Absorption of Topdressed Nitrogen by Rice through Mass Flow under Different Relative Humidities

概要

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To evaluate the contribution of mass flow to the absorption of topdressed N by paddy rice, a pot experiment was conducted under different rates of water uptake at the panicle formation stage. The rate of water uptake was modified by using two different values of relative humidity (RH, 75% and 95%). Labelled N was used to determine the amount of absorbed fertilizer-derived N in the rice plants. The amount of ammonium N (NH_4^+-N) in the floodwater was depleted within 48 h after topdressing (HAT) in all the treatments. The concentration of NH_4^+-N in the soil solution decreased with depth in the top 0.03 m of soil. N in the soil solution from 0 to 0.03 m soil depth was almost depleted by 48 HAT. The percentage of fertilizer-derived N recovered by plants and the pattern of N accumulation were the same in all the RH treatments. However, in the course of the entire experiment, the amount of N absorbed through mass flow was larger in the 75% RH treatment during the first 48 h. Moreover, under 75% RH conditions, the percentage of topdressed N in the plants that was associated with N absorbed through mass flow was 78% at 48 HAT and 29% at 168 HAT. These values were significantly higher than the previously reported values for basal N (2.5-6.3%). Therefore, it is concluded that the role of mass flow in N absorption is more significant for topdressed N than for basal N.
社団法人日本土壌肥料学会の論文