Abstract
Different methods have been proposed for in situ root-length density (RLD) measurement. One widely employed is the time-consuming sampling of soil cores or monoliths (MO). The profile wall (PW) method is a less precise, but faster and less laborious alternative. However, depth-differentiated functions to convert PW RLD estimates to MO RLD measurements have not yet been reported. In this study, we perform a regression analysis to relate PW results to MO results and determine whether calibration is possible for distinct crop groups (grasses, brassicas and legumes) consisting of pure and mixed stands, and whether soil depth affects this calibration. The methods were applied over two years to all crop groups and their absolute and cumulative RLD were compared using a linear (LR) and multiple linear (MLR) regression. PW RLD was found to highly underestimate MO RLD in absolute values and in highly rooted areas. However, a close agreement between both methods was found for cumulative root-length (RL) when applying MLR, highlighting the influence of soil depth. The level of agreement between methods varied strongly with depth. Therefore, the application of PW as the main RLD estimation method can provide reliable estimates of cumulative root distribution traits of cover crops.
Highlights
Root-length density (RLD) of cover crops is frequently assessed in crop studies due to its high relevance for crop functions such as nitrogen uptake from deep soil layers [1,2,3,4,5], erosion control [6] and crop productivity [7]
MO and profile wall (PW) methods resulted in overall higher absolute root-length density (RLD) values, higher standard deviation and larger deviations between PW and MO methods in the first 30 cm of soil compared to deeper layers
Profile wall and monolith methods were found to have high disagreements in their root-length density measurements, where values can be greatly underestimated if profile wall is chosen as the main root-length estimation technique
Summary
Root-length density (RLD) of cover crops is frequently assessed in crop studies due to its high relevance for crop functions such as nitrogen uptake from deep soil layers [1,2,3,4,5], erosion control [6] and crop productivity [7]. Different quantitative methods have been employed to measure RLD in the field, of which soil core sampling [4,5,8,9,10,11,12], field installation of minirhizotrons [1,2,3,9,13,14,15] and soil monolith (MO) extraction [8,9,16,17] are the most frequently used These methods are considered to be either very time consuming and/or expensive, but believed to be the most accurate in representing real values [8,18,19]. To have monoliths extracted at several plant stages requires high expenditure of time and labor, and the abovementioned studies demonstrate the unreliability of one mean conversion factor because it cannot do justice to the crops’ temporal dynamics
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