Effect of Late‐Season Foliar Applications of Nitrogen and Potassium on Yield and Nitrogen Uptake in Winter Barley

To investigate the effects of late‐season foliar applications of different nitrogen (N) sources and potassium (K) supplementation on yield, nitrogen uptake, and N‐use efficiency components in winter barley ( Hordeum vulgare L.), a 2‐year field experiment was conducted using a factorial arrangement within a randomized complete block design with three replications. Treatments included five foliar N regimes (no‐foliar N, urea, ammonium nitrate, ammonium sulfate, and calcium nitrate) and two foliar K levels (without foliar K and foliar potassium sulfate). Foliar N and K applications influenced yield components, grain and straw N concentration, N uptake, and N‐use efficiency components, with responses varying between N sources and cropping seasons. Urea + K 2 SO 4 produced the highest grain yield (4656.8 kg ha −1 ), whereas ammonium nitrate + K 2 SO 4 produced the highest total aboveground N uptake (145.9 kg ha −1 ) and the highest N‐uptake efficiency (NUpE). Nitrogen‐utilization efficiency (NUtE) was highest under the no‐foliar N/no‐foliar K treatment and generally declined with supplemental foliar N. Importantly, K 2 SO 4 did not significantly increase NUpE when combined with urea, although it increased N uptake and yield in some treatment combinations. Ammonium sulfate produced the highest grain and straw N concentrations among the N sources. These results indicate that late‐season foliar nutrition can modify yield and N acquisition in winter barley, but yield response, total N uptake, NUtE, and NUpE should be considered as distinct components rather than as a uniform improvement in N‐use efficiency. The results support the use of urea + K 2 SO 4 when maximizing grain yield is the primary objective, whereas ammonium nitrate + K 2 SO 4 was superior for total aboveground N uptake and NUpE under the conditions of this study.