Sunday, 29 April 2012
What it is: Infiltration is the downward entry of water into the soil. The velocity at which water enters the soil is infiltration rate. Infiltration rate is typically expressed in inches per hour. Water from rainfall or irrigation must first enter the soil for it to be of value.
Why it is important: Infiltration is an indicator of the soil’s ability to allow water movement into and through the soil profile. Soil temporarily stores water, making it available for root uptake, plant growth and habitat for soil organisms.
Specific problems that might be caused by poor function: When water is supplied at a rate that exceeds the soil’s infiltration capacity, it moves downslope as runoff on sloping land or ponds on the surface of level land. When runoff occurs on bare or poorly vegetated soil, erosion takes place. Runoff carries nutrients, chemicals, and soil with it, resulting in decreased soil productivity, off-site sedimentation of water bodies and diminished water quality. Sedimentation decreases storage capacity of reservoirs and streams and can lead to flooding.
Restricted infiltration and ponding of water on the soil surface results in poor soil aeration, which leads to poor root function and plant growth, as well as reduced nutrient availability and cycling by soil organisms. Ponding and soil saturation decreases soil strength, destroys soil structure, increases detachment of soil particles, and makes soil more erodible. On the soil surface rather than in the soil profile, ponded water is subject to increased evaporation, which leads to decreased water available for plant growth.
A high infiltration rate is generally desirable for plant growth and the environment. In some cases, soils that have unrestricted water movement through their profile can contribute to environmental concerns if misapplied nutrients and chemicals reach groundwater and surface water resources via subsurface flow.
Conservation practices that lead to poor infiltration include:
- Incorporating, burning, or harvesting crop residues leaving soil bare and susceptible to erosion,
- Tillage methods and soil disturbance activities that disrupt surface connected pores and preventaccumulation of soil organic matter, and
- Equipment and livestock traffic, especially on wet soils, that cause compaction and reduced porosity.
What you can do: Several conservation practices help maintain or improve water infiltration into soil by increasing vegetative cover, managing crop residues, and increasing soil organic matter. Generally, these practices minimize soil disturbance and compaction, protect soil from erosion, and encourage the development of good soil structure and continuous pore space. As a short-term solution to poor infiltration, surface crusts can be disrupted with a rotary hoe or row cultivator and plow plans or other compacted layers can be broken using deep tillage.
Long-term solutions for maintaining or improving infiltration include practices that increase soil organic matter and aggregation, and reduce soil disturbance and compaction. High residue crops, such as corn and small grains, perennial sod, and cover crops protect the soil surface from erosion and increase soil organic matter when reduced tillage methods that maintain surface cover are used to plant the following crop. Application of animal manure also helps to increase soil organic matter. Increased organic matter results in increased aggregation and
improved soil structure leading to improved infiltration rates. Conservation tillage, reduced soil disturbance, and reducing the number of trips across a field necessary to produce a crop help leave continuous pore spaces intact and minimize the opportunity for soil compaction.
Conservation practices resulting in infiltration rates favorable to soil function include:
- Conservation Crop Rotation
- Cover Crop
- Prescribed Grazing
- Residue and Tillage Management
- Waste Utilization
The Single Ring (Flooded/Ponded) Infiltrometer Method is described in the Soil Quality Test Kit Guide, Section I, Chapter 3, pp. 7 - 8. See Section II, Chapter 2, pp. 55 – 56 for interpretation of results.
Photo: A one inch layer of water is added to a six inch diameter ring to measure infiltration rate.
Lowery B., W.J. Hickey, M.A. Arshad, and R. Lal. 1996. Soil water parameters and soil quality. In: Doran J.W., A.J. Jones, editors. Methods for assessing soil quality. Madison, WI. p 143-55.
What it is: Earthworms are native to non-glaciated areas of North America, but non-native species from Europe and Asia also exist here. Earthworms are classified into three groups based on their habitat. Litter-dwellers live in the litter, ingest plant residues, and may be absent in plowed, litter-free soil. Mineral soil-dwellers live in topsoil that is rich in organic matter. They burrow narrow channels and feed on a mixture of soil and plant residues. Deep soil-burrowers (night crawlers) dig long, large burrows into deep soil layers. They carry with them plant residues for consumption. Earthworm cast is digested material that is excreted back into the soil. Cast is enriched with nutrients (N, P, K, and Ca) and microorganisms during its passage through the worm’s digestive system. Fresh cast is a site of intense microbial activity and nutrient cycling. Earthworms contribute nutrients to the soil and improve porosity, tilth, and root development. They are measured in number/m2.
Why it is important: Despite some reservations, there is evidence that earthworms contribute to crop production. Earthworms play a key role in modifying the physical structure of soils by producing new aggregates and pores, which improves soil tilth, aeration, infiltration, and drainage. Earthworms produce binding agents responsible for the formation of water-stable macro-aggregates. They improve soil porosity by burrowing and mixing soil. As they feed, earthworms participate in plant residue decomposition, nutrient cycling, and redistribution of nutrients in the soil profile. Their casts, as well as dead or decaying earthworms, are a source of nutrients. These beneficial effects stimulate root growth and proliferation deep into the soil to satisfy nutrient and water requirements. Roots often follow earthworm burrows and uptake available nutrients associated with casts.Lumbricus terrestris, or the night crawler, and other nonnative earthworms have displaced many native species across the United States. In Northern forests, their populations can reach such high levels that no litter can be maintained on the forest floor.
