Effect of Reaction-Finished Solution of Hydrochar (HRFS) Application on Rice Grain Yield and Nitrogen Use Efficiency in Saline Soil

We conducted a pot experiment to examine the feasibility of applying a reaction-finished solution of hydrochar (HRFS) to enhance rice production in a saline soil. With this purpose, HRFS was applied (0, 10, 20, 40, 60, 80 and 100 mL/pot) and rice yield and nitrogen (N) use efficiency (NUE) were determined. HRFS application significantly (P < 0.05) increased rice grain yield by 19.6%–30.0% compared to the control treatment (CKU, with N but without HRFS addition). Moreover, HRFS application promoted plant height and straw biomass of rice. Increases of rice yield were mainly achieved by increases in the number of panicles and grains per panicle. Compared with the CKU treatment, the NUE of HRFS amendments significantly (P < 0.05) increased by 56.3%–71.7%. This indicated that the improvement of NUE was one of the mechanisms to improve rice grain yield with HRFS amendment. The results of regression analysis showed that there was a positive relationship (R²=0.8332) between rice yield and HRFS application rate within an appropriate range. The highest rice yield was recorded with the HRFS application of 40 mL/pot, but a further increase in HRFS application rate appeared to reduce rice yield. Based on the results of this pot study, HRFS application can increase rice yield in a saline soil by regulating its yield components and enhancing NUE. However, impact of HRFS on these variables showed a “dose effect”.