Analysis of the spatial variability in maize root density

In a maize field, one inter-row out of two was compacted two years down to 30-cm depth. This compacted inter-row (CIR) had a low root density down to 85-cm depth, while the soil below the row and the non compacted inter-row (NCIR) was densely rooted. Soil water status was monitored in each of these three compartments using tensiometers, neutron probe and gravimetric measurements. Both years, the rate of water extraction was about one half in the CIR compared with the row and the NCIR. As a consequence, appreciable differences in soil water potential were observed between colonized and sparsely colonized zones of each layer. These horizontal gradients were steeper than the vertical gradient between layers. This calls into question the suitability of one-dimensional models of water extraction for non-regular root systems, which are common in the field.