COMPARISON OF PHOSPHORUS AVAILABILITY WITH APPLICATION OF SEWAGE-SLUDGE, SLUDGE COMPOST AND MANURE COMPOST

The objectives were to determine if phosphorus (P) from different orga nic wastes differs in availability to crops. Four materials: digested, dewatered sewage sludge (DSS); irradiated sewage sludge (DISS); irrad iated and composted sewage sludge (DICSS); and composted livestock man ure (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 le ttuce [Lactuca saliva L. (cv. Grand Rapids)], bean [Phaseolus vulgaris L. (cv. Tender Green)], and petunia [Petunia hybrida Vilm. (cv. Super ior Red)] in 1990, and in consecutively harvested two cuts of lettuce in 1991. Percentage of total P that was extractable by 0.5M sodium bic arbonate (NaHCO3) in CLM (30-70%) was much higher than in DSS, DISS, a nd 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 th e 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 se cond cut lettuce in 1991, was possibly due to their advanced stage of maturity. Much larger amounts of P were applied with DSS, DISS, and DI CSS than with CLM, while P uptake and extractable soil P did not incre ase compared to that in the treatment that received no P. The low avai lability of P in sludge was likely caused by iron (Fe) and aluminum (A l) which precipitated P. Sludge irradiation and/or composting had no s ignificant effect on P availability.