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

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.

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)

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

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.

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)

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.

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)

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)

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.

* 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).