Scale matters: one size does not fit all

Understanding scale is vital for interpreting soil maps

Soil information from national to farm scale

Soil surveys are conducted at various scales, depending on the purpose of mapping: from paddock/farm-scale (1:500 to 1:20,000) to catchment/regional (1:20,000 to 1:100,000) to strategic overview & broad planning maps (1:100,000 to 1:250,000). The table below shows some examples of map applications and associated common scale ranges.

Guidance on cartographic map scale, based on application or land use for conventional soil maps (after Manderson & Palmer 2006; Lynn et al. 2009)

Selected applications	Indicative smallest area of interest to identify on map (ha)	Indicative map scale range
Horticulture, market gardens, viticulture, precision farming	0.001 to 0.1	1:500 to 1:5,000
Pastoral, arable	0.1 to 1	1:5,000 to 1:15,000
Pastoral, extensive pastoral, catchment studies, forestry	1 to 10	1:15,000 to 1:50,000
Catchment planning, regional studies	10 to 40	1:50,000 to 1;100,000
Strategic overview, broad planning	40 to 250	1:100,000 to 1:250,000

Manderson A. & Palmer A. (2006): Soil information for agricultural decision making: a New Zealand perspective. Soil Use and Management, 22, 393-400. https://doi.org/10.1111/j.1475-2743.2006.00048.x

Lynn I.H., Manderson A.K., Page M.J., Harmsworth G.R., Eyles G.O., Douglas G.B., Mackay A.D., Newsome P.J.F. (2009): Land use capability survey handbook – a New Zealand handbook for the classification of land. 3rd edn. Hamilton: AgResearch; Lincoln: Landcare Research; Lower Hutt: GNS Science. 163 p. https://doi.org/10.7931/DL1MG6

The survey scale directly impacts on the level of effort required, and survey cost. You can get a feeling for the effort required at the various cartographic scale below.

Survey site density guidance provided for conventional soil mapping

Cartographic scale	Area per one observation			No. of observations per unit area
	total of 1 observation per 1 cm2 of mapped area	total of 1 observation per 2 cm2 of mapped area	total of 1 observation per 4 cm2 of mapped area	total of 1 observation per 1 cm2 of mapped area	total of 1 observation per 2 cm2 of mapped area	total of 1 observation per 4 cm2 of mapped area
	ha/observation			observations/ha
1:500	0.0025	0.005	0.01	400	200	100
1:1,000	0.01	0.02	0.04	100	50	25
1:5,000	0.25	0.5	1	4	2	1
1:10,000	1	2	4	1	0.5	0.25
1:15,000	2.25	4.5	9	0.44	0.22	0.11
1:20,000	4	8	16	0.25	0.13	0.06
1:50,000	25	50	100	0.04	0.02	0.01
1:100,000	100	200	400	0.01	0.005	0.025
1:250,000	625	1250	2500	0.0016	0.0008	0.0004

Scale determines applications

Soils information at the farm scale

Widespread implementation of farm nutrient budgets and farm environmental management plans (FEMP) greatly increases the need for accurate farm-scale soil information. And yet very few NZ farmers can currently source existing soil information at a scale and reliability that is suitable for farm management purposes (Manderson 2003; Manderson & Palmer 2006). How can this pressing issue be addressed?

Calls have repeatedly been made for a national effort for providing farm-scale soil information (Manderson & Palmer 2006, Carrick et al. 2014). The table below depicts a ‘strawman’ protocol for farmland (<15°) with multiple land use potential, with the various sources of soils information indicated. Available soils information is classed into four quality levels, from ‘poor’ to ‘premium’. It is suggested that policymakers, industry bodies, and catchment community groups can determine the most appropriate quality level required or acceptable given the context in which the soil information will be used.

Freely available S-map data – at a nominal scale of between 1:30,000 and 1:50,000 – may be considered suitable as the base level for most situations. In areas of high soil variability, a detailed 1: 10,000 soil map may be linked to the S-map factsheets to provide better information, whereas areas with intensive land use in highly sensitive catchments may require a higher level of soils information, such as detailed soil survey and site-specific measurements of key soil attributes.

‘Strawman’ proposed national standard for farm-scale soil mapping in farmland (<15°) with multiple land use potential, in relation to key land management issues. For each quality-level examples of baseline soil information are provided, but others could be added as the protocol is developed. Source: Carrick et al. (2014).

