SOIL AND CROP RESPONSES TO CONVENTIONAL, REDUCED GROUND PRESSURE AND ZERO TRAFFIC SYSTEMS FOR GRASS-SILAGE PRODUCTION

In a perennial ryegrass crop, grown for conservation as silage, two novel traffic management systems, zero and reduced ground pressure, were compared with a conventional system over a 4 year period (1986-1989). In the zero system, the grass was managed in traffic-free beds 2.4 m wide using machinery operating on permanently positioned wheeltracks at 2.8 m wheel centres. In the reduced ground pressure system, all equipment was fitted with larger-than-standard, low inflation pressure tyres. Vehicle traffic in the first year created soil compaction in the reduced ground pressure system, and especially, in the conventional system. Measurements of soil bulk density, strength, and water content indicated that poorer soil structural conditions in the conventional system compared with that in the reduced ground pressure system persisted through the four years of the experiment. The soil in the zero traffic beds remained relatively uncompacted compared with the soil in the reduced ground pressure and conventional systems. Herbage dry matter yields were heavier from the novel systems than from the conventional system at eight of the twelve harvests, and 15-16% heavier overall. The largest benefits from the zero and reduced ground pressure systems were gained at first cut in each year. The demonstrated advantages in crop productivity were attributable to enhanced soil aeration and more efficient use of applied nitrogen in the novel systems. A reduced ground pressure traffic system could be adopted readily at a farm scale, using available machinery and tyres. An efficient system for grass silage cropping which fully exploits the advantages of zero traffic requires further machinery developments.