Soils of Mohaka-Aropaoanui Area, North Island, New Zealand

SOILS OF MOHAKA-AROPAOANUI AREA, NORTH ISLAND, NEW ZEALAND

W.C. RIJKSE Soil Bureau, Lower Hutt

Part of N.Z. SOIL SURVEY REPORT 55 New Zealand Soil Bureau

Department of Scientific and Industrial Research R. B. MILLER Wellington, New Zealand 1980 Dfft:ICTOA CONTENTS

Page Summary 5 Introduction 5 Parent materials 6 Topography 8 Climate 8 Vegetation 9 Soils 9 Recent soils 11 Yellow-brown sands 12 Yellow-brown pumice soils and related steepland soils 12 Podzolised yellow-brown pumice soils and related steepland soils 12 Composite yellow-brown pumice soils on yellow-brown loams 13 Composite yellow-brown pumice soils on yellow-grey earths 13 Steepland soils related to rendzinas 13 Yellow-brown earths and related steepland soils 14 Steepland soils related to intergrades between yellow-grey earths and yellow-brown earths 14 Steepland soils related to yellow-grey earths 14 Soil limitations for potential pastoral use 15 Soil limitations for commercial forestry 16 Soil limitations for cropping 18 Value for food production 20 Conclusion 21 References 22 Extended legend Explanatory notes 23 Index to soils 24 FIGURE 1 Location maps 4 TABLES 1 Soil-forming tephra showers 7 2 Legend of soil taxonomic units arranged pedologically 9 4

1'0 r'-Rualcituri

PACIFIC

OCEAN

SEA.

111•e

Figure 1 Location maps 5

SUMMARY

Soils of the Mohaka-~..ropaoanui area are classified (NZ Soil Bureau 1968) and discussed in this report. Their parent materials, topography, climate and natural vegetation are described and the soils are classified according to their limitations for pastoral uses, commercial forestry, cropping and value for food production in terms of the Town and Country Planning Act 1977. Distribution of the soils is shown on the accompanying soil map at a scale of 1:100 OOO. An extended l~gend to the map summarises some soil and agricultural properties of the soil mapping units.

INTRODUCTION

N.Z. Soil Bureau Map 112, which accompanies this report, is based on previously published work (Pullar and Ayson 1965) and on unpublished district soil surveys generalised in the "General Survey of the soi is of North Island" (N.Z. Soil Bureau 1954).

To compile the current map, soil boundaries and soil classification were revised following field observations made in 1970. Aerial photo interpretation was used to insert more detail in areas of steep land and to adjust the position of soil boundaries in relation to roads, streams, etc.

However, a detailed examination of the soils was not made and, apart from the recent soils of the river flats, the soil names given in the "Genera! Survey of the soils of North Island" were used for the current map. These are "set" names and may in fact include several soil series, so that the soils in this area may differ in some respects from similarly named soils in other parts of the country. For example, classifications for land use for specific soils in this area may differ from classifications for similarly named soils elsewhere.

The total area of soils covered by this survey is 118 400 ha (Fig. 1). 6

PARENT MATERIALS

Parent.materials of the soils of the Mohaka-Aropaoanui area consist of a wide range of materials which may be broadly divided into 4 groups: (1) Sedimentary rocks (2) Tephra* beds (3) Alluvium (4) Wind-blown sand

Sedimenta:r>y rocks consist of a wide variety of materials including mudstone, siltstone, strongly to moderately consolidated fine or coarse sandstone, limestone and conglomerate. They form a complex pattern as shown on the Geological Map of New Zealand, sheet 8 (Grindley 1960) , but are generally covered by tephra and are soil-forming only on hilly and steep slopes.

Teph:r>a beds originating from the Taupo-Rotorua region mantle the landscape. Although erosion has removed most of the tephra from the steeper country, much remains on rolling and hilly land to form parent materials of the soils. The tephra which are important to soil formation have been described by Vucetich and Pullar (1964) and Pullar et al (1973) • A brief summary supplemented by field observations is given in Table 1.

Beneath the oldest tephra listed in the table (Waiohau Ash), loess and older tephra such as the andesitic Tongariro Ash and the Kawakawa Formation (a.22,000 years B.P.) occur in some stable areas.

Alluvium derived by erosion of tephra and sedimentary rocks has been deposited on the flood plains of the main rivers and streams. It occurs near the lower reaches of the wairoa River, the Mohaka River, the Moeangiangi River and the Aropaoanui River.

Wind-bloum sand occurs in small areas along the coastline south of Wairoa and near Waipatiki Beach.

