4. EFFECT OF GYPSUM AND CALCIUM CARBONATE ON PLANTS 4.1 Introduction4.2 Winter Crops4.3 Summer Crops4.4 Classification of Field Crops Based on Their Tolerance to Gypsum 4.5 Fruit and Forest Trees 4.1 Introduction Gypsiferous soils are very variable and there are many factors that affect their properties in relation to plant growth. Gypsiferous soils can be productive and managed profitably if they are first studied properly. The effect of the chemical properties of gypsiferous and calcareous soils on the growth of plants, both natural vegetation and crops, and their mineral contents have been investigated by numerous authors. Before further discussing the effects of gypsum on plants it is worth noting that measurements of total gypsum in soils are unreliable and do not reflect the actual amount present as proved by Sayegh et al. (1978). Figures quoted in the literature for the gypsum content of soils are commonly lower than the actual amount present. Van Alphen and de los Rios Romero (1971) conclude that up to 2 percent gypsum in the soil favours plant growth, between 2 and 25 percent has little or no adverse effect if in powdery form, but more than 25 percent can cause substantial reduction in yields. They suggest that reductions are due in part to imbalanced ion ratios, particularly K:Ca and Mg:Ca ratios. Hernando et al. (1963, 1965) studied the effect of gypsum on the growth of corn and wheat by varying the gypsum level in the soil up to 75 percent. They show that high levels of gypsum caused poor growth of corn, especially as the soil moisture was maintained at 80 percent of field capacity. However, wheat showed minimum growth where the soil contained 25 percent gypsum at all soil moisture levels ranging from 15 to 100 percent of field capacity. Akhvlediani (1962) concludes in general, that agricultural production on gypsiferous chernozem and chestnut soils is not affected when the gypsum content is between 15 and 30 percent. Bureau and Roederer (1960), report that 30 percent gypsum content in soils of Tunisia is toxic to plant growth. Van Alphen and de los Rios Romero (1971) state, from field observations in the Ebro Valley of Spain, that plant growth is reduced where the gypsum content exceeds 20 to 25 percent. Soil gypsum affects the mineral contents of plants. Hernando et al. (1965) showed, using water culture, that increasing the concentration of SO 4 mixture (K 2 SO 4 + MgSO 4 ) increased the uptake of NO 3 , K, Mg and sulphur by corn but decreased the uptake of Ca and P. Boukhris and
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4. EFFECT OF GYPSUM AND CALCIUM CARBONATE ONPLANTS
4.1 Introduction 4.2 Winter Crops 4.3 Summer Crops 4.4 Classification of Field Crops Based on Their Tolerance to Gypsum 4.5 Fruit and Forest Trees
4.1 Introduction
Gypsiferous soils are very variable and there are many factors that affect their properties inrelation to plant growth. Gypsiferous soils can be productive and managed profitably if they arefirst studied properly. The effect of the chemical properties of gypsiferous and calcareous soilson the growth of plants, both natural vegetation and crops, and their mineral contents have beeninvestigated by numerous authors.
Before further discussing the effects of gypsum on plants it is worth noting that measurementsof total gypsum in soils are unreliable and do not reflect the actual amount present as proved bySayegh et al. (1978). Figures quoted in the literature for the gypsum content of soils arecommonly lower than the actual amount present.
Van Alphen and de los Rios Romero (1971) conclude that up to 2 percent gypsum in the soilfavours plant growth, between 2 and 25 percent has little or no adverse effect if in powderyform, but more than 25 percent can cause substantial reduction in yields. They suggest thatreductions are due in part to imbalanced ion ratios, particularly K:Ca and Mg:Ca ratios.Hernando et al. (1963, 1965) studied the effect of gypsum on the growth of corn and wheat byvarying the gypsum level in the soil up to 75 percent. They show that high levels of gypsumcaused poor growth of corn, especially as the soil moisture was maintained at 80 percent of fieldcapacity. However, wheat showed minimum growth where the soil contained 25 percentgypsum at all soil moisture levels ranging from 15 to 100 percent of field capacity. Akhvlediani(1962) concludes in general, that agricultural production on gypsiferous chernozem andchestnut soils is not affected when the gypsum content is between 15 and 30 percent. Bureau
and Roederer (1960), report that 30 percent gypsum content in soils of Tunisia is toxic to plantgrowth. Van Alphen and de los Rios Romero (1971) state, from field observations in the EbroValley of Spain, that plant growth is reduced where the gypsum content exceeds 20 to 25percent.
Soil gypsum affects the mineral contents of plants. Hernando et al. (1965) showed, using waterculture, that increasing the concentration of SO4 mixture (K2SO4 + MgSO4) increased the uptakeof NO3, K, Mg and sulphur by corn but decreased the uptake of Ca and P. Boukhris and
Lossaint (1970, 1972) studied the mineral contents of 52 natural species growing on gypsiferoussoils in Tunisia, and reported that various species growing under the same ecosystemresponded differently to the excess of Ca and SO4 present in the soils, depending upon theirbiogeochemical properties. In general, the chemical composition of the leaves or aerial parts ofplants is influenced by the plant family. A comparison of field observations, with water culturestudies, confirms the behaviour of plant species toward nutrient adsorption. A high level of SO 4
in the soil can raise the SO4, level in the gypsum tolerant species (called gypsocline); but to alesser extent in the species (so-called gypsophytes) found on natural gypsum soils. However,there are some gypsophytes called thiophores which have great ability to accumulate highlevels of S in their leaves. The SO4 concentration in some thiophores is thirty times greater thanthat in other species living in the same environment (Table 4.1).
