Practical nutrient management Flashcards
What element helps grasses stand upright
Silicon
Nitrogen fixing plants need which nutrient?
Cobalt
Plant toxic nutrients
Aluminium and Mn in acid
Na and Cl in saline
B in saline too
These can be toxic to animals that eat them too
How plant roots take up nutrients
Respiration provides energy for this
How can plants impact their soil environment?
How they take up nutrients affects resulting pH of soil since they release cations or anions to take up nutrients
Types of release mechanisms of nutrients
Dissolution
Organic matter decay
Cation exchange (fast)
Do you know the tank analogy?
Differences in active nutrients in tanks with large or small pools including if that is organic or CEC tied
Organic matter decay will happen the quickest in which environments?
Moist, warm, aerated soils
Releases N, S, and P sometimes
Nutrients from cation exchange
Ca, Mg, and K (rapid process)
Weathering (Dissolution)
Most important in young soils, acid conditions
Specific adsorption/desorption
P, Mo, B, Cu, Zn
Strong bonding processes on oxides and volcanic ash
Surface chelation/release
Fe, Cu, Zn, Mn (metals)
Also toxic materials such as lead
Strong bonding processes on humus
Slow release rates
Transport in soil
Mass Flow - from soil water, solubility determines
Diffusion - individual molecules through gradients, soil is moist and warm
How roots respond to different transport mechanisms
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
Impediments to root growth
Physical: dry, structureless soils that are dense and have few macro pores
Chemical: oxygen deficiency, Ca deficiency, Al excess, organic toxins
Biological: disease organisms
What is availability?
Ability of soil to maintain high content ration in solution in vicinity to roots
Determined by:
1) concentration
2) rate of release
3) mobility
Why are nutrient losses higher in fertile soils?
You have more nutrient density so if you have erosion you’ll lose more per volume than a poor soil
Types of Losses
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
Why do healthy plants use nutrients better
More biomass so harvesting more nutrients
Where does phosphorus fertilizer come from?
Rock phosphate, mostly apatite
Where does N fertilizer come from?
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
Where does potassium fertilizer come from?
Mined from sedimentary deposits of KCl and potassium sulfate
Where does sulfur fertilizer come from?
Gypsum - mined from sedimentary rocks, abundant, fairly soluble
Elemental sulfur - mined, insoluble, oxidizes in soils
Superphosphate - contains calcium sulfate
Determining fertilizer needs
Educated guess
Interpretation of visual symptoms
Soil samples
Plant samples
Nutrient response trials (too slow and expensive)
Maximum yields are not economical rather…
Optimal determined by minimum amount of nutrients for this
How does soil testing differ across places?
Soil test procedures vary regionally and are calibrated locally
What influences fertilizer choices
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
Fertilizer methods pros and cons
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
