EVALUATION OF ORGANIC LANDSCAPE MULCHES: COMPOSITION AND NUTRIENT RELEASE CHARACTERISTICS

Abstract

Summary A 12 month field experiment was undertaken on a sandy loam soil to investigate nutrient content and nutrient release characteristics of six organic landscape mulches; cocoa shells, coarse conifer bark chips, wood chips, garden compost, horse manure and finely ground conifer bark. Comparisons were made against black polythene mulch and a bare earth control. Mulch treatments were applied to bare soil plots, left for 12 months and then cleared before sowing a crop of agricultural mustard (Sinapis alba L.). Soil analysis was carried out at the start and end of the experiment, fresh and dry masses of the aerial portion of the mustard crop were determined and their nutrient contents assessed. Initial mulch pH was not a good indicator of how that mulch would affect the underlying soil pH over time. After 12 months the organic mulches had either no significant effect on soil pH or increased it slightly relative to unamended soil. In contrast, initial nutrient content of the organic mulches proved to be a useful indicator of their impact on available nutrient levels in the soil and of their relative benefits to plant growth. Horse manure, garden compost and cocoa shell mulches, with low C:N ratios and high potassium content resulted in significant increases in soil nutrients and supported the highest yields. After twelve months, no evidence of nitrogen immobilisation or growth suppression under the wood or bark-based mulches was observed. None of the mulches had a significant effect on the underlying soil organic matter content during the experiment.