Agronomist discusses the importance of soil structure
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.
CROPPING MECHANICS: A strip tillage system in a paddock.