Yield, nutrition, and nitrogen use efficiency of sweet potato in response to nitrogen rates

Due to sweet potato's nutritional qualities, this root crop has gained increasing popularity among consumers. However, sweet potato yield is well below the crop's potential due to the need for more use of technologies such as adequate fertilizer management. Although sweet potato demand nitrogen (N), caution is needed when applying nitrogen fertilization, as excess N causes excessive growth of the shoot and a reduction in the yield of storage roots. This study aimed to assess sweet potato yield and nutrient uptake in response to increasing nitrogen (N) rates. Five N levels (0, 50, 100, 200, and 300 kg ha⁻1) were evaluated in Humic Cambisol during the 2021/2022 and 2022/2023 growing seasons. After harvesting, the total and marketable yield of storage roots and the nutrient uptake by shoot, storage root, and whole plant were evaluated. The harvest index, nitrogen harvest index, agronomic use efficiency of fertilizer N, fertilizer N recovery efficiency, partial factor productivity of fertilizer, physiological efficiency of fertilizer N, and nitrogen uptake efficiency were calculated based on data from the two harvest seasons. The maximum technical efficiency (47.07 t ha−1) was obtained at 165.50 kg ha−1 of N. The economic optimum rate was obtained with 74 kg ha−1 of N, corresponding to the marketable yield of 43.73 t ha−1. The rate of 50 kg ha−1 of N presented a better harvest index and high values for nitrogen use efficiency variables.