Soil wetting agents for water repellent forest gravel soils 2015 trial report

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Banding soil wetting agents with the seed can improve establishment on water repellent soils often having the same effect as seed placement on the furrow surface.

Some soil wetting agents are compatible with UAN, fungicides and other liquid applications and can be applied through existing liquid in-furrow banding systems. These soil wetting agents may be useful as a carrier for liquid nutrients.

Banded wetters seem particularly beneficial on water repellent loamy gravels with substantial increases in grain yield in the 2015 season.

Knife points on plot seeder

Background

Banded soil wetting agents have been typically applied in a continuous stream on top of the furrow following the press wheels to improve the consistency of soil wetting in the furrow and improve crop establishment on water repellent soils. There is some evidence that banding soil wetters near the seed can also be effective at improving establishment. Some recent soil wetters are compatible in formulations with UAN and may improve plant access to nutrients. In 2015 a number of trials were established to assess the impact of these developments on crop establishment and yield for crops growing on repellent soils.

Aims

Assess the effectiveness of wetting agents when banded with the seed compared to banded on the furrow surface.
Assess the effectiveness of soil wetting agents applied in formulations with UAN.
Assess the effectiveness of soil wetting agents on water repellent forest gravels.

Trial details

Table 1 Trial details
Property	Fairbanks, South Kojonup
Soil type	Loamy forest gravel
Growing season rainfall	April – October: 292mm

Table 2 Summary of seeding details, soil water repellence rating and treatments applied for three trials
Variety, rate and sowing date	Treatments	Topsoil (0-5cm) water repellence MED	Topsoil (0-5cm) water repellence rating
Hyola 525 RT canola, 2.5kg/ha, 5 May	Experiment 1: 1) Water only banded on furrow or with seed 2) Wetter 1: penetrant banded on furrow or with seed 3) Wetter 2: penetrant and absorber banded on furrow or with seed 4) Wetter 3: penetrant and absorber banded on furrow or with seed All wetters banded at 2L/ha	3.2	Very severe
Bass barley, 110kg/ha,13-14 May	Experiment 2: 1) Control (nil banding) 2) Water only banded on furrow 3) Wetter 1: penetrant and absorber banded on furrow at 1 or 2L/ha 4) Wetter 2: penetrant banded on furrow at 1 or 2L/ha 5) Wetter 3: absorber and penetrant banded on furrow at 1 or 2L/ha 6) Wetter 4: penetrant and absorber banded on furrow at 1 or 2L/ha	4.1	Very severe
Bass barley 110kg/ha, 13-14 May	Experiment 3: 1) Control: water banded on furrow or with seed 2) UAN banded on furrow or with seed 3) Wetter 1 banded on furrow or with seed 4) Wetter 1 + UAN banded on furrow or with seed 5) Wetter 2 banded on furrow or with seed 6) Wetter 2 + UAN banded on furrow or with seed	4.0	Very severe

Table 3 Summary of fertiliser and pesticide applications for the soil wetting agent trials
Fertiliser, herbicide, or pesticide application	Canola pre-emergent	Canola (experiment 1) post-emergent	Barley (experiments 2 and 3) pre-emergent	Barley (experiments 2 and 3) post-emergent
Fertiliser	100kg/ha urea + 120kg/ha Gusto Gold	20L/ha UAN + 50L/ha UAN	65kg/ha Urea + 100kg/ha Gusto Gold	50L/ha UAN + 40L/ha UAN
Herbicide	1.5L/ha Sprayseed + 1L/ha Propyzamide	900g/ha Roundup Dry + 1.5kg/ha Atrazine + 900g/ha Roundup Dry	1.5L/ha Avadex + 3g/ha Ally + 2L/ha Sprayseed + 2.5L/ha Trifluralin	1L/ha Velocity
Insecticide	0.5L/ha Chlorpyrifos + 0.2L/ha Bifenthrin	0.1L/ha Transform	1L/ha Chlorpyrifos + 0.3L/ha Bifenthrin	0.5L/ha Chlorpyrifos
Fungicide	None	None	None	0.3L/ha Prosaro

Results

Experiment 1: Soil wetters for canola

For some of the banded wetters early crop establishment was improved by 18-23 plants/m² an increase of 54-70% (Table 4). Improved early establishment translated into 9-17% improvement in canola yields, an increase of 260-510kg/ha. Banding the soil wetters near the seed significantly improved the grain yield compared with banding the wetter on the furrow by an average of 190kg/ha across the three soil wetters.

