Seed production and yield components of Lespedeza davurica in response to N, P, and K fertilization and plant density

Lespedeza davurica Laxm is a valuable forage because of the strong cold and drought tolerance, and its high nutritional value. This crop production is limited by seed supply. The objective of this study was to investigate the effects of fertilization and plant density on seed yield. "JinNong 1" was drill-seeded in 2016 at 15 kg ha−1 at the Forage Research Station of Shanxi Agricultural University. The seedlings were manually thinned in May 2016 to two different densities, 6 and 12 plants m−2 in the main plots. Within each main plot, a factorial combination of N, P, and K fertilization levels were applied once a year from 2016 to 2018. The N levels were 0, 75, 125, and 175 kg ha−1. The P levels were 22 and 44 kg ha−1. The K levels were 62 and 124 kg ha−1. Maximum seed yield was achieved at the density of 12 plants m−2, 75 kg ha−1 of N, 22 kg ha−1 of P, and 124 kg ha−1 of K. The seed yields were 750 and 644 kg ha−1 during 2017 and 2018, respectively. High plant density showed a tradeoff with the number of primary and secondary branches, the number of raceme per branch, and 1000-seed weight. The number of pods per raceme and the number of flowers per raceme did not show a tradeoff at high density. Therefore, selecting for higher numbers of seed pods per raceme or fertile flowers may be a practical objective for breeders attempting to increase seed production.