DRY CONDITIONS IN THE SA MALLEE
Richard Saunders Agricultural Consultant, Loxton SA While farmers in many parts of the country have had good summer rains, farmers in the northern Mallee of South Australia have now given up hoping for summer rains this year. The rainfall total for Loxton since January 1 has been 23.3 mm, which is roughly half of the long-term average for this period. Long term average annual rainfall for Loxton is 263 mm, so we farm in a dry part of the world. We have emerged from a wonderful yield season in 2020, where surprisingly we recorded 3 mm less than the long-term average, but yields were double the average (wheat and barley 2.5 t/ha, lentils 1 t/ha etc.). 2020 was a great season to catch our breath as it were, because, like other areas of Australia, there was little joy in the two seasons before that: 2018 and 2019. The issues now, with such a dry summer are: residual soil herbicides; planning for Russian Wheat Aphid; dry sowing decisions; and last-minute changes to seeding plans as a result of the dry. Herbicides with long soil residuals make rotation planning interesting – planning crops and varieties around past applied herbicides and factoring in the amount of time and rainfall since application. The chief of these herbicides are the Clearfield chemicals, clopyralid and to a lesser degree extend 2,4-D amine on sands. Many of the newer herbicides now come with a soil residual - time period and rainfall plantback requirement. The dominant landscape here is dune- swale, with 33% of the landscape as deep silicieous sand rises or dunes. These rises are generally low
fertility, low organic content and highly fragile. A key management strategy is to keep stubble cover; an important component of this is stock management. Sheep will camp on tops of these rises and quickly bare the areas creating blow outs when winds blow. Some growers have gone to confinement feeding pens over summer to minimise the erosion. This silicieous sand also tends to pack into layers. These seams can be 10 to 30 cm thick and from 15 to 60 cm below the soil surface and seriously restrict plant roots to the point where crops on the constrained hills struggle for moisture and nutrient even during good seasons. Judicious ripping
to 450 or 600 mm has seen yield increases of 1 t/ha. However, ripping without compacting topsoil can also result in loss of cover and stability. Russian wheat aphid has been with us since 2016 and seems to enjoy persisting and persecuting the wheat and barley in warm, dry areas like ours. Most growers apply an insecticide seed dressing to give some crop protection for 6-8 weeks. In 2020, growers who failed to protect and monitor crops, in extreme cases, lost very significant yield. A number of growers will start sowing to a date despite no moisture. They will sow dry into paddocks with very low grass weed numbers, or
KEY POINTS
• Northern Mallee, SA
• Residual soil herbicides
• Below average summer rains
• Planning for Russian Wheat Aphid
• Wonderful yields in 2020
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