Improving crop productivity on sands - what is the latest?

Take home messages

Not all sandy soils are poorly productive. The following suggestions only relate to sands which are currently producing very poor crops.
Strategies to improve productivity on a sand are in three categories: Quarantine (set the sandy area aside and reduce costs – cheap, but little financial reward), mitigate (leave the sand as it is, but minimise the impact of its problems – cheap, but the problem is always there), amelioration (change the sand into a better soil – expensive, but potentially good profits and problem solved for the medium to long term).
Deep ripping to relieve compaction regularly produces large and profitable increases in crop yields.
Well incorporated, solid rates of clay eliminate water repellency. Aggressive tillage (e.g., mouldboard plough, large disc ploughing, spading) will reduce repellency but this usually lasts for only for 2-3 years.
Wetting agents at seeding and seeding near the previous crop row can increase the number of established plants in the current crop on severely repellent sands.
Deep sands are often low in nutrient levels. Adding extra N, P and S early almost always improves crop growth. Zn, Mn and Cu applications can also help on some sands, especially the whitest sands.
Improving the top 30 cm of sand with incorporation of clay, N-rich OM and/or extra fertiliser can increase productivity spectacularly, but making it profitable is unlikely in low rainfall areas.
Soil-borne diseases, pests and weeds can be more of a problem on sands but tend to recede if crop production can be improved (such as by techniques mentioned above).
Putting a package of practices together which address the many constraints normally present in sands is the key to large improvements in crop productivity.

Background

Many sandy soils in the southern region are under-performing because the crops on them are not getting to their water limited yield potential. This is most obvious in the deep sands where the subsurface layers can still be quite wet in summer despite a reasonable crop having been grown on them the previous season. There is always a lack of crop roots in these wet layers. Currently there are many R,D&E activities underway attempting to understand the constraints to root growth and to convert any ‘unused’ water into improved crop productivity on these soils. This paper is a summary of their findings so far which relate to sands in the SA and Victoria Mallee regions and includes R&D outcomes over the last decade or so.

The approach I have taken is to picture a deep white siliceous sand typical of those found around Patchewollock (which are considered ‘escapes’ from the Big Desert Wilderness Area). These sands are typically:

at least 40 cm deep before you reach any clay
water repellent in the surface layers
slightly acidic/neutral throughout the profile
very low in organic matter, especially below the surface
low nutrient levels at the surface and only getting worse deeper in the profile
quite strong, especially in a zone at or just below the cultivated layer

The points summarised below have been made in the context of this sand profile. If the sands you have in mind are not as extreme as this one, then the benefits of the management strategies to follow are likely to be smaller, but the problems you are trying to fix should be smaller too. The ‘orange’ sands (such as around Ouyen and Sea Lake) are in this category.

This type of sand usually produces poorly performing crops which struggle to establish well (with fewer and weaker seedlings), have limited tillering/branching, premature senescence of old leaves which drop off, and struggle with high disease and weed pressures. There are three categories of management strategies to change this status quo (quarantine, mitigate, ameliorate) and I will attempt to outline the strengths and weaknesses of practices within each category below. The boundaries between these categories are not absolute but depend on the attitudes and resources of the manager dealing with each sandy area. The categories are also not exclusive, and multiple strategies can be employed to create a new management package for the sandy area.

Quarantine

On the worst sandy areas, the manager may be frustrated by investing in crop production for infrequent and small profits, and there is no motivation to invest more dollars to break the cycle and improve the soil. These areas typically have a high erosion risk.

Quarantining can be as extreme as fencing off the problem areas and returning them to permanent vegetation (grazed or un-grazed) as a strategy to reduce the financial losses incurred and to stabilise them from an erosion aspect.

A less dramatic option for areas where erosion is less likely is simply reducing cropping inputs and accepting low productivity, which may still mean the areas stay in the same rotation and basic management package as the rest of the paddock, but with lower input costs.

Quarantining is only attractive if the total areas of poor sands are small.

Mitigation

Practices in this category accept the existing properties of the sandy profile, while attempting to reduce the impact of those weaknesses on crop production. One way of looking at mitigation practices is that they ‘treat the symptoms of the problem not the cause’. They are usually relatively low cost but also relatively low in benefit and duration compared to amelioration approaches. The table below lists some individual strategies and their strengths and weaknesses.

