NIAB - National Institute of Agricultural Botany

Orson's Oracle

The promoted narrative

Posted on 17/03/2017 by Jim Orson

A farmer recently mentioned the term ‘the promoted narrative’ over a stimulating lunch. I rather like that because arable agriculture is full of promoted narratives.

A dictionary definition of a narrative is ‘a spoken or written account of connected events; a story’. I think the word ‘story’ summarises some of the statements that I have heard or read in recent weeks.

For instance there is the commonly made statement that an early spring application of chlormequat or another plant growth regulator will stimulate tillering in late sown winter wheat. This is a story. True enough, chlormequat will increase the number of fertile tillers or heads of wheat at harvest. However, it does this by decreasing the tiller loss that occurs from about the first to second node stage rather than by increasing the number of tillers before those growth stages. Hence, application just before the first node stage is perfect for reducing tiller loss. It cannot possibly increase the number of potential tillers when applied in the early spring because only one tiller can emerge from a leaf axil and production of new leaves is a function of thermal time (day degrees) and this process is not modified by plant regulator application.

In terms of yield, the application of chlormequat just before the first node stage of winter wheat can be a good thing in years with a dry spring and a good grain fill. 2011 is a case in point. The wheat crops, untreated by chlormequat, shed too many tillers in May because of the drought. However, the rain in early June and good levels of solar radiation during grain fill meant that there was sufficient photosynthetic activity to feed the extra heads and/or grain sites in the chlormequat treated crops. In the absence of lodging, crop responses of up to 1t/ha were recorded in trials. Sadly the opposite was true in the following year. The dire wet and dull summer of 2012 meant that there was a low natural loss of tillers in May and there was insufficient photosynthesis to fill the grain sites of the untreated crops. Therefore the additional heads and/or grain sites that occurred as a result of chlormequat application were an additional burden. In the absence of lodging, losses from chlormequat application in that year approached the gains measured in 2011.

The early spring application of chlormequat and other plant growth regulators is also said to increase the rooting of late sown wheats. It may do, but independent trials have shown that any yield increase in late sown wheat from this timing is less than that from an application just before the first node stage. Come to think of it, has anyone found that late sown wheats are short of roots in the early spring? Wheat root production increases at an exponential rate during stem extension and so logically, an application of chlormequat just before this stage would be more appropriate. However, I think that any impact on roots from growth regulators is by the bye. I realise that this is a battleground between competing plant growth regulator products but it has never been identified in the field that plant growth regulators can increase nutrient and water capture from the soil.

Another promoted narrative regarding the spring management of late sown wheats is that they need more early nitrogen. They certainly need early nitrogen but they do not need more than a typical conventional crop. This is because the plants are small and while the root system is adequate it is not as developed as a typical conventional crop at this time and so, if anything, applying less nitrogen than for conventional crops is a wiser option.

I could go on about other promoted narratives. Okay…. one more; micronutrients. The story and the products keep changing. I wonder why. A few years ago the promoted narrative was that a single application of a mixture of micronutrients was necessary for all wheat crops, even those not showing symptoms. That was eventually blown out of the water by the superb AHDB project report on micronutrients for wheat. So the selling angle has now changed to a series of applications being required and/or that high yielding crops will only be achieved with their help. Do not fall for it. High yields are a result of healthy soils, good weather and good management. The latter includes using micronutrients only to treat visual deficiency symptoms or persistently occurring deficiencies that will cause symptoms later in the crop’s life. I was surprised by one aspect of the AHDB project: wheat showing a micronutrient deficiency symptom always responded visually to the relevant applied spray but yields were not always increased. This means that the approach I suggest is precautionary.

There are plenty of other promoted narratives; a common one is that organic agriculture is good for the environment. Yet another report has recently been published, this time from Canada, which concludes that this is not true when organic and conventional production is compared on a per tonne basis. Promoted narratives particularly abound for difficult to understand issues such as trying to define the dose of nitrogen required by a specific crop or the impact of weather conditions on yields. Simple values hide the huge variations that occur in real life. I could go on …… but I’ll leave it there!

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