Sorghum agronomy to maximise yield potential

Take home messages

Low to medium yielding environments

• Early plant sorghum currently offers a more attractive proposition to growers than late plant sorghum, mostly for logistical and rotational reasons.
• Yields during the trial seasons were generally more than 1.0 t/ha higher than the long term average for this region.
• In these seasons, yield declined as effective row spacing increased.  Solid plant > single skip = superwide > double skip where average site yields were 3.46 t/ha.
• Plant populations should be targeted in the realm of 30 – 50,000 plants/ha.
• Hybrids should be selected which have a moderate to high level of tillering as this mechanism allows plants to respond to variable environmental conditions.

Medium to high yield environments

• Early plant sorghum out yielded the late planted sorghum under both dryland and irrigated trials in the 2013/14 season.
• The performance difference between hybrids was small, however the difference between varying agronomic factors was much larger, in particular the varying of nitrogen rate.
• Optimum plant populations were between 50-75,000 plants/ha in both the irrigated and dryland trials.
• There was minimal difference in the yields of 90cm row spacing compared to the twin row configuration

Introduction

Grain sorghum remains the main summer crop in northern NSW with on average 160,000 ha planted annually. The main zones for sorghum production though continue to be the area east of the Newell Highway and the Liverpool Plains.

GRDC and NSW DPI have partnered in several projects to conduct research on a range of agronomic factors which drive both the reliability of sorghum production and also raising the yield bar in areas where sorghum is already an important rotational crop. In the area west of the Newell Highway, sorghum production is variable in acreage as well as production tonnes. In an attempt to boost confidence in sorghum as a reliable summer cropping option by increasing the reliability and yields of sorghum a research project was commenced in the 2010-11 season targeting the matching of suitable hybrids to optimum plant populations and row configurations. This research has led to a series of preliminary recommendations for the low- medium rainfall zone.

In the 2013-14 season a second project commenced targeting the medium – high rainfall zone where sorghum is reliably grown but where crop modelling that suggests that there is some disparity between the potential crop yield and the actual yield harvested by growers. This high yielding cereals project is attempting to partition the impact on grain yield of altering various agronomic factors such as hybrid, plant population, row configuration and nutrition.

The data presented in this paper is a compilation of the results of four years of research in the western zone and the first year of testing in the eastern (high yielding zone).

Sorghum agronomy for the medium to high yielding environments

Three trials were conducted at two sites on the Liverpool Plains in the 2013/14 season in the medium to high yielding zone. These trials were located at Pine Ridge and Breeza. The Pine Ridge site was dryland only, whilst the Breeza site incorporated both a dryland and an irrigated trial. Results from the Breeza site only are reported in this paper.

The Breeza trials were partially factorial and designed to compare the proportion of yield which can be allocated to each of a series of agronomic management decisions. Therefore each trial included the following treatments:

1. Two times of sowing - ideal and late plant
2. Two row configurations –  90cm solid (2 rows per plot) and a twin row (4 rows with pairs of 2 rows 7.5cm apart)
3. Three hybrids – MR Buster (as a current commercial benchmark) and two recent released hybrids MR Scorpio and 85G33
4. Three plant populations – 50, 75 and 100,000 plants/ha
5. Three nitrogen application rates – 0, 100 and 200 kg/ha applied as Urea at sowing
6.   Three phosphorus application rates – 0, 10 and 20 kg/ha applied as Triple Superphosphate at sowing

The aim of the trials was to be able to allocate proportions of the final crop yield to various agronomic decision points, for example if no nitrogen was applied to a sorghum crop but all other management decisions were optimised, how much yield would a grower lose?

In this first of three seasons trial work, a range of results were produced.

Sowing time

The dryland and the irrigated trials at Breeza were sown at an “ideal” planting time and a late planting for the environment, in this season the trials were sown on the

Time of Sowing 1 (TOS1) – 30^th to 31^st October 2013

Time of Sowing 2 (TOS2) – 9^th & 10^th December, 2013

The earlier time of sowing had higher yields in both the irrigated and the dryland trial. On average TOS1 yielded 0.25 t/ha more than TOS 2 in the dryland site with the average site yields of 3.38 t/ha and 3.14 t/ha respectively.

