17 August 2001


WHEAT sown at lower seed rates using a precision drill has produced more tillers and bigger ears in independent trials, with the best yields expected from crops drilled at rates as low as 60 or 80 seeds/sq m.

The trials are also measuring the yield effects of reduced seed rates for precision-sown oilseed rape, which are also expected to show yield benefits when fewer seeds are sown, particularly with hybrid varieties.

The low seed rate wheat was drilled last year in plots in Wilts and Yorks using a prototype version of a precision drill from Stanhay Webb. A conventional drill was also used in the trials to show how yields compare when lower seed rates are combined with more random depth and down-the-row spacing.

David Langton, trials manager for Crop Technology, the research company behind the seed rate plots, says there is growing interest in the possibility of reducing the amount of seed sown for a number of crops, including cereals. He thinks the development of a drill that places seed with a high level of accuracy could be an important step towards using reduced seed rates commercially.

Yield effect

"We have had a long-term interest in the effect of seed rates on yield, particularly when linked to early drilling," he says. "I was pleased when we were able to borrow one of the new drills for our trial plots. There is some evidence that seed rates used commercially are too high and do not produce the most efficient canopies.

"We know plants grow more vigorously if they are less crowded and have more space to develop. In theory it should be possible to reduce the seed rate and improve the yield.

"However, you must have reasonably accurate seed spacing and depth to gain the full benefit of the compensatory growth. The spacing is not sufficiently accurate with a conventional drill and so far that has been the limiting factor."

Crop Technology, the research and development arm of the Masstock agricultural consultancy group, used two wheat varieties in the plots, which were drilled in early September. One was a hybrid and the other Claire.

Mr Langton says the Hyno Esta hybrid was included because hybrid seed is more expensive and this increases the financial benefits of a lower seed rate, and hybrid wheats respond well to a reduced plant population.

Lowest rate included in the wheat trials was 20 seeds/sq m, but Mr Langton believes tiller numbers and ear sizes suggest the best yields are likely to be from the 60 or 80 seeds/sq m plots. This compares with typical commercial rates of 120 to 150 seeds/sq m for early September drilling dates.

Visual differences between low and standard rate plots in early July included a tiller count averaging eight for the precision-drilled wheats sown at 60 seeds/sq m and about half that for a typical commercial seed rate. Stems were much thicker at the lower rates, and ears were significantly longer with more spikelets.

Mr Langton says stem thickness is important because of the extra weight of grain to be carried. Standing ability is said to be one of the benefits of low seed rates with precision spacing, but all the trial plots are standing well this year.

Low disease

This season has also brought a generally low incidence of disease problems in wheat, making it impossible to confirm claims that cutting the plant population could result in lower disease levels, but Mr Langton thinks this is likely.

"Having a much smaller population of evenly spaced plants will reduce the risk of root contact and, therefore, the incidence of take-all," he says. "I would also expect to see much more vigorous root development with increased access to nutrients, which should give better drought tolerance.

"Another benefit is a more even canopy to intercept light at an increased efficiency, and I think this could be an important factor."

Sowing wheat at 60 to 80 seeds/sq m will achieve worthwhile savings in seed costs. Mr Langton estimates the cost/ha for Claire in an early drilling situation at about £7.50/ha compared with £13 for a commercial rate, and figures for the hybrid wheat would be £36/ha against £62. Disadvantages of switching to a precision drill for low sowing rates are likely to include a slower work rate. The limitation is the working speed of the metering mechanism, while Mr Langton thinks forward speed is likely to be 20% slower than normal.

He also has some doubts about the Stanhay drills ability to work in the trashy seed-bed conditions of a minimum tillage situation. The precision seeder may also be less tolerant of poor quality seed with varying sizes and too much chaff could block the discs and cause uneven spacing.

"Sowing at a much lower rate means each seed has to work harder and make a bigger contribution to the crop. That may mean taking a little more care over seed-bed preparation and it would certainly mean keeping slugs under control in the early stages of crop development," he says.

"Weed control will also need more care, particularly in the early stages when there are fewer crop plants to offer competition. But after that I think a low seed rate wheat crop is likely to be less demanding because I would expect less disease pressure and a reduced risk of lodging."

The idea of precision drilling for cereals is likely to attract some farmers, and it may also interest contractors who could drill the winter oilseed rape and early wheat before the harvest has ended, with the extra cost of the drilling being offset by the reduction in seed cost. The contractor could also use the drill for precision planting other crops such as sugar beet, maize and vining peas. &#42