19/02/2016
Introduction
What Soil N Indices and Climate Variables are
Needed to Predict Grass Growth under a
Temperate Maritime Climate?
ASA,CSSA, SSSA Annual Meeting
Minneapolis, MN
17th November 2015
Session : Nitrogen Science & Management
Noeleen McDonald1, Catherine Watson2, & David Wall3
1Agricultural
Catchment Programme, Teagasc, Crops and Environment Research Centre, Johnstown Castle, Co. Wexford, Ireland.
2Agri-Food & Biosciences Institute, Belfast, BT9 5PX, Northern Ireland.
3Teagasc, Crops Environment & Land Use Programme, Johnstown Castle, Wexford, Ireland
•
Current Irish N recommendations do not account for variability in soil N
supply
•
•
•
Soil temperature (5 to 37oC).
•
Soil moisture (permanent wilting point to field capacity ~65% WFPS)
•
Soil N mineralization varies across a growing season.
•
Peak mineralization in Irish grass is from mid April to end of May (smaller peak
early Aug to end of Sep) (Herlihy,1979).
•
Laboratory investigation study:
Risk of under- or over -supply of N fertiliser in many fields?
N mineralization dependent on
Previous Project Findings
It is difficult to predict temporal soil N supply and availability for plant uptake
Based on previous project findings (lab & microcosm study)
McDonald et al. 2014a, SSSAJ
McDonald et al 2014a, SSSAJ & McDonald et al., 2014b, J Ag Science
• 35 different Irish soils
Illinois Soil N test (ISNT)
• Large range potential mineralizable N (MN)
Can these soil N tests predict grass N uptake
under field conditions?
93 - 403 mg NH4-N kg -1
• Therefore more soil specific N advice required.
• The Illinois soil N test (ISNT) was the best rapid
soil N test for predicting soil MN (R2 =0.68, p<0.0001)
Experimental Objective:
Microcosm (pot) studies:
McDonald et al. 2014b, J Ag Science
 On 2 contrasting Irish field sites
• 30 different soils in a controlled environment research
facility at Teagasc, Johnstown Castle, Ireland.
•
Examine the temporal variability soil N indices:
•
Examine the effectiveness of these soil N indices along with measured
• Grass growth period of 5 weeks
• ISNT (MN), SMN (TON + NH4-N), total soil C & N
• Grass harvest & soil sampling analysed each period
• Combining soil ISNT, Total oxidised N (TON) & C/N
ratio improved the prediction model
•
Grass N uptake R2 = 0.79 (p<0.0001)
•
Grass DM yield R2 = 0.55 (P<0.0001)
climatic variables to predict daily dry matter (DM) grass yields
Controlled Environment Research Facility
Experiment Sites
Materials & Methods
Design
•
•
•
Sub-set plots from a larger N, P, lime response experiment
8 plots (2 trt x 4 reps)
Randomised complete block design
Treatments
Well drained: WD, Fermoy, Co. Cork
Moderately drained: MD
Johnstown Castle, Co. Wexford
1. Check plot (Zero applications)
2. Lime applied ( 5t ha-1)
Experimental measurements
 Soil sampled to 10cm every 3 weeks
• Mineral N (Total oxidised N & NH4+-N ), within 24hs of sampling
• Potential mineralizable N (MN) by ISNT
• Total N & C
 Grass harvest every 3-5 weeks from Feb to Oct.
• Grass DM yield & N uptake
 Daily meteorological data provided by on site weather station
• Precipitation
• Soil temperature
Well drained Soil at Moorepark
Cambisol
Gleyic Luvisol
Sandy Loam
Clay Loam
Statistical & Prediction model analysis
•
Linear & Quadratic mixed stepwise regression analysis using SAS Ver. 9.3
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Climatic Conditions : Temperature and Rainfall
25
Average: 11.8oC
(1.8 oC – 19.7oC)
15
10
5
Soil temperature (oC wk-1)
Soil temperature (oC wk-1)
20
0
Aug 2011 Dec 2011 Apr 2012 Aug 2012 Dec 2012
60
40
20
0
Aug 2011 Dec 2011 Apr 2012 Aug 2012 Dec 2012
Average: 11.7oC
(2 oC – 20oC)
15
20
10
5
Precipitation at MD for study period
7-8 year average precipitation at MD
60
16
15
10
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
40
Sample Date 2011-2012
20
0
Aug 2011 Dec 2011 Apr 2012 Aug 2012 Dec 2012
MD Check Plot
MD Lime Treated
WD Check Plot
WD Lime Treated
14
Site X Time p<0.001
12
Large Temporal Variability
10
8
6
4
Temporal Trend of Potentially Mineralized N (ISNT)
