Saturday, 15 July 2006

pH Buffer Capacity and Lime Requirement for Korean Acid Soils.

Yoo-hak Kim and Han-Kang Kwak. National Institute of Agricultural Science and Technology, Seodun-dong 249, Kwonsun-gu, Suwon, South Korea

pH Buffer Capacity (pBC) relates to the chemicals releasing H+ into soil solution. What kind of chemicals is releasing H+ dominantly and how much H+ is released from the chemicals are essential to determine Lime Requirements (LR). A study was conducted to find the kind of chemicals governing pBC and to elucidate the relationships between pBC and LR and to develop a LR method for Korean acid soils by determining LR of 55 acid soils and by validating LR in 5 fields. pBC of Korean acid soils was not only governed by exchangeable Al (Ex. Al) but also affected by soil properties. pBC of Korean acid soil having high Ex. Al was equivalent to Ex. Al. A series of chemical reactions of liming showed that Liming Factor (LF) varied directly as total cations and Difference of pH (DpH) such as LF = 1.5 + 0.2xTotal cationsxdpH. So, LR calculated as Ex. Al and total cations was valid for correcting pH of field trials. A pH buffer was developed using p-nitrophenol and potassium chromate and sodium acetate having an equal difference in equilibrium constant. Newly developed buffer was showing a direct proportion to pH difference. LR corresponding to pH difference was so exactly agreed with that of calculating with analytical chemistry that it could be utilizable in Korean acid soils. Keywords: Lime requirement, pH buffer capacity, liming factor, pH buffer solution

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