| The nutrients of 364 farmers'paddy soils in cold area of Heilongjiang were determined to investigate the nutrient situation. A field experiment including N0 (N-omision),FFP (farmers'fertilization practice),SSNM (site-specific nutrient management) treatments were conducted around Harbin. The yield and nitrogen accumulation of rice at tested sites, and available N,organic matter,total N contents were determined. Soil mineralizable N was measured by waterlogged incubation. The study analyzed correlations between N supply index and yields,total N uptake of N0 treatments to select appropriate index for nitrogen application. Indigenous N supply was classified by analyzing correlations between above indexes and relative yield and relative nitrogen uptake of N0.Results are given below.1 The average available N content of soil was 166 mg·kg-1;the average organic matter content of soil was 41.8 g·kg-1;the average available P content of soil was 24.5 mg·kg-1;the average available K content of soil was 127 mg·kg-1;pH values of soils varied from 4.50 to 7.78. Compared with the nutrient situation of paddy soils in second soil survey conducted in later 1980's,available N decreased by 21.6%,organic matter decreased by 13.1%,available K decreased by 23.4%,and soils were partial acidified in Harbin, organic matter decreased by 15.7%,available P increased by 21.5%, available K increased by 17.4%, pH decreased by 0.57 pH value, acidification in paddy soils was also observed in Jiansanjiang.2 Average of indigenous N supply of paddy soil was 66.76 kg/hm2 around Harbin. The N uptake of 100-kg grain was in the following order: N0(1.19 kg/100kg)68.4mg/kg. 5. Rice yield of SSNM was higher than that of FFP by 1.47 t/hm2,increased by 18.8%, and the N uptake increased by 24.6 kg/hm2 compared with FFP.
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