Management practices are needed to reduce soil C losses from croplands converted from Conservation Reserve Program (CRP) grassland. We evaluated the effects of irrigation, tillage, cropping system, and N fertilization on surface residue and soil organic C (SOC) at the 0- to 85-cm depth in relation to crop yields in a sandy loam soil from 2005 to 2011 in croplands converted from CRP in western North Dakota. Treatments were two irrigation practices (irrigated vs. nonirrigated) as the main plot and six cropping systems [CRP, conventional till malt barley (Hordeum vulgare L.) with N fertilizer (CTBN), conventional till malt barley without N fertilizer (CTBO), no-till malt barley- pea (Pisum sativum L.) with N fertilizer (NTB-P), no-till malt barley with N fertilizer (NTBN), and no-till malt barley without N fertilizer (NTBO)] as the split plot arranged in a randomized complete block with three replications. Soil surface residue amount and C content were greater in CRP and NTBN than the other cropping systems. At 0 to 5 cm, SOC was greater in irrigated CRP, but at 0 to 85 cm it was greater in nonirrigated NTBN than most other treatments. At 0 to 20 cm, SOC increased by 0.26 to 1.21 Mg C ha-1 yr-1 in NTB-P and CRP but decreased by 0.02 to 0.68 Mg C ha-1 yr-1 in other cropping systems. Surface residue C and SOC at 0 to 10 cm were related to annualized crop grain yield (R2 = 0.45-0.77, P x? 0.12, n = 10). Because of positive C sequestration rate and favorable crop yields, NTB-P may be used as a superior management option to reduce soil C losses and sustain yields in croplands converted from CRP in the northern Great Plains.
