350. Zhao, F.J.; McGrath, S.P.; Blake-Kalff, M.A.; Link, A.; Tucker, M. Crop responses to sulphur fertili- sation in Europe. Proceedings of the International Fertilizer Society, 2002, p. 504. 351. Murphy, M.D.; O’Donnell, T. Sulphur deficiency in herbage in Ireland. 2. Sulphur fertilisation and its effect on yield and quality of herbage. Irish J. Agric. Res. 1989, 28, 79–90. 352. Thomas, S.G.; Hocking, T.J.; Bilsborrow, P.E. Effects of sulphur fertilisation on the growth and metab- olism of sugar beet grown on soils of differing sulphur status. Field Crops Res. 2002, 83, 223–235. 353. Li, S.; Lin, B.; Zhou, W. Crop response to sulfur fertilizers and soil sulfur status in some provinces of China. FAL–Agric. Res. 2005, 283, 81–84. 354. Singh, B.R. Sulphur requirement for crop production in Norway. Norwegian J. Agric. Sci. (Suppl.) 1994, 15, 35–44. 355. Katyal, J.C.; Sharma, K.L.; Srinivas, K. Sulphur in Indian agriculture. Proceedings of the TSI/FAI/IFA Symposium on Sulphur in Balanced Fertilisation, KS-2/1-KS-2/12, 1997. 356. Jain, G.L.; Sahu, M.P.; Somani, L.L. Balanced fertilization programme with special reference to sec- ondary and micronutrients nutrition of crops under intensive cropping, Proceedings of the FAI/NR Seminar, Jaipur, 1984, pp. 147–174. 357. Aulakh, M.S.; Pasricha, N.S. Sulphur fertilization of oilseeds for yield and quality. Sulphur in Indian Agriculture 1988, SII/3-1-SII/3-14. 358. Aulakh, M.S.; Sidhu, B.S.; Arona, B.R.; Singh, B. Content and uptake of nutrients by pulses and oilseed crops. Indian J. Ecol. 1985, 12, 238–242. 359. Survase, D.N.; Dongale, J.H.; Kadrekar, S.B. Growth, yield, quality and composition of groundnut as influenced by F.Y.M., calcium, sulphur and boron in lateritic soil. J. Maharashtra Agric. Univ. 1986, 11, 49–51. 360. Naphade, P.S.; Wankhade, S.G. Effect of varying levels of sulphur and molybdenum on the content and uptake of nutrients and yield of mung (Phaseolus aureus L.). PKV J. Res. 1987, 11, 139–143. 361. Polaria, J.V.; Patel, M.S. Effect of principal and inadvertently applied nutrients through different fer- tilizer carriers on the yield and nutrient uptake by groundnut. Gujarat Agric. Univ. Res. J. 1991, 16, 10–15. 362. Nambiar, K.K.M.; Ghosh, A.B., Highlights of Research of a Long-Term Fertilizer Experiment in India (1971–82). Technical Bulletin No. 1, Longterm Fertilizer Experiment Project, 1984, IARI, p. 100 363. Saarela, I.; Hahtonen, M. Sulphur nutrition of field crops in Finland. Norwegian J. Agric. Sci. (Suppl.) 1994, 15, 119–126. 364. Aulakh, M.S. Crop responses to sulphur nutrition. In Sulphur in Plants; Abrol, Y.P., Ahmad, A., Eds.; Kluwer Academic Publishers: Dordrecht, 2003; pp. 341–358. 365. Walker, K.C.; Dawson, C. Sulphur fertiliser recommendations in Europe. Proc. Int. Fert. Soc. 2002, 506, 0–20. 366. Schroeder, D.; Schnug, E. Application of yield mapping to large scale field experimentation. Aspects Appl. Biol. 1995, 43, 117–124. 238 Handbook of Plant Nutrition CRC_DK2972_Ch007.qxd 6/30/2006 3:59 PM Page 238 Section III Essential Elements––Micronutrients CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 239 CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 240 241 8 Boron Umesh C. Gupta Agriculture and Agri-Food Canada, Charlottetown, Prince Edward Island, Canada CONTENTS 8.1 Historical Information 242 8.1.1 Determination of Essentiality 242 8.1.2 Functions in Plants 242 8.1.2.1 Root Elongation and Nucleic Acid Metabolism 243 8.1.2.2 Protein, Amino Acid, and Nitrate Metabolism 243 8.1.2.3 Sugar and Starch Metabolism 243 8.1.2.4 Auxin and Phenol Metabolism 244 8.1.2.5 Flower Formation and Seed Production 244 8.1.2.6 Membrane Function 244 8.2 Forms and Sources of Boron in Soils 245 8.2.1 Total Boron 245 8.2.2 Available Boron 245 8.2.3 Fractionation of Soil Boron 245 8.2.4 Soil Solution Boron 245 8.2.5 Tourmaline 246 8.2.6 Hydrated Boron Minerals 246 8.3 Diagnosis of Boron Status in Plants 246 8.3.1 Deficiency Symptoms 247 8.3.1.1 