Main authors: Abdallah Alaoui, Ursula Gämperli Krauer, Tatenda Lemann, Vincent Roth, Gudrun Schwilch & iSQAPER Case Study Site teams
iSQAPERiS editor: Jane Brandt
Source document: Alaoui, A., Gämperli Krauer, U., Lemann, T., Roth, V., Schwilch, G. & iSQAPER Case Study Site teams (2018) Soil quality inventory of case study sites. iSQAPER Project Deliverable 5.2, 23 pp

 

1. Case study sites

The impacts of agricultural management practices (AMPs) on soil quality were measured in 14 case study sites, including 10 located in Europe and 4 in China, representative of the major pedo-climatic zones (Figure 1) (see also »Pedoclimatic zones of Europe and »Pedoclimatic zones of China). The case study sites represent wide agricultural management activities and were chosen because they include promising AMPs that have been shown to improve soil quality (Table 1).

D52 fig01a
Europe
D52 fig01b
China

 

2. Pedoclimatic zones

In Europe, the 10 study areas covered 6 out of the 8 climatic zones:

  • Boreal to sub-Boreal (14 plots),
  • Northern sub-Continental (5 plots),
  • Southern Sub-Continental (49 plots),
  • Atlantic (7 plots),
  • Mediterranean Temperate (31 plots) and
  • Mediterranean semi-arid (6 plots).

In China, climate variability is higher and only 3 out of 10 climatic areas were investigated:

  • Central Tropical Asia (14 plots),
  • Warm Temperate and
  • Middle (6 plots) Temperate zone (6 plots).

3. Farming systems and agricultural management practices

The classification of the farming systems used in this study was according to CORINE land cover assessment (European Environment Agency, 2006) and consist of 3 classes; Arable land, permanent crops, fodder crops, root crops, and pastures (see »Farming system classification in the iSQAPER project).

Based on WOCAT database (www.wocat.net), 18 promising AMPs with potential to improve soil quality were selected (Schwilch et al., 2011) (Table 1). Each case study identified at least 3 out of the 18 selected APMs (or combinations thereof). The selection of these AMPs was performed based on the following criteria:

  1. management practice implemented for at least 3 years;
  2. at least in 2 different soil types; and
  3. at least in 2 different first level Farming Systems (arable, permanent, grazing).

For mixed farming systems, the study site teams were asked to consider the existence of two different farming systems on the same farm, in case it includes both arable cropping and pastures. Additionally, for each AMP plot, the study site teams had to identify 3 related control plots. The idea is to compare the soil quality on a plot where management practices have changed 3 or more years ago with that on a control plot where practices did not change. Both control and AMP plots were located in the same pedo-climatic zone and having comparable soil conditions. In total, 138 sets of paired plots (138 plots with promising AMPs and 138 controls) were considered, with 112 plots located in Europe and 26 in China.  

Table 1. Promising AMPs considered, description, expected impacts/ecological benefits and the corresponding main soil threat targeted by its use (WOCAT, (Schwilch et al., 2011))

