REDUCING THE COST OF ESTIMATING ROOT TURNOVER WITH HORIZONTALLY INSTALLED MINIRHIZOTRONS

Growth and decay of individual roots (i.e., root turnover) is difficul t to quantify because the processes occur simultaneously in a root sys tem. Minirhizotrons are promising tools for assessing root turnover in natural and managed ecosystems. We investigated methodological proble ms and improvements in using minirhizotrons to estimate root turnover. Root images were collected in field plots of alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.) through minirhizotr ons installed horizontally before planting at six depths, from 7 to 70 cm, parallel to and directly below the crop rows. Forty video images (13 by 17 mm) were recorded at weekly intervals at 90 degrees from ver tical along both sides of the tubes. Images were edited into time-laps e sequences and cumulative numbers of roots that appeared and disappea red at each location were determined manually over an entire growing s eason. This required approximate to 29 h of labor for each replicate o f each depth (a total of 80 images in one tube), with the biggest shar e spent on editing. Accuracy and precision of results were not decreas ed by using only every second image along both sides of the tube (40 i mages), but declined when either only one side of the tube or only 20 consecutive images on both sides were used. Reducing the recording fre quency further reduced labor requirements: depending on date of root a ppearance and observation depth, recording intervals could be lengthen ed to 2 wk for the 12-cm depth and longer for greater depths without l osing either accuracy or precision. Analyzing every second image and i ncreasing the time interval between recordings resulted in projected l abor savings of greater than or equal to 70%, while maintaining data i ntegrity.