Effects of Tillage System, Fertilization, and Crop Protection Practices on Soil Quality Parameters - Literature review Example

? Running head: Agriculture Effects of Tillage System, Fertilization, and Crop Protection Practices on Soil Quality Parameters Insert   Insert Grade Course Insert Tutor’s Name 12 June 2012 Table of Contents Table of Contents 0 1.0 Indicators of Soil Quality 2 1.1 Biological Indicators 2 1.1.1 Microbial Biomass 2 1.1.2 Soil Basal Respiration (SBR) 3 1.1.3 Metabolic Quotient (qCO2). 4 1.1.4 Potentially Mineralizable Nitrogen (Anaerobic) 5 1.2 Physical Indicators 7 1.2.1Soil Bulk Density 7 1.2.2 Water Holding Capacity 8 1.3 Chemical Indicators 9 1.3.1 Soil pH 9 1.3.2 Soil Organic Matter 10 1.4 Tillage System (Conventional and Organic) and Soil Quality 11 1.5 Management Effects and Indicators 13 References 16 1.0 Indicators of Soil Quality 1.1 Biological Indicators 1.1.1 Microbial Biomass Soil microbial biomass is the active and the living composition of soil organic matter excluding animals and roots and usually makes up less than 5% of soil organic matter (Dalal, 1998). It participates in the C, N, P and S transformations and plays a significant task in the decomposition of xenobiotic organic compounds and the formation of the soil structure. Microbial biomass, C and N and their ratios to the total and light fraction C and N and pools in soils of the organic systems are higher in organic systems than in conventional systems due to the enhanced decomposition of the easily available pool of soil organic matter (SOM) with increasing microbial biomass levels. The higher levels of light fraction organic matter in organically managed soils are from plant residues and manure. The higher microbial biomass in organically managed soils indicates higher quality soil organic matter responsible to nutrient mineralization and short term storage of potentially leachable nutrients indicating comparative advantage of organically managed systems over conventional ones. Microbial Biomass functions as a source of nutrients as it is responsible for releasing nutrients from organic matter present in the soil (Smith and Paul, 1990). Microbial biomass and activity in the soil are very important in the transformation of carbon pools, in different ecological set ups (Bailey et al., 2002), as soils developed under different ecologies have different capabilities of storing soil organic matter and nutrients. Microbial biomass specific respiration gives the status of the substrate quality and availability in the soil (Insam et al., 1996). Microbial biomass is also used to check the improvement of degraded soils over time and serves as an early indicator of changes in the total organic matter in the soil. Long term cultivation leads to decreased levels of microbial biomass due to dwindled levels of microbial activity and soil organic C pools (Kocyigit, 2008). Higher levels of microbial biomass decrease specific respiration of micro organism, which shows that micro organisms living in low quality soils respond by increasing their specific respiration. 1.1.2 Soil Basal Respiration (SBR) Soil basal respiration is the constant rate of respiration in the soil caused by changes in organic matter levels. The rate of basal respiration in the soil indicates the amount and quality of the carbon source. Basal respiration can be used to analyze the potential of the soil biota to decompose both indigenous and antropogenically introduced (Bloem et al., 2006). Soil respiration is a key process for carbon flux to the atmosphere. Soil water content, o2 concentration and the bioavailability of carbon are the main factors that regulate soil respiration (Bloem et al., 2006). Soil basal respiration indicates the level of microbial activity in the soil and is positively correlated with biomass activity. It involves the aerobic and anaerobic energy yielding processes where the reduced organic and inorganic compounds are utilized by microbial cells and serve as primary electron donors and oxidized compounds serve as terminal electron acceptors (Bloem et al., 2006). Processes in the soil such as fermentation and abiotic processes release co2. Water is essential for soil basal respiration with the optimum water content for respiration being 50-70% of the soil’s water holding capacity (Orchard and Cook, 1983). Soil basal respiration is caused by various micro organisms including fungi, bacteria, protozoa, and algae. They contribute to around 90% of the total release of co2 in the soil while the remaining 10% is caused by the fauna (Paustian et al., 1990). Soil management systems and the ecology determine the rates of respirations because they influence the levels of the microbial population in the soils (Persson et al., 1980). Analysis of soil basal respiration usually involves the scrutiny of the consumption of o2 or the production of co2 with proper sample treatment and storage being of critical importance to obtain accurate measurements. 