|Pikul Jr, Joseph|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2011
Publication Date: 6/15/2011
Citation: Allen, B.L., Pikul Jr, J.L., Cochran, V.L., Waddell, J.T. 2011. Long-term Lentil Green-manure Replacement for Fallow in the Semiarid Northern Great Plains. Agronomy Journal. 103:1292-1298.
Interpretive Summary: Green manure crops reduce fertilizer N application and could potentially replace summer fallow. A 12-year study in NE Montana determined wheat yield during the first five years was 33% less in a non-fertilized wheat-green manure (W-GM) rotation than in a fertilized wheat-fallow (W-F) rotation, partly due to lower soil nitrate. However, during the latter six years wheat yield differed by 2%, due in part to 26% greater spring soil nitrate from increased N-cycling on W-GM rotations than on W-F rotations. Water use during non-wheat periods was similar in W-GM and W-F when lentil was killed at full bloom, but when grown to lower pod set W-GM used 20% more water than W-F. After 11 yr soil organic C (SOC) in the surface 15 cm declined 8% for W-GM and 10% for W-F. Green manure, with proper management, maintains water productivity, offsets fertilizer N needs after about three cropping cycles, and reduces SOC depletion compared with traditional wheat-fallow rotations.
Technical Abstract: Summer fallow results in inefficient precipitation use and could potentially be replaced with a green manure (GM) crop that reduces fertilizer N application. A 12-year study near Culbertson, MT on a Williams loam (fine-loamy, mixed Typic Argiboroll) determined GM impacts on soil-N fertility, soil organic carbon (SOC), water use, yield, and water productivity of spring wheat (Triticum aestivum L.). Lentil (Lens culinaris Medikus cv. Indianhead) was grown in rotation with non-fertilized spring wheat and killed by mechanical (ML) or chemical (CL) methods. Inorganic N fertilizer treatments were annually cropped wheat (AW), and wheat-fallow rotations (FR) with mechanical (MF) or chemical (CF) fallow management. Wheat yield during the first five years of the study was 33% less on GM than FR partly due to lower soil nitrate. During the latter six years wheat yield differed by 2%, due in part to 26% greater spring soil nitrate (0-0.6 m) on GM than FR. A soil nitrogen mass balance approach for the latter six years showed a 2.2-fold N-cycling advantage of GM over FR. Water use during non-wheat periods was similar in GM and FR when lentil was killed at full bloom, but when grown to lower pod set GM used 20% more water than FR. After 11 yr SOC in the surface 15 cm declined 8%, 10%, and 9% with GM, FR, and AW management, respectively. Green manure, with proper management, maintains water productivity, offsets fertilizer N needs after about three cropping cycles, and reduces SOC depletion compared with traditional wheat-fallow rotations.