BIFGA Technical Day: The benefits of maintaining healthy soil

The beneficial effects of good soil structure can often be overlooked by growers, hears Brian Lovelidge.

A healthy soil is an essential prerequisite for successful fruit production in terms of fruit size, yield, quality and cropping consistency. Yet the value of such an important raw material and efforts to create it tend to be ignored by many growers.

East Sussex independent consultant Simon Van Der Slikke has made a special study of soil health, the numerous benefits for crops grown in it and how they can be achieved. Speaking at the British Independent Fruit Growers Association (BIFGA) technical day, he said that, amazingly, one teaspoonful of a healthy soil contains no fewer than 100 million bacteria, 2,000 protozoa, 50 nematodes and an equally mind-boggling amount of fungal mycelium.

"A perfect soil contains [approximately] 45 per cent mineral, 35 per cent water, 25 per cent air and five per cent humus, all evenly distributed," he explained. "Humus remains after plants and microbes have decomposed. It improves soil structure and permeability, is a food source for the soil ecosystem and can hold 10 times its weight of water. It also reduces fluctuations in pH and increases the soil's production potential."

As micro-organisms die they become part of the soil's humus content with the protozoa feeding on the bacteria and nematodes on the protozoa to produce a balanced system. The bacteria secrete growth hormones that are taken up by plants' roots and increase the plants' resistance to pathogens. The bacteria also produce polyphenols that trigger plants' resistance to fungal diseases.

Soil ecosystem

Van Der Slikke said mycorrhiza and Trichoderma are also important parts of soil's ecosystem. They live in symbiosis with plants and can extend their root systems tenfold, reaching areas well beyond the roots' reach. They also take up phosphates and moisture that otherwise would be unavailable to the plants.

"A lot of my growers apply compost or manure to existing orchards [to improve soil conditions and quality]," he added. "But that's expensive, so to make life easier it's best done before planting. The effects of the application can last the life of the orchard but you may have to top it up. If you have soil compaction it's very difficult to eliminate after orchard establishment."

If any confirmation of the value of compost was needed, it's being provided by the work done for the Waste & Resources Action Programme by Dr Joe Lopez-Read and Mike Green.

Lopez-Read, who carried out investigations into the material for 20 years at Wye College, said the country produces enormous amounts of green and kitchen waste, which is being converted into compost for growers.

"What we can do with compost is all about increasing crop yield," he claimed. "The waste has to be decontaminated, shredded and stacked [in windrows] so that it undergoes high-temperature treatment. It has to achieve PAS100 standard otherwise the Environment Agency will still regard it as waste."

Lopez-Read admitted that they didn't do controlled trials with the compost because it would have been too expensive. Instead, they carried out big half-field demonstrations. Since then the spreading machines have improved a lot, he notes. There are now about 10 on the market, mostly American and Italian.

"We were applying compost in one-metre-wide by 10cm-deep strips. In one case the untreated trees were under moisture stress by June or July and big fissures had formed in the soil but not where the compost had been applied.

"If I were planning an orchard I would recommend incorporating the first lot of compost [and then applying a mulch]," he advised. "In the spring we could pick out the trees that had been treated by their increased volume of bloom and later by the huge increase in fruit numbers and size. The mulch lasts much longer than a year so we recommend applying it every three years."

Lopez-Read continued: "There is a big move to produce in-vessel compost, which means that kitchen waste can be used. This process changes the nature of the material because it becomes catering waste and as such falls foul of foot and mouth disease regulations — it is complete nonsense but we're stuck with it."

Nitrogen levels

He pointed out that in-vessel compost contains much more nitrogen than green waste compost due to its catering waste content. One company has obtained planning permission for a composting plant capable of handling some 100,000 tonnes of green and kitchen waste a year.

When PAS100 compost is sold, its suppliers are obliged to provide "a whole lot of nutritional and other information" to the buyer including its proportion of woody material. This usually weighs 370kg/cu m but if the material is very fine the woody fraction can be 400-450kg/cu m," said Lopez-Read.

"We do want wood in the compost but it's being treated [by the authorities] like cattle slurry in terms of its release of nitrogen and this is absolute rubbish," he continued. "Most soil scientists will agree and it makes my blood pressure go up."

The importance of good soil structure and drainage was emphasised by Robert Fovargue, who advises numerous Somerset cider producers. Success in producing cider apples is really all about good management of the soil, he said.

"The trouble is that a lot of the sites in Somerset growing cider were not selected for good apple production and so there's a huge variation in their quality," he pointed out. "As a result, yields are also very variable - relatively few growers achieving 50 tonnes/ha, which is common in Hereford."

Fovargue stressed: "If you've not got good soil drainage you might as well give up at the outset. Many growers have just stuck their trees in the ground without any forethought about drainage, yet by late March they've got to be spraying, so if conditions are wrong you don't have a prayer."

He added: "Harvesting is even more of a challenge. The main period is October-November, by which time monsoon conditions may have set in. Then you can have a massive harvesting problem, particularly since the harvester weighs at least four tonnes."

Soil contamination

If there is laying water in an orchard, soil contamination of the harvested fruit can be a problem. The herbicide strip is made as narrow as possible — wide enough to reduce weed competition — to help minimise the problem and reduce fruit rotting, which can be significant if the apples are left on the ground for a week or more.

If an orchard is waterlogged, the reason must be found. That's best done with a spade so that the state of the soil structure and the presence of compaction can be determined.

Alternative to compaction

Fovargue said a New Zealand machine is available for eliminating soil compaction without causing tree root damage. It's the Guarzae, a trailed machine that injects pulses of very high-pressure air into the soil through a narrow steel tube. Its maximum operating depth is 700mm.

"It's a very good alternative to subsoiling," he declared. "A subsoiler can bring up clods and even with a roller behind, it can leave an uneven surface. The Guarzae has been of significant benefit to a number of my growers. It's best used when the soil is moist. In New Zealand the machine has been used for injecting mycorrhiza into the tree's root zone."

The irrigation of fruit and vegetable crops is yet another matter on which growers need to be right on their toes. There are many people who argue that we should grow a lot more of each in the UK, but we do not have enough water to do so, said Kent irrigation specialist Graham Field.

"Generally, reservoirs hold five million gallons [each] and it will be up to you to protect your own water," he advised. "Fifty percent grants are available and I urge you to apply [for one]. Lined reservoirs cost practically double non-lined ones."

Field said he knows one grower who has a drip irrigation system for which he has no licence. Up stream, however, there are two other growers with licences and they have the right to use them before him, "so make sure your water is your own and that you use it when you need it. Boreholes can be sunk for drip irrigation without a licence but the situation is changing rapidly," he warned.

"The Environment Agency is introducing new statutes and we've been told they will come into being this July and will look at everything. So if you do have a licence that you've not used to full capacity you may be restricted because all licences will be taken back and looked at under the new terms."

Licensing issues

It's possible that a grower without a licence might not be allowed to pump during the summer. The answer would be for him or her to build a reservoir and fill it in the winter for summer use.

Whether or not growers have their licences reissued will depend on where they farm, said Field. "If you are in a vulnerable area like Swanley [Kent], you might be restricted quite severely, and in many areas if you apply to sink a borehole you won't get a licence."

He pointed out that the Environment Agency is encouraging growers to co-operate in building reservoirs so that they can share licensed water. However, it will be necessary for those involved to use the water wisely and monitor its use

Based on talks given at the BIFGA's 22nd technical day held at Bewl Water near Tunbridge Wells in Kent on 13 January.

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