Recharge of exchangeable K from non-exchangeable fractions as affected by exchangeable K and K acquisition by rice in Japanese paddy soils

ABSTRACT

Plants acquire potassium (K) not only from exchangeable K fractions but also from non-exchangeable K fractions. However, factors affecting the amount of K supplied from the non-exchangeable K fraction have not been well understood. In this study, the effects of soils and exchangeable K on the amount of K supplied to rice from the non-exchangeable K fraction were investigated for six Japanese paddy soils diluted with different rates of quartz sand. The amounts of K supplied from the non-exchangeable K fractions (recharged K) ranged from 14.4 to 137 mg K₂O kg⁻¹, equivalent to 10 to 61% of the total K acquired by rice. The amounts of recharged K were affected by the exchangeable K levels in three out of six soils. Although the cultivation experiments were conducted under various K conditions including severe K deficiency, exchangeable K was detected after cultivation in all soils, and the contents of exchangeable K were almost identical for each soil regardless of the dilution ratio of soil with quartz sand. Accordingly, there would be at least three types of non-exchangeable K fractions which dissolve into soil solution to attain a specific level of exchangeable K: (i) a non-exchangeable K fraction that releases K regardless of the exchangeable K level; (ii) a non-exchangeable K fraction that easily releases K with the decrease in exchangeable K under sufficient K conditions without inducing K-deficient symptoms in rice; and (iii) a non-exchangeable K fraction that releases K with the decrease in exchangeable K only under severe K-deficient conditions with accompanying deficient symptoms in rice. The application of K fertilizer would reduce the amount of recharged K acquired by rice from fractions (ii) and (iii), whereas fraction (i) would remain unaffected by the fertilized K until the level of exchangeable K reaches a specific level for each soil. The release of K from a fraction (iii) only occurred under conditions of severe K deficiency; hence, farmers should not rely on this fraction for K supply.

KEYWORDS:

• Non-exchangeable potassium
• paddy soil
• potassium deficiency
• recharged potassium
• rice

Acknowledgments

The authors thank Dr. Tetsuro Anzai (former director of the Japan Society of Soil Science and Technology), Dr. Kazuhiko Kimura (Miyagi University), Dr. Taku Otani (project leader, former Central Agricultural Research Institute, National Agricultural Research Organization), and the other project members for their guidance and support. The authors also thank the Yamagata Integrated Agricultural Research Center, Niigata Agricultural Research Institute, Miyazaki Agricultural Research Institute, and Kagoshima Prefectural Institute for Agricultural Development for their great cooperation in preparing the soil samples.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00380768.2024.2357099

Additional information

Funding

This study was conducted as a part of a research project commissioned by the Ministry of Agriculture, Forestry and Fisheries of Japan, “Development of Technology to Improve Profitability of Paddy and Field Crops,” with the subtitle “Development of Efficient and Effective Fertilizer Application Technology to Reduce Production Costs” (2015-2019).