Cumulative and Residual Effects of Organic Fertilizer Application on Selected Soil Properties, Water Soluble P, Olsen-P and P Sorption Index

Long-term application of fertilizers containing p, especially organic fertilizers, usuallyincreases the water soluble and available p of soil and at the same time may result in paccumulation in soil. organic fertilizers may also increase movement of p in the soilprofile that could result in surface and ground water pollution. an experiment wasconducted on field plots that received three applications (25, 50 and 100 mg ha-1) of soliddairy manure, sewage sludge, or urban solid waste compost, and one application ofchemical fertilizers (250 kg ha-1 urea plus 250 kg ha-1 mono-ammonium phosphate) for 1,2, 3, 4 or 5 consecutive years in order to investigate the residual and cumulative effects oforganic and chemical fertilizers on selected soil properties, water soluble and bioavailablep as well as the p sorption index of the soil. average organic matter content in the soilincreased as a result of organic fertilizer applications. the increase was proportional tothe rate of application and was highest for dairy manure and lowest for urban solidcompost. both the water extractable and bioavailable p contents of soil increased with therate of application, the nature of organic fertilizer and the number (years) of applications,with the rate being the most effective and the nature of fertilizer the least effective. dairymanure had the largest and solid waste compost the smallest positive impact on both thewater soluble and available p content of soil. effect of sewage sludge application onavailable p content of the soil was greater than its effect on the water extractable p. thephosphorus sorption index was independent of the source of p (organic or chemical), thenature and the rate of organic fertilizers and was only significantly dependent on thenumber (years) of fertilizer applications.