Specific problems that might be caused by poor function: Low or absent earthworm populations are an indicator of little or no organic residues in the soil and/or high soil temperature and low soil moisture that are stressful not only to earthworms, but also for sustainable crop production. Earthworms stimulate organic matter decomposition. Lack of earthworms may reduce nutrient cycling and availability for plant uptake. Additionally,
natural drainage and aggregate stability can be reduced. Soil remediation to increase nutrient cycling, break up compacted layers to improve aeration and drainage, and stabilize soil to protect it from erosion may be needed. Some soils are naturally productive without earthworms because of their inherent properties.
What you can do: No-till increases plant residues and improves soil structure, providing improved habitat for earthworms. Studies conducted in the Midwest showed that in no-till systems, the combination of soil moisture, temperature, and quality of food supply are essential factors for earthworm population growth. Legumes, alone or in rotation, seem to be preferred by earthworms because of the quality of food they provide (figure 1). Deep soil-burrowers are lacking in plowed fields and changing to no-till may not help their quick establishment unless they are introduced first. Seeding earthworms is a potential technique to reintroduce them, but it is not practical on a large scale. Compared to other ecosystems, agricultural soils are generally dominated by species adapted to disturbance, low organic matter content, and a lack of surface litter, so the management practices listed below should increase earthworm populations. Sandy or wet heavy clay soils may not naturally harbor significant earthworm populations, but irrigation and drainage can help provide favorable conditions for earthworms to thrive. (In areas where restoration of native species is a goal, removal of exotic species is a must.) Carefully consider pesticide applications, as some, such as carbamate insecticides (table 1) and carbendazim and benomyl fungicides, have severe adverse effects on earthworms.
The following practices boost earthworm populations:
- Tillage Management (no-till, strip till, ridge till)
- Crop Rotation (with legumes) and Cover Crops
- Manure & Organic By-product Application
- Pasture & Hayland Management
- Soil Reaction (pH) Management
- Irrigation or Drainage
Figure 1. Effect of tillage and crop on earthworm number/m2 CT=conventional till, NT= no-till; W=wheat, C=corn, S=soybean Adapted from Hubbard, et al. 1999.
|Table 1. Insecticides harmful to earthworms|
|Common Name||Trade Name|
Measuring earthworm abundance:
Earthworm populations are measured by counting the number of earthworms/m2 as described in the Soil Quality Test Kit Guide, Section I, Chapter 10, p 22-23. See Section II, Chapter 9, p 73 - 75 for interpretation of results.
Hubbard VC, et al. 1999. Earthworm response to rotation and tillage in Missouri claypan soil. Biol Fertil Soils 29:343-7.
Soil Quality Management: Key Strategies for Agricultural Land
How can you manage land in a way that improves soil productivity, water quality, and other soil benefits? Start with these six components of soil quality management. If you want to assess the effect of your existing land management practices, begin by asking which of your practices fall into each of these categories. Choosing specific practices within each category depends on your situation because different kinds of soil respond differently to the same practice.
Enhance organic matter
Organic matter management: Whether your soil is naturally high or low in organic matter, adding new organic matter every year is perhaps the most important way to improve and maintain soil quality. Regular additions of organic matter improve soil structure, enhance water and nutrient holding capacity, protect soil from erosion and compaction, and support a healthy community of soil organisms. Practices that increase organic matter include: leaving crop residues in the field, choosing crop rotations that include high residue plants, using optimal nutrient and water management practices to grow healthy plants with large amounts of roots and residue, growing cover crops, applying manure or compost, using low or no tillage systems, using sod-based rotations, growing perennial forage crops, and mulching. (Link to organic matter management practices.)
Avoid excessive tillage
Tillage management: Reducing tillage minimizes the loss of organic matter and protects the soil surface with plant residue. Tillage is used to loosen surface soil, prepare the seedbed, and control weeds and pests. But tillage can also break up soil structure, speed the decomposition and loss of organic matter, increase the threat of erosion, destroy the habitat of helpful organisms, and cause compaction. New equipment allows crop production with minimal disturbance of the soil. (Link to cultivation practices.)
Manage pests and nutrients efficiently
Chemical management: An important function of soil is to buffer and detoxify chemicals, but soil's capacity for detoxification is limited. Pesticides and chemical fertilizers have valuable benefits, but they also can harm non-target organisms and pollute water and air if they are mismanaged. Nutrients from organic sources also can pollute when misapplied or over-applied. Efficient pest and nutrient management means testing and monitoring soil and pests; applying only the necessary chemicals, at the right time and place to get the job done; and taking advantage of non-chemical approaches to pest and nutrient management such as crop rotations, cover crops, and manure management. (Link to fertility management and pest management practices.)
Prevent soil compaction
Compaction management: Compaction reduces the amount of air, water, and space available to roots and soil organisms. Compaction is caused by repeated traffic, heavy traffic, or traveling on wet soil. Deep compaction by heavy equipment is difficult or impossible to remedy, so prevention is essential. Subsoil tillage is only effective on soils with a clearly defined root-restricting plow pan. In the absence of a plow pan, subsoil tillage to eliminate compaction can reduce yield. Prevention, not tillage, is the way to manage compaction. (Link to cultivation, compaction controlled traffic practices.)
Keep the ground covered
Residue management: Bare soil is susceptible to wind and water erosion, and to drying and crusting. Ground cover protects soil, provides habitats for larger soil organisms, such as insects and earthworms, and can improve water availability. Ground can be covered by leaving crop residue on the surface or by planting cover crops. In addition to ground cover, living cover crops provide additional organic matter, and continuous cover and food for soil organisms. Ground cover must be managed to prevent problems with delayed soil warming in spring, diseases, and excessive build-up of phosphorus at the surface. (Link to residue and cover crop practices.)
