G.B. Reddy, PhD Department of Natural Resources and Environmental Design NC A&T State University – Greensboro, NC Presented at the Soil Quality Workshop held in Nong Lam University, June 2007 Vietnam Workshop on Soil Quality: Soil Biology and Chemistry Image courtesy of

Soil Quality Soil Quality is defined as “the capacity of soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality and maintain plant and animal health” (Doran and Parkin)

Soil What constitutes a good soil? This confusion is resulted from a variety of land uses, ecosystems, locations, soil types, and interactions occurring in soil

SOIL BIOLOGY Soil Biology plays a vital role in maintaining soil quality and nutrient cycling in any given agricultural ecosystem.

Louis Pasteur “The role of infinitely small is infinitely great”

have many different shapes BACTERIA SSSA bacillus filamentous cocci spirilla

–Yeasts –Mycelia –Fruiting bodies –Spores FUNGI Have many different life forms

Nematode diversity FungivoreBacterivore Predatory Plant parasitic

Arthropods ― exoskeleton ― segmented body ― jointed legs

Arthropod diversity Fungivores HerbivoresPredators Litter Shredders

EARTHWORMS

Where are the soil organisms ??

Visualizing soil habitat Bacteria occupy < 5 % of soil surfaces

Micro and Macro Organisms in Soil The collective vitality, diversity and balance among these organisms yield to a healthy ecosystem and make possible the functions of high soil quality Our job is to manage soils to encourage a healthy, diverse soil community which efficiently makes nutrients available to crops and vegetables Biological diversity is possible in soils because of limitless variety of foods and wide range of habitat conditions There may be species diversity within microbial diversity which is paralleled by high degree of functional diversity

Micro and Macro Organisms in Soil (cont.) Functional diversity brings ecosystem stability or resilience Stability means the ability of a soil to perform functions as cycling of nutrients, assimilation, and maintenance of soil structure even in wide variation in soil conditions Resilience means the ability of a soil to bounce back to functionality Soil microorganism numbers influenced by the quality and quantity of food available and variation in physical and climatic conditions

MICROBIAL FUNCTIONS IN SOIL Bacterial and Fungal Functions

Bacterial Functions in Soil What do bacteria accomplish in soil? 1.Colonize aerobic and anaerobic environments 2.Decompose labile substrates 3.Mediate redox transformations 4.Nourish bacterivores 5.Fix Nitrogen

N-fixing nodules on a cowpea plant

Fungal Functions in Soil What do fungi accomplish in soil? Decompose recalcitrant organic compounds Penetrate residues Stabilize soil structure Nourish fungivores Form symbioses with plant roots and soil fauna Compete with plant pathogens Parasitize plants and soil animals Produce toxins e.g. aflatoxin produced by Aspergillus flavus on peanut

Many plants are connected underground by mycorrhizal hyphal interconnections. Mycorrhizal (AM) fungi are not host specific. Illustration by Mark Brundrett Mycorrhizal Networks: Connecting plants intra- and Interspecifically

Increase nutrient (P) uptake Suppress pathogens Mediate plant competition Improve soil structure

Quantifying Biodiversity GROUP Known Species Estimated Total Species Percentage Known Vascular plants 220,000270,00081% Algae 40,00060,00067% Fungi 69,0001,500,0005% Bacteria 3,00030,00010% (Hawksworth, 1991) Most occur in soil

Soil Quality Assessment “A soil quality assessment provides a basic means to evaluate the sustainability of agricultural and land management systems.”

Soil Quality Indicators For soil quality indicators to be successful they must: 1.Be adequately sensitive to change 2.Reflect the functioning of the system 3.Be universal 4.Be cost-effective

SOIL BIOLOGY SOIL BIOLOGY: Indicators for Soil Quality

ORGANIC MATTER Defined as the assimilation of plant and animal residue comprises of carbon, oxygen and hydrogen

Soil Organic Matter “Soil organic matter is a major terrestrial pool for C, N, P, S cycling and availability is constantly altered by biological process.”

