Ilan Stavi

Dead Sea & Arava Science Center, Israel istavi@adssc.org

Agro-ecosystems

functioning under stress

The northern Negev

1. Dryland wheat agro-pastoral systems:

Functioning and soil organic carbon dynamics

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

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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

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1. Natural land (NAT) 2. Continuous wheat, without stubble grazing (NO) 3. Continuous wheat, with stubble grazing (GR) Pictures taken during August 2013

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2 3

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a

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b

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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

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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)

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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

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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

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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

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• 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)

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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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2. Livestock-induced geodiversity in three-phase rangelands: Effects on geo-

ecosystem functioning

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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Redistribution Patchiness

+

+

Two phase mosaic-like ecosystems shrubby vegetation patches - Sarcopoterium spinosum, Coridothymus capitatus

interpatch spaces - herbaceous, microphytes, bare soil

Two Phase Mosaic?

• Patches (Sarcopoterium spinosum, Coridothymus capitatus)

• Interpatch spaces

• Flock trampling routes

Surface cover (%)

0-2 cm

Micro-habitat*Treatment

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Spring

Micro-habitat*Treatment

Water

accumulation

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Water

contribution

Spring

Micro-habitat*Treatment

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SOM

deposition

SOM

contribution Stavi et al., 2008

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 …

3. Afforestation effects on

geo-ecosystem functioning and health

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)

Habitat effect on soil penetration resistance

Preliminary results (normalized Treatment effect)

b

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0.8

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1.6

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2-year old 9-year old Natural

Mg

ha-

1

Biomass (P < 0.0001)

b

a a

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2-year old 9-year old Natural

cm

Wetting front (P < 0.0001)

Preliminary results (normalized Treatment effect)

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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)

Preliminary results (normalized Aspect 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

4. Biochar for alleviating

agricultural footprint

and offsetting global changes

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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