1

A9 Testing soil and improving fertilityThis activity tells you how to start building soil fertility (B4.4). It has several simple tests as the first step in understanding soil as a living mass of organisms and chemistry that provide plants with water, fertility and anchorage. From these results, continue to develop an improvement plan for your particular soil.

Resources

• Clipboard/s, pen and paper

• Tools including hand fork, trowel, spade, and fork

• Soil pH testing kit, glass jars

• Materials for soil improvement, eg home-made compost (see below)

Activity 1 Follow some/all of the instructions overleaf for testing and improving your soil

a Soil texture and main characteristics

b Organic matter and living content

c Compaction and drainage (typical air and water content)

d Soil ‘acidity’ or ‘alkalinity’ (pH)

2 Review the test results and discuss implications with the group

3 Plan and implement a programme of soil improvement from the test results, eg adding organic matter, relieving compaction, improving drainage, adjusting soil pH, etc

Extended activities1 Examine the role and origin of organic matter, eg compost, well rotted manure, leafmould.

2 Make a series of holes 5-15cm deep around the garden. Put samples on a white sheet and identify soil creatures, eg earthworms, beetles, centipedes, etc.

Health & Safety

Be careful when handling soil. Cover open wounds, wear gloves if necessary, and wash hands. Keep tetanus vaccinations up-to-date. Soil and organic matter can be dusty/slippery.

See also Health and Safety Guidelines (Section B3.3)

Further information

B4.4 Building soil fertility

B5.8 Digging

B5.7 Making compost

Adding organic matter for soil improvement

2

Inst

ruct

ions

tes

ting

so

il an

d im

prov

ing

fert

ility

a. S

oil t

extu

re a

nd m

ain

char

acte

rist

ics

So

il ty

pes

Ty

pic

al

pro

per

ties

Ph

oto

of

in-m

oti

on

sh

ot

of

soil

falli

ng

of

a sh

ovel

DS

C49

72

- 76

O

R C

lose

DS

C56

54

Ru

b a

sm

all

amo

un

t o

f m

ois

t so

il b

etw

een

yo

ur

finge

rs

Ph

oto

(s

plit

sh

ot)

of

san

d a

nd

cl

ay t

est

DS

C51

24

and

D

SC

5128

Sti

r a

han

dfu

l o

f so

il in

a

jar

full

of

wat

er.

Lea

ve t

o

sett

le f

or

two

ho

urs

Ph

oto

of

jars

D

SC

5064

-

65O

R

LIG

HT

ER

DS

C55

28

- 29

Met

ho

d a

nd

re

aso

n f

or

imp

rove

men

ts

CL

OS

E P

ho

to

soil

imp

rovi

ng

– eg

dig

gin

gD

SC

5387

-402

DS

C15

27-2

8 C

RO

P

Sand

Mos

tly s

and

part

icle

s; w

ater

dr

ains

qui

ckly

(of

ten

too

quic

kly,

was

hing

out

fert

ility

an

d ca

usin

g dr

ough

t). L

ight

to

dig

; qui

ck t

o w

arm

up

in

spr

ing

Feel

s gr

itty

and

does

n’t

stic

k to

geth

er (

thou

gh

a sa

ndy

loam

will

stic

k to

geth

er a

litt

le)

Will

form

a d

istin

ct

gritt

y la

yer

at t

he b

otto

m

and

leav

e sl

ight

ly d

irty

w

ater

abo

ve

Add

org

anic

mat

ter

to im

prov

e st

ruct

ure,

w

ater

ret

entio

n an

d fe

rtili

ty. C

an a

lso

add

5-10

cm la

yer

of o

rgan

ic m

atte

r (e

g co

mpo

st –

see

bel

ow)

on t

he s

oil

surf

ace

to c

onse

rve

moi

stur

e un

dern

eath

(‘m

ulch

ing’

)

Clay

Mos

tly c

lay

part

icle

s; w

ater

dr

ains

slo

wly

(ca

n w

ater

log)

; of

ten

nutr

ient

ric

h (b

ut m

ay

be u

nava

ilabl

e to

pla

nts)