Field and Horticultural Crops 247 8.3.1.2 Other Crops 249 8.3.2 Toxicity Symptoms 249 8.3.2.1 Field and Horticultural Crops 249 8.3.2.2 Other Crops 251 8.4 Boron Concentration in Crops 251 8.4.1 Plant Part and Growth Stage 251 8.4.2 Boron Requirement of Some Crops 252 8.5 Boron Levels in Plants 252 8.6 Soil Testing for Boron 257 8.6.1 Sampling of Soils for Analysis 257 8.6.2 Extraction of Available Boron 257 8.6.2.1 Hot-Water-Extractable Boron 257 8.6.2.2 Boron from Saturated Soil Extracts 258 8.6.2.3 Other Soil Chemical Extractants 258 8.6.3 Determination of Extracted Boron 259 8.6.3.1 Colorimetric Methods 259 8.6.3.2 Spectrometric Methods 259 CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 241 8.7 Factors Affecting Plant Accumulation of Boron 260 8.7.1 Soil Factors 260 8.7.1.1 Soil Acidity, Calcium, and Magnesium 260 8.7.1.2 Macronutrients, Sulfur, and Zinc 261 8.7.1.3 Soil Texture 263 8.7.1.4 Soil Organic Matter 263 8.7.1.5 Soil Adsorption 263 8.7.1.6 Soil Salinity 263 8.7.2 Other Factors 264 8.7.2.1 Plant Genotypes 264 8.7.2.2 Environmental Factors 264 8.7.2.3 Method of Cultivation and Cropping 265 8.7.2.4 Irrigation Water 265 8.8 Fertilizers for Boron 266 8.8.1 Types of Fertilizers 266 8.8.2 Methods and Rates of Application 266 References 268 8.1 HISTORICAL INFORMATION 8.1.1 D ETERMINATION OF ESSENTIALITY Boron (B) is one of the eight essential micronutrients, also called trace elements, required for the normal growth of most plants. It is the only nonmetal among the plant micronutrients. Boron was first recognized as an essential element for plants early in the twentieth century. The essentiality of boron as it affected the growth of maize or corn (Zea mays L.) plants was first mentioned by Maze (1) in France. However, it was the work of Warington (2) in England that secured strong evi- dence of the essentiality of boron for the broad bean (Vicia faba L.), and later Brenchley and Warington (3) extended the study of boron to include several other plant species. The essentiality of boron to higher plants was decisively accepted after the experimental work of Sommer and Lipman (4), Sommer (5), and other investigators who followed them. Since its discovery as an essential trace element, the importance of boron as an agricultural chem- ical has grown very rapidly. Its requirement differs markedly within the plant kingdom. It is essential for the normal growth of monocots, dicots, conifers, and ferns, but not for fungi and most algae. Some members of Gramineae, for example, wheat (Triticum aestivum L.) and oats (Avena sativa L.) have a much lower requirement for boron than do dicots and other monocots, for example, corn. Of the known micronutrient deficiencies, boron deficiency in crops is most widespread. In the last 80 years, hundreds of reports have dealt with the essentiality of boron for a variety of agricul- tural crops in countries from every continent of the world. 8.1.2 FUNCTIONS IN PLANTS Deficiency of boron can cause reductions in crop yields, impair crop quality, or have both effects. Some of the most severe disorders caused by a lack of boron include brown-heart (also called water core or raan) in rutabaga (Brassica napobrassica Mill.) and radish (Raphanus sativus L.) roots, cracked stems of celery (Apium graveolens L.), heart rot of beets (Beta vulgaris L.) brown-heart of cauliflower (Brassica oleracea var. botrytis L.), and internal brown spots of sweet potato (Ipomoea batatas Lam.). Some boron deficiency disorders appear to be physiological in nature and occur even when boron is in ample supply. These disorders are thought to be related to peculiarities in boron transport and distribution. The initial processes that control boron uptake in plants are located in the roots (6). Some of the main functions of boron are summarized below. 