Soil and crop management - Seedbed surface geometry effects on soil crusting and seedling emergence

Seedling emergence is the crucial first step in crop establishment; however, crops frequently must penetrate or lift a thin, dense, soil layer called a crust, which is formed by drop impact or aggregate slaking during rainstorms and sprinkler irrigation. Shaping the soil surface into a small ridge or cap above the seed row may decrease crust strength and improve seedling emergence. Our objectives were to quantify the effects of surface soil geometry (25 mm high by 50 mm wide soil cap without removal) on (i) crust formation and strength, (ii) seedling emergence of selected crops, and (iii) seed zone soil temperature. Sieved (<12 mm) Pullman clay loam soil (Torrertic Palenstoll) was packed into columns (0.30 m wide by 0.45 m long by 0.15 m deep) and planted with grain sorghum [Sorghum bicolor (L.) Moench], corn (Zea mays L.), sunflower (Helianthus annuus L.), and wheat (Triticum aestivum L.) in rows with a flat or capped surface. Columns were mounted at a 5% slope on a turntable beneath a rotating disk-type rain simulator that applied reverse osmosis water for 1 h at a 48 mm h(-1) intensity with intercepted or normal drop impact energy. Compared with intercepted (INT) drop impact conditions, normal drop impact (DI) reduced infiltration 22% and formed 4.9 mm thicker crusts that prevented seedling emergence. Thickness, penetration resistance, and seedling emergence of DI soil crusts were unaffected by surface caps. Mean seed zone soil temperatures increased with INT drop impact, but was unaffected by capping. Our test shows that unremoved soil caps did not improve seedling emergence; however, intercepting raindrop impact increases seedling emergence.