Improving crop productivity and profits on sandy soils

Take home messages

• Identify the specific limitations of your sand areas on your farm to understand what issues you need to resolve and the most appropriate management strategies to target.
• Techniques that break compaction and incorporate nutrition and organic matter are successful at ameliorating sands and improving yields for the longer term.
• Use high nitrogen fertiliser rates at seeding, but seed/fertiliser separation is required especially with dry season starts.

Introduction

Sandy soils make up a large portion of Mallee farming landscape. This paper is drawn from many years of trials, demonstrations and farmer experiences of managing Mallee sands, as well as highlighting much of the current research that is exploring practical options to effectively improve our productivity and profitability from Mallee sands.

What’s wrong with Mallee sands?

While sands can vary between regions and paddocks, they are generally low in their water holding capacity, naturally low in fertility and are highly prone to wind erosion when compared to loamy or clay soils. They are also prone to water repellency, deep compaction, weeds and root disease, leaching of nutrients and often produce low and patchy yields in poor seasons.

Additionally, they contribute to recharging perched water tables that lead to saline seep formation. Seeps research at Wynarka (McDonough 2017) has shown rainfall events as low as 12mm regularly pass through the crops’ rootzone and contribute to the recharge of perched water tables beneath the crops’ rootzone, such is their lack of water holding capacity.

What’s good about Mallee sands?

Mallee sands can have a relatively higher plant available water in low rainfall years compared to heavier soil types. Their productivity and reliability can be improved through both good agronomic practices and amelioration. They respond well to no-till farming systems, which are characterised by a high turnover of organic matter. Studies have found that the soil problems of Mallee sands can be alleviated via a number of treatment with a resulting increase in crop yields. Questions remain as to the practicality, cost and longevity of some of these treatments. While new technologies are constantly being developed, many current management strategies are proving to be effective and profitable options for Mallee growers.

Key factors for improving the productivity of Mallee sands

It is important to know and understand your sandy soils, to recognise which sands may essentially be improved through less expensive mitigation approaches (such as good agronomy) and which sands may require more specific and targeted amelioration, which will involve higher, more expensive intervention that aims to have a lasting impact, through changing the properties within the soil profile. Recognising the key constraints such as compaction, repellence, poor water holding capacity and nutrition are important in deciding the best course of action.

As a grower, there are many ways to improve your sandy soils. For lasting benefits to crop and pasture production, the focus should always be on ways to:

• Improve the water holding capacity within the soil’s rootzone – by changing the nature of sand in both surface and deeper layers, as well as increasing the depth of effective root growth by addressing compaction issues.
• Improve soil fertility – though increasing the soils cation exchange capacity and microbial activity through organic matter turnover, while cost effectively increasing nutrition.

Key management strategies that focus on improving the water holding capacity and fertility of Mallee sands

Mitigation

Good agronomy, no-till, higher fertiliser rates, variable rate technology

Most of the Mallee sands, particularly midslope sands and loamy sand soils, have been greatly improved with the practice of good no-till farming systems within the last 20 years. Intensive cropping with chemical summer weed control, stubble retention, good rotations and regular fertilisation with higher (than used in the past) application rates of nitrogen (N), phosphorus (P) and trace elements has changed this land from being weed and disease infested, highly erodible, risky and low yielding, to being some of the more reliable production soils, particularly in lower rainfall years. This is mainly due to the high turnover of fresh organic matter residues, building the microbial biomass and improving the soil’s water holding capacity and nutrient exchange. This has helped make up for the sands lack of fine clay particles which are a key component of more naturally fertile loamy soils.

While sand cannot hold as much water as heavier textured soils, a greater portion of its water is plant available, which can be very beneficial in lower rainfall years when the clay soils tend to hold onto the little moisture they have, and thereby not releasing it to the crops.

In variable rate farming, it is these midslope sands that will respond well to higher fertiliser rates as they have reasonable plant available water but need higher nutrition to be able to reach their full yield potential.

