Handbook of Plant Nutrition - chapter 9 pptx

9 Chlorine Joseph R. Heckman Rutgers University, New Brunswick, New Jersey CONTENTS 9.1 Historical Information 279 9.1.1 Determination of Essentiality 280 9.1.2 Functions in Plants 280 9.2 Diagnosis of Chlorine Status in Plants 281 9.2.1 Symptoms of Deficiency 281 9.2.2 Symptoms of Excess 283 9.2.3 Concentrations of Chlorine in Plants 283 9.2.3.1 Chlorine Constituents 283 9.2.3.2 Total Chlorine 283 9.2.3.3 Distribution in Plants 284 9.2.3.4 Critical Concentrations 285 9.2.3.5 Chlorine Concentrations in Crops 285 9.3 Assessment of Chlorine Status in Soils 285 9.3.1 Forms of Chlorine 285 9.3.2 Soil Tests 286 9.3.3 Chlorine Contents of Soil 286 9.4 Fertilizers for Chlorine 287 9.4.1 Kinds 287 9.4.2 Application 287 References 288 9.1 HISTORICAL INFORMATION Chlorine is classified as a micronutrient, but it is often taken up by plants at levels comparable to a macronutrient. Supplies of chlorine in nature are often plentiful, and obvious symptoms of deficiency are seldom observed. In many crops it is necessary to remove chlorine from air, chemi- cals, and water to induce symptoms of chlorine deficiency. Using precautions to establish a rela- tively chlorine-free environment, Broyer et al. (1) was able to convincingly demonstrate that chlorine is an essential nutrient. Although crop responses to chlorine applications in the field were suspected as early as the mid-1800s, it was not until fairly recently that chlorine was considered a potentially limiting nutrient for crop production under field conditions. In the 1980s, the respon- siveness of some crops to chlorine fertilization became recognized more widely (2). Even though chlorine has gained the attention of agronomists, much of the focus on chlorine in terms of crop production continues to be over the presence of excess levels of chloride salts in soils, water, and fertilizers (3,4). This chapter, however, is concerned primarily with chlorine as a plant nutrient. 279 CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 279 9.1.1 DETERMINATION OF ESSENTIALITY Early observations of plant growth responses derived from the use of chlorine-containing fertilizers had suggested that chlorine was at least beneficial if not essential (5). Demonstrating the essentiality of chlorine is experimentally challenging because chlorine is present widely in the environment, and special precautions are necessary to remove chlorine from chemicals, water, and air to induce deficiency symptoms in most species (6). Solution culture experiments conducted in a relatively chlo- rine-free environment (1) provided the first recognition of chlorine as an essential microelement. These experiments further showed that chlorine deficiency symptoms were alleviated specifically by the addition of chloride. Using solution culture (7), acute chlorine deficiency or at least restricted growth was demonstrated in lettuce (Lactuca sativa L.), tomato (Lycopersicum esculentum Mill.), cab- bage (Brassica oleracea var. capitata L.), carrot (Daucus carota L.), sugar beet (Beta vulgaris L.), bar- ley (Hordeum vulgare L.), alfalfa (Medicago sativa L.), buckwheat (Fagopyrum esculentum Moench), corn (Zea mays L.), and beans (Phaseolus vulgaris L.). Under the same conditions however, squash (Praecitrullus fistulosus Pang.) plants failed to exhibit any signs of chlorine deficiency. Species not affected or least affected by low chlorine supply appear to accumulate more chlorine than provided by the culture solutions. It has been assumed that chlorine was absorbed from the atmosphere and that plants differed in this ability (6,7). More recently, low-chlorine solution studies have produced chlo- rine deficiency symptoms in red clover (Trifolium pratense L.) and in wheat (Triticum aestivum L.) (8–10). Thus, the essentiality of chlorine has been established by the observations of the deficiency in a wide range of species. 9.1.2 FUNCTIONS IN PLANTS Chlorine is readily taken up by plants in the electrically charged form as chloride ion (Cl Ϫ ). Although chlorine occurs in plants as chlorinated organic compounds (11), chloride is the major form within plants, where it is bound only loosely to exchange sites or is a highly mobile free anion in the plant water. As an essential element, chlorine has several biochemical and physiological func- tions within plants. Chloride appears to be required for optimal enzyme activity of asparagine synthethase (12), amy- lase (13), and ATPase (14). In photosynthesis, chloride is an essential cofactor for the activation of the oxygen-evolving enzyme associated with photosystem II (15,16). Chloride may bind (17) to the polypeptides associated with the water-splitting complex of photosystem II, and it may stabilize the oxi- dized state of manganese by acting as a bridging ligand (18–20). Chloride concentrations required for biochemical functions are