Characterization of sugar beet seedbed structure

Little information is available on the distribution and shape of aggregates or their spatial arrangement within seedbeds, although it influences crop emergence. The aim of this study was to obtain quantitative information on seedbed structure by sampling soil layers, sieving, surface photographs, and stereological analysis of embedded sample sections. Seedbeds prepared with a combined implement (spring tine cultivator and rollers) in a silt loam soil (Typic Hapludalf) with two seeders (K and Pl) on plowed (P), not plowed (NP), and not plowed and compacted (NPC) plots, were analyzed. Aggregates were described by measurements of L, l, h, the longest, intermediate and shortest axes and visually classified according to their surface roughness (smooth, 0; to rough, 4). The D fitting parameter of the power-law aggregate size distribution after seeding was significantly smaller (3.4) on NPC than on the other plots (3.8-4.0). The aggregate aspect ratios (l/L and h/L) did not vary with aggregate size or plot, their overall means were 0.77 and 0.55 respectively. Aggregates of roughness classes > 2 were 28 to 32% on NPC and NP plots, compared with 74% on P plot. Seeders reduced the number of aggregates > 10 mm by one-third compared with the values before seeding. Seeder K placed over 60% of the aggregates > 20 mm on the soil surface. Aggregates were uniformly distributed across the row by K seeder and away from the center of the row by P1 seeder. The information obtained will be used in a computerized seedbed generator.