Application of composted organic waste to agricultural land
The application of composted organic waste to agricultural lands has the potential to benefit agriculture in terms of improving soil quality, but information on the environmental and agronomic aspects of the use of compost is needed to allow farmers to assess the risks and benefits of its use. The purpose of this study was to evaluate the impact of composted organic waste applications to farmland on soil quality, crop growth and yield, and water quality in addition to assessing the economics of its application. A series of laboratory and field experiments were conducted over a four year period to determine the feasibility of applying urban generated compost to farmland for crop production. Sites for the field trials were established on loam and clay loam soils on farms near Campbellville, Ontario. The finished composts used in the trials were a mixture of food, wood, paper and yard waste sources, and were obtained from two private composting facilities. The yields of corn, soybeans, and all-grass hay were not generally depressed by the addition of compost. In fact, in some cases significant increases in production were attributed to compost. Incorporation of the compost was not demonstrated to be necessary. Clear evidence of altered nitrogen availability was not demonstrated and it appeared that normal nitrogen application rates would be required in conjunction with the compost applications. The contribution of nitrogen mineralized from compost was not significant in this study. Lettuce seed germination in sand-compost mixes in the lab indicated that high concentrations of compost in the mix and pure composts were not suitable for seed germination. Mixes containing less than 25% compost by weight were unlikely to inhibit germination provided that the composts were relatively biologically stable, or 'finished'. Such a phytotoxic effect of the composts may explain the clear preference for fall applications of compost by both corn and soybeans which was evident in a single year trial comparing rates and time of application. However, the effect was most noticeable at rates of greater than or equal to 150 Mg (wet) compost ha-1. The spring applications of compost in other trials in this study often improved crop success over that where no compost was applied. Compost improved soil quality by raising the soil test index, thus reducing the requirement for phosphorus, potassium, and zinc. However, the two compost sources varied in their ability to elevate soil test levels in relation to the amount of total P they contained. Substantial increases in the organic carbon content of the soil were evident after only three years of applying the compost on both soils. The higher organic carbon level in the soil, in turn, was related to a decrease in soil density with a corresponding increase in total porosity. A greater infiltration rate resulted from the increased porosity. A higher residual pore volume and increased water retention was observed for one of the composts. After three successive years of compost application the metal content of the surface soil was not increased to levels of potential concern. Evidence of potential nitrate nitrogen contamination of ground water supplies was not found. Only sporadic indications of a few metals (Cu, Mn, Ni, Zn) in the water percolating through the soil profile were observed. Where they appeared they were not always associated with a compost treatment. Some of the parameters measured were influenced to varying degrees by the source of the compost, a result of differing analysis of the two materials used in the experiments. An economic analysis of the use of urban compost on agricultural land indicated that the value to the producer through yield and enhanced soil fertility would barely cover the application costs if the compost were delivered to the farm site at no cost. However, since benefits of compost application to the soil have been demonstrated which were intangible, such as organic carbon and increased porosity, a farmer could justify the cost of applying the material if it were delivered free to the farm site.