Effects of different water and fertilizer use patterns on the lodging resistances of indica and japonica rice

Rice is the main food crop grown in China. Lodging is one of the main limiting factors affecting stable and high yield of rice. As for rice cultivar, japonica (J) and indica (X), which differ in their growth and physiological characteristics due to the genomic variation, are widely cultivated in southern China. As for fertilizer types, excessive application of chemical fertilizer (C) could result in numerous environmental problems, thus it is recommended to use the organic fertilizer (O) in recent years. As for irrigation modes, in addition to traditional shallow-frequent irrigation (2), various water-saving irrigation modes for rice, such as controlled irrigation (1), have been developed in the light of the ongoing global water scarcity. It has been reported that the individual effects of rice cultivar, fertilizer type, and irrigation mode could affect rice growth and thus influence lodging index (LI) of rice. However, the combined effects of these three factors on yield and lodging resistance of rice are not well understood. Furthermore, understanding the regulation of lodging resistance as a function of cultivar, fertilizer type, and irrigation mode, could benefit food security and environmental sustainability under increasing water scarcity. This study was conducted in the Water-saving Park, Hohai University, Nanjing, China from June to October in 2019 and 2020 to investigate the combined effects of rice cultivar (J or X), fertilizer type (C or O), and irrigation mode (1 or 2) on yield and LI of rice as well as the relationships between LI and morphological and mechanical traits of rice plant. A total of 2×2×2=8 treatments, Nanjing 5055 supplied with chemical fertilizer and irrigated with controlled irrigation mode (JC1), Nanjing 5055 supplied with chemical fertilizer and irrigated with shallow-frequent irrigation mode (JC2), Nanjing 5055 supplied with organic fertilizer and irrigated with controlled irrigation mode (JO1), Nanjing 5055 supplied with organic fertilizer and irrigated with shallow-frequent irrigation mode (JO2), Y liangyou 900 supplied with chemical fertilizer and irrigated with controlled irrigation mode (XC1), Y liangyou 900 supplied with chemical fertilizer and irrigated with shallow-frequent irrigation mode (XC2), Y liangyou 900 supplied with organic fertilizer and irrigated with controlled irrigation mode (XO1), Y liangyou 900 supplied with organic fertilizer and irrigated with shallow-frequent irrigation mode (XO2), were set up. For different irrigation mode, compared with shallow-frequent irrigation, controlled irrigation significantly reduced plant height and above-ground fresh weight (P<0.05); For different fertilizer types, compared with chemical fertilizer, organic fertilizer treatment significantly increased the short axis internode diameter and stem wall thickness of I1 (I1 represents the second internode counted from the shoot base to the neck of the panicle) and Young's modulus of I2 (I2 represents the third internode counted from the shoot base to the neck of the panicle) (P<0.05), and significantly decreased the second moment of area (Ib) (P<0.05); For different rice cultivar, compared with japonica, plant heights and stem morphological indexes of indica rice were significantly higher than those of japonica (P<0.05). In addition, rice cultivar also significantly affected the stem mechanical traits, such as maximum Bending force (Fmax), Bending moment at breaking (M), Bending stress (BS), Ib and LI. In 2020, the LI of I1 was affected by the interaction effects of rice varieties and fertilizer types. For japonica rice, the LI of I1 for the two fertilizer types had no significant difference (P>0.05); For indica rice, the LI of I1 under organic fertilizer treatment was significantly greater than that under chemical fertilizer treatment (P<0.05). Overall, for the consideration of yield and LI, japonica rice is suitable for supplied with organic fertilizer under controlled irrigation mode, and indica rice is suitable for supplied with chemical fertilizer under controlled irrigation mode. This study could provide data support and theoretical support for the regulation of lodging resistance of different rice cultivar by application of different irrigation modes and fertilizer types.