Maximizing potato tuber yields and nitrogen use efficiency in semi-arid environments by precision fertilizer depth application

Deep nitrogen application can increase crop yields but the optimal fertilizer depth for potato production in semi-arid regions of northwest China under irrigation is unclear. Thus, we conducted a field study for two years (2021–2022) in typical irrigated farmland on the Loess Plateau to investigate whether modifying the nitrogen fertilization depth (different depths below the soil surface of 5, 15, 25, and 35 cm denoted as D5, D15, D25, and D35, respectively) could improve the potato yield, nitrogen use efficiency (NUE), and economic benefits. We systematically examined the impacts of various nitrogen fertilization depths on the accumulation and distribution of dry matter, tuber yield, nutrient uptake (N, P, and K), NUE, and economic benefits. Compared with D5, the greatest increases in the total potato dry matter mass (17.99%) and transfer of dry matter to tubers (1.07%) occurred under D25. Moreover, compared with D15, D25 increased the NPK concentrations (1.41%) and uptake (7.13%) in potato tubers at maturity, with the greatest improvement in the tuber yield (8.56%). Furthermore, D25 substantially improved the NUE (90.18%) and net income (37.15%) compared with D5. Regression analysis showed that the maximum benefits were obtained by placing urea at the 15–25 cm depth. Partial least squares path modeling indicated that deep N application enhanced the uptake of nutrients by the roots and regulated nutrient allocation to improve the tuber yield and NUE. Therefore, changing the N fertilization depth from 5 cm to 15–25 cm can enhance the growth of potatoes, tuber yield, NUE, and economic benefits in dryland areas of the Loess Plateau under irrigation.