If you write a blog there is a huge amount of fodder in a recent report of a desk study on the contributory causes of the current ‘yield plateau’ in wheat and oilseed rape. Funded by Defra and AHDB HGCA it was carried out by my colleagues at NIAB TAG with the Scottish Rural University College (SRUC, formerly SAC) and the Department of Land Economy at the University of Cambridge. You can find the report here on the HGCA website.
I suppose the first question is have yields plateaued? The answer is clearly yes for wheat but over the last couple of years the trend for oilseed rape has been upwards. However, even for rape, the improvements in yield delivered by varieties over the past couple of decades have not been reflected in an equivalent increase in field yields. The report tries to identify reasons for this.
Naturally, it is impossible to say with absolute confidence why average yields have not increased at the rate of improvement delivered by varieties. However the report thoroughly reviews the possibilities and has come up with some well argued conclusions. It also contains, for me, some ‘I didn’t realise that’ statements.
One intriguing fact is that the rapid rise in average wheat yields in the late 1970s and early 1980s was accompanied by a rapid fall in the proportion of the crop grown as second or subsequent wheats. This would only have increased the rate of rise in average yields.
Another issue is that 20% of soil samples tested are below the target P index for arable cropping and 30% are below the target K index. Whilst there is no evidence that this has contributed to yield stagnation, it is a remarkably worrying statistic in these days of knowledge-driven agriculture. Perhaps of equal concern is that only 60% of OSR crops receive inorganic sulphur fertiliser. The report acknowledges that some OSR crops may be getting sulphur from organic manures but there must be a fair proportion of crops not receiving any sulphur at all.
What really intrigues me is that the yield gap between the top yielding farmers and the bottom yielding farmers is getting greater. Now that could mean that timeliness is not perhaps as good as it should be on some farms. If less than desirable timeliness is due to low labour and machinery availability then that may have been an acceptable risk when prices were very low but not now.
In fact, with the growing background of pesticide resistance and losses in pesticides due to legislation, the benefits of improved timeliness are likely to get even greater. Everything has just got to be closer to the optimal conditions to achieve effective crop protection in the future.
Naturally, I have to jump back to a pet theme in any discussion on stagnating yields. In the 1970s and 1980s, we exploited new technologies of plant breeding and crop protection to achieve the rapid rise in yields. These improvements in crop protection have ground to a halt and all we can try to do is to prevent a step backwards as a result of pesticide resistance and pesticide withdrawals. What is really wanted now is better technology. This will primarily be delivered through plant breeding and, I have to say it, perhaps genetic modification.
In the 1960s the United Nations Food and Agricultural Organisation (FAO) produced a report entitled ‘Six billion mouths to feed’. It expressed fears that the then world population of three billion would be six billion by the year 2000 and it wasn’t clear how they could all be fed. This created a supportive political background for new agricultural technology, including pesticides.
As a result there was no concern about world food supplies by the 1990s. It was only when the fear of potential world hunger had receded that those who opposed the means of increasing food production gained political traction. We now face the next challenge of an additional three billion mouths to feed with those same groups still holding a grip on political thought in some EU countries, but not perhaps in the UK. This may reflect the fact that UK consumers are now beginning to realise that the scare stories promulgated about GM are simply not true, but the EU is losing valuable time.
We will never be sure of the potential of GM until we start on a road where the first simple discoveries, such as herbicide resistance, are allowed to be used to help companies finance more advanced and hopefully higher yielding crops. Like all new technologies, there has to be a first step.