relatively low in comparison to concentrations required for osmoregulation. In rapidly expanding tissues such as elongating cells of roots and shoots, chloride accumulates in the tonoplast, to function as an osmotically active solute (21,22). This transport of chloride into the tonoplast occurs in association with the proton-pumping ATPase activity at the tonoplast, being specifically stimulated by chloride (14). This osmoregulatory function in specific tissues requires concentrations of chloride that are not typical of a micronutrient (23,24). The accumulation of chlo- ride in plant cells increases tissue hydration (25) and turgor pressure (26). This osmotic function of chloride works closely with potassium to facilitate cell elongation and growth. The importance of this osmoregulatory role of chloride in plants depends on growing conditions and the presence of alternative anions, such as nitrate, which might function as substitutes for chloride. Chloride along with potassium participates in stomatal opening by moving from epidermal cells to guard cells to act as an osmotic solute that results in water uptake into and a bowing apart of the guard cell pair (27). In many plant species, depending on the external supply of chloride, malate synthesis may occur in the guard cells and replace the need for chloride influx (28,29). Chloride, however, is essential for stomatal functioning in some plant species (30). In onion (Allium cepa L.), for example, where the guard cells are unable to synthesize malate, there is a requirement for an influx of chloride that is equivalent to potassium for stomatal opening to occur. Relative differences in the uptake of cations (NH 4 ϩ ,Ca 2ϩ ,Mg 2ϩ ,K ϩ ,Na ϩ ) and anions (NO 3 Ϫ , Cl Ϫ ,SO 4 2Ϫ ,H 2 PO 4 Ϫ ) by plants require the maintenance of electroneutrality in plant cells as well as 280 Handbook of Plant Nutrition CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 280 in the external soil solution (31). As an anion, chloride serves to balance charges from cations. In plants well supplied with chloride, this inorganic anion may serve as an alternative to the formation of malate in its charge-balancing role (32). This role of chloride may be of greater importance when cation uptake exceeds anion uptake, as often occurs with plants provided with ammonium nutrition. The functions of most of the over 130 chlorinated organic compounds (11) that have been identified in higher plants have not been determined. Some legume species contain chlorinated indole-3-acetic acid (IAA) in their seeds. The chlorinated form of IAA is more resistant to degra- dation, and this resistance may be responsible for increasing the rate of hypocotyl elongation over the rate of IAA production itself (4,33). 9.2 DIAGNOSIS OF CHLORINE STATUS IN PLANTS 9.2.1 S YMPTOMS OF DEFICIENCY Visible deficiency symptoms for chlorine have been well characterized in several crops by growth of plants in chlorine-free nutrient solutions (1,7,8,10). The most commonly described symptom of chlorine deficiency is wilting of leaves, especially at the margins. As the deficiency becomes more severe, the leaves may exhibit curling, shriveling, and necrosis (Figure 9.1A). Roots of chlorine- deficient plants have been described as stubby with club tips. Deficiency symptoms of chlorine are not commonly exhibited visually in most crops growing in the field, but symptoms are sometimes observed in wheat and coconut palm (Cocos nucifera L.). In chlorine-deficient wheat, the symp- toms are expressed as chlorotic or necrotic lesions on leaf tissue (Figure 9.1B). These symptoms that result from chlorine deficiency have been named ‘Cl-deficient leaf spot syndrome’ (9,10). It has also been shown that bromide (Figure 9.1C) does not substitute for chloride in the prevention of deficiency symptoms (10). In coconut palm, the symptoms are exhibited as wilting and prema- ture senescence of leaves, frond fracture, and stem cracking and bleeding (34). Chlorine deficiency is also indicated by yield increases that may occur with various crops in response to chloride fertilization. Wheat and barley often respond to chloride fertilization with increases in grain yield on soils with low chloride on the Great Plains of North America (2,35–41). Corn exhibited no response to chloride fertilization in some studies (2,42–44), but in a high-yield environment in New Jersey, fertilization of corn with 400 kg Cl ha Ϫ1 increased the 5-year average Chlorine 281 FIGURE 9.1 (A) Wheat (Triticum turgidum L. Durum Group) grown with chloride added at 30 mmol in 15 liters of nutrient solution (0.002M KC1); (B) Wheat grown in the absence of halide; (C) Wheat grown in absence of chloride and with 1.5 mmol bromide in 15 liters of nutrient solution (0.0001M KBr). Photographs from Engel et al., (9). Reprinted with permission of the authors and Soil Science Society of America. (For a