1.1.3 Metabolic Quotient (qCO2). The qco2 is lower in organically managed soils compared to conventional tillage soils because the substrate use diversity in organic soils is higher than in conventional soils (Flieback and Mader, 1997). This shows that organically managed soils have higher metabolic efficiency due to more abundance and diversity of living systems. The metabolic quotient represents the quantity of substrate that is mineralized per unit microbial biomass carbon per unit time (Gil-Sotres et al., 2005). The metabolic quotient of respiration per unit biomass indicates the C cycle flow through microbial biomass, which gives the quantity of energy essential to uphold the given microbial biomass. High qCo2 values are usually evident in the initial biomass developmental stages and biomass communities with large ratios of active to dormant biomass (Anderson, 1994). The values can also be increased by acidic pH in the soil, which increase microbial metabolic stress (Anderson and Domsch, 1993). The metabolic activity in the soil includes enzymatic activities that soil microbial communities develop under optimal and stressful conditions that are influenced by temperature, humidity, nutrients and substrates. The metabolic quotient increases significantly in a flawed ecosystem compared to stable ecosystems (Dalal, 1998). This means that conventional systems have more shortcomings than organic systems which have lower qCO2 rates. This is usually due to the reduction of the substrate utilization efficiency by the soil microbial communities usually as a response to stressful conditions that can be caused by monoculture, acidification, and heavy metal contamination that bring changes in the bacteria fungi ratio, which have different carbon utilization cycles (Dilly and Munch, 1998). Metabolic quotient are efficient in determining soil stresses caused by high heavy metal concentrations (Brookes, 1995) with very high qCO2 levels being found in the long term contaminated soils (Brookes et al 1986). 1.1.4 Potentially Mineralizable Nitrogen (Anaerobic) Potential mineralizable N is the measure of readily decomposed organic nitrogen N and is used to measure the biological activity in the soil (Hill et al., 2004). Mineralizable N is composed of a heterogeneous composition of organic substrates, which may include microbial biomass, crop residues, and humus. Its analysis in the soil is usually done by incubation assays because chemical tests selective for the mineralizable nitrogen in the soil are not available (Picone et al., 2002). Potentially, mineralizable nitrogen measures the amount of organic nitrogen in the soil converted to nitrogen derivatives available to plants and is formed under specific conditions of weather. It is a measure of biological doings and shows the amount of N that is reasonably rapidly on hand. The mineralizable values are higher in organically managed soils compared to mineral fertilized soils indicative of higher biological activities and lower instantaneous mineral N pools in the organic managed soils (Mijangos et al., 2005). These phenomena show that organically managed soils have more tightly coupled N cycles with higher turnover rates of mineral N pools than soils using conventional management practices (Drinkwater et al., 1996). Tightly coupled N cycle in organically managed soils facilitates higher crop yields without any danger of environmental pollution (Picone et al., 2002). Tillage systems affect the amount of mineralizable N with zero tillage reducing the net N mineralization due to lack of physical disturbance of the soil (Van Veen and Paul, 1981). Different tillage methods affect the soil porosity and air diffusion, which increases the chances of N loss by denitrification. Crop residues distribution on the soil also causes differences in mineralization of N due to differences in organic decomposition on the surface (Douglas et al., 1980). Soil depth affects the temperature and moisture distribution in the soil, and its changes directly correlate to the amount of N mineralized. 