Rice growth and nitrogen uptake in Takanari and Koshihikari varieties under natural farming practices: Comparison pot and field experiments

Takanari rice (Tak) outperformed Koshihikari rice (Kos) in nitrogen (N) uptake and biomass production under low-fertility sandy soil conditions. However, the influence of experimental types (pots and open-field) on the performance of these two rice varieties under natural farming practices without fertilizer application remains unclear. To address this gap, we conducted field and pot trials in Tsuruoka, Yamagata, Japan, during the 2022 growing season. The experiment involved three main treatments (small pot, big pot, and open-field) and three subtreatments (individual planting of Tak and Kos, and interplanting of Tak+Kos), aiming to assess the effect of experimental type on rice growth and N-uptake under natural farming conditions. Rice growth, biomass, and N-uptake were measured during rice growth and at the harvest and showed significant differences among all treatments. Rice biomass (g hill −1 ) in open-field was significantly lower than those in small and big pots. Whereas, N-uptake (mgN hill −1 ) in open-field was significantly lower only than that of the big pot. Compared to Kos, Tak consistently showed higher biomass and N-uptake across both pots, and open-field. The aboveground biomass ratios between Tak and Kos in interplanting were higher than those in individual planting under both pots and open-field. Despite the overall lower biomass and N-uptake in the open-field, this environment enhanced Tak’s competitive ability. Compared with the small- and big-pot treatments, the open-field condition increased Tak’s competitive ability over Kos by 11.14% and 21.26% in biomass accumulation and by 14.13% and 30.43% in N-uptake, respectively. These findings demonstrate that Tak maintains superior growth and N-uptake in all experimental types, even under open-field as unlimited space.