Plant NutritionPhotosynthesis is the major source of plant nutrition.Plants also require a number of inorganic molecules.macronutrients

carbon, hydrogen, oxygen, nitrogen, potassium, calcium, phosphorus, magnesium and sulfureach may exceed 1% dry weight of plant

micronutrientsiron, chlorine, copper, manganese, zinc, molybdenum, and boronconstitute from less than one, to several hundred, parts per million in most plants

nutritional requirements assessed in hydroponic cultures

Deficiencies of certain nutrientscause specific diseases

Complete lack of only onenutrient can result in lack ofgrowth

Leybig’s Law of the Minimumalthough all other nutrients arein abundance, a deficiency of asingle nutrient will stop growth

Under natural circumstances, nutrientscome from soil

Plant growth affected by soilcompositionMost roots found in topsoilTopsoil consists of small particles of

weathered rock, minerals, decomposing organic materials (humus), and living organisms

About half total soil volume occupiedby spaces or pores

filled with air or water, dependingon environmental conditions

weathering of bedrock releasesnutrients slowly - chemicalprocesses make mineral nutrientssoluble

In natural conditions, plants removenutrients from the soil but theirdeath and decomposition returnsnutrients to the soil

In agriculture, removal of the crop removesnutrients that the crops have taken from the soil

Agricultural land often becomes nutrientdepleted

Chemical fertilizers can be used to replenishlost nutrients

Commercial fertilizers generally have Nitrogen(N), Phosphorus (P), and Potassium (K) inpercentages given on the label:

20:20:20 = 20% N: 20% P: 20% K

They often have other macronutrients andmicronutrients also.

Nutrient depletion in soils can be reduced bycrop rotation and plowing under of unharvestedplant remains.

Sand 200 - 2000 µm

Silt 2 - 200 µm

Clay < 2 µm

Large particle soilshave large air spacesand little surface areaThey have poor abilityto hold water andnutrients

Small particle soilshave small air spacesand large surface areaThey hold water andnutrients well -sometimes too well

The best soils have amixture of particlesizes - “loam”

Nitrogen FixationPlants need ammonia (NH3) to buildamino acids.N2 most common atmospheric formPlants lack the ability to convertgaseous nitrogen to ammonia.some bacteria have the abilityA mutualism between legumes andnitrogen-fixing bacteria allowatmospheric N to be captured andmade available to the plant.

Nutritional Adaptations of PlantsCarnivorous plants

obtain nitrogen directly from other organismsallows growth in N poor environments

Mycorrhizaeextend surface area for nutrient uptake

Parasitic plantstap into vascular tissue of hostplant for nutrients