The effect of inoculation with arbuscular mycorrhizal fungi (AMF) on crop productivity under small-scale farming conditions and the persistence of the fungal inoculum in the field were investigated over 2 years. Sweet potato plants were inoculated with various combinations of AMF and grown under traditional Chinese farming procedures. Plantlets from germinated tubers were inoculated in a soil/sand mixture at the time of hand transplanting into the field. A technique for long-term preservation of the root samples and a fast, reliable DNA extraction method were developed to track and evaluate the persistence of the selected AMF in two field trials in China. The AMF rDNAwas specifically amplified by nested PCR from colonized sweet potato roots collected from the field trials, and polymorphism of the 50-end of the large ribosomal subunit was used to monitor fungi at the species level. AMF varied in their ability to establish after inoculation, and in their effect on yield and quality of sweet potato tubers.