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Title: IMPACT OF NITROGEN FERTILIZATION AND CROPPING SYSTEM ON SOIL QUALITY IN MIDWESTERN MOLLISOLS

Author
item RUSSELL, ANN - IOWA STATE UNIVERSITY
item Laird, David
item MALLARINO, ANTONIO - IOWA STATE UNIVERSITY

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2006
Publication Date: 2/1/2006
Citation: Russell, A.R., Laird, D.A., Mallarino, A. 2006. Impact of nitrogen fertilization and cropping system on soil quality in Midwestern mollisols. Soil Science Society of America Journal. 70:249-255.

Interpretive Summary: Modern agriculture is highly dependent on inputs of chemical fertilizers to maintain crop yields. However, extensive and long-term use of chemical fertilizers may cause degradation of soil quality. Soil fertility levels can also be maintained by using crop rotations that include alfalfa, but the relative impact of such rotations on soil quality has not been fully documented. We have shown that four year crop rotations that include alfalfa (corn-corn-oats-alfalfa and corn-oats-alfalfa-alfalfa) have a positive effect on many measures of soil quality relative to continuous corn and corn-soybean rotations for upper Midwestern soils. Specifically we found that the amount of soil organic matter was higher, the ability of soil to supply nitrogen and other nutrients to plants was higher, and the level of soil acidification was lower for soils with alfalfa in crop rotations compared to soil with continuous corn or corn-soybean rotations. This information will help farmers, crop consultants, environmentalists, and conservation agencies by documenting the ancillary benefits to soil quality from the use of alfalfa in crop rotations.

Technical Abstract: High grain production of corn (Zea mays L.) can be maintained by adding inorganic nitrogen (N) fertilizer, and also by using crop rotations that include alfalfa (Medicago sativa L.), but the relative impact of these management practices on soil quality is uncertain. We examined the effects on soil of N fertilization rate (0, 90, 180, 270 kg/ha, corn phase only) in four cropping systems: continuous corn (CC); corn–soybean (CS) [Glycine max (L.) Merr.]; corn–corn–oat (CCOA) (Avena sativa L.)–alfalfa; and corn–oat–alfalfa–alfalfa (COAA). The 23- and 48-year-old experimental sites, situated in northeast (Nashua) and north central (Kanawha) Iowa, were in a replicated split-plot design and managed with conventional tillage. At Nashua, we measured available N, potential net N mineralization and microbial biomass carbon (MBC) throughout the growing season; all were significantly higher in the CCOA system. At both sites, post-harvest N stocks, and soil organic carbon (SOC) concentrations were significantly higher in systems containing alfalfa. Grain yield was most strongly correlated with soil N properties. At Nashua, N fertilizer additions resulted in significantly lower soil pH (0- to 15-cm depth) and lower exchangeable Ca, Mg, and K and cation exchange capacity (CEC) in the CC and CCOA systems. In an undisturbed prairie reference site for Nashua, low available N, low pH, and high CEC suggested a strong influence of the vegetation on nutrient cycling. In terms of management of soil fertility, inclusion of alfalfa in the rotation differed fundamentally from addition of N fertilizer because high yield was maintained with fewer adverse effects on soil quality.