Sowing early in 2014 - how did it work?

James Hunt¹, Brad Rheinheimer¹, Rob Wheeler², Amanda Pearce², Ian Ludwig, Andrew Ware², Leigh Davis², John Nairn², Stuart Sherriff², Mick Faulkner³, Jeff Braun³, Lou Flohr³, Sarah Noack⁴ and Peter Hooper⁴,

¹CSIRO Agriculture; ²SARDI; ³AgriLink Agricultural Consultants; ⁴Hart Fieldsite Group.

GRDC project code: CSP00178, CSP00160

Keywords: early sowing, slow maturing wheat, winter wheat, time of sowing, frost.

Take home messages

• Despite wide-spread stem frost in the majority of 2014, time of sowing (ToS) trials in SA indicated that the highest yields still came from mid-late April sowing.
• Based on one year of data, Trojan (mid maturing) complements Mace (fast maturing) in a cropping program and allows growers to sow earlier and achieve higher yields (16%) than they could with Mace alone sown in its optimal window.
• Existing slow maturing wheat cultivars from other states are poorly adapted to most regions in SA.
• For growers in frosty environments wishing to sow before ~20 April, EGA Wedgetail is the safest option evaluated in these trials, but yields are likely to be less than Mace sown in its optimal window.

Background

In SA the time at which wheat flowers is very important in determining yield (Figure 1). With farm sizes increasing and sowing opportunities decreasing, getting wheat crops established so that they flower during the optimal period for yield is difficult. Whilst no-till and dry-sowing have been used successfully in SA to get more area of crop flowering on time, an opportunity exists to take advantage of rain in March and April to start sowing crops earlier than currently practiced. This is a tactic which complements dry sowing. Earlier sowing is now possible with modern no-till techniques, summer fallow management and cheaper insecticides and fungicides to protect against diseases associated with early sowing. 

Figure 1. The relationship between flowering time and yield at Minnipa and Tarlee – optimal flowering periods are highlighted by light and dark grey boxes. Curves are derived from APSIM from 120 years of climate data and with a yield reduction for frost and extreme heat events. Optimal flowering periods are late August-early September at Minnipa, and mid September at Tarlee.

However, in the last few decades wheat breeding has focused on mid-fast maturing varieties which are only suited to sowing in late April-May. Sowing earlier than is currently practiced requires cultivars which are not widely grown in SA, and which are much slower to mature, either through having a strong vernalisation/cold requirement (winter wheats) or strong photoperiod/day length requirement (slow maturing spring wheats – Figure 2).

GRDC funded research in NSW has demonstrated that slow maturing varieties sown early yield more than mid-fast varieties sown later when they flower at the same time . This is because early sowing increases rooting depth and water use, reduces evaporation and increases transpiration efficiency. Early sowing of slow maturing varieties is a way of increasing yield potential with very little initial investment.

APSIM modeling indicates that even with SA’s Mediterranean climate, adoption of slow maturing varieties to allow early sowing has the potential to increase whole-farm wheat yield, particularly in mid-high rainfall zones (Table 1).  GRDC have funded a series of trials across rainfall zones to experimentally evaluate the suitability of early sowing in SA.

Table 1. Average farm wheat yields from 50 years of simulation at different locations in SA assuming either current practice (mid-fast varieties sown from mid-May including dry sowing) or the addition of a slow maturing variety to the cropping program which can be planted from 1 April, but is only sown when planting opportunities arise (occurs in ~60% of years).

Methodology

GRDC early sowing trials in SA are at five locations (Cummins, Minnipa, Port Germein, Tarlee and Conmurra) and each has three times of sowing (aimed at mid-April, early-May, late-May) and 10 wheat lines (6 commercial, 4 near-isogenic lines, or NILs, in a Sunstate background ). The commercial lines are described in Table 2. Hart Field Site Group also planted a similar early sowing trial, and there are also trials funded by SAGIT evaluating different wheat lines for early sowing in the Mid North and upper YP.

