NITROGEN AVAILABILITY FROM COMPOSTS FOR GRASS AND LEGUME-GRASS FORAGE PRODUCTION

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

SUMMARY

Of the five million tonnes of municipal organic waste annually produced in Canada, over one quarter is now composted. There has been increasing interest in research focusing on the response of annual crops to application of agricultural, municipal and industrially-derived composts, when compared with manures and mineral fertilizers.

Perennial grasses require sustained, season-long N availability, and may be ideally suited for fertilization with slow N release organic amendments such as composts. Composts may also provide N to perennial forages during early spring and fall, when soil conditions can limit fertilizer application in many regions.

Difficulties in predicting N supply from composts has limited their routine use in forage production. A field study was conducted to compare the yield and protein content of a legume-grass forage mixture and a grass monocrop cut twice annually, when fertilized with diverse composts. In a three-year study, timothy-red clover and timothy swards were fertilized with composts derived from crop residue, dairy manure or sewage sludge, plus liquid dairy manure. Yields were compared with those obtained with inorganic fertilizer.

The results from this study indicate that repeat applications of some composts can provide sufficient plant available N to sustain perennial forage grass yields. The red clover in the mixed forage crop acted as an effective ‘N-buffer’ maintaining forage yield and protein content even for those compost treatments that provided little available N. Livestock farms that use legume-grass mixtures may benefit the most from routine compost use, as combining composts with legumes moderates against potential losses in crop yield and quality, and reduces unwanted soil P and K accumulation, from excessive compost use.

^aDep. of Plant and Animal Sciences, Nova Scotia Agricultural College (NSAC), P.O. Box 550, Truro, Nova Scotia, Canada B2N 5E3

^bDep. of Land Resource Science, Univ. of Guelph, Guelph, Ontario, Canada N1G 2W1

^cDep. of Environmental Science, NSAC, P.O. Box 550, Truro, Nova Scotia, Canada B2N 5E3.

Corresponding author
(t) (902) 893-7621 (f) (902) 897-9762 E-mail: dlynch@nsac.ca

The full article is published in the Journal of Environmental Quality 33:1509-1520 (2004)