Effect of fertilizer and manure application on microbial numbers, biomass, and enzyme activities in volcanic ash soils

Abstract

Fertilizer and manure application affected the microbial numbers and biomass in topsoil and subsoil fields consisting of volcanic ash upland soil.

1.	Microbial numbers (bacteria, spore-forming bacteria, actinomycetes, and fungi) were the largest in the farmyard manure plot, followed by the chemical fertilizer plot, and smallest in the no-fertilizer plot in both fields. The numbers of all the microorganisms except fungi in the samples from the topsoil field were larger than in the samples from the subsoil field in the respective plots. Microbial numbers obtained here were several times as large as the mean values of microorganisms in volcanic ash upland soils, presumably due to the use of a Waring blender for dispersing the soil samples.
2.	Soil microbial biomass carbon was the largest in the farmyard manure plot, followed by the chemical fertilizer plot, and smallest in the no fertilizer plot in both fields. Microbial biomass carbon in the samples from the subsoil field was larger than that in the samples from the topsoil field in contrast to the microbial numbers. Regarding the microbial numbers per total carbon content in the samples from both fields, the numbers of bacteria, actinomycetes, and fungi were larger in the samples from the subsoil field as in the case of the microbial biomass carbon.
3.	The rate of microbial biomass carbon to the total carbon ranged from 0.4 to 0.8% in the samples from the topsoil field and from 2.5 to 3.2% in those from the subsoil field. Therefore the values obtained in the samples from the subsoil field corresponded to the average values obtained hitherto in non-volcanic ash upland soil, whereas those in the samples from the topsoil field were remarkably lower. These results suggest that the organic substances which accumulated in such large amounts as to make the surface layer appear black, consist of a far smaller amount of decomposable organic substances than those accumulated in the subsoil

Key Words:

• soil microbial biomass carbon
• soil microorganisms
• volcanic ash soil
• fertilizer and manure application.