Riverine Plains Inc research update

 

During 2016, Riverine Plains Inc contributed to a range of research projects, however this report will focus on the ‘Maintaining profitable farming systems with retained stubble in the Riverine Plains region’ project. A subset of work within this project focused on frost risk in stubble retained systems. 

Results and discussion

The Stubble Project

The Stubble Project, ‘Maintaining profitable farming systems with retained stubble in the Riverine Plains region’ is funded by GRDC as part of a National Initiative (RPI0009) and conducted in partnership with the Foundation for Arable Research (FAR) Australia. It is looking at ways to improve and maintain profit and sustainability in stubble retention cropping systems across the region. Four large, commercial scale field trials (‘Focus Farms’) have been established across the region, which are comparing different stubble management practices and plant establishment, growth and yield (Table 1). Smaller trials are also evaluating the importance of timing of nitrogen (N) application, plant growth regulators, row spacing and cultivar selection in optimising production in stubble retained systems.

Table 1. Different stubble management strategies for focus farms as part of the ‘Maintaining profitable farming systems with retained stubble in the Riverine Plains region’ project. 

Henty No Till Stubble Retained (NTSR) NTSR + 40kg N/ha at sowing Mulched Mulched + 40kg N/ha at sowing Cultivate Cultivate + 40kg N/ha at sowing	Dookie  Long stubble (NTSR) Short stubble (NTSR) Cultivate (1 pass) Remove straw Burn
Yarrawonga Long stubble (NTSR) Long stubble (NTSR) + 40kg N/ha at sowing Short stubble (NTSR) Remove straw Cultivate (1 pass) Cultivate (1 pass) + 40kg N/ha Burn	Coreen/Corowa  TSR Cultivate (1 pass) Cultivate (1 pass) + 40kg N/ha Burn Faba Bean (forage) Faba Bean (grain)

Comparative yields across seasons

The large plot field trials are always placed into a cereal stubble. Therefore, the sites do not continue in the same location every year, but are placed in different paddocks every year to maintain the same rotation position, with the trial crop being sown into as wheat stubble. While the trial results cannot be directly compared across seasons (2014-2016), the effect of different stubble management techniques can be reviewed across years to determine if any single approach appears to consistently yield better (Tables 2-5).

Table 2. Comparative yields and protein contents for large plot field trials located at Coreen/Corowa over the 2014-2016 seasons. 

Treatment	2014		2015		2016
	Wheat yield	Protein	Wheat yield	Protein	Barley yield	Protein
	(t/ha)	(%)	(t/ha)	(%)	(t/ha)	(%)
NTSR	3.17 a	8.1 a	4.33 a	10.9 a	5.24 a	9.5 a
Cultivated	3.18 a	8.8 a	4.18 a	11.4 a	5.10 a	8.5 b
Cultivated + 40kg N/ha	3.31 a	8.4 a	4.69 a	11.5 a	5.54 a	9.9 a
Burnt	3.10 a	8.1 a	3.95 a	11.4 a	4.81 a	9.5 a
Grand Mean	3.19	8.4	4.286	11.29	5.17	9.4
LSD	0.53	1.22	0.808	1.23	1.01	0.6

NTSR = long stubble/no till stubble retained system

Table 3. Comparative yields and protein contents for large plot field trials located at Yarrawonga over the 2014-2016 seasons. 

Treatment	2014		2015		2016
	Wheat yield	Protein	Wheat yield	Protein	Wheat yield	Protein
	(t/ha)	(%)	(t/ha)	(%)	(t/ha)	(%)
Long stubble	4.43 a	10.5 bc	3.13 a	15.6 a	5.86 bc	8.5 c
Long stubble + 40kg N/ha	4.18 a	12.0 a	3.20 a	15.6 a	6.19 ab	9.7 ab
Short stubble			3.35 a	14.8 a	5.81 bc	8.9 c
Straw removed	4.53 a	9.6 c	3.03 a	14.9 a	5.60 c	8.6 c
Cultivated	4.54 a	9.9 bc	3.10 a	14.8 a	5.90 bc	9.1 bc
Cultivated + 40kg N/ha	4.30 a	11.1 ab	3.05 a	15.7 a	6.69 a	10.0 a
Burnt	4.43 a	9.9 bc	2.93 a	15.1 a	6.12 abc	8.9 c
Grand Mean	4.36	10.5	3.11	15.2	6.03	9.1
LSD	0.46	1.2	0.3	0.7	0.58	0.7

