Abstract: Using ′Jiang Da Zi Jiang 1 Hao′ as the test material，base fertilizer（CK），present bud topdressing （Q1），full flowering topdressing （Q2），and full pod topdressing （Q3）were applied to compare the effects of different topdressing periods on cowpea plant spectral parameters， leaf pigments content， and yield. The cowpea leaves′ chlorophyll spectral parameters（CRI1，WBI，PRI，PSRI，NDVI）were measured at every 7 d intervals. One week before the full flowering period of topdressing，the leaf carotenoid content and the total chlorophyll amount were determined. The final harvest period of yield was converted into yield per 667 m² according to the actual output of the area. The results showed that the carotenoid reflection index（CRI1）of ′Jiang Da Zi Jiang 1 Hao′ all increased first and then slowly decreased. The measured value of Q3 treatment was higher than that of CK by 70. 74%，and the difference was significant（P < 0. 05）. The water index（WBI）of CK，Q1 and Q2 treatments showed a trend of increasing firstly，then decreasing，and then growing. However，the measured value of Q3 treatment increased by 12. 61% compared with CK，and the difference was significant（P < 0. 05）. All treatments′ reflection index（PRI）increased first and then decreased until flat. The measured value of Q3 increased by 11. 29% compared with CK，and the difference was significant（P < 0. 05）. The vegetation aging reflectance index （PSRI） of all treatments showed a trend of rising first and then falling and then rising. The measured value of Q3 decreased by 13. 22% compared with CK，and the difference was significant（P < 0. 05）. The normalized vegetation index（NDVI）of Q3 increased by 11. 51% compared with CK，and the difference was significant （P <0. 05）. The chlorophyll and carotenoid contents of Q1 and Q2 were higher than other treatments， with significant differences （P < 0. 05）. Among the three topdressing treatments，the Q3 yield was the highest，reaching 1 150. 95 kg/667 m². Based on the analysis of the spectral parameters，pigments content，and yield of cowpea in different periods，the best period of topdressing was the full pod period.

Key words: cowpea, topdressing, spectral parameters, pigment, yield