What is the Be What is the Be est Form of est Form of Nitrogen fo g or Pecan Orchar rds? Bruce W W. Wood
#1--From a Tree e’s Perspective: Not all Forms of Nit Not all Forms of Nit trogen (N) are Equal trogen (N) are Equal N-atoms have differ N atoms have differ ent oxidation states ent oxidation states 3- (i.e., surplus N 3- (i.e., surplus of 3 electr of 3 electrons): ons): Ammoni Ammonium um N 2+ 2+ (i.e., def (i.e., deficien cient t 2 2 electr electrons): ons): Increasing availability Decreasing availability Hydrazine (roc Hydrazine (r cke ket f fuel) of chemical energy of chemical energy N 3+ 3+ (i.e., def (i.e., deficien cient t 3 3 electr electrons): ons): (gain or acceptance of (gain or acceptance of (loss or donation of (loss or donation of Amin Amine (urea, e (urea, p peptides, pr eptides, proteins); eins); electrons; reduction; electrons; oxidation; amm ammoni nia a gain of energy) release of energy) N 4+ 4+ (i.e., def (i.e., deficien cient t 4 4 electr electrons): ons): Nitrite Nitrit N 5+ 5+ (i.e., def (i.e., deficien cient t 5 5 electr electrons): ons): Nitrat Nitrate cal energy potentials for plant metabolism . Different N forms possess different chemic
From a Tree’s s Perspective: Not all Forms of Nit Not all Forms of Nit rogen (N) are Equal* rogen (N) are Equal Under normal conditions, mos st nitrate within the plant is eventually converted to ammonium, but converted to ammonium but is energetically expensive. is energetically expensive 3- (i.e., surplus N 3- (i.e., surplus of 3 of 3 electr electrons): ons): Ammoni Ammonium um N 2+ 2+ (i.e., def (i.e., deficien cient t 2 2 electr electrons): ons): Increasing availability Decreasing availability Hydrazine (r Hydrazine (roc cke ket f fuel) of chemical energy of chemical energy N 3+ 3+ (i.e., def (i.e., deficien cient t 3 3 electr electrons): ons): (gain or acceptance of (gain or acceptance of (loss or donation of (loss or donation of Amin Amine (urea e (urea, , p peptides, pr eptides, proteins); eins); electrons; reduction; electrons; oxidation; amm ammoni nia a gain of energy) release of energy) N 4+ 4+ (i.e., def (i.e., deficien cient t 4 4 electr electrons): ons): Nitrit Nitrite N 5+ 5+ (i.e., def (i.e., deficien cient t 5 5 electr electrons): ons): Nitrat Nitrate cal energy potentials for plant metabolism . *Different N forms possess different chemic
#2—Pecan Is an Amm onium Loving Species -Consider Pecan Ecosystem -Consider Pecan Ecosystem ms and Their Ecophysiology- ms and Their Ecophysiology- Ammonium loving vs. Ammonium A i l i A i m intolerant vs. Intermediate species i t l t I t di t i
Pecan Alluvial Lands: ● A Co-dominate “Climax” species in certain forest types, and a “Subclimax” in other forest types. Water Table Water Table ► P Pecan is also native to deep well drained p pockets on “upland soils”; and near small rivers/creeks o on ridges of well drained “first bottom” or where the on ridges of well drained first bottom , or where the “ second bottom” nearly intersects the watercourse.
