2019
Reducing the impact of water repellence on crop productivity through soil wetter agents Authors: Jack Desbiolles1, Nigel Wilhelm2, Melissa Fraser3, Lynne Macdonald4, Therese McBeath4, James Barr1 1 University of South Australia, Mawson Lakes, SA, 5095; 2South Australian Research and Development Institute, Urrbrae, SA, 5064; 3Primary Industries and Regions South Australia, Struan, SA, 5271; 4CSIRO Agriculture & Food, Urrbrae, SA, 5064 Funded By: GRDC CSP00203 Project Title: Increasing production on sandy soils in low and medium rainfall areas of the Southern Region Peer Review: Rodrigo Da Silva
Key Messages • • • •
A soil wetter evaluation trial conducted over 2 years compared 13 different wetter treatments under interrow sowing conditions. Six wetter treatments provided large crop establishment benefits over two years at the same site, while also producing up to 0.22 t/ha (Year 1, wheat) and 1.07 t/ha (Year 2, barley) extra grain yield. In 2019, an on-row sowing reference performed best, providing an extra 85 plants per m2 and 1.26t/ha grain yield over the inter-row sowing control. In comparison, the best soil wetter treatment achieved 66% and 85% of the on-row establishment and yield, respectively. Challenges remain in selecting wetting agents for a particular sand environment due to performance variability across water repellence contexts.
Background Non-wetting sands have low fertility and suffer from delayed and uneven wetting, which leads to erratic crop establishment, staggered weed germination and generally poor crop productivity due to low plant densities, low nutrient access, poor weed control and crop damage in areas prone to wind erosion. A range of trials in the GRDC funded Sandy Soils Project (CSP00203) are investigating effective solutions available at seeding time to mitigate the impacts of water repellence. Soil wetter chemistries are varied and complex and little is known of their individual suitability to local water repellence. Modern soil wetters typically have both surfactant and humectant properties. Surfactant chemistry lowers the surface tension between the liquid and non-wetting sand, which allows the liquid to more readily infiltrate. Humectant chemistries are designed to counter the potential for excessive drainage of the surfactant through the use of co-polymers to promote a horizontal spread of the liquid increasing the quantity of liquid retained within the furrow seed zone. Ten years of research testing soil wetters applied at seeding time in WA was recently reviewed by Davies et al. (2019) and found that: (i) Banded soil wetters were most beneficial for dry sown cereals on repellent forest gravels with less reliable benefits for break-crops; (ii) Benefits of banded wetters were minimal or at best sporadic for dry sown crops on deep sands with no benefit to wet sowing for any crop or soil type; (iii) Benefits are larger in seasons with low and sporadic germinating rains in autumn. Previous SA research at Wharminda on EP (Ward et al. 2019) conducted over 2015-17 found that two soil wetting agents evaluated among other strategies could significantly improve wheat, barley and lupin establishment and had a positive impact on grain yield, in 2 years out of 3. Building on the above, the Murlong soil wetter evaluation trial aimed to broaden the range of soil wetter types and combinations being evaluated under contrasting furrow placement scenarios.
About the trial
During 2018-19 soil wetter evaluation trials were conducted at Murlong on Eyre Peninsula (EP). In Year 2 (2019), 6 row x 25m long plots set to 0.28m row spacing were sown at 6 km/h using a deep banding knife point operating at 110mm depth, followed by twin seeding discs and a furrow stabilising V press wheel, 140mm wide. Plots were sown at 3050mm depth on the 15-17 May with CL Scope barley treated with Vibrance and Cruiser 350 at a seed rate of 68 kg/ha. Uniform fungicide at 400 mL/ha and Intake Hi-Load Gold fungicide at 250 mL/ha were also applied in furrow in 80 L/ha