soil fertility 3rd midterm

phosphorous deficiency symptom

purple coloration

stunted growth, delayed maturity

lack of germination

lack of initial root development

reduced overall plant growth and stunted plants

phosphorous functions in plant tissues

• structural component

  • DNA and RNA

  • phosphilipds in membranes

• energy transfer

  • ATP and ADP conversion

• starch and sugar utilization

  • required for starch remobiization

• concentrats in the seed

which P compound is concentrated in the seed?

phytate

effects of P deficiency

smaller leaf area, less leaf development, shoot growth impaired

P present in plant tissue

• mostly phosphate (PO43-) form

• present in vaculoes

• highly mobile inside plants, but compartamentalized

• no redox reactions in plant tissue. Only one oxidation stage for P:5+

retranslocation within the plant: when? why

when and why plant tissues leak out P?

How is P delivered to the surface of plant roots

diffusion

slow P diffusion to root surface is due to (Challenge of P uptake)

precipitation, adsorption, microbial immobilization

How plants adapt to low P availability

• grow more roots and root hairs

• release organic acids (citrate) ad phosphatase to mobilize P in rhizosphere

• high affinity P carriers (transporters)

• association with mycorrhizae

why and how root hairs are important for P uptake

root hairs are physically capable of bridging small air gaps to scavenge P

• P uptake happens ver close to the root surface

P transport

• the protein carrier at the plasmelemma is a symporter (both elements are moving in the same direction)

• most of the P as phosphate

• most of the P in the vacuole

in which range of nutrient concentrations in the soil high affinity carriers and the low affinity carriers operate

high affinity: low Km values (do best with low nutrient concentrations)

low affinity: within a range of Km values (best with high nutrient concentrations)

mycorrhizae mutualism

barley, wheat, perenials are open to mycorrhizae infestation.

ratio of N:P in plant tussues

• usually 10:1

• manure: 2:1

  • too much P

50 

Case: Using manure in terms of supplying balance N & P nutrients 

Let’s assume that a crop will require 70 units of N and 10 units of P

In the case of using manure with a N:P ratio of 2:1 as a nutrient source, an initialcalculation would be supplying 10 units of total Pand 20 units of total N from adding manure, and the rest of the N (50 units) can come from other N source (e.g., synthetic fertilizer such as urea). 

Of course we know that only some of the manure-N and manure-P are available in the first growing season (e.g., 50% of N becomes available, and 20% of P becomes available), and some of that good stuff stays residual for future seasons. Therefore, only these mineralizableN and Pto be released from the manure addition need to be accounted for; these availabilities can be quantified or estimated.

E.g., using these availability assumptions (20% of P and 50% of N), then 10 units of available Pand 50 units of available N would be sourced from manure, and the rest of the N (only 20units) could come from urea.

What is Km?

Michaelis constant. Measure of the affinity an enzyme has for its substrate (nutrient)

low km = high affinity: carrier binds its substrate eailt

high km = low affinity. Enzyme binds nutrient less easily

How does P help other nutrients flow too?

P fuels ATP needed to power uptake of other ions

_____ (aluminium sulphate) is effective in reducing ___ solubility in manures, thereby slowing accumulation of labile P in soils under repeated manure applications

alum, P

saturating the P retention capacity of soils can result in the ______ of water

eutrophication

what are the environmental risks of N

• volatilization of ammonia

• dentrification as nitrous oxide

• nitrate leaching into gw

what are the environmental risks of P

• P in surface runoff

• leaching into gw

how much P is available in solid manure in the first year

• 20%

• 2nd: 12%

• 3rd: 6%

rock phosphate (apatite) fertilizer must be finely ground, and it is better when incorporated on ____ soils.

It is for long-term build up strategy, and can be partially _____ to increase P availability

it is the P source (raw material) for many P fertilizers, including triple superphosphate, MAP, and DAP

acidic, acidulated

synthetic phosphrous ferts

ammonium phosphates

• manufactured by NH3 + H3PO4

• P uptake is enhanced by presence of N

• monammonium phosphate

• diammoniu phosphate

  • most widely used P fert

  • may cause seed damage if too much seed is places - salt effect and acidifying

• calcium orthophosphates

  • single superphosphate

    • 7-9.5% of P off which all is availabe

  • triple superphosphate

    • 17-23% P of which all is availabe

• ammonium polyphosphate

  • can be applied in liquid form

• potassium phosphate

• phosphoric acid

  • used to manufacture other fertilizers

What is the most widely used P fert, and what is one of the warning about it?

