Soil and Plant Nutrition PDF

Soil and Plant Nutrition Essentiality Criteria An element is considered essential if it meets the following criteria: 1. Must be required for the completion of the life cycle of the plant  Soil and Plant Nutrition Essentiality Criteria An element is considered essential if t...

Soil and Plant Nutrition Essentiality Criteria An element is considered essential if it meets the following criteria: 1. Must be required for the completion of the life cycle of the plant  Soil and Plant Nutrition Essentiality Criteria An element is considered essential if the meets the following criteria: 1. Must be required for the completion of the life cycle of the plant 2. Must not be replaceable by another element  Soil and Plant Nutrition Essentiality Criteria An element is considered essential if the meets the following criteria: 1. Must be required for the completion of the life cycle of the plant 2. Must not be replaceable by another element 3. Must be directly involved in plant metabolism or must be required for a specific physiological function  Soil and Plant Nutrition Essentiality Criteria An element is considered essential if the meets the following criteria: 1. Must be required for the completion of the life cycle of the plant 2. Must not be replaceable by another element 3. Must be directly involved in plant metabolism or must be required for a specific physiological function 4. Must be required by a substantial number of plant species; not just by a single plant species of two. Essential Elements - Mobility Mobile elements in Plants: 1. N, P, K, Mg 2. can easily be translocated within plants to actively growing tissue. 3. deficiency symptoms occur in the older growth Immobile elements in Plants: 1. Ca, S, B, Fe, Zn, Cu, Mn 2. not efficiently translocated within the plant. 3. deficiency symptoms occur in the new growth General symptoms- nitrogen Deficiency usually appears on older leaves first. Because N is a part of the chlorophyll molecule, a major deficiency symptom is chlorosis. Reduced growth a. Severe N deficiency in maize (corn) in the juvenile stage; right: plants fertilized with N b. Leaf of a corn plant with characteristics symptom of N deficiency; notice the V- shapes green leaf color c. Characteristic symptoms of N deficiency in the older leaves of maize from a field crop Phosphorus deficiency in corn Purple or reddish color in older leaves Most often occur in young plants Overall stunting that may persist throughout season Lower yield Induced P deficiency of maize at tasselling stage in hydroculture Maize leaves from plants in hydroculture; leaves a the left and right with severe symptoms of P deficiency Leaves of maize; above: without P deficiency (P content of leaves = 0.26%); below: with symptoms of P deficiency (P content of leaves = 0.09%). Potassium deficiency in corn Marginal necrosis of the older leaves Sometimes they call it “leaf firing” Stunted growth and most often appears near maturity or silking stage Lower yield Sulfur deficiency in corn Chlorosis similar to N but occurring on younger leaves first Delayed maturity Stunting Nutrient Uptake by plants 1. Root Interception: root moves through the soil and comes into contact with the nutrient on the colloid. generally not very important because the root only comes into contact with 1-2% of the total soil volume. Nutrient Uptake by plants 2. Mass flow: nutrients move to the root with water. most important with nutrients that will easily flow with the water. Nutrient Uptake by plants 3. Diffusion: concentration gradients are set up around the root surfaces and the soil farther away. For most cations this is the most important form of movement. Nutrient Uptake by plants 3. Diffusion: for nutrients like P and K this is the most important form of uptake. the addition of fertilizer will increase the gradient and increase uptake. Nutrient Uptake by plants - Forms Forms of nutrients taken up by the plant. - plants will only take up a nutrient if it is in some