Royal approval

5 Feb 2014

This is the 100th Orson’s Oracle and there is no better way to start it than by saying that for once I agree with one of Prince Charles’ pronouncements.  

Last week he said before an invited audience “With a barrage of sheer intimidation, we are told by powerful groups of deniers that the scientists must be wrong and we must abandon all our faith in so much overwhelming scientific evidence”.  He was talking about climate change but I am sure that those who support conventional farming and the regulated introduction of GM crops will fully support that sentiment on the grounds that good science, correctly interpreted, should always be listened to and respected.

However, it is important to point out that excellent ‘laboratory’ or ‘theoretical’ science may not always provide the answers and field testing is essential. That is why field testing of GMs is so important, but of course there are “powerful groups of deniers” who have used intimadatory measures to prevent these going ahead.

Field testing is essential because there are good examples where excellent and robust laboratory research and theories have not been delivered in the field. One example with which I became closely involved concerned spray application. Large spray droplets produced by conventional nozzles are not retained by a target plant and small ones will drift. Hence, it seems logical to produce a spray that is solely comprised of droplets that are neither too large nor too small. This is the basis of Controlled Droplet Application (CDA).

Tests with CDA in the laboratory were indeed very promising, with individual target plants having four times as much spray retained on their foliage when compared to a standard flat fan nozzle. So far, so good. However, in independently run field trials, CDA proved to be, at best, as good as conventional nozzles and often inferior. Naturally, there was a huge furore between those who were involved in the independent field trials and those who were selling CDA machines.

However, to the credit of some laboratory researchers, the reasons why the theory was not delivered in the field were identified. The droplets from CDA machines used in the trials fell relatively slowly downwards under the influence of gravity in an almost vertical trajectory. This meant that they were not good in penetrating a crop canopy. In addition, the pesticides were predominately deposited on the horizontal parts of the target plant. Research subsequently proved that pesticides are far more effective if they are deposited on the vertical surfaces of target plants.Spray patterns

There were two other reasons for the disappointing results from CDA application. Although it was proven in field trials that on average there could be more pesticides on the target, the variation between the amounts of deposit on individual plants was far larger than with conventional nozzles. Finally, CDA involved very low volumes and some pesticides were too concentrated for optimum uptake by the plant. I witnessed trials where some herbicides just ‘shot-holed’ the leaves of otherwise unaffected susceptible weeds.

The following development in spray application was electrostatic sprayers. These also failed to reach their theoretical advantages in the field because the charged pesticide spray stuck to the wrong part of the crop canopy and/or target plant for good activity. However, I wish to point out that I am not a spray application ‘denier’ and hand-held CDA machines are being used very successfully in many parts of the world. This is particularly so with pesticides whose the position on the plant has little impact on their efficacy and which can maintain their efficacy in very low volumes and also where there is no canopy to penetrate. You’ve guessed it; total weed control with glyphosate is a prime use with these machines.

One other theory which does not deliver in field trials is that the level of Soil Mineral Nitrogen (SMN) has a major influence on the optimum amount of bag nitrogen required by the crop. All the UK field trial databases show that this is not generally true for winter wheat, oilseed rape and sugar beet. I suspect that it is also generally not true for the other arable crops as well. In wheat, which has by far the largest field trials database, the optimum dose of bag nitrogen is only demonstrably reduced by levels of SMN in excess of the RB 209 N Index 3; i.e. in the minority of situations.

Fertiliser spreadingNitrogen is a major and polluting input and we urgently need to know why SMN typically has so little influence on the optimum amount of bag N required. I may have just come across a clue in a paper by some Belgian soil scientists. In their research, the more efficiently the bag nitrogen was used by wheat, the less the amount of N was taken up from the soil. So the wheat plots in this research were using SMN more as a back-up than a primary source of this nutrient. This may be one of the reasons why differences in low-moderate SMN levels have no influence on the optimum amount of bag N required by the crop. David Jones, the manager of Morley Farms, suggested an analogy for this suspected preferential uptake of bag N by wheat “why drive down the road to buy a sandwich when your fridge is full of them?”