Agro-ecosystems functioning under stress Ilan Stavi

Transcription

1 Agro-ecosystems functioning under stress Ilan Stavi Dead Sea & Arava Science Center, Israel

2 The northern Negev

3 1. Dryland wheat agro-pastoral systems: Functioning and soil organic carbon dynamics

4 Conservation farming systems 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 4

5 Conservation farming systems 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 5

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

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8 Lan-use effect on soil characteristics 16 P < a b 12 b Wheat with stubble grazing P = a a a Wheat with no stubble grazing 4 P < Natural land 2 P = a a a a a b 0 Wetness depth (m) ρb (kg m-3) Өg (%) CaCO3 (%)

9 Land-use effect on SOC and LOC P < a 20 b b No stubble grazing 15 P = Stubble grazing 10 b ab a Natural 5 0 SOC (g kg-1) LOC (x10-7)

10 )%/%( Carbon lability 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) 0.03 Lability (L) P < a b b GR NO NAT 10

11 SOC management-related indices 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 a Carbon pool index (CPI) P = b GR NO 11

12 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 Lability index (LI) P = a 1.2 b GR NO 12

13 SOC management-related indices 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 a Carbon management index (CMI) P = b GR NO 13

14 SOC management-related indices 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 landuse change from natural land to cropland is smaller under the former than that under the latter 14

15 SOC management-related indices 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

16 Implications 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

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18 Knowledge gaps / Yet to be studied 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) 18

19 2. Livestock-induced geodiversity in three-phase rangelands: Effects on geoecosystem functioning

20 Vegetative patchiness Patches (woody vegetation) Interpatch spaces (herbacaous, biological crusts, bare soil)

21 Two-phase mosaic ecosystems The Niger Tiger Bush flexibility survivability resilience Valentin and d'herbès,

22 + Redistribution Patchiness +

23 Two phase mosaic-like ecosystems shrubby vegetation patches - Sarcopoterium spinosum, Coridothymus capitatus interpatch spaces - herbaceous, microphytes, bare soil

24 Two Phase Mosaic?

25 Patches (Sarcopoterium spinosum, Coridothymus capitatus) Interpatch spaces Flock trampling routes

26 Surface cover (%)

27 Micro-habitat*Treatment 0-2 cm 27

28 Micro-habitat*Treatment Spring Water accumulation Water contribution 28

29 Micro-habitat*Treatment Spring SOM deposition SOM contribution Stavi et al.,

30 Productivity continuum, the patch scale Productive Degraded shrubby interpatch spaces trampling patches (excluding routes) routes

31 Soil quality continuum + high low shrubby patches interpatch spaces trampling routes Feedback relations

32 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

33 Proposed effects of livestock rate high Health Self-organization moderate tri-modal Geodivesity low bi-modal 3-phase no self-organization 2-phase 1-phase low moderate high Livestock rate

34 Knowledge gaps / Yet to be studied 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

35 3. Afforestation effects on geo-ecosystem functioning and health

36 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

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38 Objectives To assess in contour bench terraces (shichs) -based afforestation lands the effects of earthwork constructions on changes in health of the geoecosystem 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

39 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)

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41 Habitat effect on soil penetration resistance

42 Mg ha-1 Preliminary results (normalized Treatment effect) Biomass (P < ) a a b 2-year old 9-year old Natural

43 cm Preliminary results (normalized Treatment effect) 70 Wetting front (P < ) 60 a a 50 b year old 9-year old Natural

44 Preliminary results (normalized Treatment effect) a P = P < P = a a a 2-year old 9-year old Natural 2 b b a ab b 1 0 SM (%) Hygr. SM (%) pb (Mg m-3)

45 Preliminary results (normalized Aspect effect)

46 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

47 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), ecogeomorphic feedback lead to increased geodiversity at the patch scale, self-restoring the soil quality and ecosystem NPP

48 4. Biochar for alleviating agricultural footprint and offsetting global changes

49 cm Water: EC1, Biochar: 0 g/kg Water: EC1, Biochar : 5 g/kg Stem height, February 2013 Water: EC1, Biochar: 20 g/kg Water: EC5.5, Biochar : 0 g/kg Water: EC5.5, Biochar : 5 g/kg Water: EC5.5, Biochar : 20 g/kg

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