The present study aimed to investigate the variation of potassium (K) harvest index (KHI) among 437 wheat varieties, analyze the relationships between KHI and yield, grain K content, K absorption of different organs and K utilization efficiency; and clarify the effects of the release year of wheat varieties, plant height and awn types on KHI. The present study provided useful information for breeding wheat cultivars with high yield and K use efficiency.

Field experiments were conducted in Luoyang of Henan Province and Yangling of Shaanxi Province during the 2018-2019 and 2019-2020 growth seasons. Four hundred and thirty-seven wheat varieties with different release years, plant heights and awn types were used as materials. An augmented randomized complete block design was applied and 14 blocks were set up, with 31 experimental varieties and 5 control varieties in each block. Each wheat variety was planted with 6 rows and 3 m long. At maturity, a complete row in the middle of each plot was selected for grain harvest, and the grains were oven-dried and weighed. For tissue K concentration measurement, six tillers were blindly selected in five sampling sites in each plot. Grain, straw and glume were separated, oven-dried, and digested using H₂SO₄-H₂O₂. K concentrations of different organs were measured with a flame photometer, and parameters including KHI, grain, straw and glume K uptake, grain K utilization efficiency (GKUE) and shoot K utilization efficiency (SKUE) were calculated.

There were significant differences in KHI among different wheat varieties (P<0.01) under all the four environments (19Luoyang, 20Luoyang, 19Yangling and 20Yangling) and KHI of 437 wheat varieties varied from 0.04 to 0.40. The average KHI of Yangling was higher than that of Luoyang. Seven wheat varieties including Yangmai 18, Yannong 5158, Chuanmai 104, Huamai 5, Zhengmai 1860, Dromedaris and Space 6 had higher KHI and yield. There were significant positive correlations between KHI and wheat yield, grain K concentration and grain K uptake in three environments (P<0.05). There were significant negative correlations between KHI and straw K uptake, glume K uptake and shoot total K uptake (P<0.05). Grain yield, grain K concentration and uptake increased along with the increase of KHI, however, straw, glume and the shoot total K uptake decreased along with the increase of KHI. There was a significant positive correlation between KHI and GKUE or SKUE (P<0.001). The KHI of the wheat varieties released before 1970 and from 1970 to 1990 was significantly lower than that of the varieties released after 1990 (P<0.05). The wheat varieties released between 1990 to 2010 had similar KHI with the varieties released after 2010 (P>0.05). There was a significant negative correlation between plant height and KHI. There was no significant difference in KHI between the wheat varieties with and without awn.

There was a distinct inter-variety variation in wheat KHI. Increasing wheat KHI may positively influence the grain yield of wheat. KHI may be also a good indicator of K utilization efficiency of wheat. To further improve KHI of wheat, novel breeding technologies should be developed to improve the remobilization efficiency of K from vegetative organs to grain. Breeding dwarf or semi-dwarf wheat varieties is beneficial to improve KHI.