24  NZSC Family and Sibling

Levels 4 and 5 of the NZSC, the Family and Sibling, provide useful summaries of key whole-profile parameters.

24.1 NZSC Family

24.1.1 Soil Profile Material

The soil profile material concept is a brief summary of the overall character of the profile, in particular its mineral and stone content and major erosional/depositional origin. Some information on the likely range of bulk density values is implicit.

Table 24.1 below defines the available classes and should be used as a key. For Organic soils, skip the ‘M’ codes and start at Sl. Choose one code only per profile. Applying the key accurately requires familiarity with the major NZSC Diagnostic Criteria. Links to glossary definitions are provided below, but the source material (Hewitt 2010) should also be consulted.

Table 24.1: Soil Profile Material

Code	Name	Description
Mf	Fragmental	Rock fragments with minimal fine earth from within 20 cm to > 60 cm depth
Ml	Lithic	Other soils with a coherent- or shattered lithic contact within 45 cm
Mp	Paralithic	Other soils with a paralithic contact within 45 cm
Mt	Tephric	Other soils with at least 30 cm of tephric soil material within 100 cm
Mr	Rounded-stony	Other soils with ≥ 35% by volume rounded or sub-rounded rock fragments from within 45 cm to > 100 cm.
Ma	Angular-stony	Other soils with ≥ 35% by volume angular or sub-angular rock fragments from within 45 cm to > 100 cm.
Mm	Moderately deep on rock	Other soils with a lithic or paralithic contact at < 100 cm.
Mg	Moderately deep on rock fragments	Other soils with ≥ 35% by volume rounded or sub-rounded rock fragments from within 45-90 cm, extending continuously to 100 cm with a cumulative thickness of ≥ 50 cm (unless over rock).
Md	Stoneless	Other soils with weighted average < 3% rock fragments by volume in the top 100 cm.
Ms	Stony	Other mineral soils.
Sl	Organic-lithic	Organic soils with a coherent- or shattered lithic contact within 45 cm.
Sp	Organic-paralithic	Other organic soils with a paralithic contact within 45 cm.
Sd	Organic-deep	Other organic soils with continuous peat throughout the top 100 cm.
So	Organic-other	Other organic soils.

Profile material class places restrictions on other parts of the family and sibling definition. These are discussed as they arise below.

24.1.2 Rock class

Table 24.2: NZSC Lithology

Code	Name
Cb	Carbonaceous Rock (Coal)
Sq	Soft Quartzitic Sediments
Hq	Hard Quartzitic Sediments
Sm	Soft mudstone
Ss	Soft sandstone
Hm	Hard mudstone
Hs	Hard sandstone
Tm	Tuffaceous mudstone
Ts	Tuffaceous sandstone
Sc	Schist
Ls	Soft calcareous
Li	Hard calcareous
Ma	Marble
Rh	Rhyolite
Ig	Ignimbrite
An	Andesite
Ba	Basalt
Gr	Granite and Gneiss
Di	Diorite
Ga	Gabbro
Fe	Iron Sands

Note 24.1: What are soft rocks?

‘Soft’ rocks in this context can at most be broken readily with a light hammer blow, and can be scraped and peeled by a pocket knife. ‘Hard’ rocks can at best be scratched with a knife but not scraped or peeled, and require a firm hammer blow to crack (Lynn and Crippen 1991, p. 11).

24.1.2.1 Rock class of stone and bedrock

Rock class of in-profile stone and of bedrock (where encountered) uses the lithology codes in Table 24.2, with specific restrictions around how they are applied to the whole profile. These are:

• Md soils effectively have no stone or bedrock. Leave the property undefined.
• Rock class is only defined in reference to stones > 2 mm and bedrock (where encountered within 100 cm). The rock class of the fine earth fraction is accounted for below.
• The ‘deep and stoneless’ classes (Mt, Md, So and Sd) can still have a total of < 3% by volume stones in the top 100 cm.
• Include pumice in rock class only where pumice strength is more than ‘extremely weak’ (Lynn and Crippen 1991, p. 10) - i.e., it can only be broken by hand with difficulty. If the pumice’s lithology is uncertain, use the dominant lithology of the probable volcano of origin (e.g. Rh in the Taupō Volcanic Centre and An around Taranaki).
• Where in-profile stone lithology contrasts with bedrock lithology, two codes separated by ‘/’ can be used e.g. Sc/Gw.
• Where two lithologies are close to co-dominant in a stony profile, two codes separated by ‘+’ can be used e.g. An+Rh.
• More complicated combinations are not allowed, e.g. no An+Rh/Gw.

