黄土高原不同树龄苹果园土壤水分及硝态氮剖面特征

为揭示黄土高原农田转变为苹果园后土壤水分及硝态氮剖面变化特征,以洛川县为研究区,采集农田(对照)和8,17,25年苹果园共40个0-600 cm剖面土样,分析土壤水分、NO3--N浓度及其储量。结果表明:与农田相比,8年苹果园0-600 cm土壤水分含量及贮水量偏高(旧县镇)或相当(槐柏镇),而NO3--N浓度及其累积量则没有显著差异;17,25年苹果园0-600 cm土层贮水量则显著降低(P<0.05),分别下降150,230 mm,且该差异主要与300 cm以下土层水分变化有关;0-500 cm土层NO3--N浓度随苹果种植年限显著增加,17,25年苹果园0-600 cm土层NO3--N累积量分别为6 830,8 370 kg/hm2,二者显著高于农田(695 kg/hm2)和8年果园(440 kg/hm2)。综合可知,农田转变为苹果园这一土地利用方式变化可导致深层土壤水分亏缺(>300 cm)和硝态氮累积,黄土高原大力发展苹果种植过程中应重视蓄水保墒及氮肥减施等措施。

Evaluating the Vertical Distributions of Soil Moisture and Nitrate in Apple Orchards with Different Ages in the Loess Plateau

To characterize the changes in vertical distributions of soil moisture and nitrate following conversion to apple orchard from cropland in the Loess Plateau, 40 600 cm depth soil profiles were sampled from farmland (as control), 8, 17 and 25 yr old apple orchards in Luochuan county to determine soil moisture content, nitrate concentration and their storage. The results showed that 8 yr old apple orchards were similar to cropland in soil nitrate concentrations (SNC) and residual soil nitrate (RSN), and also presented equal (Jiuxian) or even higher (Huanbai) values of soil moisture content (SWC) and soil water storage (SWS) when compared with cropland. In contrast, the 17 and 25 yr old apple orchards significantly decreased SWS by 150 and 230 mm, respectively, which was mainly associated with the SWC changes in soils deeper than 300 cm. SNCs in the 0-500 cm layers increased significantly with the standing ages of apple orchard, and RSNs accumulated in the 0-600 cm profile were 6 830 and 8 370 kg/hm², corresponding to 17 and 25 yr old apple orchards, respectively, which were appreciably higher than that of 8 yr old apple orchard (440 kg/hm²) and cropland (695 kg/hm²). Thus, we concluded that converting cropland to apple orchard could result in soil water deficit, especially in > 300 cm soil depth, and nitrate accumulation, so, the strategies including water-conserving and strict controls on N fertilizer should be adopted to mitigate the unfavorable impacts caused by the enlargement of apple orchard in the Loess Plateau.