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Crop Rotations and Nitrogen Fertilization to Manage Soil Organic Carbon Dynamics

Facultad de Ciencias Agrarias (U.N.M.P.), Estación Experimental Agropecuaria Balcarce (I.N.T.A.), Unidad Integrada Balcarce, C.C. 276, (7620) Balcarce, Buenos Aires, Argentina

View larger version (46K): [in a new window]   Fig. 1 Arable layer soil organic C after 11 yr of conventional tillage under different crop sequences (a) without N and (b) with N applied at 3, 5, 7, 9, or 11 yr during the experiment. Crop sequences are described in Table 1. C = corn, Sb = soybean, Sf = sunflower, W = wheat. The same letters within columns indicate that the sequences do not differ according to Duncan (P < 0.05)

View larger version (43K): [in a new window]   Fig. 2 Mean annual aboveground residue C returned to the soil after 11 yr of conventional tillage by different crop sequences (a) without N and (b) with N applied at 3, 5, 7, 9, or 11 yr during the experiment. Crop sequences are described in Table 1. C = corn, Sb = soybean, Sf = sunflower, W = wheat. The same letters within columns indicate that the sequences do not differ according to Duncan (P < 0.05)

View larger version (25K): [in a new window]   Fig. 3 Arable layer soil organic C after 11 yr of conventional tillage as a function of mean annual residue C returned by different crop sequences arranged in two groups: G1, none or only one summer crop every 3 yr; G2, two summer crops every 3 yr. With N = received N fertilizer 3, 5, 7, 9, or 11 yr during the experiment (Table1); without N = never received N fertilizer

View larger version (39K): [in a new window]   Fig. 4 Change in soil organic C as a function of time under conventional cropping for different crop sequences. Curves result from fitting a model proposed by Bartholomew and Kirkham (1960). Crop sequence description and model parameters can be seen in Tables 1 and 2, respectively. With N = received N fertilizer 3, 5, 7, 9, or 11 yr during the experiment (Table1); without N = never received N fertilizer

View larger version (20K): [in a new window]   Fig. 5 Arable layer soil organic C at equilibrium according to the model proposed by Bartholomew and Kirkham (1960) as a function of mean annual residue C returned by different crop sequences arranged in two groups: G1, none or only one summer crop every 3 yr; G2, two summer crops every 3 yr. With N = received N fertilizer 3, 5, 7, 9, or 11 yr during the experiment (Table1); without N = never received N fertilizer