Effect of Local Application of Potassium on Cesium Uptake in Rice

Abstract

Purpose Soil K concentration greatly affects Cs uptake by plants, with high (low) levels of exchangeable K inhibiting (enhancing) Cs uptake. We investigated the effects of heterogeneous K concentrations in the rhizosphere on Cs uptake in rice. Methods Field experiments were conducted in Iwate, Japan (Experiment 1) and Fukushima, Japan (Experiment 2) to evaluate the effects of K fertilization on stable ( 133 Cs) and radioactive ( 137 Cs) Cs uptake, respectively. Three treatments were applied: KCl mixed with soil before transplantation (Mix_KCl), local application of KCl (L_KCl), and local application of slow-release K fertilizer (L_Kcoat). Results In Experiment 1, local K treatment resulted in heterogeneous K distribution; however, K uptake was comparable to that in Mix_KCl plots. 133 Cs uptake in L_Kcoat plots markedly increased compared with that in Mix_KCl plots, whereas that in L_KCl plots was higher, but not statistically different, compared with that in Mix_KCl plots. In Experiment 2, L_KCl and Mix_KCl treatments suppressed 137 Cs uptake with similar efficacy. The expression of most root K transport-related genes remained unaffected by local K application; however, some high-affinity K transport genes such as OsHAK1 and OsHKT2;1 were upregulated on the unfertilized side compared with those on the fertilized side under L_KCl. Conclusions Despite heterogeneous soil K concentrations, the effect on Cs uptake was small when rapid-releasing K was applied; the same amount of K applied using slow-release fertilizer accelerated Cs uptake. Therefore, the effect of local K application on Cs uptake by plants depends on the pattern and amount of K released during the rice-growing season.

Bibliographic Information