; so

il ‘b

akes

’ har

d an

d cr

acks

w

hen

dry;

heav

y to

dig

; slo

w

to w

arm

up

in s

prin

g

Feel

s st

icky

and

hea

vy. I

t w

ill h

old

toge

ther

in a

bal

l w

ithou

t cr

umbl

ing

(tho

ugh

less

so

for

clay

loam

). So

il m

ay ‘s

hine

’ whe

n sm

ooth

ed

Wat

er w

ill s

tay

clou

dy

beca

use

ther

e ar

e so

man

y sm

alle

r pa

rtic

les,

with

a t

hin

laye

r of

par

ticle

s at

th

e bo

ttom

Add

org

anic

mat

ter

to im

prov

e st

ruct

ure,

dr

aina

ge, a

nd m

ake

nutr

ient

s av

aila

ble.

In

hea

vier

cla

y, di

g in

a b

ucke

t of

‘h

ortic

ultu

ral g

rit’

per

squa

re m

etre

to

impr

ove

drai

nage

. Can

als

o ro

ughl

y di

g ov

er in

win

ter,

expo

sing

cla

y lu

mps

to

fros

t to

hel

p br

eak

them

dow

n; d

ig a

gain

in

spr

ing

Silt

Mix

ture

of c

lay

and

sa

nd c

hara

cter

istic

s.

Usu

ally

moi

stur

e re

tent

ive

with

goo

d fe

rtili

ty.

Com

pact

s ea

sily

Feel

s si

lky

or s

oapy

and

m

ay s

how

impr

ints

whe

n pr

esse

d; w

ill h

old

toge

ther

a

little

Will

leav

e a

smal

l lay

er o

f pa

rtic

les

at t

he b

otto

m a

nd

dirt

y w

ater

Add

org

anic

mat

ter

to im

prov

e st

ruct

ure

and

help

min

imis

e lik

ely

com

pact

ion

3

a. S

oil t

extu

re a

nd m

ain

char

acte

rist

ics

So

il ty

pes

Ty

pic

al

pro

per

ties

Ph

oto

of

in-m

oti

on

sh

ot

of

soil

falli

ng

of

a sh

ovel

DS

C49

72

- 76

O

R C

lose

DS

C56

54

Ru

b a

sm

all

amo

un

t o

f m

ois

t so

il b

etw

een

yo

ur

finge

rs

Ph

oto

(s

plit

sh

ot)

of

san

d a

nd

cl

ay t

est

DS

C51

24

and

D

SC

5128

Sti

r a

han

dfu

l o

f so

il in

a

jar

full

of

wat

er.

Lea

ve t

o

sett

le f

or

two

ho

urs

Ph

oto

of

jars

D

SC

5064

-

65O

R

LIG

HT

ER

DS

C55

28

- 29

Met

ho

d a

nd

re

aso

n f

or

imp

rove

men

ts

CL

OS

E P

ho

to

soil

imp

rovi

ng

– eg

dig

gin

gD

SC

5387

-402

DS

C15

27-2

8 C

RO

P

Loam

Bala

nced

mix

ture

of

diffe

rent

siz

ed s

oil p

artic

les;

easy

to

wor

k; fe

rtile

; wat

er

drai

ns fr

eely,

yet

soi

l ret

ains

m

oist

ure.

‘San

dy lo

ams’

and

‘c

lay

loam

s’ a

re c

omm

on

Feel

s sl

ight

ly g

ritt

y an

d da

rk in

col

our.

It w

ill

hold

tog

ethe

r a

little

be

fore

cru

mbl

ing

Will

set

tle t

o fa

irly

eve

n la

yers

of c

lay,

silt

and

sand

pa

rtic

les

(with

sm

alle

r cl

ay

part

icle

s at

the

top

). W

ater

le

ft s

light

ly c

loud

y

You’

re v

ery

luck

y –

this

is g

ood

soil!

