Chemical and Biological Properties of Apple Orchard Soils under Natural, Organic, Hybrid, and Conventional Farming Methods

Apples in Japan are generally cultivated under management systems that use chemical fertilizers and synthetic chemical pesticides. However, the continuous use of these fertilizers and pesticides damages the soil environment and reduces the number of soil microorganisms. In this study, we compared the chemical and biological properties of 12 soils from apple orchards in Aomori and Nagano Prefectures under four types of management systems, namely, natural conditions, with no cultivation, fertilizers, or pesticides; organic farming methods, using organic materials and pesticides approved by the Japanese Agricultural Standard organic certification system; hybrid farming methods, using a mix of organic and chemical fertilizers; and conventional farming, using chemical fertilizers and pesticides. Soil total carbon (TC), total nitrogen (TN), total phosphorus (TP), nitrate-nitrogen (NO? 3), and available phosphoric acid (SP) contents were generally found to be the highest where organic farming methods were used. Similarly, bacterial biomass, nitrification (N) circulation activity, ammonia (NH+ 4) oxidation activity, nitrite (NO? 2) oxidation activity, and phosphoric (P) circulation activity were the highest under organic farming, especially in comparison with conventional farming. This study indicated that the differences in apple sugar content, acidity, and sugar/acidity ratio between different orchard management systems were due to different soil conditions, and soil conditions under organic farming management system in apple cultivation increased bacterial biomass while enhancing N and P circulation activity and high TC. On the other hand, the soil of conventional farming has the lowest total number of bacterial biomass and lowest material cycle such as N and P circulation activity. Analysis of the chemical and biological properties of these orchard soils indicated that soil conditions under organic farming management are the most suitable for increasing microbial numbers and enhancing N and P circulation activity.