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Potassium, Sulfur, Calcium, Magnesium Section K SWES 316

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Potassium in Plants First or second in amount taken up by most plants (N is usually first) Main functions Osmotic control Enzyme activation Deficiencies Mobile nutrient--firing, spotting, necrosis of leaf tips or edges, causes weak stems

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K Deficiency Corn

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K Deficiency Alfalfa Soybean

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Nutrient Removal (kg/ha/yr) Source: Plant Nutrient Use in North American Agri., PPI, 2002 NPKN/K Ratio Broccoli (100 lb yield) 0.440.070.351.25 Celery (100 lb yield) 0.190.050.420.45 Corn (bushel of grain 56 lb) 0.750.190.243.0 Alfalfa (ton) 566.6501.12 Oranges (ton) 8.80.89.10.97

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Soils Depleted in K

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Potassium Fertility K is most likely to be deficient under conditions of: Acid, weathered soils Sandy soils With high K-use crops (e.g. alfalfa) In most of the ______ part of the U.S., K deficiencies are uncommon However, very high crop demand for K can sometimes create deficiencies in any soil western

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% of soils testing medium or lower for K Data from PPI, 2001

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Cotton Response to K in AZ Source: Silvertooth et al., 1996 Potassium source was soil incorporated after planting by banding. Sum of four 4.6 lb K 2 O/acre foliar applications using KNO 3 as the K source. observed significance level for the treatment differences, or the probability that there are no differences among treatments

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Grapefruit Response to K in Florida Source: Obreza, Better Crops with Plant Food, 2003 Initial soil test K = very low

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Alfalfa Response to K in Indiana Source: Joern et al., Better Crops with Plant Food, 2003. Initial soil test K = 90 ppm (very low)

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Turf Response to K in Georgia Source: Trenholm et al., Better Crops with Plant Food, 2001

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Potassium in Soils Almost all soil K is in inorganic forms: Minerals K-feldspars Clays (often called fixed K): Primary micas (biotite, muscovite) Secondary clays (illite) Exchangeable K + on cation exchange sites Available: K + in soil solution

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from PPI

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Interlayer (fixed) K in Illite

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K in soil clays Edge position Inner position Planar position Hydrated and exchangeable cation Hydroxy Al (or Fe) islands

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Potassium in Clays The availability of K + on clays to plants depends on position on the clay (micas, illite): inner sites - low availability, fixed K in illite edge sites - moderate availability planar sites - high availability readily exchangeable

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Potassium Equilibrium in Soils Soln. K+ Exch. K+Fixed K+Mineral K+ Solutionplanar sitesinner sitesfeldspars edge sites K in solution is usually

Properties of Selected Soils Soil SeriesTotal K (g kg-1) Exchangeable K (mg kg-1) Clay Mineralogy Antho22.0366S>MI>K Gilman21.1280S>MI>K Glenbar20.1257S>MI=K>Q Grabe24.8549S>MI>K=CA Indio17.3315S>MI=K>Q Pima26.0430S>MI K Q Casa Grande29.9560S KQ Gadsden18.1460S>MI=K>Q S-SMECTITE; MI-MICA; K-KAOLINITE; Q-QUARTZ; CA-CALCITE;PG-LYGORSKITE

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Calculated Sufficiency and K Desorption Soil SeriesSufficienc y Level K (mg kg -1 ) Difference between Exchangeable and Sufficiency (mg kg - 1 ) K Desorbed Per 30 min. (mg kg -1 ) Antho14322318 Gilman13614417 Glenbar13811915 Grabe17137816 Indio15815712 Pima16926113 Casa Grande13742333 Mohall14116816 Superstition120-2011 Gadsden17328713

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Summary of Clay Mineralogy in Arizona Clay mineralogy was a mixed composition of smectitie, mica, kalonite, palygorskite, calcite, and quartz. All soils contained K bearing mica, typically associated with high K release rates. These soils contained negligiable amounts of vermiculite, known for a high capacity to fix K.

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K Fertilizers Inorganic: Solids: KCl (0-0-60), K 2 SO 4 (0-0-52), KNO 3, (13-0-45) mixed in combination with N, P Liquids: Solutions of K solids Organic: Fresh manures average 1 to 2.5% K, all is highly soluble and available. Composted organics contain much less (