n-value The relationship between the percentage of water under field conditions and the percentages of inorganic clay and of humus.

narrow row planting Refer to tillage, narrow row planting.

natric horizon [soil taxonomy] A diagnostic, subsurface mineral horizon that satisfied the requirements of an argillic horizon but that also has prismatic, columnar, or blocky structure and a subhorizon with >15% saturation by exchangeable Na₊ (USDA, 1999).

natural levee A long, broad low ridge or embankment of sand and coarse silt, built up by a stream on its flood plain and along both sides of its channel especially in time of flood when water overflowing the normal banks is forced to deposit the coarsest part of its load. Vertically, t hey are wedge-shaped deposits that slope gently away from the stream. toward the surrounding floodplain, with its highest elevation closest to the river bank ( Jackson, 1997). Compare levee, artificial levee, meander belt.

near infrared The preferred term for the shorter wavelengths in the infrared region extending from about 0.75 µm (visible red) to around 2 or 3 µm (varying with the author). The longer wavelength end grades into the middle infrared. The term really emphasizes the radiation reflected from plant materials, which peaks around 0.85 µm. It is also called solar infrared, as it is only available for use during the daylight hours.

nearshore zone [relict] A former nearshore zone now subaerially exposed due to isostatic rebound or glacial lake drainage. Commonly a raised beach marks the former landward edge of a relict near shore zone and relict longshore bars may exist in offshore positions. Surficial sediments may display evidence of wave and current action such as sorting or particle-size discontinuities (Schoeneberger and Wysocki, personal communication, 2013).

nearshore zone A subaqueous marine or lacustrine landform area that generally parallels the shore and extends seaward or lakeward from the low water line to beyond the breaker zone including longshore bars. In the nearshore zone, waves steepen, break, and reform during passage to the beach. Sediment transport occurs both along and perpendicular to the shore via wave and current action (Schoeneberger and Wysocki, personal communication, 2013; Fairbridge, 1968). Compare nearshore zone [relict].

neck [volcanic] (not preferred, use volcanic neck).

neocutan A cutan with a consistent relationship with natural surfaces of soil material. It does not occur immediately at the surfaces. Similar to hypo-coating.

net (nonsorted) (not preferred) Use patterned ground.

net duty of water Refer to irrigation, net duty of water.

net primary productivity (NPP) Net carbon assimilation by plants. NPP = GPP – respiration losses. NPP can be estimated for a given time period as ΔB + L + H, where ΔB = biomass accumulation for the period, L = biomass of material produced in the period and shed (i.e., foliage, flowers, branches), and H = biomass produced in the period and consumed by animals and insects.

neutral soil A soil in which the surface layer, at least in the tillage zone, is in the pH 6.6 to 7.3 range. Compare acid soil, alkaline soil, pH, and reaction, soil.

neutralism A lack of interaction between two organisms in the same ecosystem.

neutron probe Probe, with radioactive source, that measures soil water content through reflection of scattered neutrons by hydrogen atoms in soil water.

niche (a) The particular role that a given species plays in the ecosystem. (b) The physical space occupied by an organism.

nickpoint The vertical face in a channel marking the point of maximum headward erosion of a downcutting cycle

nitrate reduction (biological) The process whereby nitrate is reduced by plants and microorganisms to ammonium for cell synthesis (nitrate assimilation, assimilatory nitrate reduction) or to nitrite by bacteria using nitrate as the terminal electron acceptor in anaerobic respiration (respiratory nitrate reduction, dissimilatory nitrate reduction). Sometimes used synonymously with “denitrication.”

nitric phosphates Fertilizers made by processes involving treatment of phosphate rock with nitric acid or a mixture of nitric, sulfuric, or phosphoric acids, usually followed by ammoniation. Water solubility of the phosphorus content may vary over a wide range.

nitrification Biological oxidation of ammonium to nitrite and nitrate, or a biologically induced increase in the oxidation state of nitrogen.

nitrogen cycle The sequence of biochemical changes undergone by nitrogen wherein it is used by a living organism, transformed upon the death and decomposition of the organism, and converted ultimately to its original oxidation state.

nitrogen fixation Refer to dinitrogen fixation.

nitrogenase The specific enzyme system required for biological dinitrogen fixation.

nivation The process of excavation of a shallow depression or nivation hollow on a mountain side by removal of fine material around the edge of a shrinking snow patch or snow bank, chiefly through sheetwash, rivulet flow, and solution in melt water. Freeze-thaw action is apparently insignificant ( Jackson, 1997).

nivation hollow A shallow, non-cliffed depression or hollow on a mountain side permanently or intermittently occupied by a snow bank or snow patch and produced by nivation. If the snow completely melts each summer the hollow is deepened; otherwise not; may be a cirque precursor if further enlarged and deepened by alpine glaciation ( Jackson, 1997).

no-till Refer to tillage, no tillage (zero tillage) system.

nod factors Lipo-oligosaccharides produced by rhizobia that induce root hair deformation and curling, and division of cortical cells of roots of the host legume plant.

nodule (a) A cemented concentration of a chemical compound, such as calcium carbonate or iron oxide, that can be removed from the soil intact and that has no orderly internal organization. (b) (micromorphological) A glaebule with undifferentiated fabric. (c) Specialized tissue enlargements, or swellings, on the roots, stems, or leaves of plants, such as are caused by nitrogen-fixing microorganisms.

nodule bacteria The bacteria that fix dinitrogen (N2) within organized structures (nodules) on the roots, stems, or leaves of plants. Sometimes used as a synonym for “rhizobia.”

nodulins Unusual protein produced by legume root hairs or nodules in response to interaction with rhizobia and bradyrhizobia.