242 Handbook of Plant Nutrition CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 242 8.1.2.1 Root Elongation and Nucleic Acid Metabolism Boron deficiency rapidly inhibits the elongation and growth of roots. For example, Bohnsack and Albert (7) showed that root elongation of squash (Cucurbita pepo L.) seedlings declined within 3h after the boron supply was removed and stopped within 24 h. If boron was resupplied after 12h, the rate of root elongation was restored to normal within 12 to18 h. Josten and Kutschera (8) reported that the presence of boron resulted in the development of numerous roots in the lower part of the hypocotyl in sunflower (Helianthus annuus L.) cuttings. Consequently, the numerous adventitious roots entirely replaced the tap root system of the intact seedlings. Root elongation is the result of cell elongation and cell division, and evidence suggests that boron is required for both processes (9). When boron is withheld for several days, nucleic acid con- tent decreases. Krueger et al. (10) demonstrated that the decline and eventual cessation of root elon- gation in squash seedlings was correlated temporally with a decrease in DNA synthesis, but preceded changes in protein synthesis and respiration. Lenoble et al. (11) concluded that boron additions may need to be increased under acid, high- aluminum soils, because applications of boron prevented aluminum inhibition of root growth on acid, aluminum-toxic soils. 8.1.2.2 Protein, Amino Acid, and Nitrate Metabolism Protein and soluble nitrogenous compounds are decreased in boron-deficient plants (12). However, the influence of organ age, i.e., whether the organ was actively involved in the biosynthesis of amino acids and protein or remobilization of amino acids from protein reserves, has often been ignored (13). For example, Dave and Kannan (14) reported that 5 days of growth without boron increased the protein concentration of bean (Phaseolus vulgaris L.) cotyledons compared to control seedlings, suggesting that nitrogen remobilization is hindered due to boron deficiency. By contrast, protein concentrations in the actively growing regions could be reduced by lower rates of synthesis caused by boron deficiency (15,16). Shelp (16) reported that the partitioning of nitrogen into soluble components (nitrate, ammo- nium, and amino acids) of broccoli (Brassica oleracea var. botrytis L.) was dependent on the plant organ and whether boron was supplied continuously at deficient or toxic levels. Boron deficiency did not substantially affect the relative amino acid composition (16) but did enhance the proportion of inorganic nitrogen, particularly nitrate, in plant tissues and translocation fluids (13). A number of researchers reported increases in nitrate concentration as well as corresponding decreases in nitrate reductase activity in sugar beet (Beta vulgaris L.), tomato (Lycopersicon esculentum Mill.), sunflower, and corn plants (17,18) due to boron deficiency. Boron deficiency in tobacco (Nicotiana tabacum L.) resulted in a decrease in leaf N concentration and reduced nitrate reductase activity (19). Boron-deficient soybeans (Glycine max Merr.) showed low acetylene reduction activities and dam- age to the root nodules (20). 8.1.2.3 Sugar and Starch Metabolism Boron is thought to have a direct effect on sugar synthesis. In cowpeas (Vigna unguiculata Walp), acute boron deficiency conditions increased reducing and nonreducing sugar concentrations but decreased starch phosphorylase activity (21). Under boron deficiency, the pentose phosphate shunt comes into operation to produce phenolic substances (22). Boron-deficient sunflower seeds showed marked decrease in nonreducing sugars and starch concentrations, whereas the reducing sugars accu- mulated in the leaves (23). This finding indicates a specific role of boron in the production and dep- osition of reserves in sunflower seeds. High concentrations of nonreducing sugars were also found in boron-deficient mustard (Brassica nigra Koch) (24). Camacho and Gonzalas (19) also found higher starch concentration in boron-deficient tobacco plants. In low-boron sunflower leaves, starch decreased, but there was an increase in sugars and protein and nonprotein nitrogen fractions (25). In Boron 243 CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 243 boron-deficient pea (Pisum sativum L.) leaves, the concentration of sugars and starch increased, but they decreased in the pea seeds and thus lowered the seed quality (26). Evidence on the impact of boron deficiency on starch concentration is conflicting. It is difficult to explain whether the differences are due to a variation in crop species. 