Risky ni­tro sea­son


Win­ter is a much riskier sea­son for ni­tro­gen leach­ing from urine patches on pas­ture to wa­ter­ways.

Milk­ing cows will ex­crete, in urine, about 70 per cent of the ni­tro­gen (N) they con­sume. The chance of N leach­ing from urine patches is much higher in win­ter due to weather con­di­tions.

Also, farm­ers should be par­tic­u­larly cau­tious when ap­ply­ing N based fer­tilis­ers to pas­ture or crops dur­ing win­ter be­cause of the ex­tra risks win­ter weather poses for nu­tri­ent loss.

Win­ter ap­pli­ca­tions of N are gen­er­ally least ef­fec­tive for pro­mot­ing grass growth. Slow growth of pas­ture in win­ter and more drainage can re­sult in ni­trate leach­ing be­fore plants can take it up.

Ni­tro­gen leach­ing phos­pho­rous runoff not only con­tam­i­nate the wa­ter bod­ies but also rep­re­sent a loss of eco­nom­i­cally valu­able nu­tri­ents.

Most N is leached dur­ing win­ter and early spring when rain­fall ex­ceeds evap­o­tran­spi­ra­tion. Gen­er­ally, the pas­ture species, par­tic­u­larly rye grass, are not ac­tive dur­ing low tem­per­a­tures adding to the po­ten­tial for N loss through leach­ing.

Some of the re­search on ways to mit­i­gate the N losses has fo­cussed on grow­ing pas­ture with more root­ing depth for in­ter­cept­ing ni­trates, du­ra­tioncon­trolled graz­ing for re­duc­ing the amount of time an­i­mals spend on pas­ture, and feed­ing high sugar grasses for re­duc­ing the di­etary pro­tein.

Re­cently, a dairy herd im­prove­ment com­pany has an­nounced that it is pos­si­ble to breed cat­tle that will re­duce ‘milk urea ni­tro­gen’ (MUN) re­sult­ing in re­duced amount of ni­tro­gen leached from grazed pas­tures.

It is im­por­tant for farm­ers to get clear ad­vice from their nu­tri­ent ad­vi­sor about the so­lu­tions that best fit their farm to get the best re­turn on their nu­tri­ent dol­lar and the risks in­volved with win­ter N ap­pli­ca­tions.

Nu­tri­ent bud­get­ing us­ing com- puter mod­els such as Overseer, com­bined with feed bud­get­ing, en­ables farm­ers to un­der­stand whether they are us­ing too much or too lit­tle fer­tiliser.

By do­ing this farm­ers can op­ti­mise the use of nu­tri­ents and re­duce the im­pact on the en­vi­ron­ment by work­ing out a prag­matic nu­tri­ent man­age­ment plan.

From a tech­ni­cal per­spec­tive, farm­ers need to un­der­stand the term ‘re­sponse rate’, which is the amount of pas­ture grown in kilo­grams of dry mat­ter (DM) per hectare per kilo­gram of N ap­plied.

For ex­am­ple, when 20kg N/ha is ap­plied and an ad­di­tional 200 kg DM/ha of pas­ture is grown the re­sponse rate is 10 kg DM/kg N ap­plied.

The re­sponse is de­pen­dent on sev­eral fac­tors such as soil tem­per­a­ture, plant growth, soil mois­ture, the de­fi­ciency of avail­able ni­tro­gen in the soil and the rate of ni­tro­gen ap­plied per ap­pli­ca­tion.

The tim­ing of ap­ply­ing N fer­tiliser is para­mount, both in terms of pas­ture cover and growth. It is good to ap­ply ni­troge­nous ferti- liser when the pas­ture cover is be­tween 1500-1800 kg DM/ha.

This en­sures that there is suf­fi­cient leaf area for pho­to­syn­the­sis lead­ing to good pas­ture growth.

The best re­sponse to N ferti- liser oc­curs on fast grow­ing pas­ture, when other fac­tors such as mois­ture and soil tem­per­a­ture are not lim­it­ing growth.

Bala Tikkisetty is a sus­tain­able agri­cul­ture ad­vi­sor at Waikato Re­gional Coun­cil.


The chance of N leach­ing from urine patches is much higher in win­ter be­cause of weather con­di­tions, Bala Tikkisetty says.

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.