Post-win­ter cul­ti­va­tion crit­i­cal

Waihi Leader - - News - By BALA TIKKISETTY

The fu­ture of farm­ing, on which our re­gion’s eco­nomic and so­cial well­be­ing re­lies heav­ily, could be at risk if the qual­ity and ex­tent of our soils are not main­tained.

Sed­i­ment and nu­tri­ents from farm­ing op­er­a­tions, along with path­o­genic mi­crobes, are some of the most im­por­tant causes of re­duced wa­ter qual­ity dur­ing the post­win­ter pe­riod, when farm­ers are cul­ti­vat­ing their pad­docks. 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.

Landown­ers and cul­ti­va­tion con­trac­tors can help mit­i­gate the en­vi­ron­men­tal risks as­so­ci­ated with cul­ti­va­tion, and at the same time pro­tect their soil re­sources.

The 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. Soils should be cul­ti­vated when the mois­ture con­tent is nei­ther too high nor too low. To as­sess if soils are suit­able for pri­mary cul­ti­va­tion, take a piece of soil (half the vol­ume of an in­dex fin­ger) and press firmly to form a pen­cil.

Roll the soil into a “worm” on the palm of one hand with the fin­gers of the other un­til it is about 50mm long and 4mm thick. Ex­ert suf­fi­cient pres­sure with your fin­gers to re­duce the di­am­e­ter of the worm to 4mm in 15 to 20 com­plete for­ward and back move­ments of the fin­gers. Con­di­tions are suit­able for cul­ti­va­tion if the soil cracks be­fore the worm is made. The soil is too wet to cul­ti­vate if you can make the worm.

Con­tour cul­ti­va­tion, sow­ing at right an­gles to the pre­vail­ing wind, sed­i­ment re­ten­tion, re­duc­ing run off are rec­om­mended for min­imis­ing soil loss. Other con­ser­va­tion cul­ti­va­tion tech­niques in­clude min­i­mum or no tillage. If soil has been con­tin­u­ously cul­ti­vated for many years, the struc­ture is likely to be poor due to re­duced soil or­ganic mat­ter lev­els. Notil­lage 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. An ef­fec­tive fil­ter strip needs to be es­tab­lished and main­tained where over­land wa­ter en­ters wa­ter bod­ies. Healthy ri­par­ian veg­e­ta­tion in these ar­eas will im­prove bank sta­bil­ity, in­crease wa­ter qual­ity, re­duce stock losses, fil­ter sur­face run-off and to pro­vide habi­tat for wild life.

Good ri­par­ian veg­e­ta­tion slows run off down so that sed­i­ment, phos­pho­rous (which binds to soil par­ti­cles) and fae­cal mat­ter can set­tle out be­fore the run off reaches wa­ter­ways. 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 strips will die off. In the fil­ter strips, gen­er­ally, grasses should be kept to a height of at least 10-15cm with a high den­sity of stems and leaves at ground level for max­i­mum trap­ping ef­fect.

The spread of pests, par­tic­u­larly weeds and pathogens, by ve­hi­cles, cul­ti­va­tion ma­chin­ery and equip­ment has sig­nif­i­cant con­se­quences and is an on­go­ing prob­lem. Ma­chin­ery hy­giene must be prac­ticed any time a ma­chine is moved be­tween prop­er­ties. I would like to re­mind you again that the Waikato Re­gional Coun­cil has a rule in the Re­gional Plan, which says farm­ers must not cul­ti­vate pad­docks within two me­tres of a river, stream or lake bed.

■ Bala Tikkisetty is a sus­tain­able agri­cul­ture ad­vi­sor at Waikato Re­gional Coun­cil. Con­tact him on 0800 800 401 or email bala.tikkisetty@waika­tore­

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