干旱区生态环境知识资源中心

Overwinter N leaching increases the potential for NO3 contamination of ground water under irrigated desert soils. Our objectives were to (i) identify winter cover crops for recovering N and (ii) determine the N availability following green manure cover crops relative to N uptake by a succeeding potato (Solanum tuberosum L.) crop. A 2-yr field study was conducted on commercial fields on Quincy loamy sand (mixed mesic Xeric Torripsamments). Cover crops were seeded following sweet corn (Zea mays L.) as fall-incorporated sudangrass (Sorghum bicolor L., ’sordan’); fall- and spring-incorporated white mustard (Brassica hirta Moench, ’Martegena’); and spring-incorporated wheat (Triticum aestivum L., ’stevens’), rapeseed (B. napus L., ’Jupiter’), and rye (Secale cereale L.). Potato (’Russet Burbank’) was planted 3 to 5 wk after spring incorporation of green manures. All cover crops except sudangrass accumulated 112 to 142 kg N ha(-1) when planted in August at Plymouth, WA, but N uptake was decreased by >50% when planted in September at Quincy, WA. Over-wintering cover crops lowered soil mineral N at 0 to 180 cm by 155 kg N ha(-1) compared with bare fallow at Plymouth. Fall-incorporated mustard released greater inorganic N over the winter compared with spring incorporation. Soil NH4 and NO3 increased following overwintering cover crops by potato planting, providing timely increases in N availability to the potato crop. Winter cover crops can improve N cycling and reduce the amount of N below the root zone in potato-based rotations.