The Effects of Mulches in Combination with Seed Mixes on Landfill Soil Erosion Management

by Warren S Lucero

Summary:

10 acres of recently covered landfill was treated with four treatments consisting of seed mix and mulch combinations for soil erosion control. Sample were taken from a sediment collection tube during 2/ 21 to 3/15 and 3/15 to 4/15 of 1998 with a total rainfall of 5.66 inches. Within the straw treatments no difference were detected (P< 0.96). No difference were observed with the seed mixes (P< O.32). No interaction was detected in the straw in combination with seed mixes (P< 0.98). However, the seed mix (Erosion Seed Mix) demonstrated to cover more area in terms of vegetative matter.

Introduction:

California landfills are faced with the problem of soil erosion on recently covered sites (de Roco 1997). The general practice by, some solid waste facilities is to plant a quick establishing plant species, fertilize, and depend on the natural rainfall for germination (Thomas 1997). However, the Glenn County landfill has little experience managing erosion: yet by law no pounding of water or exposure of the solid waste is allowed.The landfill must be covered with a vegetation excluding trees and shrubs, while the site is not used for further disposal of solid waste, lasting up to 2 to 3 years.

The best ways to reduce erosion is: 1) divert water 2) protect soil with mulch 3) establish a plant cover (Adams Jr. 1979). So a comparison of two mulches and two seed mixtures were used as erosion control measures.

Materials and Methods:

This experiment was conducted at the Glenn County Landfill in Artois, California (Fruto Ne Quadrangle Section 35) in December of 1997. The ten acre site had a 1:3 slope located on the eastern region of Mendocino National Forest where the valley floor turns into gentle rolling hills. The solid waste site had been covered with 4 feet of soil excavated from 15 feet below the soil surface from a near by location.

The soil type was that of a clay loam. Soil analysis results showed the pH, salinity, and potassium within acceptable ranges for the plant mixes but nitrogen and phosphorus were deficient. A 16-20-0 fertilizer was applied at 200 lb. per acre to compensate for the deficiency.

Treatments were 1) wheat straw and Cucamonga Brome, 2) wheat straw and Erosion Soil Mix (40% Rye, 40% Barley, 10% White Clover, 10% Rose Clover), 3) rice straw and Cucamonga Brome, 4) rice straw and Erosion Soil Mix. The experimental design was a randomized block with each of the four: seed mixes and mulch combination replicated in eight blocks. The plots were delineated by the Deputy County Engineer to ensure proper drainage.

The site was lightly disced before planting and fertilizing to ensure penetration due to the hard surface resulting from the clay loam soil. With a broadcast seed spreader, the Erosion Seed Mixture was planted at 100 lb. per acre and Cucamonga Brome at 20 lb. per acre. Both the rice and wheat straw were applied at the rate of 1.0 ton per acre (Adams Jr. 1979 and Caltrans Dept. of Trans. 1996).

Erosion was monitored by thirty-one closed capped 4 inch in diameter by 3 feet long tubes with 2 inch opening running the length of the tube to allow sediment collection (Gerlach 1967). Due to the variation in plot sizes, the tubes were placed so to cover a 2 foot by 35 foot surface area, while the 2 inch opening edge was against the downward slope, flush and level with the soil surface.

Planting, fertilizing, and spreading of the mulch was completed by, December 6, 1997. The collection tubes were place on the site on February 21,1998. Sediment samples were collected on March 15 with total rainfall of 1.5 inches and April 13 with 4.0 inches of rainfall. The contents of tubes were collected by removing the tube's caps and washing sediment into 10 oz. wax Dixie cups. The samples were dried at 35 degrees Celsius for 48 hours on a forced air-oven and weighted. The weights were based on grams of total sediment present inside the cup.

Results and Discussion:

All weights examined were analyzed by analysis of variance (ANOVA) using the software of Microsoft Office 95: Excel. To determine if difference lied between sample dates, data collected was combined into composite table (Note: this is only a comparison of treatments, not a measure of total sediment runoff). Among straw treatments no differences were detected (P< 0.98). Seed mixes showed no detection of difference (P< 0.32). No interaction was observed in the straw in combination with seed mixes (P< 0. 92).

Observations were made of the total area covered by -vegetation in each plot. Overall, the Erosion Seed Mix was determined to cover more surface area then the Cucamonga Brome.

References:

• Adams, Jr., T.E. Seeding for Erosion Control in Coastal and Central California Division of Agr. Sci: U.C. Leaflet 21304. 1979.
• De Roco, Jerry. Solid Waste Coordinator of Glenn County. Interview. Sept. 1997.
• Gerlach, T. Hill slope troughs for measuring sediment movement. Revue de Geomorphologic Dynamique. 1967. State of California: Department of Transportation, Division of New Technology. Control (Type D). 03-11-96.
• Thomas, Fred. CERUS ConsultinR. Interview. Sept. 1997.