Thursday, 13 July 2006

Manure: Healer of the Land.

Jessica G. Davis, Colorado State University, Soil and Crop Sciences Department, Fort Collins, CO 80523-1170

Soil degradation is a worldwide problem of considerable importance. A recent report from the International Food Policy Research Institute stated that 40% of the world's farmland is seriously degraded. Sources of this degradation include soil erosion, loss of organic matter, soil hardening, chemical contamination, nutrient depletion, and excess salinity. Most of these soil degradation problems can be lessened with manure application. In addition to being a source of nutrients for crops, manure application can increase soil organic matter levels; improve soil structure, water retention, drainage, and aeration; enhance the biological activity and diversity in soil; and increase crop yields. Potential manure uses in land reclamation include restoration of eroded land and sodic soils, and reclamation of contaminated soils or burnt soils. This paper will present a literature review including case studies from around the world. In each type of remediation, manure utilization will be evaluated using two criteria, impact on soil quality and on crop yield.

Manure application to eroded soils has been shown to improve soil physical properties such as aggregate stability, bulk density, organic matter content, infiltration, water retention, and water holding capacity. Other studies have shown increased crop yield following manuring of eroded land (Hays et al., 1948). Obi and Ebo (1995) used manure to remediate a severely degraded soil in Nigeria. They documented improvements in soil physical properties and in maize yields and showed significant correlations between soil organic matter and porosity, water retention, water holding capacity, and yield.

Drainage and irrigation alone have been shown to be ineffective in reclaiming sodic soils (Wursten and Powers, 1934). Manure applications to sodic soils (especially in combination with S) have been shown to reduce soil pH, increase Ca availability, decrease Sodium Adsorption Ratio, and improve soil structure. Case studies from India will be used to evaluate the impact of manure application to sodic soils on the yields of rice (Swarup, 1980), wheat (Swarup, 1984), and sugarcane (Choudhary et al., 2004).

There are many types of soil contamination. Manure has been shown to be beneficial in speeding degradation of organic compounds in soils. For example, petroleum hydrocarbons (Wellman et al., 2001) and pentachlorophenol used in wood preservation (Miller et al., 2004) degrade more quickly in manure-amended soils. Use of manure in reclamation of metal-contaminated soils such as mine wastes and radionuclide-polluted soils will also be discussed.

There has been limited research on the use of manure to reclaim burnt soils after a wildfire. Castro et al. (2000) demonstrated the potential for manure to restore burnt soils in a greenhouse study. Meyer et al. (2001, 2004) showed that biosolids increased plant cover, reduced the percentage of bare ground, and reduced erosion from a forest fire recovery area. Similar benefits would be expected from manure application to burnt soils.

Conclusions will be drawn regarding under what conditions manure application is likely to be a beneficial land reclamation strategy. Finally, the economics of manure utilization in restoration of degraded land will also be explored.

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