Potassium (K) is one of the most crucial nutrients for plant growth, not only quantity but also in terms of physiologically and biochemically; it is one of the most essential cations in plants. Therefore, knowing about the optimal level of this element in the soil, as well as plant responses to different amounts, can be an effective aid in the optimal fertilizer recommendation of this nutrient. Therefore, this study was conducted to investigate the effect of different levels of potassium chloride on yield and potassium concentration in quinoa (Chenopodium quinoa Willd).

Potassium-deficient soil was obtained from a depth of 0-30 cm in the agricultural fields of Taqar Tappeh village, 20 km East of Gorgan. To achieve the objectives of this study, an experiment was conducted in a completely randomized design with three replications and 11 treatments, and a total of 33 pots in the greenhouse of Gorgan University of Agricultural Sciences and Natural Resources. Fertilizer treatments including 0, 20, 40, 60, 80, 100, 120, 140, 160, 180, and 200 mg/kg of potassium of soil and potassium from potassium chloride source are applied to the soil of 5 kg pots, and 6 quinoa seeds (Titicaca cultivar) was planted at a depth of 2 cm. Two weeks after the plants sprouted, the number of plants was reduced to two. Cultivated pots were maintained for 8 weeks at the field capacity by weight method. Then fresh and dry shoot weight, upper and lower leaf SPAD, shoot potassium concentration and uptake and, available potassium plant was measured by extraction method with normal ammonium acetate.

Based on the results, the effect of different rates of potassium on all studied traits was significant at the level of 1% probability. The results showed that the highest concentration and uptake of potassium by shoots with an average of 1.35 and 2.85% were related to the treatment of 60 and 100 mg/kg potassium chloride, and the lowest values with an average of 0.89 and 0.07% were related to the control treatment, respectively. A weak and non-significant correlation was observed between potassium extracted with normal ammonium acetate and plant indices. Since most of the soils of Golestan province are of loess origin and in most soils loess is the predominant mineral or contains a large percentage of these soils, the use of normal ammonium acetate for extraction of exchangeable potassium, high efficiency in measuring the actual amount of potassium which will not be easily accessible to the plant

The results of this study showed that treatment of 60 and 100 mg/kg potassium chloride resulted in the highest concentration of potassium, uptake of potassium, and leaf SPAD respectively. At the same time, increasing more than 100 mg/kg of potassium chloride consumption could not cause a significant change in the studied traits, including potassium concentration.