Effect of late season application of different nitrogen sources and foliar application of potassium on the grain yield and quality in barley (Hordeum vulgare L.)

Barley (Hordeum vulgare L.), is one of the oldest domesticated crops. In terms of importance, it is considered the fourth most important grain in the world after wheat, corn and rice. Proper nutrition of plants is one of the important factors in improving the quantity and quality the crops. Among the nutrients, nitrogen is the most important growth limiting factor. Nitrogen foliar application, especially at the end of the growing season and reproductive stage, can be an effective factor in increasing the quality and possibly the quantity of grains. There are different sources of nitrogen for agricultural purposes. In general, for most nutrients, there is little difference between the effects of different sources. However, in the case of nitrogen, the effects of the form and source of nitrogen on many vegetative and reproductive characteristics of plants are different and significant. To investigate the effect of late season foliar application of nitrogen and potassium on the yield and quality of barley, a factorial experiment was conducted in a randomized complete block design with three replications in Sabzevar during the cropping year of 2018-2019. The factors studied were nitrogen foliar application at five levels (no foliar application and foliar application with urea, ammonium nitrate, ammonium sulfate and calcium nitrate at the rate of 3 kg N ha-1) and potassium foliar application at two levels (foliar application of 2.5 kg K2O ha-1 in the form of potassium sulfate and non-foliar application of potassium). The application rate of nitrogen and potassium in foliar application treatments were 3 kg N ha-1 from different sources and 2.5 kg K2O ha-1 in the form of potassium sulfate, respectively. Reyhan barley cultivar was used in this experiment. The results showed that nitrogen foliar application at anthesis stage had no significant effect on the plant height, number of tillers and number of fertile tillers per plant, but it caused a significant increase in the spike length, number of fertile spikelets per spike, number of grains per spike, 1000 grains weight, grain yield, biological yield, harvest index, and grain nitrogen and protein content. The lowest harvest index of barley was obtained in the control treatment, which had no significant difference with calcium nitrate and ammonium sulfate foliar application treatments. The highest harvest index was also recorded in the conditions of foliar application of urea fertilizer, which was not significantly different from the ammonium nitrate and ammonium sulfate foliar application treatments. The highest grain nitrogen (2.1%) and protein (12.4%) contents were observed under ammonium sulfate foliar application conditions. Nitrogen foliar application reduced the grain starch content compared to non-foliar application conditions. Ammonium sulfate foliar application treatment had the lowest content of grain starch with 57.91%. Late season foliar application of potassium caused a significant increase in 1000 grain weight, grain yield and biological yield of barley compared to the non-foliar application conditions, but it had no significant effect on the other studied traits. Foliar application of potassium sulfate along with urea and ammonium nitrate, significantly increased the number of grains per spike and grain yield compared to the foliar application treatments of these fertilizers alone. The highest spike length (5.8 cm), number of fertile spikelet per spike (15), number of grain per spike (46.1), grain yield (5178 kg ha-1) and biological yield (13965 kg ha-1) of barley plants were observed under the combined foliar application of urea and potassium sulfate conditions. According to the results, combined foliar application of potassium sulfate and urea in the anthesis stage is recommended to produce high yield and increase the protein content of barley grains. Ammonium nitrate foliar application in the anthesis stage of barley will also lead to high starch content in grains in addition to producing optimal seed yield.