TRAFFIC SYSTEMS AND SOIL AERATOR EFFECTS ON GRASSLAND FOR SILAGE PRODUCTION

A comparison of conventional, reduced ground pressure and zero traffic systems for grass silage production was made from 1990 to 1993. In 1990, the systems comparison was continued unchanged from that conducted on the same soil and sward from 1986 to 1989. Thereafter, variations were introduced in the treatment and management of the grass (1991, timing of cut) and of the soil (1992 and 1993, slotting). A detailed analysis of soil structure revealed a larger volume and number of macropores in the topsoil of the two novel systems than in the conventional system. The herbage dry matter yields and offtake of nitrogen from the novel systems, between which there was little difference, were significantly larger than from the conventional system. On average, over the 4-yr period, 13% more dry matter and 18% more nitrogen were yielded by the novel traffic systems than by the conventional system. Relationships were identified between the compaction penalties in yield and N-offtake inherent in the conventional system and both soil wetness at preceding harvests and the amount of rainfall after fertilizer application. Cutting the grass for earlier harvests in the zero system did not prejudice superiority in annual yield relative to the conventional system. With the exception of the second harvest in 1 yr (1992), soil slotting did not lead to significant improvements in dry matter yield or nitrogen offtake. The absence of slotting effects on those parameters suggested that grass root growth or function did not benefit from the amount, type or persistence of soil pore space formed by the aerator. Supply of a proportion of the applied nitrogen in the form of slurry did not alter the patterns of yield or nitrogen recovery between or within traffic systems.