Nutrient Deficiencies - Nutrients for Sugar Beet Production Soil

(A.P. Draycott and D.R. Christenson) 98

Deﬁciencies of nutrients result in a range of symptoms, which are somewhat unique for each nutrient. Chlorosis (yellowing), mottling, stunting and deterioration of the growing point and leaf tissue are among the signs observed. Care needs to be exercised in the evaluation of symptoms, since weather conditions, chemical and insect damage and disease may mask, confuse or exacerbate symptoms.

Identification of deficiency becomes increasingly difficult when there is more than one cause of abnormal growth or appearance.

The 16 elements generally considered essential to ﬁeld crops are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, boron, chlorine, copper, iron, manganese, molybdenum and zinc. However, an adequate supply of sodium is also necessary for sugar beet production, making it a 17th essential element.

Carbon, hydrogen and oxygen comprise the largest concentration in the plant, but are not considered as mineral nutrients. Carbon and oxygen are absorbed from the air, while hydrogen is removed from the water mole- cule through metabolic processes in the plant. Specific deficiency symptoms are not recognized for these elements and there are no diagnostic tools to identify a deficiency.

The macronutrients for all plants are nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. Sometimes cal-

cium, magnesium and sulphur are regarded as secondary fertilizer nutrients. All are present in plants at concentrations greater than 500 mg kg¹of dry plant tissue: henceforth the descriptor ‘macro’ (Anon., 2001).

Micronutrients include boron, chlorine, copper, iron, manganese, molybdenum and zinc, and are usually present in concentrations less than 500 mg kg¹ dry plant tissue (Anon., 2001). The unique role of sodium in sugar beet nutrition is discussed in Chapter 4 but deﬁciency symptoms have not been seen.

This element is considered to be a macronu- trient for sugar beet.

All nutrient deficiencies decrease the growth of sugar beet, but not all deficiencies affect sugar production. When all other nutrients are present in sufficient quantities, nitrogen deficiency increases sugar concentration in the root. If deficiency appears early in the season, loss of root yield is not offset by increase in sugar concentration. However, when nitrogen deficiency appears between 4 and 6 weeks prior to harvest, the increase in sugar concentration usually compensates for any loss in root weight. The suggestion has been made that sulphur and sometimes phosphorus deficiencies may increase sugar concentration, but the research evidence supporting this contention is not strong. It does not seem advisable to allow these deficiencies to develop as a means of enhancing

sugar concentration. The data indicate that deﬁciencies of all other nutrients tend to cause a decline in sugar yield. Any factor limiting top growth early in the season nearly always limits root weight as well as sugar production.

Plant Tissue Sample Preparation Plant tissue analysis may assist in the identification process for any nutrient deficiency symptom. Samples should be taken from unaffected as well as affected areas of the field for comparison. It is important to select specific tissue when collecting samples for analysis. A guide for sampling, along with the critical nutrient range for nutrients, is given in Table 7.1.

Sugar beet leaves and petioles are usually contaminated with soil and dust particles, whether grown in the ﬁeld or glasshouse. In the ﬁeld, plant surfaces may also be coated

with elements from foliar sprays. Pesticides, particularly fungicides, and foliar-applied nutrients leave residues on the plant surfaces. Removal of such contamination is essential for accurate assessment of the nutrition status of the plant. Sonneveld and van Dijk (1982) made a detailed study of meth- ods of preparation of plant tissue for analysis. They recommend washing in a mild 2%

(w/w) solution of a phosphorus-free deter- gent solution, followed by thorough rinsing with pure water.

The procedure must be done quickly on turgid tissue with minimum exposure to the washing solution to prevent loss of soluble elements from the plant tissue (particularly boron and potassium). Mills and Jones (1996) suggest that dust contamination can be detected by observing the aluminium, iron and silicon concentrations found in the tissue. When all three elements are 100 mg kg¹, dust contamination should be suspected. In the authors’ experience,

Table 7.1. Plant part tested, constituent analysed, critical concentration and ranges where deficiencies are and are not expected to occur (adapted from Ulrich and Hills, 1969).

