K Why is potassium represented by the symbol

K Why is potassium represented by the symbol ? In Latin and German, Kalium = Potassium 39 K is the dominant isotope. 40 K (radioactive) and 41 K (stable) are used as tracers.

Element Total Exchangeable Solution K 38, 000 190 10 -30 Ca 8000 2250 60 -120 Mg 6000 450 10 -20 N 3500 -na- 7 -25 P 900 -na- 0. 05 -0. 15 S 700 -na- 2 -10 1 kg/ha = 0. 89 lbs/ac The total potassium content of most mid-west soils is high (generally higher than all other nutrients) but most of the K is locked up in minerals like K feldspar that release K very slowly

Important potassium concepts No significant gaseous forms 3 rd most likely (after N and P) to be plant limiting Non-toxic at high concentrations Does not promote eutrophication (unlike N and P)

What Happens to Fertilizer K? – 20 to 60% of applied K is absorbed by crop in year 1 – Highest recovery on low K soils Available K Slowly Available K Unavailable K

K= K+ K fixation

Unavailable (90 to 98%) K K K+ Soil Minerals (feldspar, mica) K K K Trapped K K+ Readily available (0. 1 to 2%) K+ Soil Colloid K+ Soil solution K+ K+ Soil Colloid Slowly available (1 to 10%)

Role of potassium in plant nutrition Remains in ionic form inside plants (rather than being incorporated into organic molecules) Very important osmotic regulator (lowers water potential inside of plant cells) Activator of over 80 enzymes 1 -4% of plant dry matter (similar to N) Important for tolerance of environmental and biotic stresses (drought tolerance, winter hardiness, resistance to fungal pathogens, resistance to insects) Important for crop quality (flavor, color, stem strength)

Necrotic leaf margins are associated with severe potassium deficiency

K deficiency symptoms can occur even when soil test K levels are high Corn in ridge-till and no-till systems are often first to show K deficiency symptoms, but they can occur in other tillage systems as well. Uptake of K by plants requires an active root system, especially in the soil zone where plant-available K is located !! When this soil zone is dry, uptake is limited. Anything that exerts additional stress or limits root growth--compacted soil layers, root pruning, side-wall smearing-further reduces K uptake, especially when root growth is restricted in the zones of highest available K.

Average K 2 O application rates for fruit and vegetable crops in the US

Vegetable crops use a lot of potassium ! Crop Yield N P 2 O 5 K 2 O Bell Peppers 180 cwt 137 52 217 Cabbage 20 tons 130 35 130 Peas 25 cwt 164 35 105 30, 000 lb 90 48 158 Snap Beans 4 tons 138 33 163 Sweet Corn 90 cwt 140 47 136 Tomatoes 20 tons 120 40 160 Potatoes (white)

Maintenance rates of P 2 O 5 and K 2 O for agronomic crops

1 lb of elemental K = 1. 2047 lbs of K 2 O

The more highly weathered soils in southern IL tend to have low CECs. Pockets of sandy soils (grey shaded areas) in northern and central IL also have low CECs Most soils in the “high” region shown on this slide have CECs > 12 meq / 100 g. Most soils in the “low” region shown on this slide have CECs < 12 meq / 100 g. The U of I recommends different K management strategies for low and high CEC soils.

No maintenance Sufficiency Crop response to to extractable K K in in high low CECsoils

K fertilizer is cheap relative to grain prices K fertilizer is expensive relative to grain prices

Percent of soils testing medium or lower in K in 2001. BC AB MB SK 33 15 19 47 19 7 4 34 24 42 35 5 22 41 68 37 18 6 60 71 54 62 55 80 3 27 10 12 52 44 51 29 51 52 68 11 26 38 44 60 39 57 North America ON 66 PQ WA MT MN ID PA NE NV IL CO IN OH NH WV MO MA CT RI PEI 44 NS 90 75 47 NJ MD VA DE 12 55 KS KY AZ OK NM TX NC TN AR SC MS AL GA LA FL 43% VT MI IA CA 56 NY WI SD WY UT ME ND OR 45 NB 72 69 51

No obvious downward trend despite deficit spending In 2005, US farmers applied only 75% as much phosphorus as their crops removed —and just slightly over 50% as much potassium. What are the long term consequences ? ? ?

Soil testing methods used by US labs for potassium in 2005

Soil test K = 224 ppm Soil test K = 112 ppm

General rule of thumb: 4 lbs of K 2 O are required to raise extractable K by 1 lb

Annual application vs. build up and maintenance

The relative concentration of potassium, calcium, magnesium, ammonium, and other positively charged ions in the soil solution influences their relative uptake. Excessively high concentrations of one cation often results in inadequate uptake of other cations. For example, very high concentrations of calcium reduce uptake Grass tetany of potassium and very high concentrations of potassium reduce magnesium uptake. Cation balance affects animal health http: //www. pda. org. uk/leaflets/6/no 6 -print. htm Does Cation Balance Matter?

It’s well documented that alfalfa will take-up K beyond its needs if high levels of soil or applied K are available. This is referred to as “luxury consumption”.

Soil test values for K fluctuate during the year K is more available in wet soils

Potassium Fertilizers K 2 O Material Content % “Potash” = muriate of potash = MOP = 0 - 60 Chemical Formula potassium chloride sul-po-mag potassium nitrate KCl K 2 SO 4 -2 Mg. SO 4 KNO 3 60 20 44 potassium sulfate K 2 SO 4 50 Used in organic agriculture guaranteed analysis

The chloride in MOP has negative effects on some crops Tobacco fertilized with MOP produces cured leaves with muddy and uneven color with excessive hygroscopicity and poor burn.

MOP is salty stuff !

Potashisore is a mix of Na. Cl and salts. and White potash produced by. KCl, a process ofother dissolution The KCl is concentrated using a flotation process which recrystallization. Potash ore is dissolved under pressure in skims off the surface of a fluid suspension of finely hot brine, and MOP is precipitated as the brine cools and crushed ore. This concentrate is further processed and pressure reduces. The ironfertilizer is removed in this screened. The resulting material is ~ process, 95 percentand the resulting fertilizer isbecause white. White MOP is generally MOP. It is. MOP reddish in color iron impurities in the at least 98 not percent potassium chloride. ore are removed in this process.

Global K fertilizer production and consumption

Potash. Corp produces 23% of the world's supply of potash. It also controls almost all of the world's unused supply, and has historically held back production to keep potash prices high. It is also the world's largest fertilizer producer #1 in potash, #3 in phosphate and #4 in nitrogen fertilizers