The impact of irrigation on yield of alfalfa and soil chemical properties of saline-sodic soils

Background: Forage production in the saline-sodic soil of the western Songnen Plain Northeast China depends on irrigation. Therefore, the water use efficiency (WUE) and soil chemical properties are key factors in the overall forage productivity in this water scarce region. Improving forage yield, WUE, and soil properties under irrigation are very important for food and ecological security in this water-deficient region. Additionally, a suitable irrigation schedule for this region is necessary. Methods: A field experiment was conducted between 2015 and 2018 to evaluate the effects of irrigation on artificial grassland productivity and the changes in soil chemical properties as well as to plan a reliable irrigation schedule for the western Songnen Plain. Eight irrigation treatments were designed, which depended on the three growth stages of alfalfa. The shoot height (SH), the chlorophyll content (SPAD), the dry yield (DM), the ratio of stem to leaves (SLR), the WUE, the changes in the chemical properties of the soil, and precipitation and evaporation were investigated. Results: The SH, DM, WUE, and SLR were significantly increased by irrigation (P < 0.01). However, the SPAD resulting from irrigation was not significantly higher than the SPAD of CK (no irrigation) (P < 0.05). In addition, the soil chemical properties at the depth of 0-100 cm were significantly decreased by irrigation P (0.05). For example, the soil electrical conductivity, sodium absorption ratio, and total alkalization were reduced 182-345 mu S cm(-1), 8.95-9.00 (mmol(c)/L) 1/2, and 3.29-4.65 mmol(c) L-1 by different irrigation treatments, respectively. Finally, considering the highest WUE of I5 (irrigation at branch stage) (2.50 kg m(-3)), relative high DM of I5 (787.00 g m(-2)), the precipitation, the evaporation, the water resources, and the changes of the soil's chemical properties, 236.50 mm of irrigation water was recommended at the branching stage of alfalfa for the western Songnen Plain, Northeast China.