A late winner?

18 Jun 2012

The England match against Sweden at the weekend was a cliff-hanger. When Sweden scored their second goal I was moved to walk round the garden. Luckily I was back in front of the screen when England scored their second and third goals.England v Sweden

In many ways the match was a metaphor for wheat growing this year. We had a good establishment and thought we were leading, and then nature struck back. We’ve had pressure from grass-weeds, BYDV and septoria and also face further attacks from fusarium and potential lodging. What a year; at least there’s been no shortage of moisture this spring and early summer! So are we behind or drawing at the moment? More importantly, will we score a late goal to draw or even win?

To score a late goal we need a great grain filling period. This starts at flowering and ends at about 35% moisture content of the grain and during this period it needs to be cool and sunny.

It needs to be cool to extend the grain filling period over as many days a possible. The crop needs, according to varying sources, between 660 to 710 day degrees for grain filling. Day degrees are calculated by dividing the sum of the daily maximum and minimum temperature by two. So if the day’s maximum was 20C and the minimum was 10C, then that day there would have been 15 day degrees - the cooler the weather the longer the grain-fill.

It needs to be sunny to provide the solar radiation to fuel the process of photosynthesis in order to produce carbohydrate i.e. yield. It also helps if the nights are cool to minimise the crop respiring some of the gains made during the day. Crop physiologists’ views vary about how cool; some say below around 9C and others below around 12C. The common features of the good yield years of 1984 and 2008 were sunny cool days and cool nights. We would have had a huge national average yield in 2008 but for the wet harvest that badly delayed combining.

NIAB TAG's Stuart Knight at Cereals EventMuch of the talk at the Cereals Event last week was about wheat yields levelling off. A group of French researchers maintain that in their country this is mainly due to the trend of warmer weather negating the potential gains from variety improvement. Warmer weather has resulted in a reduction in the period of growth from stem extension to ripening and, more specifically in some years, a shorter grain fill period. These conclusions only feed the fire of climate change. However, we’ve seen cooler and warmer weather trends for centuries and so it is important not to jump to conclusions.

There’s no danger that a good UK wheat crop can’t store all the product of a good grain fill. Our varieties in New Zealand can have yields far higher than here. As I said in an earlier blog, this is because we have around the same number of days for grain fill but in New Zealand they have, on average, around 30% more solar radiation during this period. We have a New Zealand farmer staying with us and he attributes his ‘disappointing’ 2012 yields to lack of radiation (and associated very heavy rainfall) during grain fill. ‘Disappointing’ is a relative term. In 2010 he had one field average over 16 t/ha. This would be the world record if he had been minded to adopt the processes necessary to claim it. Interestingly, the variety was Cassius, a UK variety that was not widely grown over here.

So we are in the final part of the match. We need luck to draw or win but we are also carrying some injuries. There’s a lot of black-grass, more septoria on the yield-forming leaves than we would like and there is a nagging doubt about what fusarium may do concerning our ability to push any advantage home. In addition, many crops look a bit ‘wobbly’.

On a personal note, there was one winner from me walking around the garden after Sweden’s second goal. I noticed some slug activity in the bedding plants and treated accordingly. This led to lots of dead slugs on the soil surface on Saturday morning.