T Top soil zone is rich i il i i h i i in decaying organic matter d i i tt Organic-N and Ammonium-N are common (ammonia-loving species) Nitrate N dominate Nitrate-N dominate es es (ammonia intolerant sp pecies) N (3-) H 4 4 N (5+) O 3
Pecan is exposed to considerable reduced-N (organic and ammonium) in its natu ural habitats So, pecan exhibits evidence of being an “amm monium loving” (reduced-N) species!!! (typically shade tolerant mid- late-succession (typically shade tolerant mid late succession al species) al species) Nitrate loving continuous shoot growth sp ecies (Pioneer species) N (3-) H 4 N (5+) O 3 W N (5+) O Water Table
Characteristic Nitrat te-N loving Ammonium-N loving Pecan pecies z species y sp Pioneer species in forest succession Yes No No Heavy reliance on subsurface w ater table Yes No No Diffuse or semi diffuse porous cambial grow th Diffuse- or semi-diffuse porous cambial grow th Yes Yes No No No No Ring- or semi-ring porous cambial grow th No Yes Yes Indeterminate shoot grow th pattern Yes No No Determinate shoot grow th pattern No Yes Yes Early budbreak in spring Yes No No Delayed budbreak in spring No Yes Yes Produces small seeds Yes No No Produces medium to large seeds No Yes Yes Shade tolerant Shade tolerant No No Yes Yes Yes Yes Shade intolerant Yes No No Relatively small N storage pool in dormancy Yes No No Relatively large N storage pool in dormancy No Yes Yes Highly tolerant to anaerobic soils Yes No No Alternate bearing and nut masting No Yes Yes
#3—Trees Can Respond D Differently to Different Soil Solution Nitrate:A Solution Nitrate:A Ammonium Ratios Ammonium Ratios Vegetative growth is favored by nitrat te-N * usage [N:A = 5-10:1 (?)]: Tree nitrate can act as a quasi-hormone t T it t t i h to trigger downstream hormonal changes that t t igg t d t h l h g th t result in enhanced vegetative growth Nitrate-N triggers “ switching ” of tree resour rce partitioning to favor vegetative growth structures Less fruiting More likely to trigger deficiencies of esse ential and beneficial nutrient elements Nitrate-N is best if trying to get trees to grow w fast; potential issues with low P Urea-N is converted to ammonium and then n nitrate very rapidly in most soils, with little or none being absorbed as urea by roots; however, f foliar applied urea-N is rapidly absorbed and used by the plant as a preferred high energy form o th l t f d high g f f N f N Reproductive growth is favored by am mmonium-N* usage [N:A = 2-3:1 (?)]: Tree ammonium-N enhances synthesis of Tree ammonium N enhances synthesis of f carbohydrates amino acids peptides f carbohydrates, amino acids, peptides, proteins (and enzymes), and nucleic acids s, giving enhanced reproduction. Ammonium-N triggers “ switching ” of tree re esource partitioning to favor reproduction More fruiting and reduced incidence and d severity of nutrient element deficiencies Because ammonium competes with K in Because ammonium competes with K in n uptake be careful to ensure good K nutrition n uptake, be careful to ensure good K nutrition * Root uptake of nitrate and ammonium ‐ N is regulated by tree demand and sugar supply in roots
Synthetic Nitrogen Sources s: Ammonical (Ammonium) Ammonium: ~100-1000:1 preference by roots over nitrat te A high energy N form (highly reduced N atom ms) Not as easily lost as nitrate due to leaching or denitrification, as ammonia binds to soil particles Uptake is best at pH 7, declines as soil pH d rops Trees tend to have higher carbohydrate and protein levels than when fertilized with nitrate-N Easier to get phytotoxicity using ammonium m, due to rapid and great uptake preference by roots, so have to be careful to not over fertilize (very toxic to plant cells) Acidifies soils as it is converted to nitrate in the soil, and therefore affects availability of other elements (releases 3H+ ions into soil solutio l t (r l 3H+ i i t il l ti on; low CEC soils are more susceptible than higher l CEC il r r tibl th high r buffered high CEC soils) Rapidly converts to nitrate form in soils unle ess “Nitrification Inhibitors” are use to retard oxidation; conversion is more rapid in high pH soils. Subject to loss when soils are waterlogged a Subject to loss when soils are waterlogged a and also due to denitrification and mineralization and also due to denitrification and mineralization Can suppress K uptake, so can trigger K def ficiency if tree is low in K (e.g., June-drop of fruit). Can also suppress Ca, Mg, and transition metals s (Fe, Mn, Cu, Zn, Ni, Mo). Increases uptake of S, P, Cl, and Si N (3 N (3- -) H 4 ) H ---
Synthetic Nitrogen n Sources: Nitrate Nitrate: Dominate form of N in soil solution Most of N absorbed by roots is nitrate A low energy N form (highly oxidized N atoms s) More easily lost than ammonium due to leac ching , as not as much is bound to soil particles Trees will hyperaccumulate (luxury consumpt tion) nitrate, but it is not necessarily assimilated and used Trees are far more tolerant to high nitrate tha Trees are far more tolerant to high nitrate tha an to high ammonium, so low chance of phytotoxicity an to high ammonium, so low chance of phytotoxicity All N-forms will convert to nitrate in soil withi n 2-3 week unless they are bound up to soil or organic matter Can suppress P uptake, so can trigger P defic ciency if tree is low in P and add a lot of nitrate. The same is true for S Cl and Si same is true for S, Cl, and Si Enhances uptake of Ca, Mg, and transition m metals N ( N (5+) ) ) O 3 ) O 3 -
Commercial Orchards Are e Artificial Pecan Habitats ► Relatively little “reduced-N” ► Lots of vegetative growth ► Lots of nitrate-N (“oxidized-N”) ► Nutrient deficiencies ► Lots of water via irrigation ► Lots of water via irrigation ► Less reproductive growth
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