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, sulfur‐coated 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.