Improving crop productivity on sands - what is the latest?

Take home messages

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 generally lasts only for one season, so the problem is always there)
- Amelioration (change the sand into better soil – expensive but potentially good profits and the problem is solved for the medium to long term).
Deep ripping to relieve compaction regularly produces useful increases in crop yields.
Well incorporated, solid rates of clay eliminate water repellency. Aggressive tillage (e.g. mouldboard plough, large disc ploughing) will reduce repellency but 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 nutrients. Adding robust levels of nitrogen (N), phosphorus (P) and sulphur (S) early almost always boost crop growth, but sometimes this doesn’t translate into increased yield. Zinc (Zn), manganese (Mn) and copper (Cu) applications can also help on some sands, especially the whitest ones.
Ameliorating the top 30cm of sand to a better soil type with incorporation of clay, or N-rich organic matter (OM) can increase productivity spectacularly but making it profitable is still elusive.
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 together a package of strategies 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 research, development and extension (R,D&E) activities underway attempting to convert this ‘unused’ water into improved crop productivity on these soils. This paper is a summary of their findings so far which relate to sands on Eyre Peninsula and includes R&D outcomes over the last decade or so.

In this paper when discussing sands it refers to a deep white siliceous sand of a type which can be found around Wanilla, west of Cummins, east of Lock and throughout the Wharminda district. These sands are typically:

At least 40cm deep before you reach any clay
Water repellent in the surface layers
Slightly acidic at the surface and the pH is even lower below the cultivated layer
Very low in organic matter, especially below the surface
Poorly fertile at the surface and only getting worse deeper in the profile
Quite strong (i.e. compacted), 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 also be smaller too).

This type of sand usually produces poor crops which struggle to establish well (fewer weaker seedlings), have limited tillering/branching, drop off old leaves early in the season and struggle with high disease and weed pressures. There are three categories of management strategies to change this status quo (quarantine, mitigate, ameliorate) and this paper will attempt to outline the strengths and weaknesses of practices within each category in the sections to follow. 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

Quarantining the sandy areas means that you are tired of spending money on those areas for infrequent and small profits, there is no motivation to invest more dollars on those areas in an attempt to break the cycle, and the current erosion risk or reality is unacceptable.

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 made on them and to stabilise them from an erosion aspect.

Less dramatic are options of simply reducing 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 rates of inputs.

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

Mitigation

Strategies in this category are those which accept the existing properties of the sandy profile but attempt to reduce the impact of those weaknesses on crop production. Mitigation is akin to managing the ‘symptoms’ rather than treating the underlying ‘cause’. These strategies are usually relatively low in cost but also low in benefit (compared to amelioration approaches). Table 1 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
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 residual 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
Wetting agents at seeding	Low cost Allows all existing management strategies to continue. 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
Seeding approaches which increase plant numbers (e.g. cross sowing, higher 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	Of most benefit only in those years when repellency is a major problem. Improves the number of plants established but not their vigour
Increasing fertiliser application rates or types	Simple to implement Uses existing resources Can have carry over benefits Can be somewhat expensive so relies on substantial crop improvements to be profitable Need to know which nutrients are most deficient Will not increase plant numbers	Can be somewhat expensive so relies on substantial crop improvements to be profitable Need to know which nutrients are most deficient Will not increase plant numbers
Change crop type to one more adapted to sand (e.g. rye instead of wheat, lupins 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, esp. seeding and spraying Can replace a high value crop with a low one	Can complicate weed and pest control Reduces efficiencies of operations, esp. seeding and spraying Can replace a high value crop with a low one

Amelioration

Amelioration is an approach primarily designed to change the fundamental characteristics of a deep sand into a better soil, 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 attempt to address the underlying causes of poor fertility. They tend to be very expensive and require effort to implement.It is not cheap to change the nature of soil over large areas and thus amelioration practices need to have long residual benefits to be cost effective and logistically attractive. Table 2 lists some individual amelioration strategies and their strengths and weaknesses.

Table 2. 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/eliminate repellency for medium to long term Can bury weed seeds and disease inoculum Will disrupt some compaction layers Can be conducted with cheaper tillage implements Can be used to incorporate soil amendments (e.g. lime, manure or organic matter) Carry over benefits may be short Can increase plant numbers but not necessarily vigour Can mineralise OM which is already low in the profile Incorporation of soil amendments is only shallow Trafficability can be an issue after implementation resulting in poor crop establishment	Carry over benefits may be short Can increase plant numbers but not necessarily vigour Can mineralise OM which is already low in the profile Incorporation of soil amendments is only shallow Trafficability can be an issue after implementation resulting in poor crop establishment
Deep ripping	Cheapest of the amelioration options Easiest of the amelioration options to implement Can be implemented at many times of the year Current management strategies can be maintained Can be used to incorporate soil amendments to depth Trafficability can be an issue after implementation Achieving shallow and consistent seeding depth with solid seed/soil contact can be tricky Only addresses high soil strength/compaction May need to be repeated every few years if not using controlled traffic	Trafficability can be an issue after implementation Achieving shallow and consistent seeding depth with solid seed/soil contact can be tricky Only addresses high soil strength/compaction May need to be repeated every few years if not using controlled traffic
Clay spreading and incorporating	Eliminates water repellency Improves the quality of soil in the incorporated layer Can produce a ‘permanent’ change Makes weed control much better Very expensive Only an option if shallow suitable clay is close to the sandy area 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 Excessive clay rates can cause new problems Poor incorporation reduces benefits
Delving clay to the surface and incorporating	Eliminates water repellency and compaction Improves the quality of soil in the incorporated layer Can produce a ‘permanent’ change Makes weed control much better Cheaper than clay spreading Expensive Only an option if shallow suitable clay is under the sandy area Poor incorporation reduces benefits	Expensive Only an option if shallow suitable clay is under the sandy area Poor incorporation reduces benefits
Incorporation of N-rich organic matter	Produces large growth benefits Can be sourced on-farm e.g. medic hay Can have carry over benefits (3-8 years) Large volumes of OM are difficult to handle and incorporate Opportunity cost of OM can be high Long term benefits are uncertain Applications strategies not well understood Crops sometimes better at producing biomass than grain	Large volumes of OM are difficult to handle and incorporate Opportunity cost of OM can be high Long term benefits are uncertain Applications strategies not well understood Crops sometimes better at producing biomass than grain

In conclusion, Table 1 and 2 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 weaknesses and as most sands have multiple constraints, a package of strategies is almost always required to maximise impact. Identifying those constraints and implementing strategies well to overcome them are the key to substantial improvements to crop performance on sands. For some constraints (e.g. subsoil infertility), strategies are still being developed.

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.

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 also from personal communications. The author is very grateful for their freely given experience and ready access to project data.

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 authors would like to thank them for their continued support.

Contact details

Nigel Wilhelm
Building 11A, Waite Research Precinct, Urrbrae SA 5064.
0407 185 501
nigel.wilhelm@sa.gov.au

GRDC Project Code: CSP1606-008RMX, DAW00244,

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