Total and Extractable Manganese and Iron in Some Cultivated Acid Soils of India: Status, Distribution and Relationship with Some Soil Properties

A total of 400 surface soil (0-15 cm) samples were collected from cultivated soils representing four soil series, namely, Hariharapur, Debatoli, Rajpora and Neeleswaram in Orissa, Jharkhand, Himachal Pradesh and Kerala states of India, respectively, and were analyzed to measure the contents of total and extractable Mn and Fe, to establish the relationship among total and extractable Mn and Fe and soil properties, and to characterize the spatial distribution pattern of Mn and Fe in some cultivated acid soils of India. The contents of total as well as extractable Mn and Fe varied widely with extractants and soil series. However, the amounts of Mn or Fe extracted by diethylene triamine penta-acetic acid (DTPA), Mehlich 1, Mehlich 3, 0.1 mol L-1 HCl and ammonium bicarbonate DTPA (ABDTPA) were significantly correlated with each other (P < 0.01). Based on the DTPA-extractable contents and the critical limits (2 mg Mn kg(-1) soil and 4.5 mg Fe kg(-1) soil) published in the literature, Mn and Fe deficiencies were observed in 7%-23% and 1%-3% of the soil samples, respectively. The content of soil organic carbon (SOC) had greater influence on total and DTPA-extractable Fe than did soil pH. Geostatistical analysis revealed that total and DTPA-extractable Mn and Fe contents in the acid soils were influenced by soil pH, SOC content, and exchangeable cations like potassium, calcium and magnesium. Spatial distribution maps of total and DTPA-extractable Mn and Fe in soil indicated different distribution patterns.