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Nitrogen Dynamics Affected by Management Practices in Croplands Transitioning from Conservation Reserve Program

Sainju, Upendra M., Stevens, William B., Caesar-TonThat, Thecan, Montagne, Cliff
Agronomy Journal 2014 v.106 no.5 pp. 1677-1689
Conservation Reserve Program, Hordeum vulgare, Pisum sativum, ammonium nitrogen, conventional tillage, crop rotation, cropland, crops, fertilizer application, irrigated farming, irrigation, land use change, leaching, losses from soil, malt, malting barley, mineralization, nitrate nitrogen, nitrogen, nitrogen fertilizers, no-tillage, peas, sandy loam soils, soil fertility, soil nutrient balance, soil nutrients, surface storage, North Dakota
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.