Diversify cropping systems
Diversity management: Diversity is beneficial for several reasons. Each plant contributes a unique root structure and type of residue to the soil. A diversity of soil organisms can help control pest populations, and a diversity of cultural practices can reduce weed and disease pressures. Diversity across the landscape can be increased by using buffer strips, small fields, or contour strip cropping. Diversity over time can be increased by using long crop rotations. Changing vegetation across the landscape or over time not only increases plant diversity, but also the types of insects, microorganisms, and wildlife that live on your farm. (Link to cropping systems and integrated pest management practices.)
Saturday, 28 April 2012
ISLAMABAD: Pakistan can save Rs 200 billion per annum on edible oil import by enhancing of oil seeds production domestically.
Director Crops of National Agriculture Research Council (NARC), Akbar Shah Mohmand addressing the participants and farmers of the canola seeds introductory exhibition said canola oil seeds play an important role in enhancing the production of edible oil domestically and that was why the NARC has introduced the new variety of high breed canola seeds for the farmers so that the production of edible oil could be increased and help reduce dependence on the import of edible oil and save foreign exchange for the country.
Akbar said new canola highly breed seed introduced by the scientists of the NARC was highly productive.
He said the new canola breed seed could produce 32 maund per acre and its average production was 22 maund per acre.
He informed the farmers by cultivating new canola seeds they could earn Rs 40,000 to Rs 50,000 per acre and also help enhance the edible requirements of the country. He said they could also not only enhance their income but also help saving billions of rupees on import bill for the country.
Highlighting the benefits of the canola oil he said it contains mega-3 contents which is also useful for the use of heart patients. He said the quality of the canola edible oil is nearer to that of olive oil. app
Peshawar, Comsat, Agriculture and Bannu enter semis
RAWALPINDI: University of Peshawar, Comsats University Islamabad, Agriculture University Peshawar and Bannu University registered victories in the All Pakistan Intervarsity Men’s Volleyball Championship to qualify for the semifinals at Arid University here on Friday. In the first quarterfinal, University of Peshawar outclassed Iqra University Karachi by 3-0 with the score-line of 25-16, 25-06 and 25-12. Agriculture University Peshawar thrashed GCU Faislabad 3-2. Agriculture won the match with the score of 25-18, 22-25, 41-39, 22-25 and 15-12.
Comats University Islamabad defeated Quaid-e-Azam University 3-2. The score-line was 19-25, 25-20, 25-17, 32-34 and 15-11. In the last match of the day, Bannu University beat GCU Lahore by 3-1 with the score-line being 25-20, 23-25, 25-19, and 25-19.
University of Peshawar vs Comsats Islamabad
Bannu Universality vs Agriculture University Peshawar.
LAHORE - Punjab Livestock and Agriculture Minister Malik Ahmad Ali Aulakh said the poultry sector is of paramount importance and that veterinary doctors and scientists should play their role in checking chickens for the New Castle Disease (NCD).
He expressed these views while presiding over a meeting held regarding the checking of the disease, at the University of Veterinary and Animal Sciences (UVAS) on Friday.
UVAS Vice-Chancellor Prof Dr Talat Naseer Pasha, Livestock Additional Secretary Khalid Awais Ranjha, Pakistan Poultry Association representatives and veterinary doctors and scientists were also present on the occasion.
The minister said the Punjab government was paying special attention to the poultry sector so that the demand for meat and eggs could be fulfilled.
He said the sector was facing problems due to the NCD; therefore vaccines to control the disease were necessary to stave off economic losses.
The minister constituted three technical committees, headed by Dr Pasha, for suggesting long, medium and short-term measures for controlling the NCD and evolving a strategy to eliminate the sub-standard vaccines available in the market.
These committees will comprise Disease Control Laboratory Director Dr Tahir Yaqoob, Research Director General Dr Zafar Jameel Gul, Extension Director General Irfan Zahid, Deputy Secretary Dr Irfan Ali and Pakistan Poultry Association representatives.
He directed that poultry farmers should be motivated to keep their farms clean, ensure timely vaccine and bury dead chickens so that other birds could be saved from the virus.
He said a solid strategy should be evolved for the generation of energy from biomass at poultry farms.
Earlier, UVAS VC said the vaccine for NCD had been prepared locally in cooperation with the University of Veterinary and Animal Sciences, Veterinary Research Institute and the Pakistan Poultry Association and that its trials had been very successful.
What it is: Structural soil crusts are relatively thin, dense, somewhat continuous layers of non-aggregated soil particles on the surface of tilled and exposed soils. Structural crusts develop when a sealed-over soil surface dries out after rainfall or irrigation. Water droplets striking soil aggregates
and water flowing across soil breaks aggregates into individual soil particles. Fine soil particles wash, settle into and block surface pores causing the soil surface to seal over and preventing water from soaking into the soil. As the muddy soil surface dries out, it crusts over.
Structural crusts range from a few tenths to as thick as two inches. A surface crust is much more compact, hard and brittle when dry than the soil immediately beneath it, which may be loose and friable. Crusts can be described by their strength, or air-dry rupture resistance.
Soil crusting is also associated with biological and chemical factors. A biological crust is a living community of lichen, cyanobacteria, algae, and moss growing on the soil surface that bind the soil together. A precipitated, chemical crust can develop on soils with high salt content.
Why it is important: A surface crust indicates poor infiltration, a problematical seedbed, and reduced air exchange between the soil and atmosphere. It can also indicate that a soil has a high sodium content that increases soil dispersion when it is wetted by rainfall or irrigation.
