The Soil Conservation potential of Legume stubbles.
When I started farming, for some odd reason we were bare fallowing field pea stubbles, with full cultivation, after running a bunch of sheep. What a crazy idea that was – clods and stubble alone were not enough to stop the wind erosion on the best ground. And look at the first photo – locals still trying to fatten some fat lambs on beans. Ok, good for lambs, but you can see with a gust of wind what is getting lifted (maybe the finest soil particles, humus and with it, valuable nutrients?). No doubt it will get ripped up on the next rain to ‘clod it up’. It was sown into cereal stubble, but with full cultivation there is little of that left. The trouble is, our summer rains are unpredictable. The alternative is to dry cultivate.
Surface Residue Retention
Now of the second photo, see what remains (in the same district) – faba bean stubble left left in last year’s cereal. Even with the cereal falling over now, it adds to the ground cover, and the upright anchoring of anything tempted to move with a wind. And from his practices, I doubt the farmer will put sheep on it anyway. THAT is what I like. With a little bare ground showing, he may not preserve much moisture yet ready for autumn sowing, but it will be more than the bone bare bean stubble. It might also establish a cover crop better (if it conserved moisture).
Having said all that, the air temperature today, mid January, is 42C, not too different from some other days since mid December when we had our last rainfall event over 40 points. (2012 on this farm was the 3rd driest on our records.) That means that any cover crops sown into the already dry soil would still be there (and in my Dec 2012 trial, still are). Not even the weeds are germinating. These are the conditions we face when considering how or when to sow summer cover crops in the Wimmera.
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This, from Sep 2013, is a pic from the same position of the paddock with a blowing bean stubble early this year. There is every confidence this year (a bumper year in some nearby areas, still below average rainfall here). Crops are good, stubbles will be thick, and much grazing and burning will be done, I suspect (hmmm….) Recency bias and short memories are the bane of soil – it is easy to take the risk of leaving ground bare for a while and hope it doesn’t blow, knowing / hoping that the coming crop will cover the ground again.