Changes in soil nitrogen availability due to stand development and management practices on semi-arid sandy lands, in northern China
2009
Chen, F.S. | Zeng, D.H. | Fahey, T.J.
Soil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle-aged, close-to-mature) and management practices (non-grazing and free-grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH₄ ⁺-N, NO₃ ⁻-N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58 μg d⁻¹ g⁻¹ dry resin, and 0·76 to 0·97, respectively, and NO₃ ⁻-N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non-grazing sites lower than those in free-grazing sites (p < 0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area.
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