Non-calcic Brown soils [soil classification] (obsolete; not used in soil taxonomy; Baldwin et al, 1938.)

non-expanding Layer silicate type that has no intracrystalline swelling capacity in the presence of water.

non-inversive tillage Refer to tillage, non-inversive tillage.

nonlimiting water range The region bounded by the upper and lower soil water content over which water, oxygen, and mechanical resistance are not limiting to plant growth. Compare with available water.

nonreactive tracer A solute that exhibits no adsorption capacity but could exhibit physical or biological transformations that result in loss from solution.

nonsorted circle A type of patterned ground whose mesh (shape) is dominantly circular and has a nonsorted appearance due to the absence of a boarder of coarse fragments. Vegetation characteristically outlines the pattern by forming a bordering ridge. Diameters commonly range from 0.5 to 3 m. Nonsorted circles include mud boils, earth hummocks, turf hummocks, and frost boils. Nonsorted circles have various origins. Some, such as mud and earth hummocks and frost boils, involve cryoturbation activity and differential heave of frost-susceptible materials. Others, such as mud boils, involve hydraulic pressures and diapir-like displacement of water-saturated sediments ( Jackson, 1997; National Research Council of Canada, 1988). Compare sorted circle, frost boil, patterned ground.

nonsorted polygon (not preferred) Use patterned ground.

nontronite A dioctahedral smectite containing ferric iron with the majority of the charge originating in the tetrahedral layers.

nose slope [geomorphology] A geomorphic component of hills consisting of the projecting end of an interfluve, where contour lines form convex curves around the projecting end and lines perpendicular to the contours diverge downward. Overland flow (e.g., sheet wash) is divergent. Nose slopes are comparatively drier portions of hillslopes and tend to have thinner colluvial sediments and profiles, dominated by colluvium and slope wash sediments (e.g., slope alluvium). Compare head slope, side slope, free face, interfluve, crest, base slope.

notch (a) (colloquial northeast USA) A narrow passageway, or short defile between mountains; a deep, close pass. Compare gap. (b) A breached opening in the rim of a volcanic crater ( Jackson, 1997).

novaculite A dense, even-textured, extremely finely grained, siliceous, sedimentary rock recrystallized from chert with microcrystalline quartz dominant over chalcedony (cryptocrystalline quartz). It is hard, white to grayish-black in color, translucent on thin edges, has a dull to waxy luster, and displays smooth conchoidal fracture when broken. Novaculite occurs in the Ouachita Mountains of AR and OK and the Marathon Uplift of TX where it forms erosion resistant ridges. At the Ouachita Mountain type occurrence, novaculite formed by low-grade, thermal metamorphism of bedded chert. This rock serves widely as a whetstone or oilstone ( Jackson, 1997; Schoeneberger and Wysocki, personal communication, 2013). Compare chert.

nozzle Refer to irrigation, sprinkler irrigation systems terms.

nuée ardente A swiftly flowing, turbulent gaseous cloud, sometimes incandescent, erupted from a volcano and containing ash and other pyroclastics in its lower part; a density current of pyroclastic flow ( Jackson, 1997). Compare lahar.

nunatak An isolated hill, knob, ridge, or peak of bedrock that projects prominently above the surface of a glacier and is completely surrounded by glacier ice ( Jackson, 1997). Compare inselberg, monadnock.

nutrient Elements or compounds essential as raw materials for organism growth and development.

nutrient stress A condition occurring when the quantity of nutrient available reduces growth. It can be from either a deficient or toxic concentration.

nutrient antagonism The depressing effect caused by one or more plant nutrients on the uptake and availability of another nutrient in the plant.

nutrient balance An undefined theoretical ratio of two or more plant nutrient concentrations for an optimum growth rate and yield. Nitrogen and sulfur is an classic example that can be defined because both nutrients are metabolically related in the protein fraction.

nutrient deficiency A low concentration of an essential element that reduces plant growth and prevents completion of the normal plant life cycle.

nutrient efficient plant A plant that absorbs, translocates, or utilizes more of a specific nutrient than another plant under conditions of relatively low nutrient availability in the soil or growing media.

nutrient interaction A term usually used to describe the response from two or more nutrients applied together that deviates from additive individual responses when applied separately. This term may also be used to describe metabolic or ion-uptake phenomenon.

nutrient toxicity Quality, state, or degree of harmful effect from an essential nutrient in sufficient concentrations in the plant.