color presen- tation of this figure, see the accompanying compact disc.) CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 281 282 Handbook of Plant Nutrition TABLE 9.1 Diseases Suppressed by Chlorine Fertilization Crop Suppressed Disease Reference Asparagus (Asparagus officinalis L.) Fusarium crown and root rot (Fusarium 47, 53, 74, 75 oxysporum and Fusarium proliferatum) Barley (Hordeum vulgare L.) Common root rot (Cochliobolus sativus 55, 76, 77 and Fusarium spp.) Fusarium crown and root rot (Fusarium 70 graminearum) Spot blotch (Bipolaris sorokiniana)77 Celery (Apium graveolens L.) Fusarium yellows (Fusarium 78 oxysporum f.sp. apii) Coconut palm (Cocos nucifera L.) Gray leaf spot (Pestalotiopsis palmarum;34 Helminthosporium incurvatum) Corn (Zea mays L.) Stalk rot (Gibberella zeae; Colletotrichum 46, 79 graminicola; Diplodia maydis) Durum (Triticum durum Desf.) Common root rot (Cochliobolus sativus 70 and Fusarium spp.) Pearl millet (Pennisetum glaucum R. Br.) Downy mildew (Sclerospora graminicola)70 Spring wheat (Triticum aestivum L.) Leaf rust (Puccinia triticina)80 Septoria (Stagonospora nodorum)70 Tanspot (Pyrenophora triticirepentis)66 Table beets (Beta vulgaris L.) Rhizoctonia crown and root rot 81 (Rhizoctonia solani) Winter wheat (Triticum aestivum L.) Leafspot (Pyrenophora triticirepentis)9,10 Leaf rust (Puccinia triticina)82 Stripe rust (Puccinia striiformis)70 Take-all root rot (Gaeumannomyces 26, 83 graminis var. tritici) yield by 1000 kg ha Ϫ1 over the unfertilized control (45,46). Positive responses from chloride fertil- ization have also been observed with rice (Oryza sativa L.), sugarcane (Saccharum edule Hassk.), potato (Solanum tuberosum L.), kiwifruit (Actinidia deliciosa A. Chev.), coconut palm, sugar beet, and asparagus (Asparagus officinalis L.) (2,47). These responses indicate that chloride is sometimes a yield-limiting nutrient in field environments where chlorine inputs from rainfall and other natural sources are inadequate. The beneficial effects of chloride fertilization are sometimes not the result of a plant response directly to enhanced chloride nutrition, but rather may result from suppression of plant diseases. Addition of chloride has been reported to reduce the severity of at least 15 different foliar and root diseases on 11 different crops (Table 9.1). Several possible mechanisms may explain the effects of chloride nutrition on disease suppression and host resistance. In acid soils, chloride inhibits nitrification (48,49). Keeping nitrogen in the ammonium form can lower rhizosphere pH and influence microbial populations and nutrient availability in the rhi- zosphere (31,50). Competition between chloride and nitrate for uptake also tends to reduce nitrate concentrations in plant tissues (4,51). When plants take up more ammonium and less nitrate, it usually causes rhizosphere acidification, which in turn, may enhance manganese availability (52). Chloride can also enhance manganese availability by promoting manganese-reducing microor- ganisms in soil (53). Factors which increase manganese availability have been associated with improved host resistance to diseases such as take-all on grain crops (54). Higher concentrations of chloride in plant tissues can also enhance water retention and turgor when roots have been CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 282 attacked by pathogens (26). The amount of organic acids, such as malate, in plant tissues and exuded from roots, decreases with chloride supply; this action deprives pathogens of an organic substrate (55). 9.2.2 SYMPTOMS OF EXCESS Chloride toxicity symptoms have been observed in many field, vegetable, and fruit crops (6,56). Curling of the leaf margins, marginal leaf scorch, leaf necrosis, and leaf drop are typical symptoms. Older leaves are usually the first to exhibit symptoms that may progress upward, affecting the entire foliage. Dieback of the terminal axis and small branches may occur in cases of severe toxicity. These symptoms of chloride toxicity occur in the absence of sodium, but they are also similar to symptoms of salt toxicity that occur when chloride is accompanied by sodium. Crops and cultivars within crops vary widely in tolerance to high levels of chloride, with corn being relatively tolerant to chloride (56) compared to soybean (Glycine max Merr.) (57). 9.2.3 CONCENTRATIONS OF CHLORINE IN PLANTS 9.2.3.1 Chlorine Constituents Most of the chlorine in plants is present in the form of the anion, chloride. However, more than 130 natural chlorine-containing compounds have been isolated from plants (11). They may include polyacetylenes, thiophenes, iridoids, sesquiterpene lactones, pterosinoids, diterperenoids, steroids and gibberellins, maytansinoids, alkaloids, chlorinated chlorophyll, chloroindoles and amino acids, phenolics, and fatty acids. Although the functions of naturally occurring chlorine-containing com- pounds in plants have not received much attention in plant nutrition, the fact that these compounds often exhibit a strong biological activity suggests a need to investigate their potential importance. Some chlorine-containing compounds may behave as hormones in the plant, or they may have a function in protection against attack from other organisms. 