In the irrigated trial TOS1 yielded 0.35 t/ha more than TOS2 in the irrigated trial with the average site yields of 5.60 t/ha and 5.23 t/ha respectively.

Hybrid Selection

Three hybrids were selected for the trials. A commercial benchmark hybrid, MR Buster was used to benchmark against the genetic gain possible from growers changing to using newer hybrids, in this case MR Scorpio and 85G33.

In both the dryland and the irrigated trial in this season there was no significant difference in the yield of the three hybrids when sown at 90cm row spacings with a population of 50,000 plants/ha, 100 kg N/ha and 10 kg P/ha applied at sowing.

Yield differences due to hybrid selection were small but much larger differences were obtained from varying other agronomic factors.

Row Configuration

At this site, the trials were sown onto 1.8m raised beds. Two row configurations were used, a 90cm solid plant with two rows sown on top of the bed and a twin row configuration where 4 rows were sown, with the outside rows being 90cm apart and then a twin row sown 7.5cm inside each of these rows. The row spacing’s were compared using the hybrid MR Scorpio across three plant populations, 50, 75 and 100, 000 plants/ha using a base rate of 100 kg N/ha and 10 kg P/ha.

In the dryland trial the 90cm row spacing yielded more than the twin row configuration in both TOS1 and TOS 2 at all three plant populations.

In the irrigated trial the 90cm row spacing showed the same yield response across TOS1 and TOS 2 across the three plant populations as the twin row spacing in TOS1. However in TOS2 the twin rows yielded less at all three populations.

Plant population

In the irrigated trial yields increased as plant population increased from 50 to 75,000 plants/ha and then reached a plateau, however the differences were not significant between populations or across the two sowing times.

In the dryland trial there was a significant increase in yield in TOS1 only as plant population increased from 50 to 75,000 plants/ha. There was no difference in yield between the 75 and 100,000 plants/ha treatment. There was no significant response to varying population in TOS2.

Table 1. Impact of time of sowing and plant population on yield of dryland grain sorghum

Nutrition

In these trials only two aspects of crop nutrition were investigated, nitrogen and phosphorus. Both nutrients were applied at sowing.

In the dryland trials, there was a significant response to nitrogen (Table 2). In TOS 1, yield increased as nitrogen rate increased to give a significant response with each rate increase of 0.76 t/ha from applying 100 kg N/ha compared to the nil treatment, and then an additional 1.05 t/ha with the application of the 200 kg N/ha treatment. As such there was close to a 2 t/ha response from the application of 200 kg N/ha. In TOS 2, the response to nitrogen was not as great, with no difference between the 100 and 200 kg N treatments, but the 200 treatment yielding 0.85 t/ha more than the nil treatment.

Table 2. Impact of nitrogen rate and time of sowing on dryland grain sorghum yield in 2013-14

In the irrigated trial (Table 3), in TOS 1 there was a 2.9 t/ha yield benefit from applying 200 kg N compared to the Nil N treatment and 2.3 t/ha benefit compared to the 100 N treatments. The 100 kg treatment yielded more than the Nil treatment as well, but the difference was not significant. In TOS 2 the response was similar to TOS 1 but there was no significant difference between the 100 and 200 N treatments, which were 2.0 and 2.3 t/ha higher yielding than the nil treatment.

Table 3. Impact of nitrogen rate and time of sowing on irrigated grain sorghum yield in 2013-14

Responses to phosphorus were detected in the irrigated trials at both TOS, however the response to phosphorus was only significant when it was coupled with the application of nitrogen. The responses across the two times of sowing were almost identical with the exception of the TOS2 treatment which added 100 kg N/ha and 0 kg P/ha where the yields were significantly higher than the control.

In the dryland trials the P responses were not as clear. TOS 2 yielded better than TOS1, and while there was a trend for increased yields when both nitrogen and phosphorus were added this was not always significant.

The preliminary results from this project suggest that growers and agronomists should address nutritional issues as a priority for sorghum compared to the relatively minor responses to hybrid and population to ensure that crops are meeting their water limited yield potential.

