Effects of rainfall pattern on carbon and nitrogen dynamics in soil amended with biogas slurry and composted cattle manure

Soil moisture affects the degradation of organic fertilizers in soils considerably, but less is known about the importance of rainfall pattern on the turnover of C and N. The objective of this study was to determine the effects of different rainfall patterns on C and N dynamics in soil amended with either biogas slurry (BS) or composted cattle manure (CM). Undisturbed soil cores without (control) or with BS or CM, which were incorporated at a rate of 100 kg N ha –1 , were incubated for 140 d at 13.5°C. Irrigation treatments were (1) continuous irrigation (cont_irr; 3 mm d –1 ); (2) partial drying and stronger irrigation (part_dry; no irrigation for 3 weeks, 1 week with 13.5 mm d –1 ), and (3) periodic heavy rainfall (hvy_rain; 24 mm d –1 every 3 weeks for 1 d and 2 mm d –1 for the other days). The average irrigation was 3 mm d –1 in each treatment. Cumulative emissions of CO 2 and N 2 O from soils amended with BS were 92.8 g CO 2 ‐C m –2 and 162.4 mg N 2 O‐N m –2 , respectively, whereas emissions from soils amended with CM were 87.8 g CO 2 ‐C m –2 and only 38.9 mg N 2 O‐N m –2 . While both organic fertilizers significantly increased CO 2 production compared to the control, N 2 O emissions were only significantly increased in the BS‐amended soil. Under the conditions of the experiment, the rainfall pattern affected the temporal production of CO 2 and N 2 O, but not the cumulative emissions. Cumulative NO ₃⁻ leaching was highest in the BS‐amended soils (9.2 g NO ₃⁻ ‐N m –2 ) followed by the CM‐amended soil (6.1 g NO ₃⁻ ‐N m –2 ) and lowest in the control (4.7 g NO ₃⁻ ‐N m –2 ). Nitrate leaching was also independent of the rainfall pattern. Our study shows that rainfall pattern may not affect CO 2 and N 2 O emissions and NO ₃⁻ leaching markedly provided that the soil does not completely dry out.