Pulse-wheat rotations come out winners
GroundCover™ Issue: 31
Rotation cropping has come out well in front of long fallow and continuous cereal cropping in trials by the Western Farming Systems project in northern NSW and Queensland.
With two core sites in NSW, 'Willmon' near Coonamble and 'Cryon Station' nearWalgett, and 13 supplementary sites through NSW and Queensland, growers and researchers are testing crop rotation options to increase sustainability across a range of environments.
According to Jan Edwards of Agriculture NSW, the continuous cereal system is the poorest-performing system in terms of grain yield and protein, yielding up to 1 t/ha less than a pulse-wheat rotation at 'Cryon Station' alone (Table 1 shows these results), even with added nitrogen fertiliser.
"A pulse-wheat rotation, for example with wheat in 1999 following chickpea or canola in 1998, was the best-performing system over the four years of the trial in terms of protein, gross margin, water-use efficiency and reduced disease levels," says Ms Edwards.
To emphasise the relative merits of a rotation system over a continuous cereal system, Ms Edwards points out that, even with the inclusion of barley, the continuous cereal plots suffered from yellow leaf spot in the very wet winter of 1998. They also had a high incidence of crown rot, which dramatically reduced yields and water-use efficiencies.
For grower Dennis O'Brien of 'Cryon Station' these results have shown not only what they had already seen with diseases in the continuous cereal systems, but also some of the drawbacks of the long, 12-month fallow adopted by many growers in the district to store moisture.
Costs of long fallow
"Although the yields and protein levels were much better in a long fallow than in a continuous cereal system, the cost of long fallow was high in terms of wasted water, poor use of nitrogen, and lower gross margins," says Mr O'Brien. "We learnt how to store moisture, but it meant using twice as much land for a crop and that affected the bottom line."
According to Ms Edwards, at both 'Cryon Station' and 'Willmon', the 12 months fallow stored only an extra 20 mm of water but it stored a huge 150 kg/ha of extra available nitrogen, not all of which could be used by the crop.
"It is clear that the yield and protein benefits of long fallow on both trial sites have more to do with exploitation of soil nitrogen fertility than from accumulation of fallow water," says Ms Edwards.
Ms Edwards is quick to point out that it is not necessary to have a long fallow to increase soil nitrogen levels. A chickpea crop in 1998 provided an extra 99 kg/ha of soil nitrogen for the 1999 season, which was more than adequate to give 3.6 t/ha of DR1 quality Wollaroi durum grain that year (shown in Table 1).
Rotation best gross margin
These results are consistent with experience in broadacre crops around the district. The chickpea-wheat rotation had the greatest cumulative gross margins throughout the four seasons of me trials. It also had less common root rot and crown rot, and this, in combination with higher soil nitrogen, accounts for the increase in yield.
"These results will add further encouragement to growers in the Western Farming Systems project area. Chickpea plantings in the Walgett area alone are predicted to increase this year to 40,000 hectares," says Ms Edwards.
Look at lucerne as well
The nitrogen benefits of a lucerne pasture phase are also within easy reach of growers. A lucerne pasture fixed an impressive 250 kg/ha of nitrogen over two and a half years, an amount sufficient for two cereal crops.
But the trials showed it is important to remove lucerne early, at least by September, to allow the soil profile to recharge with water for the next wheat crop.
The trials also extended the legume varieties growers are willing to try. "We are now looking at not just lucerne, but other legumes such as vetch, medic, lentils, cowpea and even mung beans," says Mr O'Brien.
Total performance? Check water-use efficiency
For growers interested in the performance of their cropping system as a whole, the trials have established the value of calculating the water-use efficiency (WUE).
At 'Willmon', where the trial paddock was selected because it was run down, WUE did not exceed 10 kg/ha/mm on any system. At 'Cryon Station', by comparison, WUE ranged from around 10 kg/ha/mm on the continuous cereal systems to a satisfactory level of 15 kg/ha/mm on the chickpea-wheat system.
According to Ms Edwards, "we can say fairly conclusively that WUE at 'Willmon' appeared to be affected most by soil factors, and for each of the cropping systems at 'Cryon Station' WUE appeared to be affected more by disease levels in the crops than by other factors such as soil fertility".
"The trial block has shown us the details about direct-drill and rotations as options for doing things more sustainably and at a greater profit in the long run," says 'Willmon' grower Bob Hogland.
"We had been cropping wheat for more than 30 years. In hindsight we would probably say that we should have done things differently."
|Cropping system||Continuous cereal (W-W-B-W)||Long fallow (f-W-f-D)||Pulse-wheat rotation (CP-W-CP-D)|
|Available nitrogen at sowing||68 kg/ha||243 kg/ha||139 kg/ha|
|Wheat grain yield||2.48 t/ha||4.17 t/ha||3.62 t/ha|
|Water-use efficiency||8 kg/ha/mrn||14 kg/ha/mm||16 kg/ha/mm|