The James Hutton Institute, Dundee, UK.
Ann Bot. 2012 Jul;110(2):259-70. doi: 10.1093/aob/mcs118. Epub 2012 Jun 8.
Simple indicators of crop and cultivar performance across a range of soil types and management are needed for designing and testing sustainable cropping practices. This paper determined the extent to which soil chemical and physical properties, particularly soil strength and pore-size distribution influences root elongation in a wide range of agricultural top soils, using a seedling-based indicator.
Intact soil cores were sampled from the topsoil of 59 agricultural fields in Scotland, representing a wide geographic spread, range of textures and management practices. Water release characteristics, dry bulk density and needle penetrometer resistance were measured on three cores from each field. Soil samples from the same locations were sieved, analysed for chemical characteristics, and packed to dry bulk density of 1.0 g cm(-3) to minimize physical constraints. Root elongation rates were determined for barley seedlings planted in both intact field and packed soil cores at a water content close to field capacity (-20 kPa matric potential).
Root elongation in field soil was typically less than half of that in packed soils. Penetrometer resistance was typically between 1 and 3 MPa for field soils, indicating the soils were relatively hard, despite their moderately wet condition (compared with <0.2 MPa for packed soil). Root elongation was strongly linked to differences in physical rather than chemical properties. In field soil root elongation was related most closely to the volume of soil pores between 60 µm and 300 µm equivalent diameter, as estimated from water-release characteristics, accounting for 65.7 % of the variation in the elongation rates.
Root elongation rate in the majority of field soils was slower than half of the unimpeded (packed) rate. Such major reductions in root elongation rates will decrease rooting volumes and limit crop growth in soils where nutrients and water are scarce.
为了设计和测试可持续的种植实践，需要有一系列土壤类型和管理措施下作物和品种表现的简单指标。本研究使用基于幼苗的指标，确定了土壤化学和物理特性（尤其是土壤强度和孔径分布）在多大程度上影响了广泛的农业表土中幼苗根系的伸长。
从苏格兰 59 个农业田地的表土中采集完整的土壤芯，代表了广泛的地理分布、质地范围和管理实践。对每个田地的三个土壤芯测量水分释放特性、干体密度和针入阻力。来自同一地点的土壤样本进行筛分，分析化学特性，并填充到干体密度为 1.0 g cm(-3)以最小化物理限制。将接近田间持水量（-20 kPa 基质势）的水含量种植在完整田间和填充土壤芯中的大麦幼苗的根伸长率进行了测定。
田间土壤中的根伸长率通常不到填充土壤的一半。针入阻力对于田间土壤通常在 1 到 3 MPa 之间，表明土壤相对较硬，尽管其处于中度湿润状态（与填充土壤的<0.2 MPa 相比）。根伸长与物理特性而不是化学特性的差异密切相关。在田间土壤中，根伸长与水释放特性估计的 60 µm 至 300 µm 当量直径之间的土壤孔隙体积差异最密切相关，解释了伸长率变化的 65.7%。
在大多数田间土壤中，根伸长率比无阻（填充）速率慢一半。在养分和水分稀缺的土壤中，这种根系伸长率的大幅降低将减少根系体积并限制作物生长。