480
MD Check Plot
MD Lime Treated
WD Check Plot
WD Lime Treated
460
Temporal Variability
Stable compared to SMN
440
420
400
380
360
320
0
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sampling date 2011-2012
Sample date 2011-2012
Temporal Variability in Grass Growth
Temporal Variability in Grass Growth
3000
MD Check Plot
MD Lime Treated
WD Check Plot
WD Lime Treated
2000
Cumulative DM Yields:
15 months
MD: 11 -12.3 t/ha
WD: 10.1-10.3 t/ha
2012
MD: 6.9-8 t/ha
WD: 6.5 -6.6 t/ha
1500
1000
500
0
Herabge DM yields (kg ha-1)
3000
Herabge DM yields (kg ha-1)
Site X Time p<0.001
340
2
2500
Large Temporal Variability
0
ISNT-N (mg kg-1)
NH4-N (mg kg-1)
18
Site X Time p<0.001
5
Averages:
15m:1327mm
2012: 1152mm
Summer: 496mm
80
Temporal Variability of Ammonium Nitrogen
20
MD Check Plot
MD Lime Treated
WD Check Plot
WD Lime Treated
20
100
Precipitation (mm wk-1)
Precipitation (mm wk-1)
Averages:
15m:1329mm
2012: 1096mm
Summer: 483mm
80
25
Soil temp (10cm) at MD for study period
7-8 year average soil temp (10cm) at MD
0
Aug 2011 Dec 2011 Apr 2012 Aug 2012 Dec 2012
Precipitation at WD for study period
7-8 year average precipitation at WD
100
Temporal Variability of Total Oxidised Nitrogen (TON)
Moderately Drained (MD) Site
Soil temp (10cm) at WD for study period
7-8 year average soil temp (10cm) at WD
TON (mg kg-1)
Well Drained (WD) Site
25
2500
2000
1500
MD Check Plot
MD Lime Treated
WD Check Plot
WD Lime Treated
Grass
Growing
Season
1000
500
0
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Harvest dates 2011-2012
Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Harvest dates 2011-2012
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Predicting Grass Daily DM Grass Yields
under Field Conditions for a Growth Season
Parameter
Variable (X) estimate S.E
Site
MD
Intercept
Precipitation
Soil
temperature
NH4-N
Precipitation
X NH4-N
Intercept
Precipitation
Soil
temperature
NH4-N
Precipitation
X Soil
temperature
WD
P>t
95% Confidence
limits
3.0
-0.2
0.19
0.05
<.0001
0.0027
2.60
-0.26
3.37
-0.06
0.1
-0.1
0.02
0.03
<.0001
<.0001
0.05
-0.18
0.13
-0.07
0.1
2.7
-0.2
0.02
0.19
0.09
0.037
<.0001
0.0471
0.00
2.35
-0.37
0.10
3.11
0.00
0.1
-0.1
0.02
0.02
0.0004
0.0113
0.03
-0.11
0.11
-0.01
0.1
0.03
0.002
0.04
0.16
Predicting Grass Daily DM Grass Yields
under Field Conditions for a Growth Season
RMSE
Model
R2
0.37
0.41
0.37
0.37
Conclusions
•
SMN (TON and NH4-N) varied greatly within and between sites throughout the experimental
period.
 Hence SMN unreliable indictors of soil N mineralization potential across the growing
Site
Sites
Combined
Variable
(X)
Intercept
Precipitation
Soil
temperature
NH4-N
Precipitation
X Soil
temperature
Precipitation
X NH4-N
Soil
temperature
X NH4-N
Parameter
estimate S.E
P>t
95% Confidence
limits
3.0
-0.2
0.13
0.04
<.0001
<.0001
2.73
-0.25
3.24
-0.09
0.1
-0.1
0.01
0.02
<.0001
<.0001
0.05
-0.13
0.09
-0.07
0.0
0.01
1
<.0001
0.02
0.06
-0.1
0.02
0.0078
-0.09
-0.01
0.04
0.00
6
<.0001
0.03
0.05
RMSE
Model
R2
0.34
0.48
WATCH THIS SPACE
Multiple Sites x Years x Fertilizer Treatments
Now on-going
season.
•
ISNT-N measuring MN is more stable, especially below soil temp 12oC.
•
The combination of precipitation levels, soil temperatures, the NH4-N concentration in the
 Suggested soil sampling for MN may be best suited to spring or late autumn (fall).
soil and their interactions gave the best prediction of daily grass DM production across the
2012 growing season.
•
Climatic influences and site conditions seem to greatly influence soil N supply and plant
development and override soil N supply as the main driver of grass production.
•
As <50% of the variability in daily grass DM production could be explained, additional field
validation studies across multiple grassland sites, climates, soil type and MN capacities is
needed.
Acknowledgments
• Farmers who provided
sampling sites.
• Funding by the Irish
Department of Agriculture
Food & Marine.
• Teagasc, AFBI & QUB
supervisors, staff and
students.
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