Comparison of phosphorus availability with application of sewage sludge, sludge compost and manure compost

The objectives were to determine if phosphorus (P) from different organic wastes differs in availability to crops. Four materials: digested, dewatered sewage sludge (DSS); irradiated sewage sludge (DISS); irradiated and composted sewage sludge (DICSS); and composted livestock manure (CLM) were applied for two years at five rates (0, 10, 20, 30, 40 Mg.ha(-1).yr(-1)) with four replicates. Uptake of P was measured in lettuce [Lactuca saliva L. (cv. Grand Rapids)], bean [Phaseolus vulgaris L. (cv. Tender Green)], and petunia [Petunia hybrida Vilm. (cv. Superior Red)] in 1990, and in consecutively harvested two cuts of lettuce in 1991. Percentage of total P that was extractable by 0.5M sodium bicarbonate (NaHCO3) in CLM (30-70%) was much higher than in DSS, DISS, and DICSS (0.8-5.6%). Phosphorus uptake by crops harvested in an early stage of growth, lettuce in 1990 and first cut lettuce in 1991, and the extractable soil P linearly increased with total P applied. The lack of response in P uptake with bean pod and petunia in 1990, and the second cut lettuce in 1991, was possibly due to their advanced stage of maturity. Much larger amounts of P were applied with DSS, DISS, and DICSS than with CLM, while P uptake and extractable soil P did not increase compared to that in the treatment that received no P. The low availability of P in sludge was likely caused by iron (Fe) and aluminum (Al) which precipitated P. Sludge irradiation and/or composting had no significant effect on P availability.