Effects of Irrigation Amounts and Fertilizer Types on Seed Yield and Water-Use Efficiency of Lespedeza potaninii in Northwest China

Lespedeza potaninii is native to the Tengger Desert and exhibits a high degree of adaptation to arid conditions. It develops both chasmogamous (CH) and cleistogamous (CL) flowers with different morphologies and attachment positions. However, the manner in which the amount of irrigation and the fertilizer type affect the reproductive allocation of L. potaninii is not well known. Field experiments on L. potaninii were performed using a split-plot design in both 2023 and 2024, with three irrigation amounts (I1, 100 mm: I2, 200 mm: I3, 300 mm) for the main plots and three fertilizer types (F1, control: F2, 90 kg/ha of P fertilizer: F3, organic fertilizer) for the sub-plots. The results revealed that irrigation amounts and fertilizer types significantly affected L. potaninii yield components, total seed yield, CH seed yield, CL seed yield, and water-use efficiency (WUE). The application of P fertilizer significantly (p &lt: 0.05) enhanced CH seed yield by 7&ndash:11% compared with control or organic fertilizer. However, the impact of fertilizer type on the seed yield of CL varied under different irrigation amounts. The seed yield of the CL part was higher under a 100 mm of irrigation, while the seed yield of the CH part was higher under the I2 and I3 irrigation amounts. The maximum seed yields in 2023 and 2024 were 974 kg/ha (I2F2) and 1011 kg/ha (I3F2). Irrigation amounts had a positive and direct effect, and fertilizer types had a positive and indirect effect, on CH seed yield by positively affecting the number of racemes and pods and the thousand-seed weight of the CH part and the number of stems. Irrigation amounts and fertilizer types exhibited a positive and indirect effect on CL seed yield by positively affecting the number of stems, racemes, florets, and pods of the CL part. Treatment I2F2 resulted in relatively high WUE, IWUE, and PWUE compared with I1: and the I2 increased the WUE by 62.74% and 42.05%, on average, the IWUE by 31.05% and 27.60%, on average, and the PWUE by 162.00% and 155.21%, on average, in 2023 and 2024, respectively. Our research can further elucidate the relationship between CH or CL seed yield, on the one hand, and amount of irrigation or fertilizer type, on the other, and offer guidelines for conserving agricultural water resources and selecting fertilizer for the Lespedeza genus.