Effect of soil temperature and moisture on soil test P with different extractants

Song, C., Zhang, X., Liu, X. and Chen, Y. 2012. Effect of soil temperature and moisture on soil test P with different extractants. Can. J. Soil Sci. 92: 537-542. Temperature and moisture are important factors affecting adsorption, transformation and the availability of soil phosphorus (P) to plants. The different temperatures and moisture contents at which soil is sampled might affect the results of soil test P (STP). In order to evaluate the effect of the temperature and moisture, as well as the fertilization level, on the results of soil test P, an incubation study involving three soil temperatures (5, 10, and 20 degrees C), and three soil moisture contents (50, 70, 90% of field water-holding capacity) was conducted with Chinese Mollisols collected from four fertilization treatments in a long-term experiment in northeast China. Four soil P test methods, Mehlich 3, Morgan, Olsen and Bray 1 were used to determine STP after a 42-d incubation. The effect of temperature and moisture on STP varied among soil P tests. Averaged across the four fertilization treatments, the temperature had significant impact on STP, while the responses varied among soil P test methods. Mehlich 3, Morgan and Bray 1 STP decreased and Olsen STP increased with increase in temperature. Effect of soil moisture was only significant for Mehlich 3 P and Olsen P. Soil temperature had greater impact on STP than soil moisture content. The responses of the Olsen method to temperature differed from the other three methods tested. The interaction between soil temperature and soil moisture on soil test P was only significant for Mehlich 3 P. Fertilization level does not affect the STP in as a clear pattern as the temperature and moisture varied for all four methods. Consistent soil sampling conditions, especially the soil temperature, appear to be the first step to achieve a reliable STP for any soil P test.