24.1.2.2 Rock class of fines

The same rock class codes in Table 24.2 can be applied to report the dominant lithology of the fine earth (< 2 mm) fraction of the full profile. Again, some restrictions apply:

• Sd soils and Mf soils effectively have no fine earth fraction. Leave the property undefined.
• Where a lithological discontinuity exists in the profile, two codes separated by ‘/’ can be used e.g. Sc/Gw.
• Where two lithologies are close to co-dominant, two codes separated by ‘+’ can be used e.g. An+Rh.
• More complicated combinations are not allowed, e.g. no An+Rh/Sm+Ss/Gw.

24.1.3 Family texture class

The family texture class describes the dominant character of the top 60 cm, or to the profile material class-defining rock or gravel layer contact if that is shallower. Use the codes in Table 24.3. Note that 18% organic carbon corresponds to approximately 30% organic matter.

Table 24.3: Family texture classes

Code	Name	Organic Carbon %	Silt %	Clay %
c	Clayey	< 18	-	≥ 35
s	Sandy	< 18	< 40	< 8
l	Loamy	< 18	< 40	≥ 8 - < 35
z	Silty	< 18	≥ 40	≥ 8 - < 35
p	Peaty	≥ 18	-	-

24.1.4 Permeability class

This class estimates the permeability of the top 100 cm in units of mm/hr. Use the codes in Table 24.4 and follow the rules in Figure 24.1 to assign permeability class.

Table 24.4: Family permeability classes

Code	Name	Description
s	Slow	< 4 mm/hr
m	Moderate	≥ 4 - < 72 mm/hr
r	Rapid	≥ 72 mm/hr

Follow the flowchart to assign family permeability class:

%%{ init: { 'flowchart': { 'curve': 'stepAfter' } } }%%
graph TD
  A["Identify the uppermost horizon with the slowest permeability, or rock above 100 cm. This is Horizon X."]-->B["Does Horizon X have > 30 cm of contrasting permeability above?"]
  B--->|Yes|C("Use **m/s**, **r/s**, **r/m**")
  B--> |No|D["Does the profile have a horizon ≥ 20 cm thick below Horizon X with a different permeability class?"]
  D-->|Yes|E("Use **s/m**, **s/r** or **m/r**")
  D-->|No|F("Use **s**, **m**, or **r**")
  

Figure 24.1: NZSC Family permeability flowchart

Some additional rules apply for particular soil profile material classes:

• For soils with an S* profile material class, assess family permeability class from 20-100 cm or to rock (i.e. ignore the surface 20 cm).
• Soils with profile material class Ml or Mp and any soil with an M root barrier must use m/s or r/s.
  • Exception: Ml with F barrier can’t be */s.

24.1.5 Parent material origin

Parent material origin (PMO) is the final defining factor of the soil Family. It describes how soil parent materials have arrived at the point of observation. Allowable codes are listed in Table 24.5.

Multiple modes may have operated in different parts of the soil profile. Up to two may be recorded at Family level, in order of their occurrence down-profile (e.g. Tp/Fl). If PMO has been recorded at horizon level and more than two have been identified, the dominant two must be chosen on the basis of their cumulative thickness. Cumulative thicknesses <20 cm should be ignored unless the layers include a significant pedological feature (e.g. a pan).

Table 24.5: Parent material origin

Code	Name	Description
An	Anthropic	Deposits made by the direct actions of humans, including truncation, mixing, or deposition.
Cl	Colluvium	Weathered soil and rock material mantling slopes that has been transported primarily by gravity and sheet wash.
Fl	Alluvium	Sediments that have been deposited by streams, rivers and other running water.
Gl	Glacial till	Poorly stratified, poorly sorted rock fragments, sand and mud, surface or near-surface deposits resulting from the transportation by and deposition from ice or meltwater from beneath or in close proximity to glacial ice.
Lc	Lacustrine	Formed in and around lake beds; comprising extremely fine sediment deposited under very low-flow freshwater conditions.
Mr	Marine	Unconsolidated sediments saturated by brackish or saline water.
Lh	Lahar	A flow of volcanic material, both ash and coarser products, mixed with water; often caused by the spilling over of a crater lake. Also used to describe the mounds formed on volcanic ring-plains where lahars stop.
Tp	Tephra	A general term for all solid (rather than molten) materials ejected from a volcano during an eruption: includes boulders, lapilli and ash.
Li	Litter	Partly or fully decomposed forest litter, equal to or greater than 30 cm depth that is not almost continually saturated in the natural state (F and H horizons).
Pt	Peat	Partly decomposed plant remains in a water-saturated environment, such as a bog
Lo	Loess	A blanket deposit of silt-sized particles (0.002–0.06 mm diameter); usually carried by wind from dry riverbeds or outwash plains during glacial and post-glacial periods.
Sa	Aeolian sand	Wind-deposited sand-sized particles (0.05–2.0 mm diameter), i.e. dune sand.
Rw	Highly Weathered Rock	Highly to completely weathered rock, formed in place by chemical weathering.
Rx	Rock	In situ unweathered to moderately weathered lithified geologic material comprising one or more minerals showing rock structure.
Uk	Unknown	Origin cannot be determined with certainty.

