Oilseed rape producers are being encouraged to look to roots as much as tops to decide how to manage this season’s many backward crops.

Masstock’s West Yorkshire-based Chris Dale says many crops are coming out of winter with low plant counts and Green Area Indices.

Growers should be extra careful when assessing crop potential to avoid wasting inputs trying to achieve impossible performance, he warns.

“Our experience from low seed rate and late–sown SMART Farming demonstrations shows some will produce decent crops while others will never do so. It has far more to do with what is below the soil surface than what’s visible above.”

Current crops with fewer than 20 plants/sq m or GAIs under 0.4 can yield over 4t/ha, providing they have 5-6in of root. But those with only 1-2in are a different matter, he says.

“GAIs are only part of the jigsaw.I want to avoid farmers spending a lot of money on crops that will never deliver.You need to base spring management of backward crops as much on how well rooted they are as the leaf area they have.

“There’s a tendency to give backward crops an extra helping hand, but you need to ask whether each particular crop justifies it. After all, even the least costly input is expensive if it doesn’t improve performance.

“Well–rooted crops are likely to reward extra inputs to boost leaf area and protect against phoma and light leaf spot.”

Poorly rooted ones may be at greater risk, but the key question is whether they will repay the investment, he says.

“Little and often has to be the watchword with nitrogen on most crops this season – not least because this lets you see how the crop responds before giving it more.”

Nutriphite PGA and growth regulator fungicide Caramba (metconazole) have both shown root–stimulating value in Masstock trials, he notes.

Crops with GAIs of only 0.5 in March can still achieve the ideal canopy of 3.5 by flowering to reach the yield potential of a particular site, maintains ADAS’s John Spink.

Roots increase

“We’ve only seen responses to improved rooting when there is a dry summer and crops without adequate rooting at depth suffer drought.All the evidence is that the root system continues to increase until flowering.”

Caramba in March-April will improve rooting, Mr Spink acknowledges.

“On smaller crops, where canopy management is less important, I’d be inclined to reduce the rate. We’ve seen good rooting responses to half rate, which hasn’t knocked yield even on very small crops.

“Yield isn’t formed until flowering, so I wouldn’t write off small crops yet, and I’d concentrate early inputs, N and S particularly, on the most backward ones.”

Where viable populations, say 20 plants/sq m uniformly distributed, came through the winter. Leave them be, advises NIAB’s Simon Kightley. “They will respond to nitrogen in March.”

In Cambridge mid-September-sown trials (with pigeon grazing controlled), the plants are quite well developed with good root systems, he notes. On headlands, growth is much poorer, with very small, well–grazed plants. “But even these have well–developed roots,” he notes.

In Yorkshire, NIAB’s Peter Burgis says the plants from late autumn drilling (Arable 17 October) over-wintered successfully with good root development, though they remain small and backward.