STIMULATION OF BARLEY GROWTH AND NUTRIENT ABSORPTION BY HUMIC SUBSTANCES ORIGINATING FROM VARIOUS ORGANIC MATERIALS

We compared the effect of humic substances extracted from municipal wa stes (sewage sludge and a compost) and those extracted from more humif ied materials (leonardite, peat and a commercial humic acid) on plant growth and nutrient absorption during hydroponic cultivation. The resu lts showed that doses representing less than 10 mg C l(-1) favoured pl ant growth, while higher doses sometimes inhibited it. Humic substance s favoured the development of the aerial part rather than the root The effects of both groups of humic substances were similar both as regar ds plant growth and nutrient absorption. The absorption of macronutrie nts (nitrogen, phosphorus and potassium) was significantly affected by the addition of humic substances, but differed for each nutrient. Nit rogen absorption, for example, was stimulated by the lowest doses, suc h stimulation decreased as the dose increased, while the opposite was true for The absorption of micronutrients was the lowest doses while d oses above 10 mg C l(-1) inhibited it, which was probably one of the c auses of the depressed growth observed with the highest doses. Copyrig ht (C) 1996 Elsevier Science Ltd.