Abstract: To explore ways of maintaining high and stable crop yield in fields of yellow fluvo-aquic soil under long-term fertilization in Xuhuai region, variation of crop yield in a long-term (32 a) fertilization field experiment was characterized and relationship between production sustainability and soil organic matter content was analyzed. Results show that under long-term fertilization, crop yields fluctuated from year to year as affected by climate and some other factors. The yields of wheat and maize varied between treatments in the experiment, displaying a decreasing order of MNPK > NPK > NP > M > N > CK, which remained constant throughout the 32 years unchanged. However, the yield of sweet potato varied quite scharply between treatments and between years, as well. Among the treatments (CK exclusive), Treatment N was always the lowest in wheat and maize yield and their yields declined rapidly with each passing year. Treatment N was even 0.161 and 0.063 lower than CK in sustainable yield indexes (SYI ), respectively, of wheat and maisze. Treatment MNPK was 14% and 102.3% higher than Treatment NPK and Treatment M, respectively, in yield of wheat, and 11.5% and 24.4% higher, respectively, in yield of maize. Morerover, Treatment MNPK was low in yield variation coefficient , and good in sustainability. On the whole, maize was quite stable in yield and more than wheat and sweet potato. Balanced fertilization or combined application of organic manure and chemical fertilizer could reduce crops’ dependence on soil basic fertility. Application of organic manure (in Treatment M and Treatment MNPK) increased soil organic matter with a steady trend or a rate of 0.31- 0.37g•kg^-1•a^-1. In sand loamy yellow fluvo-aquic soil under wheat-maize rotation, soil organic matter should be maintained around 15.0 g•kg^-1, a suitable balance level. Therefore, Treatment MNPK, or combined application of organic manure and chemical fertilizer has the effects of building up soil fertility and maintaining high crop yield, and hence is an effective way to sustainable agriculture.

Key words: long-term field experiment, yellow fluvo-aquic soil, crop yield, evolution, organic matter