sign in sign up
<<
Home , Fertilizer, Fertilizer burn, Nutrient management, Potassium sulfate

north america Managing for Organic Crop Production By Robert Mikkelsen An adequate K supply is essential for both organic and conventional crop production. Potas- sium is involved in many physiological reactions, including osmoregulation, synthesis, enzyme activation, and photosynthate translocation. The K balance on many is negative, where more K is removed in harvested crops than is returned again to the . An overview of commonly used K for organic production is provided.

otassium is an essential for plant growth, but it often receives less attention than N and P in many crop Pproduction systems. Many regions of the U.S.A. and all of the Canadian provinces remove more K during than is returned to the soil in and (Figure 1). In the U.S.A., an average of only 3 units of K is replaced as fertilizer and manure for every 4 units of K removed in crops, resulting in a depletion of from the soil and increasing occur- rences of deficiency in many places. Potassium is the soil cation required in the largest amount by , regardless of philosophy.

1,400 Removal 1,200 Hay and forage crops can remove hundreds of pounds of K from the soil Manure each year, placing a heavy demand on soil resources. 1,000 Fertilizer Large amounts of K are required to maintain plant health 800 and vigor. Some specific roles of K in the plant include os- moregulation, internal cation/anion balance, enzyme activa- 600 tion, proper water relations, photosynthate translocation, and 400 protein synthesis. Tolerance of external stress, such as frost, , heat, and high light intensity is enhanced with proper 200 K nutrition. Stresses from disease and insect damage are also 0 reduced with an adequate supply of K. Although there are no CA ID IA KS known harmful effects of K to the environment or to health, the consequences of inadequate K can be severe for 1,200 crop growth and efficient utilization of other nutrients, such Removal as N and P. Maintenance of adequate K is essential for both 1,000 Potassium, million lb Potassium, Manure organic and conventional crop production. More information Fertilizer 800 and an extensive list of references are available at the website: >www.ipni.net/organic/kreference<. 600 Supplemental K is sometimes called “”, a term that comes from an early production technique where K was 400 leached from wood ashes and concentrated by evaporating the leachate in large iron pots. Clearly this practice is no longer 200 practical and is not environmentally sustainable. This potash collection method depended on the tree roots to acquire soil 0 K, which was then recovered after the wood was harvested MN NE NY TX and burned. Most K fertilizer, whether used in organic or conventional , comes from ancient marine , Figure 1. Annual balance of K inputs in fertilizer and recoverable deposited as inland evaporated. This natural geological manure compared with K removal in harvested crops in process is still visible in places such as the Great eight selected states: California (CA); Idaho (ID); Iowa and the Dead . (IA); Kansas (KS); Minnesota (MN); Nebraska (NE); New Organic Crop Production York (NY); Texas (TX). The basic principles of are the same, what- Abbreviations and notes for this article: K = potassium; N = ; ever the production system used. Both organic and conven- P = ; Mg = ; S = .

