Abstract

In last decades, large area of dry-farming field has been converted to paddy field in the Sanjiang Plain of the Northeastern China. It is assumed that this land-use change might impact the level, chemical forms, and availability of phosphorus in the soils. Five soil cores were collected separately in the paddy field and dry-farming field and were analyzed for pH, soil organic matter (OM), aluminium (Al), iron (Fe), calcium (Ca), potassium (K), total phosphorus (TP), and phosphorus forms. The topsoil of the paddy filed contained lower OM, Fe, Al, organic phosphorus (Por), and residual phosphorus and higher inorganic phosphorus (Pinor) and iron oxides-bound phosphorus (Fe-P) than that of the dry-farming field. However, TP and plant-available phosphorus (AP) levels were generally not affected by the land-use change. The bulk of soil phosphorus mainly exists in Por, Fe and Al-bounded phosphorus, and Ca-bound phosphorus, while AP was significantly correlated to Pinor, Al-bound phosphorus (Al-P), and Fe-P but not correlated to Por in the both fields. Therefore, the conversion of dry-farming field to paddy field did not impact TP and AP levels, but changed the phosphorus forms in the albic black topsoil, with increase of Pinor and iron oxides-bound P and decrease of Por.

Key words: Phosphorus fractionation, paddy field, dry-farming, plant available phosphorus.