9.2.3.2 Total Chlorine The total chlorine accumulation by crops varies greatly, depending on chloride supply from soil. Many studies (45,56,58–62) of plant responses to applied chloride have shown that plant tissue chloride concentrations increase markedly with increasing application rates of chloride. A few stud- ies have measured total chlorine uptake by crops, and these studies also indicate that chloride accu- mulation by crops increases with increasing amounts of chloride fertilization. A study (25) conducted in North Carolina with corn fertilized with 0, 50, 100, 150, and 200 kg Cl ha Ϫ1 in the form of KCl found that the aboveground biomass at 77 days after emergence accumulated 26, 50, 63, 79, and 81 kg Cl ha Ϫ1 , respectively. A Wisconsin study (62) found that alfalfa accumulated only 5 kg Cl ha Ϫ1 on unamended soil, but on soil fertilized with 1017kg Cl ha Ϫ1 as KCl in the fall of the previous season, the herbage accumulated 86kg Cl ha Ϫ1 . These accumulation values for chloride by corn or alfalfa indicate that the potential for total crop accumulation for this nutrient is potentially large on soils well supplied with chloride. Even though chlorine is classified as a micronutrient, total chlorine accumulation often exceeds the levels of crop accumulation of macronutrients such as phosphorus or sulfur. The amount of chlorine accumulation required to prevent deficiency symptoms in most crops however, is much less than that which is typically accumulated (Table 9.2). A laboratory study (7) that determined the chlorine requirements of 11 different crop species estimated that plants require 1 lb of chlorine for each 10,000lb of dry matter produced, or a concentration of about 0.1g kg Ϫ1 . On a land area basis, large crops may need about 2.24kg ha Ϫ1 or more of chlorine. This estimate for plant chlorine requirement is presumed to be for biochemical functions (2). The benefits that are Chlorine 283 CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 283 sometimes observed from higher concentrations of chlorine are likely due to its osmoregulatory role in plants (36). 9.2.3.3 Distribution in Plants Most of the chlorine in plants is not incorporated into organic molecules or dry matter, but remains in solution as chloride and is loosely bound to organic molecules. Chloride concentrations 284 Handbook of Plant Nutrition TABLE 9.2 Chloride Concentrations in Plants Concentration Ranges of Tissue Cl (mg g ϪϪ 1 DM) Crop Latin Name Plant Part Deficient Normal Toxic a Reference Alfalfa Medicago sativa L. Shoot 0.65 0.9–2.7 6.1 6, 72 Apple Malus domestica Borkht. Leaves 0.1 Ͼ2.1 6 Avocado Persea americana Mill. Leaves ~1.5–4.0 ~7.0 84, 85 Barley Hordeum vulgare L. Heading shoot 1.2–4.0 Ͼ4.0 9, 86 Citrus Citrus spp. L. Leaves ~2.0 ~4.0–7.0 84, 87 Coconut Cocos nucifera L. Leaves 2.5–4.5 Ͼ6.0–7.0 86 palm Corn Zea mays L. Ear leaves Ͼ3.2 45 Corn Zea mays L. Ear leaves 1.1–10.0 Ͼ32.7 56 Corn Z. mays L. Shoots 0.05–0.11 7 Cotton Gossypium hirsutum L. Leaves 10.0–25.0 Ͼ25.0–33.1 88 Grapevine Vitis vinifera L. Petioles 0.7–8.0 10.0–11.0 6, 64 Kiwifruit Actinidia deliciosa Leaves 2.1 6.0–13.0 Ͼ15.0 60, 89 A. Chev. Lettuce Lactuca sativa L. Leaves Ͼ0.14 2.8–19.8 Ͼ23.0 7, 90 Pear Pyrus communis L. Leaves Ͻ0.50 Ͼ10.0 91 Peach Prunus persica Batsch. Leaves 0.9–3.9 10.0–16.0 6, 91 Peanut Arachis hypogaea L. Shoot Ͻ3.9 Ͼ4.6 92 Potato Solanum tuberosum L. Mature shoot Ͻ1.0 2.0–3.3 12.2 93 Potato Solanum tuberosum L. Petioles 0.71–1.42 18.0 44.8 58, 94 Red clover Trifolium pratense L. Shoot 0.15–0.21 8 Rice Oryza sativa L. Shoot Ͻ3.0 Ͼ7.0–8.0 95 Rice O. sativa L. Mature straw 5.1–10.0 Ͼ13.6 73, 96 Soybean Glycine max L. Merr. Leaves 0.3–1.5 16.7–24.3 97, 98, 99 Spinach Spinacia oleracea L. Shoot Ͼ0.13 100 Spring Triticum aestivum L. Heading shoot 1.5 3.7–4.7 Ͼ7.0 66, 92 wheat Strawberry Fragaria vesca Shoot 1.0–5.0 Ͼ5.3 91, 92 Subterranean Trifolium subterraneum L. Shoot Ͼ1.0 101 clover Sugar beet Beta vulgaris L. Leaves 0.71–1.78 102, 103 Sugar beet B. vulgaris L. Petioles Ͻ5.7 Ͼ7.1–7.2 Ͼ50.8 102, 104 Tobacco Nicotiana tabacum L. Leaves 1.2–10.0 Ͼ10.0 6, 105 Tomato Lycopersicon Shoot 0.25 ~30.0 1, 106 esculentum Mill. Wheat Triticum aestivum L. Heading shoot 1.2–4.0 Ͼ4.0 9, 86 a The plant yields decline or the plant shows visible scorching symptoms in leaves. CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 284 expressed on a tissue-water basis may typically range from 50 to 150mmol L Ϫ1 (4). A study (25) that determined chloride in the tissue water and the dry matter of