* Tephra: A collective term for all elastic material erupted through the air from a volcanic crater.

-.J -.J

of of

to to

or or

upper upper

yellow yellow

also also

often often

band band

material material

sand sand loose, loose,

coarse coarse

a a

topsoil, topsoil,

highly highly

within within

brown brown

highly highly

loose loose

usually usually

pale pale

is is

Ash, Ash,

the the

layers: layers:

fine fine

with with

few few greasy greasy

dark dark

brown brown

in in

sand, sand,

layer layer

lapilli, lapilli,

mottling mottling

lapilli, lapilli,

Rotoma Rotoma

accumulation accumulation

with with

silty silty

yellow yellow

staining staining

strong strong

compact compact

rhyolite rhyolite

and and

fibrous fibrous

tephra, tephra,

distinct distinct

sand sand

(glints) (glints)

lower lower

to to

soft soft

sorted sorted

iron iron

2 2

to to

loam loam

Characteristics Characteristics

angular angular

AREA AREA

iron iron

and and

grey grey brown brown

fine fine

rounded rounded

of of

beneath beneath

grey grey

brown brown

and and

loam, loam,

olive, olive,

is is sandy sandy

or or evenly evenly

grains grains

to to

staining staining

large large

much much

yellow yellow vesicular vesicular

ash ash

light light

layer layer

iron iron

above above

the the

sandy sandy strong strong

dark dark soft soft

uneven-sized uneven-sized White White

Yellowish Yellowish Black Black White White Pale Pale

uniform, uniform,

Consists Consists with with

vesicular vesicular vesicular vesicular

White White

brown brown

TINIROTO-WAIROA TINIROTO-WAIROA

cm) cm)

5 5

THE THE

to to

deposits deposits

IN IN

thin thin

(10-15 (10-15

(1 (1

cm) cm)

to to

parts parts

patchy patchy

recognise recognise

deposits deposits

Occurrence Occurrence

SHOWERS SHOWERS

thick thick

deposits deposits

(10-15 (10-15

and and

to to

deposits deposits

cm) cm)

TEPHRA TEPHRA

(40 (40

thin thin

northwestern northwestern

(30-50 (30-50

Very Very

difficult difficult in in

Very Very

Thin Thin

Moderately Moderately

Very Very

SOIL-FORMING SOIL-FORMING

age age

1950) 1950)

235 235

200 200

70 70

60 60

80 80

1: 1:

Region Region

± ±

Formation Formation

± ±

Region Region

± ± ± ±

Valley Valley

Region Region Region Region

origin origin

Pumice Pumice

Tarawera Tarawera

before before

930 930

TABLE TABLE

7330 7330

3270 3270

1760 1760 1800 1800 1900 1900

and and

11250 11250

Taupo Taupo

Mt Mt

Rotorua Rotorua

Hatepe Hatepe

Taupo Taupo

Approximate Approximate

(Yrs (Yrs

Taupo Taupo

Waimihia Waimihia

named named

asht asht

Lapillit Lapillit

Formation: Formation:

Ash Ash

Lapilli Lapilli

Ash Ash

Pumice: Pumice:

Taupo Taupo

Lapilli* Lapilli*

Collectively Collectively

* *

RotOl.1\a RotOl.1\a

Waiohau Waiohau

t t

Taupo Taupo

Upper Upper

Waimihia Waimihia

Waimihia Waimihia Hatepe Hatepe shower shower

Taupo Taupo

Waimihia Waimihia

Pumice* Pumice*

Kaharoa Kaharoa Tephra Tephra 8

TOPOGRAPHY

Topography is an important factor in determining the soil pattern in a landscape that has been mantled with tephra, for this determines the erosion pattern and thickness of the surviving tephra cover. The result of erosion is a complex pattern of soils formed from tephra, from the underlying rock, and from mixtures of tephra and underlying rock materials.

Four topographical units can be distinguished in the Mohaka-Aropaoanui area:

1. Flat, and flat to easy rolling land. This is almost entirely restricted to the alluvial plains and some of the river terraces. There is little erosion, and on the flat terraces the tephra cover is intact in most places.

2. Easy rolling and rolling land with most slopes under 12° and many 0 slopes around s • Little erosion occurs on these slopes and the tephra cover is almost completely intact.

3. Moderately steep and moderately steep to steeg land with most slopes 0 0 between 20 and 30 and many slopes around 24 • The tephra has been removed from the steeper slopes by erosion, but is nearly intact on ridges and stable slopes. Soils on this land are mapped as hill soils and are more variable than those on flat and rolling land.

