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The impacts of tillage and organic fertilization on soil organic matter (SOM) are highly variable and still unpredictable, and their interactions need to be investigated under various soil, climate and cropping system conditions. Our work examined the effect of reduced tillage and animal manure on SOM stocks and quality in the 0―40 cm layer of a loamy soil under mixed cropping system and humid temperate climate. The soil organic carbon (SOC) and N stocks, particulate organic matter (POM), and C and N mineralization potential (301 days at 15 °C) were measured in a 8-yr-old split-plot field trial, including three tillage treatments [mouldboard ploughing (MP), shallow tillage (ST), no tillage (NT)] and two fertilization treatments [mineral (M), poultry manure 2.2 t/ha/yr C (O)]. No statistically significant interactive effects of tillage and fertilization were measured except on C mineralization. NT and ST showed greater SOC stocks (41.2 and 39.7 t/ha C) than MP (37.1 t/ha C) in the 0-15 cm increment, while no statistical differences were observed at a greater depth. N stocks exhibited similar distribution patterns with regard to tillage effect. Animal manure, applied at a rate representative of typical field application rates, had a smaller impact on SOC and N stocks than tillage. The mean SOC and N stocks were higher under O than M, but the differences were statistically significant only in the 0―5 cm increment. MP showed lower C-POM stocks than NT and ST in the 0-5 cm increment, whereas greater C-POM stocks were measured under MP than under NT or under ST in the 20-25 cm increment. Organic fertilization had no impact on C-POM or N-POM stocks. In the 0-25 cm increment, NT showed a lower C and N mineralization potential than MP. Our work shows that the sensitivity of SOM to reduced tillage for the whole soil profile can be relatively small in a loamy soil, under humid-temperate climate. However, POM was particularly sensitive to the differential effects of tillage practices with depth, and indicative of differentiation in total SOM distribution in the soil profile.

The fate of pig (Sus scrofa) slurry labeled with 15 N was investigated when applied on a day soil (fine, mixed, frigid, Typic Humaquept) and a sandy loam (loamy, mixed, frigid, Typic Dystrochrept) cropped to maize (Zea mays L.) in 2000 and to barley (Hordeum vulgare L.) in 200L The slurry was applied in spring 2000, and plant and soil samples were collected at 6 h (Day 1) and at Days 14, 42, 96, and 413 after application. The samples were analyzed for 15 N content in plant, in whole soil, and in soil NH + 4-N, NO - 3-N, organic N, and clay-fixed N pools. Percentage 15 N recovery was >93% in both soils at Day 1 and decreased slowly thereafter. Rapid day fixation of slurry 15 N occurred at Day 1, and was greater in the day soil (34% of applied 15 N) than in the sandy loam (11%). At Day 96, less of the applied slurry 15 N was recovered in maize grown on the clay soil (29%), as compared with the sandy loam (50%). At the same period, the residual soil 15 N was mostly present as organic N and NO - 3-N in the sandy loam, and as organic and clay-fixed N in the day soil. At Day 413, N recovery in barley was about 3% of the initially applied N in both soils. The 15 N recovery was generally higher in the day soil than in the sandy loam, but total 15 N recovery from the soil-plant system was similar for both soils. We conclude that soil type had little influence on the total 15 N recovery from the soil-plant system, but significantly influenced the fate of slurry N in the various soil pools and plant N uptake on the year of application.