1.2 Physical Indicators 1.2.1Soil Bulk Density Bulk density indicates the degree of soil compaction and is computed as the soil dry weight divided by its volume, which includes the volume of the soil particles and pores and is expressed in g/cm3. Soil is a multiphase porous system composed of the solid phase made up of mineral particles and solid organic compounds, the liquid phase composed of water and dissolved substances, and the gaseous phases composed of air and other gases. It indicates the soil’s ability for structural support, water movement, air aeration and solute movement. Conventional tillage systems have soils with high bulk densities with poor water holding capacities due to compaction which affects both field capacity and permanent wilting points due to reduced total pore volumes. Bulk density is influenced by the soil texture and the densities of the minerals present, organic materials and their compaction. Organic tillage systems have soils with lightly packed porous soils with high levels of organic matter has lower bulk densities. Bulk density increases with depth since soils in deeper depths have very low levels of organic matter, and root penetration compared to top soils and hence has fewer pore spaces. The soil is also heavily compacted by the soil above it increasing its density. Conventional tillage weakens the natural stability of the soil making it vulnerable to damage by forces of nature. Erosion increases bulk density because eroded particles fill pore spaces, thus, reducing porosity. To obtain optimum soil bulk density organic farming management practices should be cantered on increasing the soil organic matter essential in enabling the soil to allow water and dissolved nutrients to percolate through the soil profile enabling plants to grow vigorously. Addition of manure increases organic matter decreasing the soil density, which enables the soil to increase its porosity and subsequently has positive implications for plant root growth and nutrient availability and uptake to crops (Swezey et al., 1998). High bulk density hinders soil respiration reducing microbial activity, which is undesirable in crop and land management. 1.2.2 Water Holding Capacity This is the (maximum) water amounts in the soil available for use by plants expressed in percentages, and it indicates the soil’s ability to retain water. The water available for plants is water held in the soil between its field capacity and permanent wilting point. Field capacity is the water available in the solid after it has been completely saturated and allowed to gravitatively drain for one to two days. Permanent wilting level is the water content point in the soil that allows plants to wilt and fail to recover when adequate water is supplied. It is affected by soil texture, presence of large rock particles, depth and soil profile. Fine textured soils have high water capacity with salty soils having very low water holding capacity. Water holding capacity is influenced by organic compounds in the soil, compaction, and the salt concentration of the soil. Organic tillage systems have soils with increased water holding ability because organic matter can hold more water than inorganic mineral soils, even at permanent wilting points. Organic compounds increase the soils texture and characteristics, which improve infiltration, water movement and available water capacity. Conventionally, management systems incorporating high mineral fertilizers have soils with increased salt concentration, which impacts negatively on water holding capacity. Salts create unfavourable moisture gradients that hinder plants ability to absorb water because these soils retain more water at permanent wilting point. Lack of available water reduces the root and plant development and growth and can lead to stunted growth or death of the plant. Water holding capacity levels can be used to develop water mitigating plans that include the necessity for irrigation and drainage systems. This can be effectively done through increased organic tillage systems that increase organic matter, which increases by residue and tillage management. The soil organic matter should be conserved and increased when necessary. 