4. Steep and very steep land with most slopes between 30° and 45°, and 0 many slopes around 35 • Tephra has been removed or partly removed by erosion in most places except on ridges in northern parts of the area. Soils on this land are mapped as steepland soils and tend to be very variable.

CLIMATE

Mohaka-Aropaoanui area has a warm moist climate, with an annual rainfall of 1000 to 1500 mm near the coast and up to 2000 mm in northern districts. Near the coast summers are warm with day temperatures occasionally rising above 32°c; rain is unevenly distributed and unreliable in spring and summer; winter temperatures are moderate and winter rainfalls are highest.

Further inland the climate is cooler and wetter, with very heavy rain at times from the south and south-east, and an annual rainfall of about 1500 to 2000 mm (Robertson 1959). 9

VEGETATION

Pre~European vegetation in this area occurred in two vegetation belts. Ser.uh and fernlands dominated the coastal alluvial soils west of Wairoa and south of Mohaka River. A belt of podocarp-mixed hardwood forest occupied most of the country between the coast and the northern part of the Mohaka-Aropaoanui area (Holloway 1959) • At present most of the area is in pasture, except on steep slopes and valley sides where scrub and pockets of podocarp forest remain.

SOILS

The soils of Mohaka-Aropaoanui area are grouped on the basis of the New Zealand Genetic Soil Classification (N.Z. Soil Bureau 1968) in Table 2. The properties of each of the soil groups that occurs in the area are summarised in the text, and are set out in more detail in the extended legend, together with the ratings of soil limitations for potential pastoral use, commercial forestry, cropping, and value for food production.

TABLE 2: LEGEND OF SOIL TAXONOMIC UNITS ARRANGED PEDOLOGICALLY

RECENT SOILS from alluvium derived from tephra and sedimentary rocks rapidly accumulating non-gleyed Waipaoa series Esk series slowly accumulating non-gleyed Waihirere series moderately to strongly gleyed Awamate series Makauri series YELLOW-BROWN SANDS from wind-blown sand non-gleyed Opoutama series strongly gleyed Whakaki series 10

YELLOW-BROWN PUMICE SOILS AND RELATED STEEPLAND SOILS from Taupo Pumice on Waimihia Formation on weathered rhyolitic tephra Gisborne series Mohaka series Te Pohue series Tuai series Tiniroto series from very thin Taupo Pumice on waimihia Formation on mudstone, siltstone or hard fine sandstone Hangaroa series Waihua series

PODZOLISED YELLOW-BROWN PUMICE SOILS AND RELATED STEEPLAND SOILS from very thin Kaharoa Ash on Taupo Pumice on Waimihia Formation on weathered rhyolitic tephra and loess Ruakituri series Waikaremoana series COMPOSITE YELLOW-BROWN PUMICE SOILS ON YELLOW-BROWN LOAMS from thin Waimihia Formation on sandstone Tutira series COMPOSITE YELLOW-BROWN PUMICE SOILS ON YELLOW-GREY EARTHS from thin Taupo Pumice on loess on sandstone or siltstone Rissington series STEEPLAND SOILS RELATED TO RENDZINAS from limestone Te Mata series YELLOW-BROWN EARTHS AND RELATED STEEPLAND SOILS from patchy thin tephra on siltstone Pakarae series from hard fine sandstone Mangamahu series from hard fine sandstone and mudstone Whangamomona series from siltstone Mahoenui series from coarse hard sandstone Moumahaki series from sandstone and conglomerate Mokamoka series from mudstone and limestone Pahiatua series from hard fine sandstone Wharerata series 11

STEEPLAND SOILS RELATED TO INTERGRADES BETWEEN YELLOW-GREY EARTHS AND YELLOW-BROWN EARTHS from siltstone Taihape series from hard fine sandstone Whangaehu series from very thin patchy tephra on hard fine sandstone Waitaha series STEEPLAND SOILS RELATED TO YELLOW-GREY EARTHS from siltstone Kidnappers series from muddy sandstone and conglomerate Tangoio series

Recent soils

Recent soils occur on the active flood plains of the rivers and have been separated according to their position with respect to the river channel and to the amount of tephra in the soil.

Very low-lying flats occur next to the river, flood frequently, and receive relatively rapid additions of fresh alluvium. The intervals between successive additions are usually too short for deep soil profile development to take place, and flood deposits on old topsoils can be clearly recognised (Waipaoa series, Esk series).

