Glossary of Agricultural Terms

Biosolids: The term biosolids was formally recognized by the Water Environment Federation in 1991, which it defined as the “nutrient-rich, organic byproduct of the nation’s wastewater treatment process.” Biosolids is a term first used by the waste water industry to denote the usable byproduct of wastewater treatment.

Class A, Exceptional Quality biosolids: This Biosolid quality level, referred to in the U. S. generally as “Class A biosolids” or “Exceptional Quality biosolids”, satisfies the strict pathogen treatment requirements, pollutant content concentration limits and vector attraction reduction requirements of Part 503 of Title 40 of the Code of Federal Regulations promulgated by the U. S. Environmental Protection Agency.

Rule 503: The Part 503 regulations were developed with input from university, EPA and USDA researchers from around the U. S. and involved an extensive review of scientific literature and the largest risk assessment the EPA had conducted to that time. The Part 503 regulations became effective in 1993.

Organic Matter: This is the term for broken down organic components that come from plants and animals. All living organisms, including plants, animals and microorganisms, contain organic components. After any living organism dies, it decomposes and its organic components break down through a natural reactive process. The resulting organic matter moves through the environment by the natural means of water absorption and flow, animal consumption and excretion, sedimentation, and other processes. Organic matter acts much like a fertilizer, but it does not necessarily provide the required nutrients necessary for healthy plant growth and fruiting. Organic matter causes nutrients to stay near the top of the soil, and it enriches the soil because minerals and metal ions bind to it. Organic matter substantially improves the cation exchange capacity of the soil, which is a measure of soil fertility and a soil’s nutrient retention capacity. Accordingly, organic matter improves the structure, water retention and nutrient retention of the soil. Very little is known about the specific makeup of natural organic matter, which is not specifically characterized but is generally characterized as heterogeneous and very complex. Generally, natural organic matter, in terms of weight, is 45 – 55% carbon, 35 – 45% oxygen, 3 – 5% hydrogen and 1 – 4% nitrogen.

Cation Exchange Capacity (CEC): This term refers to the measure of soil fertility and a soil’s nutrient retention capacity. Cations are positively charged ions, and cation exchange capacity is a technical measure of the quantity of positively charged ions that a mineral or material can accommodate on its negatively charged surface. Cation exchange capacity is usually expressed as a number of milliequivalents (meq) per 100 grams. For most agricultural soils, the cation exchange capacity (CEC) is ideally between 10 and 30 meq/100g.

Soil pH: A term used to indicate the measure of the soil acidity or alkalinity. Soil with a pH value of less than 7 is considered an acidic soil, while soil with a pH value of greater than 7 is considered an alkaline soil. Southern row crops and forage grasses prefer a neutral or slightly acidic soil, having a pH value between 6.0 and 7.0. The sweet decay processes associated with the decay of organic matter, which greatly benefits the soil, prefer near-neutral or mildly acidic conditions. Acidic soils with a pH level of 6.0 or less are more susceptible to souring or putrefaction. In excessively acidic soils, nutrient cations such as zinc, aluminum, iron, copper, cobalt, manganese and other micronutrients become excessively available and toxic, while in excessively alkaline conditions these micronutrients become less available resulting in nutrient deficiency. Row crop farming, over time, has the effect of reducing soil pH or causing the soil to become more acidic. Soil acidity is increased by the natural decomposition of dead plant matter, the gradual depletion and leaching of the basic soil cations calcium, magnesium and potassium, which are generally replaced by acidic elements such as aluminum and iron, and the year-to-year addition of urea, urea phosphate, ammonium nitrate, ammonium phosphates and ammonium sulfate. The pH of an excessively acidic soil is raised by the addition of limestone to the soil, generally in the form of agricultural lime, which is also a source for the important nutrient cation calcium. The pH of an excessively alkaline soil is lowered by the addition of sulfur, iron sulfates and aluminum sulfate.

Soil Tilth: Soil tilth refers to the state of aggregation of a soil. Aggregates are conglomerates of clay, silt, and sand particles that are held together by biological, physical and chemical forces. A common method of determining aggregate stability is to place aggregates on a sieve and move the sieve up and down in a water bath. If a lot of soil passes through the sieve, the aggregate stability is low; if most of the soil remains on top of the sieve, the aggregate stability is high. Soils with stable aggregation tend to have better soil tilth, greater water infiltration, and better aeration for crop growth.

Anaerobic/Aerobic Digestion: Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. It is widely used to treat wastewater sludges and organic waste because of the reduction in volume and mass of the input material. The result is a nutrient-rich biosolid.

Aerobic digestion, which is very similar to composting, is the purposeful biodegradation of organic matter. The decomposition is performed by micro-organisms, mostly bacteria, but also yeasts and fungi. In low temperature phases a number of macro-organisms, such as springtails, ants, nematodes, isopods and earthworms also contribute to the process, as well as soldier fly, fruit flies and fungus gnats. There are a wide range of organisms in the decomposer community.

Nitrogen Uptake: Plants absorb nitrogen in the forms of nitrate (NO3-) or ammonium (NH4+) ions which are both water-soluble. Nitrate ions are absorbed quickly by plant roots, but leach easily. Ammonium ions are attracted to soil particles and move slowly through the soil to plant roots. Commercial fertilizers, both dry and liquid, are available with various combinations of nitrate and ammonium ions, enabling farmers to manage their nitrogen application.

