389 Environment & Ecology 35 (1A) : 389—393, January—March 2017 Website: environmentandecology.com ISSN 0970-0420 Influence of Wetting and Drying Cycles on Inorganic P-Fractions in an Acid Soil Amended With or Without Rock Phosphate Piyali Das, Sayan Majumder, Dipankar Saha Received 23 April 2016 ; Accepted 20 May 2016 ; Published online 17 June 2016 Abstract Drying-induced soil aeration and reflooding periodically alters redox conditions and therefore stimulate redox-sensitive processes influ- encing P binding forms. The release of available P from indigenous rock phosphate under this situation is another area of study. Drying stimulated mineral- ization of organic P and increased reduction soluble P into available pool. Addition of rock phosphate fur- ther accentuates release pattern of inorganic P partcularly where soils were subjected to 2 nd drying and remoistening phase. Furthermore, all fractions of inorganic P are closely related in fixation and release phenomena. Keywords Inorganic P fractions, Drying and re- moistening phases, Acid soil, Mussoorie rock phos- phate. Introduction Phosphorus is one of the essential nutrients for crop production. P-deficiency leads to incomplete repro- P. Das, S. Majumder*, D. Saha Department of Agricultural Chemistry and Soil Science, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur 741252, West Bengal, India e-mail: daspiyali 199@gmail.com e-mail: 1991sayan@gmail.com e-mail: d_saha11@yahoo.com *Correspondence ductive growth, hindrance in energy transformations in metabolic and physiological processes and ulti- mately lower yield in terms of quantity and quality. Inorganic phosphorus compounds in soils are of 2 types, (a) calcium phosphates (apatites) starting from most soluble mono-calcium to most complex tri-cal- cium phosphate ; (b) iron and aluminium phos- phates. The available P in Indian soils is generally 120 to 2166 kg ha –1 [1], much lower than the need of the plants. among the phosphatic fertilizers superphos- phates (mono and/or di calcium phosphates) are con- sidered to be best. Its production requires rock phos- phate as raw material, which is mainly imported (around 65%) [2]. Recently deposits of high grade rock phosphate (33–35% P 2 O 5 ) in Rajasthan and low grade rockphosphates (< 23–25% P 2 O 5 ) mainly in Uttar Pradesh, Himachal Pradesh are found. Many trials have been conducted to assess the feasibility of RP for direct application to soil [3]. Acid soils gen- erally exhibit poor crop yield due to low available P content. Much of the added P is fixed (adsorbed on surfaces of Al and Fe hydrous oxides) and is not available for crops. Changes in P-availability during drying and re- flooding have been widely studied in agricultural sites. Drying of soil decreases the solubility of amor- phous Fe and Al oxidesand P sorption affinity [4]. Keeping above information in view, the present investigation was conducted to study the changes in