Soil Quality Keith R. Baldwin NC A&T State University

Soil Quality “the capacity of a specific kind of soil to function within natural or ecosystem boundaries, to sustain plant and animal productivity, to maintain or enhance water and air quality, and to support human health and habitation (Doran et al., 1996).

Soil Health This term is preferred by many farmers because it provides a direct value judgment of the soil resource.

Soil Health It also clearly portrays the idea of soil as a living, dynamic organism that functions in a holistic way depending on its condition or state rather than an inanimate object whose value depends on its innate characteristics and intended use (Romig et al., 1995).

Ecosystem Functions Retain and release nutrients and other chemical constituents Partition rainfall at the soil surface into runoff and infiltration Hold and release soil water to plants, streams, and groundwater Resist wind and water erosion Buffer against the concentration of potentially toxic materials

A High Quality Soil Reflects an optimum environment for root growth, thereby enhancing crop health and productivity. Optimum root growth however, will be tempered by plant species, the genetic potential of the plant, the environmental conditions imposed by weather, and cultural practices used in production.

Interactions Soil physical properties Soil chemical properties Soil microbiological properties

Minimum Data Set Measurement of soil quality requires identification of specific parameters, or “indicators” that can be quantitatively measured over time and compared to reference conditions or judged against some common standards.

Interpretation How much change is needed for that change to be meaningful? Have random or localized changes in field conditions at any particular point in time influenced indicator values?

Trend Changes Improvements to (or degradation of) soil quality can perhaps best be visualized as trend changes that point in a positive (or negative) general direction over the years.

Qualitative vs. Quantitative Qualitative or descriptive indicators typically represent “opinions” or short term changes. Qualitative changes can be assessed using the NRCS Soil Quality Indicator Table. Quantitative changes can be assessed using the USDA Soil Quality Kit.

Field Variation It is important to keep in mind that localized and/or random changes in field conditions at any particular point in time can influence indicator values.

How Much Change Matters? Soil pH may change fro 5.9 to 6.0, but is this meaningful change? A pH change of 0.1 units would not normally be enough change to make a difference in crop production, whereas, a pH change from 5.0 to 5.8 over a two-year period certainly would.

Trends Improvements to soil quality can be visualized as trend changes that point in a general direction over the years. The identified changes need to be definitive, important, and rapid enough so that management can be altered to influence trends.

Soil Physical Properties Bulk density Porosity & pore-size distribution Aggregate stability Penetration resistance Water holding capacity Soil crusting Infiltration Hydraulic conductivity

Soil Structure, Soil Physical Properties, and Soil Quality Physically speaking, soil quality is determined by the structure of the soil. Soil structure is the network in which soil particles are arranged. The nature of this network will determine the physical properties of soil.

Soil Structure, Soil Physical Properties, and Soil Quality Soil structure is dynamic – affected by climate, biological activity, soil management, etc. There are no direct methods to measure soil structure. Soil structure is measured indirectly through measurement of soil physical properties.

Benefits of Aggregation Available water holding capacity Improved soil structure and tilth Improved infiltration Improved hydraulic conductivity Improved oxygen diffusion

Macroaggregates Macroaggregates are more transient than microaggregates because their organic binding agents, roots and hyphae, are more rapidly degradable than the older humified material making up some of the mineral—organic complexes binding the microaggregates.

Soil Chemical Parameters Nutrient Availability Soil pH N mineralization potential P buffering capacity Trace metals and pollutants

You Heard This Before? Plant nutrient availability is strongly tied to soil acidity (pH). Generally, N, P, and K can only exert a significant influence on crop yields if soil pH is correct.

Importance of Soil Chemistry Soil chemistry influences the plant availability of nutrients. Farmers can influence soil chemistry through additions of fertilizers, incorporation of cover crops, and use of other organic materials.

Soil Biological Parameters Soil organic matter Microbial respiration Microbial biomass Soil organic C Microbial biomass C and N Mineralizable N

The Soil Food Web

In 1 teaspoon of soil there are…  Bacteria 100 million to 1 billion  Fungi 6-9 ft fungal strands put end to end  Protozoa Several thousand flagellates & amoeba One to several hundred ciliates  Nematodes 10 to 20 bacterial feeders and a few fungal feeders  ArthropodsUp to 100  Earthworms5 or more Travis & Gugino - PSU

Microorganisms Bacteria UBC EM facility Ed Basgall CIMC Pseudomonas Arthrobacter Bacillus Travis & Gugino - PSU

Microorganisms Fungi PSU Em facility Trichoderma Aspergillus Fusarium D.C. Straney K.J. Kwon-Chung Travis & Gugino - PSU

Nematodes

The Microbial Biomass The C contained in microbial biomass ranges from 1 to 5% of the total organic C in the soil. Being one of the most labile pools of soil organic matter, microbial biomass is an important reservoir of plant nutrients. Because process rates are strongly dependent on the size of microbial populations, quantification of total microbial population is important in estimating the rates of C turnover.

Nutrient Cycling Soil organic carbon, in particular labile organic carbon, has an overwhelming effect on soil productivity. It is a major soil nutrient reservoir. Balance between decay and renewal processes (nutrient dynamics) in this pool controls nutrient availability.

Diversity promotes stability Abundance alone cannot explain impacts of soil organisms on soil quality

Southern Conditions The need for crop residues-manures and conservation tillage practices to sustain SOC and consequently effect changes in soil quality is greater for warmer more humid climates. In Georgia, 12 Mg ha -1 crop residues left to decompose on the soil surface were required to sustain soil quality commensurate with the inherent soil and climatic resources.

Old Rotation 107 years Continuous cotton with 0 N, 134 kg N, and crimson clover or vetch: 16% without N 2-yr cotton corn rotation with winter legume and winter legume with 134 kg N: 160% w/ legume and 188% w/leg. + N 3-yr cotton-winter legume-corn-winter cereal-soybean: 203%

Old Rotation 107 years SOC was substantially reduced under continuous cotton in the absence of legumes or N. A winter legume cover crop greatly increased SOC compared to cotton with or without N. Rotations with N increased biomass and C inputs and further increased SOC.

Old Rotation 107 years In this highly weathered soil, the 3-yr rotation, with copious residue addition to soil, resulted in the lowest bulk density, penetration resistance, and greatest hydraulic conductivity. Importantly, water-stable aggregates also increased.

Carbon Management Practices Regular applications of compost, manure, and other organic materials. Inclusion of cover crops as green manures in cropping systems. Rotations that include forage crops. Reductions in tillage.