8.1.2.4 Auxin and Phenol Metabolism Boron regulates auxin supply in plants by protecting the indole acetic acid (IAA) oxidase system through complexation of o-diphenol inhibitors of IAA oxidase. Excessive auxin activity causes excessive proliferation of cambial cells, rapid and disproportionate enlargement of cells, and col- lapse of nearby cells (27). It has been established that adventitious roots develop on stem cuttings of bean only when boron is supplied (28,29). Auxin initiates the regeneration of roots, but boron must be supplied at relatively high concentrations 40 to 48 h after cuttings are taken, for primordial roots to develop and grow. It was initially proposed that boron acted by reducing auxin to concen- trations that were not inhibitory to root growth (30,31), but more recently, Ali and Jarvis (28) reported that without boron, RNA synthesis decreases markedly within and outside the region from which roots ultimately develop. There are many reports in the literature of phenol accumulation under long-term boron deficiency (32). Since boron complexes with phenolic compounds such as caffeic acid and hydrox- yferulic acid, Lewis (33) proposed a role for boron in lignification. Absence of boron would there- fore cause reactive intermediates of lignin biosynthesis and other phenolic compounds to affect changes in metabolism and membrane function, resulting in cell damage. However, the available evidence indicates that lignin synthesis may actually be enhanced by boron deficiency. 8.1.2.5 Flower Formation and Seed Production The role of boron in seed production is so important that under moderate to severe boron deficiency, plants fail to produce functional flowers and may produce no seeds (34). Plants subjected to boron deficiency have been observed to result in sterility or low germination of pollen in alfalfa (Medicago sativa L.) (35), barley (Hordeum vulgare L.) (36), and corn (37). Even under moderate boron deficiency, plants may grow normally and the yield of the foliage may not be affected severely, but the seed yield may be suppressed drastically (38). 8.1.2.6 Membrane Function Impairment of membrane function could affect the transport of all metabolites required for normal growth and development, as well as the activities of membrane-bound enzymes. Dugger (15) summarized early reports that illustrate changes in membrane structure and organization in response to boron deficiency. Boron may give stability to cellular membranes by reacting with hydroxyl-rich compounds. Consistent with this view is evidence suggesting that a major portion of the cellular boron is concentrated in protoplast membranes from mung bean (Phaseolus aureus Roxb.) (39). The involvement of boron in inorganic ion flux by root tissue (40–42) and in the incorporation of phosphate into organic phosphate (43) was evident from earlier research. In general, the absorp- tion of phosphate, rubidium, sulfate, and chloride was suppressed in boron-deficient root tissues, but it could be restored to normal or nearly normal rates by a concomitant addition of boron or pre- treatment with boron for 1 h. This effect could be explained by a rapid reorganization of the carrier system, with boron functioning as an essential component of the membrane (15). The movement of monovalent cations is associated with membrane-bound ATPases. Boron-deficient corn roots had a limited ATPase activity, which could be restored by boron addition for only 1 h before enzyme extraction (40). 