1.3 Chemical Indicators 1.3.1 Soil pH Soil pH is the measure of alkalinity and acidity in the soil. In organic tillage systems, addition of organic matter sources lower the pH of the soil. Ammonium based fertilizers and soil organic matter (SOM) acidify the soil by producing H+ ions lowering the soil pH as organic matter mineralization results in the formation of organic and inorganic acids that add H+ to the soil. Conventional farming systems incorporating intensive cultivation and fertilization have higher pH values when compared to non fertilized and non cultivated soils (Jones et al., 2002). Soil pH affects the microbial diversity in the soil and their activities with major concerns being their ability to break down organic matter and carry out chemical transformations necessary for high quality soil limiting the availability of some nutrients. Ph values also determine the interaction of various chemicals in the soil. It affects pesticide interaction with some pH values making them ineffective or affecting their half lives, which is undesirable. Acidic soils increase the solubility of heavy metals and increase the possibility of contaminating natural and artificial water sources and reservoirs. Soil pH can be altered by natural phenomena’s including mineralogy, climate and weathering and inappropriate management of soils that include use of acid forming nitrogen fertilizers and removal of bases naturally present in the soil. 1.3.2 Soil Organic Matter Soil organic matter is any materials originally produced by living organisms going back to the soil through decomposition. Particulate organic matter (POM) and soil organic matter are higher in organic farming systems compared to conventional tillage systems (Albrecht et al., 1997). This is because very little amounts of plant material are returned to the soil after cultivation in conventional farming systems. Tillage aerates the soil and break up organic matter promoting microbial activity thus increasing soil organic matter decomposition. Soil organic matter is primarily recognized as an indicator of soil quality (Bloem et al., 2006). It comprises all soil organic matter particles less than 2mm and greater than 0.53mm in size (Cambardella and Elliot, 1992). The particle organic matter is biologically and chemically active and form part of the decomposable portion of the soil. The breakdown of soil organic matter influences the soil structure, porosity, water infiltration rates, water holding capacities, and plant nutrient availability. Organic matter in soil decomposition is increased by ploughing, disc tillage, and vegetation burning; but these practices also expose the soil to wind and water hence adequate management practices should be incorporated to reduce loss of crucial organic matter. Tillage breaks down the soil aggregate and exposes the soil organic matter to micro organisms that are later lost through mineralization. Progressive deepening of tillage mixes the subsoil low in organic matter with top soils rich in organic matter (Amezketa, 1999). This can be controlled and managed by long term consistent addition of manure, which aids in soil binding (Williams, 2004). Conservation tillage conserves organic matter, microbial biomass and the soil structure (Amezketa, 1999). Organic farming systems increase soil organic compounds that improve the soil structure by decreasing soil bulk density, improving soil aggregate, increasing pore size and increasing the percent of air filled pore spaces (Loveland and Webb, 2003). Decomposition is a biological process that involves the physical break down and biochemical transformation of complex organic molecules of the dead materials into simpler organic and inorganic molecules (Juma, 1998). Continuous decomposition of dead plants and animals form humus which colours the soul darker, increases soil aggregation and increases nutrients in the soil (Juma, 1998). 