Soil and Crop Response to Varying Levels of Compaction, Nitrogen Fertilization and Clay Content.

Compaction affects nearly all soil properties and functions, thereby affecting the growth, distribution, and function of roots, as well as crop productivity. Our objectives in this study were to determine whether alleviation of compaction improved soil properties and corn (Zea Mays L.) growth and yield, and whether N fertilization could compensate for lower yields caused by compaction. Soil was differentially compacted over three years to create four compaction treatments in year 2 and four in year 3; N fertilizer was applied at four different rates to each compaction treatment; and soil and crop growth properties were measured after two and three years. Variation in soil texture across the experimental plots allowed us to partly assess the effects of clay content on the soil/crop response to compaction. Compaction substantially reduced plant growth and productivity; yields were reduced by up to 2.7 Mg ha^-1 (33%) and dry matter by 4.1 Mg ha^-1 (26%) in compacted soils. Avoiding compaction for a year appeared to allow crop growth and yields to recover. For example, grain yield after two consecutive years of compaction (5.21 Mg ha^-1) was significantly lower than that after one year of compaction followed by no compaction (7.59 Mg ha^-1). Compaction increased soil strength near the bottom of the plough layer, where a carry-over of compaction was apparent. Compaction-induced yield reductions were greatest on soils with more clay and were attributed to adverse soil physical conditions rather than N fertility.