© CAB International2003. Nutrients for Sugar Beet Production: Soil–Plant Relationships
(A.P. Draycott and D.R. Christenson) 67
Both calcium and magnesium are major (or macro-) nutrients because they are taken up in quantity by plants. Macronutrients are those contained in plant dry matter at a con- centration greater than 500 mg kg1(Anon., 2001). In the case of sugar beet, amounts in a hectare of crop are similar to those of phos- phorus and sulphur but less than those of nitrogen and potassium. Healthy sugar beets contain much more, as shown below, in leaves and roots.
Deficiency symptoms of calcium are rarely seen because sugar beet must be grown in soils of near-neutral pH. Such soils are kept near the neutral point either by cal- cium-containing minerals in the parent mate- rial or by regular additions of lime. Thus, in temperate climates, the soil complex is usu- ally dominated by Ca2+ions in quantities far in excess of crop requirement. Calcium-defi- ciency symptoms are occasionally seen where an imbalance of cations on the soil complex has been caused, e.g. by sea-water flooding or an excess of a cationic fertilizer (see Chapter 4).
Deficiency symptoms of magnesium appear quite commonly on sugar beet where soils are sandy or parent materials contain little. On all loamy soils, clays and organic soils symptoms are rarely seen because suffi- cient is released during weathering. Only where roots are damaged (e.g. by pests) or
restricted (e.g. by compaction) or another cation is in excess (e.g. potassium or sodium) is magnesium deficiency seen. On sandy soils, minerals contain very little magnesium and, where intensive cropping has been practised on stockless farms, magnesium is continually removed and must be replaced by fertilizer.
CALCIUM Calcium in Soil
The amount of calcium in soil varies enor- mously depending on the parent material, degree of weathering and amount of leaching.
The concentration in most soils ranges from 0.1 to in excess of 3%. Old soils, soils derived from acidic parent material and those that have been highly weathered and leached have the smallest calcium content. Soils formed from alkaline or calcareous materials contain much more calcium and those that contain in excess of 3% Ca are defined as cal- careous (Anon., 2001). These are easily identi- fied by effervescence with addition of a few drops of molar mineral acid.
During soil formation, calcium is derived from calcium-containing feldspar (anorthite), pyroxene (augite) and amphibole (horn- blende). Calcium is also present in calcitic
and dolomitic limestone, chalk, apatite (cal- cium phosphate) and gypsum (calcium sul- phate (CaSO4.2H2O). In arid and semi-arid soils, gypsum may accumulate in a layer within the root zone of sugar beet.
Throughout the world where soil is formed from chalk or limestone, total calcium con- centration ranges from 3 to 25% dry weight.
Calcium released from minerals into soil solution is quickly adsorbed on the exchange complex. Consequently, the amount of cal- cium is usually greater in soils containing clay. In a survey of Michigan soils, Robertson et al.(1976b) reported that fine-textured soils contained from 1700 to 3600 mg Ca kg1soil, while coarser soils ranged from 625 to 2400.
Calcium in soil solution ranges from 30 to 300 mg l1for non-calcareous soils and up to 700 mg l1in calcareous soils.
Causes of Deficiency
Soils where sugar beet is produced generally contain sufficient calcium to provide for the nutrient need of the growing crop. Barber (1995) showed that calcium moves to the root surface by mass flow – the movement of solutes associated with a net movement of water. It follows that the quantity of water moving to the root surface will be influenced by the rate of transpiration. The transpira- tion rate generally ranges from 200 to 900 g H2O g1dry weight of plant tissue.
Aweighted average calcium concentra- tion from tops and roots is calculated by Draycott (1972) to be 4000 mg Ca kg1 dry plant tissue in the sugar beet crop. The ratio between soil-solution concentration (30–300 mg l1) and weighted average in plant tissue is 133 to 13. Any ratio of plant to solution concentration less than the transpiration ratio represents a case where ions would accumulate at the root surface. These consid- erations show that the primary cause of cal- cium deficiency in sugar beet is not usually related to supply from the soil, but rather to uptake, translocation, utilization in the plant or, most commonly, an excessive supply of another cation.
Chapter 7 below shows the damage caused to leaves by calcium deficiency.
