3 research outputs found
How Does Recycling of Livestock Manure in Agroecosystems Affect Crop Productivity, Reactive Nitrogen Losses, and Soil Carbon Balance?
Recycling of livestock manure in
agroecosystems to partially substitute
synthetic fertilizer nitrogen (N) input is recommended to alleviate
the environmental degradation associated with synthetic N fertilization,
which may also affect food security and soil greenhouse gas (GHG)
emissions. However, how substituting livestock manure for synthetic
N fertilizer affects crop productivity (crop yield; crop N uptake;
N use efficiency), reactive N (Nr) losses (ammonia (NH<sub>3</sub>) emission, N leaching and runoff), GHG (methane, CH<sub>4</sub>;
and nitrous oxide, N<sub>2</sub>O; carbon dioxide) emissions and soil
organic carbon (SOC) sequestration in agroecosystems is not well understood.
We conducted a global meta-analysis of 141 studies and found that
substituting livestock manure for synthetic N fertilizer (with equivalent
N rate) significantly increased crop yield by 4.4% and significantly
decreased Nr losses via NH<sub>3</sub> emission by 26.8%, N leaching
by 28.9% and N runoff by 26.2%. Moreover, annual SOC sequestration
was significantly increased by 699.6 and 401.4 kg C ha<sup>β1</sup> yr<sup>β1</sup> in upland and paddy fields, respectively;
CH<sub>4</sub> emission from paddy field was significantly increased
by 41.2%, but no significant change of that was observed from upland
field; N<sub>2</sub>O emission was not significantly affected by manure
substitution in upland or paddy fields. In terms of net soil carbon
balance, substituting manure for fertilizer increased carbon sink
in upland field, but increased carbon source in paddy field. These
results suggest that recycling of livestock manure in agroecosystems
improves crop productivity, reduces Nr pollution and increases SOC
storage. To attenuate the enhanced carbon source in paddy field, appropriate
livestock manure management practices should be adopted
Nitrogen Removal Capacity of the River Network in a High Nitrogen Loading Region
Denitrification
is the primary process that regulates the removal
of bioavailable nitrogen (N) from aquatic ecosystems. Quantifying
the capacity of N removal from aquatic systems can provide a scientific
basis for establishing the relationship between N reduction and water
quality objectives, quantifying pollution contributions from different
sources, as well as recommending control measures. The Lake Taihu
region in China has a dense river network and heavy N pollution; however,
the capacity for permanent N removal by the river network is unknown.
Here, we concurrently examined environmental factors and net N<sub>2</sub> flux from sediments of two rivers in the Lake Taihu region
between July 2012 and May 2013, using membrane inlet mass spectrometry,
and then established a regression model incorporating the highly correlated
factors to predict the N removal capacity of the river network in
the region. To test the applicability of the regression model, 21
additional rivers surrounding Lake Taihu were sampled between July
and December 2013. The results suggested that water nitrate concentrations
are still the primary controlling factor for net denitrification even
in this high N loading river network, probably due to multicollinearity
of other relevant factors, and thus can be used to predict N removal
from aquatic systems. Our established model accounted for 78% of the
variability in the measured net N<sub>2</sub> flux in these 21 rivers,
and the total N removed through N<sub>2</sub> production by the river
network was estimated at 4 Γ 10<sup>4</sup> t yr<sup>β1</sup>, accounting for about 43% of the total aquatic N load to the river
system. Our results indicate that the average total N content in the
river water discharged into Lake Taihu would be around 5.9 mg of N
L<sup>β1</sup> in the current situation, far higher than the
target concentration of 2 mg of N L<sup>β1</sup>, given the
total N load and the N removal capacity. Therefore, a much stronger
effort is required to control the N pollution of the surface water
in the region
Dissimilatory Nitrate Reduction Processes in Typical Chinese Paddy Soils: Rates, Relative Contributions, and Influencing Factors
Using
soil slurry-based <sup>15</sup>N tracer combined with N<sub>2</sub>/Ar technique, the potential rates of denitrification, anaerobic
ammonium oxidation (anammox), and dissimilatory nitrate reduction
to ammonium (DNRA), and their respective contributions to total nitrate
reduction were investigated in 11 typical paddy soils across China.
The measured rates of denitrification, anammox, and DNRA varied from
2.37 to 8.31 nmol N g<sup>β1</sup> h<sup>β1</sup>, 0.15
to 0.77 nmol N g<sup>β1</sup> h<sup>β1</sup> and 0.03
to 0.54 nmol N g<sup>β1</sup> h<sup>β1</sup>, respectively.
The denitrification and anammox rates were significantly correlated
with the soil organic carbon content, nitrate concentration, and the
abundance of <i>nosZ</i> genes. The DNRA rates were significantly
correlated with the soil C/N, extractable organic carbon (EOC)/NO<sub>3</sub><sup>β</sup> ratio, and sulfate concentration. Denitrification
was the dominant pathway (76.75β92.47%), and anammox (4.48β9.23%)
and DNRA (0.54β17.63%) also contributed substantially to total
nitrate reduction. The N loss or N conservation attributed to anammox
and DNRA was 4.06β21.24 and 0.89β15.01 g N m<sup>β2</sup> y<sup>β1</sup>, respectively. This study reports the first
simultaneous investigation of the dissimilatory nitrate reduction
processes in paddy soils, highlighting that anammox and DNRA play
important roles in removing nitrate and should be considered when
evaluating N transformation processes in paddy fields