Effects of representative groundwater salinity and irrigation amount on the yield and quality of Lycium barbarum in the Hetao Irrigation areas

Lycium barbarum fruit is widely used as a medicinal food in China. This study aims to clarify the effects of brackish water irrigation amount and salt ion composition on the yield, appearance quality, and nutritional quality of the Lycium barbarum. An optimal amount of brackish water was also determined under different water qualities, according to the comprehensive score after irrigation simulation. A L8 (41×24) orthogonal test was carried out with the Ningqi No.1 Lycium barbarum as the test material. Eight orthogonal treatments included the four irrigation levels (60, 70, 80, and 100 mm) and two concentrations (according to 1 or 2 times of ion concentration in groundwater in the study area) of NaCl, NaHCO3, Na2SO4, and CaCl2. The optimal levels of each factor were obtained and scored for each index, including the yield, 100 grains dry mass, and nutritional quality. The greatest correlation with the comprehensive score was selected as the salt ions. A gaussian regression model was established for the sensitive ion concentration and comprehensive score Ci, in order to obtain the optimal irrigation quantity range under different water quality using the screening program. The water quality and irrigation quantity scheme achieved higher scores than before. The results showed that there were significant effects of the brackish water irrigation amount and the concentrations of NaCl, NaHCO3, Na2SO4, and CaCl2 on the yield, dry mass of 100 grains, and nutritional quality. In the yield and appearance quality, the irrigation amount presented the most significant effects on the dry fruit yield, dry mass of 100 grains, fruit shape index, and dry fruit ratio. The maximum yield and dry mass of 100 grains were achieved at the irrigation amount of 70mm, and 100 mm, respectively. The NaCl effect on the dry fruit yield was higher than that of the rest salts. The maximum yield was reached at the N1 level. In the nutritional quality, the concentration of CaCl2 was dominated by the total amount of carotenoids, betaine, and amino acids, the highest of which was C2 (0.24%, 15.2 g/kg, and 11.67 g/100g, respectively). NaCl was determined as the total sugar, the highest which was the N1. The highest amount of flavonoids was obtained at the irrigation amount of 100mm. The comprehensive score showed that the T8 (W4, C2, HC1, N1, and S2) treatment with the high water. The CaCl2 presented the highest nutritional quality (Cpi=0.895), and planting benefit (Ci=0.719). The T5 treatment with the high water and NaCl was the lowest (Cpi=0.172, Ci=0.200). Ci was very negatively correlated with the concentration of Na+ (P- (P2+ (Pi was significantly positively and negatively correlated with Ca2+ and Na+ concentrations, respectively, and negatively correlated with Cl-. Gaussian regression showed that the brackish water with the concentrations of Na+, Ca2+, and Cl- of 34.8-38.8, 15.3-15.6, and 50.9-55.9 mmol/L were better suitable for irrigation, compared with the planting benefit fit Ci>0.7 with 96.9-97.9 mm in the single irrigation. The optimal irrigation amount was achieved under different water quality: In the Cl- content of 63.02-81.50 mmol/L, the Na+ contents were 18.55-30, 30-35, 35-40, 40-53, and 53-55 mmol/L, where the optimal irrigation amount was 91-98, 82-98, 77-83, 77-99, and 96-98 mm. In the Cl- content of 81.50-99.11 with the Na+ contents of 18.55-30 and 35-55 mmol/L, the optimal irrigation amount was 97-99 and 69-77 mm. In the Na+ content of 30-35 mmol/L with the Ca2+ concentrations of 8.77-13.00 and 13.00-17.54 mmol/L, the optimal irrigation amount was 74-98 and 78-82 mm. The findings can provide a scientific basis to utilize the brackish water for the better planting benefits of Lycium barbarum in the Hetao Irrigation area. © 2022 Chinese Society of Agricultural Engineering. All rights reserved.