Abstract: The effects of long-term fertilization and field water level variation on the contents and stoichiometric ratios of total carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) in rice straw and soil were examined based on a 36-year fertilization experiment in combination with a two water level controlling field experiment. The results showed that, compared with chemical fertilizer application, the contents of C, N, and S increased by 35%, 15%, and 56% in soil treated with normal-level organic fertilizer, increased by 67%, 42% and 43% in the soil treated with high-level organic fertilizer, respectively. Soil P contents under treatments of high-level organic fertilizer and normal-level organic fertilizer were decreased by 38% and 21%, respectively. The highest soil C and N contents were found under the treatment with highlevel organic fertilizer. In contrast, plants with long-term chemical fertilizer application had the highest levels of C, N and P. Changes in element contents of soil and plant were more dependent on subsequent fertilization scheme. In general, soil element content was more sensitive to fertilization than that in plants. The results of different water level treatments showed that soil C, N, S and P contents at high water level were significantly higher than those at low water level, except that higher P content in soil was observed at low water level treated with high-level organic fertilizer. In addition, there was an interactive effect between fertilization and water level on soil and plant ecological stoichiometry.

Key words: upland, the Second National Soil Survey, soil acidification, paddy soil, spatial variation.