Farmer’s Weekly – 09 August 2019

vegetable production

convertthemtoN 2 , which

escapesbackintotheair.

unchartedterritory

Littleis knownabouttherole

playedbymostorganismsinthe

soil,andmanyexcitingdiscoveries

remaintobemade.Forexample,

organismsthatcanliveonthe

leafsurfaceandsupplynitrogen

totheplanthavebeencultured.

Butthesearedifficulttomanage

andmoreresearchis needed

beforetheybecomepractical

andeconomicallyfeasible.

Onethingis certain:weneed

a healthyorganicenvironment

tocapitaliseonthebenefitsof

nitrogen-producingorganisms.

Ihave discovered this personally,

as I have had exceptionally

productive and healthy crops

without having to apply nitrogen

to my soil for many years.

• Bill Kerr is a vegetable specialist
  and breeder. Email him at
  [email protected]. Subject
  line: Vegetable production. ▪FW

S

implyput,nitrogencontrols

theperformanceofthecrop

justasthethrottlepedal

controlsthespeedofa car.It is

oneofmanyelementsthata crop

requirestogrow,andallthese

shouldbeavailabletotheplantin

variousproportionstooneanother.

Thisis notanexactscience,but

a ruleofthumb.Manycropsare

grownsuccessfullywithsome

imbalances,butenoughofeach

elementshouldbepresentinthe

soilbeforeplanting.Thereafter,

growthis regulatedbynitrogen.

Nearly80%ofthenitrogen

webreatheis ingaseous

form(dinitrogenorN 2 ). It is

thisthatis extractedfrom

theairandconvertedintoa

biologicallyavailableformin

nitrogen-containingfertiliser.

Rhizobiumbacteriaontheroots

oflegumescanalsoextractit

fromtheair.Thesearevisible

asnodulesprotrudingfromthe

surfaceofrootsandarepinkin

colourwhenfunctioningwell.

Thisnitrogenis sharedwith

theplantsas‘payment’for

nourishingtherhizobia.Acertain

amountis alsoreleasedinto

thesoil,whereit is availablefor

usebyneighbouringplants.

Certain legumes can have a

substantial amount of nitrogen,

and their value in this respect

varies according to species and

conditions. The rhizobia produce

less nitrogen when the nitrogen

level in the soil is high. When

the roots die off, the nitrogen

theycontainis releasedintothe

soiltoformhumusandtobe

usedbythefollowingcrop.

Duringa thunderstorm,lightning

convertssomeoftheN 2 inthe

atmosphereintoammonia,which

thenfallstoearthinrain.This

helpsboostplantgrowth,but

is a nuisanceforpoolowners,

asit fertilisesthealgaeinthe

water,turningit green.

otherplantsthat

producenitrogen

A numberofothersoilorganisms

candrawN 2 fromtheair.

Whiletheyarenotlegumes,

Casuarinaceaetrees(beefwood)

canhostnitrogen-forming

nodulesontheirroots.

Indeed,manyplantshave

a relationshipwithfree-

living,nitrogen-producing

organisms,andcanproduce

a fairquantityofnitrogen.

Nitrogencanbelostfromthe

soilwhenit becomessaturated,

especiallywhencompacted.

Inthisenvironment,anaerobic

bacteriaremovetheoxygen

moleculesfromnitrateand

ABOVE:

Nitrogen-producing

nodulesona

legumeroot.

billkerr

the future

will see many

discoveries

regarding the

role of soil

organisms

Why nitrogen is so important

BillkErr

56 farmer’sweekly 9 August 2019