ORGANIC MATTER Organic matter contains metabolic carbon and structural carbon Organic matter composition: 5% sugars and starches 8% protein 45% cellulose 18% hemicellulose 20% lignin 4% waxes and polyphenols Soil organic matter fuels the soil food web

ORGANIC MATTER Organic matter influence on Soil Properties Mulching or no-till system will increase earthworm activity Increase in granular and aggregate stability Enhanced soil water retention, water infiltration, and water holding capacity Increased CEC Increased nutrient storage Humic fraction reduce plasticity, cohesion, and stickiness of clay soil Increase in pH buffering capacity of soil Chelates metals Increase in microbial populations

Soil Fauna

Factors Influencing Organic Matter Decomposition pH Temperature Soil Moisture Soil Aeration Type of Plant Residue C/N Ratio Plant Residue location (surface Vs sub- surface)

Organic Matter Decomposition Impact of tillage on the soil food web Adapted from Hunt et al. (1986)

Organic Matter Primary Producers Primary Consumers Secondary Consumers

Diagram of the general changes that take place when fresh plant residues are added to a soil

Changes in the various organic matter fractions after bringing virgin land under cultivation

MEASURING ORGANIC MATTER IN THE FIELD Nylon Mesh Bag Technique: Measuring Active C in the Field

Microbial Biomass A living fraction of a soil Normally equal the organic matter content of soil

Organic Matter

MEASURING OF SOIL BIOMASS Fumigation Method

Soil Respiration Metabolic activity of soil biota Metabolic Activity C02-C / Biomass-C = qC02

Coefficient CO 2

Agronomic Practices on Soil Respiration and Microbial Biomass

Soil Enzymes Enzymes are proteins that act as catalysts without undergoing permanent alteration and cause chemical reactions to proceed as faster rates

Soil Dehydrogenase

Soil Phosphatase

SOIL CHEMICAL PROPERTIES To gain an understanding of the nutrient cycling in soils and availability of nutrient to plants, chemical properties and their processes must be studied. These properties indicate the functionality of soil in terms of its productivity.

Soil chemical properties and processes Precipitation plus solutes, aerosols and particulates Hydration Hydrolysis Oxidation/Reduction Complexation Ion exchange Sorption Leaching of solutes & colloids Gas exchange pH CEC pe Upward transport conductivity

SOIL QUALITY Soil Chemical Indicators

Soil pH Neutral Solution Slightly Acidic Solution pH = -log ( H+) An acid can be defined as a proton donor, a chemical that increases the concentration of hydronium ions (H 3 O + ) in solution Conversely, a base is a proton acceptor, a chemical that reduces the concentration of hydronim ions in solution (and increases the concentration of hydroxide ions, OH - )

Cationic Balance

Anionic Balance

Equilibrium relationship among residual, salt-replaceable (exchangeable), and soil solution (active) acidity in a soil with organic and mineral colloids.

H 2 SiO 4 H + sources and sinks in soils C + = Non acid cations

The acid infertility complex

Nutrient availability varies with pH

Electrical Conductivity (EC)

pH dependent charge in a Georgia Ultisol Cation/anion exchange capacity (centimol / kg) Cation Exchange Capacity (CEC) Adapted from Brady and Weil (2002)

Nutrient Availability: Nitrogen and Phoshporus 16 elements have been identified as essential for the growth of all plants N K Ca Mg P S macronutrients micronutrients air & water Soil C O H Cl Fe Mn Zn B Cu Mo Na Co Si VNi Needed by some plants

Soil solids contain nutrients minerals organic matter Where are the nutrients in soil ?

exchangeable ions soil solution Humus Clay Na + Ca +2 Al +3 K+K+ Ca +2 Mg +2 K+K+ H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 H20H20 Soil water contains nutrients + SO

What’s in the soil soup ?? Adapted from Brady and Weil (2002) Ca +2 NO 3 - Ca +2 K+K+ K+K+ Mg +2 Ca +2 Mg +2 Ca +2 Mg +2 Ca +2 NO 3 - SO 4 -2 NO 3 - H 2 PO 4 - DOM Fe +3 Cu +2 Fe +3 Zn +2

Nutrient Availability: Nitrogen and Phoshporus Mineralization – Conversion of Organic form to inorganic form Fertilizers: type, application and placement – Slow Releasing Vs Fast Releasing – Before planting or Application at Knee height – Banding or Broadcasting

Cover Crop Effect on N

Nutrient availability varies with pH

Conclusions  A soil quality assessment provides a basic means to evaluate the sustainability of agricultural and land management systems.  For soil quality indicators to be successful they must: 1.be adequately sensitive to change 2.reflect the functioning of the system 3.be universal 4.be cost-effective

Conclusions  Evaluation of soil chemical and biological properties is necessary for a full assessment of soil function.  Soil Biology plays a vital role in maintaining soil quality and nutrient cycling in any given agricultural ecosystem.  Nutrient cycling and nutrient availability is studied through evaluations of soil chemical properties. These properties indicate the functionality of the soil in terms of its productivity.

Conclusions  There are numerous soil chemical and biological properties that can be used as indices of soil quality.  Properties to be selected for the assessment must provide information on the soil functions that need to be improved for better soil health.