1.4 Tillage System (Conventional and Organic) and Soil Quality Tillage operations influence the soil environment by changing the soil geometry that affects the physical, chemical and biological characteristics of the soil, which determine the productivity of the soil. Soil organic carbon (SOC) is the most important indicator of soil quality and agricultural sustainability (Liu et al., 2006). This is because it is a source of carbon and also a sink of carbon sequestration. Tillage and cultivation reduce the soil organic matter content decreasing the soil quality and soil productivity. Soil tillage serves to mix and aerate the soil and incorporate cover crops, crop residue, manure, fertilizers, and pesticides into the rooting zone (Acquaah, 2002). Soil tillage management determine the factors that control soil respiration, substrate availability, soil temperature, water content, ph, oxidation -reduction potential and microbial numbers and diversity (Kladivko, 2001). Soil tillage increase short term co2 evolution and microbial turnover and accelerate organic oxidation to co2 improving soil aeration and contact between soil and crop residues exposing aggregate protected organic matter to microbial decomposition (Liu et al., 2006). It also exposes the organic carbon in both inter and intra-aggregate zones to rapid oxidation because of improved o2 circulation and exposure of more decomposition surfaces increasing the microbial activity in the soil. Conventional tillage reduces the living things diversity on the surface of the soil (Doran and smith, 1987) and leads to lower soil organic carbon and total nitrogen levels compared to organic tillage systems due to increased residue retention in organic framings systems. Organic farming leads to higher quality soils and more soil biological activity with organically farmed soils having higher pH, organic C and N, N mineralization potential and actinomycete abundance and diversity in organic fields (Drinkwater et al., 1995). Reganold (1988) indicated that organic farming also increased the cation-exchange capacity and several microbial-exchange enzymes in organic than in conventionally managed soils. Tillage changes the distribution of organic matter in the soil profile. In conventional tillage, the organic matter are more equitably distributed than in organic farming where the tillage is concentrated on the soil surface (Arshad et al., 1990). This makes the microbial biomass and microbial activity of zero tillage organic farming to be higher at the surface (Angers et al., 1993). Regular addition of organic matter in organic farming increases the microbial diversity and enhances natural disease suppression mechanisms (Van Bruggen et al., 2006). This suppression is attributed to the competition of total soil biomass with pathogens for resources or inhibition through more other direct antagonism methods (Weller et al., 2002). Tillage systems affect soil quality as it affects soil properties like temperature, plant root densities among others (Griffith et al., 1992). Conventional tillage leaves less than 15% of plant residue cover after planting and involves intensive tillage. Conventional tillage systems cause the loss of total organic carbon and decreases soil quality in the long term (Lal, 2004). They increase co2 emissions from the soil into the atmosphere (Bauer et al., 2006). It destroys the soil cover and structure exposing the soil to erosion and high moisture losses. Conventional tillage systems over time develop specialized microbes adapted to using small percentages of C Sources (Bloem et al., 2006). Organic farming systems have greater long term soil improvement benefits than conventional tillage systems. Organic farming increases soil organic matter better compared to conventional systems and also increases the soil organic C and total N (Marriott and wander, 2006). 1.5 Management Effects and Indicators Soil management affects the way soil performs its ecological functions of plant growth, air, and water quality and recycling of animal and plant products. There is a need for all stake holders especially farmers (in order to meet their economic and social needs) to necessitate specific tools to assess the management effects on the soil function in an orderly and timely manner. Management Practices that influence the soil organic matter are very crucial to soil quality because soil organic matter show the greatest decline when virgin prairie are first broken for cultivation (Bauer and Black, 1981). Cropping management systems involving fallow periods rather than continuous cropping systems experience more decline in soil organic matter. These systems require management strategies that add or maintain soil carbon to improve soil quality for sustainable agriculture (Karlene