IF THERE'S any silver lining to the lack of rain across the northern grains region in 2002, it is proof positive that industry best practice — conservation farming, zero/ minimum tillage and deep sowing — can deliver satisfactory crops under drought conditions.
And with the absence of disease, insect and weed problems to be expected in a better season, 2002 allowed a NSW Agriculture team, benchmarking chickpea yields, to study the effects on yield of plant-available water (PAW) based on fallow and in-crop rain.
And it was PAW at sowing that had most influence on eventual yield. Ninety per cent of the variation in chickpea yields was explained by variation in PAW — fallow and in-crop combined — Tamworth agronomist Giles Butler told a Grains Research Update for Advisers at Goondiwindi in March.
The collaborative NSW Agriculture team led by Bob Martin, John Holland and Mr Butler had made a pilot study of 15 farms in 2002. They wanted to determine the factors affecting the production and profitability of alternative crops to wheat. They were also looking for the constraints to crop diversification and adoption of sustainable practices in broadacre cropping.
They benchmarked 12 paddocks of chickpea and eight adjoining ones planted to wheat, selecting chickpea crops that were growing well despite the drought and then looking for the closest wheat paddock with a similar fallow history.
In terms of water-use efficiency, wheat performed better than chickpea in the drought. As PAW declined, water-use efficiency (WUE) remained relatively constant for wheat but harvest index and WUE declined with PAW for chickpea. However, chickpea tolerates deep sowing much better than wheat, so there were more opportunities to sow chickpeas than wheat (see related story page 19). And, with the dollar value of chickpeas being higher than wheat, the crop with the highest gross margin in NSW varied.
WUE for wheat averaged 10.6 kg/mm for header estimates, and remained fairly constant across the range of PAW experienced. WUE for chickpea declined from 11 kg/mm for a 2 t/ha crop with 160 mm PAW to just over 2 kg/mm for a 0.25 t/ha crop with 100 mm PAW.
Fallow rainfall was a stronger yield determinant than in-crop rain, as the four chickpea crops that received more than 400 mm of rain in the October-May fallow — all east of the Newell Highway — averaged 1.7 t/ha and the eight with less than 400 mm in the same period averaged 0.6 t/ha.
When to reconsider chickpeas
"We concluded that planting chickpeas on less than 400 mm of fallow rain, 100 mm available soil water or 70 cm depth of wet soil should be considered risky if the probability of in-crop rainfall is low," Mr Butler told the Goondiwindi Update.
"Harvest losses of chickpea were estimated at 0.23 t/ha (20 per cent) which was worth over $100/ha based on 2002 prices. This was the most serious problem that had potential to be managed in 2002."
Contact: Mr Giles Butler 02 6762 1100