As the river levees flood rarely to infrequently for short periods only, there is generally enough time between floods for accumulation of organic matter to darken each increment of fresh alluvium and for worms to incorporate it in the underlying soil. Thus topsails on levees are deep and soil profiles more developed than those on the lower flats. These soils are mapped as the well-drained Waihirere series which occurs on the river levees, and the imperfectly to moderately well-drained Awamate series which occurs further away from the river. These three series are formed from alluvium derived mainly from sedimentary rocks and tephra.

In a few smaller valleys west of Wairoa, recent soils are also formed on alluvium derived mainly from sedimentary rock and tephra, but they are flooded infrequently and topsoil textures are generally heavier than those of the Waihirere and Awamate series. These are the poorly drained Makauri series, with shallow dark greyish-brown and grey topsoils.

The recent soils support excellent pastures and the well-drained types, such as those of the Waihirere series, have a good potential for cropping and horticulture (Pullar and Ayson 1965). 12

Yellow-brown sands

Yellow-brown sands occur in a narrow strip along the coastline south of wairoa and at Waipatiki Beach. They are formed mainly on a complex of low rolling dunes (Opoutama series) with most slopes under 12° and on a few small plains (Whakaki series). The two series have been mapped as a soil association (a compound mapping unit consisting of a pattern of geographically associated soil units) • The soils of the dunes have distinct horizons with coarse sandy textures, and are structureless. They are somewhat excessively drained and susceptible to wind erosion especially where topsoil horizons are thin. Rapid drainage and erosion are moderate limitations for pastoral use and commercial forestry. Soils of the sand plains have a high groundwater table and require artificial drainage to maintain good pastures, but are not suited to commercial forestry. Yellow-brown pumice soils and related steepland soils

Yellow-brown pumice soils have been subdivided according to the kind and thickness of the tephra beds from which they are derived, e.g., thin sandy Taupo Pumice on Waimihia Formation on weathered older tephra (Gisborne series, Mohaka series, Te Pohue series), thick sandy Taupo Pumice on Waimihia Formation (Tiniroto series, Tuai series). These soils have generally deep, very friable topsails with weakly developed structure and loose, coarse textured subsoils that drain readily yet retain sufficient moisture for plant growth. Physically they are well suited for pastoral uses, but many of them are deficient in plant nutrients. They are well suited for commercial forestry but shallowness, weakly developed soil structure, rolling and hilly topography and low natural nutrients limit their use for cropping.

Steepland soils related to yellow-brown pumice soils (Hangaroa series, Waihua series) have a thin layer of tephra overlying sedimentary rocks. Although the steep slopes severely limit pastoral use of these soils, the tephra cover is thin enough for pasture plants to obtain nutrients from the underlying parent materials which are higher in natural nutrients. Podzolised yellow-brown pumice soils and related steepland soils

Podozolised yellow-brown pumice soils (Ruakituri series} occur in high rainfall areas at elevations above 500 metres. The soils are similar to the yellow-brown pumice soils but have a discontinuous iron pan, the result of downward movement and deposition of iron induced by higher rainfall, lower temperatures, and a mor-forming vegetation. The podzolised yellow-brown pumice soils need regular topdressings to maintain good pastures. Strong leaching, high elevation, and inaccessibility are severe limitations for pastoral use and cropping, and moderate limitations for commercial forestry. 13

Steepland soils related to podzolised yellow-brown pumice soils (Waikaremoana series) occur in the extreme north-west of the survey area. They have a cover of tephra on ridges and stable slopes and a thin layer of tephra on steep slopes. The risk of erosion is high if the vegetation is disturbed. . Slopes are mostly very steep and the soils are not recommended for pastoral use for this reason and because of strong leaching, high elevation and poor access. At present the soils support indigenous forest. Composite yellow~brown pumice soils on yellow-brown loams

These soils (Tutira series) occur near the coastline where Wairnihia Formation (20-30 cm) overlies older weathered tephra and loess on sandstone or siltstone. They have black to dark brown sandy loam to loamy sand topsails overlying yellowish-brown to dark yellowish-brown sandy loam or sand with many Waimihia Lapilli. This rests on pale yellowish-brown firm sandy loam with mottles increasing with depth, indicating that the soils are moderately well drained. Yellowish-brown sandstone or siltstone occurs at 40 to 100 cm depth, depending on slope. The composite yellow-brown pumice soils on yellow-brown loams support good pastures if topdressed adequately with potassic superphosphate. They are suited to commercial forestry except on hilly slopes where hard sandstone lies near the surface.