Specific problems that might be caused by poor function: Because they are hard and relatively difficult to break, crusts restrict seedling emergence, especially in non-grass crops such as soybeans and alfalfa. Crusts can also reduce oxygen diffusion into the soil profile by as much as 50% if the soil crust is wet. Crust development soon after a crop is planted can result in such poor emergence that the crop might have to be replanted.
Surface sealing and crusts greatly reduce infiltration, and increase runoff and erosion. Increased runoff results in less water available in soil for plant growth. The sunlight (and energy) reflectance of a surface crust is higher than that of a non-crusted soil, so soil temperature may be lower and surface evaporation reduced where a crust exists (see photo on reverse). This could negatively affect germination and development of healthy seedlings in cooler climates.
The relatively smooth surface of a crusted soil initially increases wind erosion of sandy soils. Loose sand particles blow across and abrade the smooth surface of the crust. Roughening of the surface crust eventually reduces wind erosion. For soils with a small amount of sand, hard crusts protect the soil surface from wind erosion.
Surface crusts can have other limited benefits. Crusts decrease water loss because less of their surface area is exposed to the air compared to a tilled, fluffy soil. In addition, a crust forms a barrier to evaporation of soil moisture. Reduced evaporation of soil moisture means more water remains in the soil for plant use.
Practices that lead to soil crusting include:
- Harvesting, burning, burying, or otherwise removing plant residues and mulches so as to leave the soil surface bare for an extended period of time, and
- Soil disturbing activities that destroy organic matter, soil structure and aggregation, and result in very smooth seedbeds.
What you can do: Practices reducing the development of soil crusts or minimizing their negative impacts include those that protect or increase soil structure and organic matter and provide protective vegetative or residue cover on the soil surface. No-till or reduced tillage of cropland is the best way to reduce or eliminate crust formation. If tillage is necessary, it should only be done to the minimum level required for good seed germination and emergence. Large seeded crops do not require the same degree of clod size reduction or as smooth of a seedbed as do small seeded crops. Residue intercepts the force of falling raindrops and is a source of organic matter. Organic matter stabilizes soil aggregates making them more resistant to the physical impact of raindrops. Improved aggregation results in lower bulk density and increased pore space, and improves infiltration and water movement through soil.
Improved infiltration and water movement through soil decreases surface ponding and runoff, and helps protect soil from erosion. Good soil structure and aggregate stability are vital to supporting healthy, vigorous plants. Healthy plants provide and conservation tillage methods
manage surface and subsurface plant residues needed to increase organic matter while maintaining and improving aggregate stability and soil structure.
To reduce the incidence of surface crusting of soils high in sodium, irrigation water management prevents sodium accumulation at the surface, and gypsum (calcium sulfate) can be applied to promote flocculation and inhibit dispersion of soil particles.
It may be necessary to break a soil crust with a shallow, light tillage operation such as with a rotary hoe or row cultivator, preferably when the soil is still moist. Light tillage can increase seedling emergence and help control weeds. Irrigation water can also be used to help with
Conservation practices that minimize the development of a soil crust include:
- Conservation Crop Rotation
- Cover Crop
- Residue and Tillage Management
- Salinity and Sodic Soil Management
Photo left: Note the surface crust on this soil. The field was in tall fescue sod for 11 years. It was cleared and plowed using conventional tillage methods. Photo courtesy Bobby Brock, USDA NRCS (retired). Photo right: Collected from a no-till field in Georgia's Southern Piedmont, good structure and aggregation are evident in the soil on the right. The same soil formed a structural crust under conventional tillage. Note the sunlight reflectance of the crusted soil. Photo courtesy James E. Dean, USDA NRCS (retired).
Measuring soil crusts:
Crust air-dry rupture resistance can be measured by taking a dry piece of the crust about ½ inch on edge and applying a force on the edge until the crust breaks. Generally, more force is required for crusts that are thick and have high clay content. A penetrometer to measure the penetration resistance of the crust can be used. Crust thickness can also be measured.
Social issues and soil quality
Nutrient cycling, water regulation, and other soil functions are normal processes occurring in all ecosystems. From these functions come many benefits to humans, such as food production, water quality, and flood control, which have value economically or in improved quality of life. People can increase or decrease the value of soil benefits because land-management choices affect soil functions. Thus, it is important to understand what benefits we derive from soil and their value so we can appreciate the importance of managing land in a way that maintains soil functions.
What are the social benefits of soil?
People tend to emphasize benefits with the most direct, private economic value. In rural areas, this is usually plant growth especially as crops and rangeland, but also as recreation areas. In urban/suburban areas, the most direct economic benefits of soil relate to structural support for buildings, roads, and parking. Landscaping, gardening and parklands may also be valued economically.
Those are all on-site, short-term benefits. That is, the landowner who decides how to manage the soil also reaps the benefits (and costs) of those management decisions. In contrast, many important benefits are long-term or go beyond the land being managed. The landholders who make the management choices and pay the costs of managing land may not be the same people who are affected by the landholders decisions. Society should discuss the value of these off-site benefits and to what extent the land owner or society should pay to maintain these soil functions.
Public, off-site benefits of soil relate to the following resource issues:
Water quality of streams, lakes, oceans, and groundwater
Air quality, especially particulates
Greenhouse gases, including carbon dioxide, methane, and nitrous oxide.