whole corn plants at 35 days after emergence found a concentration of 66mmol Cl L Ϫ1 (1.83 g kg Ϫ1 dry matter basis) for corn grown on soil fertilized with 200 kg Cl ha Ϫ1 applied as KCl and only 10 mmol Cl L Ϫ1 (2.5 g kg Ϫ1 dry mat- ter basis) for corn plants grown on unamended soil. In general, chloride concentrations are higher in tissues that have high water content. Chloride concentrations are presumably highest in the rap- idly expanding zones of root and shoot tissue. Pulvini and guard cells also have higher concentra- tions of chloride than the bulk tissue (4). Vegetative plant tissues usually accumulate increasing concentrations of chloride with increas- ing supply of chloride, but plants parts can also exclude chloride (4,25,63). Corn seed may have only 0.44 to 0.64 g Cl kg Ϫ1 on a dry weight basis, and chloride accumulation in the grain is not influenced by chloride supply (45). In many crops, chloride transport from roots to shoots is restricted by a mechanism that resides in the roots (4,64,65). Soybean cultivars that exclude chlo- ride from the shoots are more salt-tolerant than cultivars that accumulate chloride (57). 9.2.3.4 Critical Concentrations Reports on critical tissue concentrations of chloride for crops grown in the field are few in number (Table 9.2). Studies conducted in the Great Plains of the United States have examined the relation- ship between tissue chloride concentration and relative yield of wheat. In wheat plants at head emergence, a critical chloride concentration of 1.5g kg Ϫ1 was given in a 1986 report (66). In a more recent and larger study (67) that was based on an assessment of 219 wheat cultivars, three zones of chloride status were identified: (i) a deficiency zone with a plant chloride concentration Ͻ1.0 g kg Ϫ1 , (ii) an adequate chloride status zone with concentrations Ն4.0 g kg Ϫ1 , (iii) and a tran- sition, or critical range, between these two zones. A study (45) of corn grown in high-yield envi- ronments in New Jersey suggested a critical ear-leaf chloride concentration of 3.2g kg Ϫ1 , derived from a comparatively small database. 9.2.3.5 Chlorine Concentrations in Crops A review (4) of chlorine nutrition tabulated the concentrations of chloride in a wide variety of crops. The compilation of data in Table 9.2 shows that concentrations of chloride classified as deficient, normal, or toxic vary widely among plant species. 9.3 ASSESSMENT OF CHLORINE STATUS IN SOILS 9.3.1 F ORMS OF CHLORINE Chlorine is present in the soil solution primarily in the anionic form as chloride. Chloride concen- trations in soil extracts may range from Ͻ1mg kg Ϫ1 to more than several thousand mg kg Ϫ1 (68). Chlorine may also be present in organic forms such as chlorinated hydrocarbon pesticide residues. Some of these chlorine-containing molecules are recalcitrant, whereas others can be metabolized or mineralized to release the chlorine. Although plants can accumulate chlorine foliarly and from the atmosphere, the concentration of chlorine in plant tissue is often closely related to the supply or concentration of chloride in soil. Testing soils for chloride is routine in laboratories involved in salinity problems, but soil testing for chloride supply to predict crop response to fertilization is a fairly recent development. Soil test interpretations for chloride supply are currently conducted in the North American Great Plains and are limited to only a few crops (2). In this large land-locked geographical region, little potassium fertilizer (KCl) is applied, and chloride input from rainfall is low. Soil test interpretations for chloride have not been developed Chlorine 285 CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 285 outside this region because chloride inputs from various sources are often greater and because sup- plies of this nutrient are generally considered adequate for most crops. 9.3.2 SOIL TESTS The solubility and mobility of chloride in soil is similar to nitrate, and soil sampling depths for chloride, like nitrate, are typically greater than for less mobile nutrients. Although the best soil sampling depth may vary depending on the rooting depth of the crop, a sampling to a depth of 60 cm has been found to be a good indicator of chloride availability to potato (58) and to spring wheat (2). Crops, such as sugar beet and winter wheat with deeper rooting depths, may need a deeper sampling depth (2,37). Because chloride is highly soluble and only weakly adsorbed, it can be extracted from soil with water or any dilute electrolyte. The choice of extractant may depend on the analytical method employed to determine the concentration of chloride in the extract. Methods of analysis for quanti- fying extractable chloride may include colorimetric, potentiometric, or chromatographic procedures (69). Precautions should be taken to avoid potential sources of chloride contamination (e.g., perspi- ration, soil sample containers, dust, glassware, water) during soil sampling and laboratory analysis. 