Plant Constituent Critical Deficiency symptoms

Nutrient part analysed Unit concentration Yes No

Nitrogen Petiole Nitrate mg kg¹ 1000 70–100 350–35,000

Blade N % 2.1 1.9–2.3 2.2–4.0

Phosphorus Petiole HPO₄ mg kg¹ 750 150–400 750–4,000

Blade HPO₄ mg kg¹ – 250–700 1,000–8,000

Blade P % 0.3 – –

Potassium

1.5% Na Petiole K % 1.0 0.2–0.6 1.0–11.0

Blade K % 1.0 0.3–0.6 1.0–6.0

1.5% Na Petiole K % ^a 0.5–2.0 2.5–9.0

Blade K % 1.0 0.4–0.5 1.0–6.0

Calcium Petiole Ca % 0.1 0.04–0.10 0.2–2.5

Blade Ca % 0.5 0.1–0.4 0.4–1.5

Magnesium Petiole Mg % – 0.010–0.030 0.10–0.70

Blade Mg % – 0.025–0.050 0.10–2.50

Sulphur Blade SO₄S mg kg¹ 250 2–13 500–14,000

Boron Blade B mg kg¹ 27 12–40 35–200

Chlorine Petiole Cl mg kg¹ 0.4 0.01–0.04 0.8–8.5

Copper Blade Cu mg kg¹ – – –

Iron Blade Fe mg kg¹ 55 20–55 60–140

Manganese Blade Mn mg kg¹ 10 4–20 25–360

Molybdenum Blade Mo mg kg¹ – 0.01–0.15 0.20–20.0

Zinc Blade Zn mg kg¹ 9 2–13 10–80

aCritical value not useful when the petioles contain less than 1.5% Na.

manganese values will also be inordinately high with dust contamination. Cherney and Robinson (1982) suggest that titanium (Ti) concentration may be used as an indicator of soil or dust contamination. They found that nitric perchloric acid and sulphuric selenous acid adequately extracted titanium. Neither nitric acid nor dry-ash proce- dures extracted titanium satisfactorily.

However, analysis for titanium is readily included, using plasma-emission spectrom- etry. Any added cost would be worthwhile, given the nature of the decisions that will be made from the data.

Nutrient Deficiencies

Separation of the various symptoms may be aided by the following categories:

Uniform yellowing Nitrogen, sulphur, molybdenum Stunted greening Phosphorus

Leaf scorch Potassium,

magnesium Growing-point Boron, calcium damage

Yellowing with Manganese, iron, green veining chlorine, copper,

zinc

Nitrogen

Since nitrogen is a mobile element in the plant, deﬁciency symptoms appear on the older leaves. The initial symptom is a general light-green colour (yellowing) and often the leaves are smaller in size than normal (Plate 1). A series of increasingly nitrogen- deﬁcient leaves is shown in Plate 2.

Leaves of nitrogen-deﬁcient plants grow horizontally from the crown (Plate 3). In addition to horizontal growth, the leaves take on a long, narrow shape (Plate 4). In many cases, the new leaves in the centre of the plant are smaller in size and dark green in colour. Chlorosis continues to develop as the plant grows.

The continued development of symptoms depends on nitrogen supply. In cases of little additional supply, the leaves con-

tinue to turn yellow, wither and die. An additional supply regenerates leaves in the crown. New leaves are small and dark green and they grow horizontally. Increased supply, but insufficient to completely correct deficiency, results in new leaves growing larger, covering the older leaves and filling the space between the rows. Detection of deficiency in these cases is more difficult.

Frequent scouting of ﬁelds alerts the grower to any problems in sufﬁcient time to take corrective action.