244 Handbook of Plant Nutrition CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 244 Recently, Tang and Dela Fuente (44,45) demonstrated that potassium leakage (as a measure of membrane integrity) from boron- or calcium-deficient sunflower hypocotyl segments was completely reversed by the addition of boron or calcium for 3 h. It was not possible to reverse the inhibited process by replacing one deficient element with the other. Seedlings deficient in both boron and cal- cium showed greater effects than seedlings deficient in one element only. Basipetal auxin transport was also inhibited by boron or calcium deficiency, but the addition of boron for 2 h did not restore the process reduced by boron deficiency. This reduction in auxin transport was not related to reduced growth rate, acropetal auxin transport, lack of respiratory substrates, or changes in calcium absorption, suggesting that boron had a direct effect on auxin transport. 8.2 FORMS AND SOURCES OF BORON IN SOILS 8.2.1 T OTAL BORON The total boron content of most agricultural soils ranges from 1 to 467 mg kg Ϫ1 , with an average content of 9 to 85 mg kg Ϫ1 . Gupta (46) reported that total boron on Podzol soils from eastern Canada ranged from 45 to 124 mg kg Ϫ1 . Total boron in major soil orders, Inceptisol and Alfisol, in India ranged from 8 to 18 mg kg Ϫ1 (47). Such wide variations among soils in the total boron con- tent are mainly ascribed to the parent rock types and soil types falling under divergent geographi- cal and climatic zones. Boron is generally high in soils derived from marine sediments. 8.2.2 AVAILABLE BORON Available boron, measured by various extraction methods (see Section 8.6.2), in agricultural soils varies from 0.5 to 5mg kg Ϫ1 . Most of the available boron in soil is believed to be derived from sed- iments and plant material. Gupta (46) reported that available boron on Podzol soils from eastern Canada ranged from 0.38 to 4.67 mg kg Ϫ1 . Few studies have been conducted that attempt to iden- tify solid-phase controls on boron solubility in soils. Most of the common boron minerals are much too soluble for such purposes (48). 8.2.3 FRACTIONATION OF SOIL BORON Boron fractionation was studied in relation to its availability to corn in 14 soils (49). Up to 0.34% of the total boron was in a water-soluble form, 0 to 0.23% was nonspecifically adsorbed (exchange- able), and 0.05 to 0.30% was specifically adsorbed. Jin et al. (49) reported that most of the boron available to corn was in these three forms, and that boron in noncrystalline and crystalline alu- minum and iron oxyhydroxides and in silicates was relatively unavailable for plant uptake. For the identification of different pools of boron in soils, Hou et al. (50) proposed a fractionation scheme, which indicated that readily soluble and specifically adsorbed boron accounted for Ͻ2% of the total boron. Various oxides–hydroxides, and organically bound forms constituted 2.3 and 8.6%, respec- tively. Most soil boron existed in residual or occluded form. Recent studies by Zerrari et al. (51) showed that the residual boron constituted the most important fraction at 78.75%. 8.2.4 SOIL SOLUTION BORON In soil solution, boron mainly exists as undissociated acid H 3 BO 3 . Boric acid (also written as B(OH) 3 ) and H 2 BO 3 Ϫ are the most common geologic forms of boron, with boric acid being the pre- dominant form in soils as reviewed by Evans and Sparks (52). They further reported that boric acid is the major form of boron in soils with H 2 BO 3 Ϫ being predominant only above pH 9.2. In their review, they stated that boron occurs in aqueous solution as boric acid B(OH) 3, which is a weak monobasic acid that acts as an electron acceptor or as a Lewis acid. Boron 245 CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 245 8.2.5 TOURMALINE In most of the well-drained soils formed from acid rocks and