SOIL PHYSICAL PROPERTIES AND ORGANIC MATTER IN FORAGES RECEIVING COMPOSTS, MANURE OR FERTILIZER

D. H. Lynch^a, R. P. Voroney^b and P. R. Warman^c

SUMMARY

Spreading industrial, municipal and agricultural organic wastes on farmland may redress carbon deficits in soil. While the benefits of manure applications to soil carbon have been demonstrated, only recently have attempts been made to characterize the impact of a broader range of organic amendments on soil carbon pools. Research is needed to quantify the decomposition rates and effects of composts, sewage sludges (biosolids), and paper and forestry by-products and other diverse organic materials on soil physical properties and soil carbon under varying climatic conditions

A field study was conducted to assess the benefits of utilizing composts from a diversity of sources in perennial forage production, in relation to soil physical properties and soil organic matter. A mixed forage (timothy-red clover) and monocrop timothy sward were fertilized annually with either ammonium nitrate (AN) or with composts derived from crop residue, dairy manure or sewage sludge, plus liquid dairy manure.

Soil samples revealed that improvements in soil physical properties (soil bulk density and water content) were obtained for compost treatments alone. Composts alone influenced soil C:N ratio, increased soil microbial biomass carbon concentration and substantially increased soil carbon concentration and mass. Soil available C decreased significantly as compost maturity increased. For some composts timothy yields matched those obtained with AN, and soil carbon gains were derived from both applied-C and increased crop residue-C returns to soil. The mixed crop showed improved C returns with all types of fertility, as compared with the monocrop.

Compost use in forage production appears to provide benefits with respect to soil physical and biological properties. Higher quality composts, such as from crop residue, can evidently sustain grass forage yields, and crop-derived C returns to soil, equivalent to that of inorganic fertilizer. Matching composts of varying quality with the appropriate (legume/non-legume) target crop will be critical to promoting soil C gains from compost use in agriculture.

^aOrganic Agriculture Centre of Canada, Department of Plant and Animal Sciences, Nova Scotia Agricultural College, P.O. Box 550, Truro, Nova Scotia, Canada B2N 5E3
^bDepartment of Land Resource Science, Univ. of Guelph, Guelph, Ontario, Canada N1G 2W1 ^cAdjunct Professor, Nova Scotia Agricultural College, P.O. Box 550, Truro, Nova Scotia Canada B2N 5E3.

Corresponding author
(t) (902) 893-7621 (f) (902) 896-7095 E-mail: dlynch@nsac.ca

(Compost Science and Utilization, In Press)