Investigating the Potassium Fertilization Effect on Morphological and Agrophysiological Indicators of Durum Wheat under Mediterranean Rain-Fed Conditions

It is well known that balanced and optimal mineral fertilization (i.e., nitrogen, phosphorus, and potassium) can increase yield and improve wheat quality. However, there is little scientific knowledge on the specific effect of potassium (K) fertilization on the morphological and qualitative characteristics of rainfed durum wheat under Mediterranean conditions, especially in the context of Algerian agriculture. Therefore, the main objective of this study is to provide crucial information on this important type of durum wheat mineral nutrition for farmers and researchers working in similar areas. The field study was conducted in the Northern Algerian region of Mitidja during the 2020/2021 and 2021/2022 growing seasons. The effect of K fertilization was evaluated within five contrasted rates of K: 0 kg k 2 O ha −1 , 100 kg k 2 O ha −1 , 200 kg k 2 O ha −1 , 300 kg k 2 O ha −1 , and 400 kg k 2 O ha −1 , which were applied on one of the most commonly cultivated cultivars of durum wheat (Simeto). Results showed that increasing potassium levels had a positive and significant impact only on grain yield, spike length, spike neck, and dry matter. Hence, the highest grain yield of durum wheat (2.58 t ha −1 ) was demonstrated under low K application (100 kg k 2 O ha −1 ). This rate leads to an increase in grain yield by more than 0.6 t ha −1 , as compared to the unfertilized control. Moreover, the thousand-grain weight of durum wheat was significantly increased by 4.11 g and 1.96 g, respectively, under low and moderate (200 kg k 2 O ha −1 ) K-fertilization, as compared to the control. In terms of grain yield quality, low K application provides an increase of 1.21% in protein content as compared to that measured under the control treatment. The major finding confirmed that both growth and yield indicators of durum wheat were globally optimized under low K application. Based on grain yield and evaluated agronomic traits, this research revealed that an applied K rate of 100 kg k 2 O ha −1 is recommended as the most effective dose to maximize durum wheat yield and quality under Algerian sub-humid conditions.