ionic form. Element Plant-available Element Plant-available form form N NH4+ , NO3- B H2BO3- P H2PO4-, HPO4-2 Cu Cu+2 K K+ Zn Zn+2 Ca Ca +2 Cl Cl- Mg Mg+2 Mo MoO4-2 S SO4 -2 Fe Fe +2 Mn Mn +2 Sources of Essential Elements in the Soil 1. Organic matter Plants will not grow and complete its life cycle in the absence of some essential element This suggests that the organic matter which is derived from plants contains the essential elements To make these nutrients elements available the organic matter must be decomposed. Sources of Essential Elements in the Soil 2. Soil Minerals Example: Hornblende : CaAl2Mg2Fe3Si6O22(OH)2 Source of Ca, Mg, Fe Chlorite – has Mg Oxide in interlayer Source of Mg upon weathering Comment on how fast does this release occur Sources of Essential Elements in the Soil 3. Adsorbed Nutrients These are the nutrients that are held on the soil colloid. Influenced by CEC. This is the major source of nutrients for the plants, and is the source that is most easily controlled by man. 4. Others: rainfall, fertilizer application  Nutrient in Focus: Nitrogen Nitrogen is usually the element that limits plant growth and used by plants in largest quantities. Nitrogen is not found in large amounts in the soil except in the organic form; there is essentially none in soil minerals. The source for all nitrogen is the atmosphere (70%). Nitrogen Importance: component of all proteins, enzymes, and chlorophyll. regulates the use of K, P etc. has quickest and most pronounced effect on plants. very mobile in nitrate form (anion). Nitrogen Sources of N 1. Legumes: Legume- Rhizobia Symbiosis --- fix between 20 -150 kg N/hectare/yr. 2. Plant residue: C/N ratio effects release of N. Residues with narrow C/N ratio release more plant- available N to the soil. 3. Animal residue (wastes): type of wastes controls the amount of N present in the soil. Nitrogen Sources of N 6. Rain and Snow: Heat from lightning transforms N2 to oxide forms. These are brought to the soil by snow and rain at a rate of at least 5.6 kg/ha/year. 7. Industrial Wastes: Should be used with caution as the waste may contain other harmful substances such as heavy metals. 8. Fertilizers Nitrogen Cycle Plant N Decomposition Symbiotic N- N Uptake Fixation Ammonification Nitrification Denitrification Soil NH4+ NO3- N2 organic N Immobilization Non- Symbiotic Decomposition N-Fixation Microbial N Nitrogen Cycle Nitrogen Fixation conversion of atmospheric N2 to NH3 in cells represents a major input of N to many soils Symbiotic fixation by Rhizobium sp. Non-symbiotic by free living organisms bacteria, blue green algae Nodules N2 Rhizobium sp NH3 Nitrogen Cycle Plant N Decomposition Symbiotic N- N Uptake Fixation Ammonification Nitrification Denitrification Soil NH4+ NO3- N2 organic N Immobilization Non- Symbiotic Decomposition N-Fixation Microbial N Nitrogen Cycle Ammonification/Mineralization Conversion of organic N to mineral form NH4+ Brief review of the C:N ratio idea  At any given time no more than 1-2% of the total amount of N in the residue is available to the plant.  Only about 2-3% of the immobilized N is mineralized each year Nitrogen Cycle Plant N Decomposition Symbiotic N- N Uptake Fixation Ammonification Nitrification Denitrification Soil NH4+ NO3- N2 organic N Immobilization Non- Symbiotic Decomposition N-Fixation Microbial N Nitrogen Cycle Nitrification microbial oxidation of ammonium (NH4+) to nitrate (NO3- ) occurs under aerobic conditions. NH4+ ==== NO2- -carried-out by ammonium oxidizers -- e.g. Nitrosomonas sp., Nitrosococcus sp. NO2- ==== NO3- nitrite -carried-out by nitrite oxidizers -- e.g. Nitrobacter sp., Nitrospina sp. This produces hydrogen ions and the anion form of N which is more subject to leaching Nitrogen Cycle Nitrification Factors affecting nitrification 1. NH4+ must be present 2. Aeration: nitrification requires O2 3. Temperature 4. Moisture: nitrifying bacteria are inactive in waterlogged soils – why? 5. Neutral pH: why? 6. C:N ratio : wide vs narrow 7. Pesticides