Effects of soil fertility and compaction on root dynamics in a perennial ryegrass-white clover pasture

Pasture root mass and production were measured in two experiments in the Manawatu region. The first examined the effects of nitrogen (N) inputs and soil phosphorus (P) status over one year (2008/9) and the second examined the interacting effects of soil P status and artificial soil compaction over one year (2011/12). Root mass was measured by soil core sampling and root production was measured by an in-growth core technique, to 120 mm depth. Over most of the two periods studied there were no significant differences in root mass or production between treatments. However, higher N+P fertility resulted in 20% lower root mass but 32% higher root production during September and November 2008. In 2011/12, soil compaction reduced root production by approximately 22% year-round. Increased soil P fertility did not compensate for this effect. Fertility effects on root growth seem more influenced by N than P in this system.