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