Plant NutritionPhotosynthesis is the major source of plant nutrition.Plants also require a number of inorganic molecules.macronutrientscarbon, hydrogen, oxygen, nitrogen, potassium, calcium, phosphorus, magnesium and sulfureach may exceed 1% dry weight of plantmicronutrientsiron, chlorine, copper, manganese, zinc, molybdenum, and boronconstitute from less than one, to several hundred, parts per million in most plantsnutritional requirements assessed in hydroponic culturesDeficiencies of certain nutrientscause specific diseasesComplete lack of only onenutrient can result in lack ofgrowthLeybig’s Law of the Minimumalthough all other nutrients arein abundance, a deficiency of asingle nutrient will stop growthUnder natural circumstances, nutrientscome from soilPlant growth affected by soilcompositionMost roots found in topsoilTopsoil consists of small particles of weathered rock, minerals, decomposing organic materials (humus), and living organismsAbout half total soil volume occupiedby spaces or poresfilled with air or water, dependingon environmental conditionsweathering of bedrock releasesnutrients slowly - chemicalprocesses make mineral nutrientssolubleIn natural conditions, plants removenutrients from the soil but theirdeath and decomposition returnsnutrients to the soilIn agriculture, removal of the crop removesnutrients that the crops have taken from the soilAgricultural land often becomes nutrientdepletedChemical fertilizers can be used to replenishlost nutrientsCommercial fertilizers generally have Nitrogen(N), Phosphorus (P), and Potassium (K) inpercentages given on the label:20:20:20 = 20% N: 20% P: 20% KThey often have other macronutrients andmicronutrients also.Nutrient depletion in soils can be reduced bycrop rotation and plowing under of unharvestedplant remains.Sand 200 - 2000 µmSilt 2 - 200 µmClay < 2 µmLarge particle soilshave large air spacesand little surface areaThey have poor abilityto hold water andnutrientsSmall particle soilshave small air spacesand large surface areaThey hold water andnutrients well -sometimes too wellThe 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 plantsobtain nitrogen directly from other organismsallows growth in N poor environmentsMycorrhizaeextend surface area for nutrient uptakeParasitic plantstap into vascular tissue of hostplant for
View Full Document
Unlocking...