Injecting bio solids into grass and arable crops. Part I: Design and evaluation of a shallow injector

Shallow injection of liquid bio solids at depths of 50–70 mm into grass and arable crops offers many advantages over existing application methods. However, current shallow injection equipment only places the sludge or slurry into slots leaving it exposed with a high runoff risk. The objective of this study was to determine the benefits and limitations of injecting digested sewage sludge into land growing arable crops using shallow injection techniques. It is documented in two parts. One part describes the agronomic trials undertaken to determine the effect of application technique and timing on combinable crops. This part describes the work undertaken to understand the mechanics of shallow injection and develop an improved injector design. Here, laboratory and field studies were undertaken to compare both existing and new winged shallow injector designs. These showed that a winged injector penetrated better with an equal or lower draught than existing designs. The design also incorporated the sludge into the soil with minimal crop damage at rates of at least of 50 m3 ha−1 when working 50 mm deep.