Crop rotation and soil N amendment effects on maize production in eastern Canada

Relying less on fertilizer N and more on crop residual and biological N 2 fixation by legume crops has been suggested as an effective way to meet the challenge of maximizing economic return while minimizing environmental pollution. A field study was conducted on a Brandon loam soil (Orthic Humic Gleysol) to determine the effects of crop rotation and N amendments on grain yield, crop growth, N uptake and use efficiency (NUE) of maize (Zea mays L.) and fertilizer replacement values of legume. The rotations included maize in annual rotation with soybean [Glycine max (L.) Merrill], alfalfa (Medicago sativa L.) or continuous maize. The soil N amendments included no amendment, NH4NO3 at 100 kg N ha(-1), stockpiled or rotted dairy manure at 50 Mg ha(-1) (wet weight). Averaged across 4 yr, increases in maize grain yield, total plant N uptake, and NUE ranged from 13 to 35% in the maize-soybean and maize-alfalfa rotations compared to continuous maize monoculture. During the study, total dry matter production was 15 to 35% higher and crop growth rate was 13 to 23% higher for maize following alfalfa than for continuous maize monoculture. The effect of legumes on the subsequent growth of maize (i.e., total dry matter production and crop growth rate) was most apparent during the grain filling period. Total maize dry matter production was similar up to silking stage for all three rotation systems; however, the difference in total dry matter between maize monoculture and maize in rotation with legume continued to increase after this stage so that the greatest differences were observed at physiological maturity. Grain yield was 19% higher in the 100 kg N ha(-1) treatment and 23% higher in the repeated manure amendment than in the unfertilized treatment. Fertilizer N replacement values were on average, 68 kg ha(-1) for soybean and 133 kg ha(-1) for alfalfa. Our results indicate that maize in annual rotation with legume crops could increase the maize yields by as much as 20% and reduce the amount of chemical fertilizer N by as much as 180 kg N ha(-1). The effect of legume preceding crop on maize dry matter production and N uptake is expressed mostly in the later stages of crop growth in this mid- to short-growing-season region.