Assessing soil quality in a riparian buffer by testing organic matter fractions in central Iowa, USA

A multispecies riparian buffer strip (MRB) was established along Bear Creek in central Iowa by the Agroecology Issues Team at Iowa State University (I SU) in order to assess the ability of the MRB to positively impact soil ero sion and process non-point source pollutants to improve water quality. Soil organic matter (SOM), and especially biologically-active soil organic matt er, is considered to be an important soil quality indicator variable becaus e of it has relationship to critical soil functions like erodibility and th e capacity of the soil to act as an environmental buffer. The objectives of this study were to examine trends in SOM C accrual and to quantify intra-s easonal changes in SOM C and particulate organic matter (POM) C for each ve getation zone of a MRBS seven years after establishment on previously culti vated or heavily grazed soil. Total SOM C and POM C in soil under perennial vegetation (poplar, switchgrass and cool season grass) were significantly higher than under cropped soil. Total POM C changed within vegetation type over the four month study period, whereas total SOM C did not. After six gr owing seasons, SOM C increased 8.5% under poplar grown in association with cool season grass, and 8.6% under switchgrass. The results are very promisi ng and suggest that changes in SOM C can occur in a relatively short time a fter the establishment of perennial vegetation in a MRB. These changes shou ld increase the ability of MRB soil to process non-point source pollutants.