Whether this is related to precipitation of insoluble calcium compounds in the leaves is open to debate. In a review, Gallagher (1975) pointed out that plants that accumu- late large quantities of oxalic acid tend to contain large quantities of calcium oxalate crystals. He stated that ‘oxalic acid is a strong chelating agent and once reacted with calcium it becomes somewhat immobi- lized in plant cells’. However, some reports indicate that calcium can be reutilized from the calcium oxalate if plants are under extreme calcium stress. Van Egmond (1979) suggested that calcium deficiency (tip burn) during periods of rapid growth and high nitrogen fertilization is explained by an overproduction of oxalate in expanded young leaves. He suggested that disappear- ance of deficiency symptoms later in the season might be the result of redistribution from the root. Conversely, Mostafa and Ulrich (1976a) found no relation between the severity of deficiency and calcium oxalate in plant tissue. They inferred that deficiency was associated with an incom- plete uptake of calcium from solution, a large demand by storage roots and ineffi- cient translocation of calcium to the leaf tips. They explained that, if calcium immo- bility inhibits transport of calcium from older plant parts to younger plant parts, the formation of calcium phosphates could be a limiting factor under deficiency and not under sufficiency conditions. There appears to be no resolution of the issue of the role of phosphates and oxalates in calcium defi- ciency. At the practical level, this mecha- nism is not a factor in the nutrition of sugar beet. We feel that resolution of this issue would be of importance in the development of germ-plasm and varieties that are less susceptible to calcium deficiency.
Role of Calcium in Sugar Beet Plants The main role of calcium in plants is in pro- viding stability to cell walls by formation of calcium pectate in the middle lamella (Epstein, 1972). In some plants calcium polysaccharides are components of cell walls. Epstein also found that amylase was
one of the enzymes where calcium is a nec- essary cofactor. Furthermore, calcium appears to ‘detoxify’ other ions and coun- teracts the effect of low pH on nutrient uptake. Calcium is necessary for the organi- zational integrity and function of mem- branes within cells. Cell division and elongation depend on an adequate supply of calcium. Since calcium is translocated in the xylem but not in the phloem, calcium is rather immobile and not readily redistrib- uted within the plant.
More recently, Kauss (1987) reported that other enzymes require calcium for activation.
Bush (1995) reported that calcium regulates ionic balance, mobility, gene expression, car- bohydrate metabolism, mitosis and secre- tion. Calcium may not be the only regulator of these processes, but evidence is accumu- lating that points to the significant role of calcium as a regulator.
Amount in the Sugar Beet Crop Wallace (1945) found that healthy sugar beet leaves contained 2.65% Ca in dry matter whereas deficient leaves contained only 0.66%. Ulrich and Hills (1969) reported that deficient leaf blades contained 0.1–0.4% Ca and non-deficient leaves greater than 0.4%.
Draycott (1972) reported on a 5-year study at Broom’s Barn. The data in Table 5.1 show that sugar beet contained 12–31 kg Ca ha1 in roots and 18–67 in tops. The mean was 22, 41 and 63 kg ha1for roots, tops and total, respectively. Cooke (1967) reported that
80–100 kg Ca ha1 was removed in a 33 t ha1 crop. Viets and Robertson (1971) sug- gested that a 60 t ha1crop would contain 40–220 kg Ca ha1. Recalculated data from Robertson et al. (1976b) suggested a more modest estimate of 80 kg Ca ha1.
The variability in the amount of calcium contained in a sugar beet crop may be related to the variety grown (Finkner et al., 1958) but there is a paucity of information on varietal differences. At Colorado State University, Schmehl and his students con- ducted an excellent study concerning the accumulation of nutrients in sugar beet plants. Figure 5.1 shows the accumulation of calcium in various plant parts over the course of the growing season (Bravo et al., 1989). The pattern of uptake is similar to the growth of the crop. They reported the total uptake for the crop to be 120 kg for a 60 t crop. This value includes calcium lost to leaf senescence and unharvested roots. In an ear- lier report from the same study, Eslami M et al. (1988) noted that sugar beet leaf senes- cence accounted for approximately 70 kg Ca ha1. If tops are removed, total offtake may approach 80 kg ha1, more than half being in tops at harvest.
Dynamics of Calcium in Sugar Beet There is much evidence that sugar beet needs a continuous supply of calcium for growth and development. For example, when Ulrich and Mostafa (1976) transferred sugar beet seedlings from a complete nutri- ent solution to one where calcium was with- held, rootlets and tops soon failed to develop. When the same transfer was done at the eight-leaf stage, the rootlets became stubby and swollen at the tips. The upper portion of nearly fully developed leaf blades developed cupping or hooding, an effect typical of calcium deficiency. As each new leaf developed, the blade became smaller until only a black tip remained at the apex of the petiole. This was called ‘tip burn’ and each new petiole had the symptom. Addition of calcium corrected deficiency on new growth, but did not eliminate symptoms on old growth.
Table 5.1. Concentration and quantity of calcium in sugar beet at harvest at Broom’s Barn.
