Session

Session- Effect of Compost on Soil Quality

Compost effects on soil physical properties and field nursery production of woody ornamentals

COOPERBAND, LESLIE R. (1) and Gonzalez, Ronald (2)

(1) University of Wisconsin, Department of Soil Science (2) Guapiles, Costa Rica, USA

Field production of ornamental shrubs often results in significant degradation of surface soil physical properties. Building soil organic matter through compost amendments is one way to ameliorate effects from topsoil removal in woody ornamentals production. We amended field soils with three composts to evaluate their effects on soil physical properties and shrub biomass production. Specifically, we applied either duck manure-sawdust, potato cull-sawdust-dairy manure, or paper mill sludge-bark compost using two application methods: 2.5 cm layer of compost incorporated into the top 15 cm soil surface (incorporated only) or 2.5 cm incorporated + 2.5 cm surface applied as mulch (mulched). We grew three shrub species from liners: Spirea japonicum 'Gumball', Juniper chinensis 'Pfitzeriana', and Berberis thunbergia 'Atropurpurea.' Compost and non-amended control treatments along with shrub species were established in triplicate in a randomized split plot design. We measured total soil carbon, bulk density, aggregate stability, moisture retention capacity, volumetric moisture content and hydraulic conductivity over three years (1998-2000). We determined above and below ground biomass after one and two years of growth. Mulched treatments produced 15-20% more total carbon (TC) than incorporated only or no-amendment controls. Greater aggregate stability was related to increased TC. Saturated hydraulic conductivity (Ksat) in the control was 85% lower than in compost treatments. Mulched treatments improved more of the soil physical properties measured compared to incorporated only and control; this resulted in increased shrub growth after two years. The best predictors of plant growth were Ksat, bulk density and volumetric moisture content.

Recycling Organics, the Building Block of Carbon Based Horticulture

BOB PAULIN (1) and Kevin Wilkinson (2)

(1) Department of Agriculture, Western Australia, (2) Agriculture Victoria, Australia

A project to develop composts based vegetable production has commenced in Western Australia and Victoria that aims to improve the competitiveness and long-term sustainability of Australian vegetable production. Drivers for this work are the need to improve productivity, to sustainably produce clean safe food, and the application of zero waste principles that will facilitate the recycling of organic wastes and the development of secondary organic resource (SOR) industries. Agriculture is both a major source of SOR's and horticulture in particular, is potentially a major market for these recycled materials. Placing greater emphasis on soil carbon and more specifically on building production systems that maintain and improve soil organic has potential to accelerate progress toward economically, environmentally and socially sustainable horticultural production. The initial sequence of trials has commenced to identify changes to soil quality and nutrient release characteristics following the application of a range of compost rates and compost types under continuous vegetable cropping. A second component to the work will investigate changes to production practices that will maximise improvements to soil carbon/organic matter and lead to more significant improvements in vegetable production and the development a reliable market for recycled organics. Approaches to developing improved production systems will be based on findings from a post-graduate program that is currently under way at the University of Western Australia.

Effects of Pulp and Paper Industry Wastewater Treatment Sludge Composts On Soil Microbiology and Lignin Degradation

RANTALA, P.-R. (1) and Kuusinen K., (2)

(1) Pirkanmaa Regional Environment Centre, Kokkolankatu 4, FIN-33300, Tampere, FINLAND, (2) Biopap Oy, Baklurantie 2, FIN-10470, Fiskars, FINLAND, Finland

