SOIL AND CROP MANAGEMENT Seedbed Surface Geometry Effects on Soil Crusting and Seedling Emergence

straw intercepted drop impact energy or surface applied powdered phospho-gypsum reduced aggregate disperSeedling emergence is the crucial first step in crop establishment; sion the infiltration rate decreased more gradually, rehowever, crops frequently must penetrate or lift a thin, dense, soil quiring approximately 45 min to reach 10 mm h 1, comlayer called a crust, which is formed by drop impact or aggregate pared with the untreated control. slaking during rainstorms and sprinkler irrigation. Shaping the soil surface into a small ridge or cap above the seed row may decrease The study of soil crusts and search for suitable mancrust strength and improve seedling emergence. Our objectives were agement practices to improve seedling emergence asto quantify the effects of surface soil geometry (25 mm high by 50 mm sumes a global scope (Awadhwal and Thierstein, 1985) wide soil cap without removal) on (i) crust formation and strength, and highlights the need to improve seedling emergence (ii) seedling emergence of selected crops, and (iii) seed zone soil for greater crop yield (Daba, 1999). Emerging seedlings temperature. Sieved ( 12 mm) Pullman clay loam soil (Torrertic must either grow through a natural break in the crust Paleustoll) was packed into columns (0.30 m wide by 0.45 m long by or exert a force in excess of the crust strength to fracture 0.15 m deep) and planted with grain sorghum [Sorghum bicolor (L.) or lift the crust (Miller and Gifford, 1974). The force Moench], corn (Zea mays L.), sunflower (Helianthus annuus L.), and exerted by a germinating seedling varies from 0.15 N wheat (Triticum aestivum L.) in rows with a flat or capped surface. for alfalfa to 4.0 N for corn depending on water imbibiColumns were mounted at a 5% slope on a turntable beneath a rotating disk-type rain simulator that applied reverse osmosis water tion and other growth limiting factors such as temperafor 1 h at a 48 mm h 1 intensity with intercepted or normal drop impact ture and seed mass (Goyal et al., 1980). For cotton energy. Compared with intercepted (INT) drop impact conditions, (Gossypium hirsutum L.) seedlings exerting a force of normal drop impact (DI) reduced infiltration 22% and formed 4.9 mm 3.02 to 4.63 N, the corresponding measured axial presthicker crusts that prevented seedling emergence. Thickness, penetrasure (or maximum penetrable crust strength) varied tion resistance, and seedling emergence of DI soil crusts were unaffrom 1.25 to 1.90 MPa. Studies on the southern Great fected by surface caps. Mean seed zone soil temperatures increased Plains showed that as penetrometer resistance of a with INT drop impact, but was unaffected by capping. Our test shows crusted soil increased from 0 to 1.0 MPa cotton seedling that unremoved soil caps did not improve seedling emergence; howemergence decreased from 78 to 21% 2 d after planting ever, intercepting raindrop impact increases seedling emergence. (Bilbro and Wanjura, 1982). In a study of tillage effects on crusting following sprinkler irrigation, Unger (1984) reported little difference in sorghum seedling emerT imely seedling emergence is crucial to crop estabgence or the corresponding overall mean crust strengths lishment and overall plant vigor, but seedling emerof 0.33 to 0.54 MPa. He did report severe crusting folgence is frequently governed by soil surface conditions. lowing an intense natural rainstorm, which resulted in One such surface condition that acts as a significant mean crust strengths that varied from 0.43 to 1.15 MPa barrier to emerging crop seedlings is the presence of and could have depressed seedling emergence. a thin, dense, cemented soil surface layer or crust as Seedling emergence through soil crusts may be endescribed in review articles by Kemper and Miller hanced with irrigation (when available) that wets and (1974), Awadhwal and Thierstein (1985), and Singer softens the crust, as shown for the Pullman soil where and Warrington (1992). Physical soil crusts develop as crust strength was reduced by higher water contents raindrops disperse aggregates and detach soil particles (Unger, 1984). Management practices such as applicathat enter and occlude soil surface pores, consequently tions of straw and phospho-gypsum not only increased reducing infiltration and permitting additional sediment infiltration, but also decreased the 10-d mean crust pendeposition in the thickening surface layer or crust. For etration resistance from 0.70 MPa for the control to 0.20 example, Benyamini and Unger (1984) showed that the and 0.50 MPa for straw and phospho-gypsum treatments developing crust on a Pullman soil rapidly decreased (Benyamini and Unger, 1984). Consequently, the correthe infiltration rate of simulated rain from 42 to 4 mm sponding seedling emergence with straw increased 24% h 1 in approximately 25 min; however, where wheat compared with the control. Others have attempted to improve seedling emergence through crusts by managR.L. Baumhardt and P.W. Unger, USDA-ARS, Conservation and ing soil cracking without success (Miller and Gifford, Production Res. Lab., P.O. Drawer 10, Bushland TX 79012-0010; and 1974). Alternatively, Kemper and Miller (1974) reT.H. Dao, USDA-ARS, BARC-East, AMBL, Bldg. 306, Rm 102, ported that cotton producers in California control seBeltsville, MD 20705-2350. Received 4 Oct. 2003. *Corresponding author ([email protected]). Abbreviations: CAP, mounded surface treatment; DI, drop impact; Published in Agron. J. 96:1112–1117 (2004).  American Society of Agronomy FLAT, unmounded surface treatment; INT, intercepted drop impact; RO, reverse osmosis water. 677 S. Segoe Rd., Madison, WI 53711 USA