et al., 1992). Crop residues and animal and poultry manure provide the largest sources of organic manures that can increases soil organic matter levels (Follett et al., 1987). This is because they can increase the water stability of soil aggregate, reduce crust formation, and increase the percentage of large pores. Proper management of the crop and weed residues should be done especially in intensive tillage operations to maintain the soil organic matter. Green maturing, crop rotation and the frequencies of rotation can also be incorporated in the management practices to improve the amount and distribution of organic materials as well as forming biopores. Mulching provides food for living things in the soil, enhance nutrient availability and improve the soil structural properties. The input levels of soil organic matter must be sufficient to provide the necessary amount of biomass and should be related to the decomposition rates to maintain the necessary organic matter levels. Growing cover crops should be considered to supplement the organic matter sources. Organic matter management should also consider the organic matter quality as the carbon, nitrogen, lignin and polyphenolic composition of the plant residues can affect its decomposition rate (Coleman et al., 1989). Management of reduced tillage systems should factor in the existing soil and climatic conditions to improve the soil quality (karlen et al., 1992). Tillage effects on the soil structure are determined by the existing soil water levels during tillage operations (Kay, 1990). This is because tillage causes differences in soil aggregate dispersion with smaller aggregate particles sinking to the bottom of the tilled layers while the larger particles rise to the surface. Soil aggregate stability serve as early indicators of regeneration or degradation of soils as it is an indicator of the organic content, biological activities and nutrient cycling in soils. Large soil aggregates are highly sensitive to management effects on organic matter and can adequately infer soil quality (Kemper and Rosenau, 1986). Tillage also creates compacted zones at the base of the tillage layers and enhances mineralization of organic stabilizing materials that increases microbial activity (Elliott, 1986). Surface tillage disorganizes earthworm burrows, which exposes them to predators, and reduce crop residues on the ground surface increasing the possibility of soil erosion. Soil nematode populations indicate soil quality and are widely used as bioindicators of ecological systems (Yeates, 2003) due to their key positions in soil food webs (Neher, 2001). Effective management systems should maintain the soil biota as it is crucial to soil quality. Management practices affect different soil biota differently according to their respective species. Earthworms influence nutrient cycling and soil structure with lumbricus terrestris L. forming deep burrows that influence solute transport increasing the movement of surface applied agricultural chemicals in the soil (Tyler and Thomas, 1977). Other earthworm species existing on the surface layers mix the mineral soil and organic matters, which increases the nutrient availability for plants and, hence, for good soil quality, soil and crop management practices should be centred in increasing the earthworm effects on the soil through promotion of earthworm diversity through management practices such as reduced pesticide application. For agricultural sustainability, all farmers should adopt effective and appropriate soil and plant management practices to maintain good ecological balances. Remedial actions should be taken promptly to regenerate degraded soils at all costs. References Acquaah, G., 2002. Principles of Crop Production: Theory, Techniques, and Technology. Pearson Education, Inc., Upper Saddle River, New Jersey Amezketa, E., 1999. Soil aggregate stability: A review. Journal of Sustainable Agriculture, 14, 83-151. Anderson, T.H., 1994. Physiological Analysis of Microbial Communities in Soil: Applications and Limitations. p. 67–76. In K. Ritz et al. (ed.) Beyond the Biomass. British Society of Soil Science, John Wiley Biol. Biochem. 