黄土丘陵沟壑区坝地和梯田土壤养分特征与演变

目的]了解黄土丘陵沟壑区坝地和梯田土壤养分状况,为合理利用土地资源和恢复改善生态环境提供科学依据。方法]以陕西省延安市碾庄沟流域为研究区,以荒坡地作为对照,研究黄土丘陵沟壑区坝地和梯田土壤演变特征。结果]速效磷、速效钾、有机质、全磷和全钾含量表现为梯田坝地,全氮含量表现为坝地梯田,除土壤钾素处于中等变异水平,其他土壤养分均处于高等变异水平,其中磷素和全氮变异系数较大。在80 cm剖面内,坝地和梯田土壤速效磷、速效钾、有机质和全氮均具有明显的表聚性特征,全钾和全磷剖面分布均匀。在水平位置上,坝尾和上坡梯田养分含量更高,供肥性能更好。随着利用年限的增加,除全钾外,梯田养分表现为明显的先减后增的趋势;坝地速效磷、全氮和全磷表现为先减后增的趋势,速效钾、有机质和全钾表现为先增后减的趋势。坝地土壤养分变化的分水岭年限(45～50 a)比梯田(30 a)滞后至少15 a。结论]目前该区域除钾素外,土壤磷素、氮素和有机质均处于缺乏状态,亟待补充,应定期关注接近拐点年限的土壤养分状况。通过合理的管理措施,延长土地利用年限,促进农田土壤肥力可持续发展。相较于坝地和梯田,荒坡地土壤养分最高,供肥性能最好,变异系数最小,但其剖面分布不均匀,需翻地改善。

Characteristics and Evolution of Soil Nutrients of Dam Land and Terrace in a Loess Hilly Area

Objective] The soil nutrient status of dam land and terrace in a loess hilly area was studied to provide a scientific basis for the rational utilization of land resources, and restoration and improvement of the ecological environment.Methods] The characteristic evolution of soil nutrients of dam land and terrace was studied in contrast to a barren slope in the Nianzhuang Gully watershed of Yan''an City, Shaanxi Province.Results] The content of rapidly available phosphorus (AP), rapidly available potassium (AK), organic matter (OM), total phosphorus (TP), and total potassium (TK) was found in the order of terrace > dam land, whereas the total nitrogen (TN) content was of the order of dam land > terrace. AK and TK were found at medium variation levels, whereas the other soil nutrients were at higher variation levels. In the 80 cm section, the AP, AK, OM, and TN in the dam land and terrace displayed phenotypic characteristics, and the distribution of the TP and TK profiles was uniform. In the horizontal position, the nutrient content of the dam tail and uphill terrace was higher than that of the other positions, and fertilizer performance was better. With an increase of the years of utilization, the nutrients found in the terrace (except for TK content) showed a significant trend of a decrease at first and then an increase. The AP, TN, and TP content of the dam land showed the same trend of a decrease at first and then an increase, whereas AK, OM, and TK content of the dam land showed an increase trend at first and then a decrease. The critical year (45~50 years) of the degradation of soil nutrient change in the dam land lagged by at least 15 years that of the terrace (approximately 30 years).Conclusion] At present, except for TK, the TP, TN, and OM content of dam land, terrace, and barren slope are in short supply. Thus, regular attention should be paid to the condition of soil nutrients close to the turning point and targeted supplementary fertilizer should be added promptly to extend the land use life via reasonable management measures and the promotion of the sustainable development of farmland. Compared with dam land and terrace, the soil nutrients in the barren slope were the highest, the fertilizer supply performance was the best, and the coefficient of variation was the smallest. However, the profile distribution was not uniform and required soil preparation.