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Immobilization of Fertilizer Nitrogen in Rice

Effects of Straw Management Practices

^a Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616
^b Univ. of California Cooperative Extension, Kearney Agricultural Center, Parlier, CA, 93648
^c Dep. of Agronomy and Range Science, University of California, Davis, CA 95616

View larger version (18K): [in a new window]   Fig. 1. Percent soil 15N fertilizer recovery over a two year period (1997–1999) in the 0- to 15-cm soil depth when straw was incorporated or burned and the fields were winter-flooded (WF) or nonwinter flooded (NF). Two kg 15N ha-1 was added prior to planting in May, 1997. All treatments were flooded during the cropping season while only the winter flooded treatments were flooded during the winter fallow period. Least-squares means, standard errors (N = 12).

View larger version (19K): [in a new window]   Fig. 2. Extractable inorganic N (NO-3 and NH+4) over a two year period (1997–1999) in the 0- to 15-cm soil depth when straw was incorporated or burned and the fields were winter-flooded (WF) or nonwinter flooded (NF). All treatments were flooded during the cropping season while only the winter flooded treatments were flooded during the winter fallow period. Least-squares means, standard errors (N = 12).

View larger version (20K): [in a new window]   Fig. 3. 15N atom excess values (%) of soil inorganic N (NO-3 and NH+4), soil microbial N and total soil N, 1997 to 1999 (0- to 15-cm depth). Least-squares means, standard errors (N = 48, average of all treatments). Zero 15N atom excess (%) represent natural abundance measured in adjacent main plots. All treatments were flooded during the cropping season while only the winter flooded treatments were flooded during the winter fallow period.

View larger version (25K): [in a new window]   Fig. 4. Effects of winter flooding (WF), nonwinter flooding (NF) and straw incorporation on soil microbial biomass N (top), C (center) and C:N ratio (bottom) in the 0- to 15-cm depth, 1997 to 1999. All treatments were flooded during the cropping season while only the winter flooded treatments were flooded during the winter fallow period. Least-squares means, standard errors (N = 12)

View larger version (19K): [in a new window]   Fig. 5. Percent soil microbial immobilized 15N fertilizer recovery over a two year period (1997–1999) in the 0- to 15-cm soil depth when straw was incorporated or burned and the fields were winter-flooded (WF) or nonwinter flooded (NF). Two kg 15N ha-1 was added prior to planting in May, 1997. All treatments were flooded during the cropping season while only the winter flooded treatments were flooded during the winter fallow period. Least-squares means, standard errors (N = 12).