EFFECTS OF LONG-TERM FERTILIZATION ON SOIL CARBON, NITROGEN, PHOSPHORUS AND RICE YIELD

Fertilization plays an important role in soil fertility and rice yield. A long-term (19902006) field experiment was conducted at a typical subtropical hilly agriculture region in south central China. The objectives of this study are to investigate the effects of long-term fertilizations on i) accumulations and distributions of soil carbon (C), nitrogen (N) and phosphorus (P) in different sizes of water-stable aggregates (WSA); ii) dynamic change of soil C, N, and P over years; and iii) the rice yield. Application of organic materials (OM), especially in combination with chemical fertilizers, increased soil organic C (SOC), soil total N (NT), and soil total P (PT) concentrations in all sizes of WSA, and they more concentrated in WSA (>1 mm). However, single chemical fertilizers had little impact on SOC and NT. There were significantly positive correlations between SOC and NT in each size of WSA, (r0.977, n = 15, P < 0.01). It illuminated that application of organic materials benefited the conservation of soil nitrogen. However, application of organic materials had less impact on PT. Variation of C/P was larger than C/N. PT was mainly affected by input of phosphorus. Data over years showed that SOC and NT continued to rise, whereas PT tended to decline irrespective of treatments. Furthermore, economical chemical fertilizers application combining with green manure and half straw returning (NPKe + SR) can produce approximate effects on PT as conventional dose of chemical fertilizers (NPKc). Average rice yield of NPKc for 17years was 9399kg ha1. Compared with NPKc, OM decreased yield by only 4.4%, which indicated that traditional organic fertilization could obtain relatively high yield. NPKe + SR obtained approximate yield as NPKc did, which showed that green manure and half amount of straw effectually reduced chemical fertilizers by about one third.