Phosphate management of peat/organic soils under pasture: (a) Seven key facts you need to know
1. New Zealand has over 200,000 ha of peat (aka organic) soils, mostly in the Hauraki Plains and the Waituna catchment in Southland. Most have been drained and underdairying.
2. The use of soluble P fertiliser like superphosphate and DAP on these soils is disastrous . Most of the soluble P is lost in surface run-off from dry soil after rainfall; the rest by leaching.
3. Changing to dicalcic, whether it be true imported DCP (around 16%P), or the NZ-made low-spec dicalcic-lime (about 4% P, made by incubating super about 45:55 with Aglime) DO NOT stop these losses.
4. This is because the P in DCP is very rapidly (1-3 days) converted back to soluble P in NZ’s acid soils. Like all soils in NZ, peat/organic soils are usually very acid. So once the DCP is quickly turned back to water-soluble P, it is right back to being very susceptible to runoff and leaching.
5. Peat/organic soils contain little of the clays such as allophane that help in binding and reducing P runoff and leaching from other soils, especially those produced from volcanic ash or very highly weathered greywacke.
6. Peat holds little moisture, and following a dry spell, suffers huge losses in runoff of soluble and particulate P when rain does come, as the surface soil has become temporarily hydrophobic. Then, when the hydrophobicity has been overcome, more P gets leached.
7. If you are still hungry for your rebate on super, please get your super incubated by Quinfert for at least 2 weeks with the correct ratio of allophanic clay (not with lime) prior to application. This coverts the water-soluble P to non-leaching P that is loosely-bound (and extractable from for a period) allophane clay. This in turn promotes an accumulation of more organic C and N, sequestering tonnes more soil C.
Ring Quinfert on 0800QUINFERT or Bert Quin direct on 021 427 572 for more details about “Super-All” 0-8-0-8. Currently available at $355/t + GST @ McPhersons, Te Poi.