Mean Range
Concentration (%)
Tops 1.00 0.70–1.60
Roots 0.24 0.16–0.35
Quantity in crop (kg ha1)
Tops 41 18–67
Roots 22 12–31
Total 63 30–98
Soils usually contain ten times as much calcium as potassium in solution. However, sugar beet plants at harvest contain approxi- mately three times as much potassium as cal- cium (Draycott, 1972). There appear to be two interrelated factors associated with this phenomenon. First, calcium is absorbed only by young root tips, where the cell walls of the endodermis are unsuberized, whereas other cations are absorbed along the entire length of the root (Clarkson et al., 1968, 1971).
Secondly, and interrelated to the first, Berry and Ulrich (1968) showed that sugar beet plants depleted the concentration of potas- sium, sodium and magnesium in solution to 1 mg l1 before deficiency symptoms appeared, whereas calcium deficiency symp- toms occurred when the concentration in solution was 50 mg Ca l1.
Mostafa and Ulrich (1974) evaluated the effect of the concentration or activity of cal- cium in solution on the uptake of calcium.
They showed that sugar beet plants devel- oped calcium deficiency symptoms, even though the concentration and/or activity of calcium in solution was relatively great.
They concluded that deficiency symptoms were probably caused by cation interactions
rather than calcium availability. Earlier, Berry and Ulrich (1970) studied the effect of potassium on uptake of calcium by sugar beet seedlings grown in solution culture.
Calcium deficiency symptoms developed progressively as potassium concentration was increased. However, it was shown that a sufficiency of both elements was necessary for translocation of calcium throughout the plant and complete absence of deficiency symptoms. If potassium was limiting, cal- cium was taken up by the roots, but not translocated to the leaves.
Calcium and magnesium also interact, each inhibiting uptake of the other. Mostafa and Ulrich (1976b) observed that sugar beet did not grow well when the calcium : mag- nesium ratio was 0.33 or less. This was true regardless of concentration of the respective ions. They further showed a mutual inhibitory effect of calcium and magnesium on ion uptake. Their conclusion was that the ratio of calcium : magnesium in the nutrient solutions might limit calcium uptake by sugar beet.
The effect of cation ratios on crop growth and yield has been the subject of numerous studies over the past 60+ years. Generally,
Petioles
Blades Crowns Roots
12 Jul. 26 Jul. 9 Aug. 23 Aug. 6 Sep. 20 Sep. 4 Oct. 18 Oct.
0 12.5 25 37.5 50
Uptake (kg Ca ha–1)
Fig. 5.1. Calcium uptake (after Bravo et al., 1989).
significant effects occur only when the exchangeable calcium : magnesium ratio on a molar basis is significantly less than 1. This situation is known to occur only on soils derived from serpentine, but only small areas of the world have such soils, e.g. Cornwall (UK), Scotland, the eastern USAand Canada.
Imbalance due to an excess of magnesium has been suggested but never proved on soils formed from dolomitic limestone.
Extrapolating from research on other crops, it seems unlikely that there is a cal- cium : magnesium ratio that gives best yield.
McLean et al.(1983) conducted a long-term study to evaluate the effect of cation ratios on yield of maize, soybean, wheat and lucerne. Cation concentrations were adjusted annually by the addition of appropriate salts.
They concluded that a specific cation ratio for ideal crop production does not exist.
Rather, each cation should be supplied in adequate, but not excessive, amounts and soil and plant analyses should be utilized to provide guidelines, as described in Chapter 4 for potassium and sodium and below for magnesium.
MAGNESIUM Magnesium in Soil
Total magnesium in soil is usually in the range 0.1–1.0%, being present in primary minerals such as biotite, serpentine, horn- blende and olivine. In addition, clay miner- als, such as chlorite, vermiculite, illite and smectite, have magnesium as part of their structure. All these minerals and clays release the element during weathering, usu- ally in quantities sufficient for most crops.
Some soils may contain over 10% magne- sium when formed on a parent material of dolomitic limestone (a mixed carbonate of magnesium and calcium) or magnesite (mag- nesium carbonate). Also, in some arid and semi-arid regions, epsomite (MgSO4.7H2O) and other salts may be present, resulting in large total soil magnesium concentration.
Sugar beet and similar plants take up magnesium from soil solution as Mg2+. This exchangeable or ‘available’ concentration in
soils usually ranges from 10 to 500 mg Mg l1 soil. Magnesium is present on the exchange complex as well as in soil solution, and a simple extraction procedure with an aqueous salt solution (commonly ammo- nium nitrate or acetate) reflects the amount readily available to sugar beet and other crops, as described below.
