CROPPING SYSTEM EFFECTS ON NITROGEN REMOVAL, SOIL-NITROGEN, AGGREGATESTABILITY, AND SUBSEQUENT CORN GRAIN-YIELD

Cropping systems can affect soil quality and productivity of subsequen t crops. We conducted this study to evaluate effects of several annual and perennial crop species on N removal, residual soil N, aggregate s tability, and subsequent corn (Zea mays L.) production. Thirteen cropp ing systems were grown with various rates of N fertilizer for 6 yr on a Typic Calciaquoll soil in central Iowa. Perennial plant species were then killed, corn was planted, and half of each plot was fertilized w ith 224 kg N ha(-1) and half was left unfertilized. Plant analyses sho wed that the perennial C-4 species, switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii Vitman var. gerardii), consisten tly removed the least N. There was little difference for soil total N, NH4-N, or NO3-N concentrations to a depth of Im among reed canarygras s (Phalaris arundinacea L.), switchgrass, sweet sorghum [Sorghum bicol or (L.) Moench], and alfalfa (Medicago sativa L.). Residual NO3-N conc entrations were higher to a depth of lm for subplots fertilized with 2 80 kg N ha(-1) for 6 yr than for plots fertilized with less N. Aggrega te stability did not differ following reed canarygrass, switchgrass, s weet sorghum, or alfalfa. Without N during the 7th yr, corn following sweet sorghum produced the lowest yield (7.5 t ha(-1)), whereas the hi ghest yield following a nonlegume crop was for corn after big bluestem (11.8 t ha(-1)). Corn without N following soybean [Glycine max (L.) M err.] yielded 11.1 t ha(-1), while that following alfalfa yielded 13.6 t ha(-1). Fertilizer N reduced the rotation effect, but increased pro file N with both perennial and annual crops. Corn following reed canar ygrass, big bluestem, alfalfa, soybean, and sorghum intercropped into alfalfa had significantly higher yields (14.1, 14.2, 15.7, 14.2, and 1 5.3 t ha(-1), respectively) than corn following corn (13.0 t ha(-1)). Non N rotation effects (those remaining despite applied N) could not b e explained by residual soil N or aggregate stability measurements.