Nitrogen cycle Plant N Decomposition Symbiotic N- N Uptake Fixation Ammonification Nitrification Denitrification Soil NH4+ NO3- N2 organic N Immobilization Non- Symbiotic Decomposition N-Fixation Microbial N Nitrogen cycle Plant N Decomposition Symbiotic N- N Uptake Fixation Ammonification Nitrification Denitrification Soil NH4+ NO3- N2 organic N Immobilization Non- Symbiotic Decomposition N-Fixation Microbial N Nitrogen cycle Plant Uptake At what ionic forms is nitrogen taken up by plants? How is nitrogen taken up by plants? Immobilization conversion of mineral N (nitrate and ammonium) to the organic form Incorporation of N to microbial bodies Why is this called “immobilization”? Nitrogen cycle Plant N Decomposition Symbiotic N- N Uptake Fixation Ammonification Nitrification Denitrification Soil NH4+ NO3- N2 organic N Immobilization Non- Symbiotic Decomposition N-Fixation Microbial N Nitrogen cycle Denitrification Reduction of NO3 to N2, NO, and N2O Carried out by facultative anaerobic (major genus: Pseudomonas) Requires wet, anaerobic, reducing condition; like to have a large amount of plant residue available. An environmentally-relevant transformation – why?  Why worry about excess nitrate? Other Effects: decreasing biodiversity (Horrigan et al.) favoring new species invasion (Bertness et al.) production of toxins (Anderson; Gupta) Nitrogen cycle Denitrification Requirements for denitrification to occur: 1. Nitrate must be present 2. Anoxic/ reducing conditions 3. Stagnant hydrology/very slow-moving water 4. Presence of active microbes (temperature effect) 5. Presence of organic matter (source of electrons) Is denitrification good ? or bad ? Nitrogen cycle Volatilization  Loss of nitrogen as gaseous ammonia (NH3)  Ammonium applied to soils above pH 7. At high pH, OH concentration is so high Released to NH4+ Release H+ to solution NH3 atmosphere Review Slide 1. Nutrient in Focus: Nitrogen 1. Importance 2. Nitrogen Cycle 1. N-Fixation 2. Mineralization/Ammonification (C/N) 3. Nitrification 4. Plant uptake/Immobilization 5. Denitrification 3. Volatilization Nitrogen cycle Volatilization  Loss of nitrogen as gaseous ammonia (NH3)  Ammonium applied to soils above pH 7. At high pH, OH concentration is so high Released to NH4+ Release H+ to solution NH3 atmosphere Nutrient in Focus: Phosphorus Importance: 1. component of: a. DNA and RNA b. ADP and ATP Phosphorus is important in "energy storage and transfer" at the cellular level. 2. role in plant maturation - flowering, fruiting, root development, straw strength Nutrient in Focus: Phosphorus Crop Demands 1.Only N and K (and sometimes Ca) are taken up in larger amounts by the plants. 2.P is required for N fixation to take place. The microbes in the system require that some P be present. Nutrient in Focus: Phosphorus Forms of P in soil 1.Mineral P (mainly apatite mineral) – form of P-containing mineral that is being mined 2.Organic P – about 30-50% of total P in soils. It is a component in nucleic acids and phospholipids 3.Solution P – inorganic forms of P such as PO43-, HPO42- and H2PO4- and soluble organic forms of P. Nutrient in Focus: Phosphorus Plant Uptake plants take up P from soil water. Because only small amounts of P are found in the soil water at any one time, the P must be constantly replenished. soil organic matter contains P. As with other nutrients, the organic matter must first be broken down before the plant can use the P. Main P-uptake mechanism is diffusion Nutrient in Focus: Phosphorus P Fixation formation of "fixed" or unavailable P compounds By Fe, Al, (acid conditions) : FePO4 ,Al(PO4), MnPO4 By Ca ang Mg (alkaline conditions) By clays : Fe and Al associated with clay enough P must be added to overcome the fixation capacity and the plant needs Phosphorus Cycle Plants P in P-containing Uptake Weathering Minerals Mineralization Decomposition P in Plant and Solution P Organic P animal Residues Immobilization P fixed to Soil Sorption/ Immobilization Minerals desorption Microbial Biomass