Sustainability of land productivity
Summary of soil benefits
|Soil Function||Benefit of Value to Humans|
Delivery of nutrients to plants
Carbon storage improves a variety of soil functions
Enhances water and air quality
Storage of N and C can reduce greenhouse gas emissions
|Maintaining biodiversity and habitat|
Supports the growth of crops, rangeland plants, and trees
May increase resistance and resilience to stress
Reduces pesticide resistance
Helps maintain genetic diversity
Supports wild species and reduces extinction rates
Improves aesthetics of landscape
Provides erosion control
Allows on-site water recharge of streams and ponds
Makes water available for plants and animals
Provides flood and sedimentation control
|Filtering and buffering||Can maintain salt, metal and micronutrient levels within range tolerable to plants and animals||Improves water and air quality|
|Physical stability and support|
Acts as a medium for plant growth
Supports buildings and roads
|Stores archeological items|
|Multiple functions||Sustains productivity||Maintains or improves air and/or water quality|
The quality of a soil is a combination of inherent and dynamic soil properties. The focus of most soil quality work is dynamic soil properties and how they change in relation to the inherent features of the soil.
Inherent or use-invariant properties change little, if at all, with land use or management practices. They may include soil texture, depth to bedrock, type of clay, CEC, and drainage class. These properties were established as soil formed over millennia. How soils form depends on the five soil-
forming factors identified by Hans Jenny (1941) and others:
- climate (precipitation and temperature)
- topography (shape of the land)
- biota (native vegetation, animals, and microbes)
- parent material (geologic and organic precursors to the soil)
- time (time that parent material is subject to soil formation processes)
Dynamic properties or use-dependent properties can change over the course of months and years in response to land use or management practice changes. Dynamic properties include organic matter, soil structure, infiltration rate, bulk density, and water and nutrient holding capacity. Changes in dynamic properties depend both on land management practices and the inherent properties of the soil. For example, the organic matter levels in soil depend on tillage practices and the types of plants growing (management), but the total amount of organic matter is constrained by soil texture and climate (inherent features). Some properties, such as bulk density, may be considered inherent properties below 20-50 cm, but are dynamic properties near the surface.
Jenny, H. 1941. Factors of Soil Formation: A System of Quantitative Pedolog. Dover Pub., Mineola, N.Y.
Agricultural Management Practices And Soil Quality: Measuring, assessing, and comparing laboratory and field test kit indicators of soil quality attributes.
Greg Evanylo, Extension Specialist, Crop and Soil Environmental Sciences, Virginia Tech, and Robert McGuinn, Former Research Associate, Crop and Soil Environmental Sciences, Virginia Tech
What makes a healthy soil? Is soil merely a solid medium that holds nutrients for plant growth? Increasing concern for the sustainability of our natural resources has led to the development of a more complex concept of soil health. Karlen et al. (1997) proposed the following as vital soil functions: (1) sustaining biological activity, diversity, and productivity; (2) regulating and partitioning water and solute flow; (3) filtering, buffering, degrading, immobilizing, and detoxifying organic and inorganic materials, including agricultural, industrial and municipal by-products and atmospheric deposition; (4) storing and cycling nutrients and other elements within the Earth's biosphere; and (5) providing support of socioeconomic structures and protection for archeological treasures associated with human habitation.
The term "soil quality" has been coined to describe the combination of chemical, physical, and biological characteristics that enables soils to perform a wide range of functions. We have described in this publication: (1) some indicators of soil that can be measured with a simple test kit developed by the United States Department of Agriculture, Natural Resource Conservation Service (USDA-NRCS); (2) directions for interpreting these measurements; (3) the effects of soil amendments on soil quality attributes; and (4) comparisons of field kit and laboratory results.
Quantifying Soil Quality Indicators
The assessment of soil quality requires quantification of critical soil attributes. Initial measurements of soil quality attributes should be made in high and low productivity areas to establish ranges of values that are site specific. Changes occurring over time can then be measured to evaluate effects of different practices. Detailed information on when, where, why, and how to measure soil quality is presented in the Soil Quality Testing Kit Instruction Manual and the Soil Quality Interpretation Guide published on the USDA-NRCS - Soil Quality Institute website (see the "Resources" section of this document for the address). Descriptions of soil biological, physical and chemical indicators follow.
Soil Biological Indicators
Soil microorganisms (fungi and bacteria) and other fauna (e.g., earthworms, insects, arthropods) influence the availability of nutrients for crop growth by decomposing soil organic matter and releasing or immobilizing plant nutrients. Biological activity improves soil aggregation through the secretion of soil binding mucilages and hyphal growth. Improved aggregation, in turn, increases water infiltration and the ease of plant root penetration. Soil biological activity is considered an integral attribute of a healthy soil.
Soil respiration rate
Soil respiration rate [as assessed by carbon dioxide (CO2) evolution] is an indicator of soil biological activity. Soil CO2 evolution results from the decomposition of organic matter; thus, soil respiration rate is an indicator of the amount of decomposition that is occurring at a given time.
Soil respiration can be limited by moisture, temperature, oxygen, soil reaction (i.e., pH), and the availability of decomposable organic substrates. Optimum respiration usually occurs around 60% of water filled pore space. Soil respiration will decrease under saturated or dry conditions. Biological activity doubles for every 18°F rise in temperature until the optimum temperature is reached (varies for different organisms). Activity declines as temperature rises above optimum. The most efficient soil organic matter decomposers are aerobic; thus, soil respiration rates decline as soil oxygen concentration decreases. Oxygen is most limiting in soils that are saturated with water. Greater oxygen flow occurs in well-aggregated soils that have many macropores.