24.2 NZSC Sibling

These codes help define level 5 of the NZSC, the soil sibling.

24.2.1 Soil Depth

Soil depth from a sibling perspective is the depth to where digging becomes difficult, e.g.

• A horizon with ≥ 35% stones by volume (V or X functional horizons, Section 21.2)
• A soft- or hard-rock surface (M rooting barrier, Section 24.3.2)
• A shattered-lithic contact (F rooting barrier, Section 24.3.2)
• A pan (Q functional horizons, Section 21.2.1.4)
• Firm strength with massive or coarse structure (*Cf functional horizons, Section 21.2.2)

Use the codes in Table 24.6 to assign a depth class to a profile.

Table 24.6: Sibling depth classes

Code	Name	Description
d	Deep	> 100 cm
md	Moderately deep	≥ 45 - < 100 cm
s	Shallow	≥ 20 - < 45 cm
vs	Very Shallow	< 20 cm

24.2.2 Topsoil stoniness

Topsoil stoniness assesses the amount of rock fragments (as % by volume) in the top 20 cm of the soil profile, including those resting on the soil surface.

A weighted average calculation is required if the top 20 cm contains more than one horizon. As an example,

Horizon Thickness (cm)	Relevant thickness (cm)	Horizon proportion of top 20 cm	Horizon stone (%)	Weighted average topsoil stone (%)
12	12	0.6	15	9
20	8	0.4	25	10
				19

Use the codes in Table 24.7 to assign stoniness.

Table 24.7: Sibling topsoil stoniness classes

Code	Name	Description
1	Stoneless	< 1 %
2	Slightly stony	≥ 1 - < 5 %
3	Moderately stony	≥ 5 - < 35 %
4	Very stony	≥ 35 %

24.2.3 Sibling texture classes

These classes are assessed over the top 100 cm, or to rock or gravel layer contact if those are shallower. Note that this is deeper than the family-level texture control section. The following rules apply:

• Mf, Mr, Ma, Ml, and Mp soils must match their family texture code (c, s, l, or z).
• Sl and Sp soils must use one of Tp, Tc, Tl or Ts to align with their family texture code of p.
• Sd soils must use Tp.
• Upper and lower textures can be defined for other soil profile classes, but only the dominant two are recorded. Both contributing layers must be at least 20 cm thick.
• When there are more than two texture layers within the control section, then the texture profile is identified according to the uppermost texture contrast.
  • For example, if a sandy horizon occurs at 80 cm depth and a clayey horizon overlays a silty horizon at 40 cm, then the texture contrast is reported as clayey over silty (c/z) and the sandy layer is ignored.
• Silty and loamy horizons are not considered contrasting and can be added together where contiguous.
  • For example, a profile with silty (0–15 cm) over loamy (15–25 cm) over sandy (25-90 cm) is considered to have a contrasting upper layer of 25 cm, and is identified as silty over sandy (z/s). The texture specification uses the uppermost of the silty or loamy layers together with the lower layer.
• Skeletal horizons (k) may only be used for Ms, Mm, Mt and So soils. The skeletal material must be non-tephric.
• Skeletal horizons in moderately deep gravelly soils (Mg) are ignored in favour of describing the overlying fine sediments.

Use the codes in Table 24.8 to assign sibling level texture class(es).

Table 24.8: Sibling texture classes

Code	Name	Organic Carbon %	Silt %	Clay %	Stone %
k	Skeletal				≥ 35
Tp	Peat or litter	≥ 30			< 35
Tc	Clayey peat	≥ 18 - < 30		≥ 35	< 35
Tl	Loamy peat	≥ 18 - < 30		≥ 8 - < 35	< 35
Ts	Sandy peat	≥ 18 - < 30	< 40	< 8	< 35
c	Clayey	< 18		≥ 35	< 35
s	Sandy	< 18	< 40	< 8	< 35
l	Loamy	< 18	< 40	≥ 8 - < 35	< 35
z	Silty	< 18	≥ 40	< 3	< 35

24.2.4 Drainage

Profile drainage is determined from horizon depths and per-horizon drainage ratings completed according to Section 22.3.

