Im­por­tance of soil struc­ture

The Northern Star - Northern New South Wales Rural Weekly - - NEWS - PAUL MCIN­TOSH

I SAID on Twit­ter this week that Oc­to­ber 2018 may be the saviour month for many farm­ing op­er­a­tions want­ing to plant a sum­mer crop.

Still how­ever, many of our num­bers have missed all of these nar­row, and pos­si­bly in­tense, rain­fall events.

I have dis­cussed mois­ture in­fil­tra­tion into our dry and some­times very bare soils in the past cou­ple of Ru­ral Weekly is­sues. I have also writ­ten about the low fal­low ef­fi­ciency rat­ing we can get, af­ter not many sig­nif­i­cant rain events and evap­o­ra­tion tak­ing its huge toll.

This week I would like to look at soil struc­ture and how it can im­pact on crit­i­cal fac­tors like mois­ture lev­els and seed soil con­tact.

The term struc­ture refers to the ar­range­ment of soil par­ti­cles and the vol­ume of pore spa­ces be­tween them. A well struc­tured healthy soil has a def­i­nite soft feel and a very earthy smell to it. These soils would pro­vide good seed soil con­tact and also al­low some good lev­els of wa­ter in­fil­tra­tion and move­ment with­out run off and very min­i­mal sur­face crust­ing. Of course these well struc­tured soils also con­tain plenty of air in­fil­trat­ing through the pore spa­ces and sur­face rough­ness. Air is a ma­jor com­po­nent of a healthy soil make-up.

Of course, the way we treat our soils with heavy ma­chin­ery track­ing around and some ro­bust me­chan­i­cal ac­tion can re­ally im­pede this term called good soil struc­ture.

Ma­chin­ery move­ment, cul­ti­va­tion and live­stock in­cur­sion can all cause soil com­paction, es­pe­cially if the soil has a level of free mois­ture around the soil par­ti­cles. As we all re­alise, ma­chin­ery wheel tracks can lit­er­ally squeeze the life out of soil be­ing pro­duc­tive. It can then take a long time of nat­u­ral ex­pan­sion and con­trac­tion to re-achieve a good soil struc­ture. None of this is new to us as landown­ers, how­ever we sure do need re­mind­ing of these im­por­tant fac­tors of look­ing af­ter our soils to re­main pro­duc­tive.

One of the ma­jor re­sul­tant rea­sons of why the phe­nom­e­non of zero till or min­i­mum till prac­tices were in­tro­duced into our farm­ing sys­tems lan­guage all those years ago. We all know or ac­cept that zero till is the op­ti­mum farm­ing sys­tem practice in our heavy or medium clay based soils and yet just last week, I dis­cov­ered that we may need to tweak our crop­ping sys­tem me­chan­ics.

The pic­ture at­tached should in­ter­est many of us, de­pict­ing this sys­tem of strip tillage as ex­actly the way it is said.

Much stub­ble can re­main up­right or on the sur­face at least and then these nar­row strips of coun­try of ap­prox­i­mately 40cm wide are cul­ti­vated by points or discs and fol­lowed by a rolling steel bas­ket of the same 40cm width. So you have a strip of zero tilled soil and next to it a worked/cul­ti­vated strip and this pat­tern al­ter­nates across your en­tire pad­dock.

This strip tilled por­tion across the pad­dock is the fu­ture plant­ing row of your seed and of course with the depth cul­ti­vated, al­lows deeper pre plant place­ment of solid or gas fer­tiliser op­tions.

My sur­prise re­ac­tion last week on the Dar­ling Downs, was when I was dig­ging with a large pinch­bar, of the amount of per­fectly wet­ted soil down to 160 to 200mm deep in the strip tilled sec­tion. Out of cu­rios­ity, I tried to do the same pinch­bar dig­ging oper­a­tion down to that 160mm level on the zero-tilled sec­tion right next to the tillage strip. There was a vast dif­fer­ence in soil mois­ture lev­els be­tween the two side-by-side sites, with our de­sir­able zero tillage sec­tion con­sid­er­ably drier and very full of hard, cloddy lumps. Not much mois­ture at all was present at those deeper lev­els men­tioned in the un­cul­ti­vated sec­tions. I re­peated this same com­par­i­son in other parts of this same block lo­ca­tions with a sim­i­lar re­sult. So why was the strip cul­ti­vated sec­tion much bet­ter mois­ture-wise? And it has to mean that the scat­tered and not very large rain events in­fil­trated the cul­ti­vated soil sec­tions bet­ter and more evenly. Does that mean we should all go out and cul­ti­vate be­fore the next rain? Not re­ally, how­ever it cer­tainly al­lows us to think and con­sider that some cul­ti­va­tion op­er­a­tions per­formed at the cor­rect time as far as soil struc­ture goes can be very ben­e­fi­cial in mois­ture ac­cu­mu­la­tion and struc­ture for­giv­ing. That is the first thought, how­ever we all know that re­tain­ing up­right stub­ble par­tic­u­larly, is hugely im­por­tant in our fal­low pe­riod and for slow­ing over­land wa­ter flow and ero­sion ac­tiv­ity.

That is why the strip tillage sys­tem ap­peals to me so very much. It is not the first time, over many years, that I have seen the ben­e­fits of this best of both worlds strip tillage sys­tem. It cer­tainly pleas­antly sur­prised me to see this ef­fect af­ter an ex­tremely dry pe­riod.

PHOTO: CON­TRIB­UTED

CROP­PING ME­CHAN­ICS: A strip tillage sys­tem in a pad­dock.

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