Iron and Calcium Availability to Groundnut Plants as Affected by Calcium Carbonate and Water Levels in Calcareous Soil

To assess possible causes of soil and plant iron deficiency and chlorosis in groundnut (Arachis hypogaea L.) on calcareous clay loam soils of Karnataka, India, a pot experiment was conducted to evaluate the availability of iron and calcium at varying levels of CaCO3 and soil water and their influence on pod yield. The CaCO3 levels of the soil achieved by liming were: 5% (C1), 7% (C2), 10% (C3), 15% (C4), and 20% (C5) (on mass basis). Three soil water levels, i.e., 75% (M1), 150% (M2), and 200% (M3) of field capacity, were imposed for one week each at flowering and pegging stages. Amorphous iron oxide-occluded iron, free iron oxide, and water-soluble calcium increased significantly with increasing levels of soil water. The diethyl triamine pentaacetic acid salt (DTPA)-extractable Fe, however, decreased at higher levels of CaCO3 and soil moisture. Conversely, the concentration of bicarbonate ions increased at higher levels of CaCO3 and soil water. The pod yield of groundnut, which was highest under M2C2, decreased at higher levels of CaCO3. This decrease in groundnut yield at higher levels of CaCO3 was attributed to deficiency of available Fe, DTPA-Fe, as caused by the increased concentration of bicarbonate ions.