Is British weather a basket case?

20 Dec 2011

We reviewed all our 2011 experimental results recently. One trial result particularly interested me - chlormequat increased wheat yield in the absence of lodging. This doesn’t typically occur, despite what many are led to believe. So why did it this year?

The yield increase was found at a trials location that witnessed a lengthy spring drought from late-February to late-May. It then rained in June and July and this, combined with low temperatures, provided very good conditions for grain fill.

This is the ideal scenario for chlormequat to increase yields. The growth regulator increases potential grain sites, usually by reducing tiller loss during the period of rapid growth. This year there was a very high loss of tillers in the drought conditions, often resulting in sub-optimal populations of heads. Hence, the additional extra grain sites, from the use of chlormequat, were able to exploit fully the excellent grain filling conditions.

Mind you, the opposite can occur.

Yield losses from chlormequat can happen following good growing conditions in the early spring followed by hot and dry weather before and during grain fill. So, the impact on yield from chlormequat use is a gamble on the weather.

This is true, to a greater or lesser extent, for most decisions on crop input management. If we knew future weather conditions then it would be a lot easier. But we don’t, which means compromises, in the guise of risk management, have to be made.

Everyone can quote examples where decisions are compromised by having to take into account the weather not doing what we would wish it to do. One good example is nitrogen application timing for wheat. If we knew that there was going to be a decent amount of rain at flag leaf emergence then we would apply most of the nitrogen just before that stage to optimise yield.

The unpredictability is not just restricted to input decisions. This year’s spring drought followed by rain in late-May reduced the relative yield of early winter wheat varieties in many cases. Obviously these varieties were less able to compensate for the spring drought than the varieties that were less advanced when the drought broke, which is just sod’s law!

Some crop physiologists say that a way to help combat the warmer and drier summers forecast is to have earlier flowering and ripening wheat. It goes to prove that no-one should put all their eggs in one basket when the basket is as fickle as our climate.

After saying all that, we have little to complain about regarding the variable impact of weather on yields and crop input decisions. In parts of Australia the yields between seasons can vary from nothing to around five or six tonnes per hectare. In some seasons much of this variation is explained by rain falling after the time most input decisions are made. This is risk management in the raw.

By the way, I accept that the main reason for the use of chlormequat in winter wheat is to help keep it standing. Another unpredictable risk.