Managing the canopy - A path to higher yields

THE new thinking, that will be outlined in these articles over the next few months, has become known loosely as "canopy management", but, it entails management of: plants, shoots, roots, stems, leaves and heads, as well as canopies.

Canopies are measured in GAI (Green Leaf Area Index). A GAI of 3 means, that if the plants growing on one meter square of soil were flattened out on paper, the green area of leaves and stems that can intercept light would measure three meters square. Conventional crops have, in the past, had canopies of 7-9 at ear emergence. We know from experiments that, for top yields, wheat needs no more than 6. Optimum canopy size can be achieved by first managing the plant stand, through appropriate adjustment of seed rate, then by managing nitrogen to give the necessary number of shoots and finally ears.

Light is the driving force behind yield. Canopy size determines the crop's photosynthetic capacity, so managing canopy expansion and senescence is the key to maximising crop output. There is an optimum canopy size for growth. Managing canopy size is primarily achieved through seed rates and nitrogen use. Small canopies (3-5) waste light, large canopies (8-10) cost more to produce and maintain than is necessary to intercept all the available light. The aim is to produce each tonne of grain at the minimum cost to achieve increased profit.

Three years of trials have shown that this approach generally reduces costs, and slightly increases yields. Protein and Hagberg Falling Number have been similar, but Specific Weight tends to be higher than with conventional husbandry.

High yields are a consequence of cool and bright conditions, especially during the grain-filling period, leading to slow development and maximum growth, which results in higher yields.

Low yields are as a consequence of warm and dull conditions which promote development but restrict growth and so lead to poor grain yields. Cool and dull, or warm and bright conditions, both fit somewhere between these two extremes regarding their influence on yield. This year we have had warm dull conditions so it will be no surprise to me if yields are disappointing.

Sorry to be so cheerful just as harvest starts.

May, June and July are the most important months to have a full healthy leaf canopy intercepting radiation, as these are the brightest months in the UK,

Once crops are able to intercept 70pc of incoming radiation (canopy of GAI of 3), crops can accumulate 0.2 t/ha/day of dry matter. It is important to achieve this as early in May as possible.

Wheat crops should be managed to have a leaf canopy sufficient to intercept most of the sunlight during the final phases of development: ear emergence through to the end of grain fill. Large canopies are unnecessarily costly to produce and protect. They have had extra seed, need more PGRs and need more fungicide, an agricultural merchant's dream.

Plant establishment at drilling, and subsequent shoot management with N, should be a compromise. Aim for minimal over-production of shoots (so giving strong stem bases and minimising the risk of losing yield and quality through lodging). In crops with smaller canopies, the lower leaves ( leaf 2 and 3 ) contribute more to yield and therefore need better protection from disease than in thicker crops, however disease develops more slowly in these thinner crops.

As many as two-thirds of the shoots produced in a winter wheat crop may fail to survive to form ears and yield grain. At normal plant populations, varieties differ in tiller production and tiller survival, but at low plant densities all varieties show high tiller production and good survival.

Excessive production of tillers, which are subsequently lost, wastes water resources, since the dry matter contained in dead tillers is not effectively redistributed to surviving plant tissues.

To find out more and how you can start to reap the benefits of this new technique join us next week for part two.