Post on 26-Mar-2018
Ilan Stavi
Dead Sea & Arava Science Center, Israel istavi@adssc.org
Agro-ecosystems
functioning under stress
On-site retention of crop residue has been widely
perceived as means in promoting soil conservation:
• increases soil organic carbon (SOC) pools
• improves soil structure formation
• decreases raindrop splash impact, mechanical crust formation, and erosional processes
• decreases evaporation loss
Conservation farming systems
4
Crop residue elimination has been widely perceived to:
• diminish of SOC pools
• causes deformation of the soil structure
• increases erodibility
Stubble grazing has been widely perceived to:
• increase soil compaction
• further exacerbating soil degradation
• Yet, stubble grazing has been a very common practice due to the (permanent) shortage of feed for livestock
Conservation farming systems
5
1. Natural land (NAT) 2. Continuous wheat, without stubble grazing (NO) 3. Continuous wheat, with stubble grazing (GR) Pictures taken during August 2013
1
2 3
a
a
a
b
a
a
a
b
a
b
a
a
0
2
4
6
8
10
12
14
16
Wetness depth (m) ρb (kg m-3) Өg (%) CaCO3 (%)
Lan-use effect on soil characteristics
Wheat with stubble grazing
Wheat with no stubble grazing
Natural land
P = 0.3409
P < 0.0001
P = 0. 718
P < 0.0001
b
b
b
ab
a
a
0
5
10
15
20
25
30
SOC (g kg-1) LOC (x10-7)
Land-use effect on SOC and LOC
No stubble grazing
Stubble grazing
Natural
P = 0.0067
P < 0.0001
Carbon lability
b
a
b
0
0.005
0.01
0.015
0.02
0.025
0.03
GR NO NAT
)%/%
(
Lability (L) P < 0.0001
Lability (L): L = (LOC) / (non-LOC) [%/%] (Blair et al., 1995) (where the non-LOC fraction was calculated by subtracting the LOC from the total SOC; indicates the ratio between LOC and non-LOC)
10
SOC management-related indices
a
b
0.66
0.68
0.7
0.72
0.74
0.76
0.78
0.8
0.82
0.84
0.86
GR NO
Carbon pool index (CPI) P = 0.0005
Carbon pool index (CPI): CPI = (total SOC in sample soil) / (total SOC in reference soil) (Blair et al., 1995)
•where the soil under NAT treatment was referred to as the reference •indicates the effect of land-use change or management practice on total SOC
11
b
a
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
GR NO
Lability index (LI) P = 0.0015
SOC management-related indices
Lability index (LI): LI = (L in sample soil) / (L in reference soil) (Blair et al., 1995)
where, the soil under NAT treatment was referred to as the reference
12
SOC management-related indices
a
b
0.87
0.88
0.89
0.9
0.91
0.92
0.93
0.94
GR NO
Carbon management index (CMI) P = 0.0491
Carbon management index (CMI): CMI = CPI * LI (Blair et al., 1995)
reflects the changes in total SOC and LOC as a result of agricultural practice,
with an emphasis on the changes in LOC
13
• Overall, the more abrupt the land-use change (e.g., from natural land to cultivated land), or the more intensive the applied management practice, the steeper the decrease in each of the CPI, LI, and CMI (Blair et al., 1995)
• The greater CPI and CMI observed for GR than those for NO suggest that the overall disturbance of SOC pool by the land-use change from natural land to cropland is smaller under the former than that under the latter
SOC management-related indices
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• It seems that (concordantly with some previous studies), livestock trampling during the summer (when the soil is dry) has not compacted the soil and neither deteriorated the soil structure
• It seems that the qualitative effect of stubble grazing on OM (through the addition of manure), has improved the aggregation and hydraulic properties of soil, and therefore more than compensating for the quantitative loss of OM (through grazing)
15
SOC management-related indices
In the long-run, moderate stubble grazing does not adversely affect the SOC pool. Partial explanations to this could be:
• the moderate disturbance of the soil surface by hoof action breaks the thin crust cover and increases the mixing of the coarse stubble residues in the soil matrix, accelerating its degradation and incorporation into the SOC pool, and compensating for the loss of stubble through consumption
• the qualitative effect of stubble grazing on OM input – through the addition of droppings – is of relatively high impact, compensating for the quantitative loss of OM through stubble consumption
Implications
• Studying the mechanisms through which each of the hoof action, biomass consumption, and droppings excretion affect the soil organic carbon pools and dynamics
