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Title:   Author  item
                                            Sainju, Upendraitem
                                            Stevens, William

                                                         - *Bart*item
                                            Caesar, Thecanitem
                                            MONTAGNE, CLIFF - Montana State University
  Submitted to: Agronomy Journal
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 6/11/2014
                                    Publication  Date: 8/8/2014
                                    Citation: Sainju, U.M., Stevens, W.B., Caesar, T., Montagne, C. 2014. Nitrogen dynamics affected by management practices in croplands transitioning from Conservation Reserve Program. Agronomy Journal. 106(5):1677-1689.Interpretive Summary: Increased demand for food due to a growing world population has accelerated conversion of grasslands, such as Conservation Reserve Program (CRP), into croplands. Conversion of grasslands into croplands can reduce soil N storage due to increased N mineralization and losses through leaching, volatilization, denitrification, and surface runoff. Nitrogen fertilization can increase crop yields, but excessive application can degrade soil and environmental quality by increasing soil acidification, N leaching, and emissions of N2O, a highly potent greenhouse gas that contributes to global warming. An increase in soil N storage can reduce N losses through leaching, volatilization, denitrification, surface runoff, erosion, and N2O emissions. Improved management practices are needed to restore soil N levels and reduce N losses from CRP land converted to croplands. 
We evaluated the effects of irrigation, tillage, cropping system, and N fertilization on surface residue N, soil total N (STN), NH4-N, NO3-N, and N balance at the 0-85 cm depth in a sandy loam soil from 2005 to 2011 in the CRP land converted to cropland in western North Dakota, USA. Treatments were two irrigation practices (irrigated vs. non-irrigated) and six cropping systems (CRP, conventional till malt barley with N fertilizer [CTBN], conventional till malt barley without N fertilizer [CTBO], no-till malt barley-pea with N fertilizer [NTB-P], no-till malt barley with N fertilizer [NTBN], and no-till malt barley without N fertilizer [NTBO]). 
Soil surface residue N content was greater in non-irrigated CRP than other treatments, except irrigated CRP and NTBN. Soil total N at 0-10 cm was greater in irrigated CRP, but at 0-85 cm was greater in non-irrigated NTBN than other treatments, except non-irrigated CRP, CTBN, CTBO, and NTBO. From 2005 to 2011, STN at 0-20 cm increased from 66 kg N ha-1 yr-1 in CTBN and CTBO to 173 kg N ha-1 yr-1 in CRP, regardless of irrigation practices. Soil NH4-N content at 0-20 cm was also greater in irrigated CRP than other treatments, except irrigated CTBN and NTBN. Soil NO3-N content at 0-85 cm was greater in NTB-P than in CRP, CTBO, and NTBO. Estimation of N balance using N sources and sinks from 2005 to 2011 indicated that non-irrigated CTBN gained 1131 kg N ha-1 compared to losses of 320 to 1554 kg N ha-1 in irrigated cropping systems, except irrigated NTB-P which gained 237 kg N ha-1. 
Perennial cropping systems, such as CRP, increased soil N storage at surface layers, compared to annual cropping systems. Because of increased soil N sequestration and greater NO3-N level, irrigated NTB-P may be used as a management option to increase soil N storage and optimize N availability to crops compared to other treatments in annual cropping systems and reduce N losses from the CRP land converted to croplands.
                                Technical Abstract: Soil N may be lost through mineralization, leaching, and other processes when land under the Conservation Reserve Program (CRP) is converted into croplands. Improved management practices are needed to restore soil N levels and reduce N losses. We evaluated the effects of irrigation, tillage, cropping system, and N fertilization on surface residue N, soil total N (STN), NH4-N, NO3-N, and N balance at the 0-85 cm depth in a sandy loam soil from 2005 to 2011 in the CRP land converted to cropland in western North Dakota, USA. Treatments were two irrigation practices (irrigated vs. non-irrigated) and six cropping systems {CRP, conventional till malt barley (Hordeum vulgaris 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]}. Soil surface residue N content was greater in non-irrigated CRP than other treatments, except irrigated CRP and NTBN. Soil total N at 0-10 cm was greater in irrigated CRP, but at 0-85 cm was greater in non-irrigated NTBN than other treatments, except non-irrigated CRP, CTBN, CTBO, and NTBO. From 2005 to 2011, STN at 0-20 cm increased from 66 kg N ha-1 yr-1 in CTBN and CTBO to 173 kg N ha-1 yr-1 in CRP, regardless of irrigation practices. Soil NH4-N content at 0-20 cm was also greater in irrigated CRP than other treatments, except irrigated CTBN and NTBN. Soil NO3-N content at 0-85 cm was greater in NTB-P than in CRP, CTBO, and NTBO. Estimation of N balance using N sources and sinks from 2005 to 2011 indicated that non-irrigated CTBN gained 1131 kg N ha-1 compared to losses of 320 to 1554 kg N ha-1 in irrigated cropping systems, except irrigated NTB-P which gained 237 kg N ha-1. Perennial cropping systems, such as CRP, increased soil N storage at surface layers, compared to annual cropping systems. Because of increased soil N sequestration and greater NO3-N level, irrigated NTB-P may be used as a management option to increase soil N storage and optimize N availability to crops compared to other treatments in annual cropping systems and reduce N losses from the CRP land converted to croplands.


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