Effect of drip irrigation on seed yield, seed quality and water use efficiency of Hedysarum fruticosum in the arid region of Northwest China

Shortage of high-quality seeds of native species, particularly for xerophyte shrubs, have severely limited grass-land restoration in the arid region of China. However, little attention has been devoted to improving seed yield and quality in the xerophyte shrub. We conducted a three-year field experiment from 2019 to 2020 to investigate the effects of four irrigation treatments (i.e., W0: non-irrigated control; W1: irrigation at winter; W2: irrigation at winter and regreening; W3: irrigation at winter, regreening, and peak flowering) via subsurface drip irrigation on the seed yield and quality of Hedysarum fruticosum, a dominant leguminous shrub in the desert areas of China. The results showed that seed yield increased as irrigation frequency increased regardless of growth season. The yearly average seed yields were 98.0, 107.7, 179.3, and 265.5 kg hm-2 for W0, W1, W2, and W3 irrigation, respectively. Seed yield decreased in each subsequent growth year in all irrigation treatments, and the variation in seed yield each year was the highest in W0 and lowest in W3 irrigation. Compared to 2019, the seed yield of W0 decreased by 47 % and 66 %, but yields of the W3 irrigation treatment decreased by 8 % and 19 % in 2020 and 2021, respectively. Meanwhile, irrigation significantly affected seed yield components; the number of florets and pods per stem under the W3 irrigation treatment was two to three times that of W0 irrigation for three years. The structural equation model revealed that pods per stem had the largest direct positive effect on seed yield (path factor p = 0.44), followed by seeds per pod (path factor p = 0.36). Irrigation treatments affected seed germination percentage and seed size, which increased as irrigations times increased. A similar water use effi-ciency was achieved in W0 and W3 in three years, and W1 treatment had the lowest water use efficiency. In conclusion, we recommend W3 treatment to increase seed yield and quality, especially in arid regions. Future breeding objectives and agronomic practice for H.fruticosum should pay more attention to increasing pods per stem. Our study can be used as a reference for taking appropriate agronomic measures to improve the seed yield of H.fruticosum and similar shrubs.