Practical nutrient management

Question 1

What element helps grasses stand upright

Answer 1

Silicon

Question 2

Nitrogen fixing plants need which nutrient?

Answer 2

Cobalt

Question 3

Plant toxic nutrients

Answer 3

Aluminium and Mn in acid
Na and Cl in saline
B in saline too
These can be toxic to animals that eat them too

Question 4

How plant roots take up nutrients

Answer 4

Respiration provides energy for this

Question 5

How can plants impact their soil environment?

Answer 5

How they take up nutrients affects resulting pH of soil since they release cations or anions to take up nutrients

Question 6

Types of release mechanisms of nutrients

Answer 6

Dissolution
Organic matter decay
Cation exchange (fast)

Question 7

Do you know the tank analogy?

Answer 7

Differences in active nutrients in tanks with large or small pools including if that is organic or CEC tied

Question 8

Organic matter decay will happen the quickest in which environments?

Answer 8

Moist, warm, aerated soils
Releases N, S, and P sometimes

Question 9

Nutrients from cation exchange

Answer 9

Ca, Mg, and K (rapid process)

Question 10

Weathering (Dissolution)

Answer 10

Most important in young soils, acid conditions

Question 11

Specific adsorption/desorption

Answer 11

P, Mo, B, Cu, Zn
Strong bonding processes on oxides and volcanic ash

Question 12

Surface chelation/release

Answer 12

Fe, Cu, Zn, Mn (metals)
Also toxic materials such as lead
Strong bonding processes on humus
Slow release rates

Question 13

Transport in soil

Answer 13

Mass Flow - from soil water, solubility determines
Diffusion - individual molecules through gradients, soil is moist and warm

Question 14

How roots respond to different transport mechanisms

Answer 14

They have to branch out to nutrients who use diffusion by making a diffusion gradient through surface area. They put at the surface of soils because that’s where nutrients are added

Question 15

Impediments to root growth

Answer 15

Physical: dry, structureless soils that are dense and have few macro pores
Chemical: oxygen deficiency, Ca deficiency, Al excess, organic toxins
Biological: disease organisms

Question 16

What is availability?

Answer 16

Ability of soil to maintain high content ration in solution in vicinity to roots
Determined by:
1) concentration
2) rate of release
3) mobility

Question 17

Why are nutrient losses higher in fertile soils?

Answer 17

You have more nutrient density so if you have erosion you’ll lose more per volume than a poor soil

Question 18

Types of Losses

Answer 18

Erosion - mostly P and N in solids
Crop removal - N and K removed most , can minimize by returning back residues
Gaseous - ammonia volatilization in alkaline soils, nitrate and sulfate reduction in wet environments, burning of N and S
Leaching - loss of soluble nutrients through water, phosphate loss only in sandy soils, minimize loss by fertilizing at right time

Question 19

Why do healthy plants use nutrients better

Answer 19

More biomass so harvesting more nutrients

Question 20

Where does phosphorus fertilizer come from?

Answer 20

Rock phosphate, mostly apatite

Question 21

Where does N fertilizer come from?

Answer 21

Ammonia is the base for most N fertilizers and can be created from Haber Bosch. It can be turned into anhydrous ammonia by putting through pressure and low temps

Question 22

Where does potassium fertilizer come from?

Answer 22

Mined from sedimentary deposits of KCl and potassium sulfate

Question 23

Where does sulfur fertilizer come from?

Answer 23

Gypsum - mined from sedimentary rocks, abundant, fairly soluble
Elemental sulfur - mined, insoluble, oxidizes in soils
Superphosphate - contains calcium sulfate

Question 24

Determining fertilizer needs

Answer 24

Educated guess
Interpretation of visual symptoms
Soil samples
Plant samples
Nutrient response trials (too slow and expensive)

Question 25

Maximum yields are not economical rather…

Answer 25

Optimal determined by minimum amount of nutrients for this

Question 26

How does soil testing differ across places?

Answer 26

Soil test procedures vary regionally and are calibrated locally

Question 27

What influences fertilizer choices

Answer 27

Nutrient content
Release rates
Availability and cost (also transportation)
Convenience and ease of use (also application method)
Side effects - soluble salts damage, organic materials in excess clog soils, create anoxic conditions, produce organic toxicities, also leaching, acidification by ammonium, secondary deficiencies are enhanced

Question 28

Fertilizer methods pros and cons

Answer 28

Broadcasting - fast, convenient
Port nutrient accessibility, more soil contact, volatile gas loss

Injection and banding - reduced soil interaction, reduce volatile loss
Root toxicity in band

Soluble form - convenient for irrigation controlled rate
Cost of transporting bulk

Foliar - fast response, accurate timing, no soil immobilization
Needs repeated application so costly