Madras Agric. J., 105 (7-9): 276-281, September 2018 *Corresponding author’s email: prakashranjanbehera.prb@gmail.com Efect of Moisture Regimes and Amendments on Iron Transformation in Acid Soils Prakash Ranjan Behera*, D. Jegadeeswari and T. Chitdeshwari Department of Soil Science and Agricultural Chemistry, Tamil Nadu Agricultural University, Coimbatore – 641 003 An incubation experiment was conducted at Department of Soil Science and Agricultural Chemistry, Directorate of Natural Resources Management, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu during 2017-18, with an objective to study the iron transformation and changes in soil reaction in acid soils of Ambasamudram series (Aquic Haplustalf). There were two levels of FeSO 4 (0 and 50 kg ha -1 ), two sources of amendments viz., lime (as per requirement @ 22.5 t ha -1 ) and FYM @ 12.5 t ha -1 , with three moisture regimes viz.,continuous submergence, alternate wetting and drying, and feld capacity. The experiment was conducted for 60 days and the soil samples were drawn at 15, 30, 60 days after incubation, analyzed for pH, DTPA Fe, water soluble Fe and exchangeable Fe. Liming @ 22.5 t ha -1 was found to be efective for bringing the acidic pH to near neutral. Available iron and water soluble iron was noticed to be higher under submerged condition than compared to alternate wetting drying and feld capacity moisture regimes. The recovery of Fe in various pools revealed that 25 to 33 percent of Fe entered into water soluble + exchangeable form at 60 days after incubation. Key words: Acid Soil, Exchangeable iron, DTPA iron, Soil pH, Water soluble iron Soil acidity is a serious constraint for crop production in many regions of the world including India. Acid soils have a pH less than 6.5 in the top layer covers 30 per cent of global arable land acounting for 3950 million hectares (Uexkull and Mutert, 1995). Out of total acidic soil exist in our country, 25 million hectares have pH below 5.5 and 23 million hectares have a pH range of 5.6 to 6.5 (Mandal and Hazra, 1997). Majji et al. (2012) reported that out of the total geographical area of India, strongly acid soil and moderately acidic soil accounts for 6.24 and 24.41 million hectares respectively. Which is 1.9 and 7.4 per cent of the total geographical area of the country. Majority of these soils (≥ 95%) are concentrated in the northeastern region of India, whereas, 65 percent of soil has extreme acidity (pH less than 5.5), Sharma and Singh (2002). Iron as a fourth most copious element plays a vital role in earth bio-geo-chemistry (Borch et al., 2009). Additionally to its abundance within the earth’s crust, iron in aerobic soils is found principally within the form of insoluble Fe3+ oxides or hydroxides that decrease iron bioavailability to plants (Stein et al., 2014). The low land rice soils under submergence create an anaerobic condition which results in low redox potential and pH (Gotoh and Patrick, 1974) and under such conditions Fe2+ is released into the soil solution from its otherwise less soluble forms and hence available to the plants at concentrations that’s normally be toxic (Jefery, 1961; Ponnamperuma et al., 1967). However, iron toxicity may occur in submerged soils as a consequence of high amounts of reducible iron, low pH, and low cation-exchange capacity (Becker and Asch, 2005). In fact, iron toxicity is the most widespread nutritional disorder that afects wetland rice production (Dobermann and Fairhurst, 2000). Keeping the soils continuously fooded throughout the growth period, generally recommended for successful cultivation of rice. But due to uncertainty in rainfall or lack of adequate irrigation water, rice felds in tropical countries are often subjected to varying moisture regimes, resulting in changes in the intensity of reducing condition developed in the soil. This may infuence the transformation of nutrients particularly iron and manganese and consequently their availability in soil.The organic matter, texture and calcium carbonate content also restricts the iron availability. In this context the changes in iron availability, soil reaction and iron transformation were investigated under three moisture regimes viz., continuous submergence, alternate wetting and drying, and feld capacity with application of diferent amendments (FYM, lime and 2 levels of FeSO4). Material and Methods Bulk soil collection and characterisation Acid soils (surface soil samples) in bulk from the plough layer (15 cm) was collected from the farmer’s feld at V.K.Puram, Ambasamudram, Thirunelveli district, situated in the southern zone of Tamil Nadu at 77º38’ East longitude and 8º71’North latitude. Sub sampling was done from the collected bulk soil samples. Air dried and gently broken to pass through 2 mm sieve. Again the sieved samples were thoroughly mixed and analysed for various physico