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Half term report

Posted on 09/07/2013 by Jim Orson

Around this time last year I wrote a blog suggesting that winter wheat yields could be ‘disappointing’.  This was based on the lack of solar radiation in the first half of grain fill. What I didn’t foresee was the devastating impact of waterlogging on yields in some parts of the country.

This year it’s likely that the end of the first week of July was about halfway through grain fill for the majority of winter wheat crops. Again solar radiation has generally been well below the average – the map shows the total accumulated surface solar radiation for the period 15th-30th June 2013, approximately the first two weeks of grain fill, expressed as a percentage of the 1983-2005 average for the same period. Once more this suggests that yields will possibly not be that great unless we have a strong second half.

Surface solar radiation 15-30 June 2013

The big difference this year is that we don’t have a surplus of water. In fact it’s very dry in many areas and that cannot be good for yields. Ideally we need more than average of both solar radiation and rainfall over the next two or three weeks.  Clearly, if we get one of these we are unlikely to get the other unless we have a series of thunderstorms at night.

There’s also a huge area of late sown winter wheat this year.  In general, these crops have come together extraordinary well through the prolonged cool spring and are not far off providing sufficient plant cover to maximise the interception of solar radiation. I’ve been thinking about the possible implication of lower than average solar radiation levels on these crops in particular.

The central issue of my debate with myself is whether less than average solar radiation levels are as important to these late sown crops as to those crops with a higher yield potential. Typically, later sown crops are more likely to have a lower ‘sink’ for the products of photosynthesis i.e. the amount of grain fill is limited by the number of grain sites. Therefore, it may be that the lack of solar radiation so far this year may not be as important because of this huge area of late sown crops and their associated lower yield potential.

However, I’m not going to fall into the trap of thinking that just one factor alone can determine yields. Late sown crops tend to be more vulnerable to drought and, as I mentioned earlier, some areas of the country are now particularly dry.      

The current unbroken sunshine can only be good for yields provided that the wheat has a reasonable supply of water. Excessive heat can lead to the ‘cooling system’ of the plant breaking down which can limit eventual grain size. This is particularly damaging at flowering but it’s never welcome. Very warm nights are also not welcome because the crop will have a higher respiration rate, using up more of the photosynthate that was accumulated during the day.

It’s no wonder that farmers are fixated by the weather. Every twist and turn can have an impact on the business but in the end only the harvested yields will determine how good a growing season we have had. At the moment I’m not bullish about yield prospects.

NIAB TAG Network members can log-in to their area of the Network website to see the daily solar radiation received at eight sites in England in June and July (kindly provided by UEA/Weatherquest). The data is updated on a weekly basis.

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