Improving Soil Conditions for Desert Restoration Success

1. Improving Soil Conditions for Desert Restoration Success David A. Bainbridge Restoration Ecologist San Diego

2. Understanding disturbance • Start with a site history • Then field checks • infiltration • soil strength • fertility • ecology Infiltrometer studies

3. Decompaction • Most restoration sites will benefit from ripping, subsoiling, forking or decompaction • Rototilling is less desirable but can help • A spader is a better choice because it does not invert the soil or leave a tiller pan - but not widely available

4. Soil treatment • Hand treatment is rarely possible • A tractor with ripping teeth will help with road restoration • Spaders can loosen soil and fold in mulch

5. Surface configuration • Once the soil is loosened up it can be shaped to improve water retention and create planting spots • Pitting, basins, imprinting, ridges, and other contouring can be done by hand or machine • Try to understand the topography at the macro and microscale • Think watersheds

6. Check dams • Check dams may be needed to protect flow channels • These can be rock, gabion, brush • Permeable dams are generally more resistant • Design for overflow and undercut, side cut protection

7. Soil Pitting • Pitting is often the best alternative • Increases water retention - up to 1000 cubic feet per acre • Creates spots that capture dust, micro-organisms, seeds • Pitting, mulch, seeding and container plants at Hungry Valley shown

8. Basins • Larger pits can also be made with a machine or by hand • I often used hand labor - but would recommend equipment now (a small excavator would be very effective)

9. A Camel Pitter • I would also buy a Camel pitter • This can be hauled behind a truck or larger SUV • Low cost easy to transport

10. Imprinting • Bob Dixon’s imprinters have worked very well in some cases • They make microwatersheds with a large drum with teeth designed for specific rainfall/soil conditions • Larger models can even imprint asphalt (be careful)

11. Imprints • I have found they do not work as well in the California winter rainfall deserts • But in bimodal rainfall areas they have been effective • Good for rangeland rehab

12. Ridges and catchments • Ridges and contour catchments can help • A very low cost option for abandoned ag lands

13. Erosion control • Save the soil by thinking about water flows and erosion • Check dams, contour lines, rock lines, brush, mulch, straw • Cheaper to prevent than restore damage • Beware of water run-on to your site from the watershed above

14. Straw flake dams • Flakes of weed seed free straw placed in trenches are very effective and low cost • Unlike straw wattles in netting there is no risk of entrapment of reptiles

15. Punched straw • Straw can also be punched in by hand • Rice straw will last for several years • Rice straw is also less likely to have desert adapted weeds • Termites will eventually get to it Punched straw after 5 years

16. Bark and brush • Recalcitrant mulch can also be very helpful • Bark, chipped wood, almond hulls and other heavy materials will resist wind • They provide food for organisms Bark mulch after five years

17. Brush spreading • Organic matter and brush from construction projects can be respread • Reducing erosion and saving many seeds, organisms • Discourages OHVs

18. Matting, fabric, etc. • In some cases coir fabric, jute netting, or straw/mesh mats can be used • These are expensive and usually only used near buildings, roads or steep slopes • Pin or weight carefully to resist wind In an experimental plot the best cover and greatest number of plants per square meter (7 times control) were in punched straw, followed by EncS2 straw/coir mat, and jute netting. Coir mat was better than control with almost 3 times as many plants.

19. Straw wattles • One of the most commonly prescribed erosion control methods • Rarely installed correctly • Must be set in a trench and pinned to work well and resist wind • Entrapment of reptiles in the netting reported in the desert Straw wattle set in trenches and pinned with rebar staples

20. Fertility • Soil fertility is rarely a problem • Most desert plants are adapted to low nutrient levels • Nitrogen deposition from air pollution in fact, may be helping drive the invasion of alien species • However - check levels, added phosphorus may help root development in borrow pits • Be aware of alkali, salts, boron, selenium • Check organic matter - low is expected but none can be a problem

21. Soil salvage • Topsoil can be scraped off and saved • This is costly but can be very effective • Seeds, organic matter and organisms can all be respread • Best if done quickly but can be stockpiled CMM soil salvage operation

22. Soil Ecology • More costly to check but a good indicator of soil health • Check mycorrhizal fungi - spores or bioassay • Check rhizobial bacteria - N fixers by bioassay or root checks • Compare ant colony counts on disturbed v/s less disturbed areas

23. Cryptobiotic crusts • Living crusts are often important • Even in the desert we see them in some locations • Even when you don’t see them they may be present • Protect them • You can try inoculation but I have not had much luck

24. Integrated treatment • Soil treatment is an often neglected aspect of desert restoration • Understand what was and what is • The plants that used to grow may be unsuitable for current soil conditions • Soil rehabilitation and time may be needed to restore soils to health

25. What changed? • Worst case scenario • Borrow pit • 20 feet of soil removed • All plants and organisms removed • Not quite as bad • OHV damage in state park • Soil compaction and plant destruction • Changes in soil texture CalTrans borrow pit ABDSP Hill climbs

26. Success • Getting it right will take thought, careful work, monitoring and followup • Managing soil and water are intimately related • Restoring plant cover helps - the shrubs help capture dust and nutrients • These islands of fertility provide habitat for many other species

27. Mesquite Mound • How much dust and sand can a plant capture? Quite a bit! • These plant mounds or nebkas are very important ecologically

28. Soil treatment - before

29. Soil treatment - after • Ripped, pitted, mulched and seeded • The image on left is hill top exposed, grasses on the right are on a north facing slope nearby (same seed mix) after 3 years

30. Soil restoration is possible • Think it through • What problems are evident? • Test • Then • What can you do? • What equipment is available? Allowed? • What can you afford? • When? How? Who? • Monitor and followup

31. Further reading • A Guide for Desert and Dryland Restoration. 2007. Island Press. • The Mojave Desert : ecosystem processes and sustainability. 2009. Univ. Nevada Press. • The California Desert, 2 volumes. 1995. June Latting Books.