Comprehensive definitions of agricultural terms, soil science concepts, and farming practices. Click a letter to jump to that section.
A soil condition with pH below 7, caused by hydrogen ions. High acidity reduces nutrient availability and can inhibit root growth.
The process of creating small holes in soil to allow air, water, and nutrients to penetrate. Critical for root health and microbial activity.
The binding of soil particles into larger units (aggregates). Good aggregation improves soil structure, water infiltration, and erosion resistance.
A soil condition with pH above 7, caused by carbonate, bicarbonate, or hydroxide ions. High alkalinity can lock up iron, zinc, and other micronutrients.
A plant-available form of nitrogen. Ammonium is held by soil particles (cation exchange) and is less prone to leaching than nitrate.
A negatively charged ion (e.g., nitrate NO3-, phosphate H2PO4-, chloride Cl-). Anions are generally not held by soil particles and are prone to leaching.
The percentage of soil cation exchange capacity occupied by basic cations (calcium, magnesium, potassium, sodium). Ideal base saturation: Ca 60-70%, Mg 10-20%, K 2-5%.
The mass of dry soil per unit volume (g/cm³). Ideal bulk density: 1.0-1.4 g/cm³ for loams. High bulk density (>1.6) indicates compaction and restricts root growth.
The activity of soil microorganisms (bacteria, fungi, protozoa, nematodes) and earthworms. Measured by respiration (CO2 release), enzyme activity, or microbial biomass carbon.
A measure of soil's ability to hold and exchange positively charged ions (cations). Higher CEC means greater nutrient-holding capacity. Sand: 1-5, loam: 10-20, clay: 20-50, organic matter: 200-400 meq/100g.
Organic matter that has been decomposed and stabilized through aerobic microbial action. Compost improves soil structure, adds nutrients, and increases microbial diversity.
A crop planted primarily to protect and improve soil rather than for harvest. Cover crops prevent erosion, add organic matter, fix nitrogen (legumes), suppress weeds, and scavenge nutrients.
The practice of growing different crops in sequence on the same land. Crop rotation breaks pest/disease cycles, improves soil fertility, reduces weed pressure, and spreads labor.
A positively charged ion (e.g., calcium Ca2+, magnesium Mg2+, potassium K+, ammonium NH4+). Cations are held by negatively charged soil particles and organic matter.
A water-efficient irrigation method that delivers water directly to plant root zones through emitters or drip lines. Drip irrigation is 85-95% efficient, compared to 50-70% for flood irrigation.
The removal of excess water from soil. Good drainage is essential for root aeration and prevents waterlogging. Poor drainage leads to root rot, nutrient loss, and reduced yields.
The combined loss of water from soil evaporation and plant transpiration. Reference ET (ETo) is measured from a standard grass surface. Crop ET (ETc) = ETo × Crop Coefficient (Kc).
The removal of soil by water or wind. Water erosion includes sheet, rill, and gully erosion. Control measures: cover crops, no-till, contour plowing, terracing, windbreaks.
The percentage of applied nutrients that the crop actually absorbs. Nitrogen: 50-70%, Phosphorus: 20-40%, Potassium: 60-80%. Improved by split applications, proper timing, and placement.
The amount of water held in soil after gravitational water has drained away (typically 24-48 hours after irrigation/rain). At field capacity, water is readily available to plants. Sandy soils: 8-12%, loams: 20-30%, clays: 30-40% by volume.
The application of nutrients or pesticides directly to plant leaves. Foliar feeding is useful for correcting micronutrient deficiencies quickly, but should supplement (not replace) soil fertilization.
The percentage of seeds that sprout and produce normal seedlings under optimal conditions. Commercial seed typically has 85-95% germination. Test by placing seeds on moist paper and counting sprouts after 7-14 days.
A cover crop that is incorporated into the soil while still green, adding organic matter and nutrients. Leguminous green manures (clover, vetch) can add 50-200 kg N/ha.
A measure of accumulated heat above a base temperature for crop development. Daily GDD = ((Max + Min Temp) ÷ 2) - Base Temp. Corn needs ~2700 GDD from planting to maturity.
Stable, dark-colored organic matter in soil that has been fully decomposed by microorganisms. Humus improves soil structure, water-holding capacity, nutrient retention, and microbial diversity.
A method of growing plants without soil, using nutrient-rich water solutions. Hydroponics can produce higher yields with less water and space, but requires careful nutrient management and energy input.
The speed at which water enters the soil (mm/hour). High infiltration: >20 mm/h (sand, well-structured loam). Low infiltration: <5 mm/h (compacted clay, crusted soil). Improved by organic matter and reduced tillage.
A sustainable approach to pest control that combines biological, cultural, physical, and chemical methods. IPM prioritizes prevention and monitoring, using pesticides only when thresholds are exceeded.
The downward movement of nutrients (especially nitrate) and other substances through soil with water. Leaching wastes fertilizer and can contaminate groundwater. Reduced by split N applications, cover crops, and controlled-release fertilizers.
