Oxygenated compound fertilizer could effectively increase redox potential of paddy soil and nutrient uptake of rice

Objectives  Poor aeration in paddy soil is one of the main limiting factors for the growth of rice (Oryza sativa L.). We tried to prepare oxygenated compound fertilizers to deal with the limitation.

Methods  Calcium peroxide, used as an oxygenous agent, was amended into a compound fertilizer (4.5–4.5–4.5) in ratio of 3.6% (OCF1), 4.8% (OCF2) and 6.1% (OCF3), and those new fertilizers were named oxygenated compound fertilizers (OCFs). A pot experiment was conducted using two rice cultivars of Q681 and EK1 as tested materials. In the experiment, water logging throughout whole rice growing (WL), irrigation with micro-bubble aerated water (MBWI) and fertilizing calcium peroxide 4 times (FCP) were used as controls, the three compound fertilizers were once basal applied separately. At the main growing stages of rice, soil samples were collected for determination of soil Eh, pH and mineral N content. The photosynthetic efficiency was measured, and the yield and NPK contents of rice were measured at the harvest stage.

Results  oxygenated treatments OCF2 and OCF3 could increase soil Eh without changing soil pH at the transplanting, tillering, full heading and milky stage. The Eh in the OCF1, OCF2 and OCF3 treatments at tillering stage and full heading stage were significantly higher than those in WL, MBWI and FCP treatments. OCFs also increased the activity of soil catalase at the full heading stage of rice. Compared with WL treatment, all the oxygenation treatments could maintain or improve the ammonium N content in the surface soil, and OCF2 and OCF3 treatments had the best effect. However, all the oxygenation treatments did not significantly increase soil nitrate N content, and OCFs only could keep or slightly increase soil nitrate N content. Compared with WL treatment, the photosynthetic rates in all oxygenation treatmentsof rice leaves were increased at different degrees, among which OCF3 treatment increased the most (> 11%), and significantly higher than that in FCP treatment. In OCF3 treatment, more than 25% higher effective panicle number, 38% higher 1000-grain weight and 107% higher yield were obtained than those in WL treatment, and the rice yield was 29%–58% higher than those in MBWI and FCP treatments. OCF3 treatment had highest yield response among the three OCFs.

Conclusions  Oxygenation is effective in keeping high soil aeration (Eh values) for long periods. Compared with irrigation with micro-bubble aerated water and applying CaO₂ for several times, the application of oxygenated compound fertilizers is more effective and easier to operate, especially when the ratio of added CaO₂ reaches 6.1%, which is an alternative way to increase the efficiency of special compound fertilizer for rice.