New Zealand Journal of Agricultural Research abstracts
Effects of dairy factory effluent application on nutrient
transformation in soil
Anwar Ghani
Moira Dexter
Upali Sarathchandra
John Waller
AgResearch
Ruakura Research Centre
Private Bag 3123
Hamilton, New Zealand
Abstract Dairy factory effluent (DFE)
contains significant amounts of nutrients such as nitrogen
(N), phosphorus (P), potassium (K), and sulphur (S) which are
beneficial to plant growth. It also contains high amounts of carbon
(C). Lately, there has been some concern that DFE application to
pastoral land is adversely affecting plant growth in some regions of
New Zealand. In this study, we determined the mineralisation and
immobilisation of nutrients particularly C, N, S, and cations, in a
DFE-treated Omeheu sandy loam soil. We report findings from
laboratory-based open incubation studies carried out at 10, 20, and
30°C, with four rates of DFE application (0, 150 000,
300 000, and 450 000 litres ha–1)
alone and with added NO3– (100 kg N ha–1).
The DFE was applied at two-weekly intervals into packed soil columns
which were leached with 0.01 M CaCl2 solution.
Leachates were analysed for total C, total N, SO42–,
NO3–, NH4+, K+,
Na+, and Mg2+. Effects of DFE application on soil
microbial biomass-C, hot-water extractable-C, and anaerobically
mineralisable-N were also determined. Addition of DFE increased the
size of the microbial biomass pool and thereby enhanced immobilisation
of nutrients, mainly N and S. The immobilisation was greater at
higher temperature. At 10°C, microbes were unable to utilise all of
the added C, even at the lowest rate of DFE application, and 40–50% of
the C was leached from soil columns. However, at 30°C soil microbes
either immobilised or respired between 95–97% of the C added from DFE,
and only small amounts of C were measured in the leachates. Addition of
NO3–-N had no significant influence on the C
immobilisation or respiration. Most of the added N (92–97%) from DFE
remained immobilised in the soils throughout the study. A high
proportion of the NO3–-N added with DFE was
immobilised in soils at 10 and 20°C, showing the dominating
influence of soluble C, added through the two-weekly application of
DFE, in stimulating microbial activity and causing a prolonged
immobilisation of N. There was a net mineralisation of about
100 µg NO3–-N g–1
soil at 30°C, indicating faster metabolic use of soluble C from DFE
by microbes at this temperature. Between 15–35% of the SO42–-S
applied from DFE was either immobilised by soil microbes or was
adsorbed on soil organic matter. The presence of significant amounts of
NH4+ in DFE-treated soils suggests that parts of
the soil columns may have become anaerobic during incubation, causing
mineralisation of N from the death of aerobic microbes or decomposition
of soil organic matter. A high proportion of the cations (K+,
Na+, and Mg2+) that were added with DFE leached
out, indicating that DFE application would have very little effect on
the availability of these cations for plant uptake. This study, in
part, explains that the poor performance of DFE application on pastoral
soils predominantly arises through its effects on the availability of N
for plant growth.
Keywords dairy factory effluent; nitrate; soluble
C; microbial biomass-C; immobilisation; mineralisation; sulphate
A04069; Received 30 June 2004; accepted 30 March 2005; Online
publication date 30 May 2005
New Zealand Journal of Agricultural Research, 2005, Vol. 48:
241–253
0028–8233/05/4802–0241 © The Royal Society of New Zealand 2005
PDF file of entire paper: Print-quality
(475K) | screen-quality (666K)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
