Information on soil test phosphorus
(P) in soil treated with organic amendments is important to a sound management
of manure additions to agricultural fields. This study compared the recovery of
cow manure, chicken manure, city compost P relative to triple super phosphate P
(TSP) for an acidic soil with different antecedent soil test P (STP).
Phosphorus was added at rates of 0, 100, 200, 400 and 800 mg P kg-1 soil based on total P. The soil was incubated at field capacity for 1, 4, 8 and
16 weeks (wk) after which they were extracted using NaHCO3 (Olsen)
Mehlich-3, Kelowna
and Bray & Kurtz-1 extractants. Regardless of extractants, after 1 wk
incubation, the highest STP source was the TSP and the least was the city
compost. Soil Test P increased with the addition of amendments from different P
sources. Among the amendments, soil test P in TSP amended soil gradually
decreased but in the city compost amended soil slightly in- creased with incubation time, whereas
the changes of soil test P with time in the cow and chicken manures amended
soil was very negligible. Across the amendments and rates of P additions, the
value of extractable P with Olsen was of 55 mg kg-1 (16%), with
Mehlich-3 was of 112 mg kg-1 (32%),
with Kelowna was of 88 mg kg-1 (24%) and with Bray & Kurtz was
of 104 mg kg-1 (29% of total added P). The P extraction efficiency
was in the order: NaHCO3 < Kelowna
< Bray & Kurtz-1 < Mehlich-3. This study indicates that P in organic
amendments reflects plant available P through the entire incubation period but
P in the TSP are likely to under estimate after 8 wk of incubation.