Composite yellow-brown pumice soils on yellow-grey earths

Composite yellow-brown pumice soils on yellow-grey earths are mapped in small areas in the south-west of the area, south of the Moeangiangi River. The soils (Rissington series) occur under low (1000-1400 mm) annual rainfall, formed from thin tephra over loess and sandstone or siltstone. Subsoils show features of yellow-grey earths including gammation, mottling and concretions.

The soils have very dark greyish-brown friable sandy loam topsails on dark yellowish-brown very friable sandy loam. The structure in the subsoil ranges from moderately to weakly developed blocky.

The soils are only moderately suited to pastoral uses because of moderate slip and gully erosion and summer droughts. Potassic super phosphate is needed to maintain good pastures. Erosion potential and very firm to hard subsoils are severe limitations for commercial forestry. Steepland soils related to rendzinas

Steepland soils related to rendzinas (Te Mata series) occur in the south-west of the area, mapped in association with Taihape steepland soils, on steep and very steep slopes with limestone outcrops.

Te Mata series has dark grey sandy loam topsails and light yellow sandy loam subsoils overlying sandy limestone. 14

Steep and very steep slopes, low rainfall and somewhat excessive natural drainage resulting in summer droughts, are severe limitations for pastoral use and commercial forestry.

Yellow~brown earths and related steepland soils

Yellow-brown earths occur in southern parts of the area (Pakarae series) • They are characterised by friable dark brown topsoils with moderately developed nut structure and yellowish-brown subsoils with weakly developed blocky structure. The soils are moderately well drained and have higher natural nutrient levels than the yellow-brown pumice soils.

When topdressed adequately, they support excellent pastures. Although suited to commercial forestry, the soils show some deep-seated slumping. Their hilly slopes are a severe limitation for cropping.

Steepland soils related to yellow-brown earths (Mangamahu series, Whangamomona series, Mahoenui series, Moumahaki series, Mokamoka series, Pahiatua series and Wharerata series) are extensive throughout the Mohaka Aropaoanui area. They have been subdivided according to parent material (Table 2) and kind and intensity of erosion (extended legend). Soil profiles show similar physical characteristics to those of the yellow-brown earths, but they are shallower, generally overlying unweathered rock. Extensive slip erosion occurs on most of these steepland soils and is a moderate to severe limitation for pastoral use and commercial forestry. Steepland soils related to intergrades between yellow-grey earths and yellow-brown earths

These soils (Taihape series, Whangaehu series, Waitaha series) are similar to steepland soils related to yellow-brown earth3but occur under lower (1000-1250 mm) annual rainfall. They have moderate nutrient levels and have good potential for pastoral use if slopes are stabilised and soil conservation techniques are applied. Their steep slopes are a severe limitation for commercial forestry and cropping. Steepland soils related to yellow-grey earths

Steepland soils related to yellow-grey earths (Kidnappers series, Tangoio series) occur in thesouth·westof the area, especially the coastline, under low (750-1150 mm) annual rainfall. are moderately well drained, generally having friable shallow topsails and firm subsoils.

Steep and very steep slopes, shallow soil profiles, low annual rainfall, and moderate to severe erosion are severe limitations for pastoral use, commercial forestry and cropping. 15

SOIL LIMITATIONS FOR POTENTIAL PASTORAL USES

A classification of soils according to their limitations for potential pastoral use (Gibbs 1963} is described below. The class for each soil is included in the extended legend.

CLASS 1 Soils of flat and rolling land with slight soil limitations for pastoral use

lA Limitations of nutrients Waipaoa soils Waihirere soils Esk soils Gisborne soils Tutira soils lB Limitations of drainage and nutrients Awamate soils Makauri soils Whakaki soils Mohaka soils

CLASS 2 Soils of flat and rolling land with moderate soil limitations for pastoral use

2A Limitations of insufficient moisture and, to a lesser extent, nutrients Opoutama soils

2B Limitations of texture, structure, or elevation Te Pohue soils Tuai soils Tiniroto soils

CLASS 3 Soils of flat and rolling land with severe soil limitations for pastoral use

3A) 3B) Not present in this survey 3C) 3D Limitations of elevation with cool wet climate Ruakituri soils

CLASS 4 Soils of hilly and steep land with slight to moderate soil limitations for pastoral use

Limitations of nutrients Gisborne hill soils Tuai hill soils 16

Tiniroto hill soils Tutira hill soils

CLASS 5 Soils of hilly and steep land with moderate to severe soil limitations for pastoral use