Leaf symptoms of nitrogen deficiency may be confused with virus yellows. This disease exhibits a patchy yellowing on the individual leaves, as compared with the general yellowing of nitrogen deficiency. Nevins and Loomis (1970) have shown that nitrogen deficiency decreases chlorophyll concentration and the rate of photosynthesis in the old but not in the new leaves. General conditions for the development of nitrogen deficiency are described in Chapter 2.

Sugar beet in soils with little organic matter and in coarse sandy soils is susceptible to inadequate nitrogen supply. Excessive rain- fall after nitrogen application and inadequate supply from fertilizers are also conditions contributing to nitrogen deficiency. Often deficiency is in patches in the field, due to differences in mineral nitrogen supply brought on by variation in the soil (Draycott, 1972). The effects of inadequate water supply, soil compaction and pest damage are described in Chapter 12.

Phosphorus

Phosphorus deficiency is probably the most difficult disorder to diagnose in the field. The main symptoms of phosphorus deficiency are a reduction in leaf size, gradual development of a deep green colour followed by red or purple coloration of the leaves and stunting due to slow growth. The leaves may develop a metallic lustre from greyish green to blue-green.

The development of deﬁciency in seedlings often shows yellow cotyledons with the ﬁrst pair of leaves green (Plate 5).

Stunting of the plant is also a symptom, as

shown with the eight-leaf plant in Plate 6.

Comparison of the eight- to ten-leaf plants in Plate 7 – one is phosphorus-deﬁcient and one has an adequate supply – emphasizes this point. A leaf-colour series (Plate 8) shows a range of symptoms, including purple coloration, brown veining and smaller leaf size.

In long-term experiments where phosphorus fertilizer has been withheld for many years, leaves have a purple coloration.

However, development of purple colouring may not be a good indicator of phosphorus deﬁciency in sugar beet (Ulrich and Hills, 1969). The formation of a group of coloured compounds known as anthocyanins cause this coloration in the leaves of plants. Any environmental factor that favours an increase in sugar content in the plant tissue will promote the formation of anthocyanins.

Among the factors that will increase sugars in plant tissue are low temperature, drought or low nitrogen supply. Residues of herbi- cide may also cause purple coloration.

Potassium

One of the earliest reports described initial potassium deﬁciency as a ‘scorch’ on the margins of the leaf blade (Hale et al., 1946).

The scorch may be described as a leathery tan colour. Initially, symptoms show leaf- margin scorching accompanying a smooth leaf surface (Plate 9). More severe conditions cause the symptom to extend all the way to the midrib, but not involving the veins of the leaf (Plate 10). The youngest leaves may be hooded, similar to those with calcium deﬁ- ciency (Plate 11). The plant shown here was grown without sodium. When sodium is adequately supplied, the severity of the potassium deﬁciency is markedly reduced (Plate 12).

Draycott (1972) observed:

Scorch symptoms develop after chlorosis or may develop independently of it. Necrosis generally follows, both forming an unbroken border around the leaf and lobes between the veins. The necrotic tissue is dull or reddish brown; it is tough but soft to handle and it does not crumble or disintegrate like the necrosis associated with magnesium deﬁciency.

Cook and Millar (1953) reported that the scorch moves toward the centre of the leaf. It primarily affects the recently mature leaves on the plant. The centre leaves remain green and may have a hooded appearance. Dark, longitudinal lesions may form on petioles of the older leaves (Ulrich and Hills, 1969).

Potassium deﬁciency is most likely to develop on sandy, high organic matter and organic soils. Where the coarse fraction of sandy soils is formed from quartzite, supply will be less than if the fraction is formed from the potassium feldspar, arkose. Dry conditions, cool temperatures and poorly aerated or compacted soils limit uptake.

Magnesium

Magnesium deficiency symptoms on sugar beet are unique and not easily mistaken for any other deficiency. Deficiency first devel- ops as small, pale yellow areas near the out- side margins of recently mature leaves (Plate 13). The youngest mature leaves are affected.