9.3.3 CHLORINE CONTENTS OF SOIL In the Great Plains of the United States, soil tests are performed to assess the soil chloride level as a factor to be considered in decisions regarding application of chloride fertilizer. The relative responsiveness of the various wheat and barley cultivars to chloride is also considered. Some culti- vars of spring wheat and barley frequently exhibit responses to chloride, while others seldom exhibit a response (41,66,70,71). Chloride response trials conducted at 36 locations found that a critical level of 43 kg Cl ha Ϫ1 in the top 60 cm layer of soil would generally separate responsive sites from nonresponsive sites (66,70). On the basis of this research, soils were classified as low (Յ34kg Cl ha Ϫ1 ), medium (35 to 67 kg Cl ha Ϫ1 ), or high (Ͼ67 kg Cl ha Ϫ1 ) in relation to the probability of observing a response to chloride addition. Chloride fertilization is recommended according to this equation: Cl Ϫ to apply (kg ha Ϫ1 ) ϭ 67–Cl Ϫ (kg Cl ha Ϫ1 to 60 cm sampling depth). This recom- mendation is specific to wheat and barley crops grown in the region, and it should not be extrapo- lated to other areas under different climate, soil, and cultural conditions. Soil test calibration data on chloride are unavailable for most crops and soils around the world. However, an observation of chloride deficiency in Australia provides some insight into concentra- tions of chloride in soil that may limit growth of some plants (72). In this instance, it was found that subterranean clover (Trifolium subterraneum L.) exhibited poor growth when the soil contained only 3 to 5 µeq of Cl per 100 g (1 to 2mg kg Ϫ1 ). When other factors limit crop yield potential, the potential for a response to chloride fertiliza- tion is also limited. For example, corn grown in high-yield environments in New Jersey (18 miles from the Atlantic Ocean) exhibited yield increases from chloride addition on soils that held 20 kg Cl ha Ϫ1 in the top 60 cm layer of soil (45,46). In other studies with corn under less favorable con- ditions, yield increases due to chloride fertilization were either small or nil (2,42–44). In many instances, chloride is frequently supplied to crops as a consequence of the widespread use of KCl-based fertilizers that are applied with the intention of providing potassium. Recommended application rates of potassium, when applied as KCl, will generally supply sufficient chloride to most crops. It is possible that the supply of chloride is sometimes limiting for crops grown on a wider range of soils but that the crop responses to chloride go unrecognized because they are attributed to potassium. Chloride is widely distributed in soils. Concentrations normally range from 20 to 900mg kg Ϫ1 with a mean concentration of 100 mg kg Ϫ1 (68). Because igneous rocks and parent materials in gen- eral contain only minor amounts of chloride, little of this nutrient arises from weathering. Most of 286 Handbook of Plant Nutrition CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 286 the chloride present in soils arrive from rainfall, marine aerosols, volcanic emissions, irrigation waters, and fertilizers (4). Chloride is not adsorbed by minerals at pH levels above 7.0 and is only weakly absorbed in kaolinitic and oxidic soils that have positive charges under acid conditions (68). Chloride accumu- lates primarily in soil under arid conditions where leaching is minimal and where chloride moves upward in the soil profile in response to evapotranspiration. Poorly drained soils and low spots receiving chloride from runoff, seepage, or irrigation water also may accumulate chloride (57). Near the ocean, soils have high levels of chloride, but with increasing distance from the ocean, chloride concentration in soils typically falls (2,4). How a crop is harvested influences the amount of chloride in soil. When harvested only as seed, the amount of chloride removed is limited (Ͻ8 kg ha Ϫ1 for a corn yield of 11.3 Mg ha Ϫ1 ), but when harvested as green biomass the amount of chloride removal may be substantial (81kg ha Ϫ1 for corn as silage) (25). Because chloride leaches from aging leaves, harvest of mature biomass may remove only about half as much chloride as does harvest before the onset of senescence (59,61). 