The effect of phosphorus split application on use efficiency and dynamic of phosphorus and zinc at the soil, aerial parts, and grain, and Zinc biofortification of two rice varieties (Oryza sativa L.) (Hashemi and Guilaneh)

Introduction: Despite the P vitality for rice cultivation, its recovery index in paddy soils is very low and less than 25% of added P, and the rest goes out of reach of rice plant through the P fixation by soil particles at different fractions. Also, despite abundant studies on the effect of basal soil P application, we face a lack of knowledge on research findings of the P splitting application and its effect on soil Zn concentration and tissues Zn content. Thus, the current research project was done to explore the effect of P splitting application at flooded conditions on the soil and rice plant tissues P and Zn variation trend at the different rice growth stages of two more common varieties (Hashemi and Guilaneh varieties).
Materials and methods: The outdoor pot experiment was conducted on a three factors factorial experiment in a randomized complete block design with three replications in 2017 at the research farm of the rice research institute of Iran, Rasht. The experimental treatments were: phosphorus fertilizer split application at five levels, soil at two levels, and rice varieties at two levels (Hashemi (local variety) and Guilaneh(improved variety)), The P application treatments were: control (no added P), 100% basal, P split application at 50% basal and 50% at 20 days after transplanting (DAT), P split application at 50% basal and 50% at 60 days after transplanting (DAT), P split application at 50% basal, 25% at 20 days after transplanting, and 25% at 60 days after transplanting.
Results: The results indicated that the highest soil available P and Zn concentrations were recorded at the flowering stage about 95.3 and 90.10, and 8.6 and 8.7 mgkg-1by two and three P split for Hashemi and Guilaneh, respectively. Also, the maximum P of rice grain was obtained about 0.17 and 0.20 mgkg-1 for Hashemi and Guilaneh, respectively. The Zn content of rice grain at P split pots was significantly more than control and 100% basal application. The highest agricultural recovery (13.31 and 12.72), physiological (693.19 and 740.10) and physiological-agricultural efficiency (482.00 and 753.00), P use efficiency (5.34 and 5.66), and apparent recovery (1998 and 1272.22 kg kg-1) were found for Hashemi and Guilaneh, respectively, in the two and three P split application. Furthermore, stepwise multiple regression analysis revealed that the soil available P concentration at ripening stage, Zn content of the grain, and Zn concentration at rice aerial parts can explain 52% of grain yield variations for studied rice cultivars.
Conclusion: The three-stage P splitting (50% soil basal, 25% 20 DAT, and 25% 60 DAT) increased the Zn content of the Hashemi variety by about 54.72% at slit loam soil, whereas the Guilaneh rice variety was received a 37.5% increase in Zn content of grain in silty clay through two-stage P splitting (50% soil basal and 50% 20 DAT) compare to control (100 % basal). It can be concluded both three and two-stage P splitting might be positively significantly effective on rice grain nutritional quality.