THE WAGENINGEN RHIZOLAB - A FACILITY TO STUDY SOIL-ROOT-SHOOT-ATMOSPHERE INTERACTIONS IN CROPS .2. METHODS OF ROOT OBSERVATIONS

Roots in the Wageningen Rhizolab are observed using two methods: (i) n on-destructively, using horizontal, glass minirhizotrons at intervals of 14 days between observations; (ii) with destructive sampling using augers on three dates in the season. This paper reports changes with d epth and time in root numbers per unit interface area of the minirhizo tron tube (number of intersections) of four crop species (wheat, Bruss els sprouts, leek and potato). The number of root intersections of Bru ssels sprouts, wheat and potato declined with depth at any time, where as leek showed a different pattern because maximum root growth was obs erved at a depth of 10-20 cm. Root density generally decreased in the following order: Brussels sprouts, wheat, potato and leek. Plots of ro ot length densities, L(IV)(cm. cm(-3)), obtained by auger sampling, ve rsus the number of intersections showed considerable variation in slop e with species, time in the season and year, implying that a single, u niversal equation to convert minirhizotron observations into volumetri c root densities does not exist. Causes of variation in the slopes are discussed. It is concluded that limited auger sampling combined with minirhizotron observations yield adequate quantitative estimates of re levant root properties.