PNP (Pacific Nut Producer) March, 2012
Joe Traynor
Why potassium chloride could be your best fertilizer bet
Terms used herein:
potassium = K chloride = Cl
KCl = potassium chloride = muriate of potash (MOP)
K2S04 = potassium sulfate = sulfate of potash (SOP); K20 = potassium oxide
Rising fertilizer costs, esp. for potassium fertilizers, are taking an increasing bite out of farming budgets. Potassium (K) is necessary to maintain high almond yields – a 3000 lb/acre almond crop removes over 200 lbs of K20 from the orchard each year. When considering potassium fertilizers, the choice is usually between two materials: potassium sulfate (sulfate of potash) or potassium chloride (muriate of potash). The cost of other K fertilizers per unit of K20 is prohibitive.
Potassium sulfate is 52% K20; potassium chloride is 61% K20. Besides having a significantly higher K analysis, potassium chloride is also cheaper per ton and cheaper yet on a cost per unit of K20 basis. When forced to choose between the sulfate and chloride forms of K, many growers opt for sulfate because of concerns that chloride will harm their trees. These concerns are well-founded because almonds are a salt (and chloride) sensitive crop. In many cases, however, potassium chloride should be the material of choice. An explanation follows.
To get a handle on the potential of Cl damage to crops, one must first know how much chloride is being applied. Potassium chloride is 47.5% Cl (note: adding 61% K20 to 47.5% Cl gives 108%, but there is no K20 in KCl, only K and Cl; KCl is 51% K, which makes the numbers come out --- 51 + 47.5 (+ 1% impurities) = 100% (see sidebar K20 vs. K for further explanation).
A 500 lb/acre application of muriate of potash supplies 305 lbs of K20 per acre but also 238 lbs of Cl, a scary figure, but will it damage trees? How many lbs of Cl can almond trees tolerate? Fortunately, there are guidelines to answer this critical question. Irrigation water contains Cl, and guidelines have been established (by UC and others) as to how much Cl can be safely applied to almonds in a given year. These guidelines state that irrigation water with a Cl level of 140 ppm or less is safe for almonds (Cl levels can be higher for almonds on the salt-tolerant hybrid rootstocks). To be ultra-safe, let’s figure that irrigation water should contain no more than 100 ppm Cl for almonds. A 100 ppm Cl water supplies 270 lbs of Cl per acre foot of water (an acre foot of water weighs 2.7 million lbs). At a reasonable figure of 3 acre feet applied annually, water with a Cl content of 100 ppm would safely apply 810 lbs of Cl each year, a figure well above the 238 lbs from 500 lbs/ac. of KCl.
In order to know the amount of KCl that can be safely applied to your orchard, you need to know the Cl content of your irrigation water. Cl is often reported in milliequivalents per liter (meq/l); to convert to ppm, multiply by 35.5 (1 meq/l of Cl = 35.5 ppm). Allowable amounts of KCl for different levels of Cl in water are given below:
AMOUNT OF KCl ALLOWED PER YEAR AT DIFFERENT LEVELS OF Cl IN IRRIGATION WATER
Joe Traynor
Why potassium chloride could be your best fertilizer bet
Terms used herein:
potassium = K chloride = Cl
KCl = potassium chloride = muriate of potash (MOP)
K2S04 = potassium sulfate = sulfate of potash (SOP); K20 = potassium oxide
Rising fertilizer costs, esp. for potassium fertilizers, are taking an increasing bite out of farming budgets. Potassium (K) is necessary to maintain high almond yields – a 3000 lb/acre almond crop removes over 200 lbs of K20 from the orchard each year. When considering potassium fertilizers, the choice is usually between two materials: potassium sulfate (sulfate of potash) or potassium chloride (muriate of potash). The cost of other K fertilizers per unit of K20 is prohibitive.
Potassium sulfate is 52% K20; potassium chloride is 61% K20. Besides having a significantly higher K analysis, potassium chloride is also cheaper per ton and cheaper yet on a cost per unit of K20 basis. When forced to choose between the sulfate and chloride forms of K, many growers opt for sulfate because of concerns that chloride will harm their trees. These concerns are well-founded because almonds are a salt (and chloride) sensitive crop. In many cases, however, potassium chloride should be the material of choice. An explanation follows.
To get a handle on the potential of Cl damage to crops, one must first know how much chloride is being applied. Potassium chloride is 47.5% Cl (note: adding 61% K20 to 47.5% Cl gives 108%, but there is no K20 in KCl, only K and Cl; KCl is 51% K, which makes the numbers come out --- 51 + 47.5 (+ 1% impurities) = 100% (see sidebar K20 vs. K for further explanation).
A 500 lb/acre application of muriate of potash supplies 305 lbs of K20 per acre but also 238 lbs of Cl, a scary figure, but will it damage trees? How many lbs of Cl can almond trees tolerate? Fortunately, there are guidelines to answer this critical question. Irrigation water contains Cl, and guidelines have been established (by UC and others) as to how much Cl can be safely applied to almonds in a given year. These guidelines state that irrigation water with a Cl level of 140 ppm or less is safe for almonds (Cl levels can be higher for almonds on the salt-tolerant hybrid rootstocks). To be ultra-safe, let’s figure that irrigation water should contain no more than 100 ppm Cl for almonds. A 100 ppm Cl water supplies 270 lbs of Cl per acre foot of water (an acre foot of water weighs 2.7 million lbs). At a reasonable figure of 3 acre feet applied annually, water with a Cl content of 100 ppm would safely apply 810 lbs of Cl each year, a figure well above the 238 lbs from 500 lbs/ac. of KCl.
In order to know the amount of KCl that can be safely applied to your orchard, you need to know the Cl content of your irrigation water. Cl is often reported in milliequivalents per liter (meq/l); to convert to ppm, multiply by 35.5 (1 meq/l of Cl = 35.5 ppm). Allowable amounts of KCl for different levels of Cl in water are given below:
AMOUNT OF KCl ALLOWED PER YEAR AT DIFFERENT LEVELS OF Cl IN IRRIGATION WATER
ppm Cl | lbs Cl applied/year* | Amount of KCl allowed per year |
10 ppm | 81 | 1536 lbs (936 lbs of K20) |
25 ppm | 202 | 1280 lbs (780 lbs of K20) |
50 ppm | 405 | 852 lbs. (520 lbs of K20) |
75 ppm | 607 | 427 lbs (260 lbs of K20) |
100 ppm | 810 | best to use sulfate of potash or closely monitor leaf Cl |
*in water; assuming 3 acre feet of water applied per year |