metamorphic sediments, tourmaline is the most common boron-containing mineral identified (53). The name tourmaline represents a group of minerals that are compositionally complex borosilicates containing approximately 3% B. The tourmaline structure has rhombohedral symmetry and consists of linked sheets of island units. The boron atoms are found within BO 3 triangles, forming strong covalent B–O bonds (54). Tourmalines are highly resistant to weathering and virtually insoluble. Additions of finely ground tourmaline to soil failed to provide sufficient boron to alleviate boron deficiency of crop plants (55). 8.2.6 HYDRATED BORON MINERALS Industrial deposits of boron are usually produced by chemical precipitation. Precipitation occurs following concentration on land, in brine waters in arid regions or as terrestrial evaporites and arid playa deposits (56). Precipitation also occurs as marine evaporites after concentration due to evap- oration of seawater. Borates also form in salt domes and by further concentration of underground water in arid areas (56). The borate deposits of economic importance are restricted to arid areas because of the high solubility of these minerals. Hydrated borates are formed originally as chemical deposits in saline lakes (57). The particular mineral suite formed is dependent on the chemical composition of the lake. Two kinds of borate deposits are formed in the arid western United States (57). Hydrated sodium borates form from lakes that have a high pH and that are high in sodium and low in calcium content. Hydrated sodium–calcium borates form from lakes of higher calcium content. 8.3 DIAGNOSIS OF BORON STATUS IN PLANTS Boron deficiency in crops is more widespread than deficiency of any other micronutrient. This phe- nomenon is the chief reason why numerous reports are available on boron deficiency symptoms in plants. Because of its immobility in plants, boron deficiency symptoms generally appear first on the younger leaves at the top of the plants. This occurrence is also true of the other micronutrients except molybdenum, which is readily translocated. Boron toxicity symptoms are similar for most plants. Generally, they consist of marginal and tip chlorosis, which is quickly followed by necrosis (58). As far as boron toxicity is concerned, it occurs chiefly under two conditions, owing to its presence in irrigation water or owing to acciden- tal applications of too much boron in treating boron deficiency. Large additions of materials high in boron, for example, compost, can also result in boron toxicity in crops (59,60). Boron toxicity in arid and semiarid regions is frequently associated with saline soils, but most often it results from the use of high-boron irrigation waters. In the United States, the main areas of high-boron waters are along the west side of the San Joaquin and Sacramento valleys in California (61). Boron does not accumulate uniformly in leaves, but typically concentrates in leaf tips of mono- cotyledons and leaf margins of dicotyledons, where boron toxicity symptoms first appear. In fact although leaf tips may represent only a small proportion of the shoot dry matter, they can contain sufficient boron to substantially influence total leaf and shoot boron concentrations. To overcome this problem, Nable et al. (62) recommended the use of grain in barley for monitoring toxic levels of boron accumulation. The main difficulty in using cereal grain for determining boron levels is the small differences in the grain boron concentration as obtained in response to boron fertilization (63). Low risk of boron toxicity to rice in an oilseed rape (Brassica napus L.)–rice (Oryza sativa L.) rota- tion was attributed to the relatively high boron removal in harvested seed, grain, and stubble, and the loss of fertilizer boron to leaching (64). Boron toxicity symptoms in zinc-deficient citrus (Citrus aurantium L.) could be mitigated with zinc applications. This finding is of practical importance as boron toxicity and zinc deficiencies are simultaneously encountered in some soils of semiarid zones. 