INFLUENCE OF COMPOST MATURITY ON NUTRIENT STATUS OF SUNFLOWER

The influence of the degree of compost maturity on the nutritional status of sunflower (Helianthus annuus L.) plants was investigated by growing sunflower in 1:1 mixtures of soil and with three different kinds of composts. Samples were taken at regular intervals during the composting process. Substrate composted for more that 30 days did not show evidence of toxicity, but the nutritional status of plants was very poor-with iron (Fe), zinc (Zn), and boron (B) deficiencies. Progressive immobilization of nitrogen (N), in spite of the increasing nitrifying activity, and phosphorus (P) caused a reduction in yield, particularly for the compost derived from sugarcane bagasse and poultry manure plus olive press cake. The nutritional status did not improve when plants were grown in compost matured for more than 60 days. Correction of available macro- and micro-nutrient content is necessary before these substrates can be profitably utilized as soil amendants.