10:215–221. Anderson, TH and Domsch, KH., 1993. The Metabolic Quotient For CO2 (Qco2) As A Specific Activity Parameters To Assess The Effect Of Environmental Conditions, Such As Ph, On The Microbial Biomass Of Forest Soils. Soil Biol. Biochem, 25: 393-395. Angers et al., 1993. Microbial And Biochemical Changes Induced By Rotation And Tillage In A Soil Under Barley Production. Can. J. Soil Sci.73, 39–50. Arshad et al., 1990. Effect Of Till Versus No Till on the Quality of Soil Organic Matter. Soil Biology and Biochemistry, Vol. 22, Issue 5, 1990, Pages 595–599 Bailey et al., 2002. Fungal To Bacterial Biomass Ratios In Soil Investigated For Enhanced Carbon Sequestration. Soil Biol. Biochem. 34: 997-1007. Bauer et al., 2006. Soil CO2 flux from a Norfolk loamy Sand after 25 Years of Conventional and Conservation Tillage. Soil and Tillage Research 90, 205–211 Bauer, A. and Black, A.L., 1981. Soil Carbon, Nitrogen, and Bulk Density Comparisons in Two Cropland Tillage Systems after 25 Years and In Virgin Grassland. Soil Sci. Soc. Amer. J. 45:1166-1170. Bloem et al., 2006. Microbiological Methods for Assessing Soil Quality. London, CABI publishing Brookes et al., 1986. Soil Microbial Biomass Estimates In Soils Contaminated With Metals. Soil Biology & Biochemistry 8, 383–388 Brookes, P.C., 1995. The Use of Microbial Parameters in Monitoring Soil Pollution by Heavy Metals. Biol. Fert. Soils 19, 269–279. Cambardella, C.A., and Elliott, E.T. 1992. Particulate Soil Organic-Matter Changes across a Grassland cultivation Sequence. Soil Sci. Soc. Am. J. 56:777–782. Coleman et al., 1989. Dynamics of Soil Organic Matter in Tropical Ecosystems. University of Hawaii Press, Honolulu, Hawaii Dalal, R.C., 1998. Soil Microbial Biomass—What Do The Numbers Really Mean? Australian Journal of Experimental Agriculture 38, 649–665. Dale, V., and Beyeler, S., 2001. Challenges in the Development and Use of Ecological Indicators. Ecological Indicators 1, 3–10. Dilly, O., and Munch, J.C., 1998. Ratios Between Estimates Of Microbial Biomass Content And Microbial Activity In Soils. Biol. Fertil. Soils. 27: 374-379. Doran J.W., and Smith, M.S., 1987. Organic Matter Management and Utilization of Soil and Fertilizer Nutrients. In: Follett R.F. et al. (eds.): Soil Fertility and Organic Matter as Critical Components of Agricultural Production Systems. SSSA Spec. Publ. No. 19, ASA and SSSA, Madison, WI: 53–72. Douglas et al., 1980. Wheat Straw Composition and Placement Effects On Decomposition In Dry Land Agriculture Of The Pacific Northwest. Soil Sci. Soc. Am. J. 44: 833-83 Drinkwater et al., 1995. Fundamental Differences between Conventional and Organic Tomato Agroecosystems in California. Ecol. Appl. 5:1098–1112. Drinkwater et al., 1996. Potentially Mineralizable Nitrogen as an Indicator of Biologically Active Soil Nitrogen. In: Doran JW, Jones AJ, editors. Methods for Assessing Soil Quality, SSSA Special Publication 49. Madison, WI: Soil Science Society of America; 1996.p. 217–29 Elliott, E.T., 1986. Aggregate Structure and Carbon, Nitrogen, and Phosphorus in Native and Cultivated Soils. Soil Sci. Soc. Amer J 50:627-633. Flieubach, A., and Mader, P., 1997. Carbon Source Utilization by Microbial Communities in Soils under Organic and Conventional Farming Practice. In: Insam, H., Rangger, A. (Eds.), Microbial Communities ? Functional versus Structural Approaches. Springer-Verlag, Berlin, Germany, pp. 109±120. Follett et al., 1987. Conservation Practices: Relation to the Management of Plant Nutrients for Crop Production. p. 19-51. In R.F. Follett. J.W.B. Stewart, and C.V. Cole (ed.) Soil Fertility and Organic Matter as Critical Components of Production Systems. ASA Special Publication No. 19. ASA, CSSA. and SSSA. Madison, Wisconsin. Gil-Sotres et al., 2005. Different Approaches to Evaluating Soil Quality Using Biochemical Properties. Soil Biology & Biochemistry 37 pp.877–887 Griffith et al., 1992. Crop Response to Tillage Systems. p. 25-33. In MidWest Plan Serice Committee (Ed) Conservation tillage systems and management: Crop residue management with no-till, Hill et al., 2004. Soil quality monitoring in New Zealand: practical lessons from a 6-year trial. Agriculture, Ecosystems and Environment, 104, 523 - 534. Insam et al., 1996. Effects of Heavy Metal Stress On The Metabolic Quotient Of Soil Microflora. Soil Biol. Biochem. 