Better Crops/Vol. 92 (2008, No. 2) Crops/Vol. Better tional production systems have many common objectives and 26 Better Crops/Vol. 92 (2008, No. 2) 27

- 7 8 8 6 45 10 11 10 10 K/ton 100 lb Harvest K removal, to soil and growth and Plant uptake potassium potassium Application of Disposal of human salts The Cycle Global Separation of individual Potassium Scientific name Medicago sativaPrunus dulcis Zea mays Zea mays Solanum tuberosumSpinacia oleraceaCucurbita pepoOryza sativa Lycopersicon esculentumTriticum aestivum in water in dissolved Potassium ). However, much less attention has 1). However, Table Resources 2007; Natural Institute, Plant Nutrition by by Extraction Conservation Service, 2007). harvested the in portion K removal of some Average and horticultural agronomic common (Interna crops tional as salt Water deposited Since off- sales will always lead to a removal of K and K of removal a to lead always will sales off-farm Since The demand for K by various crops has been estab- Corn silage Tomatoes Almond Corn grain Table 1. Table Crop conventions. Moisture is based on marketing Alfalfa Potatoes Spinach Squash Figure 2. The K cycle. global Potassium Balance amounts of K from the subsoil. The contribution of subsoil K to the plant K requirement depends on the amount of plant- available K in the top and subsoil, factors, and the root potentialdistribution pattern of the specific crop. root-limiting this for account not will surface soil the near done testing Soil subsoil contribution to the K supply. additional loss of K through and runoff is inevitable, is runoff and leaching through K of loss additional the potential of a cropping management system to replenish the K reserve is important. The use of farm budgets is useful to and system farming a within flow nutrient the describing for mixed and rotations long-term for planning nutrient with assist on-farm the factors, of variety a on Depending systems. farming and budgets K of on N, organic P, farms have been shown to range from a surplus to a deficit. por- harvested the in concentration K the measuring by lished tion of the crop ( growing to supplied be must K which at rate the to paid been In general, the objectives of organic plant nutrition are Plant-available K is usually measured in the , but Crop rotations are a central part of organic production There are many variations possible for successful K In general, regulations for mined K sources specify that The use of approved nutrient sources is governed by a Using On-Farm Resources Which Organic Standards to Follow? Which Organic to (i) work within natural systems and cycles, (ii) maintain or (iii) use renewable resources increase long-term , whole- safe, is that food produce (iv) and possible, as much as some, and nutritious. generally generally work with vary the same may basic global options resources. and While techniques management nutrient specific supporting processes fundamental the systems, two the between do not change. and plant nutrition soil fertility some deep-rooted plant species can take up considerable systems. While this practice can be leach- helpful K for supplying reduce N also may and included are crops when ing losses, rotations alone do not supply any additional K to soil enhance to shown been have roots Plant farm. the in shift a causing and K rhizosphere depleting by weathering and processes natural speed can shift This equilibrium. K the enhance the rate of clay transformations. Subsoil K reserves deep- where systems rotation crop some for important be may rooted plants can extract K which may be subsequently used influence may crops rotational While crops. shallow-rooted by the availability of existing soil K, the removal of any plant material from the field continually depletes the soil nutrient supply and ultimately reduces long-term productivity. management in organic production systems. The largest dif- crops and both produce that farms on occur ferences compared with farms that strictly produce crops for off-farm the of nutrition the systems, livestock/crop mixed the In sale. manure residual the and priority first takes generally animals imported cases, these In cropland. surrounding to returned is K in feed and bedding frequently exceeds the output in milk and meat products, sometimes leading to an accumulation of losses Large manure. receive that fields surrounding the in K of K may occur on these farms during manure storage composting. Since and excreted K mostly goes into , if this fraction is not effectively recovered it will not be returned to the field with the solid portion of the manure. they must not be processed, purified, ordiffer- between disagreement alteredis there However, fromform. original their used. be can materials specific what over bodies certifying ent some Unfortunately, of these restrictions on certain nutrient materials do not have solid scientific justification and their inclusion or exclusion on various lists should not be viewed as one material being more or less “safe” than another fertil- izer material. variety of regional, national, and international oversight or- ganizations. Each organization maintains somewhat different standards and allows different materials to be used in their the interpret individually they as systems production organic grower a result, a As principles. agricultural organic of intent seeking advice on permissible organic materials should first know where the agricultural