Farm soil map quality level	Irrigation management		Nutrient, soil, and sediment management			Farm dairy effluent
	Design	Monitoring	N and P leaching	P, sediment, and bacteria runoff	Compaction / pugging	Design	Monitoring
Poor	Fundament soil layer (LRIS 2014)	Visual / tactile inspection of soil moisture	Farm-scale LUC-based nutrient budgets	LUC maps 1:50,000	Farmer awareness of area of land that pug, compact or pond after heavy rain	Fundamental Soil layer	Visual / tactile inspection of soil moisture
	Coarse scale published historical soil data (e.g., Kear et al. 1967)	Surface ponding	OVERSEER inputs from Fundamental Soil Layer	Classification or top maps to identify poorly drained and artificially drained areas, sloping areas, and location of waterways and water bodies		Coarse scale published historical data	Surface ponding
	“Rules of thumb” soil attribute data	Subsurface drains are flowing indication excess irrigation				“Rules of thumb” soil attribute data	Subsurface drains are flowing indicating excess irrigation
Basic	S-map derived map and factsheets (medium or high soil map quality confidence)	Handheld soil moisture meter	S-map derived map and factsheets (medium or high soil map quality confidence)	10- and 25-m DEM-based landform, waterway and ‘connectivity to waterway’ maps	S-map derived map and factsheets (medium or high soil map quality confidence)	S-map derived map and factsheets (medium or high soil map quality confidence)	Handheld soil moisture meter
	Field check of key soil types by consultant	Desktop soil water balance scheduling	OVERSEER soil type inputs from S-map	On-farm identification of critical source areas	Farm-scale LUC map	Field check of key soil types by consultant	Desktop soil water balance scheduling
			On-farm monitoring topsoil fertility status	Farm-scale LUC map	On-farm visual soil assessment (VSA guideline)	10- and 25-m DEM-based landform, waterway and ‘connectivity to waterway’ maps
Good	Farm-scale soil map (e.g., 1:10,000 scale with high soil variability)	On-farm soil moisture sensor on dominant soil types	Farm-scale soil map (e.g., 1:10,000 scale in high soil variability)	10- and 25-m DEM-based landform, waterway and ‘connectivity to waterway’ maps	Farm-scale LUC map	Farm-scale soil map (e.g., 1:10,000 scale in high soil variability)	On-farm soil moisture sensor on dominant soil types
	Field analysis of key attributes for main soil types matched to S-map fact sheets	Real-time soil water balance scheduling for each soil / management zone	Field analysis of key attributes for main soil types matched to S-map fact sheets	On-farm identification and monitoring of critical source areas	Regular on-farm visual assessment (VSA guideline)	Field analysis of key attributes for main soil types	Real-time soil water balance scheduling for each soil / management zone
		On-farm visual soil assessment (VSA guideline)	On-farm monitoring topsoil fertility status	Farm-scale LUC maps		Soil factsheets for each soil from S-map	On-farm visual soil assessment (VSA guideline)
Premium	Farm-scale soil map with high confidence (e.g., ± 10% variance in area of each soil type)	Replicated on-farm soil moisture sensors for each soil type	Farm-scale soil map with high confidence (e.g., ± 10% variance in soil type area)	< 25-m DEM-based landform, waterway and ‘connectivity to waterway’ maps	Farm-scale soil or LUC map	Farm-scale soil map with high confidence (e.g., ± 10% variance in area of each soil type)
	Statistically replicated field and laboratory measurements of attributes for main soil types using accredited methods	Real-time soil water balance scheduling for each soil / management zone	Statistically replicated attributes measurements for main soil types	On-farm identification and monitoring of critical source areas	Regular on-farm visual soil assessment (VSA guidelines)	Statistically replicated attributes measurements for main soil types	Replicated on-farm soil moisture sensors for each soil type
		On-farm visual soil assessment (VSA guideline)	On-farm monitoring topsoil fertility status.	On-farm monitoring of temporally dynamic soil attributes (e.g., infiltration rate, microporosity, topsoil fertility)	On-farm monitoring of temporally dynamic soil attributes (e.g., infiltration rate, microporosity, topsoil fertility)		Real-time soil water balance scheduling for each soil / management zone
		On-farm monitoring of temporally dynamic soil attributes (e.g., infiltration rate, microporosity)	On-farm targeted leachate monitoring to validate models (e.g., lysimeters)				On-farm monitoring of temporally dynamic soil attributes (e.g., infiltration rate, microporosity, topsoil fertility, visual soil assessment)

References:

Manderson, A.K. 2003. Farming from the ground up: The use of land resource information as a basis for planning farm sustainability in New Zealand. PhD thesis, Massey University, Palmerston North, New Zealand. https://mro.massey.ac.nz/handle/10179/2010

Manderson A. & Palmer A. (2006): Soil information for agricultural decision making: a New Zealand perspective. Soil Use and Management, 22, 393-400. https://doi.org/10.1111/j.1475-2743.2006.00048.x

Carrick et al. (2014): S-map @ the farm scale? Towards a national protocol for soil mapping for farm nutrient budgets? http://flrc.massey.ac.nz/workshops/14/Manuscripts/Paper_Carrick_2_2014.pdf

Scale matters: one size does not fit all

Understanding scale is vital for interpreting soil maps

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