Table 4 Impact of soil wetting agents applied at 2L/ha and their placement, banded either on the furrow surface or near the seed, on canola establishment and grain yield
Treatment	Crop establishment (plants/m²)	Grain yield (t/ha)
Control (nil)	33	2.93
Water only (control)	34	2.92
Wetter 1 - furrow banded	45	3.19*
Wetter 1 - seed banded	56*	3.37*
Wetter 2 - furrow banded	51*	3.26*
Wetter 2 - seed banded	54*	3.44*
Wetter 3 - furrow banded	45	3.10
Wetter 3 - seed banded	44	3.31*

Note: Least significant difference (lsd) 95% confidence: Crop establishment - 15; yield - 0.22; * denotes a significant increase relative to the untreated control at 95% confidence

The improved crop establishment, due to treatment, can be seen in the photos below showing the comparison between the control (Image 1), furrow banded wetter (Image 2) and seed banded wetter (Image 3).

Image 1 Canola establishment and growth in untreated control plot (photo taken 28 July 2015)

Canola establishment with wetter on furrow

Image 2 Canola establishment and growth with wetter banded on furrow (photo taken 28 July 2015)

Canola establishment of seed banded wetter

Image 3 Canola establishment and growth following wetter banded with seed (photo taken 28 July 2015)

Experiment 2: Soil wetters for barley

Banded soil wetting agent improved barley plant numbers by 51-73%, an increase of 63-90 plants/m^₂ (Table 5, Image 4).

Grain yields were improved by 15-30%, a yield increase of 0.53-1.02t/ha (Table 5) as a result of using the soil wetters. For most of the wetters there was no benefit from using the higher application rate.

Barley establishment with wetter application compared to untreated control in centre

Image 4 Barley establishment and growth in an untreated control plot (centre) with Wetter 2 at 1L/ha on the left and Wetter 3 at 2L/ha on the right (photo taken 5 August 2015)

Table 5 Impact of banded soil wetting agents and the rate of application on barley establishment and grain yield growing water repellent loamy forest gravel near Kojonup, 2015.
Treatment	Crop establishment (plants/m²)	Grain yield (t/ha)
Control (nil)	123	3.45
Water only - 1L/ha	117	3.48
Wetter 1 - 1L/ha	195*	4.24*
Wetter 1 - 2L/ha	179	4.41*
Wetter 2 - 1L/ha	186*	4.47*
Wetter 2 - 2L/ha	187*	4.27*
Wetter 3 - 1L/ha	213*	4.35*
Wetter 3 - 2L/ha	206*	4.17*
Wetter 4 - 1L/ha	163	3.98*
Wetter 4 - 2L/ha	191*	4.08*

Note: Least significant difference (lsd) 95% confidence: Crop establishment - 63; yield - 0.42; * denotes a significant increase relative to the untreated control at 95% confidence.

Experiment 3: Soil wetters and UAN for barley

Soil wetters on their own and in formulation with UAN did not significantly increase plant numbers (Table 6). This is despite the fact that, visually, crop growth along the rows was clearly more consistent on the plots treated with soil wetter (Image 5 and 6).

The grain yield was increased by 9% (0.34t/ha) from furrow banded wetter applied on its own and by 0.59-0.63t/ha, an increase of 15-16%, when applied in combination with UAN (Table 6).

Unlike the canola experiment (Experiment 1), banding the soil wetting agents on the surface of the furrow generally improved yield more reliably than banding them in-furrow, near the seed. There was no consistent evidence of UAN toxicity issues affecting establishment when banded either on-furrow or near the seed.