Addition of organic materials will generally increase soil respiration. Organic matter provides the food or substrate on which heterotrophic soil microbes feed. Organic materials with low carbon to nitrogen (C:N) ratios (e.g. manure, leguminous cover-crops) are easily decomposed; thus, the addition of these materials to soil will increase soil respiration. Materials with high C:N ratios (e.g., compost, sawdust) decompose more slowly but provide a more stable, long term supply of organic material than legumes, biosolids, and manures. Soil microbes will compete with plants for nitrogen when soil is amended with products having C:N ratios higher than 25:1.
Agricultural chemicals that directly kill or otherwise impair soil microorganisms, such as fungicides and nematocides, reduce soil respiration. Although these chemicals target pathogenic organisms, they may also impair the viability of beneficial organisms.
Organic matter decomposition provides benefits and drawbacks. Decomposition of organic matter is the primary route through which some essential nutrients (e.g., nitrogen) are released, but organic matter destruction reduces the benefits that organic matter confers to soil physical and chemical properties. The addition of organic materials to the soil must equal the loss due to decomposition for the sustainability of the system to be maintained.
|Management factors influencing soil respiration|
|Increases soil respiration||Decreases soil respiration|
Interpretation of soil respiration values
In general, a higher respiration rate indicates better soil quality. Low respiration rate, when soil temperature and moisture are favorable for biological activity, would indicate less than desirable organic matter input. This value must be interpreted within the context of other indicators. For example, a very low nitrate concentration plus a high respiration rate may indicate a high nitrogen immobilization rate, possibly due to the addition of crop residues or other soil amendments that possess wide C:N ratios. Some general guidelines to interpreting respiration values are presented in Table 1. These are only guidelines and should not be applied to every soil type and management situation.
|Table 1. General soil respiration class ratings and soil condition at optimum soil temperature and moisture conditions, primarily for agri-cultural land uses (Woods End Research, 1997).|
(lbs. CO2 -C/ac/day)
|0||No soil activity||Soil has no biological activity and is virtually sterile.|
|< 9.5||Very low soil activity||Soil is very depleted of available organic matter and has little biological|
|9.5 - 16||Moderately low soil activity.||Soil is somewhat depleted of available organic matter, and biological activity is low.|
|16 - 32||Medium soil activity||Soil is approaching or declining from an ideal state of biological activity.|
|32 - 64||Ideal soil activity||Soil is in an ideal state of biological activity and has adequate organic matter and active populations of microorganisms.|
|> 64||Unusually high soil activity||Soil has a very high level of microbial activity and has high levels of available organic matter, possibly from the addition of large quantities of fresh organic matter or manure.|
Soil Physical Indicators
The physical properties of soils - texture, structure, density, porosity, water content, strength, temperature, and color - determine the availability of oxygen in soils, the mobility of water into or through soils, and the ease of root penetration. Some of these properties are immutable (e.g., texture) and cannot be modified by cultural practices, but density, water holding capacity, and porosity can be improved using appropriate soil management techniques.
Soil bulk density
Soil bulk density is the mass of soil per unit volume in its natural field state and includes air space and mineral plus organic materials. Bulk density gives useful information in assessing the potential for leaching of nutrients, erosion, and crop productivity. Runoff and erosion losses of soil and nutrients can be caused by excessive bulk density when surface water is restricted from moving through the soil. Bulk density provides an estimate of total water storage capacity when the soil moisture content is known.
|Management factors influencing bulk density|
|Increases bulk density||Decreases bulk density|
Interpretation of bulk density measurements
Bulk density can be used to determine if soil layers are too compact to allow root penetration or adequate aeration. Bulk densities that limit plant growth vary for soils of different textural classes (Table 2) (Arshad et al., 1996).
|Table 2. General relationship of soil bulk density to root growth based on soil texture.|
|Soil texture||Ideal bulk densities|
|Bulk densities that may affect root growth|
|Bulk densities that restrict root growth|
|Sands, loamy sands||<1.60||1.69||>1.80|
|Sandy loams, loams||<1.40||1.63||>1.80|
|Sandy clay loams, clay loams||<1.40||1.60||>1.75|
|Silts, silt loams||<1.30||1.60||>1.75|
|Silt loams, silty clay loams||<1.40||1.55||>1.65|
|Sandy clays, silty clays, some clay loams (35-45% clay)||<1.10||1.49||>1.58|
|Clays (>45% clay)||<1.10||1.39||>1.47|
Infiltration is the process of water entering the soil. Infiltration rate is dependent on the soil type; soil structure, or amount of aggregation; and the soil water content (Lowery et al., 1996). Soil crusting, compaction, vegetative cover, and root and earthworm channels also influence the ability of water to move through (infiltrate) soil layers. Infiltration is important for storing water in the soil profile for plant growth and for reducing runoff and erosion. Infiltration rates are best determined when the soil is at or near field capacity, usually12 to 48 hours after the soil has been thoroughly wetted (i.e., soaking rain or irrigation).
