Response of yield and water use efficiency to different irrigation levels at different growth stages of Kenaf and crop water production function

To provide a rational irrigation management for high yield cultivation of Kenaf, the effects of three irrigation levels at the three growth stages on raw fiber yield, shoot dry mass and water use efficiency of two Kenaf varieties were investigated, and crop water production function was simulated by the Jensen's model. Two Kenaf varieties (V) included hybrid variety (Hongyou 2, V1) and conventional variety (Fuhong 992, V2). Three irrigation levels at different growth stages included (1) high water level (A1), middle water level (A2) and low water level (A3) at the seedling stage, (2) high water level (B1), middle water level (B2) and low water level (B3) at the vigorous growth stage, and (3) high water level (C1), middle water level (C2) and low water level (C3) at the flowering and fruiting stage. Orthogonal test with replicates, unequal level and the existence of interaction was designed. Orthogonal test indicates that significant effects of variety and irrigation level at the vigorous growth and flowering and fruiting stages on raw fiber yield were found, and the raw fiber yield of Hongyou 2 was significantly higher than that of Fuhong 992. The best combination of two varieties and three irrigation levels at the three growth stages was V1A2B1C1 for raw fiber yield and shoot dry mass and V1A3B1C3 for water use efficiency on the basis of dry raw fiber yield (WUErf). Simulation results of the Jensen's model show that the sensitivity coefficient (λ2) was the highest at the vigorous growth stage, and significantly higher than those of other growth stages, showing that Kenaf was the most sensitive to water deficit at the vigorous growth stage, and the vigorous growth stage was the critical stage of water requirement for Kenaf. For Hongyou 2 and Fuhong 992, raw fiber yield was improved with the increase of irrigation amount at the vigorous growth stage and flowering and fruiting stage, and the simulation of the Jensen's model also proved that Kenaf was very sensitive to water deficit at the vigorous growth stage, so Kenaf should be supplied by adequate irrigation at the vigorous growth stage. The raw fiber yield of two varieties had the highest at A2B1C1, but Honyou 2 had more raw fiber yield. As the response of Fuhong 992 to irrigation level at different growth stages was not more significant than that of Hongyou 2, Hongyou 2 should be planted under better water and fertilizer condition.