Source: The Crop Doctor, Grains Research & Development Corporation

The dream of every irrigation farmer is to regularly produce an eight tonne wheat crop. Given their control over soil moisture that should be possible, it should even be possible one year in five in the higher rainfall areas of our wheat belt, but for most it's an unobtainable dream.

Dr Maarten Stapper, Research Scientist, CSIRO Plant Industry, is putting the pieces together to make the big crop a reality and surprisingly suggests things should start with the previous harvest. Good seed quality with at least 70 percent of the seeds emerging is important, that's emergence, not germination.

His paddock measurements in the irrigation country have turned up many examples of 50 percent emergence rates and he even saw some down to 25 percent. Cracked seed is the culprit and the remedy is to harvest next year's seed early, at the right moisture content.

That done, time of sowing becomes important. Of course, available moisture dictates the sowing date but it's a case of matching variety to that date to get the optimum flowering time and while the problem of late sowing and frost risk is well understood, much less obvious, but equally damaging, is the impact of heat on the crop flowering too late. Expect a five percent yield loss for every one degree celsius increase in average post-flowering temperatures.

The ultimate frustration is the big crop that either doesn't finish or that falls over and plant breeders are doing something about lodging. All our current varieties depend on one of two dwarfing genes, neither particularly associated with straw strength. In recent times an additional 18 dwarfing genes have been identified two of which seem to be associated with stronger stems. They're now being used in our breeding programs to back cross with some of our higher yielding, quality varieties but we don't have to wait for new varieties to address the problem of the big crop lodging.

Wheat is from the cool-temperate climate areas and the winter in our irrigation and high rainfall country is too good for the plant. The result is a crop out of balance, with too much vegetative growth before flowering and without the structure needed to support a high grain yield. The big crop depends on the right frame and that means controlling the growth of the crop by timing the application of nitrogen fertiliser.

There has to be enough to produce the 600 to 800 tillers per square metre at the end of tillering needed for an eight tonne crop, but nitrogen applied too early in the plant's growth results in too many tillers, weak straw and lodging. Stem strength increases when about 70 percent of the ground is covered at the start of stem elongation. The critical time for application is as the crop moves through mid-stem elongation, about five weeks before flowering.

This season, in a series of trials in the irrigation area, Dr Stapper is pulling together all of these factors. Under test will be 70 lines from all over Australia in a straw strength comparison with 30 released varieties. Included will be some interesting international lines from France and CIMMYT. Some have already proved to have good straw strength but poor quality and we're widening the basis of our breeding programs evaluating the new dwarfing genes.

The use of growth regulants in big crops is standard practice overseas, but here the results are more variable. Dr Stapper speculates that our higher winter temperatures may be the cause and he'll trial some old and some new chemicals. He'll also compare sowing rates, arguing that lower rates produce stronger straw and bigger yields and he'll continue the work he's been doing on the timing of nitrogen application.

Overall he'll continue to argue the case for biological farming - not organic farming but a system that starts with getting the soil biota in balance to secure plant anchorage by stronger roots, the start of the dream eight tonne crop.