OPICO Variocast seeder which places seed behind a 2.5 metre OPICO 5 leg Vari-Tilth sub soiler and Vari-Disc combination.

Using an integrated system of cultural, biological and chemical methods, Wyevale Trees managing director Chris Mason has been able to improve soil productivity across 500 acres (200ha) of silty and sandy clay loam to enable the production of 250,000 ornamental trees in combination with an arable rotation.

Healthy, well structured soils are vital to his cropping plans at Stretton Court Farm near Hereford, where approximately one third of the land is in tree production to supply amenity landscape and wholesale customers of Wyevale Trees.

Since taking on a 25 year lease in1988, Mr Mason has concentrated on continually improving soil quality to make tree production commercially viable and to improve combinable yields.

"I need soils that resist erosion and nutrient loss, drain well and warm up quickly in the spring and can soak up heavy rains with little runoff. Because we don't have the facility to irrigate, soil must be able to store moisture through drought periods," he says.

Over the past 20 years, soil organic matter has increased to above 3%. The backbone elements to boosting soil organic matter are 'green manure' catch crops and a multipurpose cultivator and seeder to produce a healthy tilth. He says green cropping is comparable to applying farm yard manure at about 10 t/acre on his soil types, while roots penetrate down beyond a metre depth to further open up the soil profile and help drainage.

Catch crops of mustard are planted at 5kg/acre (12.5kg/ha) soon after the last trees are cleared in April and between a cereal and tree crop using an OPICO Variocast seeder which places seed behind a 2.5 metre OPICO 5 leg Vari-Tilth sub soiler and Vari-Disc combination.

The cultivation combination is also used at different times during the year to prepare fields for tree planting and to sow the range of arable crops including sugar beet grown at Stretton Court.

"Ground is prepared for mustard using an initial pass with subsoiler tines working to a depth of 250mm while the discs are set shallower at about 150mm, which helps bury weeds and rectify soil compaction," says Mr Mason. "During a second pass we turn the seeder on to place seed to about 40mm depth just before a packer roller that provides seed to soil contact and firms up the soil surface. Once we pull out of the field we don't have to interfere with the crop again until it's incorporated."

The OPICO combination is used again after the mustard is chopped just after flowering. "Working to the same depth, we angle the discs differently to be able to chop and incorporate the cut mustard crop. This method of incorporation is much cheaper and quicker than ploughing."

Chris Mason says mustard crops can also thwart soil-borne diseases like V erticillium wilt, which is highly infectious to trees and can lead to c omplete branch die back. Research is also looking at how some crops can offer nematode control in soils growing sugar beet and potatoes.

"There is evidence that various mustard species have the added advantage of acting as soil fumigants. Trials have shown that once in the soil and in the presence of water the chopped plant cells break down producing isothiocyanate gas. This gas is reported to kill weed seeds and soil pathogens," explains Mr Mason.

Stretton Court has also grown more long term red clover mixes to help boost fertility by using clover's ability to fixate atmospheric nitrogen in addition to significantly boosting organic matter content over a 3 to 4 year period.

A three-year break between each tree crop also helps prevent soil disease build-up. Planted at up to 3,000 per acre, trees are harvested every three years, from November through to April. Prior to planting, the ground is sub soiled to 450mm.

"Just like cereals, trees grow best when soil indices are maintained at 2 for phosphate and potash. We take soil nutrition seriously and test before, during and after each tree crop. Our soils are potash hungry so we have to correct this at planting and during the growing season together with nitrogen."

Soil pH needs to be kept at 6 to 6.5. Tree production for a number of species is seriously affected if soils become too alkaline, he adds.

After trees are planted, the cultivator and seeder combination is used to establish 2.5 metre grass/clover pathways between the trees to help minimise damage to soil structure during the many field operations required over the three years when trees are growing.