Add

or

gani

c m

atte

r to

mai

ntai

n so

il st

ruct

ure

and

fert

ility

in a

ccor

danc

e w

ith c

rop

rota

tion

(see

Silv

er a

nd G

old

book

let)

Chal

kG

ener

ally

sha

llow

with

lu

mps

of c

halk

and

flin

t st

ones

; fre

e dr

aini

ng;

low

-med

ium

fert

ility

; hig

h pH

(al

kalin

e); t

extu

re c

an

mak

e di

ggin

g di

fficu

lt

Usu

ally

pal

e in

col

our

an

d of

ten

ston

y w

ith b

its

of c

halk

Will

mak

e th

e w

ater

go

pale

gre

y co

lour

with

a

gritt

y la

yer

at t

he b

otto

m

(pos

sibl

y w

ith s

mal

l w

hite

bits

)

Add

org

anic

mat

ter

to im

prov

e st

ruct

ure,

w

ater

ret

entio

n, s

oil f

ertil

ity, a

nd b

uild

up

the

dep

th o

f top

-soi

l (ra

ised

bed

s ca

n he

lp).

Take

out

big

gest

sto

nes

if in

conv

enie

nt fo

r di

ggin

g an

d cr

ops;

smal

ler

ston

es c

ause

no

harm

Peat

yVe

ry r

ich

in o

rgan

ic m

atte

r; da

rk c

olou

red,

oft

en v

ery

dry

in s

umm

er a

nd w

et in

w

inte

r; lo

w-m

ediu

m fe

rtili

ty;

low

pH

(ac

id);

easy

to

dig

Feel

s sl

ight

ly s

pong

y. D

ark

colo

ured

and

glis

tens

w

hen

wet

.

Will

leav

e m

ater

ial f

loat

ing

in d

irty

wat

erU

nusu

al t

o fin

d na

tura

lly, b

ut s

een

in

rais

ed b

eds

fille

d ju

st w

ith c

ompo

st. M

ix

at le

ast

50:5

0 w

ith t

op-s

oil (

boug

ht o

r fr

om a

spa

re p

ile in

you

r ga

rden

). If

peat

is

nat

ural

ly o

ccur

ring

, add

a b

ucke

t of

‘h

ortic

ultu

ral g

rit’

per

squa

re m

etre

to

impr

ove

drai

nage

. See

als

o A

11.

4

b. O

rgan

ic m

atte

r an

d liv

ing

cont

ent

• M

ake

a se

ries

of h

oles

5-1

5cm

dee

p ar

ound

the

gar

den

in d

iffer

ent

grow

ing

loca

tions

, inc

ludi

ng c

urre

nt a

nd p

oten

tial g

row

ing

area

s, eg

ve

geta

ble

beds

.•

Com

pare

the

col

our

of t

he s

oil r

emov

ed fr

om t

he h

oles

. Dar

ker

soil

will

hav

e m

ore

orga

nic

mat

ter

whe

re it

was

add

ed b

y pr

evio

us

gard

ener

s or

bui

lt up

nat

ural

ly, e

g by

leav

es fr

om n

earb

y tr

ees.

Ligh

ter

soil

less

so.

• T

here

sho

uld

be m

ore

livin

g or

gani

sms

in s

oil w

ith h

igh

orga

nic

mat

ter

cont

ent.

Eart

hwor

ms

are

the

best

indi

cato

r as

the

y ar

e pa

rt

of t

he d

ecom

posi

tion

cycl

e of

org

anic

mat

ter.

• Po

or g

row

th o

f pre

viou

s cr

ops

and

surr

ound

ing

plan

ts c

an a

lso

sugg

est

a so

il lo

w in

org

anic

mat

ter.

c. C

ompa

ctio

n an

d dr

aina

ge (

typi

cal a

ir a

nd w

ater

con

tent

)

• D

ig a

hol

e at

leas

t 60

cm a

cros

s, w

ide

and

deep

. In

mos

t so

ils, y

ou

shou

ld s

ee d

istin

ct la

yers

of

° dar

k co

lour

ed t

opso

il;

° lig

hter

‘sub

-soi

l’ w

ith fe

wer

org

anis

ms,

and

poss

ibly

;

° a

base

laye

r of

‘bed

roc

k’.

• Ba

d co

mpa

ctio

n is

sug

gest

ed b

y

° Sol

id lu

mps

of s

oil w

hen

digg

ing

that

don

’t br

eak

up e

asily

;

° th

ere

is a

n im

perm

eabl

e la

yer

of s

ever

ely

com

pact

ed s

oil (

‘pan

’ be

twee

n to

p an

d su

b so

il);

° po

or d

rain

age.