Table 2. Commercial wheat varieties used in the SA trials at Cummins, Minnipa and Port Germein.

Results

Results from all experiments are presented in Table 3. At four out of five sites, Trojan sown in mid to late April was the highest or equal highest yielding treatment. Slow maturing cultivars bred in other states (e.g. EGA Wedgetail, EGA Eaglehawk and Rosella) showed poor adaptation to all sites. 

Table 3. Grain yield for five out of six early sowing trial sites in SA in 2014 (results for Conmurra not available at time of preparation). Treatments known to have been affected by frost are marked with an asterisk.

Putting early sowing into practice in SA

Based on the 2014 trial data, growers in SA could improve whole-farm yields by including Trojan in their cropping program to complement Mace (Figure 3). Trojan has an unusual photoperiod sensitivity allele inherited from a European parent which is rare in Australian cultivars. This allele seems to delay flowering from an April sowing relative to Mace quite successfully (Table 4). 

Figure 3. Mean yield performance (Minnipa, Cummins, Port Germein, Hart, Tarlee) of Trojan and Mace at different times of sowing relative to Mace sown in its optimal window of early-mid May. Error bars are standard error of means.

Table 4. Flowering dates for Trojan and Mace from different times of sowing at Minnipa in 2014.

Despite performing strongly from a mid-April sowing in these trials, it is not recommended that Trojan be planted this early in the majority of SA locations as it incurs excessive frost risk. As a rough rule of thumb, it is best suited to being planted ~10 days earlier than Mace. As an example of how it may fit in a program, if 10 May is the optimal sowing time for Mace in a given environment, then the optimal sowing time for Trojan is 1 May. If a grower has an 20 day wheat sowing program and wants to grow half Trojan and half Mace, to maximize whole farm yield they should start with Trojan on 25 April, switch to Mace on 5 May and aim to finish on 15 May.

Sowing mid-April in low-frost environments such as Port Germein carries little risk, and as the results from this year show, significant yield gains (0.9 t/ha relative to Mace) can be achieved by sowing Trojan in mid-April purely because its longer growing season allows it to accumulate more dry matter.

For growers in frosty environments who wish to sow earlier than is safe with Trojan/Mace, EGA Wedgetail is probably the best option in most environments.  However, because of its poor adaption to SA even if sown in early-mid April it is unlikely to yield as well as Mace sown in its optimal window. In this set of trials there was an average yield penalty of 0.5 t/ha between EGA Wedgetail sown mid April and Mace sown in mid-May. Grazing early sown EGA Wedgetail would offset some of the reduction in income compared to mid-May sown Mace.

Remember that early sown crops require different management in order to get the most out of them:

•  Don’t dry-sow slow maturing varieties (EGA Wedgetail, EGA Eaglehawk), they will flower too late if not established early. There needs to be seed-bed moisture and ideally some stored soil water to get them through to winter.
•  If growing winter wheat (EGA Wedgetail) and not grazing, sow at lower plant density and defer N inputs until after Z30.
•    Pick clean paddocks – winter wheat at low plant densities is not competitive with ryegrass and common root diseases are exacerbated by early sowing.
•  Protect against diseases associated with early sowing – barley yellow dwarf virus (imidicloprid on seed backed up with in-crop insecticides at the start of tillering if aphid pressure high), Septoria tritici in some areas (flutriafol on fertilizer and timely foliar epoxiconazole applications at Z30 & Z39). Many slow maturing varieties also have poor resistance to stripe rust (flutriafol on fertilizer and timely foliar fungicide application at Z39)

Conclusion

Despite a frosty July and August, highest yields in most trials came from mid-April sowing, with Trojan being the stand-out performer.  Trojan complements Mace in a cropping program and extends the sowing window to about ten days earlier. EGA Wedgetail was the best performing variety suited to very early sowing, but even when sown early it yields less than Mace planted in its optimal window.

Contact details

James Hunt
GPO Box 1600, Canberra ACT 2601
0428 636 391
james.hunt@csiro.au
@agronomeiste