Worms to the rescue of hard-packed soil

Press, 13 July 1984, Page 26

Worms to the rescue of hard-packed soil

Continuous onion cropping with a rotary hoe has destroyed earthworm populations in some areas of the Heretaunga Plains. M.A.F. staff at Hastings have identified one area where the soil structure has been badly damaged and the earthworm population wiped out. The 40ha property on the outskirts of Hastings was planted in kiwifruit four years ago but earthworms have not reinvaded the area and the soil structure is still poor. Grower estimates of production losses are about $lO,OOO per ha a year. M.A.F. staff hope to boost soil fertility by introducing three earthworm species to the area. Mr Geoff Crouchley, senior technical officer, Research Division, Hastings, said the land was being prepared for earthworm survival by adding organic matter — mushroom compost and fowl manure. Checks were being made to ensure there were no toxic materials that could kill earthworms.

Topsoil worms (allolobophora caliginosa) and compost worms would then be introduced by taking turfs from pastoral land and placing them at intervals along the rows of kiwifruit. “To begin with, we will probably put in 10 worms

every four or five metres,” said Mr Crouchley. An ideal population would, be about 10 to 20 earthworms per square metre, he said. A third species, allololbophora longa, presently being bred in captivity on east coast hill country in Hawke’s Bay, would be introduced later in the trial. “We hope to breed the allolobophora longa up in captivity and when we have sufficient numbers we will introduce them.” The deep burrowing worm was scarce and was only found in one area in Hawke's Bay and a few other places in New Zealand. It could burrow two feet deep and was the most effective species in improving soil structure and conditions. Mr Crouchley said a significant number of orchards on the plains had low earthworm populations. He attributed it to a combination of factors, one being that a lot of the orchard land had been used for intensive vegetable cropping before being planted in kiwifruit. The rotary hoe was the main implement used for preparing the vegetable crops’ seed beds. In some cases the soil 'structure had been so badly damaged that it prevented water penetrating the soil

even when the kiwiiruit crops were irrigated extensively. Introducing earthworms would overcome the problem. “Once the earthworms are in the ground they would have an immediate effect by allowing penetration of moisture and aeration of. soil for root development, but the full benefit would probably not occur for four or five years.” Mr Roy McCormick, a Hastings M.A.F. horticultural adviser, said the area involved was like “concrete.” The kiwifruit plants were finding it difficult to survive with a lack of holes in the soil preventing water drainage. “The soil is compacted and hard. Even the roots are finding it difficult to grow.” The mechanical action of hoes had cut up the earthworm population. He said 50 per cent of orchards in Hawke’s Bay could be affected by the problem as five to 10 years ago a lot of the land was used for intensive vegetable cropping — onions, peas, beans and sweetcorn. An added problem was that most of Hawke’s Bay’s soils were naturally low in organic matter and unable to withstand heavy cultivation.