The use of deep furrow moisture delving, on-row or edge-row sowing strategies and soil wetters could help growers to achieve greater crop establishment and increased yields in non-wetting sands.

This is one of the messages from a GRDC investment led by Dr Lynne Macdonald at CSIRO, which is investigating techniques to overcome or mitigate constraints associated with sandy soils, such as:

• water repellence;
• erratic crop establishment;
• low fertility; and
• generally poor crop productivity.

Several trials have been exploring how to maximise seeder strategy benefits through combining aspects of seed placement, furrow management, and/or wetter placement.

Key partners in the research are the University of South Australia (UniSA) and the research division of Primary Industries and Regions SA, the South Australian Research and Development Institute (SARDI).

Soil wetters

UniSA agricultural research engineer Dr Jack Desbiolles says the first trial (in 2018) at Murlong on SA's Eyre Peninsula compared a range of 13 soil wetter treatments.

Subsequent trials aim to combine different speeder strategy approaches (row placement, deep furrow tillage), with the use of wetting agents (see Figure 1).

Figure 1: Visual representation of seeder-based strategies for non-wetting sands evaluated various project trials. The schematic highlights the previous year's crop (red/blue plant); the seeding tyne (brown) and placement of seeds and wetting agents; the zone of furrow and deep moisture (red hash). Top panel: inter-row sowing; centre panel: edge-row sowing; Bottom panel: on-row sowing. b

The soil wetter trial included different products with surfactant chemistries, surfactant-humectant blends, and nutrient enriched surfactant-humectant blends.

Surfactants help overcome water repellency and improve water infiltration, while humectants improve the retention of soil water within the application zone, reducing drainage or evaporation losses.

Dr Desbiolles says soil wetter treatments applied with inter-row sowing strategies had a relatively consistently impact on establishment in 2018 (wheat) and 2019 (barley) with an average increase in establishment density by 25 and 17 plants per square metre in the two years respectively.

"In both years, the best responses produced an extra 55-60 plants per square metre, but there was a large variation in the wetters' effectiveness," he says.

Yield responses to wetting agents were much larger in the second season (up to 1.07 t/ha) compared to the first seasons (up to 0.22 t/ha).

"The larger yield responses to all 13 soil wetters in the second year is attributed to the water harvesting furrows produced by the seeding system," Dr Desbiolles says.

"In 2019, the furrows remained intact well into the season - while in 2018, furrows suffered sand drift and back-filling, cancelling moisture and establishment benefits and minimising yield responses."

Another aspect of the soil wetter trial has been the contrasting placement of the wetters as recommended by the suppliers, either on the furrow surface or within the seed zone, or a combination of both.

Dr Desbiolles says an interesting finding from this work has been that all wetters applied on the inter-row furrow surface had a limited effect on early crop establishment. However, two seed zone products with humectant properties and some dual placement products did increase plant establishment density.

Although absent in 2018, on-row sowing strategies were included in the 2019.

On-row sowing (without soil wetter) demonstrated better crop establishment compared to any of the wetter-based treatments - an extra 85 plants per square metre. The on-row treatments also showed the biggest yield improvements, with an extra 1.26 tonnes per hectare above the inter-row sown control (1.1t/ha).

Dr Desbiolles says this indicates plants sown on-row had greater access to soil moisture stored under the stubble row, which is a critical factor in achieving uniform and fast seed germination in nonwetting sand.

Seeding strategies

A range of research projects in the SA Mallee and in Western Australia have demonstrated the potential for techniques such as edge-row, on-row, paired-row and 230-millimetre deep furrow till sowing to deliver establishment and yield benefits in water repellent sands.

Within this project, early results on repellent sands (Lameroo, 2017-2019) have quantified benefits of edge-row and on-row sowing cereal crop establishment and grain yield.

Significant biomass and grain yield responses have been measured under edge-row sowing following season opening rains. The seeding system included deep furrow tilling to 230mm acting to lift deeper moisture into the seed zone.

Building on this work, the research at Murlong (2019) demonstrated the impact on sowing strategy on yield, where interrow, edgerow and onrow sowing yielded 0.59, 1.45 and 2.0 t/ha, respectively.

Dr Desbiolles says on-row sowing treatments did not benefit from the inclusion of a soil wetter. However, the wetting agent brough a 0.22 t/ha benefit to the edge-row treatments. Deep-furrow tillage also showed promise in bringing yield gains to inter-row and edge-row strategies.

"Inter-row sowing also benefited from the soil wetter, with a 0.37 t/ha gain, and even more drastically when combined with deep-furrow tilling, which delivered 1.16 t/ha additional gain," he says.

"The soil wetter had no effect on grain yield when applied onrow where furrow moisture was sufficient to achieve good germinations.

"In this trial, grain yield responses to treatments were also strongly correlated with plant density, indicating improved establishment was a key factor driving grain yield under the experimental conditions.

"The benefits of on-row and edge-row sowing at multiple sites has been associated with greater soil moisture under the stubble rows, equivalent to approximately 7-9 mm rainfall over the 0-40-centimetre soil depth.

Grower application

Dr Macdonald says the project team will be working with growers this year to test project findings and look to address practical adoption challenges at farmer scale across different sand environments.

"These initial trials have been implemented with using precision guidance, liquid-based technologies, and depth adjustable tillage, fertiliser and seed placement technologies," she says.

"To transfer our research results to farmer scale application will require a certain level of simplification and practical problem solving through working closely with growers.

"Some of the benefits highlighted by this research could be achieved with lowtechnology options to improve access to existing moisture, such as upgrading seeders for deep moisture delving and seeding at a small angle to existing stubble rows without RTK guidance."

GRDC Research Code CSP00203

More information: Dr Jack Desbiolles, UniSA, jack.desbiolles@unisa.edu.au, 0419 752 295; Dr Lynne Macdonald, CSIRO, Lynne.Macdonald@csiro.au, 0472 848 392.

Detailed results can be found in the GRDC Grains Research Update paper, Seeder-based approaches to reduce the impact of water repellence on crop productivity, presented in Adelaide in February 2020.