DAP - diammonium phosphate

• can cause seed damage. Salt effect and acidifying

triple __________ is high analysis, widely used and safer than DAP or MAP

superphosphate

ammonium _______ can be applied in liquid form, and sometimes reacted with urea to increase N content

polyphosphate

phosphorous and zinc ferrilization interaction

• Zn fert helps when also adding P

• added P is precipitated and removed from the soil solution any existing zn when no zn was added

• only having both nutrient additions led to the highest yield

p cycle

soil factors and P bioavailability

• pH: max availability ~6.5

• mineraology

  • acid soils controlled by al and fe compounds

  • neutral and alkaline soils controlled by ca and mg

• buffer capacity

• soil “age” or time (weatherin)

• total amount of P present and form (organic vs inorganic)

phosphorous bioavailibility and pH

phosphorous bioavailability and pH

pH effect on P adsorption and precipitation

• the least adsorption and precipitation at intermediate pH

buffer capacity (quantity/intensity)

• ratio between changes of nutrient concentrations in soluble vs solid states during nutrient additions or removals

• mostly affected by soil states that exchange rapidly with soluble state (adsorbed) but also by precipitated and organic states

the two ways to model isothermms

• freundlich

• langmiur

what does P sorption depend on

the more clay the more sorption, but it also depends strongly in the type of clay present

buffer capacity of P - low P

• when there is little P in the soil, there are many adsorption sites that are unoccupied, so a high proportion of P is adosrbed

buffer capacity: medium P

when P is added to a soil, the adsoprtion sites become more occupied with some of this P, and hence a higher proportion of P remains in the solution

buffer capacity high P

when there is a lot of P in a soil, the adsorption sites may become fully occupied (saturated), so no more P adsorption

the buffer capacity of potassium and phosphorous

20, 200

about _____ % of total p in agricultual soils is in inorganic form; however, only _____ in forest soils

75, 25

how much soil P

• soils contain 500-2500 lbs p/acre

• phosphours in soil solution usually <1 mg P L-1

• remaining P (which is nearly all of it) is tied up in OM and minerals that are relatively insoluble

• 75% of total P in agricultural soils in in inorganic form; 25% in forest soils

available P is in what form in soils

inorganic soluble (mineralized)

how does pH affect adsorption-desorption of inorganic P

• «5.5 —> greater density of positively charged exchange sites —> greater P adsorption in very acidic soils

• »7.5 greater density of carbonate sites (Ca

  • greater P adsorption in very basic soils

adsorption-desorption is dependent on

• surface density of Al and Fe oxides

• kinds of clays

  • allophae and imogilite > 1:1 clays > 2:1 clays

• soil organic matter effects

• temperature (higher temp —> more rapid reactions of sorption)

precipitation-dosolution
soluble P concentrations are in dynamic equilibtrium with Ca,___ and __ phosphate minerals

Al, Fe.

• concentrations of soluble P at which equilibrium is reached depends strongly on pH

an example with a Fe-phosphate mineral is ____

strengite (FePO4)

with an acid pH, the reaction for the dissolution—-recipitation of strengite goes into _____ P form

precipitated

the Ca-phosphate mineral, dicalcium phosphate:

at a pH <7.8 forces reaction to _____ P form

soluble

ca-phosphate mineral dicalcium phosphate, pH >7.8 and in the presence of CO2, forces reaction to _____ P form

soluble

which fixed P dominates around AB?

calcium bound (ca-P)

• because they are less weathered and have a high PH

• weathered + low pH —> precipitated ot adsorbed (tropics)

P is rapidly fixed in soil solution by Fe, Al, Ca. In acidic soils, fixed P can occur on the surface of:

• aluminum oxides and hydroxides such as _____

• iron oxides and hydroxides such as _______ or ______

gibbsite

geothite, hematite

in alkaline soils, fixedP IN or ON _______ phosphate ot tricalcium phosphate or HPO42-

dicalcium

soil tests to measure available P in acidic soils

bray 1

soil test to measure available P in neutral, alkaline, or calcarous soils

olsen

mehlich 3 soil test is universal?