In recent years, CSIRO research conducted on Mallee Sustainable Farming (MSF) trial sites has concluded that good early N nutrition remains a key driver of yield in Mallee sands and in most seasons, penalties can occur with delays in applications until the first node stage (McBeath et al. 2017). Di-ammonium phosphate (DAP) placed with seed can cause a yield penalty in seasons like 2017 (a later, drier season opening), particularly on sands which hold less moisture. This is due to the conversion of N and not just the salt index of the fertiliser. Mono-ammonium phosphate (MAP) has been shown to be less toxic on these soils in these later, drier seasons. Separating seed and fertiliser with N below the seed is advantageous. Trials have indicated that zinc (Zn) coated urea provides a more efficient form of N application (McBeath et al. 2015), but these products are not currently commercially available in Australia.

Copper (Cu) and Zn remain important to apply on sands and the use of sulphate of ammonia (SOA) is encouraged for growers to trial in order to test whether their sands are sulphur (S) responsive. Manganese (Mn) application can become important where clay-spreading and incorporation has occurred on sands.

Amelioration

Amelioration is required for the very poor sand that requires more than just good agronomy and higher fertiliser rates to improve productivity, generally this will involve high initial costs. It is therefore important to understand what issues you are trying to fix before embarking on a specific management plan.

Is compaction an issue?

Soil compaction is common in Mallee sands, often occurring between 20cm to 40cm depth, as shown in Figure 1 at a CSIRO trial site near Loxton. Western Australian research (DPIRD report 2018) is now suggesting that crop roots will not grow through a penetration resistance of 2500Kpa rather than 3000Kpa. One indication of whether compaction is a major soil constraint in a paddock is to dig a hole (spade or auger) after the crop has matured (late October, but prior to any major harvest rainfall event) to see if the soil is still moist at 20-40cm depth. Even after drought years it is not uncommon to find wet soil in this zone where compaction exists.

Figure 1. CSIRO Sand Trial Site penetration, Loxton 2015 (Llewellyn, pers. comm.)

Spading

Research conducted on numerous Mallee trial sites has shown that spading; highly nutritious organic matter (for example chicken manure, lucerne pellets or cereal stubble with added fertiliser) has substantially increased crop yields for up to four years so far (Figure 2).

Figure 2. Yield gains of selected treatments at Karoonda (Fraser et al. 2017), relative to the unmodified control. Wheat was seeded in all years since 2014, except for 2016 when peas were used.

The spading of both 6t/ha and 9t/ha chicken manure at a trial site near Karoonda (McDonough 2016) showed yield advantages compared with the unmodified control, averaging 1.7t/ha/year in the first two seasons following spading which was conducted in 2015. This resulted in two-years of a gross margin in excess of $400/ha (accounting for both spading and manure costs), showing that this form of soil amelioration, although expensive, can be profitable even in the short term. Soil tests revealed that despite the large export of nutrients in the high yielding crops, higher ongoing mineralisation and release of nutrients during the second growing season from the chicken manure compensated for this loss and helped to maintain a high yield advantage over the control.

However, where spading-only had taken place, there was only a 0.6t/ha yield increase over the control, and a severe depletion in soil nutrition. In the second season it yielded slightly less than the control plots because of the depletion in soil nutrition. Moisture probe analysis has clearly shown that much more plant available water was maintained in the top 40cm of the spaded chicken manure plots which was readily utilised by the crop roots as the crop established. The control site by contrast, held very little moisture in the top 40cm and there was very little crop root moisture use below 30cm depth, with most of the excess rainfall quickly flowing through to recharge.

The spading operation was expensive and there was variation of spading depth of between 20-40cm across the spader width as well as the direction travelled. There was some reduction of surface soil fertility as it was mixed into the soil profile with evidence of weed seed burial. Despite this, spading in of nutritious organic matter remains the most effective method of ameliorating Mallee sands, as it provides a lasting break to deep soil compaction and greatly improves soil water holding capacity and fertility.

