Ni­trate loss is a big risk in wet weather

South Waikato News - - Farming - BALA TIKKISETTY

OPIN­ION: It’s been a wet one all right – Met­ser­vice is al­ready de­scrib­ing 2017 as ‘‘the year it didn’t stop rain­ing’’ with Waikato rain­fall at record lev­els for Jan­uary to Septem­ber.

It is a legacy farm­ers are tak­ing into spring as they pre­pare to fer­tilise pad­docks in com­ing months with those sat­u­rated soils start­ing to warm up.

Gen­er­ally speak­ing, get­ting the best bang for buck out of fer­tiliser while pro­tect­ing eco­nomic and en­vi­ron­men­tal bot­tom lines is a key goal for farm­ers.

Find­ing that bal­ance can be tricky and re­quires ad­vice from qual­i­fied farm con­sul­tants and nu­tri­ent man­age­ment ad­vi­sors.

There are a range of risks when ap­ply­ing fer­tiliser. I rec­om­mend all farm­ers have a nu­tri­ent bud­get and a nu­tri­ent man­age­ment plan for their prop­er­ties and dis­cuss their sit­u­a­tion with their fer­tiliser rep­re­sen­ta­tive.

It’s also a re­quire­ment of our cur­rent re­gional plan to have such a bud­get and plan if ni­tro­gen (N) use ex­ceeds 60 kilo­grams per hectare per year.

Nu­tri­ent bud­get­ing is widely ac­cepted as the ap­pro­pri­ate first step in man­ag­ing nu­tri­ent use and it’s also the pre­ferred tool for eval­u­at­ing the en­vi­ron­men­tal im­pacts of farm man­age­ment prac­tices.

Overseer, a com­puter de­ci­sion sup­port model, is used to ad­vise on nu­tri­ent man­age­ment and green house gas emis­sions.

It pre­dicts what hap­pens to the nu­tri­ents that are brought on to the farm in the form of fer­tilis­ers and sup­ple­men­tary feed in the same way that a fi­nan­cial bud­get can track money. A new ver­sion of Overseer was re­cently re­leased by Agre­search.

An im­por­tant is­sue to con­sider is ni­trate leach­ing.

Plants need N for healthy leaf growth, but N is an ex­tremely mo­bile nu­tri­ent. If more ni­troge­nous fer­tiliser is ap­plied than plants can take up most of the un­used ni­tro­gen ends up leach­ing down through the soil into ground­wa­ter.

Some­times N will also be lost to wa­ter­ways as run-off and some is al­ways re­leased back into the air as gas.

Time fer­tiliser ap­pli­ca­tion to avoid pe­ri­ods when plant up­take of N is low, such as when soils are sat­u­rated, dur­ing heavy rain, cold pe­ri­ods and low soil tem­per­a­tures.

Ap­ply­ing N fer­tiliser in split dress­ings.

Ir­ri­gat­ing farm dairy ef­flu­ent to a large enough area.

Ad­just­ing fer­tiliser pol­icy for ef­flu­ent ir­ri­gated ar­eas to ac­count for the nu­tri­ent value of ef­flu­ent. Use fenced wet­lands and well­man­aged open drains as nu­tri­ent traps. The nu­tri­ent phos­pho­rus (P) be­haves very dif­fer­ently to N be­cause it binds with the soil and only dis­solves slowly in wa­ter over time.

❚❚❚❚This means it doesn’t read­ily leach to ground­wa­ter.

But it can dam­age the health of wa­ter­ways through soil ero­sion and sur­face run-off into wa­ter. Typ­i­cally, 80 per cent of P loss can some­times come from about 20 per cent of the farm area.

Farm­ers can re­duce the amount of P run-off by keep­ing Olsen P to op­ti­mum agro­nomic lev­els and by:

Fol­low­ing the NZ Fer­tiliser Man­u­fac­tur­ers’ Re­search As­so­ci­a­tion Code of Prac­tice for Nu­tri­ent Man­age­ment. Ap­ply­ing fer­tiliser when grass is in an ac­tive grow­ing phase.

Leav­ing a grassed buf­fer strip be­tween pad­dock and wa­ter­way – the strip fil­ters the P be­fore the run-off reaches the wa­ter.

Con­trol­ling run-off from tracks, races, feed and stand-off pads.

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

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SUP­PLIED

Han­dling a wet win­ter.

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