Posted on 19/11/2015 by Jim Orson
Looking at the husbandry of those achieving extremely high winter wheat yields this year suggests that it was the weather, good crop management and possibly higher rates of applied N that were key. There are those who sell a programmed approach of trace element applications who are trying to claim that this was also a factor but I am very far from being convinced. Field yields of 16-17 t/ha were achieved without using any trace elements, except in some cases of manganese sulphate.
The requirement for above typical rates of nitrogen for extremely high yields is debatable because some farmers achieved these yields with their typical doses of nitrogen; around 200 kg N/ha for a first wheat on long term arable soils where no organic manures are being used. However, NIAB TAG have some trials’ evidence that there were cost effective responses from doses above 220 kg/ha when plot yields of feed wheat exceeded 14 t/ha. We are still deliberating on how this information can be used in practice.
It is also a matter of debate as to why this year was so special for achieving such high wheat yields. We did have around more than 10% extra radiation than average during the growing season but this cannot be the sole explanation because it is certainly not unique.
Air temperatures were bang on or close to average from March onwards and so the growth and development of wheat proceeded at its average rate. Higher than average radiation is often associated with warmer than average air temperatures which in turn result in a more hurried growth and development and so there is less time to trap all the extra radiation and convert it into yield. Hence, higher than average radiation combined with typical or below average air temperatures can only be beneficial for yield potential.
One reason why air temperatures may have been restrained this year was because the sea surface temperatures of the North Sea and the North Atlantic were significantly cooler than average. Temperatures of the surface of the North Atlantic go up and down in a multi-year cycle known as the North Atlantic Oscillation. This year we seem to have been towards or at the bottom of the current cycle. There are many learned papers that suggest that this cycle influences our air temperatures. The map below, which compares current sea surface temperatures to the average, clearly shows how cold the sea surface was around the UK this June.
Does all this explain the extremely high yields achieved by some growers? I personally do not think so. I discussed the subject with Eric Ober, a crop physiologist who works for NIAB. He gave me a few leads which I have followed up. As a result I have concluded that it was not only the above average radiation combined with average temperatures this year that were behind the extremely high yields but also that it was ‘the right kind of radiation’. I realise that this sounds a bit quirky and so I need to explain myself.
I examined the daily hours of sunshine received in March-July on the on-line automatic weather station at the Cambridge Computer Laboratory and compared their pattern with the four years in the previous ten years when we received similar levels of sunshine hours during these same five months. 2015 was very different. There was less than half the totally sunless days in these months and the total sunshine hours were accumulated more on a little and often basis than in the other years. In addition, I remember that this spring and early summer we regularly had sunny mornings until around 11.00 BST and then light cloud for the rest of the day. Some academic research shows that little and often bursts of lower intensity solar radiation (i.e. with a greater proportion of diffuse radiation) are better for photosynthetic efficiency than receiving the same overall level of radiation in longer and more intensive bursts. Similarly, there are several studies that show that solar radiation is more efficiently used by wheat when it occurs in the morning or evening rather than at midday (1:00 BST) when it is at its most intense.
In conclusion, I think that the reasons for the extremely high yields of wheat in some parts of the country this year are:
• The crops came out of the winter in good condition and there was little over-winter water logging.
• The very high yielding areas had a good dollop of rain in May, perhaps at the expense of some solar radiation.
• Temperatures from March onwards were around average but solar radiation was well above average, particularly in April and June. The April weather helped to ‘set up’ the foundations for potentially high yielding crops and June is the key month for grain fill.
• The higher than average radiation was supplied on a ‘less intense and more often basis’, which is conducive to high photosynthetic efficiency.
It was not just wheat that achieved very good yields this year and so other crops may have responded to some or all of these factors. Perhaps ‘the right kind of solar radiation’ is not so quirky after all.
Posted on 16/11/2015 by Jim Orson
This is continuing the theme of my previous blog. It summarised some of the very sensible and practical approaches that can be taken to reduce pesticide movement to water in order to meet the very demanding targets set by the Drinking Water Directive (DWD).
Research in France over the last twenty years and practical experience in the UK show that pesticide choice and dose is not such a significant issue in meeting the DWD standards when the soil profile is relatively dry at the time of application and there is no significant rain for at least a week or so following application. The issue of pesticide choice and dose becomes critical when the soil profile is close to soil moisture capacity at application, particularly if it rains within a few days after application. In France there are guidelines on pesticide choice and dose where the soil is relatively dry and where it is approaching soil moisture capacity. These guidelines make interesting reading, particularly because they are derived from field experimentation rather than modelling.
It is also interesting to note that in field trials in France there has been more pesticide movement to water in some Integrated Pesticide Management approaches, when compared to more conventional treatments. The explanation is obvious. The conventional treatments were applied when the soil profile was reasonably dry but the IPM treatments involved delayed autumn drilling and pesticide applications were made to a wetter soil profile. Although less pesticide was applied in the IPM treatments they resulted in more pesticide movement to water. This goes back to the dilemma of what we are trying to achieve with IPM, namely a reduction in pesticide use or a reduction in pesticide impact. This example demonstrates that reducing pesticide use does not necessarily mean reducing impact and I hope that our researchers have the nouse to aim for a reduction in impact rather than use.