Management practices that affect soil crusting and compaction, vegetative cover, and soil porosity will increase or decrease the rate of water infiltration. For example, slow infiltration can be caused by increased soil compaction or loss of surface soil structure (reduced aggregation) through tillage. Leaving crop residues on the soil surface or increasing the organic matter content in the soil surface may maintain aggregation and enhance infiltration
|Management factors influencing infiltration rates|
|Increases infiltration rate||Decreases infiltration rate|
Interpretation of infiltration rates
The infiltration rate is most responsive to conditions near the soil surface and changes drastically with management (Sarrantonio et al., 1996). Infiltration is rapid into large continuous pores at the soil surface and decreases as the size of these pores is reduced. Some general values for infiltration into soils of varying textural classes are presented in Table 3. These are average values and should not be generalized for all soil types.
|Table 3. Steady infiltration rates for general soil texture groups in very deeply wetted soil (Hillel, 1982).|
|Soil type||Steady infiltration rate|
(inches per hour)
|Sandy and silty soils||0.4-0.8|
|Sodic clayey soils||<0.04|
Field water-holding capacity
Field water-holding capacity is the amount of water a soil can hold after being saturated and allowed to drain for a period of one to two days. Field water-holding capacity is influenced by soil texture (relative amount of silt-, clay-, and sand-sized particles), aggregation, organic matter content, and overall soil structure.
|Management factors influencing field water-holding capacity (WHC)|
|Increases field WHC||Decreases field WHC|
Interpretation of field water-holding capacity
Generally, a soil with a high water-holding capacity will provide more plant-available water, but soil texture also determines what portion of the soil water is available to plants. Clayey soils hold the most, sandy soils the least, and loamy soils intermediate amounts of water; however, loamy soils provide the most plant available water because much of the water in the small pores in clayey soils is held too tightly to be available to plants (Figure 1). Organic matter physically holds more water than does mineral matter; thus, increasing a soil's organic matter content increases its water-holding capacity. The major management practices that influence water-holding capacity are tillage and crop residue management. Soils that are highly tilled tend to lose water-holding capacity. Tillage reduces the content of organic matter and reduces pore volume.
Soil Chemical Properties
Soil chemical properties are determined by the amounts and types of soil colloids (clays and organic matter). Chemical properties include mineral solubility, nutrient availability, soil reaction (pH), cation exchange capacity, and buffering action.
Soil pH indicates how acid (pH<7, high H+ concentration) or basic (pH>7, high OH- concentration) is the soil solution. Soil pH is influenced by parent soil materials and tends to decrease with time. Soils with low base (Ca, Mg, K, etc.) status, such as those in the Southeastern United States, are sensitive to the acidifying effects of nitrogen fertilizers (including organic N sources). The addition of limestone and other basic materials is normally used to maintain soil pH in a desirable range. Although organic matter additions may not directly affect soil pH, soils that receive significant amounts of organic materials tend to maintain (buffer) soil pH values for longer periods of time.
Interpretation of Soil pH
Most crops grown in the temperate mid-Atlantic and southeastern United States prefer slightly acidic soils (i.e., pH of 5.6 to 6.8). Lower or higher pH values can cause plant nutrient deficiencies (e.g., P, Mn, Zn, Cu, Fe, Mo) or elemental toxicities (i.e., Al, Mn), which have adverse effects on crop yield (Figure 2).
Nitrate (NO3-) and ammonium (NH4+) are the only forms of nitrogen that can be used by plants. Chemical nitrogen fertilizers add ammonium or nitrate directly to soil. The organically complexed forms of nitrogen in crop residues, compost, and manure must be mineralized into inorganic ammonium before they can be used by plants. Ammonium is either directly taken up by plant roots or soil microorganisms, or converted to nitrate. Most inorganic N in agricultural soils is taken up by crops in the nitrate form of nitrogen.
Nitrate can leach through soil if it is not taken up by plant roots or soil microorganisms. Nitrate that is leached through the soil profile may contaminate surface water and groundwater and is unavailable for plant uptake. The goal in managing nitrogen in the soil should be to balance crop needs with supply. This will reduce pollution potential and maintain economically viable crop yields.
Interpretation of nitrate values
The nitrogen cycle is so complex that it is difficult to predict the amount of available N from various forms of the nutrient in soil. Soil nitrate analysis may be used to compare the available N from different soil amendments and the effects of soil management on nitrate leaching potential. Nitrate concentration in the top 12 inches of soil at the 10 to 12 inch stage of corn growth has been used successfully to predict the sufficiency of N for the crop (Evanylo and Alley, 1996; Evanylo and Alley, 1997); however, further calibration will be necessary to develop soil nitrate sufficiency norms for other crops.
The effect of organic amendments on soil quality indicators and comparison of field and laboratory methods
Soil amendments vary in their effects on soil properties. Organic amendments maintain soil aggregate stability and contribute to a soil's water holding capacity, while inorganic amendments, such as commercial fertilizer, do not benefit soil physical properties. Furthermore, differences exist in the quality of organic matter. More stable organic amendments may have more lasting effects on soil physical properties, but may not be as easily assimilated by soil organisms as less decomposed materials. A study was designed to demonstrate the effects of incorporated inorganic chemical fertilizer, cover crop, cotton gin trash compost and swine manure on soil quality. The specific objectives were:
- To compare the results of the soil quality field test kit with standard laboratory procedures for the same tests, and
- To determine if the soil quality indicators measured by the soil quality field test kit are responsive to various soil amendment treatments.
Methods and Materials
Soil testing was performed on research plots at the Center for Environmental Farming Systems in Goldsboro, NC, on June 3-4, 1998. These plots had been amended twice in a 16-month period with agronomic rates (i.e., the amount estimated to supply the crop N needs of 120 lbs N per acre) of inorganic fertilizer, composted cotton gin trash (CGT), and swine manure, or an incorporated cover crop residue. Each treatment was replicated four times. All plots were roto-tilled and hilled prior to transplanting tomato (Lycopersicon esculentum Mill.) for the second consecutive season. No tillage was performed during the growing season and surface mulching with straw was used for weed control.
