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Effects of Soil Structure Disturbance on Mineralization of Organic Soil Nitrogen

^a USDA-ARS Environmental Chemistry Lab., Beltsville, MD 20705 USA
^b Dep. of Terrestrial Ecology, National Environmental Research Inst., Vejlsøvej 25, DK-8600 Silkeborg, Denmark

View larger version (25K): [in a new window]   Fig. 1 One subunit of the system for leaching intact soil samples with unsaturated flow. Components of assembled subunit: (A) funnel bottom (Nalgene part no. 4280-0550, 45 mm i.d.); (B) No. 9 rubber stopper; (C) three hypodermic needles (0.8 mm o.d., 2.5 cm length); (D) air hole (3 mm); (E) polycarbonate tube (41 mm i.d., 1.6 mm wall); (F) soil core; (G) Büchner funnel (Nalgene part no. 4280-0550, 45 mm i.d.); (H) 2.5 µm glass fiber filter (Fisher Scientific); (I) 0.45 µm cellulose nitrate membrane filter (Whatman) prerinsed with water; (J) vacuum manifold (-80 kPa); (K) 120 mL bottle. The leaching solution (0.01 M CaCl2) was supplied to each subunit of the system by use of a peristaltic proportioning pump (Technicon Model III, pump tubing 0.51 mm i.d.)

View larger version (23K): [in a new window]   Fig. 2 The amount of 15NO-3–N and NO-3–N collected during leaching of incubated soil samples obtained from fields under plow- (PT) or no-tillage (NT) management. The soil structure of the samples had been disturbed or was kept intact, and the arrow indicates the time of the disturbance. Different letters indicate significant differences between collected amounts within day of leaching ( ; t test, P < 0.05)

View larger version (30K): [in a new window]   Fig. 3 The amount of NO-3–N released from active or protected soil N pools during incubation of intact and disturbed plow- (PT) or no-tillage (NT) soil samples. The arrows indicate the time of soil structure disturbance. The bars indicate standard errors of the total amount released at each leaching event ( )

View larger version (72K): [in a new window]   Fig. 4 The distribution of 15N and N after the 35 day incubation of plow- (PT) or no-tillage (NT) soil samples ( ). The values indicate size of the specified N pool on a mg N kg-1 soil basis

View larger version (21K): [in a new window]   Fig. 5 The availability ratio for N in leachates collected during the incubation of plow- (PT) or no-tillage (NT) soil samples. The soil structure of the samples had been disturbed or was kept intact. The arrow indicate the time of disturbance. Different letters indicate significant differences between availability ratios within day of leaching ( ; t test, P < 0.05)

View larger version (17K): [in a new window]   Fig. 6 Linear regressions between properties of plow- (PT) or no-tillage (NT) soil samples that were incubated and leached weekly during a period of 35 d. The soil structure of the samples had been disturbed or was kept intact. The linear regressions shown are (A) the availability ratio against the soil N content; (B) the soil N content against the soil C/N ratio; and (C) the availability ratio against the soil C/N ratio