| Summary: | Sweet potato (Ipomoea batatas L.) has potential to overcome food security issues with world production covering an area of about 9.4 million hectares. However, the sweet potato supply has decreased over the years due to lack of mechanization in harvesting, cost increase of nitrogen (N) fertilizers and loss of nitrogen-based nutrients in the soil due to ammonia volatilization, mineralization and immobilization. Thus, N-(N-butyl) thiophosphate triamide (NBPT) is used with urea fertilizer to reduce the mineralization process and minimize nutrient loss. An experiment was conducted on the growth of sweet potatoes using the randomized complete block design (RCBD) with four replications. One treatment comprised 5 t/ha of chicken manure (+CM) with varying treatments of NBPT-coated urea (NCU), while the other used the same amounts of NCU, but without chicken manure (-CM). The treatments were labelled as follows: (T1) 96 kg N/ha urea+CM (farmer’s practice), (T2) 0 kg N/ha NCU+CM, (T3) 57.6 kg N/ha NCU+CM, (T4) 76.8 kg N/ha NCU+CM, (T5) 96.8 kg N/ha NCU+CM, and (T6) 115.2 kg N/ha NCU+CM. For those without manure, the NCU treatments were: (T7) 96 kg N/ha urea–CM (farmer’s practice), (T8) 0 kg N/ha NCU–CM, (T9) 57.6 kg N/ha NCU–CM, (T10) 76.8 kg N/ha NCU–CM, (T11) 96.8 kg N/ha NCU–CM, and (T12) 115.2 kg N/ha NCU–CM. The results showed T4-treated crops producing the highest fresh and dry weight of shoot, tuber fresh and dry weight, root to shoot ratio, tuber diameter and length, and yield. In conclusion, using T4 seems to be the most suitable top soil fertilization because of the delay in urea hydrolysis, besides producing more ammonium, nitrate and urea-N content that are readily taken up by crops. © 2022
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