Farmer’s Weekly – 30 August 2019

vegetable production

sizeandcolouroftheleaves.

Keepthenitrogenlevelsup

righttotheendofthecrop.

OrganiccOntent

Theorganiccontentofthesoil

makesa hugedifferencein

securingandregulatingnitrogen.

I oncehadfairlyhigh-volume

sprinklersrunningona section

ofland.I openedthesprinklers

atmidday,intendingtoswitch

themoffat5pm.I forgottodo

soandtheyranrightthrough

thenightuntilthenextmorning.

Therewasnodifferencein

theareaover-irrigatedeven

aftera coupleofmonths.

I have5%humusinmy

soil and this prevented

leaching. If I had 1%, I would

have lost my nitrogen.

• Bill Kerr is a vegetable specialist
  and a breeder of a range of vegetables.
  Email him at farmersweekly@
  caxton.co.za. Subject line:
  Vegetable production. ▪FW

O

f alltheelements,

nitrogenhasthe

mostprofoundeffect

ona crop,andthisis why

youneedtouseit wisely.

Differentcropsrequire

differentamountsofnitrogen

foroptimumgrowth.A high

availabilityofmostother

mineralsmighthavea negligible

effectona crop,buttoomuch

nitrogencanbea hugeproblem.

Toolittle,ontheotherhand,

canhaltgrowthaltogether.

Addtheeasewithwhichit

canbelostfromthesoil,and

weneedtocloselymonitorthis

element.Someguidelines:

• Leafycrops
  Incropswheretheleaf
  portionis eaten,nitrogen
  playsanimportantrolein
  thevolumeproduced.
  Anaspectoftenneglected
  is thattherehastobeenough
  nitrogenintherootareaof
  transplantsforthecroptomake
  thelargeouterleaves,which
  providetheframeworkforthe
  planttoproducea goodyield.
  Addtoolittlenitrogen,andthe
  plantwillgointosurvivalmode
  ratherthanproductivemode.


• tomatoes
  Withtomatoes,theplantneeds
  enoughnitrogentomakea good-
  sizedplant.Unlessleachingtakes
  place,there’susuallysufficient
  nitrogenfromthebasicfertiliser
  applicationatthisstage.

When flowering is in full swing,

lower nitrogen levels will

encourage fruit set. When fruit

is filling, you need to increase

the nitrogen to provide size and

gettheplanttofillthetrusses.

Getthisrightbyobserving

thecolouroftheleaves.

Also,don’toverdothe

nitrogenata laterstage.This

canresultina changein

fruitshapeandfirmness.

• carrots
  Althoughcarrotscando
  witha fairamountofnitrogen,
  theirdeepandextensive
  rootsystemenables
  themtosourcethisright
  downtodeeplayers.
  Indeed,carrotscanmakeuseof
  nitrogenthathasleachedbeyond
  therootzoneoftheprevious
  cropsgrown.Onaccountofthis,
  youcangetawaywithplanting
  carrotswithnofertiliser.
  Aslongastheyhaveaccessto
  sufficientsunlight,theleavescan
  be a medium colour and the plant
  will still be equally productive.


• Peppers
  Peppers need a healthy
  amount of nitrogen in order
  toproducethick-walled,
  heavyfruit.Again,gaugethe
  crop’srequirementsbythe

ABOVE:

Monitortheleaf

colourandvigour

in regulating

thenitrogen

requirementsof

tomatoesand

othercrops.

billkerr

PePPers need

a h ealthy

amount of

nitrogen

Using nitrogen as an accelerator

BillkErr

44 farmer’sweekly 30 August 2019