Originally published:1988-06 as Special publication / Tussock Grasslands and Mountain Lands Institute ; no. 31 by Lincoln College. Tussock Grasslands and Mountain Lands Institute.
Pasture phosphorus requirements to replace on farm losses through animals and soil were calculated for a range of soil sets, and summarised for major soil groups economic farm classes and provinces.
Predicted responses to P fertiliser on South Island "unimproved" soils
were similar for 33 major soil groups out of 401Five further groups were
almost similar in response. Olsen P data collected recently were similar
to an earlier set (1977-79), and corresponded to relative pasture yields of
top farmers within each group of soils. There were differences between the
MWD estimates of stocking rates and census data of 578,000 stock units for
the South Island and 100,000 for the North Island with however more
variability between provincial totals (average of 1,031,000 +- 600,000 for
the North Island and 519,000 +- 400,000 for the South Island).
For the South Island, if Olsen P levels were below 10.2 for low producing
pastures and 11.0 for high producing pastures, more P was needed for first
year maintenance than for long-term at average farmer stocking rates. At
top farmer stocking rates below an Olsen P of 12.4 more P was needed in the
first year than for long-term on low producing pastures, while on soils
with high producing pastures only one major soil group needed more P in the
first year than for long-term. At potential farmer stocking rates all
major soil groups with high producing pastures needed more P in the first
year than for long-term maintenance, while all soils with high producing
pastures with an Olsen P < 19.5 needed more P in the first year.
Less P is needed for first year maintenance than for long-term at average
and top farmer stocking rates for almost all the economic farm classes of
the South Island. Unimproved soils of the North Island appear to be low in
Olsen P and there are only two major soil groups where less P is needed for
the first year than for long-term at average and top farmer stocking rates
Olsen P levels of improved soils in the North Island were not available.
Olsen P levels of "unimproved" soils in the South Island were correlated
with P retention levels, demonstrating an important relationship (effect)
of P retention on their P status.
Pasture utilisation (and relative yields) for North Island low and high
producing grasslands were similar, but there were lower levels on low
producing than on high producing pastures for the South Island. Although
efficiency of P use (kgP/s.u.) decreases rapidly at relative yields
approaching the potential farmer stocking rates, on some soils, e.g. South
Island high country yellow grey earths, efficiency of P use is better than
for some North Island soils at average farmer stocking rates where soil P
losses are high.[Show full abstract]
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