These lemon-yellow areas spread between the veins towards the midrib. Necrosis starts near the edge of the leaf and gradually expands to include most of the interveinal tissue except for the triangular area near the base of the leaf (Plate 14). Leaves in the final stages of magnesium deficiency show black necrotic tissue between the veins, followed by brown necrosis (Plate 15). Late-season deficiency often shows a ‘washing out’ of necrotic tissue resulting in holes in the leaves (Plate 16). Magnesium deficiency (as well as potassium) should not be mistaken for virus yellows. The main difference between magnesium deficiency and virus yellows is that the latter shows vein clearing or vein yellowing in younger leaves of the plant. Older leaves on plants with virus yellows have a characteristic thickened and brittle feel.

Symptoms of magnesium deﬁciency usually appear in July and August, but may not be seen until September (Draycott, 1972).

Coarse-textured soils, particularly those with subsoils as coarse as or coarser than the surface soil, are most prone to magnesium deﬁ- ciency. These coarse-textured soils, when heavily fertilized with potassium, may show

magnesium deﬁciencies since potassium suppresses magnesium uptake. Deﬁciencies are likely when soil-test potassium plus fertilizer potassium (kg ha¹) is more than three times greater than soil-test magnesium (Christenson et al., 1992).

Calcium

Calcium deﬁciency affects the growing point of sugar beet. As a result, most of the symptoms are in the crown and on new leaves.

Ulrich and Hills (1969) grew sugar beet in solution culture to develop deﬁciency symptoms. Key symptoms are shown in Plates 17–20. Centre leaves have severe tip burn and the blades of the older leaves are crinkled and deformed and fail to expand (Plates 17 and 18). Young leaf blades are also hooded (downward cupping) and have a crinkled appearance (Plate 19). As deﬁciency progresses, the leaf blades may be reduced in size to a mere stub of blackened tissue at the end of the petiole (Plate 17).

A range of symptoms on leaf blades from a deformed leaf to a black-tipped stub, are shown in Plate 20. ‘Tip burn’ symptoms are seen on plants in ﬁelds where plant growth is vigorous. They usually disappear with a decrease in the supply of nitrogen from the soil or a change of climate or growth stage.

When calcium deﬁciency remains chronic, the growing point is often permanently damaged and lateral shoots develop abnormally.

Such a condition can produce damage to the conducting system and cambium tissue of the storage root. This results in concentric rings of darkened tissue when the storage root is cut in cross-section. This may be followed by a permanent wilting of the top and then death of the plant. A low supply causes poor root development and, in severe cases, the roots fail to grow.

Deﬁciency as described above is seldom seen, as most mineral soils are well supplied with available calcium (Mengel and Kirkby, 1978). The supply of calcium is usually adequate in soils that are limed and where sugar beet thrives best. Mass ﬂow carries more calcium to the root surface than is needed by the growing sugar beet in most

soils with pH values above 5.5. An exception is where sea-water ﬂooding has left a large residue of sodium, which antagonizes the uptake of calcium.

Sulphur

Ulrich and Hills (1969) and more recently Connors (2000) have described sulphur deficiency symptoms for sugar beet. The initial appearance of sulphur deficiency is very similar to that of nitrogen deficiency. There is a general yellowing across the entire leaf with both nutrients. There is no veining with either nitrogen or sulphur deficiency. When sulphur is in short supply, the leaves of the entire plant change gradually from green to light green and then to light yellow with a faint tinge of green remaining (Plate 21).

Since sulphur is not as mobile as nitrogen, the new centre leaves in sulphur-deﬁcient plants become light green to yellow, rather than dark green as in nitrogen deﬁciency.

Leaves remain erect, the petioles and blades are brittle, breaking readily when com- pressed by the hand. A progression of increasing severity of sulphur deficiency symptoms is shown in Plate 22. With severe sulphur deficiency the petioles develop brown, longitudinal lesions. In the field there is a general yellowing in patches, similar to nitrogen deficiency (Plate 23).

Connors (2000) suggests that a slow crop growth response to applied nitrogen should arouse suspicions of sulphur deﬁciency.