produce will be sold in order to meet the requirements of that market. plants. Both the total amount required (quantity) and the rate of supply (intensity) are equally important. This concept is important for all crop growth, but requires special attention when using low- nutrient sources that may provide an adequate amount of total K, but not at a rate sufficiently rapid to meet peak-demand periods of plant growth. Potassium Release from Soil Minerals The most common mineral sources of K in are feld- spars and micas...soil minerals remaining from the primary parent material. Weathering of these primary minerals pro- duces a range of secondary minerals that may also serve as a source of K in soil. These minerals include micaceous clays such as illite and . Crushed rocks and minerals have been evaluated as K sources in many field and experiments. In general, plants are able to gain a very limited amount of K from miner- als applied as biotite, phlogopite, muscovite, and nepheline. Organic production frequently occurs on smaller-sized farms where the use Feldspar K is not plant available without additional treatment of organically approved K sources is feasible for maintaining soil fertility. or weathering. The rate of K release from minerals is influenced by factors Approved and Restricted Potassium Sources such as soil pH, temperature, moisture, microbial activity, the The National Organic Program in the U.S. and the Canadian reactive surface area, and the type of vegetation. Therefore, a General Standards Board classifies products as either allowed, mineral that is somewhat effective as a K source in one condi- restricted, or prohibited for use in organic production. Allowed tion may be ineffective in another environment. products are permitted for organic production when applied as Some soil minerals may act as a sink for removing K from directed on the label. Restricted materials can only be applied solution. When K is adsorbed in the interlayer sites of illite, for certain uses and under specific conditions. Prohibited prod- vermiculite and other smectite clays, the clay layers collapse ucts may never be used for organic production. The properties and trap the K within the mineral lattice. This fixation process and value of these materials as sources of plant nutrients vary is relatively fast, while the release of this interlayer K is very considerably. The following K sources are used sometimes for slow. Non-exchangeable K should not be confused with min- organic production. eral K, since non-exchangeable K is held between adjacent tetrahedral layers of clay, instead of being covalently bonded in mineral crystal structures. Potassium Sources for Organic Production Regular applications of soluble K, regardless of the source, will increase the concentration of K in the soil solution and the proportion of K on the cation exchange sites. All of the has a very slow K commonly used soluble K sources (including , com- release rate, which limits its nutritional benefit. posts, and green manures) contain this nutrient in the simple cationic K+ form. Most soluble inorganic fertilizers and organic manures are virtually interchangeable as sources of K for plant Greensand Greensand is the name commonly applied nutrition. When using readily available forms of K, the overall to a sandy rock or sediment containing a high percentage of goal of replacing the harvested K is generally more important the green mineral . Because of its K content (up to than minor differences in the behavior of the K source. Any 5% K), greensand has been marketed for over 100 years as a differences in plant performance are usually due to the ac- natural fertilizer and . The very slow K release - 2- rate of greensand is touted to minimize the possibility of plant companying anions, such as chloride (Cl ) or (SO4 ) or the organic matter that may accompany the added K. damage by fertilizer “burn”, while the mineral’s moisture reten- There is no general evidence that tion may soil conditioning. However, the K release rate is too slow to provide any significant nutritional benefit to plants (K2SO4) is more effective than (KCl) as a 2- - at realistic application rates. Soluble K is generally <0.1% of source of plant-available K, and both SO4 and Cl provide essential nutrients that are required for plant health. Chloride the total K present. Deposits of greensand are found in several is sometimes disparaged as being harmful to soil, but there states (including Arkansas and Texas), but the only active is no evidence for this claim at typical rates of application. greensand mine in North America is located in New Jersey. It has a well-documented role in improving plant health and prevention of a variety of plant diseases. Chloride-derived salinity was the same as sulfate-based salinity on its effect on common soil microbes (e.g. Li et al., 2006) and the addition of K decreased the harmful effects of salinity on soil microbial