Table 24.9: Profile drainage rules

Code	Name	Description
VP	Very Poor	Profiles with very poorly drained horizons starting <10cm from the land surface
PO	Poor	Profiles with poorly drained horizons starting <30cm from the land surface
IP	Imperfect	Profiles with poorly drained horizons starting 30-60cm from the land surface, or Profiles with imperfectly drained horizons starting <30cm from the land surface
MW	Moderately Well	Profiles with moderately well-drained horizons starting <90cm from the surface, or Profiles with poorly-drained horizons starting 60-90cm from the surface, or Profiles with imperfectly drained horizons starting 30-90cm from the surface
WE	Well	All horizons starting within 90cm of the surface are well-drained.

Workers classifying drainage for NZSC Sibling construction have no need to subdivide within those profile ratings. For other types of work e.g. agricultural suitability assessment, it may be useful to recognise subgroups – e.g. for a deep-rooted, wetness-intolerant crop, there’s a difference between a profile that is at its worst imperfectly drained in the top 1 m, vs one that is dominantly imperfectly drained but has poor drainage below 60 cm.

24.2.4.1 Natural vs Artificial drainage

Profile drainage is often modified by human activity. Many of these modifications require ongoing maintenance. Use the codes in Table 24.10 to signify the degree of drainage modification.

Table 24.10: Profile drainage modification level

Code	Name	Description
N	Natural	No evidence of human impacts on the local drainage regime
M	Minor	Drainage regime passively altered by e.g. conversion to or from forest; or ambiguous evidence of any human impacts beyond clearing
A	Major	Clear evidence of directed human alteration to the drainage regime e.g. drain or dam construction adjacent to site, flow diversions, infill, levelling or contouring works

24.3 Rooting barriers

Rooting barriers may be identified in some soils, potentially determining their Family and Sibling codes. Use N to confirm no barrier.

24.3.1 Horizon barriers

Table 24.11: Horizon-specific root barriers (Lilburne et al. 2021)

Code	Name	Description
C	Chemical	Chemical toxicity affecting pasture growth, that is not readily alleviated through management. Not salinity.
D	Densely packed gravels	Has very dense particle packing (4) Requires a V*d FH Requires s in family permeability
G	Extremely gravelly	Has at least 70% gravels by volume and a sandy matrix, or is a very stony horizon with a clean sand matrix Requires ≥ 85% sand and FH with VAl, XA, or Xx
L	Extremely dense	Penetration resistance of >3000 kpa, or packing density of > 1.85 mg/m3 Requires FH with d, YC, VLc, VAc , or z Requires s in family permeability
P	Pan - continuous	Meets the diagnostic criteria for any NZSC pan Requires FH with: Q, YC, VAc, VAd, LCf, VLc, VLd Requires NZSC to mention pan status (cemented, placic, ironstone, duric, ortstein subgroups) Requires s in family permeability
Pd	Pan - discontinuous	Meets the diagnostic criteria for any NZSC pan, but is discontinuous within 100 cm Requires FH with: Q, YC, VAc, VAd, LCf, VLc, VLd Requires NZSC to highlight pan status (e.g. cemented, placic, ironstone, duric, ortstein groups and subgroups) Requires s in family permeability
S	Clean sand	Requires ≥ 85% sand and FH with Aa or Al – can be S but not V or X

Notes

These barriers must be connected to a soil horizon, signified with a number, e.g. P(3) for a pan in Horizon 3.

24.3.2 Other barriers

Table 24.12: Whole-profile root barriers (Lilburne et al. 2021)

Code	Name	Description
A	Anoxic	Air-filled porosity < 5%
F	Fractured rock	Lithic contact present within top 100 cm Fractures are ≥ 30 cm apart
M	Massive Rock	Lithic or paralithic contact within top 100 cm If fractures are present, they are > 30 cm apart

Notes

Many water tables are not anoxic and many plant species’ roots are able to live under oxygenated water at least for short periods. Anoxic water tables generally occur in loamy or clayey horizons, are tightly packed, or have significant organic matter (> 1% carbon).

Hewitt AE 2010. New zealand soil classification (v. 3.0). 3rd ed. Wellington, New Zealand: Manaaki Whenua Press. https://doi.org/10.7931/DL1-LRSS-1-2010

Lilburne LR, Webb TH, Hewitt AE, Lynn IH, De Pauw B, Vickers S 2021. S-map manual - data definitions. Lincoln, Canterbury, New Zealand.

Lynn IH, Crippen TF 1991. Rock type classification for the new zealand land resource inventory. [Internet]. Lower Hutt, New Zealand: DSIR Land Resources. https://doi.org/10.7931/DL1-DLRSR-10