Soil Profile Imaging for Estimating the Depth Distributions of Clay, Iron, and Hydrological Conditions of Soils Under Rice in Northern Taiwan

Abstract

Soil color variation, clay illuviation, and translocation of Fe and Mn are influenced by hydrological conditions. Soil profile imaging has been considered to predict the distribution of clay, Fe and Mn oxides, and hydrological conditions. Ten Ultisol and Alfisol profiles were selected at elevations ranging from 15 m to 40 m a.s.l. at Chungli Terrace, northern Taiwan. Sixty soil horizons were collected for redoximorphic features (RMFs) identification and analysis of soil texture and selective extraction of Fe and Mn oxides. All soil properties were correlated with the RMFs. There was a significantly positive correlation between gray mottle (GM) (value ≥5, chroma ≤3) amounts and annual reduction duration (ARD) (r = 0.80**, p < 0.01) and a negative correlation between red mottle (RM) (value ≥4, chroma ≥3) amounts and ARD (r = 0.75**, p < 0.01) at surface horizons (within 30 cm). A significantly positive correlation was also found between RM and clay content (r = 0.32*, p < 0.05), indicating clay might determine the formation of RM. Moreover, the ratios of iron activity (Feo/Fed) and iron crystalline ((Fed-Feo)/Fet) could also be good indices for ARD prediction. The Mnd/Fed seemed an index of frequent fluctuation of water table in soil profiles. Using image analysis technique, replacing naked eye identification of RMF could improve correlations between soil color and hydrological conditions.