Objectives Silicon (Si) is necessary for the growth and development of rice. We investigated the effects of Si-enriched biochar on Si form, rice yield, and Si uptake of a reddish paddy soil, to provide a scientific basis for a sustainable nutrient cycling in rice production.

Methods A pot experiment was established, with rice cultivar ‘Meixiangzhan2’ as test material. The treatments included one lower Si biochar (BW3), two medium Si biochar (BH7 and BB7), and two high Si biochar (AH and AB), and each biochar was added at two rates (0.4% and 0.8% of the pot soil weight). No biochar was used as control. The rice yield and Si uptake were analyzed at harvest, and the soil samples were collected at the same time for the extraction and determination of chemical forms of Si in the soil.

Results The addition of Si-enriched biochar significantly increased the content of soil available Si, organic Si, and Fe/Mn-oxide bound Si, among which the AB treatment exhibited the highest increase, with increments of 184.23%, 59.53%, and 117.54% in the available Si, organic Si, and Fe/Mn-oxide bound Si compared with CK. The biochar types, application rate, and their interactions significantly affected the rice yield, straw biomass, and root biomass (P<0.01). Except for the low rate of BW3, all the biochar treatments significantly increased the rice yield, and there was no significant difference among the treatments (P<0.05), however, the high rate of each biochar elicited higher rice yield than the low rate (P<0.05). The Si accumulation in different parts of rice was in order of straw>grain>root. The total Si uptake of rice under the two addition was AB>AH>BB7>BH7>BW3. At high rate, the total Si uptake of rice attained its maximum in AB treatment, which was 73.68% higher than that of CK, followed by AH biochar.

Conclusions Silicon-enriched biochar is more effective than medium and low Si biochar in increasing the availability of Si in soil, which translated to increased Si uptake by rice, and improved yield and biomass of rice. Higher application rate of biochar produces better results; therefore, silicon-enriched biochar can serve as a potential Si source of paddy soil.