An investigation of upland soil fertility from different soil types

Soil type is a vital determinant of soil fertility because of its characteristic biological, chemical, and physical properties. However, the soil fertility of upland soil is probably changed by different agricultural management practices regardless of soil type. This study investigated the features of soil fertility (bacterial biomass, total carbon (TC), and total nitrogen (TN)) in upland fields in Japan. One thousand soil samples from different soil types were collected from upland fields located on 36 prefectures in Japan. The soil fertility was analyzed using the Soil Fertility Index (SOFIX). There were six soil types included in this study: Organic soils (B), Andosols (D), Lowland soils (F), Red-yellow soils (G), Stagnic soils (H), and Brown Forest soils (I). Of these, the soil types D and F occupied the largest percentage of samples. The values of bacterial biomass, TC, and TN varied greatly, regardless of soil type. The soil fertility does not seem to be characterized by the soil type in upland soils in Japan. The correlations between bacterial biomass and TC (r = 0.23, p < 0.01) and bacterial biomass and TN (r = 0.16, p < 0.01) were relatively weak. Conversely, the correlation between TC and TN (r = 0.68, p < 0.01) was moderate. In soil type D, up to 40% of samples had no bacterial biomass detected and 17% possessed a low bacterial biomass. The effect of the soil types may not be a critical factor in soil fertility in the upland fields.