9.4 FERTILIZERS FOR CHLORINE 9.4.1 K INDS Chlorine is added to soil from a wide variety of sources that include chloride from rainwater, irri- gation waters, animal manures, plant residues, fertilizers, and some crop protection chemicals. The amount of chloride deposited annually from the atmosphere varies from 18 to 36kg Ϫ1 ha Ϫ1 year Ϫ1 for continental areas to more than 100 kg Ϫ1 ha Ϫ1 year Ϫ1 for coastal areas (4). Most of the chloride applied as animal manures or plant residues is soluble and readily available for crop uptake. Because most of the chloride in animal manure is probably present in the liquid fraction, manure management and handling may influence the concentration of chloride. Potassium chloride is the most widely applied chloride fertilizer. Although KCl is usually intended as a potassium fertilizer, it in effect supplies 0.9 kg of chloride for each kg of potassium. Other chloride fertilizers include NaCl, CaCl 2 , MgCl 2 , and NH 4 Cl (Table 9.3). All these salts are soluble and readily available to supply chloride for plant uptake. Organic agriculture, which dis- courages the use of KCl and most salt-based fertilizers, obtains chloride primarily from manure and other natural sources. 9.4.2 APPLICATION Chloride, like nitrate, is susceptible to loss from soil by leaching in areas of high rainfall (62,73). Management practices that minimize chloride leaching will enhance chloride accumulation by crops. When crops with high chloride requirements are grown, the application of chloride in the Chlorine 287 TABLE 9.3 Sources Commonly Used as Chlorine Fertilizers Source Chlorine Concentrations (%) Potassium chloride (KCl) 47 Sodium chloride (NaCl) 60 Ammonium chloride (NH 4 Cl) 66 Calcium chloride (CaCl 2 )64 Magnesium chloride (MgCl 2 )74 CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 287 spring or close to the time of plant growth should enhance chloride accumulation. Owing to the potential for salt injury, it is safer to broadcast chloride fertilizers than to apply them as a band. REFERENCES 1. T.C. Broyer, A.B. Carlton, C.M. Johnson, P.R. Stout. Chlorine — a micronutrient element for higher plants. Plant Physiol. 29:526–532, 1954. 2. P.E. Fixen. Crop responses to chloride. Adv. Agron. 50:107–150, 1993. 3. Anonymous. The trends towards chloride-free specialty fertilizers: always fully justified? New Ag. Int. 2:36–49, 2001. 4. G. Xu, H. Magen, J. Tarchitzky, U. Kafkaf. Advances in chloride nutrition of plants. Adv. Agron. 28:97–150, 2002. 5. C.H. Lipman. Importance of silicon, aluminum, and chlorine for higher plants. Soil Sci. 45:189–198. 6. F.M. Eaton. Chlorine. In: H.D. Chapman, ed. Diagnostic Criteria for Plants and Soils. Riverside: University of California, 1966, pp. 98–135. 7. C.M. Johnson, P.R. Stout, T.C. Broyer, A.B. Carlton. Comparative chlorine requirements of different plant species. Plant Soil 8:337–353, 1957. 8. D.C. Whitehead. Chlorine deficiency in red clover grown in solution culture. J. Plant Nutr. 8:193–198, 1985. 9. R.E. Engel, P.L. Bruckner, D.E. Mathre, S.K.Z. Brumfield. A chloride-deficient leaf spot syndrome of wheat. Soil Sci. Soc. Am. J. 61:176–184, 1997. 10. R.E. Engel, L. Bruebaker, T.J. Emborg. A chloride deficient leaf spot of durum wheat. Soil Sci. Soc. Am. J. 65:1448–1454, 2001. 11. K.C. Engvild. Chlorine-containing natural compounds in higher plants. Phytochemistry 25:781–791, 1986. 12. S.E. Rognes. Anion regulation of lupin asparagine synthetase: chloride activation of the glutamine- utilizing reaction. Phytochemistry 19:2287–2293, 1980. 13. D.E. Metzler. Biochemistry—The Chemical Reactions of Living Cells. New York: Academic Press, 1979, pp. 357–370. 14. K.A. Churchill, H. Sze. Anion-sensitive, H ϩ -pumping ATPase of oat roots. Direct effects of C1 Ϫ , NO 3 Ϫ , and a disulfonic stilbene. Plant Physiol. 76:490–497, 1984. 15. D.I. Arnon, F.R. Whatley. Is chloride a coenzyme of photosynthesis? Science 110:554–556, 1949. 16. S. Izawa, R.L. Heath, G. Hind. The role of chloride ion in photosynthesis. III. The effect of artificial electron donors upon electron transport. Biochim. Biophys. Acta 180:388–398, 1969. 17. I.C. Baianu, C. Critchley, Govindjee, H.S. Gutowsky. NMR study of chloride ion interactions with thylakoid membranes. Proc. Natl. Acad. Sci. USA 81:713–3717, 1984. 18. C. Critchley. The role of chloride in photosystem II. Biochim. Biophys. Acta 811:33–46, 1985. 19. W.J. Coleman, Govindjee, H.S. Gutowsky. The location of the chloride binding sites in the oxygen- evolving complex of spinach photosystem II. Biochim. Biophys. Acta 894:453–459, 1987. 20. P.H. Homann. Structural effects of chloride and other anions on the water oxidizing complex of chloroplast photosystem II. Plant Physiol. 88:194–199, 1988. 21. E.V. Maas. Physiological responses to chloride. In: T.L. Jackson, ed. Special Bulletin on Chloride and Crop Production. Atlanta, GA: Potash & Phosphate Institute, No. 2, 1986, pp. 4–20. 22. A. Hager, M. Helmle. Properties of an ATP-fueled, Cl-dependent proton pump localized in membranes of microsomal vesicles from maize coleoptiles. Z. Naturforsch 36C:997–1008, 1981. 23. D.F. Gerson, R.J. Poole. Chloride accumulation by mung bean root tips. A low affinity active transport system at the plasmalemma. Plant Physiol. 50:603–607, 1972. 24. T.J. Flowers. Chloride as a nutrient and as an osmoticum. In: B. Tinker, A. Lauchi, eds. 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J. 73:1053–1058, 1981. 