Wheat yield prediction for 2012

30 Jul 2012

A couple of weeks ago I summarised the weather conditions for the first half of wheat grain fill. There is a strong link between solar radiation received during this period and final yield. However, there are other factors at play, such as whether the crop has a sufficient ‘sink’ for the products of photosynthesis during grain fill, is there sufficient green leaf to absorb the radiation, and while the crop is not short of water whether the nights are so warm that the crop respires much of the gains of the day.

Hence, I am not so naïve as to believe that yield can be accurately predicted based on solar radiation intercepted by the crop during grain fill. For instance, we had great conditions for grain fill in 2011 but the wheat crops in the areas of the early summer drought had insufficient ‘sink’ (in this case lack of grain sites) to use all of the products of photosynthesis.

At first hand there appears to be no danger of lack of potential grain sites or an ‘overall’ sink in 2012. On the other hand fusarium in the ear may be affecting the final number of viable grain sites and high levels of septoria have resulted in less green area on the final three leaves.

On average there are about 660 day degrees (some studies have concluded a little longer) between flowering and maximum dry matter yield. This means that on average grain fill takes 42 days. I’ve assumed this year that this lasted from 10th June to 21st July inclusive for the following analysis. Whilst doing this, I recognise that this year has been cooler than average and so grain fill will take two or three days longer than usual.Ear of wheat

The data, kindly provided by Stephen Dorling of the University of East Anglia, comes from the two weather stations mentioned in my previous blog on the subject; Watnall in Nottinghamshire and Wattisham near the Suffolk Coast.

For those 42 days the radiation was about the same as in 2007, a relatively poor yielding year. We had sufficient rain in June and July in 2007 and so there was no great shortage of moisture during grain fill. However, we’ve had cooler nights in 2012 than in 2007 but crops were cleaner in 2007.

The big difference is that in 2007 we had a spring drought. There was no real significant rain in many areas for around six weeks from mid-late March. April was exceptionally warm and the crops were potentially on fire with brown rust. However, the crops did not suffer from the drought as much as they did last year.

So, where does that leave us? Some farmers are expecting tremendous yields this year. I’m not so sure; there are too many potential downsides. Hence, if I was to stick my neck out I would say that yields are not going to exceed the recent averages achieved. I hope that I’m wrong but if I’m correct - at least the prices are not too bad!