中文摘要：

为了确定小麦（Triticum aestivum）、玉米（Zeamays）根系的最优取样位置和更准确地模拟根长密度在土壤剖面的分布，在冬小麦和夏玉米的灌浆后期，采用根钻法取样，比较了不同取样位置对根系分布的影响；采用Gerwitz和Page模型对根长密度的分布进行了模拟。结果表明，冬小麦行间和行上取样在0-10cm土层根长密度差异显著，在10cm以下土层差异减少。在确定根长密度分布的取样中，在0-20cm土层应考虑根长密度分布的空间差异，即行上密度大于行间密度；而在20-100cm土层，需要考虑行间根长密度大于行上的空间差异；在lm以下土层两个位置的差异逐渐消失，可不考虑空间差异。夏玉米根长密度在上层土壤表现出距离植株不同位置差异显著的特征。植株位置（株上）、距植株10cm和距植株20cm位置根长密度在土壤中的分布特征是：0-10cm土层3个位置根长密度差异在50％以上，根长密度大小是株上〉距植株10cm〉距植株20cm；而在10-30cm层次，根长密度表现为距植株10cm〉株上〉距植株20cm，30—50cm土层株上位置的根长密度最小，50cm以下各位置根长密度差异不明显。对于玉米根系取样，50cm以上土层需要考虑根长密度的空间差异，50cm以下土层可不考虑。采用Gerwitiz和Page模型，结合华北平原机械化耕作下形成的土壤犁底层变厚及其犁底层容重增加对根系分布的影响，在模型中加入土壤容重参数订正可以使模型更准确地模拟根长密度在土壤剖面的分布。

英文摘要：

Aims Our objectives were to optimize the positions for root sampling of winter wheat and maize and to simulate the distribution of root length density （RLD） throughout the root zone profile in the North China Plain. Methods Soil cores were taken at different locations in fields of winter wheat and summer maize at the grain-fill stage, and results were compared to decide the positions for root sampling. The bulk density parameter was used to modify the Gerwitz and Page model to increase the accuracy in simulating the distribution of RLD throughout the soil profile. Important findings There was a larger spatial difference in RLD in the 0-10 cm soil layer for winter wheat. The difference became smaller below the 10 cm soil layer. For the top 20 cm soil layer, RLD on the row was greater than that between two rows. However, below 20 cm, the situation was reversed, i.e., RLD between two rows was greater than that on the row, indicating the strong proliferation ability of the root system of winter wheat. For maize, RLD sampled at the stem was greater than that sampled 10 cm away from the stem, and much greater than that sampled 20 cm away from the stem for the 0-10 cm soil layer. Below the 10 cm soil layer, RLD was highest sampled 10 cm away from the stem. RLD sampled at the stem around the 30-50 cm soil layer was the lowest among the three positions. The results indicated that in the top soil layer, RLD immediately under the plants was the highest, and RLD decreased with increased distance away from the plant stem. However, with increased soil depth, root proliferation reduced the differences among locations. The high bulk density of soil pan around 10-30 cm significantly influenced the shape of the curve of RLD distribution along the soil profile. Introducing the bulk density parameter into the Gerwitz and Page model significantly reduced the errors of simulated and measured RLD throughout the root zone profile.