@book{518,
	author = {Colwell, J. D.},
	title = {Estimating fertilizer requirements :},
	publisher = {CAB International,},
	year = {c1994.},
	address = {Wallingford, UK :},
	url = {http://www.loc.gov/catdir/enhancements/fy0635/95161876-d.html}
}