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Weed management strategies impact on nutrient uptake and soil microbiology of organically managed small fruits

Hammermeister, A.. 2013.


The organic food market is one of the most active and rapidly growing sectors in North America. Within this growing market, a large portion of the organic producers are diversifying and expanding their operations through the addition of high-value crops such as small fruits and berries. Within the Maritimes, 52% of the organic producers are fruit and berry producers. During a 2008 survey conducted by the Organic Agriculture Centre of Canada (OACC) these producers listed effective and economical weed-management options as one of their top ten research needs. Ground cover management is more important in organic berry and fruit production than conventional agriculture. Unlike conventionally farmed orchards which rely on inorganic fertility inputs, plants in organic systems rely on soil fertility derived from organic sources which only become available to plants through an active soil biology. Therefore ground cover management must nurture this soil biology while minimizing competition from other vegetation. Typical ground cover management options for organic orchards include: periodic cultivation, mulching (synthetic or organic) or a continuous surface treatment such as an organic herbicide like acetic acid, flaming or mowing. The effect of eight ground cover management strategies (mowing, cultivation, cultivation acetic acid, black plastic, black fabric, white fabric, hay under plastic and straw) on plant growth and yield, nutrient availability (PRS™ probes and leaf nutrients), soil biology (earthworm population, insect abundance and diversity and microbial biomass) and weed-suppression under the small-fruit production of blackcurrants was investigated for two growing seasons. The trial was established in Brookside, NS in 2011, and planted with blackcurrant (cv. 'Resista'), and weed treatments were applied throughout the growing seasons of 2011 and 2012. PRS™ probes and growth measurements were taken throughout, as well as a harvest in 2012. Plants in the Mowing treatment experienced severe water and nutrient stress and this treatment is not recommended. However, the other treatments produced satisfactory weed control and bush growth. After two years of growth, cultivation produced the greatest bush growth, while White Fabric proved the best yield. Nutrient supply rate tended to be greater in the Hay Plastic treatment, but was not directly related to bush growth or yield. Cultivation had the greatest cost-effectiveness, but soil biology parameters were low. Soil moisture was greatest under Straw and White Fabric, and temperatures were lowest. Temperature was greatest under Black Plastic, with high fluctuations during hot summer days. While K supply rates were greatest under Straw, this did not influence bush growth, yield or berry size and sugars. Earthworm and beetle populations were also greatest in the Straw treatment, but beetle species diversity was low. Greatest beetle diversity was found in the Hay Plastic treatment. Hay is recommended for use with Black Plastic, as it increased the supply rate of essential nutrients, notably P, which appeared to have increased soil biology.