Effect of micro-nano bubbles on the yield of different rice types

Increasing the rhizosphere oxygen in the rice paddy can influence the paddy field environment and improve the physiology, metabolism, and grain yield of rice. The traditional methods of mechanically or chemically aerating subsurface irrigation could produce large air bubbles, which can escape from the soil along the pores adjacent to the roots. Aerating irrigation efficiency improvement is an issue not yet to be resolved. One way is to use water rich in micro-nano bubbles (MNB). MNB are small air bubbles that cannot escape from the soil easily, thereby, supplying more oxygen. Different rice types vary in their ability to absorb and utilize oxygen. A pot experiment was carried out in which the experimental group was treated with MNB water and the control group with running water as check (CK) during 2019−2020 to determine the effect of MNB and CK on the growth and yield of two paddy rice varieties (inbred rice ‘Ganwanxian 37’ and super rice ‘Wufengyou T025’). The results showed that 1) MNB increased the dissolved oxygen concentration of soil solution, increased the number and volume of rice roots, enhanced α-NA oxidation, improved the total and active absorption area of root, promoted the SPAD and net photosynthetic rate (P_n) value of leaves, increased the biomass accumulation, raised the harvest index, improved the rice panicle characteristics such as length and number of grains per panicle, enhanced the number of primary and secondary branches and also the main spike-stalk, seed-setting rate on the primary and secondary branches and on spike-stalk, and enhanced the grain yield. 2) Compared to CK, MNB enhanced the yield of inbred rice by 8.46%–17.9% and super rice by 11.32%–22.09%, with the super rice showing higher grain yield than the inbred rice. 3) In case of inbred rice, MNB mainly increased the panicles (6.67%–16.67%), whereas in super rice it increased the spikelets per panicle (3.23%–7.2%) and the seed-setting rate (1.14%–6.57%). 4) The MNB enhanced the panicles number of inbred rice by promoting the tiller occurrence in the early growing period. The MNB enhanced the number of spikelets per panicle and the seed-setting rate in the super rice by increasing the rate of photosynthesis of leaves (improved the SPAD and P_n value). It also slowed down the leaf senescence, improved the bearing rate of tillers, biomass accumulation, increased the number and seed-setting rate in the secondary branches and the main spike-stalk, and it improved the harvest index. It was, thus, evident that MNB could improve the yield of both types of rice. In inbred rice, supplying MNB before the tillering stage increases the yield by increasing panicles number. In super rice, MNB supply after the earing stage increases the yield by producing more spikelets per panicle and through higher seed-setting rate.