Deep ripping

Deep ripping is relatively cheap and a practical first option for amelioration of compaction on sands. It often leads to a dramatic yield increase in the first season, and documented evidence from WA suggests that the benefits will last for about three years (Moodie and Macdonald 2017), depending on soil types, farming systems and machinery. However, grower trial and demonstration work in the Mallee has, on occasion, seen the first year benefits of deep ripping disappear in the second year. Deep ripping of nutrients has not shown benefits over deep ripping alone in recent trial work in the Victorian Mallee (Moodie and Macdonald 2017). SARDI are currently conducting deep ripping trials to explore issues of depth, row spacing, crop use and soil/plant/water interactions over time at three sites across the SA Mallee.

There is evidence that under controlled traffic systems the benefits of deep ripping has lasted up to ten years (Bakker et al. 2017; Hagan 2015). There is current machinery development work being led by the University of South Australia, exploring the placement of organic matter down behind the ripping tines to help keep rip lines open for longer as well as improving deep soil fertility and water holding capacity. More work is required to determine practical and efficient delivery mechanisms in terms of machinery and organic materials before this becomes a commercially viable option for growers.

Delving

Where clay is within the top 40cm of the soil profile then delving is an excellent option. Delving tines can scrape into the top of the clay layer (which is not generally as hostile as the deeper clay with high boron, salinity and sodicity) and lift and mix it through to the surface in the rip-line. It is far simpler and less costly than some of the other amelioration techniques (e.g. claying), while still breaking compaction, improving soil function around the delved lines, and allowing crop roots to break through the bleached sand layer into the subsurface. Delving row widths of 1m or less are effective and need to follow the same direction as the seeding lines.

Non wetting sands

Clay spreading

Water repellence remains a major issue in many Mallee sands, leading to patchy crop establishment, staggered weed germination and poor crop performance. Poor water and nutrient retention are also issues. Clay spreading with appropriate rates and good incorporation remains an excellent remedy where clay and funds are readily available. Clay spreading increases the surface soil stability; ensuring better furrow establishment and retention, as well as reduced frost risk, improved weed control and increases in yield.

Relatively low rates of clay (125t/ha) are adequate where water repellence is the prime concern. However, higher rates (170t/ha) mixed well into the top 30-40cm will also improve water and nutrient retention in deep sands and be more effective in overcoming water repellence. Higher clay rates that are incorporated mostly in the surface have reduced crop growth and yield in low rainfall seasons due to reduced plant available moisture. During the dry start to the 2018 season, correct technique of clay spreading has been the difference between good crop establishment and poor emergence leading to erosion.

Mouldboard ploughing

Mouldboard or offset disc ploughing is being widely used in WA to ameliorate stratified and infertile sands, and bury herbicide resistant weed seeds. Trial results at Coomandook (Tonkin 2013-2015) showed that the spader had the best effect of the soil modification treatments. While mouldboard ploughing reduced water repellence in the soil, it did not improve productivity as much as spading. The addition of surface applied grape marc and composted pig manure had the highest yield benefits, but the costs of transport and product meant that the most profitable treatment at this site was not the most productive treatment.

Wetting agents

Wetting agents are also being currently trialled to identify optimal products and application placement. Wetting agents can be either surfactants – which break surface tensions and allow water to pass through soil, or humectants – that help draw and retain water within the soil. Preliminary trials from WA (Davies et al. 2015) have shown that while wetting agents often improved crop establishment on non-wetting sands, this did not always translate into a yield benefit.

This work, along with anecdotal evidence from Mallee demonstrations suggest that wetting agents placed around or below the seed were more effective than placement on the surface. There are new products and application techniques being currently evaluated. Water repellence trials on Eyre Peninsula (Wilhelm, pers comm. 2018) did find wetting agents to be more effective than on-row seeding as a management technique for improved crop establishment.