AMP list AMP description  Expected impacts / Ecological benefits
Soil management
1 - No-till A system where crops are planted into the soil without primary tillage 
  • Reduces decomposition of OM rates leading to its increase in soil, enhances cycling of nutrients, enhances soil structure and increases water infiltration.
  • Improves soil biological life including disease and weed suppression.
2 - Min-till Tillage operation with: a) reduced tillage depth; b) strip tillage; c) mulch tillage; or or a combination thereof
  • Reduces decomposition of OM rates leading to its increase in soil, enhances cycling of nutrients, enhances soil structure and increases water infiltration.
  • Improves soil biological life including disease and weed suppression.
3 - Permanent soil cover / Removing less vegetation cover Avoiding a bare or sparsely covered soil exposed to weather conditions (rain, wind, radiation, etc) by ensuring a permanent cover (at least 30% of the soil surface) throughout the year, e.g. through cutting less grass, leaving a volunteer crop or crop residues, etc. (see also cover crops and residue maintenance / mulching)
  • Improves infiltration and retention of soil moisture resulting in less severe, less prolonged crop water stress and increases availability of plant nutrients.
  • Provides source of food and habitat for diverse soil life: created channels for air and water, biological tillage and substrate for biological activity through the recycling of organic matter and plant nutrients.
  • Increases humus formation.
  • Reduces the impact of rain drops on soil surface resulting in reduced crusting and surface sealing.
  • Reduces runoff and erosion.
  • Reduces wind erosion.
  • Increases soil regeneration.
  • Mitigates temperature variations on and in the soil.
  • Improves the conditions for the development of roots and seedling growth.
4 - Cover crops
  1. Cover cropping: planting close-growing crops (usually annual legumes),
  2. Relay cropping: specific form of mixed cropping / intercropping in which a second crop is planted into an established stand of a main crop. The second crop develops fully after the main crop is harvested. Better crop cover: selecting crops with higher ground cover, increasing plant density, etc.
  1. Protects soil, between perennials or in the period between seasons for annual crops. N-fixation in case of leguminous crops.
  2. Continuously covered soil. Reduces the insect/mite pest populations because of the diversity of the crops grown. Reduces the plant diseases. Reduces hillside erosion and protected topsoil, especially the contour strip cropping. Attracts more beneficial insects, especially when flowering crops are included in the cropping system.
  3. Protects soil against the impacts of raindrops or wind and keeps soil shaded; and increases moisture content.
5 - Residue maintenance / Mulching Maintaining crops residues or spreading of organic (or other) materials on the soil surface.
  • Reduces sheet and rill erosion.
  • Reduces wind erosion.
  • Maintains or improves soil organic matter content.
  • Conserves soil moisture.
  • Provides food and escapes cover for wildlife.
6 - Cross-slope measure Structural measure along the contour to break slope lengths, such as terraces, bunds, grass strip, trashlines, contour tillage Reduces surface runoff and erosion (increase infiltration capacity).
7 - Measures against compaction
  1. Breaking compacted soil: e.g. deep ripping, subsoiling (hard pans); Digging the soil up to twice as deep as normally.
  2. Growing deep rooted plants in the rotation such as: annual alfalfa, beet, sunflower, okra, flax, turnip.
  3. Controlled traffic farming: is a system which confines all machinery loads to the least possible area of permanent traffic lanes
  4. Soil compaction models (considering tire size, inflation pressure, weather and soil conditions) to predict allowable wheel load and soil compaction maps to show how soil compaction varies at different locations and depths across the field
a-b) Looses soil to improve drainage, infiltration, aeration and rooting characteristics, and brings nutrients up from deep below
c-d) Minimizes soil damage and preserves soil function in terms of water infiltration, drainage and greenhouse gas mitigation, and (d) provides useful information for decision making process for site-specific applications such as variable deep tillage to benefit from increased timeliness (and reduced management costs)
Nutrient management
8 - Leguminous crop A leguminous crop is a plant in the family Fabaceae (or Leguminosae) that is grown agriculturally, primarily for their grain seed called pulse, for livestock forage and silage, and as soil-enhancing green manure. Well-known legumes include alfalfa, clover, peas, beans, lentils, lupins, mesquite, carob, soybeans, peanuts, and tamarind.
  • Provides soil with nitrogen and additional nitrogen from chemical fertilizers can be reduced. (See also cover crop and green manure)
9 - Green manure / Integrated soil fertility management Green manure is a crop grown to be incorporated into the ground, while the more general term ‘integrated soil fertility management’ refers to a mix of organic and inorganic materials, used with close attention to context-specific timing and placing of the inputs in order to maximize the agronomic efficiency.
  • Increases organic matter content, thereby improving fertility and reducing erodibility. In case of leguminous green manure, tilling it back into the soil allows exploiting the high levels of captured atmospheric nitrogen found in the roots.
10 - Manuring (a) / composting (b)
  1. Manure is organic matter, mostly derived from animal feces (except in the case of green manure, which can be used as organic fertilizer in agriculture).
  2. Compost is organic matter that has been decomposed and recycled as a fertilizer and soil amendment. Compost is a key ingredient in organic farming.
  1. Contributes to the fertility of the soil by adding organic matter and nutrients, such as nitrogen, that are trapped by bacteria in the soil.
  2. Improves soil fertility through nutrient content and availability, soil structure and microbiological activity; impacts plant growth and health directly and indirectly.
Pest management
11 - Crop rotation (a) / Control or change of species composition (b) Practice of alternating the annual crops grown on a specific field in a planned pattern or sequence in successive crop years so that crops of the same species or family are not grown repeatedly on the same field Diversify species in rotation systems or grasslands.

a) Reduces risk of pest and weed infestations.