28:691-694. Jones et al 2002. Metal concentrations in three Montana soils following 20 years of fertilization and cropping. Commun.Soil Sci. Plant Anal. 33 (9&10):1401-141 Juma, N.G., 1998. The Pedosphere and Its Dynamics: A Systems Approach To Soil Science. Volume 1. Edmonton, Canada, Quality Colour Press Inc. 315 pp. Karlen et al., 1994. Crop Residue Effects on Soil Quality Following 10-Years of No-Till Corn. Soil Till. Res. 31, 149–167 Kay, B. D., 1990. Rates of Change of Soil Structure under Different Cropping Systems. p. 1-52. In B. A. Stewart (ed.) Advances in Soil Science. Vol. 12. Springer-Verlag, New York, N.Y. Kemper, WD. and Rosenau, R.C., 1986. Aggregate Stability and Size Distribution. In: Klute A, editor. Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods. Madison, WI. p 425-42. Kladivko, E.J., 2001. Tillage systems and soil ecology. Soil Till. Res., 61: 61–76. Kocyigit, R., 2008. The Effect of Soil Management Systems On Microbial Activity International Meeting On Soil Fertility Land Management And Agro Climatology. Turkey, Gaziosmanpasa University Turkey. p: 899-907 Lal, R., 2004. Soil Carbon Sequestration to Mitigate Climate Change. Geoderma 123, 1–22. Liu et al., 2006. Effects of Agricultural Management on Soil Organic Matter and Carbon Transformation – A Review. Plant Soil Environ, 52, 2006 (12): 531–543 Loveland, P. and Webb, J., 2003. Is There A Critical Level Of Organic Matter In The Agricultural Soils Of Temperate Regions: A Review. Soil and Tillage Research, 70, 1-18. Marriott, E. and Wander, M., 2006. Total and Labile Soil Organic Matter in Organic and Conventional Farming Systems. Soil Science Society of American Journal, 70:950-9. McGeoch, M.A., 1998. The Selection, Testing and Application of Terrestrial Insects as Bioindicators. Biological Reviews 73, 181–202. Mijangos et al., 2005. Effects of Fertilization and Tillage on Soil Biological Parameters. Enzyme and Microbial Technology, 40 (2006) 100–106. Neher, D.A., 2001. Role of Nematodes in Soil Health and Their Use as Indicators. Journal of Nematology 33, 161–168. Orchard, A.V. and Cook, F.J., 1983. Relationship between Soil Respiration and Soil moisture. Soil Biology & Biochemistry 15, 447–453. doi: 10.1016/0038-0717(83)90010-X Paustian et al., 1990.Carbon and Nitrogen Budgets of Four Agroecosystems with Annual and Perennial Crops, With And Without N Fertilization. J.Appl. Ecol. 27, 60±84.Persson, T., 1989. Role of soil Persson et al., 1980. Trophic Structure, Biomass Dynamics and Carbon Metabolism of Soil Organisms in Scots Pine Forest. In: Agren, G.I.,Andersson, F., Falk, S.O., Lohm, U. andPerttu, K. (eds) Structure and Function of Northern Coniferous Forests. (EcologicalBulletin) 32, 419–459. Picone et al., 2002. A Rapid Method to Estimate Potentially Mineralizable Nitrogen in Soil. Soil Sci. Soc. Am.J. 66: 1843–1847. Reganold, J.P., 1988. Comparison of Soil Properties As Influenced By Organic and Conventional Farming Systems. Am. J. Altern. Agric 3:144–155. Smith, L., and Paul, E., 1990. The Significance of Soil Microbial Biomass Estimations. In: Soil Biochem. (Ed. J. M. Bollag and G. Stotzky), Dekker, New York, USA, pp.357-396. Suter, I.I., 2001. Applicability of Indicator Monitoring To Ecological Risk Assessment. Ecological Indicators 1, 101–112. Swezey et al., 1998. Comparison of Conventional and Organic Apple Production Systems during Three Years of Conversion To Organic Management In Coastal California. Am. J. Altern. Agric. 1998, 13, 162-180. Tyler, D.D. and Thomas, G.W., 1977. Lysimeter Measurements of Nitrate and Chloride Losses from Soil under Conventional and No-Tillage Corn. J. Environ. Qual. 6:63-66. Van Bruggen et al., 2006. Relation between Soil Health, Wave-Like Fluctuations in Microbial Populations, And Soil borne Plant Disease Management. Eur. J. Plant Pathol. 115,105–122. Van Veen, J.A. And Paul, E.A., 1981. Organic Carbon Dynamics in Grassland Soils: Background Information and Computer Simulation. Can. J. Soil Sci. 61: 185-201. Wardle, D.A. and Ghani, A., 1995. A Critique of the Microbial Quotient (Qco2) As a Bioindicator of Disturbance and Ecosystem Development. Soil Biology & Biochemistry 27, 1601–1610. Weller et al., 2002. Microbial Populations Responsible For Specific Soil Suppressiveness to Plant Pathogens. Ann. Rev. Phytopathol. 40, 309–348 Williams, J.D., 2004. Effects Of Long Term Winter Wheat, Summer Fallow Residue And Nutrient Management On Field Hydrology For A Silt Loam In North-Central Ohio. Soil and Tillage Research, 75, 109-119. Yeates, G.W., 2003. Nematodes as Soil Indicators: Functional and Biodiversity Aspects. Biology and Fertility of Soils 37, 199–210 Read More