Module 3 Flashcards
(25 cards)
Chemical formula of phosphate in soil solution?
H2PO4-
Chemical formula of Sulphate in soil solution?
SO4-2
Chemical formula of Nitrate in soil solution ?
NO3-
Chemical formula of Sodium in soil solution?
Na+
Chemical formula of Magnesium in soil solution?
Mg2+
Chemical formula of Potassium in soil solution?
K+
3 types of ion mechanisms?
Root interception
Mass Flow
Diffusion
What mechanism does phosphorus adopt to reach the plant root?
Diffusion
How does phosphorus behave in soil?
As phosphate isn’t very mobile (is adsorbed by soil), fertiliser placement is critical but the potential for nutrient loss is small. Phosphorus doesn’t move more than 6mm to get to a root. Phosphorus is only lost if the soil itself is lost through erosion. Phosphorus accumulates in the soil.
How does nitrogen behave in soil?
As nutrient mobility increases, fertiliser placement becomes less critical, but the potential for nutrient loss becomes greater. Nitrogen placement relative to the plant isn’t very critical for uptake, but the potential for loss of nitrogen once it is applied to the soil is generally very high, and little available nitrogen will accumulate in the soil.
how do micronutrients behave in soil?
The behaviour of most micronutrients is similar to that of phosphorus. The other nutrients fall somewhere between these two extremes in mobility behaviour (phosphorus and nitrogen)
proportion of nutrient uptake by every mechanism
nitrogen - 99% mass flow phosphorus - 90% diffusion potassium - 78% diffusion calcium - 72% mass flow magnesium - 87% mass flow sulphur - 95% mass flow all consist of some root interception
what is pH buffering?
When a solution resists pH change of soil when acidic or alkaline materials are added.
what happens when lime is added to an acidic soil?
CaCO3 is a basic salt - it dissolves in water to form a strong base (Ca(OH)2) and weak acid (H2CO3), so the net effect is a basic solution.
For every mole of CaCO3 that reacts with water, 2 moles of OH- ions are generated. These two moles of OH- ions neutralise excess H+ in soil solution. H+ then moves into soil solution from the soil surface, buffering the change in pH.
explain “Point of Zero Net Charge”?
PZNC is the pH at which the amounts of negative and positive charges on the soil particle surface are the equal resulting in zero net charge.
PNZC related to the dissociation of H+/OH- ions?
When the pH is above PZNC, the soil is net negatively charged, resulting in more cation (H+) retention; when the pH < PZNC the soil is net positively charged, resulting in more anion (OH-) retention.
definition of Cation Exchange Capacity?
This is the number of cation adsorption sites ( or negative charge) per unit mass of soil
what causes a soil to have a high CEC value?
high CEC is when cations are held by the negatively charged clay and organic matter particles in the soil through electrostatic forces. (negative soil particles attract the positive cations). High CEC is caused by high negative charge.
what is the benefit of high CEC?
high CEC means more plant available cations. It represents the total amount of exchangeable cations that the soil can adsorb. The cations used by plants in the largest amounts are calcium, magnesium, and potassium.
what is flocculation?
the process in which particles disperse in a solution contact and adhere each another, forming clusters, flocks, flakes, or clumps of a larger size.
what is a diffuse layer?
the DL is the specific distance from the clay surface that the concentration of the bulk soil solution is equal, the anionic and cationic charges are balanced in solution.
Below the PZNC?
the surface bears a positive charge and can attract anions
Above the PZNC?
the surface bears a negative charge and can attract cations
increase of K+ from effluent…
K+ over time can displace adsorbed Ca2+ and Mg2+, releasing these cations into soil solution and thereby increasing their risk of leaching. Over time the Diffuse Layer may increase leading to soil deflocculation