Sorghum agronomy for the low to medium yielding environments

A series of nine dryland trials was conducted over four years; from 2010 – 2014 under the Sorghum in the Western Zone Project at sites west of the Newell Highway. Trials were located at; Mungindi, Morialta Junction, Rowena, Tulloona, Gurley, Garah, and Bullarah. The trials focused on establishing a data set around three primary factors; row configuration, plant population and hybrid selection although additional data was gathered from each site on issues such as crown rot, soil water and nitrogen.

Sowing time

Six of these trials were planted in the early planting window, between September and October and three of these trials were planted in the late planting window of January. The three late plant trials were all in the 2012/13 growing season, which needs to be considered since only one seasons climatic conditions can be used to draw any conclusions on planting time. Additional late plant trials are underway this season to add to the data set.

Average yields from the six early plant trials ranged from 4.53 t/ha down to 1.04 t/ha. In comparison yields from the three late planted trials, all from within the 2012/13 season ranged from 4.30 t/ha down to 3.52 t/ha.

While it is not possible to draw conclusions on which planting time is preferred from this limited data set, it is worth considering other drivers within the farming system which often have a great influence.

Early plant sorghum, sown in September / October is intended to escape the summer heat at flowering; as well as splitting the labour/ equipment requirements more evenly across the year so winter crop planting and summer crop harvest do not coincide. Early planted sorghum is also typically harvested while conditions are still warm meaning a quick dry down time, no grain drying and harvest before the pressures of winter planting. The early harvest timing also allows the option of a double crop back into chickpeas or a winter cereal should sufficient rainfall occur to fill the profile sufficiently, thus expediting the move back into the more dominant winter cropping sequence. On the downside, cool soil temperatures with the early planting time can slow early growth and sometimes affect establishment.

Late planted sorghum typically avoids the heat at flowering, but has to be planted into high soil temperatures which rapidly dry out the seedbed. In addition most growers in this western zone are unwilling to let an early planting opportunity pass them by in case there is not another opportunity to plant.  Late plant sorghum also comes with the risk of cool temperatures during flowering and the risk of sorghum ergot. Late planting also means late harvest where dry down may be slow and difficult due to high grain moisture resulting in the need to dry sorghum as well as the crossover with winter planting causing additional demands on labour and machinery. Late planted sorghum also means the need to either short fallow to another summer crop or long fallow to the next winter crop, reducing the cropping frequency and subsequent cash flow.

Currently the case for or against early or late sowing time is largely based on the impacts on the farming system as there is insufficient data to build a more robust case on the impact on crop yield.

Crop modelling has provided simulated data across multiple years and seasons which suggest late planted sorghum to be the more reliable.

Hybrid Selection

In this research project three hybrid types were selected with diverse plant characteristics currently commercially available. Three hybrids were selected for these characteristics.

1. Low tillering, High staygreen – 2436 and LT10 (both experimental lines)
2. Moderate tillering, moderate staygreen – MR 43
3. High tillering, low staygreen – MR Bazley

In these trials, across all sites and seasons, the hybrids with moderate to high levels of tillering have produced higher yields. In these trials the hybrids MR Bazley and MR 43 have been higher yielding than 2436 and LT10 by on average 0.5 t/ha as shown in Table 1. The full potential of stay green as a plant characteristic has not been seen in this research either as the majority of seasons had higher than average yields and the required plant stress did not occur.

The general conclusion has been that hybrids with a low level of tillering have not been able to respond to the variable seasonal conditions by producing additional tillers (which equates to more heads) to capture additional yield potential unlike the hybrids with moderate to high levels of tillering, in this case MR 43 and MR Bazley.  There has been very little difference in the grain yields of the moderate and high tillering hybrids.

Table 4. Impact of hybrid type on yield (t/ha) in 2010-2014

Row Configuration

The most common row configuration in this zone was double skip until recent years where there has been more interest in 1.5m super wide row configuration.

Four row configurations were used at the trial sites; a 1.0 m solid plant, single skip, double skip and a super wide (1.5 m solid) with the exception of Byra in the 2012/13 season which was on raised beds so a 2.0 m solid plant was substituted for a super wide configuration.

Across these nine trials, the yields declined as effective row spacing increased, hence solid > single skip = super wide > double skip. Average site yields ranged from 1.04 t/ha to 4.53 t/ha.