The application of calcium- and magnesium-rich materials (agricultural lime, dolomitic lime) to raise soil pH. Lime also improves soil structure, increases microbial activity, and enhances nutrient availability.
Nutrients required in large amounts by plants: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S). N-P-K are the primary nutrients; Ca-Mg-S are secondary nutrients.
Nutrients required in small amounts: Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), Chlorine (Cl). Deficiencies are common in high-pH soils and can be corrected with foliar or soil applications.
A layer of material (organic: straw, wood chips, leaves; or inorganic: plastic, landscape fabric) applied to soil surface. Mulch conserves moisture, suppresses weeds, moderates soil temperature, and adds organic matter as it decomposes.
The most plant-available form of nitrogen. Nitrate is highly mobile in soil and prone to leaching. Most crops take up nitrogen primarily as nitrate. Excess nitrate in drinking water is a health concern.
The conversion of atmospheric nitrogen (N2) into ammonia (NH3) by nitrogen-fixing bacteria (Rhizobium in legume root nodules, Azotobacter in soil). Legumes can fix 50-300 kg N/ha per season.
A conservation agriculture practice that avoids disturbing soil through tillage. No-till preserves soil structure, increases organic matter, reduces erosion, improves water infiltration, and saves fuel and labor.
Plant and animal residues in various stages of decomposition in soil. Includes fresh residues, decomposing material, and stable humus. Target: 3-5% organic matter for most agricultural soils. Each 1% increase adds ~20,000 kg organic matter/ha in top 15cm.
The movement of water across a semipermeable membrane from an area of low solute concentration to high solute concentration. In plants, osmosis drives water uptake from soil and maintains cell turgor. High soil salinity disrupts osmotic water uptake.
The soil moisture level at which plants can no longer extract water and wilt permanently. PWP: sandy soils 3-5%, loams 10-15%, clays 15-25% by volume. Available water = Field Capacity - PWP.
A measure of soil acidity or alkalinity on a scale of 0-14. pH 7 is neutral, below 7 is acidic, above 7 is alkaline. Most crops prefer pH 6.0-7.0. pH affects nutrient availability, microbial activity, and aluminum toxicity.
The binding of phosphorus to soil particles (iron/aluminum in acid soils, calcium in alkaline soils), making it unavailable to plants. Fixed P is not lost but becomes available very slowly over years. Reduced by banding P near roots and maintaining optimal pH.
The narrow zone of soil surrounding plant roots (1-3mm), where root exudates stimulate high microbial activity. The rhizosphere has 10-100x more microorganisms than bulk soil and is critical for nutrient cycling and plant health.
See Crop Rotation. The systematic sequencing of different crops on the same land over years. Essential for sustainable agriculture.
The concentration of soluble salts in soil. Measured by electrical conductivity (EC) in dS/m. Non-saline: <2 dS/m, moderately saline: 4-8, strongly saline: >16. High salinity reduces water uptake (osmotic stress) and can cause ion toxicity.
The arrangement of soil particles into aggregates (crumbs, blocks, prisms, plates). Good structure (granular/crumb) improves aeration, water infiltration, and root penetration. Degraded by tillage, compaction, and low organic matter.
The relative proportion of sand (0.05-2mm), silt (0.002-0.05mm), and clay (<0.002mm) particles. Texture affects water-holding capacity, drainage, nutrient retention, and workability. Determined by feel or laboratory sedimentation.
The soil layer below the topsoil (typically 20-60cm depth), containing less organic matter but important for water storage and deep root growth. Subsoil compaction is a major yield-limiting factor in many agricultural soils.
Farming practices that meet current food and fiber needs while preserving natural resources and environment for future generations. Key practices: crop rotation, cover crops, reduced tillage, integrated pest management, nutrient cycling, water conservation.
The weight in grams of 1000 seeds. Used to calculate seeding rates and estimate yield. TGW varies by crop: wheat 30-50g, corn 250-350g, rice 20-30g, soybeans 150-250g.
The uppermost soil layer (typically 0-20cm), richest in organic matter and microorganisms, where most plant roots and nutrient cycling occur. Topsoil loss through erosion is a major global agricultural problem.
The loss of water vapor from plant leaves through stomata. Transpiration drives water and nutrient uptake from roots and cools plants. Crop transpiration is a major component of evapotranspiration (ET).
The amount of water a soil can retain against gravity. Determined primarily by texture and organic matter. Sand: 8-12% by volume, loam: 20-30%, clay: 30-40%. Each 1% organic matter increases water-holding capacity by ~2-3%.
A condition where soil is saturated with water, displacing air from pore spaces. Waterlogging causes root oxygen deficiency, nutrient loss (denitrification), root rot, and reduced yields. Improved by drainage, raised beds, and reduced compaction.
📖 53 terms defined | Last updated: September 2026 | Browse our farming guides →