Moisture and temperature effect on soil phosphorus availability

The effect of desiccation temperature upon soil phosphorus availability was evaluated under laboratory conditions in soil samples of different texture. Soil samples of 1.4 g were weighed in 25 mL glass tubes and desiccated in an oven at 40, 60, 80 and 1000 C using 2 different moisture levels: dry and wet. A total of 10 treatments were carried out with two replicates per treatment. Soil variables analyzed were: extractable phosphorus (Pe), organic phosphorus (Po), pH, organic carbon (OC), soil microbial activity (SMA), CaCO 3 and texture (sand, silt and clay %). A marked increase in Pe was observed through the combined effect of moisture and temperature. Medium and fine textured soils showed higher Pe increments than coarser textured soils. Whereas in medium textured soils (loam) the increment in Pe varied between 4 mg kg -1 and 8 mg kg 1 as a result of the effect of temperature and temperature plus moisture, respectively, in the case of fine and coarse textured soils (clay loam and loamy sand) the increment was between 1 mg kg' and 6 mg kg 1 . The soil variable analysis did not show any statistically significant relationships for Pe. However, high correlations were found between Po and SMA (r = 0.73, P < 0.0 1) and between SMA and silt content (r = 0.86, P < 0.01). Thus, the results infer that soil microorganisms play an active role in the process of Po mineralization and the consequent increase in Pe.