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The importance of plant roots

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The second is a three part series by Ausplow owner and managing director John Rya AM. 

More than 50 years ago farmers were satisfied in the knowledge that building soil structure was the sensible pathway to sustainable and profitable cropping. It became a priority for many, after decades of clover-ley farming, to renovate pastures by deep tillage and/or incorporating stubble to alleviate soil compaction issues and build soil structure. Today we see more farmers turning back to sheep and assessing pasture rotations involving serradellas, clovers and grasses, in a similar way to those who farmed in the sixties, seventies and eighties. For many full-time croppers, however, we still lack a profitable legume for rotation. So what’s the answer? Years ago I remember sowing sorghum and the resultant effect it had in the soil. The plant’s fibrous roots provided a biological till of sorts while building soil structure. What also impressed me was the residual effect which was for a longer period than deep tillage. This is why I talk about the timing of deep tillage. Ideally you want plants growing in deep tilled soil to ensure the soil doesn’t collapse back and seal. Some farmers have deep tilled immediately after sowing – if conditions are ideal – or opportunistically on spring rain or after summer rain events. Depending on moisture levels in the soil, an additional program would be to establish an opportunity crop on the deep tilled country (Coil packers are very good to firm up soil before seeding). The whole exercise is beneficial in reducing non-wetting issues, reducing soil hardpans and creating an environment where moisture can “cleanse’ the top soil. And the focus is on root systems which are beneficiaries of subsoil cultivation and improved moisture infiltration and retention. Remember that moisture increases the amount of oxygen in the soil at depth which is vital for biological activity to decay matter and turn it into soil humus. If you’re mouldboarding and inverting the soil, sow a crop as quickly as possible, perhaps oats, to replace the roots you’ve inverted. In the early days of deep tillage, many farmers had seed boxes on them to plant pasture or a summer crop. The extension of keeping roots in the soil, I think, will lead to a diminution of deep tillage. The focus is on digging deeper, beyond 18 inches, but I don’t think that’s necessary. With a seven inch blade on your DBS, you can break the shallower hard pans and build an environment where plant roots virtually take over the job of tilling. A seven inch blade will scratch the surface of the next layer of hardpan and moisture will soften the “scratch” allowing roots access. How many times have you seen plants growing out of rock? Those of you who have dug soil pits are aware of how far down plants roots travel. You might argue the classic L-shaped roots you often see on canola plants, for example, are a sign that roots can’t access hardpans. Closer analysis of the soil might be more revealing, taking into account issues like acidity, sodicity and actual plant strength to penetrate hardpans. I believe maintaining a good root structure in the soil will provide many benefits, apart from the residual effects I spoke about earlier. NEXT WEEK: Building soil structure.

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Saturday, February 25, 2017