The main objective of this study was to compare potassium (K), calcium (Ca), and magnesium (Mg) utilization and grass tetany potential of orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinaceae Schreb.) fertilized with dairy manure or commercial fertilizer. The study was conducted from 1994 through 2000 in Willsboro, NY on a Kingsbury clay soil (very-fine, illitic, mesic Aeric Ochraqualf) of somewhat poor drainage. The design was a split-plot in a randomized complete block with two manure rates (16.8 Mg ha(-1) and 33.6 Mg ha(-1)) and one fertilizer treatment (84 kg N ha(-1) at spring greenup and 56 kg N ha(-1) prior each regrowth harvest) as the main plots and grass species as subplots replicated six times. Potassium concentration and uptake increased after two years of manure application compared to commercial fertilizer treatment and residual effects of manure were large at least three years following manure application. Calcium concentration and uptake decreased after two years of manure application compared to the commercial fertilizer treatment, but there were no differences in treatments three years after manure application had ceased. Magnesium concentration and uptake at the high manure rate did not differ from fertilizer treatment in all years. Orchard,grass was more grass tetany prone than tall fescue as a result of dairy manure application. The K/(Ca+Mg) ratio in plant tissue was as high as 3.26 for orchardgrass and as high as 2.11 for tall fescue for spring harvests at the highest manure Fate. The K/(Ca + Mg) ratio in plant tissue was in the range of 0.34-1.74 (below the 2.20 critical level) for all three years with no manure application. Soil K increased in manure treatments from an initial 76.8 kg ha(-1) (1993) to 171.7 kg ha(-1) (1997) in the highest manure treatment. After three years of no manure applications, soil K had been reduced to the initial level.
