A CONSERVATIVE approach to soil moisture management in dry years has been the key to success of double-skip sorghum trials in the Eastern Farming Systems based in northern NSW and southern Queensland.
The trials aimed to compare the yields and gross margins of double-skip sorghum, where two adjacent rows are unplanted and two are planted, with two other popular configurations - solid planted sorghum sown on I-metre rows, and single-skip sorghum, in which one row in three is unplanted. The work was supported by growers and the Federal Government through the GRDC and by NSW Agriculture, CSIRO, Queensland Department of Primary Industries, and MCA Agricultural Consultants.
According to one of the participating growers, James Clark of 'Colane' near North Star in northern NSW, double-skip sorghum reduces the total risk of his wheat-cotton- sorghum-chickpea farming system.
"Although both solid and single-skip sorghum have yielded better than doubleskip in wetter years, I don't believe this will be the case in dry years," says Mr Clark. "Double-skip sorghum eliminates my chance of growing a loss-making crop."
In a very wet year with a full soil profile, Mr Clark says he would probably consider planting single-skip sorghum, to take advantage of the extra moisture. Data from other sites in the same trials reinforce this point (see table for sorghum yield and soil moisture comparisons). In wetter than average seasons, double-skip planting has tended to give lower yields than solid or single-skip planting.
Scientists and agronomists involved in the trials say that APSIM simulation models developed from these and other trial data predict that benefits would be most clear in a very dry year in which yields were as low as around 2.5 tlha.
Extra water from skipped rows
"In this case, the extra water available from between the rows of double-skipped sorghum would reduce the water stress at flowering and grain fill, resulting in more grains per head and larger grain for double-skipped sorghum," says NSW Agriculture agronomist Giles Butler. This effect has already been seen in yields of single-skip sorghum compared to solid planted sorghum at the North Star site (see table).
An additional benefit, forecast by 50 years of model simulations, is that planting and harvesting double-skip sorghum early give the soil moisture time to build up for the next chickpea crop, increasing total farm profitability. Benefit for following chickpeas?
In Mr Clark's experience, chickpeas planted into a double-skip paddock are taller and have yielded more than the other row configurations. "With chickpeas at $5OO/tonne and sorghum at $120/tonne, a yield increase of 0.4 tlha of chickpeas more than pays for the 0.5 tlha loss in sorghum yield from double-skipped paddocks."
By combining his experience with the APSIM model predictions, Mr Clark has been able to set a rough benchmark for how his crop should be performing. It is then a matter of identifying reasons for major differences.
"I have been aiming to manage the farming system to reduce my exposure to risk and to maximise profits over the whole rotation," says Mr Clark. "I'm not aiming simply to grow the best sorghum crop in any single year."
Program 4 Contact: Dr Jeremy Whish 07 4688 1419 Mr Giles Butler 02 6763 1266 Mr James Clark 02 6754 5212
Yield, soil moisture and rainfall data for MR Goldrush sorghum (quickmaturing variety) and MR Buster (medium-maturing variety) from field testing at selected sites in northern NSW and southern Old in the 1998-99 and 1999-2000 seasons.(MR stands for Midge Resistant.)
|Location||Planting strategy||Yield (t /ha)||In-crop rain (mm)||Chance of a better season||Plant available water at harvest (mm)|
|Within rows||Between rows|
|North Star, NSW (planted MR Goldrush on 28/9/98)||Solid||3.66||226||50||37|
|North Moree, NSW (planted MR Goldrush on 27/9/98)||Solid||4.70||300||27||20|
|Meandara, Old (planted MR Goldrush on 6/1/99)||Solid||4.32||260||28||0|
|North Moree, NSW (planted MR Buster on 28/9/99)||Solid||5.48||296||28||57|