• Defining optimal stubble retention rate – for maximizing economic input on the short run while sustaining soil quality on the long run
• Environmental footprint – erosional processes; GHGs emissions
• Long-term temporal sequence – for covering all ‘types’ of years (drought / average / rainy)
• Geophysical background effect – climate and soil gradient (latitudinal transect)
Knowledge gaps / Yet to be studied …
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Vegetative patchiness
Patches (woody vegetation)
Interpatch spaces (herbacaous, biological
crusts, bare soil)
flexibility
survivability
resilience
Valentin and d'Herbès, 1999
The Niger Tiger Bush
Two-phase mosaic ecosystems
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Two phase mosaic-like ecosystems shrubby vegetation patches - Sarcopoterium spinosum, Coridothymus capitatus
interpatch spaces - herbaceous, microphytes, bare soil
• Patches (Sarcopoterium spinosum, Coridothymus capitatus)
• Interpatch spaces
• Flock trampling routes
Productivity continuum, the patch scale
Productive Degraded
shrubby interpatch spaces trampling
patches (excluding routes) routes
Soil quality continuum
high low
shrubby patches interpatch spaces trampling routes
Feedback relations
+
+
+
+
Implications
Livestock trampling routes:
• increase geodiversity at the patch scale
• modify the ecosystem self-organization
• affect resilience and ecosystem health
• impact NPP of the rangeland ecosystem
Proposed effects of livestock rate
2-phase
3-phase
1-phase
bi-modal
tri-modal
no self-organization
moderate
high
low
low moderate high
Livestock rate
Health
Self-organization
Geodivesity
• Actual effects of livestock-induced geodiversity on:
• spatial redistribution of resources at the patch scale
• surface processes at the hillslope scale
• ecosystem health
• ecosystem’s NPP
Knowledge gaps / Yet to be studied …
Afforestation in the semi-arid Negev
• Forestry systems have been acknowledged as an efficient means in restoration of degraded lands
• The afforestation lands in the Negev have been based on rainwater harvesting systems
• Recent studies alerted that earthworks involved in the preparation of the water runoff harvesting systems have led to geo-ecosystems degradation
• Among the adverse effects: decreased spatial heterogeneity, smaller plant diversity, and reduction in pastoral productivity
Objectives
• To assess – in contour bench terraces (shichs) -based afforestation lands – the effects of earthwork constructions on changes in health of the geo-ecosystem along a temporal sequence after establishment
• This was conducted by investigating several soil quality indicators and herbaceous biomass productivity among two-years old systems (established in 2012), nine years old systems (established in 2005), and reference (control, without earthwork constructions nor tree planting) systems
Hypotheses
• Geo-ecosystem degradation on the short time-span (two-years after the shich's system construction)
• Self-restoration of the ecosystem on the long time-span (nine-years after the shich's system construction)
Preliminary results (normalized Treatment effect)
b
a
a
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2-year old 9-year old Natural
Mg
ha-
1
Biomass (P < 0.0001)
b
a a
0
10
20
30
40
50
60
70
2-year old 9-year old Natural
cm
Wetting front (P < 0.0001)
Preliminary results (normalized Treatment effect)
a
a
a
a
b ab
a
b b
0
1
2
3
4
5
6
7
8
9
10
SM (%) Hygr. SM (%) pb (Mg m-3)
P = 0.0975 P < 0.0001 P = 0.0490
2-year old
9-year old
Natural
Preliminary results (normalized Treatment effect)
Functioning
• It was observed that micro-topographic surface roughness of the source areas of the nine-year old systems was greater than that under the two-year old systems
• This is assumed to increase retention of water and soil resources at the patch scale of the inter-terraces spaces
Interim conclussions
• Afforestation-related earthworks increase geodiversity at the hillslope scale, but at the same time, decrease geodiversity at the patch scale
• Yet, at the long-run (a decade and over), eco-geomorphic feedback lead to increased geodiversity at the patch scale, self-restoring the soil quality and ecosystem NPP
0
1
2
3
4
5
6
7
8
Water:EC1,
Biochar: 0g/kg
Water:EC1,
Biochar : 5g/kg
Water:EC1,
Biochar: 20g/kg
Water:EC5.5,
Biochar : 0g/kg
Water:EC5.5,
Biochar : 5g/kg
Water:EC5.5,
Biochar :20 g/kg
cm
Stem height, February 2013