Estimation of the addition of converter furnace slag and lime hydrate for weak alkaline correction by clay and carbon content in paddy soils

Abstract

Adjusting soil pH to weakly alkaline (approximately 7.5) can inhibit filamentous fungi, such as Plasmodiophora brassicae, which causes Brassicaceae clubroot disease. Since pH increase in response to the addition of alkali materials depends on soil composition, a simple method is needed to estimate the quantity of alkali material added. In this study, simple sigmoidal soil pH buffer curves were drawn from the data obtained from adding converter furnace slag or lime hydrate to approximately 230 paddy soil samples from eastern Japan and Hokkaido. The constant part of the curve, which is an indicator of soil pH buffering capacity, was expressed as a function of the clay and total carbon content. The estimated formula-derived value was linearly correlated with the actual value of the constant parts of the curves (R²=0.333 for converter furnace slag and 0.429 for lime hydrate). The linearity of the calculated values derived from the formula with respect to the measured pH was examined after inputting five material volume points to verify the practicality of the equation. The measured and estimated pH after the converter furnace slag added were well fitted when the material input was 0.025–0.25 g⋅10 g⁻¹ of dry soil as alkaline content (R²=0.81–0.61), which corresponded to an acidic to weakly alkaline pH; whereas for the lime hydrate they were well fitted when the material input was 0.025–0.05 g⋅10 g⁻¹ of dry soil as alkaline content (R²=0.55–0.70), also corresponding to an acidic to weakly alkaline pH. Thus, the present equation can be used for acidification and soil pH adjustment to weak alkalinity.