On-row and edge-row sowing

On-row and edge-row sowing has improved crop establishment in Mallee trials on non-wetting sands but the technique has not proved to be advantageous on sands where repellence is not a problem. Eyre Peninsula trials (Cook and Richter 2017) have also shown some advantages in drier season openings. There remains multiple technical issues in achieving on-row and edge-row sowing, in particular problems with the accuracy of the guidance system and the consistency of machinery operations between years. However, research is continuing with trial work established at Lameroo through the University of SA. This ongoing research also involves investigating the potential to create enhanced zones of fertility through an annual application of a range of amendments through the seeder, including carbon and other nutrients, on the same rows over multiple years.

Conclusion

Mallee sand productivity can be greatly improved through various management techniques aimed at reducing repellence, improving water and nutrient holding capacity and breaking compaction. A good understanding of what soil issues are constraining crop productivity is critical to developing a cost-effective soil mitigation or amelioration strategy. While there are high up-front costs for many of the deep soil amelioration options, many are proving to be both practical and profitable over time. New technologies are developing rapidly, many of which are currently being researched and demonstrated throughout the Mallee, and these should provide valuable insight into the many unanswered questions that Mallee growers currently face.

References

Monitoring Mallee seeps, progress report July-Dec 2017, for Natural Resources SAMDB Management Board, by C. McDonough, Insight Extension for Agriculture.

Nutrition packages for wheat on sands (2017), T. McBeath, R. Llewellyn, V. Gupta, B. Davoren, W Shoobridge, CSIRO Agriculture & Food Waite Campus; M Moodie T. McDonald, M. Brady,
Mallee Sustainable Farming.

Managing nutrition in sandy soils to close the yield gap (2015), T. McBeath, B. Davoren, R. Llewellyn and W. Shoobridge, Agriculture, CSIRO, Waite Campus, Adelaide.

Soil compaction overview (2018), Dept. Primary Industries and Regional Development, WA

Source, Rick Llewelyn, CSIRO Agriculture & Food Waite Campus. Pers. Comm.

Spading increases yields on Mallee sands (2017), M. Fraser, PIRSA Rural Solutions SA, N. Wilhelm, D. Davenport, SARDI

Monitoring Mallee seeps, progress report July-Dec 2016, for Natural Resources SAMDB Management Board, by C. McDonough, Insight Extension for Agriculture.

Increasing water extraction and production on Mallee sands through enhanced nutrient supply in the root zone (2017) M. Moodie, Moody Agronomy, L. Macdonald, CSIRO, Waite Campus.

Deep ripping for soil compaction (2017) D. Bakker, S. Davies, B. Isbister, Dept. Primary Industries and Regional Development, WA.

Ripping benefits quickly negated by wheel traffic. J Hagan, DAFWA Goundcover Supplement Issue 118 (2015).

Coomandook Ag Bureau spader, mouldboard and organic matter 3 year report 2013-2015, for the SA MDB Natural Resources Management Board, by R Tonkin, Rural Solutions SA.

New opportunities for soil wetting agents on repellent soils (2015) S. Davies, G. McDonald, G. Anderson, L. Harte, G. Poulish, Department of Agriculture and Food, Western Australia, R. Devlin, R. Jenkinson, Living Farm. Eyre Peninsula Farming Systems 2015 Summary.

Source, Nigel Wilhelm, SARDI Waite, pers comm.

Crop establishment on non-wetting sand (2017) A. Cook, I. Richter, SARDI, Minnipa Agricultural Centre, Eyre Peninsula Farming Systems 2017 Summary.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC — the author would like to thank them for their continued support.

Additionally, the author thanks the contributions of Lynne McDonald, Jack Desbiolles, Nigel Wilhelm, Therese McBeath, Michael Moodie and Trevor Hancock for information provided in this paper.

This paper draws on information from many project sources funded through GRDC, SAGIT and the South Australian Murray-Darling Basin Natural Resources Management Board and the Australian Government’s National Landcare Program.

Contact details

Chris McDonough
Insight Extension for Agriculture
C/o PO Loxton North SA 5333
0408 085 393
cmcd.insight@gmail.com