Continuous Nitrogen Application Differentially Affects Growth, Yield, and Nitrogen Use Efficiency of Leymus chinensis in Two Saline-Sodic Soils of Northeastern China

Leymus chinensis (Trin.) Tzvel. (Poaceae) is a dominant plant in the western Songnen Plain of northeastern China. Soil salinization, N deficiency, and current management practices have resulted in grassland degradation in the region. The objective of this study was to investigate the effect of N application on L. chinensis. A 3-yr field experiment was conducted in two nearby fields at the Da'an Sodic Land Experiment Station (DASLES) from 2009 to 2011. Both fields were classified as moderate saline-sodic grassland (MSSL) and severe saline-sodic grassland (SSSL), respectively. Nitrogen application rates were 0 (no fertilizer as control), 30, 60, 90, 120, 150, 180, and 210 kg N ha(-1). Nitrogen application improved herbage yield from 2.0 t ha(-1) without N to more than 107 t ha(-1) with 180 kg ha(-1) N in MSSL, and from 1.0 t ha(-1) without N to 4.9 t ha(-1) with 180 kg ha(-1) N in SSSL, herbage yields increased 5.4 and 4.9 times in MSSL and SSSL, respectively. Nitrogen use efficiency (NUE) was generally higher in NISSL than that in SSSL, the highest values of average NUL were the treatments with 120 kg N ha(-1) in MSSL and 150 kg N ha(-1) in SSSL based on the results of regression analysis. Our overall results support N applications of 90 to 120 kg N ha(-1) in MSSL and 120 to 150 kg N ha(-1) in SSSL. Nitrogen application can improve L. chinensis yield, and prevent grassland degradation in the region.