The solid plant configuration produced the highest yields, on average 4.19 t/ha, compared to 3.47 and 3.48 t/ha for single skip and super wide respectively and 2.73 t/ha for double skip. The one trial site with a 2.0 m solid plant treatment averaged 3.13 t/ha. This equates to solid plant yielding 17 % more than the single skip or super wide and 34% more than the double skip.

The average yield of these sites was 3.46 t/ha which is more than a 1 t/ha higher than the long term average for grain sorghum in the north west at 2.49 t/ha (NSW DPI Grains Report 1992-2012). This reinforces that the seasons over which this research has been conducted are more favourable than is the norm for this environment.

The data supports two conclusions, firstly that in above average seasons the solid plant configuration will always yield the highest, however it also comes with a greater risk of total crop failure in the less than average seasons, secondly that double skip configurations sacrifice significant yield potential but are inherently a safer option as they store more water in the “skip” area for use during grain fill. In was interesting to note that in the low yielding 2013/14 season there was no significant response to varying row configuration.

Table 5. Effect of row configuration on yield (t/ha) in 2010-3

Plant population

Over the research period four plant populations were targeted; 15, 30, 50 and 70,000 plants/ha; but only three populations were trialled at each trial site.  The 30 and 50,000 plants/ha treatments were included in all trials.

In the 2010/11 and 2011/12 seasons there was no statistical difference between the yields from the 50 and 70,000 plants/ha treatments; which both produced the highest yields; as such the 70,000 population was dropped from the treatment set as it incurred additional seed costs for growers without providing additional return.

The 15,000 plants/ha treatment was added as “how low can we go?” is a common question from growers and advisors. From this research the 15,000 treatment has always yielded lower than the 30 and 50,000 plants/ha except where the average site yield was only 1.04 t/ha.

Establishing a uniform plant stand with a target plant population of 15,000 plants/ha commercially is also more difficult where airseeders are more common than precision planters for sowing sorghum.

Average yields showed an increase of 0.9 t/ha as plant population increased from 15 to 70,000 plants/ha across the trial sites. However there was little distinction between the 30 and 50,000 plants/ha treatments. In two of the trials there was no significant difference between these two populations, while in another two trials the 50,000 produced significantly more yield than the 30,000 plant population. In the remaining data sets there was no significant response to varying population.

Table 6. Effect of plant population on yield (t/ha) in 2010-2014

Conclusions

In order to optimise grain sorghum production in both the low- medium and medium – high rainfall zone there is a greater emphasis on matching agronomic management to the environment than there is in hybrid selection.

Certainly hybrids have a role to play based on their suitability for environmental conditions and the relevant plasticity of their characteristics such as tillering, however in the trials conducted across both projects to date, the genetic potential of the hybrid has rarely been the limiting factor.

The major agronomic drivers of yield seen to date have been crop nutrition, in particular nitrogen and phosphorus in combination, row configuration in the western zone and achieving optimum planting densities.

Acknowledgements

The funding from the GRDC, in collaboration with NSW Department of Primary Industries and with support from Pacific Seeds is gratefully acknowledged. The research undertaken as part of this project is made possible by the significant contributions of growers through trial cooperation, we thank them for their continued support, in particular Charles & Fiona Brett, Bullarah, Justin & Justine Malone Garah, Scott Carrigan Gurley, Max, David and Maree Onus Gurley, Tom Greentree Morialta, Charles Boyle Mungindi, Phil & John Harris Rowena, Daryl Radford, Tulloona and Ian Carter Pine Ridge.

In addition we would like to thank the following agronomists for their assistance with the sites, Gary Onus, Landmark Moree, Brad Coleman Coleman Ag, Rob Holmes HMAg and Peter McKenzie, Agricultural Consulting and Extension Services.

Also, the technical assistance of Nicole Carrigan, Peter Perfrement, Angus Hombsch, Peter Formann and Scott Goodworth, LPFS is gratefully acknowledged.

Contact details

Loretta Serafin and Guy McMullen, NSW Department of Primary Industries
4 Marsden Park Rd, Calala
Ph: 02 67 63 1100 or Loretta 0427 311 819, Guy 0428 256 544
Email: Loretta.serafin@dpi.nsw.gov.au or guy.mcmullen@dpi.nsw.gov.au