Barley establishment and growth is improved in response to soil wetter with UAN compared to poorer patchy esatablishment with UAN only

Image 5 Barley establishment and growth response to in-furrow UAN on the left compared with on-furrow Wetter 2 with UAN on the right (photo taken 5 August 2015)

Barley establishment and growth response to wetter

Image 6 Wetter 1 and UAN banded in-furrow (near the seed) on left compared with UAN only banded in-furrow on the right (photo taken 5 August 2015)

Table 6 Impact of soil wetting agents and their placement, banded either on top of the furrow or near the seed, on barley establishment and grain yield growing on water repellent loamy forest gravel near Kojonup, 2015. Soil wetting agents were applied either on their own or in formulations with UAN.
Treatment	Crop establishment (plants/m²) - furrow banded	Crop establishment (plants/m²) - seed banded	Grain yield (t/ha) - furrow banded	Grain yield (t/ha) - seed banded
Water only (Control)	161	173	3.97	3.99
UAN	173	143	3.84	4.05
Wetter 1	192	188	4.31*	4.11
UAN + Wetter 1	189	165	4.56*	4.21
Wetter 2	209	212	4.30*	4.39*
UAN + Wetter 2	212	178	4.60*	4.05

Note: Least significant difference (lsd) 90% confidence: Crop establishment - not significant; yield - 0.29; * denotes a significant increase relative to the untreated control at 95% confidence.

Financial analysis

The cost of banding wetters typically ranges from $8-16/ha depending on application rate.

Across the three experiments the average grain yield increases from the use of soil wetters ranged from 0.34-0.81t/ha and increased average returns by $84-227/ha (Table 7).

In Experiment 2 the yield responses of barley on loamy gravel to the 1L/ha wetter application rate was equivalent to that achieved at double the rate, 2L/ha, so cost of the treatment is low - less than $10/ha.

Table 7 Average grain yields, yield increases in response to soil wetting agents and net returns for three soil wetting agent experiments
	Average control yield (t/ha)	Average yield increase with wetter (t/ha)	Soil wetter cost ($/ha)	Grain value ($/t)*	Returns after cost of wetter ($/ha)
Experiment 1, canola	2.93	.35	15	548	177
Experiment 2, barley	3.45	.81	9	291	227
Experiment 3, barley	3.98	.34	15	291	84

* Grain price based on quoted contract price, February 2016, awb.com.au

Comments

On repellent loamy gravels crop yield increases in response to banded soil wetters were impressive and more consistent than those on deep sand (Davies et al. 2015; Davies et. al. 2016a). Yield increases were 0.3-0.5t/ha for canola, 0.3-1.0t/ha for barley.

In another experiment on repellent loamy gravel north of Kojonup in 2015, a broader range of treatment options was measured (refer to Assessing options for managing water repellent gravel soils 2015 trial report). That trial resulted in banded soil wetters increasing barley yield by 0.7t/ha for furrow banded and 1t/ha for seed banded (Assessing options for managing water repellent gravel soils 2015 trial report). Blanket applied soil wetter was also effective in that trial increasing yield by 1t/ha, but at a higher cost due to higher application rate when applying as a blanket application.

In 2016, research on soil wetting agents will continue on these loamy forest gravels. Several long-term sites will be established, one to determine if wetting agents positively interact with other practices to manage soil constraints, such as liming, and another to determine the residual value of wetting agents. The impact of wetting agent placement will continue to be assessed as well as the benefits of splitting the wetter application so that it is applied to both the top of the furrow and near the seed at the same time.

Acknowledgements

The ‘Delivering enhanced agronomic strategies for improved crop performance on water repellent soils in WA’ project (DAW00244) is funded by DAFWA and Grains Research and Development Corporation (GRDC) and is part of GRDC's Soil Constraints West Initiative. Thanks to support from the SoutherDIRT grower group, Jono Clifton for hosting the trials and technical support from DAFWA and Vincent Galluccio (Living Farm).

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