This research was aimed at developing a composting process of organic waste using natural and modified zeolites by ascertaining how effective they were in retaining phosphorus (P) after 60 days. The experiments included compost (C) containing natural (N) and modified (M) zeolite (Z) treatments (applied at 10% and 15% on a weight basis of the total waste): CNZ10, CNZ15, CMZ10, CMZ15 and C (which is the control treatment with no zeolite addition). The second objective was to compare the barley shoot biomass and nutrient concentration of the various compost treatments mixed with soil and control treatment (just soil) after 45 days of planting in the greenhouse. In general, the benefits of co-addition of compost and zeolite on sandy soil were tested in a completely randomized experimental design. The results indicated that the treatments with the highest zeolite treatments (CNZ15 and CMZ15) proved most effective at retaining P by the end of the composting process (2.8mg and 2.9mg respectively) compared to the lower zeolite ratios and the control treatment; CNZ10 (2.0mg), CMZ10 (1.9mg) and C (0.7mg). The barley shoot biomass results indicated that the treatments that had a combination of soil (S) and modified zeolite (SCMZ10 and SCMZ15) had biomass of 7.67g and 7.24g respectively, followed by the natural zeolite and compost treatments (SCNZ10, SCNZ15 and SC) having 6.19g, 6.38g and 5.99g respectively and were significantly different from the control treatment (S) which had the lowest biomass of 0.48g. With respect to the plant nutrient concentration, N and P were significantly higher in the control treatment (S) compared to the other treatments while K concentration was significantly highest in the compost and some of the zeolite treatments (SC, SCNZ15 and SCMZ15) compared to other treatments. These results were in line with some previous findings where zeolite was used as a soil amendment in agriculture.