SA Limitations of insufficient or excessive moisture Rissington hill soils SB Limitations of erosion Te Pohue hill soils Hangaroa steepland soils Waihua steepland soils Ruakituri hill soils Pakarae hill soils Mangamahu steepland soils Mahoenui steepland soils Pahiatua steepland soils Taihape steepland soils Whangaehu steepland soils Waitaha steepland soils

CLASS 6 Soils of hilly and steep land with severe to very severe soil limitations for pastoral use 6A Limitations of nutrients and erosion Te Mata soils Whangamomona steepland soils Moumahaki steepland soils Wharerata steepland soils Kidnappers steepland soils Tangoio steepland soils 6B Limitations of rapid soil erosion Waikaremoana steepland soils Mokamoka steepland soils

SOIL LIMITATIONS FOR COMMERCIAL FORESTRY

A classification for each soil according to limitations for commercial forestry after Cutler (1968) is described below. Classes are included in the extended legend.

CLASS 1 Soils of flat, rolling and hilly land with no, or slight limitations for forest growth. Soils of this class are suitable for a wide range of native and exotic trees for production and amenity uses. 17

lA No significant limitations for forest growth waihirere soils Gisborne soils and hill soils Te Pohue soils and hill soils Tuai soils and hill soils Tiniroto soils and hill soils Tutira soils and hill soils lB Soils with limitations of excessive or poor drainage Pakarae hill soils

CLASS 2 Soils of flat, rolling and hilly land with moderate limitations for forest growth. Soils of this class are suitable for a restricted range of exotic species; they are not suitable for Northern Hemisphere temperate hardwoods.

2A Not present in this survey 2B Limitations of coarse sandy textures and nutrients Esk soils Opoutama soils 2C Limitations of elevation (range 600 to 900 m) Ruakituri soils and hill soils

CLASS 3 Soils of flat, rolling and hilly land with severe limitations for forest growth. The range of exotic species is severely restricted and only species such as Pinus contorta, P.muricata, P.syZvestris and BetuZa penduZa are suitable.

3A) Not present 3B) in this survey 3C Limitations of poor natural drainage and flooding Waipaoa soils Awamate soils Makauri soils Whakaki soils Mohaka soils Rissington hill soils CLASS 4 Soils of steep land with slight to moderate limitations for forest growth. Limitations are those of steep and very steep slopes with shallow profiles, elevation and erosion.

Hangaroa steepland soils Waihua steepland soils Mahoenui steepland soils Pahiatua steepland soils Wharerata steepland soils Whangaehu steepland soils Waitaha steepland soils Kidnappers steepland soils Tangoio steepland soils 18

CLASS 5 Soils of steep land with moderate to severe limitations for forest growth. Soils in this class are suitable only for protection forest species.

Waikaremoana steepland soils Te Mata steepland soils Mangamahu steepland soils Whangamomona steepland soils Moumahaki steepland soils Mokamoka steepland soils Taihape steepland soils

LIMITATIONS FOR CROPPING

Crops are more sensitive to small variations in soil properties than pasture plants and a certain soil may have slight limitations for pastoral production but severe limitations for a given crop. Although there is variation in the ideal growing environment for different crops, most crops require relatively flat areas with deep, well drained, fertile soils that are friable and, ideally, have strongly to moderately developed structure at least in the upper horizons. In the Mohaka-Aropaoanui area where nearly all soils are used for pastoral production, there are only small areas ideally suited for intensive crop production. The following classification is a guide only to li:rnitationsfor intensive cropping (excluding fodder cropping) of the various soils. The classification follows Cutler (1967) and the class for each soil is included in the extended legend.

CLASS 1 Soils of flat and easy rolling land with slight limitations for crop production. These soils are suitable for market gardening and other intensive cropping.

lA Soils most suitable for cropping with limitations that can be easily overcome Waihirere soils Esk soils lB Not present in this survey le Soils which require drainage before they can be successfully cropped Awamate soils Makauri soils

CLASS 2 Soils of flat to rolling land with moderate limitations for crop production. These soils are not as versatile as Class 1 but are generally suitable for crops such as cereals and some field crops. 2A Not present in this survey 19

2B Soils with limitations of texture and nutrients, including some shallow and poorly drained soils Whakaki soils Mohaka soils Te Pohue soils 2C Soils with limitations of slope Gisborne soils Tuai soils Tiniroto soils Tutira soils

CLASS 3 Soils of flat and rolling land with severe limitations for crop production. These soils are generally unsuitable for crop production. The limitations are physical (shallowness, instability} and environmental (high elevation, high rainfall) and are thus not likely to be modified by known techniques.

