New Zealand soil Olsen P levels

The majority of soil data is from pastoral farms, with much smaller numbers of samples from arable or horticulture land use. This is simply a reflection of the relative land areas in these land-use activities.

As a single data set, the national median value of Olsen P showed some fluctuations over time, but little change, with a small increase across the overall time period.

The graphs are reporting median levels of Olsen P, and (in grey) the 25^th to 75^th percentile range.

Figure 1: Time series of the national median value of Olsen P across all farm and soil types and regions.

Olsen P levels by farm type

We have analysed the data for individual land uses.

Land use categories such as horticulture or orchard cover a wide range of crops with differing nutrient needs. This means that the results from orchard and horticulture land uses show a very wide range of Olsen P results (Figures 2 and 3).

Figure 2: Time series of the national median value of Olsen P across all soil types for horticultural properties.

Figure 3: Time series of the national median value of Olsen P across all soil types for orchards.

Figure 4: Time series of the national median value of Olsen P across all soil types for arable and fodder crop farms.

The bulk of the data reflects tests from pastoral soils (dairy and dry stock farming). The national median values across all soil types are at the high end of target soil Olsen P values for dairy farms on Ash or Sedimentary soils, (20-40, with 30-40 for high producing farms) shown in Figure 5.

The median value for drystock farms across all soil types, is trending toward the middle of target soil Olsen P values for Ash or Sedimentary soils, (20-30), shown in Figure 6. There is some variability attributable to differences in soil type and production intensity.

Figure 5: Time series of the national median value of Olsen P across all soil types for dairy farms.

Figure 6: Time series of the national median value of Olsen P across all soil types for dry stock farms.

Olsen P levels by soil type

When broken down to specific soil types, the higher Olsen P target ranges for Pumice and Organic soils are reflected in the results for those soils (Figures 7 to 10 respectively).

Figure 7: Time series of the national median value of Olsen P across all farm types for Ash soil.

Figure 8: Time series of the national median value of Olsen P across all farm types for Sedimentary soil.

Figure 9: Time series of the national median value of Olsen P across all farm types for Pumice soil.

Figure 10: Time series of the national median value of Olsen P across all farm types for Peat soil.

Variations to the target range

Figures 11 to 18 include the target range for the optimum pasture response.

The target ranges apply to representative farm systems across a combination of farm and soil types. While the vast majority of soil sample results fall within the target range, there remains a considerable 'scatter' of results above and below this range.

Where Olsen P values exceed the target range for the particular farm production system, steps should be taken to understand the circumstances and best ways to ensure any excessive phosphorus use is reduced.

Dairy

Where milksolids production is near the average for the supply area, best economic return is provided by maintenance of soil Olsen P levels in the target range for near maximum pasture production (20-30 for Ash and Sedimentary soils, 35-45 for Pumice and Peat soils).

If milksolids production is in the top 25% for the supply area, or it is intended to increase to this level, increasing soil Olsen P to 30-40 for Ash and Sedimentary soils and to 45-55 for Pumice and Peat soils, may be justified where a response in pasture production is obtained.

Figure 11: Yearly time series of the median level of Olsen P across Ash soils for Dairy farms nationally.	Figure 12: Yearly time series of the median level of Olsen P across Sedimentary soils for Dairy Farms nationally.
Figure 13: Yearly time series of the median level of Olsen P across Pumice soils for Dairy farms nationally.	Figure 14: Yearly time series of the median level of Olsen P across Peat soils for Dairy Farms nationally.

Drystock

Figure 15: Yearly time series of the median level of Olsen P across Ash soils for Drystock farms, nationally.	Figure 16: Yearly time series of the median level of Olsen P across Sediment soils for Drystock farms, nationally.
Figure 17: Yearly time series of the median level of Olsen P across Pumice soils for Drystock farms, nationally.	Figure 18: Yearly time series of the median level of Olsen P across Peat soils for Drystock farms, nationally.

Arable and Fodder Crops

Figure 19: Yearly time series of the median level of Olsen P across Ash soils for Arable and Fodder Crop farms, nationally.	Figure 20: Yearly time series of the median level of Olsen P across Sedimentary soils for Arable and Fodder Crop farms, nationally.
Figure 21: Yearly time series of the median level of Olsen P across Pumice soils for Arable and Fodder Crop farms, nationally.	Figure 22: Yearly time series of the median level of Olsen P across Peat soils for Arable and Fodder Crop farms, nationally.

Horticulture

Figure 23: Yearly time series of the median level of Olsen P across Ash soils for Horticulture properties, nationally.	Figure 24: Yearly time series of the median level of Olsen P across Sedimentary soils for Horticulture properties, nationally.
Figure 25: Yearly time series of the median level of Olsen P across Pumice soils for Horticulture properties, nationally.	Figure 26: Yearly time series of the median level of Olsen P across Peat soils for Horticulture properties, nationally.

Orchard

Figure 26: Yearly time series of the median level of Olsen P across Ash soils for Orchards, nationally.	Figure 28: Yearly time series of the median level of Olsen P across Sediment soils for Orchards, nationally.
Figure 29: Yearly time series of the median level of Olsen P across Pumice soils for Orchards, nationally.	Figure 30: Yearly time series of the median level of Olsen P across Peat soils for Orchards, nationally.