By David A. Bainbridge
Associate Professor
United States International College of Business
Alliant International University
San Diego, CA 92131
http://www.ecocomposite.org/restoration/soilpit.htm
Soil pitting is a practical and proven surface modification treatment to improve water infiltration and retention and reduces evaporation and increases surface storage and the time available for infiltration to occur. Pitting can double absorption rates.
Pits also capture blowing litter, seeds, and fine dust and protect seedlings from wind and sand blast. The increased availability of water in and around the pits provides suitable niches for plant establishment and stimulates plant growth.
The size of the pit will depend on the soil type, the rainfall variation, species type and seeding method, and equipment availability. Large shallow sloped pits provide a range of conditions for seeds to germinate. Where seeds germinate in a given year will depend on rainfall amounts, timing, and temperature.
Seed germination location varies from year to year.
Implements may use disks, tines, or scrapers to make the pits. The typical Western Australia pitter uses four disks or tines producing four rows of pits with each pass. These break the hard surface crust which often forms on flat, overgrazed and degraded rangeland. These pitters makes pits that are 3 feet long (1 m long), 6-8″ wide (15 to 20 cm wide) and 4-5 inches (10 cm) deep. Scrapers and blades can also be used to create pits in any size.
Several types of disk plows have been used as pitters, but most are modified one-way disk or brushland plows. The standard disks are cut and half of the disks removed. The brushland spring-mounted disks are preferable on more difficult sites.
Cut Out Disk Pitter
Disk pitters can also be made by offsetting the axle location in the disk, creating an eccentric rolling motion, leaving alternate pits.
Pitting without seeding has led to mixed success in the Southwest. In degraded areas with limited seedbanks seeding should be done along with the pitting. A broadcast seeder may be mounted on the pitting implement or the site can be broadcast seeded by hand. These do not allow precise seed placement and many seeds may be misplaced and fail to germinate.
Few pitting studies have been done in the California desert’s with predominant winter rain and very dry summers. However, from limited field experience and trials we feel this is the most effective low cost method of starting degraded dry lands on the way to recovery.
Studies in other areas of the West have found similar results. Barnes (1950) found that pitting was superior to all other treatments for improving short grass range. Soil pitting allowed 32% more sheep to be carried per acre, with a 50% increase in perennial grass left at the end of the year. Double the number of western wheatgrass plants existed 10 years after pitting. Pitting with an eccentric disk pitter increased foliage production 32-68% on deep soils in Wyoming (Lang, 1958).
The results of the experiments conducted by Stern et al. (1992) at Roodeplaat, South Africa on a silty clay loam showed that pitting was beneficial in reducing surface runoff, maintained higher plant evapotranspiration rates and yields than the control treatment and cultivation costs were low.
The effectiveness of the soil pits declines as they fill in with blown or washed soils and debris. Pits in sandy soil in a high wind environment were largely filled in after one season at Anza Borrego Desert State Park (Bainbridge, unpub.). The increased fertility of the pits due to the capture of fines, litter, seeds, and microsymbionts may still provide a significant advantage for plant establishment.
Pitting should be more commonly selected as the preferred method for treating large areas of degraded lands and construction impacted soils.
Further Reading:
Bainbridge, D.A. 1997. Soil pitting; a technique to improve arid land revegetation.
SDSU Soil Ecology and Restoration Group, Bulletin #1, 12 p.
Barnes, O.K. 1950. Mechanical treatments on Wyoming rangeland. Journal of
Range Management 3(3):198-203.
Barnes, O.K. 1952. Pitting and other treatments in Wyoming Range Land.
Wyoming Agricultural Experiment Station, Bulletin #318.
Barnes, O.K., D. Anderson and A. Heerwagon. 1958. Pitting for range
improvement in the Great Plains and the Southwest Desert Regions. USDA
Prod. Research Report #23.
Gintzburger, G. 1987. The effect of soil pitting on establishment and growth of
annual Medicago spp. on degraded rangeland in Western Australia. Australian
Rangeland Journal 9(1):49-52.
Oliveira, C.A.S., R.J. Hanks, and U. Shani. 1987. Infiltration and runoff as
affected by pitting, mulching and sprinkler irrigation. Irrigation Science
8(1):49-64.
Rauzi, F. 1968. Pitting and interseeding native shortgrass rangeland. Wyoming
Agricultural Experiment Station Research Journal 17. 14 pages.
Slayback, R.D. and D.R. Cable. 1970. Larger pits aid reseeding of semiarid
rangeland. Journal of Range Management 23(4):333-335.
Stern, R., A.J. Van der Merwe, M.C. Laker and I. Shainberg. 1992. Effects of soil
surface treatment on runoff and wheat yield under irrigation. Agronomy
Journal 84(1):114-119.
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