In order to elucidate the effects of fertilizers and crop residues on crop yield of the crop sequences spring rice - summer rice - winter maize on grey degraded soil in Bac Giang, as well as phosphorus balance in fields and phosphorus forms in soil, this study was conducted by collecting and analyzing crop yield information and soil samples in a long term experiment which has been carried out since 1998. The experiment included 2 factors: *factor 1 included 7 fertilizer treatments (designed as N, P, K omission plots); * factor 2 included 2 treatments of using crop residues (with and without crop residues from previous seasons). Research results showed that rice yield decreased by fertilizer treatments NPK+PC NPK NK PC NP PK DC, and maize yield decreased by NPK+PC NPK NK PC, PK, NP and DC(no fertilizer). Using crop residues increased crop yield from 5 to 10 percent compared to non using and decreased the deference of crop yield in fertilizer treatments. P out put in fields of most fertilizer treatments (except treatments non applying mineral phosphorus) was much lower than P input. After 14 year continuous cultivation, applying NPK+PC, NPK, PK and NP treatments, P remaining in field were 1,700 - 1,900, 694-809, 1,200 kg P2O5/ha, respectively. Applying farm yard manure (PC) only, P remaining was 800900 kg P2O5/ha. P remaining in field was depended on mineral P application, increased 20-50 percent compared to the non mineral P application treatments; using crop residues increased P organic fraction in soil, around 10 percent compared to non using crop residues.
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