The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 215

Broadbalk

Organic N
920

NH 4 +
immobilization
0.59

Gross
mineralization
0.67 (0.26)

NH 4 +
consumption
0.76 (0.10)

Inorganic NH 4 +
0.23 (0.02)

+

Consumed NH 4

Gross
nitrification
0.17 (0.04)

Inorganic NO 3 −
6.04 (0.23)

Park Grass

Organic N
4740

+
immobilization
21.69

Gross
mineralization
18.28 (2.19)

NH 4

+
consumption
21.88 (3.02)

NH 4

+

Inorganic NH 4

Consumed NH 4 +

16.05 (1.0)

Gross
nitrification
0.19 (0.05)

Inorganic NO 3 −
1.98 (0.08)

Fig. 4.1. Gross rates of N transformations (mg kg − 1 day − 1 ) and pool sizes (mg kg − 1 ) in soils from
unfertilized plots of the Broadbalk and Park Grass experiments at Rothamsted (Tlustos et al.,
1998).

of magnitude. This particular Broadbalk plot is not typical of conventional
arable land since it does not receive any N fertilizer, only 35-40 kg N ha −1
year −1 from the atmosphere (Goulding et al ., 1998). The soil has a slow
rate of gross mineralization and a very slow rate of gross nitrification.
Immobilization dominates over nitrification. The soil is N limited, with