• Po

or d

rain

age

is s

ugge

sted

by

° freq

uent

pud

dlin

g w

hen

wat

er d

oes

not

drai

n aw

ay q

uick

ly fr

om

soil

surf

ace,

and

° st

agna

nt s

mel

l, po

ssib

ly c

ombi

ned

with

‘blu

e-m

ottli

ng’ o

n th

e so

il su

rfac

e or

low

er d

own.

Top

tip

Vis

ual

Ass

essm

ents

The

se a

sses

smen

ts a

re

sim

ple

indi

cato

rs o

f soi

l he

alth

for

grow

ing

food

pl

ants

. If o

rgan

ic m

atte

r is

lo

w, a

dd e

xtra

(se

e be

low

). T

he s

oil l

ife w

ill in

crea

se

natu

rally

, inc

ludi

ng b

enef

icia

l ba

cter

ia a

nd fu

ngi.

Top

tip

Vis

ual

Ass

essm

ents

The

se a

sses

smen

ts a

re

also

inte

nded

as

sim

ple

indi

cato

rs o

f soi

l hea

lth.

Red

uce

com

pact

ion

and

impr

ove

drai

nage

by

digg

ing

(A26

). T

his

adds

air

and

le

ts w

ater

dra

in. A

ddin

g or

gani

c m

atte

r al

so h

elps

by

impr

ovin

g so

il st

ruct

ure.J J

5

Mai

n ty

pes

of o

rgan

ic m

atte

rP

hoto

Ty

pica

l app

licat

ion

Hom

e-m

ade

com

post

G

ood

NPK

and

tra

ce e

lem

ents

‘Gre

en w

aste

’ com

post

fro

m lo

cal

coun

cil h

as g

ood

K; N

re

leas

ed s

low

ly

P Cro

p fr

om D

SC_3

320

(avo

idin

g gr

een

edge

s)

Up

to o

ne

whe

elba

rrow

ful p

er

5m2

per

year

(3m

2 fo

r gr

een

was

te)

Anim

al m

anur

esVa

ried;

usua

lly h

ighe

r N

PK t

han

com

post

. Mus

t be

wel

l rot

ted

and

from

unc

onta

min

ated

sou

rce

(n

o w

eedk

illers

)

P DSC

1658

- 6

1U

p to

one

w

heel

barr

owfu

l pe

r 10

m2

per

year

(2

0m2

for

rich

er

poul

try

man

ure)

Leaf

mou

ld (

rotte

d le

aves

) Ve

ry lo

w N

PK. E

xcel

lent

for

impr

ovin

g so

il st

ruct

ure.

See

Silve

r an

d G

old

book

let

P DSC

4983

A

pply

laye

r up

to

2-3c

m d

eep.

Can

be

adde

d in

au

tum

n w

ith n

o da

nger

of l

each

ing

Top

tip

Ben

efit

s o

f ad

din

g o

rgan

ic m

atte

r

• A

dds

the

thre

e m

ajor

nut

rien

ts p

lant

s ne

ed. T

hese

‘min

eral

s’ a

re n

itrog

en (

N),

phos

phor

us (

P) a

nd p

otas

sium

(K

), kn

own

as N

PK.

A r

ange

of ‘

trac

e’ m

iner

als

are

adde

d as

wel

l (eg

zin

c an

d ir

on).

• T

he r

esid

ue o

f org

anic

mat

ter

(‘hum

us’)

clin

gs t

o so

il pa

rtic

les,

eg im

prov

ing

drai

nage

in c

lay

soils

and

wat

er r

eten

tion

in s

andy

soi

ls, p

lus

enla

rgin

g th

e su

rfac

e ar

ea fo

r av

aila

ble

plan

t nu

trie

nts.

Als

o ad

ds

air,

redu

cing

soi

l com

pact

ion.

Wh

en: a

pply

org

anic

mat

ter

whe

n pl

ants

are

ac

tivel

y gr

owin

g, us

ually

spr

ing

and

sum

mer

is

bes

t. A

pply

ing

in a

utum

n ca

n le

ave

surp

lus

nutr

ient

s to

was

h ou

t th

e so

il (‘l

each

’) un

less

pl

ants

are

gro

win

g th

roug

h w

inte

r.