form of potassium in soil

• nearly all K is in the inorganic form in soils

• tied up as part of primary minerals (feldspar, micas)

• tied up in the interlayers of clay minerals

• relatively immobile in soil (some movement in sandy)

the P cycle

fixation of K+ in soil depends on the type of clays

2:1 clay

• interlayer K —> slowly available K

soils that are K fixers vs non-fixers

• montmorillonite

• illite

• vermiculate

non-fixers

• OM

• kaolinite

• chlorite

• micas

potassium slides

how soil moisture infuences k+ availability

• effect on K diffusion

• higher tortuosity in dry soil

• diffusion path increases at low soil moisture

• saturated soils decrease K uptake

How temperature influences K+ availability

• plant root growth reduced at low temps

• high soil temps increase K release rate from solid phase (don’t oven dry soil samples being tested for K)

how soil mineralogy and textire effects k+ availability

2:1 clays fix and release K+

nearly all K is in the ____ form in soils. It is relatively ____ (mobile/immobile) in soils

inorganic, immobile

most soil K is tied up as part. ofprimary minerals such as ______ and ______ or tied up in the interlayers of clays (illlite, montmoriilonite, vermiculite)

feldspars, micas

the P cycle has no _____ and no _____

redox, atmosphere

______ of structural Fe3+ to Fe2+ INCREASES 2:1 layer charge, fixing K+

reduction

Oxidation of sructural Fe2+ to Fe3+ ______ (increase/deceases) 2:1 layer charge releasing K+

decreases

K fixers include:

• montmorillonite (smectite clay)

• illite (clay-sized mica)

• vermiculite (clay)

K non-fixers

• OM

• kaoloinite (clay)

• chlroite (clay)

• micas

factors influencing K+ availability

soil moisture (effect on K diffusion)

temp

soil mineralogy and texture

• 2:1 clays fix and release K+

• long-term availaibilitty of K in soils is greater with 2:1 clays

• more overall K availability with clayey soils than sandy soils

• higher CEC increases K availability

  • less availabiity with coarse/sandy soil

what is the affinity sequency for exchangeabe sites

al3+ > H+ >Ca2+ >Mg2+ > K+

other factors that influence K availability

• interactions with other nutrients

• activity of base cations (Ca2+, Mg2+)

• K avilaibility ratio (K+/ (Ca2+ + Mg2+)

• tillage management

• reduced or no till

• PM

• micas vs feldspars

NOT commonly deficient in prairie soils (unlike N and P) =

K+ is also responsible for _____ translocation within plants

sugar

K+ deficiency symptoms appear on ____ (older/younger) leaves

older

K+ deficiency symtpoms

• yellow leaf margins

• slow growth

• weak root systems

• brittle stems

the most widely used K fert is potassium _____, which is often known as muriate of ______ (MOP_

chloride, potash

potassium sulfate is good for ___ sensitive crops such as _____

Cl, tobacco, potato

 

What are the three main pools of K in soil? 

mineral

fixed

exchangeable

 

What is the largest pool of K in soil?

structural

 

HowdoesK become exchangeable or fixed in soil? 

weathering of primary minerals

k+ trapped in clay

 

Which clay types are responsible for fixing or exchanging K? 

 

What factors influence K availability insoil?

soil texture, mineraoligy, CEC, PM, pH, moisture

 

What function does K have in soil? 

(in plant)

regulates water balance

enzyme activation

sugar transport

(in soil)

• fixed in 2:1 clays

• buffer capacity, involved in cation exchange

 

What are different types of K fertilizers? 

potassium chloride, potassium sulfate

What visual deficiency are expected for N,P,K,S?

n - yellowing

p - dark green leaves

k = browning on edges

s - yellowing

What areadvantages/ limitations of using plant visual deficiency symptoms? 

Whatis‘hidden hunger’?

nutrient deficiency symptoms not visible, but lower than optimal

Whatisthecriticalnutrientconcentration?

What information can we gather from nutrient ratios? 

antagonistic and synergistic relationships

17:1 wheat N:S
s needed to use N