In Finland, pulp and paper industry wastewaters are mainly treated in activated sludge plants. The annual amount of sludge generated is approximately 450 000 t (as 100 % dry matter). This is three times the amount generated from municipal treatment plants. A half of the industrial sludges is disposed of to landfills. More stringent environmental regulations force the industry to find alternative methods for sludge handling and utilization. The objective of this research was to study whether these lignin containing sludges can be composted and how the lignin degradation effects the soil characteristics. Five different sludges were composted in piles. After four months composting the composts were moved to a field for post-composting and agricultural field experiments. The agricultural experiments lasted for three years. Test plots were established with barley as a test plant. The field experiments included also non-fertilized and ordinary NPK-fertilized test plots. The soil characteristics were analysed by measuring the length of fungi and the quantity of soil micro-organisms as well as the lignin content. Samples were taken twice during composting. Nutrient concentrations were also analysed several times from the soil and from the crop during the agricultural field experiments. The results showed that all composts were suitable for soil improvement in the agricultural plant production. The addition of compost increased both lignin concentration and the quantity of fungi in soil. The lignin content varied between 2 - 23.6 % in compost plots. Test plots with compost addition contained more lignin than non-fertilized plots and ordinary NPK-fertilized plots. After four months post-composting the lignin content decreased to 1.7 - 10.2 %. Lignin degradation increased the humus concentration and the quantity of micro-organisms in soil. The humus concentrations and porosity were smaller in plots with no compost addition.Barley grain yield was as good with composted sludges as with NPK-fertilizers. However, the improvement of soil characteristics in sludge compost plots were clearly better compared to the non-fertilized and NPK-fertilized plots.

Compost Utilization and Fate of Heavy Metals and Organic Contaminants in Vegetable Production

Potential users may be nervous about contaminants in composted products made from municipal solid waste, yard waste contaminated with pesticides or feedstock co-composted with biosolids. They need to be confident that the composts are physically, chemically and biologically safe. In order to remove barriers to compost acceptance, definitive information must be generated for end-users that shows the safe use of compost products. A research project was conducted to evaluate (1) the effect of compost application on vegetable yields and (2) the fate of heavy metals and organic contaminants in plant tissues. This report focuses on the fate of heavy metals and organic contaminants in leaf lettuce and broccoli heads under field conditions. The results of compost effect on vegetable yields were reported separately. Compost products and nitrogen from ammonium nitrate fertilizer were utilized in a field experiment in Santa Barbara County, California to grow lettuce (Lactuca sativa var. Lollarosa) and broccoli (Brassica oleracea botrytis, var. Brigadeer). Six compost products were selected for this experiment including three feedstocks, used alone or in various ratios: urban plant debris (UPD), biosolids/UPD (Bio) and municipal solid waste (MSW). The soil type was a Golita loam, a well-drained soil on flood plains and alluvial fans. The basic design of the site for each compost type was a replicated split-split plot with compost type on the main plot, three rates of compost application (0, 37, 74 Mg ha-1) on the split plots and three supplemental N rates (0, 75, 150 kg ha1) applied to split-split plots. Chemical analyses were performed on soil, all compost products and lettuce leaf and broccoli heads at time of harvest. Analyses included trace elements, macro-nutrients, organic toxicants such as: Aldrin, alpha-BHC, beta-BHC, gamma-BHC (lindane) alpha-Chlordane, gamma-Chlordane, 4,4-DDD, 4,4-DDE, 4,4-DDT, Dieldrin, Endosulfan I, Endosulfan II, Endosulfan sulphate, Endrin, Endrin aldehyde, Endrin ketone, Heptachlor, Heptachlor epoxide, Methoxychlor, Toxaphene and PCBs. The trace element content of composts, including the heavy metals, was much lower than EPA 503 regulation limits. Except for a few toxicants found in very low concentrations, no other toxicants could be detected in either the compost products or the soil. Of the five toxicants present in the soil and compost products, two were found in higher concentrations in soil than in the compost products. No PCBs could be detected in any of the compost products used in these experiments. Chemical analyses of lettuce leaf and broccoli head plant tissue indicated that in general, no significant relationship was found between the compost application and trace element content of the plant tissues. The organic toxicants present in some of the compost products were either not detected at all in plant tissue or in very low concentrations. In some cases more organic toxicants were absorbed by the plants in the control plots with no compost than by the plants in compost treated plots. Although some toxicants were present in compost products, the plant did not absorb them. No PCBs could be detected in plants grown in control or compost treated plots. These results indicate that heavy metals and organic toxicants were either absent or of very low concentrations in both the compost and amended soil. In addition, they were absent in plants grew in amended plots.