How

mu

ch: s

ee t

able

for

typi

cal a

pplic

atio

n.

Nut

rien

ts c

an a

lso

leac

h ou

t be

fore

the

y’re

us

ed b

y pl

ants

if t

oo m

uch

orga

nic

mat

ter

is

adde

d. T

his

was

tes

valu

able

nut

rien

ts a

nd c

an

pote

ntia

lly p

ollu

te w

ater

cou

rses

, dam

agin

g na

tura

l eco

syst

ems.

The

sam

e ap

plie

s w

hen

appl

ying

‘con

cent

rate

d fe

rtili

sers

’ suc

h as

liq

uid

feed

s.

Wh

ere:

app

ly t

o di

ffere

nt a

reas

of t

he

gard

en a

ccor

ding

to

thei

r ne

eds

usin

g cr

op

rota

tion

(Silv

er a

nd G

old

book

let)

.

How

to

ap

ply

: Dig

into

the

top

soil

(A26

) or

sp

read

ove

r th

e so

il su

rfac

e, ie

‘mul

chin

g’ a

nd

‘no-

dig’

gar

deni

ng (

Silv

er a

nd G

old

book

let)

.J

6

d. S

oil ‘

acid

ity’

or ‘

alka

linit

y’ (

pH)

pH m

eter

• In

sert

the

pro

be in

to t

he s

oil a

t ro

ot le

vel

(abo

ut 1

0cm

dee

p). R

ecor

d re

adin

gs a

t se

vera

l di

ffere

nt lo

catio

ns a

roun

d th

e gr

owin

g ar

eas.

Wip

e cl

ean

betw

een

uses

. Fol

low

any

oth

er

man

ufac

ture

rs’ i

nstr

uctio

ns.

• M

eter

s ar

e us

ually

abo

ut £

10.

pH li

quid

tes

ting

kit

• Ta

ke a

sm

all s

ampl

e of

soi

l fro

m a

bout

10c

m

deep

and

put

it in

the

tub

e. C

aref

ully

ope

n th

e ca

psul

e an

d po

ur t

he p

owde

r in

to t

he

tube

and

add

wat

er. S

hake

wel

l and

allo

w t

o se

ttle

. Com

pare

the

col

our

of t

he w

ater

with

th

e pH

iden

tific

atio

n ch

art.

Follo

w a

ny o

ther

m

anuf

actu

rers

’ ins

truc

tions

.•

Rep

eat

in s

ever

al lo

catio

ns w

ith n

ew k

it, o

r m

ix

seve

ral s

ampl

es t

oget

her

in a

buc

ket

and

test

th

is (

repr

esen

tativ

e) s

ampl

e.

• K

its a

re u

sual

ly a

bout

£2

each

. Tr

y th

e O

rgan

ic G

arde

ning

Cat

alog

ue

ww

w.o

rgan

icca

talo

g.co

m

Top

tip

So

il A

cid

ity

The

soi

l ‘ac

idity

’ or

‘alk

alin

ity’,

mea

sure

d on

a

scal

e of

1-1

4 (v

ery

acid

to

very

alk

alin

e; n

eutr

al p

H7)

. M

ost

soils

are

pH

4-8.

The

m

ajor

ity o

f veg

etab

les

pref

er

pH6.

5-7

and

mos

t fr

uit

pH6-

6.5.

Som

e di

seas

es

like

‘pot

ato

scab

’ are

mor

e tr

oubl

e on

alk

alin

e so

il w

hile

‘c

lubr

oot’

in t

he c

abba

ge

fam

ily s

prea

ds in

soi

l tha

t is

to

o ac

id.

Adj

ust

pH b

y ad

ding

do

lom

ite li

mes

tone

(le

ss

acid

) or

sul

phur

chi

ps

(mor

e ac

id).

Onl

y m

inor

sh

ifts

in p

H a

re p

ossi

ble;

ea

sier

to

rais

e pH

tha

n lo

wer

. Onl

y al

ter

if ne

cess

ary.

J