| Term | Definition |
|---|
| hydroponic culture | Plants grown in solutions full of minerals but lacking soil |
| essential element | an element that is required for the plant to grow |
| macronutrient | Nutrient that a plant needs in large amounts |
| micronutrient | Nutrient that a plant needs in small amounts |
| topsoil | Particles from humus + rock + organisms |
| humus | the remains of partially decayed organic material |
| horizon | Distinct soil layer |
| loam | Consists of equal amounts of sand, silt (particles of intermediate size), and clay |
| cation exchange | Secretion of H+ by the root to dislodge cations adhering to soil particles |
| sustainable agriculture | Long-term productive farming methods that are environmentally safe |
| phytoremediation | An emerging nondestructive technology that seeks to cheaply reclaim contaminated areas by taking advantage of the remarkable ability of some plant species to extract heavy metals and other pollutants from the soil and to concentrate them in easily harvested portions of the plant |
| nitrogen-fixing bacteria | Microorganisms that restock nitrogenous minerals in the soil by converting nitrogen to ammonia. |
| nitrogen fixation | The assimilation of atmospheric nitrogen by certain prokaryotes into nitrogenous compounds that can be directly used by plants. |
| nitrogenase | The enzyme that turns N2 into NH3 by adding H+ and electrons |
| nodule | Swelling along the roots of legumes that nitrogen fixing bacteria live in |
| bacteroid | A form of Rhizobium contained within the vesicles formed by the root cells of a root nodule |
| crop rotation | The alternation of planting a nonlegume one year and a legume the next year to restore concentration of fixed nitrogen in the soil |
| mycorrhizae | Mutualistic associations of plant roots and fungi |
| flavonoid | Plants secrete this molecule that enters bacteria and activates Nod factors |
| Nod factor | Causes a plant to start forming nodules |
| ectomycorrhiza | A type of mycorrhiza in which the mycelium forms a dense sheath, or mantle, over the surface of the root. Hyphae extend from the mantle into the soil, greatly increasing the surface area for water and mineral absorption. |
| endomycorrhiza | A type of mycorrhiza that, unlike ectomycorrhizae, does not have a dense mantle ensheathing the root. Instead, microscopic fungal hyphae extend from the root into the soil. |
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