黄土丘陵区小流域土地利用对土壤有机碳和全氮的影响

Effects of land use type on soil organic C and total N in a small watershed in loess hilly-gully region

通过野外调查和室内分析,研究了黄土丘陵沟壑区燕沟流域农地、果园、林地和草地0～20cm表层土壤的有机碳(SOC)和全氮(TSN)积累特征.结果表明:该区SOC含量平均值为7·56g·kg-1,TSN平均值为0·71g·kg-1.其中,农地SOC和TSN平均值分别为4·67和0·48g·kg-1,且梯田较低,川坝地较高.与农地相比,果园SOC(4·33g·kg-1)和TSN(0·46g·kg-1)平均值略有降低,草地较高.林地SOC和TSN平均值较农地高117·7%和89·4%.该区SOC和TSN含量的变异系数为69·7%和58·4%,以林地最大(62·8%和54·5%),草地和农地次之,果园最小(18·0%和22·9%).土壤C/N依果园、农地、草地和林地的顺序递增.该区各类土地利用方式下的SOC和TSN都呈极显著正相关(r=0·9791).黄土丘陵沟壑区基本农田建设和果园建设对SOC和TSN积累作用不明显;退耕还林还草、封山育林等土地利用优化措施明显促进了SOC和TSN的积累.

Based on field survey and laboratory analysis, this paper studied the storage of surface soil （0-20 cm） organic C （SOC） and total N （TSN） in farmland, orchard, woodland and grassland in the Yangou watershed of loess hilly-gully region. The results showed that in the test area, the mean contents of SOC and TSN were 7.56 and 0. 71 g·kg^-1, respectively. On an average, farmland had 4. 67 g·kg^-1 of SOC and 0. 48 g·kg^-1 of TSN, and terrace farmland had lower storage of SOC and TSN than other types of farmland. Compared with farmland, the contents of SOC and TSN in orchard had a slight decrease, being 4. 33 g·kg^-1 and 0. 46 g·kg^-1, respectively, while those in grassland were higher. The average contents of SOC and TSN in woodland were 117.7% and 89. 4% higher than those in farmland. In this area, the variation coefficients of SOC and TSN contents were 69. 7% and 58.4%, respectively, being the highest （62. 8% and 54. 5% ） in woodland, the second in grassland and farmland, and the smallest （ 18.0% and 22.9% ） in orchard. Soil C/N ratio was increased in the order of orchard, farmland, grassland, woodl and. Under these four landuse types, there was a significant positive correlation between SOC and TSN （ r = 0. 9791 ）. The construction of farmland and orchard didn＇ t increase the contents of SOC and TSN significantly, while the conversion of farmland into woodland or grassland and the hill-closure forestry promoted the accumulation of SOC and TSN distinctly.