Table 1. Mitigation strategies for deep sands and their major strengths and weaknesses.

Practice	Strengths	Weaknesses
Wetting agents at seeding	Low cost. Allows all existing crop management strategies to continue unchanged. Of little benefit in years when repellency is less of a problem. Requires a fluid delivery system on the seeder. Improves the number of plants established but not their vigour.	Of little benefit in years when repellency is less of a problem. Requires a fluid delivery system on the seeder. Improves the number of plants established but not their vigour.
Near row seeding to reduce impact of water repellence	Cheap if you already have precision guidance and a high trash flow seeder. Also makes better use of last year’s fertiliser. Of little benefit in years when repellency is less of a problem. Works best in ungrazed stubble. Can be counterproductive if there are weeds and/or diseases in last year’s stubble row.	Of little benefit in years when repellency is less of a problem. Works best in ungrazed stubble. Can be counterproductive if there are weeds and/or diseases in last year’s stubble row.
Other seeding approaches for water repellence (e.g. cross sowing, high seeding rate, ribbon or split seeding boots)	Simple to implement. Low cost if timing is not compromised. Compensates for poor tillering/crop vigour. Of most benefit only in those years when repellency is a major problem. Improves the number of plants established but not their vigour. Must allow for other soil types on the farm.	Of most benefit only in those years when repellency is a major problem. Improves the number of plants established but not their vigour. Must allow for other soil types on the farm.
Increasing fertiliser application rates or types	Simple to implement. Uses existing resources. Can result in nutrient carry over benefits. S and K are two ‘new’ deficiencies to look out for, as well as N, P and trace elements. Can be expensive so relies on substantial crop improvements to be profitable. Need to know which nutrients are in worst supply. Will not increase plant numbers.	Can be expensive so relies on substantial crop improvements to be profitable. Need to know which nutrients are in worst supply. Will not increase plant numbers.
Change crop type to one more adapted to sand (e.g. rye instead of wheat, lupins or woolly pod vetch instead of lentils)	Reduced erosion risk. More grazing potential. Can be low direct cost. Has been used historically to good effect. Can complicate weed and pest control. Reduces efficiencies of operations, especially seeding and spraying. Can replace a high value crop with a lower one.	Can complicate weed and pest control. Reduces efficiencies of operations, especially seeding and spraying. Can replace a high value crop with a lower one.

Amelioration

Amelioration approaches are primarily designed to improve the properties of a deep sand and thus reduce the original weaknesses without losing the strengths of the original profile (e.g. high infiltration rates for water, crops can benefit from small rainfall events, easy to get precise seeding depth and solid seed/soil contact during the seeding operation). These practices tend to be very expensive because large quantities of inputs and/or labour are required to change the nature of soil over large areas. To be cost effective and logistically attractive, they need to provide significant and long residual benefits. They also require a commitment to develop new crop management packages which target a higher production potential (e.g. higher fertiliser rates).

Table 1. Amelioration strategies for deep sands and their major strengths and weaknesses.