Better Crops/Vol. 92 (2008, No. 2) Crops/Vol. Better activity (Okur et al., 2002). 28 Better Crops/Vol. 92 (2008, No. 2) 29 is crops of high quality Production proper to attention with sustained soil nutrition. Ash from hardwood trees served as one of the of one as served trees hardwood from Ash KCl is restricted Sylvinite (Potassium Ash Wood Growers using organic production practices, like all grow- all like practices, production organic using Growers earliest sources of K for building soil fertility. This highly vari- highly This fertility. soil building for K of sources earliest in present initially elements the of composed is material able is ash Wood burned. when volatilized not were which wood the has and 13, to 9 from ranging pH a with material, alkaline an neutralizing total the of 90% and 8 between of effect a fertil- commercial of terms In limestone. commercial of value approximately of analysis an have would ash wood average izer, manures, from derived ash of use The K. 4% and P, 1% N, 0% organic for prohibited is substances some and coal, , production. Check with the certifying organization prior to applying ash to soil. for field-scale use, especially especially use, field-scale for area. the harvesting far from Chloride) in the USDA standards un- source mined a from is it less under- and sylvinite) as (such It processing. further no goes manner a in applied be must accumula- Cl minimizes that tion in the after soil. used be Generally, only should KCl certify- the with consultation ing agency. The Canadian GSB has included KCl on the “Permitted Substancesproduc- food organic for List” tion systems. Unprocessed sylvinite often contains ap- proximately 17% K. References Soils. 42:366-370. 2006. Biol. Fertility Singh, and Z. Rengel. Li, B. Li, X., F. 17: 455-460. R.L. 2007. HortMikkelsen, . Göçmez. Acta Hort. 2002. and S. M. Çengel, 573: 189-194. N., Okur, Conclusions located Director, Region America North Western IPNI is Mikkelsen Dr. California; e-mail: [email protected]. at Merced, For more information and a list of references, visit <. >www.ipni.net/organic/kreferences the website at ers, have need for an adequate supply of soil healthy K and to high-yielding sustain crops. There are many excellent sources of K that are available for replacing the nutrients re- ad- maintain to Failure crops. harvested in soil the from moved efficiency, use water poor in result will rootzone the in K equate reduced and quality, harvest decreased problems, pest greater yields. Regular soil testing for K is the key for establishing K supplemental for need a If fertilization. for requirement the locally consider first should generally producers organic exists, available K resources and supplement with mineral sources. content nutrient low applying and transporting of expense The amendments must also be considered. BC in North 4 SO 2 from is available is derived from natural from derived is 4 SO 2 as is allowed It sources. several nutrient if used source an organic crushed form without raw, in the further refinement. Since these organic materials ) 4 When K When Mined rocks, including ballast, biotite, •MgSO 4 SO 2 Since sea water contains an average of 0.4 Potassium Sulfate Potassium Rock Powders Seaweed Manure and Langbeinite (Potas- are extremely variable (based on their raw materials and their and materials raw their on (based variable extremely are concentrations. K variable highly contain also they handling), Composted organic matter is generally allowed as a nutrient source. Raw manures have restrictions on the timing of their in K The agency. certifying the on depend details the but use, these organic materials is largely available for plant uptake, applications Repeated sources. inorganic approved to similar the in accumulation K in result can manure of amounts large of plant. the by K of consumption luxury to lead may which soil, is composition compost or manure the of analysis chemical A benefit. maximum for resources these use to order in necessary K manure or compost the where consider to helpful be may It digestion animal nor composting neither since from, coming is produces any nutrients. America comes from the in Utah. It may not undergo further processing or purification afterevaporation, other miningthan or crushing and sieving. This product is not allowed in some European countries without special permission from the certifying agency. It generally contains approximately 40% K and 17% S. mica, feldspars, granite and greensand are allowed without restriction. Tremendous variability exists in the K rate release from these mineral limited their sources.to due nutrition Some plant for sources of K as themunsuitable are wholly may others while nature, bulky and heavy their and solubility have value over long and periods reactivity, of area, surface time. greater In a to general, translates a size smaller particle materials rock specific for information Obtain rate. weathering before using. g K/L, seaweed may accumulate up to When harvested, seaweed severalbiomass can be used directly as a percent K. sources K These extracted. be may K soluble the or source K While K. 2% that less contain typically and soluble readily are K low their sources, K excellent are products seaweed-derived problematic it make can costs transportation high and content is allowed assource a if nutrientit is used raw, in crushedthe form without any further refinementpurification. or Several excel- approved this of sources lent use for available are product production. crop organic with Langbeinite typically con- tains 18% K, 11% Mg, and major The uptake. plant for available readily forms in S 22% source of langbeinite in North America is from underground deposits in New . sources, it is allowed for organic crop production. Much of the of Much production. crop organic for allowed is it sources, current production of organically approved K sium-magnesium sulfate) (K material This