The experiment was carried out on cultivation patterns of winter wheat and summer corn in Huantai County, Shandong Province, China. The purpose of the study was to understand how soil fertility maintaining practices, such as chemical fertilizer application, the use of organic manure and the return of crop straw to the field affected soil microbial biomass carbon (MBC) dynamics in a low production agro-ecosystem of northern China. Seven treatments of fertility maintaining practices in the field were carried out (where the symbol “+" means combination application): ①wheat straw+corn straw+chemical fertilizer, ②wheat straw+corn straw+chemical fertilizer+organic manure, ③wheat straw+chemical fertilizer, ④wheat straw+chemical fertilizer+organic manure, ⑤chemical fertilizer, ⑥double wheat straw+chemical fertilizer, ⑦control randomly designed and applied in the experimental plots. The content of soil MBC was measured in laboratory for different crop growth stages. The experimental results showed that: manure application enhanced the content of MBC throughout the experimental stage; a single chemical fertilizer application could elevate the content of MBC, but chemical fertilizer cooperating organic material could more increase the content of MBC; and that different compositions of straw (wheat straw+corn straw, double wheat straw and wheat straw) returned to the field produced distinct variations in different seasons. Organic manure showed an obvious increase in the content of MBC. The content of MBC had the following ascending trend with regard to annual average the content of MBC: Wheat Straw+Corn Straw+Chemical Fertilizer+Organic Fertilizer>Wheat Straw+Chemical Fertilizer+Organic Manure>Wheat Straw+Corn Straw+Chemical Fertilizer>Double Wheat Straw+Chemical Fertilizer>Wheat Straw+Chemical Fertilizer>Chemical Fertilizer>Control. Therefore, manure applications heighten soil microbial activity and improve soil fertility. The best soil fertility maintaining practice was a combination of chemical fertilizer incorporating organic material in low fertility agro-ecosystem.