Plant tissue analysis should be used to further conﬁrm the problem. Sulphur deﬁciency is more pronounced with large nitrogen inputs and is accompanied by a wide nitrogen : sulphur ratio (17 : 1) in young tissue.

Organic matter is the primary source of sulphur from soils. Hence, sulphur deﬁciency is more likely on sandy soils with low organic matter (see Chapter 3).

Boron

Boron deﬁciency was thought to be a disease and was referred to as heart rot and dry rot.

Brandenburg (1931) ﬁrst showed that boron

deﬁciency was the cause of these two ‘rot’

conditions. Heart rot is the term applied when the growing point blackens and dies while dry rot describes the symptoms on the tap root that usually appears after heart rot is observed.

One of the best descriptions of the anatomical effects of boron deficiency on the root crop is that of Rowe (1936). She found that the apical meristem of the shoot, the youngest leaves and the newly developed cambia were the most sensitive to boron deficiency and these were the first to degenerate. Cells of the vascular rings in the process of differentiating and sporadic groups of parenchyma cells adjacent to conducting elements were also sensitive to deficiency. Later stages of the deficiency were characterized by decay of cambial and adjacent parenchyma cells, together with com- plete disintegration of the phloem. The root tip did not degenerate but merely ceased to grow. A concentration of 0.17 mg kg¹in the culture solution was enough for normal growth and development. Recovery in boron-starved plants involved the activation of axillary buds at the top of the beet, each of which developed its own system of secondary vascular rings.

Boron deficiency can be identified without supporting soil and plant tissue analysis because of unique symptoms on the leaves, petioles, crowns and roots. Symptoms may appear on either or both the roots and above- ground growth. Boron is relatively immobile in plants and symptoms appear on growing points and in meristematic tissues. Boron deficiency not only decreases yield but also damages the roots, decreasing their value and keeping qualities.

One of the first symptoms of boron deficiency is a blackening/dying of the growing- point/centre of the crown (Plate 24). Mature leaves may have netting and cracking symptoms (Plate 25). The most prominent symptoms in a field-grown plant include blackening of the centre of the crown and proliferation of small leaves, along with a prostrate habit, and cracked and corky areas on the petioles (Plate 26). Conductive tissue in the roots deteriorates, showing heart and crown rot (Plate 27). Plants may appear

wilted even when grown in moist soil or in aerated culture solution. Young leaves wilt the most, instead of the least, as they do in true water shortage. In time, they collapse and fail to develop.

Ulrich and Hills (1969) report that boron deﬁciency appears to have a twofold effect:

(i) the conducting tissue is damaged, causing wilting and occasionally the exudation of syrupy materials from the leaf blades; and (ii) the meristematic tissues of the growing- point collapse and die. A further effect is on root growth, as ﬁbrous roots fail to develop in solutions deﬁcient in boron. This may be the primary cause of wilting in the tops.

Cambium tissues of storage roots darken, cells collapse, growth stops and the storage root become subject to decay.

Deficiencies are associated with alkaline soils. The symptoms are often greater on sandy soils than on finer-textured soils. Dry weather will promote the appearance of deficiency (see Chapter 6). As affected plants age, many leaves die and fall off. If growing conditions improve, plants usually begin to grow again from secondary growing points.

Tissue round the shoulder of the taproot also begins to decay in advanced stages of deﬁ- ciency. Such roots are invaded by fungi and begin to rot. Hull (1960) described this secondary attack and some of the fungi involved.

Stoker and Tolman (1941) working in Oregon, USA, ﬁrst showed the need for boron to ensure normal development of the seed stocks. The main ﬂowering stem is stunted and the growing point dies.

Similarly, if other stems shoot, although they are taller than the ﬁrst one, their growing points also die. The growing points of later- als along these stems also give rise to stunted growths, which appear as small rosettes of discoloured bracts, and eventually these growing points also die.

Manganese

Field experiments testing the response to applications of manganese (whether to soil or plant) generally conclude that only where symptoms would otherwise appear on

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