A Modified Soil Monolith Technique for Characterizing Root Systems

A soil and root system sampling technique that accurately measures root distribution within the soil profile without causing excessive damage to experimental plots would improve the efficiency of root system research. A monolith mapping root sampling technique is described that combines the positive attributes of the soil monolith and profile wall methods with a less destructive hand tool sampling protocol. The objective of this field study was to compare monolith mapping with a standard monolith washing technique for the purpose of measuring root distribution in the upper 30 cm of the root zone. Root systems of maize (Zea mays L.) (V6 stage of development) from plots (Vienna loams oils; fine-loamy, mixed Udic Haploborolls) treated with broadcast or banded P were sampled using the modified monolith method. The roots present in the soil monolith were mapped (monolith mapping method), and the maps used to represent two-dimensional root distribution. The soil monolith was then grid-sectioned into 5.1 by 5.1 by 7.6 cm rectangular blocks and washed to separate roots from the soil. Root length was then measured using a line-intersect method (monolith washing method). Monolith mapping and monolith washing methods both detected differences in root system distribution in the soil profile. A significant linear relationship (r = 0.87) between root length density and root number as measured by the two methods allows conversion of the numerical data collected by the monolith mapping method into root length density values. We conclude that monolith mapping works well for determining the spatial differences in root distribution in the upper 30 cm of the root zone. The relative time requirements, accuracy, and less destructive nature of the technique (compared with the trench profile and framed monolith methods) result in more efficient collection of data on root system characteristics. Cooperative investigation between USDA-ARS, and the South Dakota State Univ. Agric. Exp. Stn. Journal Series no. 2680.