Abstract:

The Songnen Plain faces an escalating ecological threat due to persistent soil salinization. This study aimed to establish an artificial grassland system integrating straw biochar application （CK： 0 t·ha^-1， T₁： 20 t·ha^-1， T₂： 40 t·ha^-1） with Leymus chinensis and Puccinellia tenuiflora， two forage grasses tolerant to salt-alkali soil. We analyzed the effects of biochar addition on soil physicochemical properties， grass physiology， and production performance. The results showed that soil pH and electrical conductivity did not significantly change in the first year following biochar application. However， in the second year， the soil pH and electrical conductivity showed the largest decreases in the T₁ treatment， with increasing biochar application leading to sustained increases in water content and porosity and continuous decreases in soil bulk density. Biochar addition significantly reduced the sodium ion （Na⁺） content in soil in L. chinensis grassland （P<0.05）， whereas the soil Na⁺ content in P. tenuiflora grassland only decreased in the second year. The calcium ion （Ca²⁺） content in soil was higher in the T₁ treatment than in CK over the 2-year observation period， with the difference being more pronounced in the second year （L. chinensis： 0.91-1.60 mg·kg^-1； P. tenuiflora： 0.91-1.08 mg·kg^-1）. The magnesium ion （Mg²⁺） content in soil decreased by 35.2% （P<0.05） under the T₂ treatment in P. tenuiflora grassland in the first year， while in the second year， the soil Mg²⁺ content significantly increased under the T₂ treatment in both grasslands （L. chinensis： 45.5%， P. tenuiflora： 66.8%）. In both grasslands， the sodium adsorption ratio （SAR） and exchangeable sodium percentage （ESP） of the soil generally showed significant reductions under the T₁ treatment， but showed greater fluctuations in the T₂ treatment. The contents of soil ammonium nitrogen （NH₄⁺-N） and nitrate nitrogen （NO₃^--N） in soil did not change significantly in the first year. However， in the second year， the ammonium nitrogen （NH₄⁺-N） content in soil was signigicantly higher in the T₁ and T₂ treatments than in CK， and the nitrate nitrogen （NO₃^--N） content in soil was also increased. Biochar application significantly enhanced the chlorophyll content in L. chinensis （T₁： 10.3%， T₂： 8.2%）， but reduced the contents of proline （T₁： 18.7%， T₂： 38.1%） and soluble sugars （T₁： 15.0%， T₂： 26.7%）. Under the synergistic soil-plant interaction in this grassland system， biochar addition significantly increased the forage yield of L. chinensis （T₁： 12.9%， T₂： 18.3%）， but only the T₂ treatment promoted the forage yield of P. tenuiflora （by 28.8%）， indicating that a higher biochar application rate is required to increase P. tenuiflora yield. Comparative analysis of the effects of forage grasses to improve soil quality revealed that L. chinensis reduced the Na⁺ content more effectively than did P. tenuiflora. Therefore， priority should be given to the integrated biochar-L. chinensis artificial grassland system in moderately saline-alkali regions， because it facilitates the restoration of degraded grassland and enhances the forage yield.

Key words: saline-alkali land, biochar, soil improvement, Leymus chinensis, Puccinellia tenuiflora