NI­TRO­GEN IN CATCH CROPS AND GRASS­LAND NEEDS CARE­FUL MAN­AGE­MENT

Irish Independent - Farming - - FEATURE -

NEW re­search from Tea­gasc shows that while there is fi­nally some im­prove­ment in in terms of pH, Phos­pho­rus (P) and Potas­sium (K) lev­els, our soils are still far from op­ti­mum fer­til­ity and the re­quire­ment for sig­nif­i­cant in­vest­ment in fer­tilis­ers con­tin­ues.

While they don’t come cheap, fer­tiliser pro­grammes to ad­dress soil fer­til­ity is­sues are not com­pli­cated.

There are three lay­ers to a fer­tiliser pro­gramme: the soil pH level; the Phos­pho­rus (P) and Potas­sium (K) sta­tus, and the ap­pro­pri­ate ni­tro­gen (N) rate to be ap­plied.

Un­less the soil pH level is at a work­able level, growth re­sponse to any nu­tri­ent ap­plied, whether that is N, P or K will al­ways be dis­ap­point­ing. If the soil P lev­els or soil K lev­els are de­fi­cient, re­sponse to ap­plied N will also be muted.

There is no point ap­ply­ing more ni­tro­gen on a soil that is de­fi­cient in lime. The crop, be it grass, ce­real, potato or vegetable, just won’t re­spond.

A soil sam­ple cost­ing €30 will de­ter­mine the soil pH level. One tonne of lime costs slightly more than one 50kg bag of com­pound fer­tiliser. If the soil is lime de­fi­cient, that bag of com­pound won’t work the way it should. If a soil is se­ri­ously lime de­fi­cient, it is bet­ter to spend money on rec­ti­fy­ing the soil pH first and spend lit­tle or noth­ing on any other fer­tiliser.

The ap­pli­ca­tion of lime of­ten has an added ben­e­fit of re­leas­ing pre­vi­ously ap­plied nu­tri­ents that were un­avail­able as they couldn’t be ‘ac­ti­vated’ be­cause of the soil pH is­sues. So in the ab­sence of ap­ply­ing other nu­tri­ents, lime ap­pli­ca­tion can re­sult in the soil sup­ply­ing other nu­tri­ents to the crop from re­serves, so there is a ‘dou­ble whammy’ ben­e­fit from ap­ply­ing lime.

Once the soil pH has been ad­dressed, the next step is to build up the P and K lev­els.

There are two main sources of P and K: ap­pli­ca­tion of in­or­ganic or chem­i­cal fer­tiliser and through re­cy­cling of or­ganic nu­tri­ents.

For a well-run live­stock farm, the re­cy­cling of nu­tri­ents is nor­mally a sim­ple process: ap­ply the slurry or farm­yard ma­nure back on to the land from which the silage or hay that was fed to the live­stock came from.

Where soil P and soil l K level are at op­ti­mum lev­els, the only P and K off­take from a live­stock farm is through sales of live­stock, meat or milk. Con­cen­trate feed brought on to the farm can re­plen­ish a lot of this nu­tri­ent loss, as con­cen- THE catch crops and short term grass crops that were sown last au­tumn now re­quire man­age­ment and de­ci­sions. Given the ex­cel­lent grow­ing con­di­tions ex­pe­ri­enced this au­tumn and win­ter, many of th­ese crops are in ex­cel­lent rude health, which may cause is­sues.

First and fore­most the op­tion of off­take must be con­sid­ered, whether, pit, bale, zero graze or best op­tion of all, ac­tual graze. Run­ning th­ese crops through sheep and cat­tle will act as the best ‘bio-stim­u­lant’ pos­si­ble to worn out tillage fields.

In the ab­sence of off­take, th­ese crops must be man­aged care­fully.

Mi­crobes

trate feed con­tains quite a lot of P and K.

So for a farm with good over­all soil nu­tri­ent sta­tus, the over­all P and K re­quire­ment is While th­ese crops con­tain huge amounts of ni­tro­gen that po­ten­tially will be avail­able to fu­ture crops, this ma­te­rial has to be bro­ken down by soil mi­crobes, which will take up avail­able ni­tro­gen dur­ing the break­down process.

If not man­aged cor­rectly, the break­down of the cover crop will be like a bad dose of in­di­ges­tion for the soil.

The mi­crobes will take up all avail­able nu­tri­ents in the soil and will starve the emerg­ing com­mer­cial crop of fer­til­ity and could cause es­tab­lish­ment prob­lems. The cover crop is cre­at­ing a rel­a­tively mod­est on an on­go­ing ba­sis.

Where soil P and K lev­els are high in a highly stocked hold­ing, it may not be the best eco­nomic or en­vi­ron­men­tal use of th­ese ex­pen­sive and use­ful nu­tri­ents to re­cy­cle them back on the farm.

A well-de­signed nu­tri­ent man­age­ment plan is in­valu­able in de­ter­min­ing where the ex­cesses are and where more nu­tri­ents can use­fully be ap­plied.

Or­ganic ma­nure sources, whether from cat­tle slurry, farm­yard ma­nure, pig and poul­try slurry, or spent mush­room com­post, are very vi­able sources se­vere dis­ad­van­tage to the fol­low­ing crop, not an ad­van­tage.

To min­imise this risk, the cover crops should be in­cor­po­rated at the first op­por­tu­nity in the spring, and chopped up very finely. Sub­se­quent crop sow­ing should be de­layed as much as is prac­ti­ca­ble to give the mi­crobes a chance to get their pro­cesses com­plete be­fore the emerg­ing crop calls upon soil re­serves in which to grow. Cover crops have the po­ten­tial to make more nu­tri­ents avail­able to spring sown crops, but the tim­ing of this avail­abil­ity is cru­cial for suc­cess­ful man­age­ment of th­ese and sub­se­quent crops. of P and K to meet tillage crop re­quire­ments. The ben­e­fit in terms of nu­tri­ent load­ing is only part of the pic­ture.

Bi­o­log­i­cal ac­tiv­ity

Or­ganic ma­nures bring bi­o­log­i­cal ac­tiv­ity to our in­creas­ingly dam­aged tillage soils, and the ben­e­fit from ap­pli­ca­tions of ma­nures over and above the nu­tri­ent con­tent is be­com­ing more and more ap­par­ent to those that make the ef­fort.

This brings us to the third layer of the process: ni­tro­gen ap­pli­ca­tion.

We are in a for­tu­nate po­si­tion this year in that many grass and ce­real crops are com­ing into the spring in a very strong po­si­tion.

In many cases Ni­tro­gen ap­pli­ca­tions will have to be ad­justed to take this strong growth into ac­count.

Whether grass or ce­real, ini­tial Ni­tro­gen ap­pli­ca­tion may be de­layed, re­duced or elim­i­nated al­to­gether. This can re­duce costs, which is a straight ben­e­fit.

How­ever, it is also cru­cial to take over-win­ter up­take into ac­count as ex­ces­sive early growth may cause lodg­ing, which will re­duce grass qual­ity and be hugely detri­men­tal to ce­real crop yields.

LIME CAN HELP AC­TI­VATE PRE­VI­OUSLY UN­AVAIL­ABLE NU­TRI­ENTS

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