Improving N management for corn (Zea mays L.) production with precision agriculture technologies requires that spatial N recommendations adequately represent in‐field variability in N availability. Our objective was to evaluate corn response to increasing N rates in several in‐field locations that represented the range of soil organic matter (OM) content in the field. In a 2‐yr study, three center pivot–irrigated fields were selected in south‐central Kansas and south‐central Nebraska. Four or five locations were selected within each field. At each location, five or six N treatments (0–336 kg N ha−1) were surface‐applied early in the growing season. The minimum N rate to achieve maximum yield varied by as much as 130 kg N ha−1 among in‐field locations at three site‐years. The least amount of N to achieve maximum yield did not coincide with locations representing greater soil OM. Yield response at two site‐years was the same among in‐field locations; however, mean yield among in‐field locations varied by as much as 4.2 Mg ha−1, representing potential for improvement in N use efficiency. Leaf tissue N was below the critical threshold for 60 to 100% of observations at three different in‐field locations but below the critical threshold for <35% of the observations at all other in‐field locations. The reason for the discrepancy in N availability among in‐field locations was not conclusively identified but was not only related to soil OM content. Variable N recommendations based only on soil OM is too simplistic to reflect variability in N availability within a field.

N ha Ϫ1 (corresponding to maximum yield), NO 3 leaching increased exponentially. Reducing N application rates Improving N management for corn (Zea mays L.) production with by 5% less than required to achieve maximum corn yield precision agriculture technologies requires that spatial N recommendations adequately represent in-field variability in N availability. Our reduced NO 3 leaching by 40 to 45% (Sexton et al., 1996). objective was to evaluate corn response to increasing N rates in severalApplying an economically optimal N rate minimizes in-field locations that represented the range of soil organic matter (OM)

Abstract. Lack of adequate topsoil depth and perception of lost soil fertility on pipeline construction rights-of-way are major concerns for landowners and can become extensive post-construction costs for pipeline companies. Reduction in crop productivity can occur in agricultural fields after pipeline construction due to numerous factors including compaction, drainage, and changes in surface soil characteristics. Significant changes in soil texture and/or organic matter content can change cation exchange capacity (CEC) and water holding capacity of the soil. Reduced CEC, as well as low soil fertility levels, can reduce the crops ability to withstand environmental stress, therefore reducing crop yield. Topsoil stockpiled and replaced on the construction right-of-way (ROW) of a 42-inch (107 cm) natural gas pipeline through Kansas and Missouri was evaluated and compared to the topsoil adjacent to the ROW. Soils were evaluated on and off the ROW to compare topsoil depths, soil fertility, texture and other agronomic factors. Varying amounts of topsoil loss were found at a majority of sample sites. Differences between the on-ROW and off-ROW values for the other soil parameters tested were not significant. The lack of significant change in tested parameters on-ROW, compared to the undisturbed topsoil off-ROW indicate no loss of crop yield potential would be expected due to the reduction in topsoil depth.

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