last update February 18, 2001
In areas where water is scarce all year (or seasonally), surface modification to retain precipitation should be considered an essential part of a restoration program. Surface modification techniques like pitting increase infiltration and surface storage, reduce runoff, increase soil water content, and improve vegetation establishment and growth. Soil pitting is a low cost, practical and proven surface modification treatment, and this technique is not limited to use in desert areas.
Pitting can double rainfall absorption rates and that can make the difference between success and failure in plant survival. A disk pitter that spaces pits about 16 inches apart provides almost 1,000 cubic feet of water storage per acre. Changes in the physical properties of the soil due to pitting are also effective in controlling runoff and increasing infiltration of water into the soil.
On sandy loam, moisture penetration reached 24 inches on pitted sandy loam vs 5 inches on untreated land; 15 inches on pitted loam vs 7 inches on untreated; and 11 inches on pitted clay vs 2 inches on untreated. 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; but seed germination and plant establishment at the very bottom of the pit can be impaired if water remains for more than a week. In one of our research plots survival of transplants in pitted plots was 76%, while imprinted plot survival was 63% and the control was only 52%.
Determining the size and shape of the pit to be prepared will depend on the soil type, rainfall variation, species type, seeding method, and equipment availability. Large, shallow sloped pits provide a wide range of conditions for seeds to germinate. Where seeds germinate in a given year will depend on rainfall amounts, timing and temperature.
Pitting is a simple process, but like most dry land treatments it involves a complex set of relationships and uncertainties. Success in any given year will depend on the weather, timing of pitting, seedling, and rainfall. Pit effects may persist for many years. One of our treated desert plots finally got rain after 3 years - and 31 species established in these degraded soils versus only 21 undisturbed natural land nearby.