151 Brown Soils 1

Lecture 9.

Brown Soils

Widespread throughout NZ

Rainfall greater than 1000mm: relatively even distribution

(except for Sandy Brown and Stony Brown Soils)

Moisture deficit in summer not pronounced

151 Brown Soils 2

Brown Soils

Formerly known as yellow brown earths

or brown earths (Molloy)

Parent materials commonly loess, colluvium, alluvium, gravels

Parent rocks usually greywacke-argillite, schist, granite, mudstone, sandstone

Quartzo-feldspathic minerals (quartz, feldspar and rock fragments).

Common on river and marine terraces, hill country and steepland.

151 Brown Soils 3

Brown Soils

Photo 9.1

Levin and Lake Horowhenua

Photo 9.2

151 Brown Soils 4

Brown Soils

physical properties

Simple “brown” appearance

Crumb, granule and nut structures

Well-moderately well drained

Horizon sequence Ap/ABw/Bw1/Bw2

Moderate dry bulk density:

- Topsoils 0.9 – 1.2 t m-3

- Subsoil 1.1 – 1.4 t m-3

Moderate macroporosity (8-15 %)

RAWC high in topsoils, moderate in subsoils

TAWC moderate - high (15-25 %)

Moderate hydraulic conductivity

151 Brown Soils 5

Brown Soils Ashhurst stony

silt loam

Otaki River and

Hautere Plains

Photo 1.2

Photo 9.3

Photo 9.4

151 Brown Soils 6

Brown Soils

Chemical Properties

pH and BS% decrease as rainfall increases (leaching)

pH and BS% decrease down the profile (contrast with Pallic Soils)

P and K reserves vary with parent material.

151 Brown Soils 7

Brown Soils

Chemical Properties

CEC varies with weathering:

- High country: weak weathering; chlorite and illite clay; 15% clay; low CEC.

Photo 2.1 Photo 2.2 Rakaia Valley Hurunui soil

151 Brown Soils 8

Brown Soils

Chemical Properties

- Southern SI: weak- moderate weathering; illite and vermiculite clay; 20 % clay; high CEC

Photo 9.5 NZSSS

Photo 9.6 NZSSS

Southland, near Gore

Waikiwi silt loam

151 Brown Soils 9

Brown Soils

Chemical Properties

- Central NZ: Moderate weathering; vermiculite clay; 30% clay; high CEC

Photo 9.7 NZSSS NE of Porirua, Wellington Photo 9.8

NZSSS Belmont silt loam

151 Brown Soils 10

Brown Soils

Chemical Properties

- Northern NI: Strong weathering: kandite clays; 50-80 % clay; low CEC.

Photo 9.9 NZSSS

Puhoi District, Northland.

Whangaripo silty clay loam

Photo 9.10

NZSSS

Southland: intensive heavy lamb production; dairying but

environmental problems emerging; cropping; cut flowers and

bulbs.

High Country: extensive pastoralism, but widespread

degradation and problems with pastoral leases

Central NZ: Sheep and beef, dairying and some horticulture

Northern NI: Dairy, sheep and beef on fertile sites, forestry on

weathered soils.

Hill and steepland: Breeding and trading sheep and beef,

forestry.

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Brown Soils

Land use

Please Read Molloy Chapter 13 p193-

203 and p137