Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 105

Table 3.1.1. Summary of the field experiments.

Harwood Mackay Tully

Climate Temperate Tropical Tropical

Latitude, longitude 29.50 S, 153.20 E 21.10 S, 149.07 E 17.56 S, 145.56 E

Annual rainfall (mm)
(30-50 year mean)

1021 1668 4067

Crop age 1st ratoon (late harvest)

2nd ratoon (early harvest)

3rd ratoon (late harvest)
4th ratoon (early harvest)

6th ratoon (late
harvest)

Soil texture Clay/loam Loam Clay

Previous cropping Vegetables, sugarcane Sugarcane Sugarcane

(ii) TB: sugarcane harvested without burning and trash retained on the
soil surface, soil not cultivated. The Mackay and Harwood sites each had
one experiment harvested early in the harvesting season (July) and one
experiment harvested late (December). The experimental designs were
randomized complete blocks with three or four replicates. In all cases,
the variety was Q124, row spacing was 1.5 m and annual N fertilizer
application was 180 kg ha −1 as urea (applied 1-6 weeks after harvest).
At the time of this study, the experiments had been running for between
1 and 6 years, having been ratooned (above-ground portions harvested,
remainder left to regrow) annually.
To measure trash decomposition in the TB treatments, a standard
mass of trash was placed (on the soil surface) within sufficient quadrats
(0.75 × 1.50 m) to allow destructive sampling of one quadrat per replicate
on 8-10 occasions over the following (12-month) growing season. The
quadrats were held in place by tent pegs, and covered with 20 mm mesh
netting.
At each sampling, trash that had not become incorporated with the soil
(termed 'free trash', current year's trash only) was sampled first. Soil was
then sampled within the quadrat by taking 12 cores (30 mm diameter) in
two regular transects across the row. The cores were cut into the depth
layers (0-20, 20-50, 50-100 and 100-250 mm) and samples pooled from
each depth. Trash that had become incorporated with the surface 10 mm of
soil ('incorporated trash', current year's trash and older trash) was then
sampled by removing a strip (1750 mm long × 175 mm wide × approxi-
mately 10 mm deep) of soil between the holes left by the soil sampler.
Soil microbial biomass C was determined by chloroform fumigation
extraction (Vance et al ., 1987). This method gave some negative results
when C from the unfumigated control was subtracted from C from the
fumigated soil. The quantity of C from fumigated soil was highly correlated
with (C from fumigated soil − C from unfumigated soil) ( r = 0.88-0.95 for
all data from individual experiments, negative results excluded), therefore