  • Improves distribution of channels or biopores created by diverse roots (various forms, sizes and depths).
  • Improved distribution of water and nutrients through the soil profile.
  • Allows exploration for nutrients and water of diverse strata of the soil profile by roots of many different plant species resulting in a greater use of the available nutrients and water.
  • Increases nitrogen fixation through certain plant-soil biota symbionts and improved balance of N/P/K from both organic and mineral sources. Increases humus formation.

b) Introduces desired / new species, reduces invasive species, controls burning, residue burning.

12 - Integrated pest and disease management incl. organic agriculture Appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to reduce or minimize risks to human health and the environment.
  • Emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms.
Water management
13 - Water diversion and drainage A graded channel with a supportive ridge or bank on the lower side. It is constructed across a slope to intercept surface runoff and convey it safely to an outlet or waterway
  • Reduces hazard towards adverse events (floods, storms,…), reduces soil waterlogging
14 - Irrigation management Controlled water supply and drainage: mixed rainfed – irrigated; full irrigation; drip irrigation
  •  Improves water harvesting; increased soil moisture; reduces evaporation; improves excess water drainage; recharge of groundwater
Crop management
15 - Major change in timing of activities Adaptation of the timing of land preparation, planting, cutting of vegetation according weather and climatic conditions, vegetation growth, etc.
  • Reduced soil compaction, soil loss, improved biomass, increased biomass, increased soil OM
16 - Layout change according to natural and human environment/needs eg exclusion of natural waterways and hazardous areas, separation of grazing types; increase of landscape diversity.
  •  Reduces surface runoff and erosion, increases biomass, nutrients and soil OM, controls pests and diseases
17 - Area closure / rotational grazing Complete or temporal stop of use to support restoration
  • Improves vegetative cover, reduces intensity of use, and soil compaction and erosion.
18 - Change of land use practices / intensity level eg change from grazing to cutting (for stall feeding), from continuous cropping to managed fallow, from random (open access) to controlled access (grazing land), from herding to fencing, adjusting stocking rates.
  •  Increases biomass, nutrient cycling, soil OM, improves soil cover, beneficial species (predators, earthworms, pollinators), biological pest / disease control, and increases / maintains habitat diversity. - Reduces soil loss, soil crusting/sealing, soil compaction, and invasive alien species.

4. Soil quality indicators:

In order to assess the impact of AMPs on soil quality, 11 soil quality variables based on a visual soil assessment methodology were selected based on extensive literature review (e.g. Shepherd, 2000) (Table 2). For each variable, clear and precise instructions were compiled in a manual. A newly developed infiltrometer was used to easily assess the soil infiltration capacity in the field and to investigate hydrodynamic flow processes (Alaoui et al., 2018).

Table 2. List of the variables used to assess soil quality.
Indicators 1 and 2 provide general information, 3 to 8 are derived from visual soil assessment (VSA) methodology, and 9 to 11 are based on measurements.

Soil quality indicator  Soil threats addressed 
1 Susceptibility to Wind and Water Erosion  Erosion 
2 Surface ponding (under cropping) Soil compaction
3 Presence of a cultivation pan Subsoil compaction
4 Soil Colour OM decline
5 Soil porosity Soil compaction
6 Soil structure and consistency Soil compaction
7 Soil slaking test (soil stability) Erosion
8 Biodiversity (earthworm density) Biodiversity decline
9 pH Acidification
10 Infiltration rate / Penetration resistance Soil compaction
11 Labile organic carbon Organic carbon decline

It is worth mentioning that the indicators selected to evaluate soil quality are mainly related to soil structure (3 – 8 and 10) since they are based on »Visual soil and plant quality assessment (VSA). In this article, soil quality concerns mainly soil structure.

A quantitative investigation of soil quality in terms of physical, chemical and biological is given in »Impact of promising land managment practices.

For the evaluation of soil quality, a qualitative score was established for the 11 variables according to 3 conditions: good, moderate, and bad, illustrated with standardized photos serving as references. The improvement in soil quality was checked through the comparison between the AMP plot and the control.

  • Where at least a single variable shows a better soil quality score in a plot with AMP (compared with the control), a soil quality improvement was considered.
  • If better scores were shown in the control, the impact of AMP was considered negative.
  • If the scores were similar, the AMP was assumed to have no impact.

The inventory and the scoring of soil quality were done together with land users, for all study sites under the constraints of carrying out the assessment of the paired AMP plot – control to insure comparable soil conditions. The farmers were requested to express their own opinion with regard to the variables that have meaning for soil quality within the list we proposed (Table 2). We then compared their variables with the ones that have been shown to improve soil quality in all study sites.

 


Note: For full references to papers quoted in this article see

» References

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