246 Handbook of Plant Nutrition CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 246 8.3.1 DEFICIENCY SYMPTOMS 8.3.1.1 Field and Horticultural Crops Alfalfa (Medicago sativa L.). Symptoms are more severe at the leaf tips, although the lower leaves remain a healthy green color. Flowers fail to form, and buds appear as white or light-brown tissue (65). Internodes are short; blossoms drop or do not form, and stems are short (66). Younger leaves turn red or yellow (67,68), and topyellowing of alfalfa occurs (69) (Figure 8.1). Barley (Hordeum vulgare L.). No ears are formed (70). Flowers were opened by the swelling of ovaries caused by partial sterility due to B deficiency (36). Boron deficiency was also associated with the appearance of ergot. Beet (Beta vulgaris L.). Boron deficiency results in a characteristic corky upper surface of the leaf petiole (69). Beet roots are rough, scabby (similar to potato scab) and off-color (71). Broccoli (Brassica oleracea var. botrytis L.). Water-soaked areas occur inside the heads, and callus formation is slower on the cut end of the stems after the heads have been harvested (72). Symptoms of boron deficiency included leaf midrib cracking, stem corkiness, necrotic lesions, and hollowing in the stem pith (73). Brussels sprouts (Brassica oleracea var. gemmifera Zenker). The first signs of boron deficiency are swellings on the stem and petioles, which later become suberised. The leaves are curled and rolled, and premature leaf fall of the older leaves may take place (58). The sprouts themselves are very loose instead of being hard and compact, and there is vertical cracking of the stem (74). Carrot (Daucus carota L.). Boron deficiency results in longitudinal splitting of roots (75). Boron-deficient carrot roots are rough, small with a distinct white core in the center and plants show a browning of the tops (71). Cauliflower (Brassica oleracea var. botrytis L.). The chief symptoms are the tardy production of small heads, which display brown, waterlogged patches, the vertical cracking of the stems, and rotting of the core (74) (Figure 8.2). When browning is severe, the outer and the inner portions of the head have a bitter flavor (76). Stems are stiff, with hollow cores, and curd formation is delayed (77). The roots are rough and dwarfed; lesions appear in the pith, and a loose curd is produced (69). Clover (Trifolium spp.). Plants are weak, with thick stems that are swollen close to the grow- ing point, and leaf margins often look burnt (78). Symptoms of boron deficiency in red and alsike clover may occur as a red coloration on the margins and tips of younger leaves; the coloration grad- ually spreads over the leaves, and the leaf tips may die (65). Boron 247 FIGURE 8.1 Symptoms of boron deficiency in alfalfa (Medicago sativa L.) showing red and yellow color development on young leaves. (Photograph by Umesh C. Gupta.) (For a color presentation of this figure, see the accompanying compact disc.) CRC_DK2972_Ch008.qxd 7/14/2006 4:03 PM Page 247 [...]... elongation New Phytol 73 :82 1 83 2, 1974 44 P.M Tang, R.K Dela Fuente The transport of indole-3-acetic acid in boron-and calcium-deficient sunflower hypocotyl segments Plant Physiol 81 :646–650, 1 986 45 P.M Tang, R.K Dela Fuente Boron and calcium sites involved in indole-3-acetic acid transport in sunflower hypocotyl segments Plant Physiol 81 :651–655, 1 986 46 U.C Gupta Relationship of total and hot-water soluble boron,... 