Leaching: Leaching occurs when a leachate, in most cases water, trickles through soils. During this process, plant nutrients are dissolved and filtered through the soil.

Nitrogen Deficiency: This condition in plants, also known as “nitrogen robbery,” is more likely on light soils and those low in organic matter content, although all soils are susceptible. Cold weather, especially early in the season, can also cause a temporary shortage. All crops apart from nitrogen fixing legumes are prone to this disorder. The signs include poor plant growth, as well as yellowing on the tip of lower leaves with a gradual yellowing of the middle vein and ultimately the whole leaf. Lower leaves show symptoms first. Leaves in this state suffer reduced chlorophyll. Flowering and fruiting may be delayed.

How Plants Use Nutrients:

Nitrogen: This nutrient is responsible for the healthy green color of your plants. It is an essential part of proteins and chlorophyll, the plant pigment that plays a vital role in photosynthesis.

Phosphate: Technically, phosphorus is an element (P), and phosphate is a molecular anion (PO4_3-), part of phosphoric acid (H3PO4). In fertilizers, the phosphorus content is expressed as a percentage (by weight) measured as P2O5, the anhydride of phosphoric acid. Phosphorus promotes healthy root growth, fruit and seed development, and increased disease resistance. Plants with a shortage of phosphorus are often stunted, have dark green foliage, followed by reddening of the stems and leaves. The symptoms generally appear on the older leaves first.

Potassium: Also referred to as potash, potassium promotes vigorous growth and disease resistance. Signs of a deficiency show up as browning of the edges of leaves, and mottled yellow or pale green mature leaves. Older leaves are affected first.

Calcium: Much of the Calcium in a plant exists as a structural element in primary cell walls, and as a regulator controlling new growth. It also affects structure and permeability of membranes, and helps to regulate hydration of the protoplast. Calcium deficiency symptoms appear initially on the young leaves and the shoot apex. New leaves are distorted with hooked tips and curled margins, which are irregular and may show brown scorching or spotting. Calcium deficiency can also cause roots of the plants to become stunted, translucent, and bulbous with dead tips.

Iron: This secondary nutrient is a component of many of the enzymes and light energy transferring compounds involved in photosynthesis. Once inside the plant, the iron is bound up into an inactive form so that it cannot poison the plant tissue. It is transported by being bound to proteins, such as nicotianamine and other specialized iron binding proteins. Uptake and trafficking of iron throughout the plant is a highly integrated process of membrane transport, trafficking between binding proteins and movement through the plant to where the iron is required.

Sulfur: This secondary nutrient is essential for nitrogen-fixing nodules on legumes, and necessary in the formation of chlorophyll. Plants use sulfur in the processes of producing proteins, amino acids, enzymes and vitamins. Sulfur also helps the plant’s resistance to disease and aids in growth and seed formation.

Zinc: This nutrient is an essential component of various enzyme systems for energy production, protein synthesis, and growth regulation. Zinc deficient plants also exhibit delayed maturity. Zinc is not mobile in plants so zinc-deficiency symptoms occur mainly in new growth. Poor mobility in plants suggests the need for a constant supply of available zinc for optimum growth. The most visible zinc deficiency symptoms are short internodes and a decrease in leaf size. Delayed maturity also is a symptom of zinc-deficient plants.

Poultry Litter: Poultry litter is a combination of poultry manure and poultry house bedding material, with the nutrient concentration of the litter depending on the type and amount of bedding material (which can include rice hulls, sawdust, wood shavings and shredded paper), litter type (broiler, hen or turkey litter), number of flocks between poultry house cleanouts, and nutrients included in the poultry diet. The majority of the poultry litter available in Arkansas, Missouri and Oklahoma is broiler litter, with small amounts of breeder hen and turkey litter. Poultry litter is subject to wide variability in nutrient values and moisture levels. Fresh poultry litter generally has a much higher moisture level (with averages between 20 to 24 percent) than pelletized poultry litter (with averages between 10 and 15 percent), which is in effect dried fresh poultry litter that has been run through a pelletizer. Fresh poultry litter applied to and remaining on the soil surface for extended periods of time is susceptible to movement by wind and water. Poultry litter is generally an alkaline or high pH material, and a great deal of the nitrogen in fresh poultry litter can be lost to ammonia volatilization in warm and windy conditions, particularly in alkaline soils. Fresh poultry litter should be stored for short periods, because of its susceptibility to degradation and quick loss of nutrient values.

Microbial Activity: The activity of microscopic organisms responsible for the natural decay of dead and inanimate material. The basic chemistry of Earth’s surface is determined by biological activity, especially that of the many trillions of microbes in soil and water. Microbes make up the majority of the living biomass on Earth and, as such, have major roles in the recycling of elements vital to life.

Soluble/Insoluble Nitrogen:

Soluble nitrogen is in a form readily available for uptake by plants. Soluble nitrogen fertilizers provide quick color and growth response, have a limited response duration and have potential for high foliar burn and leaching. Soluble nitrogen sources, such as urea, are typically less expensive per pound of nutrient than insoluble nitrogen sources.

Insoluble nitrogen is in a form not readily available for uptake by plants. Water-insoluble types of fertilizers, such as organic biosolid fertilizers, release nitrogen over time. They are often applied at higher rates and less frequently than quick release formulas. They will not burn plants, even if applied at high rates, and are not prone to leaching.