Crop growth was measured with the aim of demonstrating differences in growth patterns between Till and No-Till crops. Growth was measured at three stages: GS30 (early stem elongation), GS65 (anthesis) and GS99 (maturity). For cereals, these growth stages mark (approximately):
- The end of vegetative growth (GS30), which sets up the canopy for grain set and grain growth,
- The grain set period (GS30 to GS65), where grain number is (mostly) determined, and
- grain growth (GS65 to GS99), when assimilate stored in the plant is transferred to the growing grains.
To simplify operations, the same measurement timings were used for pulse crops, although the GS30 measurement was often not made. Hay making in some paddocks (eg. Yaapeet, Patchewollock Till) made it difficult to collect final measurements.
Biomass
Despite the poor seasons, farmers in some areas each year were able to grow cereal crops with reasonable biomass (up to 8 t/ha) at anthesis (Figure 31a-c). These were often crops on fallow. Most cereal crops though were in the range 1-6 t/ha. As a comparison, a study with narrow row spacings and a range of seeding systems measured anthesis biomass 4-9 t/ha in the Wimmera and 4-11 t/ha in the Mallee between 1989 and 1992 (O'Leary and Connor 1997).
The GS30 biomass was generally less than 1.5 t/ha, with most high GS30 biomass coming when the measurements were made late (eg. Donald in 2006, Yaapeet Till in 2007). Due to the poor seasons, GS99 biomass was generally similar to or less than anthesis biomass, and yield (with a few exceptions) much less than the potential indicated by biomass at maturity (low harvest index).
The year 2006 was best for comparing Till and No-Till crops in biomass, because they had similar history and were planted to similar crops (the Sea Lake paddocks are an exception). No-Till crops all had lower GS30 biomass, but tended to have more growth between GS30 and anthesis, and similar yield. In 2007, the Culgoa crops were comparable and again biomass at GS30 and GS65 was greater, but final yield similar. There were no comparable crops in 2008. In general, Till crops had higher GS30, GS65 and often GS99 biomass, but not necessary yield.
Figure 31. Crop biomass at sample points in focus paddocks, measured at GS30, GS65, GS99, and grain yield, in years 2006 (a) – 2008 (c). Where there are no measurements, the paddock was in fallow. Where measurements are missing, hay has been made in the paddock (missing GS65/99) or the paddock had a pulse crop (missing GS30).
A striking feature of the GS99 biomass and yield measurements (Figure 31a-c) was that yield was often low compared to GS99 biomass (low harvest index). Within and across years, there was a relationship between higher harvest index and higher yield (Figure 32). In 2006 the Till and No-Till crops were on a similar relationship, but in 2008 the Till crops had higher yield for a given harvest index. In 2007 there were too few Till crops harvested (Yaapeet and Patchewollock crops were hayed) to make a distinction. Note that the 2006 Till crop with low harvest index (0.15) and higher yield (0.9 t/ha) was the frosted wheat crop at Sea Lake.
Figure 32. Relationship between yield and harvest index.