Management practices are needed to reduce N losses from croplands converted from Conservation Reserve Program (CRP). We evaluated the effects of irrigation, tillage, cropping system, and N fertilization on surface residue N, soil total nitrogen (STN), NH 4-N, and NO 3-N at the 0- to 85-cm depth in a sandy loam from 2005 to 2011 in croplands converted from CRP in western North Dakota. Treatments were two irrigation practices (irrigated vs. non-irrigated) and six cropping systems (CRP, conventional till malt barley [ Hordeum vulgaris L.] with nitrogen fertilizer [CTBN], conventional till malt barley without nitrogen fertilizer [CTBO], no-till malt barley-pea ( Pisum sativum L.) with nitrogen fertilizer [NTB-P], no-till malt barley with nitrogen fertilizer [NTBN], and no-till malt barley without nitrogen fertilizer [NTBO]). Surface residue N was greater in non-irrigated CRP than irrigated and non-irrigated CTBN, CTBO, and NTBO and non-irrigated NTB-P. Soil total N at 0 to 10 cm was greater in irrigated CRP, but at 0 to 85 cm was greater in non-irrigated NTBN than irrigated CRP, CTBN, CTBO, and NTBO and non-irrigated NTB-P. Soil NH 4-N content at 0 to 20 cm was also greater in irrigated CRP than irrigated and non-irrigated CTBO, NTB-P, and NTBO. Soil NO 3-N at 0 to 85 cm was greater in NTB-P than CRP, CTBO, and NTBO. Because of increased soil N sequestration and NO 3-N level, irrigated NTB-P may be used to reduce soil N losses and optimize N availability compared to other treatments in croplands converted from CRP.
