Liming reduces nitrogen uptake from chemical fertilizer but increases that from straw in a double rice cropping system

Liming materials are widely applied to alleviate soil acidification and increase rice yield in acidic soils, but their effects on nitrogen (N) use efficiency are still unclear. Here, we conducted a field-, pot-, and micro-plot experiment to investigate how the application of slaked lime (i.e., Ca(OH)₂) affects the fate of chemical fertilizer-N and straw-N in a double rice cropping system. In the field experiment, liming increased grain yield and N uptake by an average of 9.0% and 10.6%, respectively. In contrast, CaCl₂ application did not affect rice yield and N uptake, suggesting that the effects of lime application were not related to the addition of Ca²⁺. Results from a ¹⁵N tracer experiment (i.e., ¹⁵N-labeled urea and straw) indicated that liming reduced N uptake from fertilizer (?5.7%), but increased N uptake from straw (+31.3%). Liming also reduced soil retention of both urea- and straw-N and increased their loss rates. Taken together, our results indicate that although liming increases rice yield and N uptake, it lowers the use efficiency of fertilizer N and facilitates N losses. In addition, our results emphasize the need for long-term studies on the impact of liming on soil N dynamics in paddy soils.