112: 280 – 281 , 1971 131 X Yu, P.F Bell, X.O Yu Nutrient deficiency symptoms and boron uptake mechanisms of rice J Plant Nutr 21:2077–2 088 , 19 98 132 C.G Sherrell Boron nutrition of perennial ryegrass, cocksfoot, and timothy N Z J Agric Res 26:205–2 08, 1 983 133 A Rashid, E Rafique, N Bughio Micronutrient deficiencies in rainfed calcareous soils of Pakistan III Boron nutrition of sorghum Commun Soil Sci Plant. .. Agarwala Boron nutrition of cowpeas Proc Indian Acad Plant Sci 100:311–3 18, 1990 22 S.G Lee, S Arnoff Boron in plants: a biochemical role Science 1 58: 7 98 799, 1967 23 C Chatterjee, N Nautiyal Developmental aberrations in seeds of boron deficient sunflower and recovery J Plant Nutr 23 :83 5 84 1, 2000 24 P Sinha, R Jain, C Chatterjee Interactive effect of boron and zinc on growth and metabolism of mustard Commun... 99 86 , 149 86 , 149 86 , 149 CRC_DK2972_Ch0 08. qxd 7/14/2006 4:03 PM Page 257 Boron TABLE 8. 3 257 (Continued ) mg B kgϪ1 in Dry Matter Crop Plant Part Sampled Deficiency 8 severely deficient Roots Strawberries (Fragaria x ananassa Duch.) Sufficiency 13 Old and young leaves at active growth stage Tomatoes (Lycopersicon esculentum Mill.) Mature young leaves from top of the plant 63-d-old plants Whole plants... 1 1 1 1 1 0 boron 1 boron soil) B (mg kgϪ1 tissue)b 33.5 18. 4 17.4 19.9 31.6 26.5 29.9 112 1 18 104 1 08 88 92 88 25.3b 103a Soil pH After Harvest 5.6 6.6 6.3 6.3 4 .8 4.9 4.9 5 .8 6.5 6.3 6.6 4.9 5 5 Treatment consisted of 24 mol kgϪ1 soil either as a Ca or Mg salt or as a mixture in a 1:1 molar ratio of Ca and Mg Control received 8 mmol each of CaCO3 and MgCO3 kgϪ1 soil b Values followed by a common... (67, 68) (Figure 8. 4) CRC_DK2972_Ch0 08. qxd 250 7/14/2006 4:03 PM Page 250 Handbook of Plant Nutrition FIGURE 8. 4 Symptoms of boron toxicity in alfalfa (Medicago sativa L.) showing scorch at margins of lower leaves (Photograph by Umesh C Gupta.) (For a color presentation of this figure, see the accompanying compact disc.) Barley (Hordeum vulgare L.) Boron toxicity is characterized by elongated, dark-brown... Raton, FL: CRC Press, 1993, pp 53 85 10 R.W Krueger, C.J Lovatt, L.S Albert Metabolic requirement of Cucurbita pepo for boron Plant Physiol 83 :254–2 58, 1 987 11 M.E Lenoble, D.G Blevins, R.J Miles Prevention of aluminum toxicity with supplemental boron II Stimulation of root growth in acidic, high-aluminum subsoil Plant Cell Environ 19:1143–11 48, 1996 CRC_DK2972_Ch0 08. qxd Boron 7/14/2006 4:03 PM Page... Influence of boron on amino acid contents in tomato plant I sap Agrochimica 27:4 98 505, 1 983 13 B.J Shelp Boron mobility and nutrition in broccoli (Brassica oleracea var italica) Ann Bot 61 :83 –91, 1 988 14 I.C Dave, S Kannan Influence of boron deficiency on micronutrients absorption by Phaseolus vulgaris and protein contents in cotyledons Acta Physiol Plant 3:27–32, 1 981 15 W.M Dugger Boron in plant metabolism... Encyclopedia of Plant Physiology, new series, New York: Springer, 1 983 , pp 626–650 16 B.J Shelp The influence of nutrition on nitrogen partitioning in broccoli plants Commun Soil Sci Plant Anal 21:49–60, 1990 17 I Bonilla, P Mateo, A Garate Accion del boro sobre el metabolismo nitrogenado en Lycopersicon esculentum cv Dombo, cultivado en hydroponica Agrochimica 32:276– 283 , 1 988 18 R Kastori, N Petrovic Effect of. .. light-yellow bleached leaf tips (63) Onion (Allium cepa L.) Boron toxicity results in burning of the tips of leaves, gradually increasing up to the base, and no development of bulb occurs (93) Pea (Pisum sativum L.) Boron toxicity results in suppression of plant height and in the number of nodes ( 98) Unpublished data of Gupta and MacLeod (83 ) showed that boron toxicity results in burning of the edges of . Genotypes 264 8. 7.2.2 Environmental Factors 264 8. 7.2.3 Method of Cultivation and Cropping 265 8. 7.2.4 Irrigation Water 265 8. 8 Fertilizers for Boron 266 8. 8.1 Types of Fertilizers 266 8. 8.2 Methods. 251 8. 4.2 Boron Requirement of Some Crops 252 8. 5 Boron Levels in Plants 252 8. 6 Soil Testing for Boron 257 8. 6.1 Sampling of Soils for Analysis 257 8. 6.2 Extraction of Available Boron 257 8. 6.2.1. 257 8. 6.2.1 Hot-Water-Extractable Boron 257 8. 6.2.2 Boron from Saturated Soil Extracts 2 58 8.6.2.3 Other Soil Chemical Extractants 2 58 8.6.3 Determination of Extracted Boron 259 8. 6.3.1 Colorimetric