PELLETIZED SEWAGE-SLUDGE AS A FERTILIZER FOR CONTAINERIZED PLANTS - PLANT-GROWTH AND NITROGEN LEACHING LOSSES

To evaluate the effectiveness of sewage sludge pellet fertilizers (SPF s) for growing containerized greenhouse crops and their potential for nitrogen (N) leaching, three experiments were conducted where SPFs wer e compared to conventional water-soluble fertilizer (WSF) and controll ed-release fertilizer (CRF). In different experiments 'First Lady' mar igold (Tagetes erecta L.) and 'Selenia' New Guinea Impatiens (Impatien s sp. hybrids) (NGI) were grown in 0.5-liter pots of soilless growth m edium and plants were fertilized with 20N- 4.3P-16.6K WSF, 14N-6.2P-11 .6K CPF, or two types of SPF, 3N-1.OP-0.1K or 5N-1.3P-0.1K. CRF and SP Fs were incorporated in the growth medium at planting. In each experim ent, treatments received the same amount of N and volume of irrigation water. Leachate was analyzed for ammonium-nitrogen (NH4-N) and nitrat e-nitrogen (NO3-N) at regular intervals and shoot dry weight was measu red at the end of each experiment. SPFs alone as the sole source of N resulted in less N leaching compared to WSF or CRF alone but did not p rovide adequate N for marigold as shoot dry weight was reduced compare d to WSF and CRF and foliar N deficiency symptoms developed. However, SPFs alone caused no such effects on NGI and shoot dry weight was equa l to WSF and CRF with less N leaching. Growth of marigold increased an d N deficiency symptoms wereprevented by combining SPFs with a dilute solution of WSF, but the same treatment did nor affect NGI. Combining SPFs and WSF in this manner for marigold resulted in less N leaching t han SPFs alone, however with NGI more N leaching occurred, but not to the level of WSF and CRF. Results suggest that SPFs can provide adequa te N for slow-growing plants with low N uptake rates like NGI, but for fast-growing plants with high N uptake rates, SPFs must be combined w ith more soluble fertilizers.