The studies were designed to examine the influence of varying rates of ash-and-sewage and ash-and-peat blends on the yield of a grass mixture with birdsfoot trefoil and the levels of iron, cobalt, manganese, aluminium and silicon in the mixture. A pot experiment was conducted on mineral soil to which ash-and-sewage and ash-and-peat blends were added at a rate of 1-30% of the total weight of soil. The experimental design included also treatments comprising only individual components of the blends. The yields of plants depended on the treatment and study year, ranging from 9.61 to 135.38 g d.m. · pot-1. The highest yield was obtained in the third year, and the lowest in the first year of experiment. In treatments with ash, peat or their blends the yield was significantly lower than in the control treatment (mineral soil). Ash-and-sewage blends added to the soil significantly increased the yield, whereas ash-and-peat blends had a decreasing effect. The element contents of the grass mixture varied according to the treatment and study year, and were in the following ranges: 49.57-104.99 mg Fe; 0.04-0.58 mg Co; 20.67-713.87 mg Mn; 20.81-42.69 mg Al; 28.78-64.07 mg Si per kg d.m. The silicon content systematically increased, and the levels of iron, cobalt, manganese and aluminium decreased with the increasing proportion of ash-and-sludge and ash-and-peat blends.

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