Turning stubble beats burning

A stubble load of 15 t/ha is incorporated across the whole area (beds andforrows) but ends up with most of it in the beds. The effect is about 10 t/ha in the beds - a huge amount of stubble.

Maize stubble carefully turned into the soil is out-performing burning as a method of preparing the soil for higher-yield crops.

Irrigated maize grown as part of on-farm field research at Whitton in NSW yielded 14.2 t/ha through stubble incorporation compared to 12.8 t/ha for conventional burning treatment. These results were similar to a nearby farmer-initiated trial where irrigated maize yielded 12.5 t/ha through incorporation compared to 10 t/ha under burning.

Research leader Clive Kirkby of CSIRO Land and Water, Griffith, said stubble was incorporated or burnt in August 2000 and the next crop was planted in November.

“Sampling throughout the season showed that the soil with stubble incorporated held about 2 per cent more moisture, had lower soil strength, higher microbial biomass and 72 kg/ha more usable nitrogen than the burnt soil,” Dr Kirkby said.

“The strong performance of stubble incorporation is good news at a time when there is increasing opposition to burning and various regulations are being introduced.”

Fungi, Rhizoctonia stay dormant

“One worry about incorporation was the presence of fungi, but we saw no evidence of an increase in disease at any stage. In fact, at the farmer-initiated trial, we found that burned soil is very susceptible to the undesirable microbe Rhizoctonia. The burned area was severely infected with Rhizoctonia while the incorporated area seemed to suppress it.”

The formula for turning in stubble is targeted at maximising decomposition rate through close soil to stubble contact, good oxygen supply, adequate nitrogen and sufficient moisture and temperature.

How It’s done

The process is as follows:

  • chop the stubble to 100 mm or less and mix closely with soil. Offset discing is adequate, rotary hoeing is better, rotavator is the best
  • incorporate the stubble in the top 15 cm to ensure an adequate supply of oxygen while preserving as much of the natural soil structure as possible
  • when switching from burning to incorporation, it may be necessary to add nitrogen to really get things moving in time for the next planting. Nitrogen supplementation was not needed during this research and therefore the preferred form and application rate were not studied
  • incorporate the stubble as soon as possible after harvest to take advantage of any moisture available between harvest and planting and to allow maximum decomposition time.

Ongoing questions

“While our low-tech incorporation approach looks promising, we still have some obstacles to overcome: the right level of decomposition, measuring decomposition in the field and ensuring we are not going to get a long-term disease build-up,” said Dr Kirkby.

“If the ground is too wet to incorporate early or if the erosion potential is so high that surface retention is preferable, we need to look at other ways to maximise decomposition rate and that’s where biological control may come in.”

The research team is hoping to build upon the research at the farmer-initiated trial and compare burning (full and flag), incorporation and surface retention in a maize-wheat rotation as part of a further farmer-run trial at the Coleambally demonstration farm.

Program 3.4.2

Contact: Dr Clive Kirkby 02 6960 1596