Fertiliser recycling does occur

Such long term residual benefit of fertiliser is testament that fertiliser applied to pasture is commonly rarely wasted, provided it corrects known soil deficiencies.

Results from this trial also provides further evidence that nutrients supplied via fertiliser can recycle through pasture for many years perhaps because unlike cropping removal rates of nutrients via produce in a grazing system are actually quite low.

Results from this trial also refute claims that nutrients like phosphorus supplied via superphosphate and other similar products quickly bind up in the soil and become unavailable to plants.

Clearly a lot of recycling of these nutrients can occur.

This trial began in 1987 on Ambrose and Lisa Doolan’s property “Toorawandi”, on a hard-setting gravelly, stony soil, although basalt derived. A previous owner had told us (from my DPI days) that we had chosen a hard bit of country and not very productive.   

Soil tests showed it to be however quite reasonable in phosphorus but very low in sulphur.

Results from the first 15 years of the trial showed SF45 (40 per cent sulphur, 5.6 per cent available phosphorus) performed similar to annual applications of single super (11 per cent sulphur, 8.6 per cent available phosphorus).

Typical fertiliser applied plots yielded as much as five times more than nil fertiliser ones.

That fertilised areas remain so productive for long after non-application is partly explained by sulphur being the main deficiency at this site.

Not a lot of applied phosphorus has corrected its lower deficiency level with recycling probably explaining why phosphorus run down has been slow. 

Sulphur deficiency correction on a clay loam or clay soil can also cycle effectively for many years with commonly only slow rundown.

Lighter soils and higher rainfall years can be responsible for more rapid loss of sulphur but that has not occurred at this site.

Assessments some years ago showed soil health, organic matter, water infiltration rates, groundcover and soil biological activity were far higher on fertilised plots compared with non-fertilised ones. Clearly this research shows that addressing soil fertility issues in pastures does not necessarily involve a great regular application of fertiliser.

When fertiliser was applied it was either 100kg/ha singe superphosphate or SF45. The research strongly supports that correcting soil deficiencies is not only good for productivity but also when in conjunction with good management for natural resource management (NRM) outcomes like better quality soil and reduced risk of erosion. Native perennial grasses with annual legumes that include naturalised clovers (hairsfoot clover, narrow leaf clover, ball clover, burr medic) and sub clover are the main makeup of the pasture on the trial site.

One should not assume periodic fertiliser application is applicable for all pasture situations.

As has been the case in this study, monitoring fertility by soil analysis from accredited laboratories correlates well with the need or otherwise for fertiliser. 

Next week. City versus farm environmental management.