Table 4. Comparative yields and protein contents for large plot field trials located at Dookie over the 2014-2016 seasons.

Treatment	2014		2015		2016
	Wheat yield	Protein	Wheat yield	Protein	Wheat yield	Protein
	(t/ha)	(%)	(t/ha)	(%)	(t/ha)	(%)
Long stubble	4.98 b	11.6 a	2.41 a	15.0 a	5.80 a	10.7 a
Short stubble	5.66 a	10.6 ab	2.52 a	13.6 b	5.37 a	10.7 a
Cultivated	5.56 a	10.3 b	2.39 a	12.9 c	5.60 a	11.3 a
Straw removed	5.66 a	10.9 ab	2.32 a	13.5 bc	6.00 a	10.5 a
Burnt	5.85 a	10.4 b	2.49 a	13.3 bc	6.23 a	11.1 a
Grand Mean	5.54	10.7	2.42	13.6	5.80	10.9
LSD	0.45	1.05	0.22	0.6	1.02	1.6

Table 5. Comparative yields and protein contents for large plot field trials located at Henty over the 2014-2016 seasons. 

Treatment	2014		2015		2016
	Canola yield	Oil	Canola yield	Oil	Canola yield	Oil
	(t/ha)	(%)	(t/ha)	(%)	(t/ha)	(%)*
NTSR	1.96 c	43.2 a	1.24 a	44.5 a	2.40 a
NTSR + 40kg N/ha	2.35 ab	42.7 a	1.32 a	41 b	2.26 a
Mulched	2.23 abc	43.8 a	1.44 a	43.6 a	2.48 a
Mulched + 40kg N/ha	2.14 bc	42.7 a	1.39 a	43.6 a	2.53 a
Cultivate	2.41 ab	43.7 a	1.43 a	44.3 a	2.80 a
Cultivate + 40kg N/ha	2.54 a	44.2 a	1.35 a	43.7 a	2.72 a
Grand Mean	2.27	43.4	1.36	43.4	2.53
LSD	0.35	0.45	0.62	1.59	0.72

*Oil quality not yet available at time of printing

Summary of yields under different stubble management techniques from 2014-2016

Coreen/Corowa

There have not been any differences in cereal yields due to stubble management techniques. 

Yarrawonga

The only difference seen at Yarrawonga was in 2016, where the addition of 40kg N/ha at sowing resulted in yield increases in both the stubble retained and cultivated treatments.

Dookie

The only difference in yield was seen in 2014 when the long standing stubble incurred a yield penalty compared to all other treatments.

Henty

The mulched treatment with the addition of N at sowing had a higher canola yield in 2014.

Generally, across the past three seasons (2014-2016), stubble management has not been a key driver of yield, except for stubble height at Dookie, and addition of N at sowing at Yarrawonga and Henty in 2014. This general lack of effect may be largely due to extreme weather through the growing season (heat stress in October 2015, waterlogging in winter/spring 2016), which would have overridden any effects of stubble management on yield.

Biomass lag with retained stubble

Over the 2014–2015 seasons, it was observed that the stubble retained treatments had lower dry matter contents during the earlier growth stages, however by flowering there was little difference between plants grown in no till stubble retained (NTSR) systems or where the stubble had been burnt or cultivated. The impact of this delay in biomass on the physiological development of the plant was unknown. 