288 Handbook of Plant Nutrition CRC_DK2972_Ch009.qxd 6/30/2006 4:12 PM Page 288 [...]... rate of nitrogen and chloride applications for the control of summer patch in Kentucky bluegrass Plant Dis 79: 51–55, 199 5 53 W.H Elmer Association between Mn-reducing root bacteria and NaCl applications in suppression of Fusarium crown and root rot of asparagus Phytopathology 85:1461–1467, 199 5 CRC_DK 297 2_Ch0 09. qxd 290 6/30/2006 4:12 PM Page 290 Handbook of Plant Nutrition 54 D.M Huber The role of nutrition. .. Effect of salinity on the nutritional level of the avocado: optimization of plant nutrition 8th International Colloq Optimum Plant Nutrition, Lisbon, Portugal, 199 2, pp 593 – 596 86 R.E Engel, J Eckhoff, R Berg Grain yield, kernel weight, and disease responses of winter wheat cultivars to chloride fertilization Agron J 86: 891 – 896 , 199 4 87 P.F Bell, J.A Vaughn, W.J Bourgeois Leaf analysis finds high levels of. .. potato plants (Solanum tuberosum) Agron J 52 :94 96 , 196 0 94 L Bernstein, A.D Ayers, C.H Wadleigh The salt tolerance of white potatoes Proc Am Soc Hortic Sci 57:231–236, 195 1 95 M.J Yin, J.J Sun, C.S Liu Contents and distribution of chloride and effects of irrigation water of different chloride levels on crops Soil Fert (in Chinese) 1:3–7, 198 9 96 Q.S Zhu, B.S Yu Critical tolerance of chloride of rice... low levels of zinc and manganese in Louisiana citrus J Plant Nutr 20:733–743, 199 7 88 N.X Tan, J.X Shen A study on the effect of Cl on the growth and development of cotton Soil Fert (in Chinese) 2:1–3, 199 3 89 G.S Smith, C.J Clark, P.T Holland Chloride requirement of kiwi-fruit (Actinidia deliciosa) New Phytol 106:71–80, 198 7 90 S.Q Wei, Z.F Zhou, C Liu Effects of chloride on yield and quality of lettuce... incidence of corn as affected by chloride in potassium fertilizer Agron J 50:426–4 29, 195 8 80 G.E Russell Some effects of applied sodium and potassium on yellow rust in winter wheat Ann Appl Biol 90 :163–168, 197 8 CRC_DK 297 2_Ch0 09. qxd Chlorine 6/30/2006 4:12 PM Page 291 291 81 W.H Elmer Influence of chloride and nitrogen form on rhizoctonia root and crown rot of table beets Plant Dis 81:635–640, 199 7 82 D.W... Sci 10:66– 79, 195 7 102 A Ulrich, K Ohki Chlorine, bromine and sodium as nutrients for sugar beet plants Plant Physiol 31:171–181, 195 6 103 N Terry Photosynthesis, growth, and the role of chloride Plant Physiol 60: 69 75, 197 7 104 B.K Zhou, X.Y Zhang Effects of chloride on growth and development of sugarbeet Soil Fert (in Chinese) 3:41–43, 199 2 105 L.T Li, D.H Yuan, Z.J Sun Influence of a Cl-containing... 87:415–4 19, 199 5 46 J.R Heckman Corn stalk rot suppression and grain yield response to chloride J Plant Nutr 21:1 49 155, 199 8 47 W.H Elmer, D.A Johnson, G.I Mink Epidemiology and management of the diseases causal to asparagus decline Plant Dis 80:117–125, 199 6 48 B.E Hahn, F.R Olson, J.L Roberts Influence of potassium chloride on nitrification in Bedford silt loam Soil Sci 55:113–121, 194 2 49 R.J Rosenberg,... value of tolerance Chin J Soil Sci 30:262–264, 198 9 91 J.B Robinson Fruits, vines and nuts In: D.J Reuter, J.B Robinson, eds Plant Analysis: An Interpretation Manual Sydney, Australia: Inkata Press, 198 6, pp 120–147 92 D.Q Wang, B.C Guo, X.Y Don Toxicity effects of chloride on crops Chin J Soil Sci 30:258–261, 198 9 93 E.G Corbett, H.W Gausman The interaction of chloride and sulfate in the nutrition of. .. 337:345–350, 199 7 29 K Raschke, H Schnabl Availability of chloride affects the balance between potassium chloride and potassium malate in guard cells of Vicia faba L Plant Physiol 62:84–87, 197 8 30 H Schnabl, K Raschke Potassium chloride as stomatal osmoticum in Allium cepa L [onion], a species devoid of starch in guard cells Plant Physiol 65:88 93 , 198 0 31 J.R Heckman, J.E Strick Teaching plant- soil relationships... tobacco leaves through the harvesting season J Plant Nutr 13:485– 493 , 199 0 60 M Prasad, G.K Burge, T.M Spiers, G Fietje Chloride induced leaf breakdown in kiwifruit J Plant Nutr 16 :99 9–1012, 199 3 61 W.K Schumacher Residual Effects of Chloride Fertilization on Selected Plant and Soil Parameters M.S thesis, South Dakota State University, Brookings, SD, 198 8 62 D Smith, L.A Peterson Chlorine concentrations . Biol. 90 :163–168, 197 8. 290 Handbook of Plant Nutrition CRC_DK 297 2_Ch0 09. qxd 6/30/2006 4:12 PM Page 290 81. W.H. Elmer. Influence of chloride and nitrogen form on rhizoctonia root and crown rot of. as a plant nutrient. 2 79 CRC_DK 297 2_Ch0 09. qxd 6/30/2006 4:12 PM Page 2 79 9.1.1 DETERMINATION OF ESSENTIALITY Early observations of plant growth responses derived from the use of chlorine-containing. Diagnosis of Chlorine Status in Plants 281 9. 2.1 Symptoms of Deficiency 281 9. 2.2 Symptoms of Excess 283 9. 2.3 Concentrations of Chlorine in Plants 283 9. 2.3.1 Chlorine Constituents 283 9. 2.3.2