IRON AVAILABILITY IN CALCAREOUS SOILS

Abstract

Iron (Fe) is a widely deficient micronutrient in agriculture particularly on alkaline and calcareous soils due to formation of insoluble compounds in soil as well its inactivation in plant body. Several soil-related characteristics may lead to development of Fe chlorosis. Prediction of development of Fe chlorosis on basis of single soil parameter is not easy for perennial crops. To cure Fe deficiencies, right choice of rootstock and efficient Fe sources for soil application need to be explored. The present project was designed to study the different soil Fe forms, soil properties and their relation with citrus leaf Fe. For soil solution Fe studies, Buchner Funnel Technique (BFT) was used to determine water soluble Fe in different soils and Fe buffer power of different soils. Different Fe sources were tested in their ability to provide soluble Fe over period of time. Responses of different citrus rootstock seedling were evaluated in calcareous medium. DTPA-extractable Fe and water soluble Fe though represents the available Fe in soils were found unable to justify the symptoms of Fe chlorosis on citrus leaves in our study. Ferrihydrite Fe oxide is the main source of soil Fe in calcareous soils and controls plant available Fe at each depth. Soil pH was found in inverse relation to leaf active Fe. Water soluble Fe extracted from different soils using BFT revealed that all soils were above the critical level of 1 μM Fe required for mass flow. While comparing different Fe sources, we found organic amendments better than inorganic amendments in their ability to supply Fe over long period of time. Inorganic Fe sources rapidly became insoluble regardless of soil type. Vivianite was found slightly resistant to oxidation as compared to FeSO 4 . Among chelates EDDHA is highly stable as compared to DTPA. Citrus rootstock seedlings responded differently with application of Fe with and without CaCO 3 in growth medium. Rootstocks differed in their ability to take up Fe from CaCO 3 medium and to efficiently utilize Fe. Rough lemon found to be efficient rootstock to cope Fe nutrition disorders