There are some situations in the UK where there can be a very real conflict between optimising pesticide performance and reducing pesticide movement to water. The clearest example was covered in the previous blog. Propyzamide is an essential element in black-grass control in autumn sown oilseed rape and it has to be applied to wet and cold soils to optimise control. Subsequent rain can mean huge (in terms of the DWD) spikes in propyzamide levels in the water courses feeding water works although such levels comply with the Environmental Quality Standards. Whilst buffer strips, particularly in high risk fields, will reduce surface run-off, the movement through the soil to field drains can alone cause spikes.
It is absolutely essential to reduce the size and number of these spikes which can result in the closure of water works until the content supplied to domestic users meets the DWD standard. It seems to me, and this is not an original thought, that a way out is to try to close off the intake of the water works during the few hours when the spike occurs in addition to the other stewardship guidelines issued by the pesticide and water companies and the Voluntary Initiative. This is more difficult than it seems. First of all the water company has to be able to shut off the intake i.e. be able to supply water from another source or have reservoir storage it can utilise whilst the intake is off. Unfortunately, these facilities are not available at all water treatment works. The water company then needs to know when and where the propyzamide is sprayed and then it has to calculate the travel time of the spike to the intake of the water works.
The latter is getting more possible with more understanding of pesticide movement to water but locating when and where propyzamide is applied remains a difficult issue for water companies. Perhaps help is at hand with so-called ‘crowd-sourcing’ software on mobile phones. NIAB TAG is pioneering such an approach in order to improve further the services to its farmer subscribers. It was first tried last April by asking farmers the stage of flowering of their oilseed rape in order to improve the prediction of sclerotinia risk. Each farmer’s response was automatically geo-referenced and within a few hours the map in this article was achieved. NIAB TAG is rolling out other uses for this approach and it is envisaged that the information provided can only result in more precise and timely advice.
Whilst I realise that NIAB TAG members have a common cause for taking part in crowd-sourcing approaches, I would suggest that farmers in the relevant catchments have every reason for working with water companies in a similar way in order to reduce the problem of spikes of pesticide content in the raw water entering water works.
IT can also help by providing improved field specific advice. The WaterAware app. from Adama is an encouraging start but its designers accept that improvements are needed. Nevertheless, it gives the platform for the farmer or adviser to assess the risk of pesticide movement to water on a field by field basis through geo-referenced information on soil type and weather. Such an approach will still need the expertise of the farmer or adviser in order to make final decisions but it should lead to an improvement in decision making.
Posted on 02/11/2015 by Jim Orson
It is now the time of year when there is concern about pesticides moving to water and exceeding the challenging limits specified in the Drinking Water Directive. The maximum level for an individual pesticide is 0.1 µg/l (0.1 parts per billion) when measured at the tap i.e. after processing at the water works. This is not based on risk to human health and the environment but the limit of detection when the Directive was first introduced. The industry has long argued against this limit but I suspect that it is here to stay.
The real concern at this time of year centres on the slug pellet metaldehyde and the oilseed rape herbicides carbetamide and propyzamide. Metaldehyde cannot be removed from water by the processes that are adopted in water treatment works. On the other hand, with these oilseed rape herbicides any small exceedances of the level specified in the Drinking Water Directive can be reduced by water treatment to meet the requirements. The real problem is the large spikes of concentrations in the water following rainfall shortly after application. An example is given in the graph below, in this case propyzamide. Without these herbicides it would be difficult or impossible to grow winter oilseed rape in the vast majority of situations and so a solution has to be found or the area of oilseed rape grown in the UK could be significantly reduced.
There is a huge effort being made by the pesticide manufacturers and The Voluntary Initiative to provide guidelines on how to reduce levels in raw potable water. This involves the use of buffer strips, identifying high risk fields, weather forecasting and specifying best practice etc. However, it is a difficult problem to overcome.
There can be conflict between getting good pesticide activity and reducing environmental impact: propyzamide offers a good example. The requirements for good activity are a moist and cool soil. This means that applications are made as soon as the conditions are suitable, often in early to mid-November. Not only are soils already moist at application but the fact that everyone tends to spray in a small window means that large peaks in the content of propyzamide can occur in raw potable water. Such peaks have resulted in water treatment works being closed down for a couple of weeks.
So, what is to be done? I recently attended the BCPC Brighton Congress and the session on the Water Framework Directive (that includes the Drinking Water Directive) provided some direction. There was a brilliant talk by the lead catchment scientist of a very large UK water company. This included targets for their catchment management initiatives. It is the first time I have heard a water company declare their targets and such statements are a real help to those working to reduce pesticide movement to water.