Each plot was sampled during the growing season at one location on the hilled portion for assessment of soil respiration (CO2 evolution), water infiltration, bulk density, soil pH, soil nitrate, and field water-holding capacity. Bulk density, soil pH, soil nitrate, and field water-holding capacity were each analyzed by standard laboratory and field kit. Soil respiration and water infiltration were only measured with the field kit. Laboratory analyses were conducted by the following methods: bulk density (Blake, 1965), field water-holding capacity (Klute, 1965), pH (McLean, 1982), and nitrate (Keeney and Nelson, 1982; Lachat QuickChem methods No. 12-107-04-1-B, Zellweger Analytics, Inc., 6645 West Mill Road, Milwaukee, WI 53218-1239). For detailed descriptions of the materials and methods used for the field soil quality test kit, consult the soil quality handbook on the NRCS website: (http://www.statlab.iastate.edu:80/survey/SQI/sqihome.shtml) or Sarrantonio et. al. (1996).
High air temperatures (e.g., 94°F on the sampling date) and below average rainfall for May and June 1998, resulted in high soil temperatures (83°F at 4 to 6 inch depth) and low available soil moisture at the time of sampling.
The soil respiration measurements under actual field temperature and moisture conditions were not statistically different among treatments. The data from the post wetting respiration test (after water saturation and draining overnight) was less variable and provided the best reflection of the trend of treatment differences because differences were more likely to be due to treatments than soil water status (Figure 3). Higher CO2 evolution occurred with amendments that provided greater amounts of easily decomposable (volatile) organic matter. Respiration response followed the pattern of manure > CGT > cover crops > inorganic fertilizer, although the respiration rate for cotton gin trash compost-amended soil was not significantly different than any soil. Carbon availability of microbially-stabilized plant-based compost is less than uncomposted manure and similar to weathered cover crop residue.
Water infiltration rate was highest with the composted cotton gin trash compost as demonstrated by the shortest time for the water volume to infiltrate the soil (Figure 4). Infiltration rates for the other treatments were equal and somewhat slower than the cotton gin trash compost. The high organic matter content (~45%) of the compost probably increased the surface soil aggregation, prevented crusting, and maintained soil macropore flow more than the other treatments.
Bulk density was lowest in the cotton gin trash compost amended soil, but no other treatments were different (Figure 5). The soil quality test kit bulk density test did not correlate well with the standard test for bulk density because we sampled soil from 3 to 6 inches with the standard core method and from 0 to 3 inches, where treatment effects were more apparent, with the field test kit. Another factor contributing to bulk density differences may have been the lower variability in the greater volume of soil sampled by the quick test kit than with the standard method. In this case, the test kit outperformed the standard test in assessing soil quality differences.
The lab and field pH measurements were positively correlated, but the field measurements were between 0.5 and 1.0 pH units higher than the lab (Figure 6). The large difference between the lab and the field pH measurements makes the field pH meter a poor choice for assessing soil pH. There were no treatment effects on soil pH with either the laboratory or the field kit measurements.
Laboratory and field soil nitrate concentrations responded similarly to treatments, but nitrate concentrations were lower when measured by the field test kit. Soil nitrate was highest with the composted cotton gin trash and the swine manure and was lowest with the cover crop and inorganic fertilizer (Figure 7). The organic N sources were more effective than the inorganic fertilizer in maintaining soil nitrate concentrations in the root zone.
Field Water-Holding Capacity
Field water-holding capacity values were different when assessed by both methods, but the variability was less with the standard laboratory procedure (Figure 8). The general trend for both the test kit and the lab method was cotton gin trash > manure > cover crop > inorganic fertilizer. The most stabilized organic material (composted cotton gin trash) increased field moisture capacity more than inorganic fertilizer.
Differences among procedures probably occurred because: 1) the field kit measured the moisture content of an intact core, while the lab method measured the moisture content of a soil sample that was air-dried and sieved, which destroyed natural aggregation; and 2) the field kit employed actual field conditions to simulate water movement and holding capacity, whereas, lab method imposed an artificial pressure of -1/3 bar to simulate gravitational forces.
Conclusions and evaluation of the soil quality test kit
The test kit procedures are simple to understand and can be performed rapidly compared to standard laboratory analyses. A complete analysis of one sample takes approximately 30 minutes for the first day and 30 minutes to complete the second day's respiration measurement and water-holding capacity sampling. Two or more samples will take less than double or triple the time because analysis starting times can be staggered. The kit may have other on-farm applications besides soil testing. For example, the nitrate test can be used to monitor water quality.
The soil quality test kit results correlated well with standard laboratory analyses, although field measurements of pH were higher than acceptable. The field kit distinguished between soil management treatments in the field. The post-wetting or second day respiration test was more indicative of treatment differences because the variability due to soil moisture levels was reduced.
In general, organic amendments improved soil physical properties (infiltration rate, water-holding capacity, and bulk density) and increased biological activity (respiration rate) more than the inorganic commercial fertilizer. The organic amendments also maintained the highest concentrations of nitrate-N in the topsoil despite the higher application rate of readily plant-available nitrogen from commercial fertilizer than from the other amendments. The slow-release nature of the organic N probably prevented leaching losses of the same magnitude as from the inorganic fertilizer. Soil infiltration rate, water-holding capacity, bulk density, and nitrate-N were increased by the organic amendments in the order of their expected carbon stability (i.e., cover crop < manure < cotton gin trash compost), while respiration rate was highest with the manure.
The test kit should be used to identify the effects of management practices on general trends in soil quality rather than to measure absolute soil property values. Farmers, consultants, and educators can assess changes in soil properties to allow for the selection of management practices that can best enhance soil quality. The kit is an excellent tool for teaching the concepts of soil quality and is appropriate for use by Extension specialists (esp., Agriculture and Natural Resources, and 4-H) and other educators.
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