Effects of Deep Placement of Fertilizer on Growth, Productivity, and Fertilizer Use Efficiency of Rice in Cool Climatic Region

Deep application (DP) of fertilizer has the potential to optimize fertilizer use, mitigate environmental impacts, and improve crop yields. However, most DP studies in rice have been carried out under subtropical/tropical climates. In this study, we assessed the effects of DP on productivity and fertilizer use efficiency of rice in the cool climate of northeastern Japan.

A three-year field study was performed in the experimental paddies at Iwate University using rice cultivar “Akitakomachi” with three fertilization treatments: Mix (broadcast), DP1 (one-position-DP), and DP2 (two-position-DP) with a ratio of N:P: K of 8:6.5:7.5 (g/m²).

The tiller increase was delayed in both DP treatments compared to that in the Mix treatment, particularly in 2022, when low temperatures persisted after transplantation. The tiller increase was gradually recovered from the panicle formation stage to the heading stage, and the number of panicles was similar to or exceeded that in the Mix treatment. The yield of the DP treatments was higher than that of the Mix treatment throughout the three years, with an increase in the number of spikelets per panicle (2020, 2021) and the number of panicles (2022) contributing to an increase in spikelet density. As a result, the agronomic nutrient-use efficiency for N, P, and K was higher in the DP plots.

These findings indicate that the DP of fertilizers can significantly enhance rice yields in cool climates and underscore the importance of considering DP as a valuable strategy in promoting sustainable agriculture in regions with similar climatic conditions.