NITROGEN AVAILABILITY FOR CORN IN SOILS AMENDED WITH UREA, CATTLE SLURRY, AND SOLID AND COMPOSTED MANURES

This study was conducted to determine whether manure N availability fo r corn (Zea mays L.) was best estimated by a component of the manure N or by soil inorganic N in May or June. Liquid dairy cattle manure, so lid beef cattle manure, and composted beef cattle manure were applied in the spring of 1988, 1989 and 1990 at rates of 100, 200 and 300 kg N ha-1. Urea was applied at rates of 50, 100 and 150 kg N ha-1 for comp arison. The N recovery by the harvested portion of the corn (grain + s tover) in 1988 and 1990 averaged 49, 18, and 5% of the total N in urea , liquid dairy cattle manure, and solid or composted beef cattle manur e, respectively. There was no yield response to any N source in 1989 b ecause of high soil fertility. Relative nitrogen uptake by the corn gr ain + stover in 1988 and 1990 was significantly correlated with inorga nic N applied as manure or fertilizer (r2 = 0.56), but not with total N applied (r2 = 0.02). When the data from all 3 years were analyzed, r elative nitrogen uptake was better correlated with soil NH4 + NO3 in m id-May and soil NO3 in early-June (r2 = 0.83 and 0.76, respectively), than with inorganic N applied as manure or fertilizer (r2 = 0.20). A s oil N test after manure application in mid-May to early June may be th e best N management tool for corn production on livestock farms in Ont ario.