The Long-Term Effect of Blanket Phosphorus Fertilizer Application on the Available P Content in Sawah Soils; Comparative Study in Java, Indonesia

The Long-Term Effect of Blanket Phosphorus Fertilizer Application on the Available P Content in Sawah Soils:Comparative Study in Java, Indonesia (Darmawan, K. Kyuma, T. Masunaga, Asmar, I. Darfis, and T. Wakatsuki): Inorder to evaluate the effects of long-term phosphorus fertilizer application on the sawah soils, a comparative studywas conducted in Java Island as a pioneer of Green Revolution (GR) technology application in Indonesia. Soilsamples taken in 1970 by Kawaguchi and Kyuma were compared with new sample taken from the same site or the sitesclose to 1970 in 2003. The results showed that available phosphorus (P) sharply increased during the study period.The average content of available P in topsoil layer changed from 10.5±11.6 mg kg-1 P in 1970 to 19.6±22.4 mg kg-1 P in2003, or increased by 118%. Long-term application of 125 kg super-phosphate [Ca(H2PO4)2] per hectares per croppingseason as P fertilizers was also affected the profile distribution of available P in whole sites studied, especially inVertisols. The land management differences between seedfarms planted with rice in monoculture systems wholestudy period and non-seedfarms cultivated rice and upland crops in some rotation patterns found affected thechanging rate of available P in the soils. During the period of 1970-2003, average content of available P in seedfarmschanged from 15.7±16.2 mg kg-1 P to 31.1±29.1 mg kg-1 P,while in non-seedfarm from 6.9±8.7 mg kg-1 P to 11.5±8.2 mgkg-1 P in 1970 and 2003, respectively. The great variation on the changing rate of available P observed in this studyindicated that general chemical fertilizers recommendation in Indonesia was caused excess P input in some sites, butinsufficient in others. To avoid the adverse effect of P fertilizer application in the future, recommendation of P shouldbe based on the site characteristic and taking into account of natural resources contribution.