Effects of different irrigation methods and phosphorus application on alfalfa yield, quality and water and phosphorus use efficiency

Irrigation and phosphorus application are two of the most important factors for the rapid plant growth in the oasis region of Xinjiang in northwest China. Subsurface drip irrigation and micro-sprinkler irrigation are widely used as efficient water-saving ways in agricultural production in arid and semi-arid regions. Phosphorus fertilizer is often used in large quantities to promote alfalfa growth. The water-fertilizer combination is more conducive to the alfalfa growth and nutrient quality. However, there are only a few reports on the differences between water and phosphorus fertilizer use efficiency of alfalfa under subsurface drip and micro-sprinkler irrigation. This study aims to explore the response of alfalfa production, nutritional quality and water and phosphorus utilization efficiency to the irrigation modes and phosphorus application. The optimal irrigation and phosphorus application were determined for the high-quality and efficient production of alfalfa in the oasis region. A series of experiments were carried out at the Water-saving Irrigation Experimental Station of Shihezi University in 2023. Two irrigation modes were set: underground drip irrigation (I₁) and micro-sprinkler irrigation (I₂). Four levels of phosphorus application were set: 0 (P₀), 50 (P₁), 100 (P₂), and 150 (P₃) kg/hm². A total of eight treatments were obtained in the interactive coupling (I₁P₀, I₁P₁, I₁P₂, I₁P₃, I₂P₀, I₂P₁, I₂P₂, I₂P₃), with three replications for each treatment. The experimental plot area was in the size of 24 m² (4 m×6 m). The 1 m wide isolation strip was set between the plots to prevent water and nutrient interpenetration. Some parameters were measured, including the alfalfa hay yield, nutrient quality, water and fertilizer use efficiency under different irrigation and phosphorus application levels. Principal component analysis was implemented to determine the response of each index to the irrigation and phosphorus application. The comprehensive performance of each treatment was evaluated in the growth period of alfalfa. The results showed that there were significant effects of irrigation modes and phosphorus application on the alfalfa production performance, nutrient quality, and water and phosphorus fertilizer use efficiency (P<0.05). Subsurface drip irrigation promoted the growth of alfalfa for the higher utilization efficiency of water and phosphorus, compared with the micro-sprinkler irrigation. Furthermore, the hay yield, leaf-to-stem ratio, phosphorus fertilizer use efficiency and water utilization of alfalfa tended to increase and then stabilize or decrease with the increase of phosphorus application under the same irrigation. The crude protein content tended to increase and then stabilize or decrease. The contents of the neutral and acid detergent fiber tended to decrease and then increase or stabilize. A better performance was achieved in the production, water and phosphorus utilization efficiency of alfalfa in the subsurface drip irrigation under the same phosphorus application, compared with the micro-sprinkler irrigation. Specifically, the subsurface drip irrigation increased the water use efficiency by 5.68% to 13.12%. The first principal component scores under different treatments were ranked as I₁P₂, I₂P₂, I₁P₁, I₂P₁, I₁P₃, I₂P₃, I₂P₀, I₁P₀ in descending order. The highest scores of alfalfas were obtained from the I₁P₂ treatment using principal components 1 and 2, in terms of the production performance, nutritional quality indexes, as well as water and phosphorus utilization efficiency indexes. An optimal combination was achieved in the subsurface drip irrigation and phosphorus application rate of 100 kg/hm². The higher utilization efficiency of water and phosphorus was achieved to significantly improve the production performance and nutritional quality of alfalfa. The finding can provide a sound basis for the production capacity, water and phosphorus utilization efficiency of alfalfa in Shihezi Reclamation Area and similar areas in Xinjiang of northwest China.