Saturday, 15 July 2006

Compost Use in Urban Landscapes.

John J. Sloan, Cynthia McKenney, James Heitholt, Wayne Mackay, and James McAfee. Texas Agric. Exp. Stn., Texas A&M Res. & Ext. Center, 17360 Coit Rd., Dallas, TX 75252-6599

Construction of new homes and businesses is a continuous process in rapidly growing urban areas. Post-construction landscaping is usually approached from only the plant-selection viewpoint and little effort is devoted to the severely disturbed soil. Subsoil and construction debris are often mixed with or completely replace the original top soil. Although ornamental plants and turf grasses planted in these disturbed soils may perform well in the short term due to abundant watering and fertilization, they frequently decline with time when heat and drought stress become prevalent. Dairy manure compost (DMC) is a readily available soil organic matter amendment in many areas due to the presence of large dairy operations. These dairy operations need alternative ways to dispose of their manure because soils surrounding the diary operations are often elevated in soil P. Consequently, dairy farmers and state regulatory agencies are considering urban markets for composted dairy manure. The objective of this study was to evaluate the effect of large single applications of DMC on the establishment and subsequent growth of typical urban landscape plants and to evaluate the effects on soil nutrient levels, especially phosphorus.

Experimental plots measuring 6x6 m were established on a fallow agricultural field. Dairy manure compost was applied at rates of 0, 90, 180, and 270 Mg/ha (approximately equivalent to 0, 1.25 2.5 and 6 cm depth) and incorporated into the soil. Half of each plot was established with bermudagrass sod and the other half was established with 6 different ornamental plants consisting of annual, perennial, and woody species. Plant performance data was collected for three summers. Soil samples were collected each summer for nutrient analysis. Soil compaction was measured using a hand-held penetrometer and infiltration rate was measured with a Guelph infiltrometer.

Annual, and to a lesser degree, perennial ornamental plants responded favorably to increased rates of DMC in terms of overall performance, but woody ornamental plants showed little response to DMC applications. Bermuda turf grass exhibited increased growth and increased uptake of nitrogen and phosphorus with increasing rate of DMC. Dairy manure compost generally increased rates of water infiltration and decreased soil penetrometer resistence to a depth of 45 cm. Reduced penetrometer resistance was possibly due to greater levels of sub-soil water content compared to the control. Mehlich 3 extractable P in the upper 7.5 cm of soil ranged from 89 to 170 mg/kg in the compost-amended plots, which exceeded the critical P level of 45 mg/kg, but there was no difference among treatments at the 15 to 22.5 cm depth. Bermuda grass showed no response to inorganic N fertilization in the 120 ton/acre plots up to 18 months after application of the composted dairy manure.

Results of this study show that dairy manure compost can effectively improve the establishment of ornamental landscapes in urban soils. However, repeated applications of DMC should be avoided in order to prevent excess concentrations of soil N and P. An initial 1 to 2 cm application of dairy manure compost to soils impacted by construction is sufficient to promote healthy plant growth and reduce the future need for fertilizer and irrigation.

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