ASH FROM CEREAL AND RAPE STRAW USED FOR HEAT-PRODUCTION - LIMING EFFECT AND CONTENTS OF PLANT NUTRIENTS AND HEAVY-METALS

The composition of 79 samples of straw ash from seven heating plants i n Sweden was analysed with the aim of evaluating straw ash as a fertil izer and liming agent. The variation in ash composition was explained mainly by ash fraction (bottom ash vs. fly ash) and straw type (wheat, barley, rye, rape) but also by heating plant. Compared with concentra tions of Zn, Pb and Cd in bottom ash, levels in fly ash were 10-90 tim es higher. Fly ash also contained more Cu and K compared with bottom a sh. The Cd/P ratio was 0.03 in bottom ash and 0.6 g Cd/kg P in fly ash . Ash from rape straw had a higher Ca content and liming effect compar ed with ash from cereal straw; e.g., the liming effect of rape ash was more than three times higher than that of wheat ash. The liming effec t varied between 3.5 and 44% CaO and depended mainly on the Ca content . The average P content was 1.7% (0.2-4.4%), with slightly higher conc entration in rape ash than in wheat ash. The potential for using straw ash as a fertilizer and liming agent is discussed. Compared with comm ercial fertilizers the use of bottom ash as a P fertilizer results in a lower addition of Cd. However, the total heavy metal content of stra w ash poses a potential problem.