Were the plants growing in NTSR systems at the same growth stage, with less biomass, or was there a difference in growth stage? If there was a difference in physiological development of plants in NTSR and burnt/cultivated systems, this could relate to differences in how the crops handle frost (due to a difference in vulnerability) and heat stress. 

In order to understand if this biomass lag was simply a difference in the rate of dry matter accumulation or if it related to differences in growth stage, a series of growth stage assessments were done at the Coreen, Yarrawonga and Dookie sites in the 2016 season to understand what was happening. 

At the Yarrawonga site (Figure 1), stubble management did not influence plant growth and development until stem elongation (11 July 2016) at which point all treatments except the tall stubble treatment began stem elongation. The tall stubble treatment took an extra three weeks to move into stem elongation.

The Dookie site (Figure 2) showed differences in growth stage from seedling stage, with treatments separating from  27 June 2016. Plants in the burnt treatment were slightly more developed than the other treatment, with this increase largely maintained over the next four weeks. In comparison, while plants in the tall stubble treatment lagged in development from  27 June 2016, and showed minimal development at the next reading on  4 July 2016, by  18 July they had caught up to the short stubble and disced treatments, while the burnt treatment was still slightly ahead.

In comparison, there were no significant differences in growth stage development at the Coreen site (Figure 3), with plants in the stubble standing, disced and burnt treatments all developing at the same rate.

Figure 1. Growth stage assessments at the Yarrawonga stubble management trial. Growth stage relates to Zadok’s growth scale; 0-9 Germination, 10-19 Seedling growth, 20-29 Tillering, 30-39 Stem elongation, 40-49 Booting. Bars are measures of standard error (Order of columns from left to right: tall, short, disc and burn).

Figure 2. Growth stage assessments at the Dookie stubble management trial. Growth stage relates to Zadok’s growth scale; 0-9 Germination, 10-19 Seedling growth, 20-29 Tillering, 30-39 Stem elongation, 40-49 Booting. Bars are measures of standard error (Order of columns from left to right: tall, short, disc and burn).

Figure 3. Growth stage assessments at the Coreen stubble management trial. Growth stage relates to Zadok’s growth scale; 0-9 Germination, 10-19 Seedling growth, 20-29 Tillering, 30-39 Stem elongation, 40-49 Booting. Bars are measures of standard error (Order of columns from left to right: tall, short, disc and burn).

The impact of stubble on canopy temperature 

From the start of the Stubble Project, there was a lot of interest from growers about the interaction between retaining stubble and frost risk — were crops more likely to suffer frost damage under retained stubble? 

As the large field trial plots used within the Stubble Project are ideal for measuring temperature due to minimal ‘edge effects’, extra investment from the GRDC enabled three of the field sites to be instrumented for temperature monitoring (in-crop temperature loggers and a weather station next to the field site). 

In-crop monitoring of canopy temperatures began in 2015, with field sites again instrumented in 2016. 

The three sites which were instrumented in 2016 were:
Yarrawonga (loggers installed 27/5/16):

• Treatments monitored: Long Stubble, Short Stubble, Cultivate, Burn.
• In-canopy data loggers at 300mm height, moved to 600mm height in September.
• In-canopy data loggers at 50mm height above the soil.

Dookie (loggers installed 4/6/16):

• Treatments monitored: Long Stubble, Short Stubble, Cultivate, Burn.
• In-canopy data loggers at 300mm height, moved to 600mm height in September.
• In-canopy data loggers at 50mm height above the soil.
• Data loggers buried 50mm under the soil surface.

Coreen (loggers installed 27 /5/16): 

• Treatments monitored: NTSR, Cultivate, Burn.
• In-canopy data loggers at 300mm height, moved to 600mm height in September
• In-canopy data loggers at 50mm height above the soil.

Figure 4. The number of hours that each stubble treatment spent below each temperature threshold at the Yarrawonga site, as monitored at the loggers placed 300mm above the soil surface, which were moved to 600mm height in September 2016 (Order of columns from left to right: burnt 300mm, disc 300mm, low 300mm and high 300mm).