BioCycle Magazine

Erosion control performance of compost prepared from harvested aquatic weed

A rainfall simulator was used to measure the ability of compost prepared from harvested aquatic weed (AWC) to reduce runoff and erosion from experimental plots compared with a bare earth control and commercially produced composted mulch and soil conditioners. A 1 in 10 year intensity rainfall event (67 mm hr-1) was applied to each plot for 30 min and runoff water was captured and water volume recorded. Treatment had no effect on the amount or rate of runoff. Water quality samples were collected and analysed for a number of parameters including the concentration of nutrients and total suspended solids (TSS). Load of exported nutrient and sediment (kg ha-1) was also calculated for total runoff. The application of AWC significantly (P<0.05) reduced the export of suspended solids from the plots, relative to the bare earth control by 34%. However, AWC was less effective in reducing nutrient and sediment export compared with the other compost treatments because it contained a smaller proportion (5.5%) of the larger (>15 mm) sized particles, which physically shield the soil surface and help trap entrained soil particles. Assessment of pasture growth and ground cover at 6 and 12 weeks after the rainfall simulations showed that AWC significantly (P<0.05) increased pasture dry matter production and ground cover relative to the bare earth control, which indicates it would be a good medium for pasture establishment, particularly in soils denuded of topsoil. Moreover, applying AWC at a depth of 20 mm supplied an equivalent of 699 and 95 kg TN and TP ha-1, respectively. Over time this should mineralise and provide some benefits with respect to soil fertility and plant nutrition.

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