Abstract

Water shortage and poor soil fertility are two main limiting factors for crop production in semiarid region. We evaluated the effect of five irrigation times (0, 2, 3, 4 and 5 times with 50 mm per time) and four phosphorus fertilizer rates (0, 60, 90 and 120 kg/ha) on chasmogamous (CH) and cleistogamous (CL) part of Lespedeza potaninii on seed yield, total seed yield, seed yield components and agronomic traits from the year 2022 to 2023. The CH and CL seed yield, total seed yield of L. potaninii was significantly (p<0.001) affected by the year, irrigation, phosphorus fertilizer, and irrigation×phosphorus. The maximum average total seed yield over 2 years (1,126 kg/ha) occurred at the 5 times irrigation (250 mm) and 90 kg/ha phosphorus fertilizer rate (P). The CL seed yield exceeded the CH seed yield under the no irrigation and I2. Conversely, the CH seed yield was higher than the CL seed yield under the I3, I4, and I5 treatments. All the seed yield components were significantly (p<0.01) correlated with CH and CL seed yield. Correlation and structural equation model analyses were used to determine the contribution of yield components to seed yield. Increasing irrigation times and fertilization indirectly boosted CH and CL seed yield by raising the number of CH and CL racemes per stem, respectively. We found that the maximum water use efficiency was achieved with 4 times irrigation (200 mm) and 90 kg/ha P. At each irrigation level, the partial phosphorus fertilizer productivity at 60 kg/ha P was significantly (p<0.05) higher than that at other phosphorus application levels. Economic analysis showed that a considerable net profit was achieved after 5 times irrigation (250 mm) and 90 kg/ha P. Our findings enable further understanding of the mechanism of dimorphic seed yield response to irrigation and P in L. potaninii and provide a reference for appropriate agronomic measures to improve its dimorphic seed yield.