NIAB - National Institute of Agricultural Botany

Orson's Oracle

A noisy summer

Posted on 02/09/2013 by Jim Orson

We live very close to the centre of Cambridge. Despite that, it’s a normally a quiet area but this summer has been different. The garden has been exceptionally noisy with bees buzzing and butterfly wings flapping.

The only thing missing is bird song. Despite the best efforts of the neighbourhood to feed them, small birds have all but disappeared and those that do appear skulk in the bushes hoping that they will not be seen by the local sparrow hawks. One bird that has completely disappeared from our garden is the magpie. We’ve had high numbers in the previous couple of years when I assume that they hoovered up the nests of small birds and so having exhausted the local territory they have now moved on. The only birds we now see and hear regularly are pigeons although a green woodpecker makes an occasional visit.

The increased number of bees and butterflies could perhaps have been predicted. I’d noticed that the cool and consequently ‘long’ spring resulted in a relatively constant high number of flowers in hedgerows and field edges.  

The relatively high numbers at any one time were possibly due to two factors. Firstly the flowering period of each plant lasted a bit longer in the cool conditions. And secondly the constancy of the supply of flowers may have been due to the fact that in a cool spring the flowering periods of different plants were more likely to overlap rather than occur closely together. This may be because the time of flowering of some species is more determined by day length and in other species by accumulated temperature.

So in a warm spring the flowering of some species may be brought forward to a time when other plant species whose development is more determined by day length are also flowering. I must admit that this is pure conjecture based on observation and that this year’s dry spring might also have contributed to higher numbers of some species.

To take this conjecture to a further stage, are the reported warmer springs, compared to previous decades, contributing to a decline in biodiversity? It is perhaps an issue that is worth investigating. Please do not take this as an answer for all the decline in biodiversity on arable land but it may be that it should be explored as a contributory factor.

There is a lot of debate in the national press about the decline of one ‘cuddly’ garden species. Whilst I realise that you really cannot cuddle a hedgehog, they are a very popular animal. The Sunday times devoted a whole page to their decline and the usual suspects were mentioned, land change and pesticides. What was not mentioned was the fact that their main predator is the badger, whose numbers are flourishing. Surely there is a connection here but badgers were not mentioned once. My allotment is in a semi-urban environment and yet when it is dry there are signs of badger activity, suggesting that they are a less shy species than I had presumed.

The Sunday Times article reflects much of the press output on other ‘cuddly’ species. Everything but natural predators are mentioned along with an anti-food production message. In the natural world there are inconvenient truths but pressure groups do not mention them possibly because they may upset other pressure groups and/or they may upset their subscribers. So they retreat into a rather surreal world where there is a common enemy on which they can all agree. Perhaps this is a core reason why some consumers have totally unrealistic fears about pesticides and pesticide use.

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Confused over blackgrass

Posted on 22/08/2013 by Jim Orson

A number of farmers have confessed to me that they are confused over the best approach to take to control black-grass. After reading many articles in the press over the past couple of weeks, I can see why. Conflicting views have been expressed and some are, in my opinion, plainly wrong.

Let’s take the simple issue of the impact of primary cultivation. What’s the impact on black-grass populations if the land is ploughed every year compared to the long- term adoption of shallow non-plough tillage, deeper non-plough tillage or direct drilling? 

The answer is clearly that the lowest populations occur with ploughing. However, ploughing is painfully slow, an awful lot more equipment is needed to maintain timeliness and there are other arguments against the plough from a weed control point of view. Ploughing can result in poorer seedbeds, with less black-grass germination and emergence prior to sowing, their roots establishing at greater depths compared to very shallow tillage or direct drilling and a reduced level of control with pre-emergence herbicides.Small blackgrass

Despite these negative features, every LONG-TERM experiment, both in northern Europe as well as in the UK, has demonstrated that, although this position must be weakened by the increased reliance on pre-emergence herbicides, the plough is best.

However, in the SHORT-TERM it may not be best. 

Typically, the plough can result in higher numbers of black-grass where seed shed has been low in the year of ploughing but high in the year before. Higher numbers of viable seed can then be brought to the surface when compared to non-plough tillage.

This is why there is always some experimental data around to show that an alternative approach may be better. It also shows that, in general, farmers should not slavishly follow one particular cultivation approach, because herbicide resistance results in us all having to be more tactical nowadays.

