Ch. 4: Soil Water, Plant Nutrition, Soil Symbioses

Soil Supplies water and nutrients to plants 1) What influences soil water supply? 2) What nutrients do plants need, and what influences soil nutrient supply?

Soil water What determines water potential soil? g = + total m p s What determines water potential soil? gravitational potential: unimportant pressure potential: unimportant

Soil water solute potential: important saline soils g = + total m p s Dauphin Island: salt marsh

Soil water g = + total m p s matric potential: #1 in importance

Soil water Matric potential determined by texture Soils have pore space: air spaces Clay most Sandy least

Soil water Water added, pores fill When pores filled, soil saturated: Saturation water content Note sand<clay loam

Soil water Allow gravity drain water Gravitational water Most coarse (sandy) soil, least fine (clay) soil Soil at field capacity: fully charged with water 1.7 3

Soil water Plant uses water: becomes stressed Soil @ permanent wilting point (PWP): plant psi = soil psi, no water flows into plant For mesophytes (“normal” plants), PWP @ -1.5 MPa

Soil water Field Capacity - PWP: available water capacity Greatest loam, less clay, least sandy soil 1.8 2 1

Soil water Unavailable water: water held too tightly Greatest clay soil, least sandy soil

Soil water Recap: coarse soil little water @ field capacity, delivers little. Hold loose! Fine soil lots water @ field capacity, delivers good amount, retains lots @ PWP. Hold tight! Loam (& silt loam soil): hold just right! Fig. 4.9b

Soil water Texture impacts infiltration: ability water to penetrate soil

Soil water Texture impacts infiltration: ability water penetrate soil Coarse soil: high infiltration. Fine soil: low Structure can impact infiltration

Soil water Vertical water movement in soil: not always “a downer!” Hydraulic lift: movement water by plant roots from deep to shallow soil at night Soil dry: Low psi water Soil moist: High psi

Soil water Ex, Acer saccharum (sugar maple) NY forest Helps understory herbs Herbs larger within 2 m tree (greater moisture).

Dew in soil Soil distillation: movement water from deep to surface soil May occur in deserts hot cold med. Day med. Nite Water vapor cold warm Relative temperatures in day and nite