Archive Article: 1997/08/02

2 August 1997

The drought of 76 prompted one Norfolk grower to go in search of water. Spring subsoiling was, and is still, the answer. Edward Long investigates.

BETTER yields and improved crop reliability are the benefits of subsoiling for Norfolk sugar beet grower, Paul Childerhouse.

Theres no irrigation at Brick Kiln Farm, Weeting, near Brandon so subsoiling is one route to tapping into water reserves held in underlying chalk.

Since roots have been able to penetrate into the sponge-like rock the performance of sugar beet, on blow-away sand at DJ Childerhouse & Sons 188ha (470 acre) farm, has greatly improved.

Before subsoiling the average beet yield was no more than 30t/ha (12t/acre) of roots – and during the 1976 drought the wilted crop gave just 20t/ha (8t/acre).

"Now I average over 20t/acre," says Mr Childerhouse. "Some of the extra is due to better varieties, use of Temik (aldicarb) to control docking disorder and better seedbeds – but about half of it is due to subsoiling."

The severe drought 21 years ago triggered the search for water.

It was found when holes were dug down to 90cm (3ft). Although barley had dried out and was dead on the surface the underlying chalk was moist.

Mr Childerhouse realised he had stumbled upon the answer to his water needs – by subsoiling into the chalk, beet roots could reach water.

The top of the chalk under the farm varies in depth, in most places it is about 50cm (20 inches) down, but elsewhere it is either at the surface or beyond reach of farm equipment.

Initially subsoiling was done with a single leg subsoiler working at 150cm (5ft) centres behind the farms 80hp tractor in the autumn.

"This was our biggest tractor, yet it was not sufficiently powerful to cope with rock-hard chalk. The subsoiler could only penetrate to 14 inches and when the leg hit the white stuff, the tractor was pulled 90í to the line of work.

Tyres stripped

"It did little good, a lot of metal was eaten and tyres stripped. The job was nearly abandoned as an expensive waste of time. We borrowed a big crawler, but it was not strong enough to cope with sufficiently deep subsoiling to make the job worthwhile."

Then a lucky delay showed how it could work. Because of work pressure in the autumn of 1980 subsoiling was not possible. But after a few days of good weather in February Mr Childerhouse decided to return to subsoiling beet land.

It proved to be far easier and quicker; the chalk was softer and the tines worked deeper. There was also less wear and tear on the tractor.

"It seemed to be the best time. After autumn subsoiling we spread pig muck and a big fertiliser spreader ran on the land. It made sense to do the job in the spring.

"Unlike clay, a subsoiler does not shatter chalk, it just gouges out a groove which soon closes up to form an impenetrable barrier. So the later it is done the better."

The benefits were obvious in beet and the following spring barley with lines of green crop seen along the subsoiled track.

"When we harvested beet after the first year of spring subsoiling we were amazed. Roots, instead of being short and fangy, were long, and perfectly shaped with no sign of fanginess. We harvested a sugar adjusted root yield of over 20t/acre – easily the highest we have ever achieved."

The next job was to close up the spacings still further. Now a 2-legged model on a 100hp tractor runs so that one leg works in the wheeling from the previous pass to give a spacing of 60cm (24 inches).

As straight legs created a deadweight which needed a lot of power, a radical redesign of the subsoiler was undertaken five years ago.

"I chopped off the straight legs and after modifying the frame I replaced them with the curved and more pointed ones from a Dutch machine. These work better with a power requirement of about 50hp/tine when working to 2ft."

Now the beet land is left unworked until the spring.

Stubble from the previous cereal is sprayed with glyphosate in September. In January fertiliser is spread to give 50kg/ha (40 units/acre) of phosphate, 150kg (120 units) each of potash and sodium, and 30kg (24kg) of magnesium.

Good dressing

Shortly afterwards a good dressing of pig manure is applied. The subsoiler moves in during late February, about three weeks before drilling, and works at a depth of 50cm (20 inches).

This is done at right angles to the drill line to make the job easier. Then the land is ploughed to 30cm (12 inches) and pressed.

Subsoiling not only breaks the chalk but also smashes unstructured sand to provide better rooting conditions.

Subsoiling is done every three years in land earmarked for beet. The plough press helps reduce the risk of another serious threat to sugar beet profits – soil blowing. The sandy land is highly prone to blowing in a dry time and the crop is particularly vulnerable.

"We suffered more blows last spring than for 25 years. The sand-blasting effect cut off 40 acres of beet when plants had four leaves. Most of it was taken down to the ground and six acres had to be re-drilled, where the green heart remained the crop was left to recover.

"There are many ways to stop blowing, the cheapest is to plough late. This, and subsoiling with a curved leg in the spring, normally brings moist soil to form a cap on the surface.

"No subsequent cultivations are needed as the front press wheel on the drill is sufficient to create a seedbed for beet on this land. The rest of the soil retains the cap so its less vulnerable to wind. But this year was so dry, we had just 28mm of rain in February and only 18 in March so there was no moisture available to make the cap."

Spring subsoiling works well on the Norfolk farm allowing roots to exploit the chalk, which is always damp. During this seasons early drought Mr Childerhouse was pleased a way had been discovered to tap into it.

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