Effects of Compound Salt Concentration on Growth, Physiological and Nutritional Value of Hydroponic Forage Wheat

(1) Background: Hydroponic forage plays an increasingly important role in animal breeding during winter and spring in arid and cold regions due to its rich nutrient and good palatability. In the present study, the profiles of growth, physiological indexes, nutritional value and in vitro degradation of hydroponic forage cultivated with different salt concentration were evaluated. (2) Methods: The compound salt was extracted from soil surrounding the Tarim River Basin, and five compound salt solution treatment groups (three replicates each) with concentrations of 0%, 0.4%, 0.8%, 1.2% and 1.6% were prepared. Winter wheat seeds were selected as hydroponic forage for germination experiments, and the germination, physiological indicators, nutritional value and in vitro fermentation degradation rate were analyzed. (3) Results: The results showed that the germination and growth of hydroponic herbage were significantly ( p < 0.05) inhibited by compound salt concentration higher than 0.8% from the third day. Compared with the 0% concentration group, the chlorophyll content in the 0.4% concentration group was significantly increased ( p < 0.05), and contents of chlorophyll a, chlorophyll b and total chlorophyll were 729.71 mg·g −1 , 223.19 mg·g −1 and 952.9 mg·g −1 , respectively. The total chlorophyll content in the 0.8% and 1.2% concentration groups were significantly lower than those in the 0% and 0.4% concentration groups ( p < 0.05), and in the 1.6% concentration group, the content undetected. With the increase in compound salt concentration, the contents of soluble sugar and proline were significantly increased ( p < 0.05). The nutrient compositions were significantly increased ( p < 0.05) under the 0.4% and 0.8% concentration groups, in which the content of crude protein in 0.4% concentration group was 15.23%. The results of gas production and fermentation parameters suggested that the 0.8% concentration group could enhance rumen fermentation characteristics. (4) Conclusions: In summary, 0.8% as the upper limit concentration and 0% to 0.4% as the optimal concentration range of compound salt can be considered for cultivating hydroponic forage wheat.