Intercropping maintains soil fertility in terms of chemical properties and enzyme activities on a timescale of one decade.

Background: Overyielding (i.e., mixtures of crops yielding higher than expected when compared with monocultures) and increased nutrient acquisition have been found in many intercropping systems. However, there are very few published studies on long-term changes in soil chemical and biological properties in intercropping systems compared to sole cropping. Methods: A field experiment was established in 2003 in Gansu province, northwest China. The treatments comprised three intercropping systems (either continuous or rotational wheat/maize, wheat/faba bean, maize/faba bean intercropping), rotational cropping (wheat-maize, wheat-faba bean, faba bean-maize, and wheat-maize-faba bean rotations), and monocropping (sole wheat, faba bean and maize) systems. In 2011 (ninth year of the experiment) and 2012 (tenth year) the yields and some soil chemical and biological properties were examined after all crop species were harvested. Results: There was overyielding by 6.6 % and 32.4 % in wheat/maize intercropping in 2011 and 2012, respectively. Faba bean/maize intercropping was enhanced by 34.7 % and 28.6 %, respectively but not wheat/faba bean intercropping. Soil organic matter, total nitrogen, Olsen P, exchangeable K and cation exchange capacity in all intercropping systems did not differ from the monocultures except for soil pH in wheat/maize and faba bean/maize intercropping in 2011 and soil exchangeable K and cation exchange capacity (CEC) in 2012. Soil pH in wheat/maize and faba bean/maize intercropping was significantly reduced by 3.2 % and 1.9 %, respectively. Soil exchangeable K in wheat/maize, faba bean/maize and wheat/faba bean intercropping declined markedly by 15 %, 21.7 % and 12.1 %, respectively. Soil cation exchange capacity in wheat/maize, faba bean/maize and wheat/faba bean intercropping was notably lower than the corresponding monocultures by 17.5 %, 23.3 % and 18.3 %, respectively. Soil enzyme activities after 9 and 10 years of intercropping differed little from monocultures or rotations. Conclusions: The results indicate that intercropping overyielded compared with monocropping or rotational cropping and also maintained the stability of most of the soil chemical and enzyme activities relative to rotations and monocropping in the relatively fertile soil studied. [ABSTRACT FROM AUTHOR]