Effect of soil acidity and nitrification of fertilizer introduced by row application on sugar beet growth in several soil types

The present study was carried out to analyze the factors that affected the growth of sugar beet in four different soil types by using concrete-framed plots as follows: soil acidity (soil pH, exchange acidity y 1 ) and nitrification of fertilizer introduced by row application. Comparison of the value of the exchange acidity y 1 of the four soil types with the pH value adjusted to the same level (pH 5.1) revealed that the Humic Gray Upland soil displayed the highest y 1 value (y 1 : 18.0), followed by the Humic Volcanogenous Regosol (y 1 : 6.9), Haplic Brown Lowland soil (y 1 : 5.3), and Low-humic Andosol (y 1 : 2.2). Al release to the soil solution was considered to occur at soil pH values of 4.8 and lower except in the Low-humic Andosol. Al concentration in the soil solution of the Low-humic Andosol was substantially lower than that of the other soils. On the other hand, the soil pH value decreased temporarily by nitrification of the fertilizer introduced by row application, especially in the Humic Gray Upland soil. In this case, the soil pH value became lower than 4.8 for a time. At this pH level, Al release to the soil solution was assumed to occur. As described above, the soils displayed different properties in terms of soil acidity. In the four soils, although the growth of sugar beet was significantly related to both soil pH and exchange acidity y 1 values before sowing, these relations were not strictly valid. On the other hand, the linear correlation coefficients of the relationships between the growth of sugar beet (leaf length) and NO 3 -N content in rows were higher than those of the soil pH and exchange acidity y 1 . No appreciable variation associated with the differences in the soil types was observed in this relation. Furthermore, the values of both soil pH and exchange acidity y 1 were closely related to the NO 3 -N content in rows and the relationship between the NO 3 -N content and y 1 value appeared to be somewhat closer than that with the soil pH. These closer relations had two important implications. Firstly, NO 3 -N content reflected the nitrogen nutrient conditions. NO 3 -N promoted the growth of sugar beet directly. Secondly, the NO 3 -N content was affected by the soil acidity, which is expressed by the value of the exchange acidity y 1 . Low NO 3 -N content indicated indirectly the toxicity of soil acidity to sugar beet growth. It was thus suggested that in the present study, nitrification of the fertilizer expressed by the NO 3 -N