Irrigation- and nitrogen-management impacts on nitrate leaching under potato

As potato (Solanum tuberosum L.) production increases in the North- Central Region of the USA, so does the potential for deep seepage of nitrogenous compounds into the ground water. The objectives of this 2-yr study were to determine how different irrigation schemes (sprinkler and drip), irrigation triggers (70 and 40% of the available soil water [AW] remaining), drip placement (at the soil surface or buried at 25-cm depth), and various N sources (urea, sulfurcoated urea [SCU], and turkey [Meleagris gallopavo] manure) and timings (three- vs. five-N splits) affect percolation and NO₃ leaching. As expected, water percolation was generally higher from the sprinkler-irrigation than from the drip-irrigation treatments. Within the sprinkler irrigation, percolation was higher when irrigated at 70% than at 40% of AW remaining. Small but frequent irrigation in drip treatments helped reduce water percolation. Within irrigation treatments, 70% AW had the most N leaching, followed by 40% AW and the drip, the last two treatments being about the same. The trend in N leaching among fertilizer treatments was similar for various irrigation methods. Splitting N applications five times vs. three times reduced N leaching from unforeseen rains. Sulfur-coated urea reduced N leaching, whereas turkey manure-amended treatments showed no significant difference in N leaching compared with the urea-N treatment. In conclusion, alternatives such as 40% deficit irrigation, five-N application splits, drip irrigation, S-coated urea, and turkey manure not only reduce N leaching but also have a minimal impact on potato tuber yield and tuber quality.