Evaluation of growing media containing farmyard manure compost, household waste compost or chicken manure for the propagation of lettuce (Lactuca sativa L.) transplants

Organic substrates, based on sphagnum peat and farmyard manure compost, household waste compost or chicken manure were tested for their suitability for plant propagation of lettuce. Net N mineralization in the substrates was followed, as well as uptake of plant nutrients and heavy metals in lettuce transplants. Net N mineralization from the compost-based substrates was not significantly secured and very low, about 1% of initial organic N content during the 28-day period from the time of sowing the lettuce to the end of the propagation period. In the two chicken manure substrates, net N mineralization was higher, 9 and 28%, respectively, during a period of 50 days, which included the 3 weeks from mixing of substrates until the start of the propagation period. However, it was not only the total amount of net N mineralized that differed considerably between the two chicken manure substrates but also the rate of nitrification. There was a strong negative correlation between pH in the substrates and Cd concentrations in transplants, resulting in unacceptably high Cd levels in transplants grown in substrates with very low pH. Of the tested organic substrates, the one with the lowest concentration of farmyard manure was the most suitable for plant propagation of lettuce.