Comparison of minirhizotron and soil core methods for quantifying root biomass in a temperate alley cropping system

A study was carried out in southern Indiana, USA with the objective of comp aring soil core sampling and the minirhizotron technique in quantifying fin e root biomass and root distribution patterns in an alley cropping system w ith black walnut (Juglans nigra L.), northern red oak (Quercus rubra L.) an d maize (Zea mays L.). Spatial variation in tree rooting pattern was invest igated prior to planting maize. Tree fine root biomass was quantified at di stances of 0, 1.1, 2.3, 3.5, and 4.3 m where 0 m represents the tree row an d 4.3 m represents the middle of the alley. Root samples were collected to a depth of 90 cm using a hydraulic auger. Maize rooting pattern was determi ned 65 days after planting to the same depth. Using plexiglass access tubes installed near the actual soil core locations and a minirhizotron camera r oot images were recorded on a VHS tape. These images were later analyzed us ing a raster based GIS software (ERDAS-IMAGINE). Regression analysis reveal ed significant relationships between root surface area measurements from mi nirhizotron observations and fine root biomass data from soil coring for al l species. Predicted fine root biomass data were also in close agreement wi th actual fine root biomass for all species examined. Maize root biomass wa s slightly, but not significantly, underestimated by the minirhizotron tech nique in the top 30 cm soil layer. No significant underestimation or overes timation of root biomass in surface or deeper soil layers was observed for the tree species. The results indicate that minirhizotron can be used in qu antifying fine root biomass if site and species specific predictive models can be developed.