May 1, 2005
Organic NZ Magazine - May/June 2005.On the much lauded Heritage Farms, just out of Cambridge, manager Richard Prew has had a surprisingly large and successful crop of asparagus. It was enough to draw commercial grower Annie Wilson to check things out.
The Waikato is the main asparagus growing area in the North Island, chiefly because it has areas of flat, fertile, well drained sandy loam – soil suited to the needs of asparagus, which is a long-lived perennial and likes good fertilisation.
The diseases mostly commonly associated with asparagus are stem phylium, a fungus visible as the yellowing of the needles on the fern of the plant, and phytothphora, a soil borne fungus causing root rot. Both have debilitating effects on production levels on conventional farms.
For treatment there are two main fungicides used, at least three times during the growing period, with withholding periods. Evidence suggests that these conventional fungicides are starting to lose their efficacy.
Herbicide is another conventional asparagus grower’s tool and the entire field is usually sprayed prior to the crop’s emergence, and then during harvest as needed to keep weeds down so that the crop is easily visible to pickers. Some growers spray a thistle specific herbicide also. Add to that the cocktail of superphosphate and Nitrophoska fertiliser applications, and the delight of the first asparagus in early spring is dimmed somewhat.
Where conventional growers are reaping a harvest of between 2 to 5 tonnes per hectare, Heritage Farms, a property that is partially Bio-Gro certified, has achieved 8.5 tonnes per hectare, the highest yield in the district.
Richard is quick to point out that some of the other growers’ crops did suffer from wind damage this last season, where the emerging crop was damaged by the sand blasting effect of bare soil blown by wind. This didn’t happen at Heritage Farms because being managed organically, the crop had a sward cover between the rows, thus no sand blasting effect.
There are also no visible signs of the two fungal diseases, which Richard attributes to his diligent use of compost tea. The crop also receives fish and seaweed fertilisers but the main application is of compost tea, brewed on site.
Richard has a 2000 litre brewer in the shed, with a huge industrial pump forcing air through the barrel at a great rate. Into it he adds 6 to 10 kgs of compost and a number of fungus/bacteria foods – molasses, humic acid, seaweed powder, ground mussel shell; the recipe varies depending on whether fungally rich tea is needed, or a more bacterial brew (see ONZ issues March/April 04 and May/June 04, “Tea in the Garden”). Asparagus likes a bacteria dominated soil environment, so a bacterial tea is applied at Christmas after the picking has ceased, to really feed the crowns.
During the winter however, after the fern crop has been mowed over a couple of times with a mulching mower, Richard sprays a fungal tea, usually six times between May and June, which aids in the speedy breakdown of what he calls “the trash” – all the mowed fern, and loosened weeds.
The main weeding happens over winter using power harrows which go down 25mls, and a tine cultivator which is used 3 or 4 times. Both of these implements successfully uproot weeds without damaging the asparagus crowns, which are 50 to 75mls under ground level.
When I went to visit the farm at the end of January the ferns were already seven feet high, with another three feet to grow, as estimated by Richard
I’ve never seen anything like it. The conventional growers would have a fit at the sight. In between the ferns the weeds were three feet high and diverse – clover, vetch, dock, cat’s ear and hawksbeard to name a few. It was a very healthy sight.
The actual asparagus beds are thermally treated after picking, usually three times during the harvest period so that the weeds are knocked down enough for the crop to be visible for the next pick. The thermal weeder doesn’t actually kill the weeds, just kills off their tops. Richard has
a thermal weeder attachment for the back of the tractor. A large water tank is mounted on the front of the tractor and feeds water back to three chutes where elements heat the water to steam.There are three dwell chambers out past the chutes which help to maintain the heat of the steam over
the ground.
In between the asparagus beds are mown strips of sward, and Richard has had a mower made to just the right width to handle the strips. It is, it would seem, a recipe for success.
