Analysis of the spatial variability of maize root density

Abstract

The spatial arrangement of maize roots was studied in a clay loam field in order to test the regularity of root arrangement, which is implicitly assumed when distances between neighbouring roots are calculated. For that. we carried out a mapping of root contacts on six superposed horizontal planes which cut the rooting volume of several area samples. Three situations were studied: (i) one inter-row out of two was compacted down to the base of the ploughed layer (28 cm), but not in non-tilled layers (28 to 200 cm); (ii) a mechanical obstacle was placed at the base of the ploughed layer; (iii) one inter-row out of two was compacted down to half the depth of the ploughed layer. On all horizontal planes, the spatial arrangement or root contacts followed a non-regular, clustered pattern for a 10−2m scale of study, even in parts of soil which had not been disturbed by compactions. In the first two situations, where obstacles met the base of the ploughed layer, root density in non-tilled layers was several times lower below the obstacles than below the remaining parts of the ploughed layer. This caused a 10−1 m sized variability which was superimposed on to the 10−2 m one. Conversely in the third situation, obstacles had no appreciable effect on root density in non-tilled layers. Obstacles located at the base of the ploughed layer therefore prevented root access to non-tilled layer and caused a ‘shadow effect’ in the non-tilled layers. This effect is probably due to the main vertical direction of roots in these layers.