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Nitrogen and Carbon Mineralization From Canola, Pea, and Wheat Residues With Differing N Content and Carbohydrate Composition.

Poster Number 2202

Tuesday, November 5, 2013
Tampa Convention Center, East Hall, Third Floor

Tai McClellan Maaz1, Taylor Lynn-Marie Beard1 and William L Pan2, (1)Crop and Soil Sciences, Washington State University, Pullman, WA
(2)Washington State University, Pullman, WA

Understanding the decomposition of crop residues and the release of nitrogen (N) is critical when implementing diversified crop rotations in no-till systems.  Nitrogen content, proximate fiber analysis [Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF)], and spectroscopic techniques are often proposed as suitable predictors of carbon (C) and N mineralization from crop residues.  This study compared the C and N dynamics in soil over a period of 112 days following the additions of 3 types of canola and wheat, and 2 types of pea residues, with differing C:N ratios and contrasting biochemical composition.  After 7 days, soil amended with the pea and canola residue types sustained greater rates of CO2 evolution than the wheat residues. The lower C mineralization rate corresponded with a smaller NDF fraction in the pea and canola residues than wheat, thus comprising of a lesser proportion of structural carbohydrate compounds (e.g. hemicellulose, cellulose, and lignin).  However, these differences were reduced after 14 days; and by 42 days, the CO2 emissions did not differ from the unamended soil.  The addition of all residue types resulted in initial net N immobilization as compared to the soil without residue.  By 28 days, soil amended with the high N pea residue (C:N ratio of 25:1) had a positive N balance, while all other residues maintained negative N balances relative to the control soil possibly due to their higher ADF fraction (between 0.45 and 0.50). The overall net N immobilization was strongly correlated with N content (R2 = 0.90), but poorly related to C:N ratios (R2 = 0.58).  Despite differences in the NDF fraction among crops, structural carbohydrate content did not greatly influence N mineralization dynamics (R2 = 0.53).  13C NMR CP/MAS analysis is currently being conducted to examine differences in C-chemistry among the residue types.

See more from this Division: SSSA Division: Soil Fertility & Plant Nutrition
See more from this Session: Soil Fertility and Plant Nutrition Division and Nutrient Management and Soil and Plant Analysis Division Graduate Student Poster Competition (PhD degree)

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