Cul­ti­vate with care af­ter wet


OPIN­ION: Fol­low­ing the wettest win­ter on record, farm­ers are cul­ti­vat­ing their pad­docks for pas­ture or crop ro­ta­tion. As they do so, it’s im­por­tant to be aware of and man­age the as­so­ci­ated en­vi­ron­men­tal risks. Sed­i­ment and nu­tri­ents from farm­ing op­er­a­tions, along with ero­sion gen­er­ally, are some of the most im­por­tant causes of re­duced wa­ter qual­ity and cul­ti­va­tion in­creases the po­ten­tial for prob­lems.

Top soil ero­sion, es­pe­cially in hill coun­try, of bare or cul­ti­vated land leads to the loss of valu­able nu­tri­ents. It also dis­rupts in­fra­struc­ture and in­creases the costs of main­te­nance ac­tiv­ity, such as clean­ing cul­verts and drains. The time of great­est risk can be at times like now when the pro­tec­tive plant cover is lost through cul­ti­va­tion of soils for pas­ture re­newal and crop es­tab­lish­ment.

How­ever, there are a range of mea­sures farm­ers can take to help mit­i­gate the en­vi­ron­men­tal risks as­so­ci­ated with cul­ti­va­tion, and with ero­sion gen­er­ally, while at the same time pro­tect­ing soil re­sources. Con­tour cul­ti­va­tion, sow­ing at right an­gles to the pre­vail­ing wind, sed­i­ment re­ten­tion, di­vert­ing over­land flow, and re­duc­ing runoff are rec­om­mended for min­imis­ing soil loss.

Other soil con­ser­va­tion cul­ti­va­tion tech­niques in­clude the suite of prac­tices known as min­i­mum tillage or no tillage. When soil has been con­tin­u­ously cul­ti­vated for many years, the struc­ture is likely to be poor be­cause cul­ti­va­tion re­duces soil or­ganic mat­ter lev­els.

No-tillage will not re­pair the dam­age overnight but, with residue re­ten­tion, it will even­tu­ally. Chem­i­cal spray­ing fol­lowed by di­rect drilling is an op­tion on light erodi­ble soils. Sed­i­ment and some nu­tri­ents, par­tic­u­larly phos­pho­rus, are car­ried to streams pri­mar­ily in the over­land flow of wa­ter. Dis­solved nu­tri­ents such as ni­tro­gen and other ma­te­ri­als can also move through the soil in un­der­ground flows and con­tami- nate wa­ter­courses.

The area be­side wa­ter­ways that forms the in­ter­face be­tween wa­ter and land is called the ri­par­ian mar­gin. This area is a cru­cial buf­fer be­tween land use ac­tiv­i­ties and the nat­u­ral wa­ter­way. To help pre­vent the trans­fer of sed­i­ment and nu­tri­ents to wa­ter­ways, an ef­fec­tive fil­ter strip needs to be es­tab­lished and main­tained. Healthy ri­par­ian veg­e­ta­tion in these ar­eas, as well as grass mar­gins, should be main­tained to im­prove bank sta­bil­ity, in­crease wa­ter qual­ity, re­duce stock losses, fil­ter sur­face run-off and pro­vide habi­tat for wild life.

Stud­ies show that up to 90 per cent of sed­i­ment can be caught in an ef­fec­tively con­structed fil­ter strip. Any fae­cal bac­te­ria that are trapped in long grass fil­ter strips will die off in sun­light. Ri­par­ian veg­e­ta­tion also has an ad­di­tional ben­e­fit in pro­vid­ing shade to the stream, thereby re­duc­ing wa­ter tem­per­a­tures and the growth of nui­sance plants and al­gae.

Waikato Re­gional Coun­cil’s Pro­posed Plan Change 1 for the Waikato and Waipa rivers catch­ment has a sug­gested rule which says farm­ers must main­tain ap­pro­pri­ate buf­fers (a min­i­mum of five me­tres) be­tween cul­ti­vated ar­eas and wa­ter bod­ies.

Bala Tikkisetty is a sus­tain­able agri­cul­ture co­or­di­na­tor at Waikato Re­gional Coun­cil


Bala Tikkisetty and dairy farmer Bob Rigter dis­cuss the is­sues around cul­ti­va­tion. Tikkisetty says there are a num­ber of is­sues to con­sider when plan­ning cul­ti­va­tion.

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