Soil phosphorus fractions and their transformation in normal and salt affected soils as affected by organic amendments

The soil salinity causes physiological drought resulting in hindrance in the bio-availability of essential nutrients. The interaction between salinity and phosphorus uptake by plants is less explored. Two independent incubation experiments were conducted to study the distribution and transformation of various P fractions in normal and salt affected soils as influenced by various organic amendments application. In first experiment, three different levels of P (200, 400 and 600 mg kg^-1 of soil) were applied in three soils differing in soil EC and SAR. Changes in various fractions of soil P (Ca₂-P, Ca₈-P, Al-P, Fe-P, Olsen-P) were estimated at different time intervals. All three soils behaved differently for P distribution among various fractions. Maximum available P (12.18 mg kg^-1) was found in PROKA soil (saline sodic) at 400 mg kg^-1 of P applied. In 2^nd experiment, various organic amendments [farmyard manure (FYM), poultry manure (PM), crop residue (CR)] and sewage sludge (SS) were used, with and without adding P fertilizer @ 400 mg kg^-1 to study their effect on changes in soil P, at different time intervals. Plant available Olsen-P fraction significantly increased after 90 days in all soils (normal, saline sodic, marginal saline sodic) with amendments FYM and PM but not as much with amendments CR and SS. Overall, increase in Olsen-P was higher with PM (23.2, 21.7 and 19.4 mg kg^-1) and FYM (20.6, 17.6 and 20.6 mg kg^-1) as compared with SS (14.3, 15.5 and 15.7 mg kg^-1) and CR (12.9, 14.4 and 14.0 mg kg^-1) in normal, saline sodic and marginal saline sodic soils, respectively. On the basis of these results, it was concluded that integration of PM and FYM with P level 400 mg kg^-1 is an effective approach to mobilize more P available for plant uptake in normal and salt-affected soils with order of normal> saline sodic> marginal saline sodic.