Practice	Strengths	Weaknesses
Aggressive tillage (e.g., mouldboard ploughing, large disc ploughing, spading).	Will reduce repellency. Can bury weed seeds and disease inoculum. Will disrupt some compaction layers. Can be conducted with cheaper implements. Can be used to incorporate soil amendments such as lime. Carry over benefits may be short. Most beneficial if they reach clay layers. Can increase plant numbers if repellency is a problem, but not necessarily vigour. Can mineralise OM which is already low in the profile. Incorporation of soil amendments is only shallow. Trafficability and erosion can be issues after implementation.	Carry over benefits may be short. Most beneficial if they reach clay layers. Can increase plant numbers if repellency is a problem, but not necessarily vigour. Can mineralise OM which is already low in the profile. Incorporation of soil amendments is only shallow. Trafficability and erosion can be issues after implementation.
Deep ripping	Cheapest of the amelioration options. Easiest of the amelioration options to implement. Can be implemented at many times of the year. Very good benefit to cost ratios where high soil strength (e.g. compaction) is an issue Current crop management strategies can be maintained. Can be used to incorporate soil amendments to depth. ·	Trafficability can be an issue after implementation and consolidation via rolling may be required. Achieving shallow and consistent seeding depth with solid seed/soil contact can be tricky. Only addresses high soil strength, unless incorporating soil amendments. Incorporation of topsoil/amendments is most effective with inclusion plates but these increase cost and erosion. risk Depending upon the type of sand and recompaction rates, may need to be repeated every 3-4 years.
Delving clay to the surface and incorporating	Eliminates water repellency and compaction. Improves the quality of soil in the incorporated layer. Can produce a long-lasting ‘permanent’ change. Improves crop establishment, early growth, and weed management. Cheaper than clay spreading. Expensive. Only an option if shallow suitable clay is under the sandy area. Need to test the clay to ensure it is beneficial. Poor clay incorporation reduces benefits.	Expensive. Only an option if shallow suitable clay is under the sandy area. Need to test the clay to ensure it is beneficial. Poor clay incorporation reduces benefits.
Clay spreading and incorporating	Eliminates water repellency. Improves the quality of soil in the incorporated layer. Can produce a long-lasting change. Improves weed management. Very expensive. Only an option if shallow suitable clay is close to the sandy area. Need to test the clay to ensure it is beneficial. Excessive clay rates can cause new problems. Poor incorporation reduces benefits.	Very expensive. Only an option if shallow suitable clay is close to the sandy area. Need to test the clay to ensure it is beneficial. Excessive clay rates can cause new problems. Poor incorporation reduces benefits.
Incorporation of N-rich organic matter (OM)	Produces large growth benefits if rainfall allows. Can be sourced on-farm e.g. lucerne hay. Can have carry over benefits. Large volumes of OM are difficult to handle and incorporate. Opportunity cost of OM can be high if grown on-farm. Long term benefits are uncertain. Applications strategies not well understood. Better at producing biomass than grain.	Large volumes of OM are difficult to handle and incorporate. Opportunity cost of OM can be high if grown on-farm. Long term benefits are uncertain. Applications strategies not well understood. Better at producing biomass than grain.

In conclusion, the two previous tables summarise a wide range of strategies which are available, or under development, for improving the productivity of sands. Many of them only target one or two soil constraints, but sands can have multiple constraints, a package of strategies is often required to maximise impact. Identifying the constraints and implementing sounds soil and crop strategies to overcome these are the key to substantial improvements to crop performance on sands. For some constraints (e.g., subsoil nutrient deficiencies) strategies are still being developed.

If you are close to a source of animal-based manures (e.g. pig or poultry enterprises, or feed lots) which are very cheap (e.g. just the cost of transport) then value-adding to deep ripping by incorporating manures can be attractive. Using legume or fertiliser enriched cereal hays in a similar way is still a long way from being profitable.

Useful resources

GRDC web site and GroundCover for articles and reports from current and recent R&D projects. E.g., CSP00203 (Sandy soils) and DAW00244 (Water Repellency).

Clay Spreading and Delving Fact Sheet. (GRDC)

Clay spreading and delving on Eyre Peninsula: a broadacre clay application manual for farmers. 2006, compiled by Rachel May; editors: David Davenport et al.

Davies SL, Gazey C, Gilkes RJ, Evans DJ, Liaghati T (2006) What lies beneath? – understanding constraints to productivity below the soil surface. 2006 Regional Crop Updates, Geraldton, Department of Agriculture and Food, Western Australia.

Davies S, Parker W, Blackwell P, Isbister B, Better G, Gazey C, and Scanlan C (2017) Soil amelioration in Western Australia. (Department of Agriculture and Food, Western Australia) | Date: 07 Feb 2017

Isbister B, Blackwell P and Hagan J (2018) The changing options for soil compaction management. GRDC Grains Research Update. GRDC Project Number: DAW243

McBeath T, Macdonald L, Llewellyn R, Gupta V, Desbiolles J, Moodie M, Trengove S and Sheriff S (2019) Getting the edge on improving crop productivity on Southern sandy soils. Perth GRDC Updates.

Mallee Sustainable Farming - SAGIT Deep Ripping

Acknowledgements

This summary of management options for improving sands has been drawn together from a vast array of existing and recent R&D projects, both from published information and from personal communications. The author is very grateful for their freely given experience and ready access to project data.

Contact details

Nigel Wilhelm
South Australian Research and Development Institute
Building WT19, Waite Research Precinct, Urrbrae SA 5064.
0407 185 501
nigel.wilhelm@sa.gov.au

GRDC Project Code: CSP1606-008RMX,