One target is that the maximum levels of metaldehyde in raw potable water should not exceed the 0.1 µg/l limit. It is a sensible target because this pesticide cannot be removed at the water works. The second target is to reduce peak pesticide peaks in water by half. In my opinion this is a realistic target and, if it is shared by other water companies, gives me hope that the industry can rise to the challenge without too much disruption.
All the current and future initiatives on the management of those herbicides which are likely to move to water should, if adopted, enable us to creep closer to reducing pesticide peaks by half. Notice that I said ‘if adopted’. The water companies are still supporting voluntary measures but these have to reap results. Unfortunately, this may mean that some farmers will have to compromise on cropping choice and management if they have high risk fields. However, there may be alternative ways of tackling the problem which could result in less disruption to farmers. I will investigate these in a later blog.
Posted on 16/10/2015 by Jim Orson
My blog in early July suggested that yields might be good except in those parts of the country where a very dry May/June could limit the yield potential on all but the most moisture retentive soils. This was along the right lines and yields have been exceptionally high in some areas but the dry conditions in May/June perhaps did not limit yields as much as I thought they would.
So I have revisited some of the weather data I reviewed for the July blog in order to try to explain the exceptionally high yields experienced by some growers. Unfortunately, I am still pursuing solar radiation data that is hard to come by and will continue with my quest. In the meantime I thought I would set out my preliminary thoughts in this blog.
The solar radiation data that I have, and which does not cover some of the extremely high yielding areas, suggest that it was well above average for the whole growing season. However, it was not exceptionally high during grain fill.
Overall, temperatures from January to July were very close to average for the arable areas of England. In the July blog I noted that the cool nights in June could be beneficial only because the crop would not respire overnight so much of the gains made during the day. These cooler than average overnight temperatures were a particular feature in North Yorkshire and Northumberland where some of the highest yields occurred. These areas also had good levels of rainfall in May/June.
What may also have been very significant in determining yields this year was the higher than average amounts of solar radiation in March, April and May. The amounts in April were exceptionally high. This may have resulted in higher than average levels of tiller growth and survival, grain sites/ear and stem reserves. Hence, it may be reasonable to suggest that the higher yield potential established in the spring was realised by much better than average, but not exceptional, conditions during grain fill. It is interesting to note that a recent AHDB (the old HGCA) Project Report 496 suggests that modern wheat varieties have higher levels of stem reserves than those introduced over a decade or two ago.
My July blog suggested that overall yields would be higher north of the Wash because of rainfall patterns and the fact that temperatures on the 1st July were not as exceptionally high as those which occurred further south. We will never know the impact, if any, of that very hot day on final yields.
So it seems that there was no one standout feature that resulted in the very high yields this year. On the other hand, the weather throughout the year favoured high yields. The crops wintered well, with little or no waterlogging, and experienced very favourable weather in the spring and summer, except in those areas which suffered from drought stress during May/June.
There will be another blog on this issue when I have more data on the structure of some of the very high yielding crops and on the weather, particularly solar radiation.
Posted on 02/10/2015 by Jim Orson
We got up at 2:30 a.m. the other day to view the eclipse of the super moon. The fact that we had a good view of the event meant that the sky was clear. The weather was set fair and so I knew that cereal drilling would soon be going ahead at a frantic pace.
Do not take this wrongly but I was hoping for another few days of delay in drilling winter wheat. Wet weather delayed drilling until about 10th October in 2009 and ensured high levels of black-grass emergence prior to that date. This was also the first autumn of the wider adoption of stacking of the pre-emergence herbicides. The resulting black-grass control was generally more than satisfactory. The level of control was attributed by many to the stacking of the pre-emergence herbicides but the involuntary adoption of the cultural control measure of delayed drilling also played a significant role.
After a wet spell there is always the temptation to get on the land and drill before it is really suitable. The most extreme case was in the autumn of 2000 when it seemed to rain almost every day. Surveys of NIAB TAG members clearly showed that those who puddled-in wheat that autumn had inferior yields to those who waited for the better soil conditions in the first couple of months of 2001.
What has always amazed me is the rate of reduction in soil moisture below a depth of 30cm. One day the spade would tell me it was too wet to cultivate but the next day it seemed dry enough to cultivate. Salle Farms in Norfolk, which keeps meticulous records, have shown that for a few days yields increase with every day’s delay in drilling after a sodden soil starts to dry.
Now, there is data to demonstrate the impact of leaving the soil just another day (see the diagram) or preferably two days before wheeled or tracked vehicles run over it. This data was collected by the University of East Anglia as part of their government funded research project, the Demonstration Test Catchment study of the River Wensum in Norfolk. It shows the rapid drying of the medium textured soil at 30-50 cm depth between 5th February and 6th or 7th February 2013 despite little change in the moisture status of the shallower layers. As farm equipment has got heavier over the years this information takes on added significance in trying to avoid compaction in the deeper layers of the soil.
The take home message is quite obvious, do not rush back onto the land as it starts to dry after it was sodden. A day or two’s delay may be handsomely rewarded in terms of crop yield. Regular use of a spade will only confirm the message and improve decision making. So keep digging.