3A Soils with limitations of slope, sheet erosion and stoniness Waipaoa soils Opoutama soils 3B Soils with limitations of high elevation or poor access Ruakituri soils

CLASS 4 Soils of hilly and steep land unsuitable for crop production. Steepness of slope is a very severe limitation for cropping and although some fodder cropping is carried out on hill soils, it is unlikely that crop production will ever be of any commercial importance.

Gisborne hill soils Te Pohue hill soils Tuai hill soils Tiniroto hill soils Hangaroa steepland soils Waihua steepland soils Ruakituri hill soils waikaremoana steepland soils Tutira hill soils Rissington hill soils Te Mata steepland soils Pakarae hill soils Mangamahu steepland soils Whangamomona steepland soils Mahoenui steepland soils Moumahaki steepland soils Mokamoka steepland soils Pahiatua steepland soils Wharerata steepland soils Taihape steepland soils Whangaehu steepland soils 20

waitaha steepland soils Kidnappers steepland soils Tangoio steepland soils

VALUE FOR FOOD PRODUCTION

The classification for food production follows Cowie (1974) and is worded in terms of the Town and Country Planning Act 1977. The class for each soil is included in the extended legend.

CLASS 1 Soils of iligh actual or potential value for food production

lA Soils of high actual value for food production. These are soils with minimal limitations of nutrients. Waihirere soils Gisborne soils Esk soils lB Soils of high potential value for food production. Soil limitations are those of moderate to poor natural drainage. Awamate soils Makauri soils Tutira soils

CLASS 2 Soils of moderate actual or potential value for food production. Soil limitations are those of frequent flooding~ poor natural drainage, rolling to hilly slopes, and moderate soil erosion.

Waipaoa soils Whakaki soils Gisborne hill soils Mohaka soils Te Pohue soils Tuai soils and hill soils Tiniroto soils and hill soils Tutira hill soils

CLASS 3 Soils of low actual or potential value for food production. Limitations are those of steep and very steep slopes, cold climate, very strong leaching, low moisture-holding capacity or severe erosion.

Opoutama soils Te Pohue hill soils 21

Hangaroa steepland soi.ls Waihua steepland soils Ruakituri soils and hill soils Waikaremoana steepland soils Rissington hill soils Te Mata steepland soils Pakarae hill soils Mangamahu steepland soils Whangamomona steepland soils Mahoenui steepland soils Moumahaki steepland soils Mokamoka steepland soils Pahiatua steepland soils Wharerata steepland soils Taihape steepland soils Whangaehu steepland soils Waitaha steepland soils Kidnappers steepland soils Tangoio steepland soils

CONCLUSION

The classifications of soil limitations for pastoral uses, commercial forestry, cropping and value for food production in terms of the Town and Country Planning Act 1977, show that:

1. The greatest potential for intensive land uses such as cropping (including horticulture) lies in the recent soils of Wairoa Valley.

2. Composite yellow-brown pumice soils on yellow-brown loams, yellow brown earths and yellow-brown pumice soils are suited to pastoral uses and commercial forestry. Their main limitations are steep slopes with present or potential erosion, and also low natural nutrient status.

3. Podzolised yellow-brown pumice soils have moderate to severe limitations for most land uses. They are therefore rated low in value for food production. 22

REFERENCES

COWIE, J.D. 1974: Soils of Palmerston North City and Environs, New Zealand. N.Z. Soil Su:r>vey Report 24

CUTLER, E.J.B. 1967: Soils of the Otago Region. Pp.35-51 National 0 - in Resources Survey, Part V - Otago Region. Compiled by Town and Country Planning Branch, Ministry of Works, Wellington. 572p.

FAO 1974: Pp.20-3 in "FAO-Unesco Soil Map of the World. 1:5 OOO OOO. Vol.l Legend." Unesco, Paris. 59 p.

GIBBS, H.S. 1968: Soil classification for land use. Pp.124-30 in N.Z. Soil Bureau Bulletin 26(1) 142p.

GRINDLEY, G.W. 1960: Sheet 8 - Taupo. "Geological Map of New Zealand 1:250 OOO". Department of Scientific and Industrial Research, Wellington, New Zealand.

HOLLOWAY, J.T. 1959: Pre-European vegetation of New Zealand. Pp.23-4 in "A descriptive atlas of New Zealand". A.H. McLintock (Ed.). Government Printer, Wellington.

N.Z. SOIL BUREAU 1954: General survey of the soils of North Island, New Zealand. N.Z. Soil Bu:r>eau Bulletin 5 286p.