There has also been some remarkable advice in one or two recent press articles saying that the pre-emergence herbicides should be applied straight after drilling regardless of soil conditions. The advice is that even if it is bone-dry the herbicides should still be applied; the argument put forward is that they are true pre-emergence herbicides and the risk of a delay in application cannot be taken. 

There are lots of things to say about this.

Firstly, these herbicides enter the plant through the developing roots and/or shoots. If it is bone-dry the weeds will not germinate and so the herbicides will be degrading on the soil surface whilst not contributing at all to weed control. All pre-emergence herbicides apart from tri-allate are far more efficacious when applied to a moist soil surface and they also rely on soil moisture to be taken up by the plant. 

The dread scenario is that which occurred in the autumn of 2011 when the soil surface was dry but there was just sufficient moisture below the soil surface for some black-grass to germinate and emerge. This is the situation we should fear the most. If it is so dry that the black-grass will not germinate - do not apply pre-emergence residual herbicides including tri-allate.

Secondly, on the subject of whether or not pre-emergence herbicides should be applied as soon as possible - peri-emergence application is just as effective as pre-emergence. In fact, one of the more widely used herbicides is consistently more effective when applied peri-emergence. Seedbeds are more likely to be moist and settled peri-emergence. When they are dry pre-emergence, but moist peri-emergence, the advantage of peri-emergence application is very significant. Although saying this, I recognise that the peri-emergence window of application is vanishingly small, but please remember the principles. 

I have to say it … in order to avoid confusion over the various and often conflicting statements in the press, consider subscribing to an organisation such as NIAB TAG which retains both a scientific and practical perspective on technical issues. 

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Harvest progress

Posted on 15/08/2013 by Jim Orson

It is still too early to get a good overview of the yields of timely sown wheats.  Some reports say that the yields are ‘nothing special’ and others are saying that yields have been slightly above average.  So the jury is still out on my overall prediction that timely sown wheats will not yield above average.

As regular readers of this blog will know, this prediction was based on the fact that yield potential is influenced significantly by the amount of solar radiation intercepted by the crop and this year this has been about average.   Potential yields are, almost by definition, never achieved and I think that this year’s dry and hot conditions during grain fill will not see yields being any closer to the potential than usual.

What I may have overlooked is the impact of the long cool spring on wheat yields.  This seems to have benefited the yields of well established winter oilseed rape crops and may also have had a positive influence on wheat yields.  Indeed, warmer than average weather from the start of stem extension was cited as a negative factor for yield in an analysis of why French wheat yields are plateauing.

In fact the harvest so far indicates that it was a good spring but that crops were slowly running out of water. So whilst autumn sown crops that matured earlier have done relatively well, wheat which needs good supplies of water for longer into the summer may not have done as well, particularly on lighter soils and in areas that were particularly dry.  It is interesting to note that in north western Europe, wheat yields relative to oilseed rape yields are generally higher than in the drier parts of Europe, again reflecting wheat’s requirement for water later into the summer.

Another clue to wheat running short on moisture this year is the very good quality of the crop.  Hagberg falling numbers and proteins are good.   This reflects research done by the University of Reading and published in 2003.  In experiments when the crop was ‘droughted’ for a 14 day spell during grain fill, yield started to suffer once water supplies were below 70% of the potential held by the soil (available water capacity).  At the same time, Hagberg falling number values and protein levels increased.  Thousand grain weights particularly suffered from this period of water shortage and a separate experiment indicated that the earlier during grain fill that moisture became restricted and/or high temperatures occurred, then the greater the impact on grain weight.

What is not so easy to explain in these experiments is that this period of water shortage mid-grain fill also reduced specific weights, which are incidentally also reported to be good this year.  However, specific weights are notoriously difficult to predict.  It could be that this season’s cold winter and spring reduced the number of grains set leading to well-shaped grain despite the fact that the dry conditions reduced grain fill.

So the dry and perhaps hot conditions during the grain fill of wheat this year may have had a significant impact on both yield and quality of the wheat crop. I await with particular interest the yields of wheat in north eastern England.   Theoretically at least, yields are more promising in that area.  I will try to summarise my thoughts once the yield patterns across the country become clearer.  In the meantime, we are off to France for a nine day holiday.  Yes, I have to admit, it is tough being semi-retired.     

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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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