Be­ware dam­age to soil struc­ture

Matamata Chronicle - - Rural Delivery - By BALA TIKKISETTY Bala Tikkisetty is a sus­tain­able agri­cul­ture co­or­di­na­tor at Waikato Re­gional Coun­cil. Con­tact him at bala.tikkisetty@waika­tore­ or 0800 800 401.

The win­ter months are when farm soils can come un­der par­tic­u­lar pres­sure from things like pug­ging and com­paction.

So farm­ers are ad­vised pay par­tic­u­lar at­ten­tion at this time of year to en­sur­ing, as much as pos­si­ble, their soils re­main healthy, as this is es­sen­tial to any prof­itable farm­ing op­er­a­tion and its long-term sus­tain­abil­ity.

If the soil is phys­i­cally healthy and fer­tile, crop and pas­ture pro­duc­tion will be high.

The phys­i­cal struc­ture of soil con­trols the move­ment of air and wa­ter through the soil, and the abil­ity of roots to pen­e­trate into the soil. It also pro­vides habi­tat for ben­e­fi­cial or­gan­isms, in­clud­ing earth­worms. Soil with good struc­ture has a sig­nif­i­cant num­ber of pores that pro­vide aer­o­bic con­di­tions, good drainage and high wa­ter-hold­ing ca­pac­ity.

Plants re­quire about 10 el­e­ments in large quan­ti­ties (macronu­tri­ents), and about eight in small quan­ti­ties (mi­cronu­tri­ents). Of the ma­jor el­e­ments, car­bon, hy­dro­gen and oxy­gen are ob­tained from oxy­gen and car­bon diox­ide in the air. Oth­ers in­clude ni­tro­gen, phos­pho­rus, potas­sium, sul­phur, cal­cium and mag­ne­sium. Mi­nor el­e­ments in­clude iron, man­ganese, cop­per, zinc, molyb­de­num, boron, chlo­rine, sil­i­con and cobalt. In nat­u­ral ecosys­tems when plants and an­i­mals die many of these nu­tri­ents are cy­cled back into the soil. How­ever, in farm­ing ecosys­tems, plant or an­i­mal biomass is re­moved with har­vest­ing. To sup­ply es­sen­tial el­e­ments for plant growth farm­ers add nu­tri­ents to the soil in a num­ber of ways such as us­ing fer­tiliser and an­i­mal ef­flu­ent ap­pli­ca­tion to land. So, dur­ing the win­ter months, it’s im­por­tant to safe­guard this in­vest­ment in soil health and fer­til­ity and the time and money in­volved.

Com­paction and pug­ging of wet soils in win­ter can par­tic­u­larly dam­age the soil struc­ture.

Pug­ging is caused by an­i­mals’ hooves sink­ing into the soil sur­face (some­times as deep as 15 cen­time­tres) when they tread in very wet soils. This leaves a ‘pud­dle’ ef­fect and can lead to com­pacted layer of soil.

Such com­paction oc­curs when the soil is com­pressed or squeezed. In ad­di­tion to be­ing caused by an­i­mal tread­ing, ve­hi­cles or farm ma­chin­ery also con­trib­ute to this prob­lem.

Com­paction on dairy and dry­s­tock sites is a par­tic­u­lar con­cern as it re­duces the num­ber and size of pores avail­able for wa­ter and gas move­ment in soil. It re­duces aer­a­tion, nu­tri­ent up­take, root growth and dis­tri­bu­tion, and po­ten­tially de­creases in­fil­tra­tion and in­creases runoff. The most sen­si­tive in­di­ca­tor of com­paction is macro­p­oros­ity. Pre­vi­ous re­search re­veals that macro­p­oros­ity below 10 per cent will in­hibit pas­ture growth.

Soil sci­en­tists have found that com­pacted soil can re­duce the amount of dry mat­ter in pas­ture by 200 kilo­grams per hectare per month. (Aer­at­ing the com­pacted soil at the cor­rect depth and time can in­crease the amount of dry mat­ter by about 30 per cent within six months.)

Other prob­lems caused by pug­ging and com­paction in­clude more fre­quent and per­sis­tent sur­face pond­ing, as well as in­creased sed­i­ment, nu­tri­ent and ef­flu­ent losses to waterways through sur­face run-off. It also takes longer for pugged or com­pacted pas­ture to re­cover af­ter graz­ing and weed in­va­sion of­ten oc­curs in the bare sites pug­ging and com­paction cre­ate.

Prob­lems like these can be min­imised by:

re­duc­ing stock den­sity, es­pe­cially on sen­si­tive pad­docks like those that are wet

not feed­ing out on sen­si­tive pad­docks

con­stantly mon­i­tor­ing pug­ging and com­paction dur­ing at-risk pe­ri­ods and mov­ing stock off be­fore dam­age oc­curs

graz­ing the back of the pad­dock first.

Another im­por­tant is­sue for soil health man­age­ment and wa­ter qual­ity is how an­i­mals are win­tered.

Losses ap­pear to be ex­ac­er­bated by high den­sity urine patches de­posited at times of the year when plant growth rates are low and drainage is high (the types of con­di­tions typ­i­cal in win­ter). Con­se­quently, on a per hectare ba­sis, ni­tro­gen leach­ing losses from grazed win­ter for­age crops are high rel­a­tive to losses mea­sured un­der pas­ture.

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