N.Z. SOIL BUREAU 1968: Soils of New Zealand, Part 1. N.Z. Soil Bu:r>eau Bulletin 26(1) 142p.

PULLAR, W.A.; AYSON, E.C. 1965: Soils and agriculture of Wairoa Valley, Hawke's Bay, N.Z. N.Z. Soil Bureau Report 2/1965 35p.

PULLAR, W.A.; BIRRELL,K.S.; HEINE, J.C. 1973: Named tephras and tephra formations occurring in the central North Island with notes on derived soils and buried paleosols. N.Z. Jou:r>nal of Geology and Geophysics 16(3) 197-518

ROBERTSON, N.G. 1959: The climate of New Zealand. Pp.19-22 in "A descriptive atlas of New Zealand", A.H. McLintock (Ed.), Government Printer, Wellington.

TAYLOR, N.H.; POHLEN, I.J. 1970: Soil survey method. N.Z. Soil Bureau Bulletin 25 242p.

VUCETICH, C.G.; PULLAR, W.A. 1964: The stratigraphy of Holocene Ash in the Rotorua and Gisborne Districts. N.Z. Geological Survey Bulletin n.s. ?3 43-63. 23

EXTENDED LEGEND EXPLANATORY NOTES

Soil mapping unit

On flat and rolling slopes the basic soil mapping units ideally consist of a collection of soils with uniform site and profile characteristics. In practice, however, the mapping unit may have up to 10-15% of its area occupied by inclusions of other soils with dissimilar profiles.

On hilly and steep slopes there is a very great variation in soil profiles and the soils are shown as hiLt -00,{1)., or -OZeepi.a.nd ~o,{1).,. The profile variation depends on the stability of the slope, position on the slope, aspect, and variations in parent materials. Parent material

Parent material is the weathered material from which the soil is formed and, for purposes of agriculture, is not examined much below a depth of a metre. Topography

Average slopes of the soil mapping units are indicated in classes of landforms according to compound slopes {Taylor and Pohlen 1970):

Flat and flat to gently undulating Easy rolling (most slopes under 5 ) Rolling (most slopes under 12°) Moderately steep (most slopes under 23 0 , many between 12 and 23°) Moderately steep to steep (most slopes under 30°, many slopes between 18 and 30 0 ) Steep (many slopes between 30 0 and 38 0 ) Very steep (many slopes of 40° and over) Brief description of representative soil profile The profile is formally described horizon by horizon starting from the surface. Horizon characters include horizon designation (A, B, C etc.), thickness (cm), dominant moist colour (Munsell Soil Colour Charts notation), texture (proportion sand, silt and clay), consistence (friable, firm), and structure. Further information recorded in the profile description includes mottling and occurrence of tephra and clay skins.

The modal or most frequently occurring profile within the soil mapping unit is selected for each description, which includes only the more 24

important morphological features. Terms used follow Taylor and Pohlen (1970) except horizon notations which follow FAO (1974) • Natural drainage (class) This refers to the overall natural drainage which indicates the rate at which water is removed from the soil and the time for which the soil is at field capacity. The classes include very poorly drained, poorly drained, imperfectly drained, moderately well drained, well drained, somewhat excessively drained and excessively drained (Taylor and Pohlen 1970) • The class refers to the natural drainage under original conditions and also indicates the overall drainage the soil would revert to if artificial drainage is not maintained. If the drains are well maintained then overall drainage class could be upgraded by one or more classes. Present land uses These are listed as at 1970 for the whole area of each soil mapping unit. Notes

Included are notes on soil erosion, some notes on specific land use, comparison with similar soil series, and likely responses to pastoral topdressing. Area Soil areas were obtained by cutting and weighing the soil map, and were rounded where possible to the nearest 50 ha. Where two soils are mapped as an association (e.g. Gi + Mo) the total area of the mapping unit is split by arbitrarily assigning 60% to the dominant (first named) soil and 40% to the subdominant. INDEX TO SOILS

Page Page Awamate 11 Taihape 14 Esk 11 Tangoio 14 Gisborne 12 Te Mata 13 Hangaroa 12 Te Pohue 12 Kidnappers 14 Tiniroto 12 Mahoenui 14 Tuai 12 Makauri 11 Tutira 13 Mangamahu 14 Waihirere 11 Moh aka 12 Waihua 12 Mokamoka 14 Waikaremoana 13 Moumahaki 14 Waipaoa 11 Opoutama 12 Waitaha 14 Pahiatua 14 Whakaki 12 Pakarae 14 Whangaehu 14 Rissington 13 Whangamomona 14 Ruakituri 12 Wharerata 14