By Claire Browne and Jessica Lemon, BCG
- Time of sowing had a significant effect on yield.
- There was no interacting effect of the way the stubble was managed and the time of sowing on yield.
Retaining stubble in broadacre cropping systems is recognised as an effective soil water conservation method. The stubble ground cover acts as a barrier to evaporation, thus making more soil water available to the crop (Hunt, 2013). However, a higher stubble load may also hinder early crop development as a physical barrier at crop emergence.
Previous research conducted by BCG in 2011 indicated that grazing stubbles does not reduce the amount of soil water stored during the summer fallow period or subsequent crop yield (Jones and Ferrier, 2011).
This research investigated whether the effects of stubble position and load on crop productivity varied with time of sowing.
In situations where stubble load needs to be managed or reduced in some paddocks, the risks of reduced stubble load might be reduced by sowing the paddock earlier in the program.
Aim: To determine if the emergence and yield of wheat was influenced by stubble residue management prior to sowing across a range of sowing dates.
Table 1: Methodology
Following harvest of the barley in 2014, treatment plots were slashed in March 2015, burnt in mid-April or left standing. Stubble was approximately 40cm high. At sowing the standing treatments were inter-row sown.
This experiment was developed based on the assumption that stubble-retained paddocks have greater moisture conservation and these paddocks might be able to be sown later in the program without yield penalty.
While the majority of the Mallee experienced a decile 1-2 season, the Wemen trial site had the advantage of being on lighter soil with the option to irrigate. The four times of sowing (TOS) produced varying grain yields, and with the earlier sowing times yielding more than the last TOS.
There was a penalty of 0.9t/ha for delaying sowing 25 days from the first to the last TOS. It is likely that the TOS 4 treatment was flowering during a heat wave, which negatively affected the yield. The later TOS would also have been establishing in cold soil, which perhaps reduced tillering.
Throughout the sowing period the trial site only received 10mm of rainfall one day after the fourth TOS (Figure 1). Due to a large rainfall event, the site had a full profile prior to TOS 1. We were trying to ascertain if a delay in sowing after this first rain event meant the seed bed dried, resulting in delayed germination. However, further rain between TOS 1 and TOS 2 may have reduced the potential for this effect to occur (Wemen received 53mm in April in 2015 which is much higher than its long term average of 21mm).
While TOS had a significant effect on yield, there was no interaction between TOS and stubble treatment, nor an effect of stubble treatment alone (Table 1). Contrary to our expectations, there was no interacting effect of the way the stubble was managed and the TOS on yield.
This interaction requires testing over a range of season types to develop confidence that there is no effect, and there is likely to be a substantial difference between the effects of a one-off stubble management treatment compared with repeated interventions to the level of stubble load.
Table 2: Wheat yield (t/ha) under the three stubble treatments and wheat yield for the four different TOS.
The stubble project – maintaining profitable farming systems in Victoria and Tasmania with retained stubble (project number BWD00024) is funded by the GRDC.