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Short-term effect of soil disturbance by mechanical weeding on plant available nutrients in an organic vs. conventional rotations experiment

Owen, J., S. Leblanc and S. A. E. Fillmore . 2006. Aspects of Applied Biology 79: 301-305

Abstract

The question whether soil disturbance from mechanical weeding in organic systems affects nutrient release from organic matter in compost-amended soil was examined in a long-term organic-versus-conventional rotational cropping system experiment over three years. The experimental design included continuous snap beans, and a fully phased snap beans/fall rye crop rotation sequence. Treatments were combinations of yearly applied fertiliser (synthetic fertiliser, 1 x compost, 3 x compost) and weed control (herbicide, mechanical weeding). The 1x compost rate was calculated to deliver the equivalent of 50 kg N ha-1: equal to the rate of N in the synthetic fertiliser treatments. Ion exchange membranes were buried for 24 hours following mechanical weeding in bean plots. Adsorbed ions were then eluted and quantified. Available ammonium-nitrogen was not affected by weeding treatment, but nitrate-nitrogen was consistently less in mechanically weeded plots than in plots treated with herbicide. Principal component analysis of NH4-N, NO3-N, P, K, Ca and Mg availabilities showed distinct groupings of treatments according to fertility treatment rather than weeding treatment. The effect of cropping sequence on available nutrients was pronounced (P ≤ 0.001) only in plots amended with synthetic fertilizers.

Key Words

Mechanical weeding, compost, organic matter, nitrate, ion exchange