Medium- and fine-textured soils contain more magnesium than sandy soils, so defi- ciencies are seen more often on sandy soils than on loams and clays. For example, Robertson et al. (1979a) noted that clay and clay loam soils ranged from 250 to 500, loam and sandy loam from 150 to 450 and loamy sand and sands from 30 to 175 mg Mg kg1.
Role in the Plant
Amajor function of magnesium in plants is its role as the central atom in chlorophyll. It also plays an indispensable role in protein synthesis as a bridging element for the aggregation of ribosome units. Another important role of magnesium in plants is enzyme activation and energy transfer.
Groups of enzymes activated are phos- phatases and carboxylases. Energy transfer involves ATP and a group of enzymes referred to as adenosine triphosphatases (ATPases), which use magnesium ATP as a substrate. Magnesium plays a wide role in reactions associated with respiration and photosynthesis.
Amount in Sugar Beet
Ulrich and Hills (1969) defined a critical concentration of 0.1% Mg in dried leaf- blade tissue but suggested that deficiency symptoms may appear below 0.2% Mg. A summary of results from a number of stud- ies supports the idea that magnesium defi- ciency can be expected below about 0.2%
(Table 5.2). Draycott (1993) in a further sum- mary reported that leaf blades contained 0.6% Mg in the spring, declining to 0.2%
late in the summer. Leaves with magnesium deficiency symptoms contained 0.1–0.2%
Mg in dry matter.
Bolton and Penny (1968) found that the average amount of magnesium removed by sugar beet tops and roots was 21, 37 and 46 kg ha1with treatments of 0, 50 and 100 kg Mg ha1, respectively. Jacob (1958) in a review of magnesium as a plant nutrient gave the uptake of sugar beet as 35 kg ha1. Warren and Johnston (1962b) found that sugar beet removed only 12 kg without mag- nesium and 15 kg with magnesium fertilizer, but their yields were small.
Adams (1961c) measured the uptake of magnesium by sugar beet periodically from June to October. The concentration increased rapidly until September and was then fairly constant. Uptake was 27 kg ha1(assuming 74,100 plants ha1). Durrant and Draycott (1971) found that maximum uptake of mag- nesium was in August, but this decreased slightly by harvest in November due to leaf senescence. On these soils, which were prone to magnesium deficiency, total uptake was only 25 kg Mg ha1.
Bravo et al. (1989) also measured the uptake of magnesium over the course of a growing season. The results (Fig. 5.2) show a rapid increase in the amount until the mid- dle of August and then a slower accumula- tion as the amount in crowns, petioles and leaf blades decreased. The amount stored in roots increased as the season progressed.
These data show that the crop contained between 35 and 40 kg Mg ha1. Taking into account the magnesium in senescent leaves
and fibrous roots contributes to the higher values reported (Eslami M et al., 1988). In good commercial sugar beet production we expect the total uptake of magnesium to range between 40 and 50 kg Mg ha1, a little more than half being in the taproots.
Predicting Response to Magnesium by Soil Analysis
As pointed out earlier, magnesium deficien- cies are more common on sandy soils than on finer-textured soils. The incidence of magne- sium deficiency in the UK increased rapidly over the 23-year period 1946–1969 (Draycott, 1972). This was attributed to a large decrease of farmyard manure used, higher yields and intensive cash-cropping on sandy soils.
In general, magnesium deficiency may appear on sandy soils containing little in the exchangeable fraction. Table 5.3 from Draycott and Allison (1998) shows the relationship between exchangeable soil magnesium and the recommended magnesium application.
Soil containing less than 50 mg kg1 should have magnesium applied. They reported that soils ‘with less than 15 mg kg1require special treatment because there are likely to be severe deficiency symptoms and significant yield depression’. In the range of 15–25 mg kg1 application should improve and from 25 to 50 mg should maintain the magnesium status of the soil. Periodic application is needed to maintain magnesium supply for sugar beet.
Table 5.2. Concentration of magnesium in dry matter of sugar beet leaf blades with and without deficiency symptoms.
Leaf magnesium (%)
With symptoms Without symptoms Reference
0.096 0.546 Wallace, 1945
0.150 0.390 Hale et al., 1946
0.170 0.490 Björling, 1954
0.096 0.546 Jacob, 1958
0.010–0.030 0.100–0.700 Ulrich, 1961 0.149–0.030 0.217–0.559 Birch et al., 1966
0.110 0.480 Bolton and Penny, 1968
0.100–0.200 0.200–0.650 Draycott and Durrant, 1970b
Range 0.010–0.219 0.100–0.700
Mean 0.120 0.444