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Commonly used minirhizotrons consisting of a transparent tube inserted into the soil seldom attain good contact between the tube and the soil, which leads to root growth occurring in a gap rather than in the soil. A new system is described involving an inflatable flexible rubber wall, made from a modified motorcycle tube. Pressure ensures a proper tube/soil contact so that the environmental circumstances for root growth along the tube more closely correspond to those in the undisturbed soil. Before the endoscope slide is introduced into the minirhizotron for taking pictures, the inflatable tube is removed, so that there is n o -o f t e n opaque-wall between the endoscope and the roots. This improves the picture quality and facilitates the analysis of root images.

In field trials in 1993-94 on sandy soils at 2 sites in the Netherlands, cattle slurry was applied by injection into slots 25 cm apart (standard injection) or 75 cm apart (banded injection). Subsequently, maize cv. Melody or Mandigo was sown at a row spacing of 75 cm parallel to the slots, either at random lateral positions in the standard injection treatment or 10 cm from the injection slots of the banded injection treatment. All treatments, including a control without slurry, were combined with 0 or 20-31 kg/ha of subsurface banded P starter fertilizer. Dry matter yields of silage maize were on average reduced by 8% when standard injection of slurry was not supplemented with P. However, the yield reduction was only 2% when slurry was banded.

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