mu u
‘REGD‘MMENDED SCALE 0? sum PARTICLE SIZES
mm .
[Alter McDonald Hal]
rin- olay c a sea
clay nimoles a 002
sor n m . 0 oz
sun: on . z.n
lino 0,02 , o z \
ooaiss 0.2 - 2
GRAVEL z . so
Fl"! 2 , s
Moo-um 5 ~ 2::
coaiu 2n . so
CDEBLES so e 200
STONES zoo , soo
aouwsns sow
ahsorphon.
rural

Hamus or humic decay and bacteria) producla pioyide
colloids, as do llnely ground graphiio and silica, line
clays lpariieics ol 2-200 millimioronsi such as illiies,
henlonilc (usually deposiled on clay pans isom
evaporaiion of clays in iuipellsiml), grain iiours and
animal lgeiaunous) nours, eg iroin hooves, horns,
sinew wislzs, album and so on aamna also seeiele
polysacciurides which ioi-m soil gels,

Son condilioncis which iorm slabie colloids are sold
under a variely oi iradc names (ask a local agncullural
supplieil, e g. Agrusuhem, lkedagzm. Tenasorl:®.
which are hydrophiiir laliraci waleri as are many
naniral gels irom grain ymduns and seaweed, Ware.
conservanon iii up lo 50% is claimed lor some oi rhesc
addirives Mosa arlilicial gels are Icryllc-based
nacrylaniid polym) and supplied as granules able lo
aosoro hundreds oi nines lheir weighr in wales. rhsy
sie used hi gut eifed in nursery planla, row crops,
Ilrw nee planiings m desens, and in rransplanling. The
acrylics are applied ro soils al 5 log/ha or more, and
conserye irrigalion waler by psevsnring eyaporaiinn
lsiraii rurmer, New Zealand, Aug ‘34) These
subshues are 0! value in seed penning.

Calloids also loml hydvaphnblc irepei waleri
snbshms such as lhose oi clays and some soil hingi
produce. The surraces oi colloid panislcs are usually
negalively chill-geld, as are rool hairs, and ihus aiiraer
posinve ions ro ihsar suriaces, cg rhe posinve ions or
sulphates nirrares, and iii meials lsodium, calcium
magnesium, ironl Aboua 99; al such ions are so held
in soils chepcr, i952), Colloids irom liumus are
hundreds oi limes more eiiecme ihan clay colloids in
ion exchange in soils

Ammmua and sodium can dislodge lheac ions, and

lhey can oscome av ilaiile lo planl ioois, which aliracl
lliein by producing nogahyc rill charges wilh ioo
much i-iushing by sodium, ihe calcium and meralhr
ions can he losl io lcaching pnsceoaes and carried hi
sueams, hence lo seas or lakes.

Cullmds used in waier solienrng capruie cslcium
ions and release sodium ions, allowing soaps lo laiher
Ferric uxide colloids have pusml‘l‘ charges and glvl‘
warer a brown srairi, iypicai oi waler: issuing lrom
acid pears and pmc ioissls. ihe colloid paniclcs can lse
nocculaled iaggmgaredl and selile our ii aluminium
salrs lsulpholesi are added. and rhis may happen as a
resulr oi acid rain, or can be induced Wirh ihe acid
iorms ol any negarive parricles Sall also iloccuiares
colloids up is rhe poinl where excess sodium
dr/lorrulorcs days, wirh calcium and oiher ions, which
is ihe efiocr ol high sall conconrrarions in dryiand soils
loyer lcs ppm salli.

Burning desnoys rhe colloidul properues ol surlace
clays and is anoiher reason why descn soils leach our
airer iiies. aurni clay panicles no longer farm (nVIul'dsi
and become poor in iruneral nuri-ienls, which are rhen
lound only in deep soil profiles Oeganie humus ionns
blxk slimy pools on rop ol ihecoliapsed soils

ir is rhe clay panicles and colloids lorganic and
inorganic colloidal lhai oind waier and nurrienr in
soils. in ihe oopics ai loasl, mosaol lhesc oolloids are in
ihe biomass oi rho soil as cellular gels, or aie produced
as shealhing maierial by soil omens wirhoui colloids,
soil minerals rapidly leach our and become poor in
nulrienl Fire. clearing, ploughing, and cuiiivarion
desrioy such colloids and soil srnicrnre, as does extess
sodium ions. rhus. iii hold and sachangc nuincnls, we
as gardeners need lo develop narurai or arriiicial
colloid conicni in soils, iiom where planr ml: and soil
launa or llora derive iheir waier and ossenrisl
numenls Very e clay is needed in sandy gardens lo
cioalc a svll dal soil environmeni, and liie iorms are
encouraged and developed by humus, mulch, and
perenmal planl crops. Good soil siruciure lro hold ihe
coflnlds) is developed iiy careiul easin husbandry,
aogelhcr th iloeailaling additives such as gypsum
and humus.

 

solL WATER

The waier conlenr oi soils is a soup oi iieehvrng
organisms, dissolved gases and sairs, minerals, gels,
and ihe washoii iiom ihrougliiall in lrees lwaxes,
lnssi iree ”body wines"? Organic and inorganic
paniclea are held in - warer soils have a widely
vamblt wares-holding capaciry dependeni on rheir
composirion and manure, so ihai sands absorb and
ielain warer more quickly lhan clays, hul clays hold
more walcr per unir volume Available water ihus
varies horn 2% lsririace sandal lo 40-7. or more oi soil
yehsine. We can assisr rhe quamuy held in dry sires by
swallng, conrouring or rerracing, loosening soils,
adding ilocsulanis, inrioducing aniricial or narurai gels
lscaweeds or plaslic aoso-laisi, or lay placing a clay or

 

103