Measuring Subsidence in a Degraded Peat Soil: Nitrogen Mineralization under Rice Cultivation Emilie Kirk Bruce Linquist Chris van Kessel University of California, Davis
Measuring Subsidence in a Degraded Peat Soil: Nitrogen Mineralization
under Rice Cultivation
Emilie Kirk Bruce Linquist
Chris van Kessel University of California, Davis
Aragon, 2013
Sacramento - San Joaquin River Delta
Cross-section of Twitchell Island
Deverel et al., 2007
Average soil loss of 1-3 cm per year!!
>6m below mean sea level
160 levee failures in the last century in California DWR, 2007
Why grow rice in the Delta?
• Slow or reverse soil subsidence
• Maintain flooded conditions most of the year, mimicking seasonal wetlands
Anaerobic soil should reduce microbial activity
• Agriculture continues in Delta
N Fertilizer Study
• 180 kg N/ha average uptake with no N fertilizer!
• N uptake in well-fertilized CA rice ~140 kg N/ha Linquist et al., 2009
Nitrogen Budget Objectives
Quantify the environmental sources of N under rice production on Twitchell Island
Use N mineralization as a proxy to estimate subsidence
Nitrogen Budget Hypotheses
1. Majority of plant-available N from peat mineralization
2. A small amount of N from previous year’s crop residue
3. N from water sources are negligible
Materials & Methods: Site Setup
- RCBD experiments with 4 blocks
- Replicated in 2 fields
- Soils are Typic Haplosaprists
13-15% C in the upper 30cm
- Conventionally managed paddy rice fields
Materials & Methods
Residue • In situ mesocosms
+ H2O
- H2O
• Surface water sampled for growing season
Water
• 15N-tracer method for growing season
• Field residue sampled over-winter
30 c
m
60 cm
Annual N Budget Components
Growing Season Over-winter
Peat +
Residue +
Subsurface Water +
Irrigation Water
Peat +
Residue
Growing Season N Budget: Surface water
Irrigation water 3 kg N/ha
Methods:
[Inlet N] * ET
Unfertilized N Uptake = 167 kg N/ha
Growing Season N Budget: Crop residue
Irrigation water 3 kg N/ha
Rice residue 4 kg N/ha
Methods: 15N-labeled rice residue tracer study
Unfertilized N Uptake = 167 kg N/ha
Subsurface N 40 kg N/ha
Growing Season N Budget: Subsurface N
Irrigation water 3 kg N/ha
N assumed from peat mineralization! • Peat layer extends several meters • NH4
+ enriched groundwater •No difference in d15N between treatments
Unfertilized N Uptake = 167 kg N/ha
Rice residue 4 kg N/ha
Subsurface N 40 kg N/ha
Growing Season N Budget: Peat
Irrigation water 3 kg N/ha
Peat mineralization 120 kg N/ha
Methods: By difference – remaining N from surface peat mineralization
Unfertilized N Uptake = 167 kg N/ha
Rice residue 4 kg N/ha
Growing Season Mineralization Section 1: Plant N derived from source Field 1
N uptake from peat (kg N ha-1) 160 (12)
N uptake efficiency (NUE) (%) 0.50
Total N mineralized from peat (kg N ha-1) 320 (25)
0
300
600
900
1200
1500
1800
0 10 20 30 40 50 60 70 80 90 100
N m
iner
aliz
ed f
rom
pea
t
(kg
N h
a-1)
NUE (%)
Over-winter Mineralization
Spring soil NO3 – rice straw mineralization N
= over-winter peat mineralization N
Section 2: Overwinter mineralization Field 1
Spring soil NO3-N (kg N ha-1) 42 (0.5)
N mineralized from straw over-winter (kg N ha-1) 21 (2)
Over-winter peat N mineralization (kg N ha-1) 21 (2)
Mineralization Subsidence Growing season
mineralization
320 kg N ha-1
+
Over-winter mineralization
21 kg N ha-1
=
Total N mineralized from peat
341 (44) kg N ha-1
Factors for calculations:
- C:N
- Carbon input from straw
- Soil C%
- Bulk density
Mineralization Subsidence
Field 1
Mass soil lost
-24300 (5103) kg soil ha-1
↓ Bulk density 0-30cm
78200 (2000) (kg cm-1 ha-1)
Estimated Subsidence
- 0.31 (0.03) cm
Field 2
Mass soil lost
-22440 (4264) kg soil ha-1
↓ Bulk density 0-30cm
55500 (2500) (kg cm-1 ha-1)
Estimated Subsidence
- 0.40 (0.05) cm
The Big Picture
Corn
Soil loss
- 2.5cm/year (Hatala et al. 2012)
Rice
Soil loss
- 0.3 - 0.4cm/year
Wetlands
Soil gain
Special thanks to
Funding: NIFA - Ag. and Food Research Initiative UCD Dept. Plant Sciences
C. Abernilla J. Casey B. Gornto
C. Mikita M. Lundy M. Simmonds
G. Pearson And many others!
Emilie Kirk MSc. Candidate, Soils & Biogeochemistry [email protected] 530 – 204 – 9030
Threat to fresh water supply
RMA, in CALFED 2007
NUE Assumptions and Subsidence
y = 110.71x-1.528
R² = 0.9693
0
0.5
1
1.5
2
2.5
3
3.5
4
0 10 20 30 40 50 60 70 80 90 100
Est
ima
ted
Su
bsi
den
ce (
cm y
r -1
)
Nitrogen Uptake Efficiency (NUE) (%)
Range I: Mineralization pulses, poor synchrony
Range II: Mineralization continuous, good synchrony
15N recovery – only a small proportion was accumulated in the
AGB
0
10
20
30
40
50
60
70
80
90
100
Straw Straw+Fert Straw Straw+Fert
Field 3 Field 4
Per
cen
t 15N
rec
ov
ery
(%
)
Soil Aboveground Biomass Losses
Subsurface N Discussion
0
4
8
12
16
20
0 5 10 15 20
Wel
l dep
th b
elow
soil
surf
ace
(ft)
NH4-N (ppm)
Twitchell Island Groundwater NH4-N by Well Depth, 7-8 Aug.
2012
Field 1 NH4-N Field 10 NH4-N
Response to N fertilization: grain yield and N uptake across 4 siteyears
ab ab a
ab b
a ab
bc c c
R² = 0.8937
R² = 0.9841
0
100
200
300
400
500
0
2000
4000
6000
8000
10000
12000
0 40 80 120 160
N U
pta
ke
(kg N
ha
-1)
Gra
in Y
ield
(k
g h
a-1
)
N Fertilizer Applied (kg N ha-1)
Grain yield Aboveground Biomass N uptake