A very wet early March (130mm in our case) resulted in big delays for sowing dual purpose crops in many paddocks across NSW, especially in one with poor drainage, at least in some parts of the paddock. Further rains in late March, just as many of these were becoming trafficable again, further delayed sowing.
While dual purpose crops sown early, are commonly less critical in a year with a good autumn, and possibly winter, they nevertheless are a good option for providing quality winter feed that can allow other grazing paddocks more time to develop a good winter feed base. So the dilemma what to do with the proposed crop.
Despite good summer herbicide weed control, including "double knock" for fleabane and windmill grass, two of our three dual purpose paddocks had, in early March, a reasonable uniform population of self-sown oats. We felt that if these were left to develop they had the potential to provide good winter grazing. In contrast if we had sprayed them out and sown when dry conditions allowed this would not have been possible until well into April. Good winter feed from late sowing would be months behind the self-sown option.
Many other mixed farmers were also taking up this option. A few critical points can help make this a sound decision. Having good sub soil moisture, via fallow weed control, plus little fallow weed growth to tie up nitrogen was a good starting point.
Variety type of the previous crop is important. In our case oat variety Eurabbie, and in other cases triticales like Kokoda and wheats like Illabo, all with "winter habit", suit for self-sown early establishing dual purpose or grazing only situations. Germinating in February to March, varieties with winter habit remain vegetative generally through to late winter, before deciding to run to head. Spring habit self-sown varieties in contrast run prematurely to head, often heading by mid-autumn. These decline in quality as they stem up and need to re-form new tillers for further grazing.
Soil phosphorus is another important consideration. Research has long established that where soil phosphorus deficiencies exist placing fertiliser close to the seed at sowing is the most efficient way to address this issue. However if good levels of phosphorus fertiliser have been used in previous cropping and pasture programs, as often has been the case, soil levels may well be better than commonly expected.
Recent research by Grain Orana Alliance (GOA), with GRDC funding, in central west NSW, has often found that applying fertiliser phosphorus to the soil surface, works better than commonly expected. While normally not as efficient as applying phosphorus close to the seed, responses have commonly been good.
Using our example, previous fertiliser use has resulted in a moderate soil phosphorous level, although still in the fertiliser responsive category. We applied MAP, purchased for sowing at seeding, via topdressing ahead of a good late March rain event. Rate used was 70 kg/ha, enough to supply around 15 kg/ha available phosphorus.
We also applied urea at 100 kg/ha (46 kg/ha nitrogen) at the same time of MAP application to cover a likely moderate nitrogen deficiency. It is more important for nitrogen to be applied ahead of a likely good rain event than it is for phosphorus.
Commonly weeds are more likely to be an issues in self-sown crops than sown ones. This has been addressed in our case via early herbicide treatment. MCPA is a good general purpose broadleaf herbicide suited to earlier application than 2,4-D. There are a multitude of other herbicide choices for early post emergent crop weed control (see the NSW DPI Weed Control in Winter Crops publication). Adding a fungicide to the herbicide treatment may also be a sound decision, especially in rust susceptible oat varieties (most of them). Rust can be especially a problem in early establishing oats.
Clearly this is not an endorsement of self-sown crops compared to sown ones, but sometimes we have to "think outside the square". Sometimes when it is too wet to sow on time options like self-sown can feasible. Another, that may occur later this year, is flying on seed to paddocks too wet to sow.
Next week: Strategy to combat stripe rust in wheat.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
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