Results!

Soil mineral nitrogen differences in the systems will relate to differences in mineralisation, leaching, nitrogen application (fertiliser/legumes) and removal. Surface soil nitrogen was generally maintained at a higher level in the No Till paddocks across all measurements (Table 8). This may reflect different dynamics of mineralisation (eg. more before-sowing with cultivation, more in-season with No-Till).

In root zone measurements none of the paddocks were especially high in nitrogen (Table 9), indicating a lack of chemical or physical limitation, but also potentially a limit to yield in higher rainfall years. The stability of the sowing measurements was interesting – there was very little change from year to year despite harvest measurements often showing evidence of use during the crop phase. This may reflect mineralisation of soil organic matter buffering any depletion by crop offtake, rather than fertiliser nitrogen being sufficient.

The subsoil was often very low in nitrogen (Table 10). The Till paddocks were often (not always) an exception to this, containing high nitrogen at sowing at Sea Lake, Yaapeet and Culgoa.

Table 8. Soil mineral nitrogen 0-10cm at sowing in 2006-8.

Table 9. Soil mineral nitrogen 10-70cm at sowing and harvest in 2006-8.

Table 10. Soil mineral nitrogen 70-100cm at sowing and harvest in 2006-8.