Table 4.1 CHEMICAL COMPOSITION OF WILD PLANTS ON GYPSIFEROUS SOILS
In the literature, it is reported that the chemical as well as the physical properties of thegypsiferous soils affect plant growth and mineral composition of plants.
From intensive field observations of gypsiferous soils in Iraq, Smith and Robertson (1962) foundthat root growth was inhibited where the gypsum content of soil was over 10 percent. This is
apparently because of the poor transmission of air and water caused by poor structure. Theyalso found that soils containing more than 25 percent gypsum in the rooting zone give poorgrowth. In the spring, wheat crops wilt on shallow gypsiferous soils when other crops on deepersoils show no signs of distress. Roots do not penetrate the gypsum layer, even when it is quitewet. Kovda (1954) and other workers observe that plant roots do not penetrate a soil layercontaining 25 percent of gypsum or more. Mardoud (1980) observes that pine roots cannotpenetrate a soil layer with 60 percent of gypsum. The roots extend horizontally and the treesshow signs of poor growth compared with trees on soils with gypsum horizons at greater depth.Boyadgiev (1974) shows that the presence of well-crystallized gypsum within the first metre ofsoil affects the performance of cotton crops significantly. He found it difficult to evaluate theadverse effect of gypsum content on the cotton yields because of its link to other variableswhich also cause these soils to be less than ideal for cotton production. Boyadgiev (1974) also
noted that crops such as alfalfa could grow very well and give high yields even in soilscontaining up to 50 percent of powdery gypsum as long as no gypsic layer impeding rootelongation and extension is present in the soil profile at shallow depth. Similar effects have beennoted by Amami et al. (1967) in the oasis at Tozeur in Tunisia, where good yields of alfalfa anddate palms were obtained in the highly gypsiferous soils. Similar results were obtained in theEbro Valley of Spain with crops such as alfalfa, wheat and apricots.
It appears from the above results that the gypsum content of soils is only one of several factorswhich affect plant growth and yield of crops. The other factors are:
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i. the depth of the topsoil over a gypsic layerii. the hardness and degree of crystallization of the gypsic layeriii. the total and active calcium carbonate contentsiv. the availability of plant nutrients and moisture content in the root zonev. the type of crops grown and their relative tolerance to gypsumvi. the drainage conditions and salinity of the soil.
The performance of plants grown on shallow soils depends to a large extent on their rootsystem, the gypsum content, the fertility level of the topsoil, and the water availability during thegrowing season. In particular the presence of a hard impervious gypsic layer has a strong effecton crop production under irrigation. Percolating water dissolves gypsum and salts and stagnatesat the top of the gypsic layer creating a perched water-table, often resulting in an accumulationof gypsum and salts. The resulting high water-table may rise to the soil surface leaving salts andgypsum. Under these conditions, the performance of crops will be affected by both gypsum andsalinity. Extensive areas of gypsiferous soils in Syria, Iraq, Tunisia and elsewhere are saltaffected.
4.2 Winter Crops
Wheat
Wheat grows least well when the gypsum content in soils is around 25 percent (Hernando et al. 1963). Smith and Robertson (1962) observe that wheat grown on shallow gypsiferous soilsshows signs of wilting in the spring and the roots were unable to utilize moisture from the wetgypsic layer below. Van Alphen and de los Rios Romero (1971) record high yields of wheat ongypsiferous soils in the Ebro Valley, Spain. Mardoud (1980) found that Mexican wheat cultivarsyielded an average of 4 tonnes per hectare on the shallow gypsiferous soils of the EuphratesValley (gypsum content less than 25 percent in the 0-15 cm layer and 25-35 percent in the 15-30 cm layer). This yield is considered very satisfactory under the conditions in the Valley.
Barley
Barley (H. vulgare) is an important crop well adapted on gypsiferous soils under dry farmingagriculture, and is widely used by farmers in Northern Syria and Iraq. A two-course rotation ispractised. Fallow is extensively used after wheat or barley, in localities where the averageannual rainfall is 200-300 mm. All the evidence suggests that barley like wheat is tolerant togypsum. Yields of 1.5 to 3 tonnes per hectare were obtained under rainfed agriculturedepending upon total seasonal rainfall and distribution. However, Mardoud (1980) obtained upto 4 tonnes per hectare in the Euphrates Valley with supplementary irrigation.
Vetches
American vetch (Vicia dassicarpa) was tested under irrigation on various types of gypsiferoussoils of the Euphrates Valley. The active nodules were very limited in number in the firstcropping season and yield, on the very shallow gypsiferous soils, ranged between 1 to 2 tonnesof seeds or 8.4 tonnes of green fodder per hectare. The yield during the second seasonimproved significantly averaging 2.5 tonnes of seeds or 25 tonnes of green fodder per hectare.Lower yields were obtained on sandy gypsiferous soils. Under rainfed farming agriculture andwith rainfall exceeding 250 to 300 mm, vetches could be a good crop to follow wheat or barley inthe rotation.
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Lentils
Lentils (Lens esculenta) is a dry farming crop, which is usually alternated with wheat or barley ina two-course rotation. Lentils are used as well as vetches on the rainfed, gypsum-affected soilsof Iraq and Syria as a break crop. Lentils under irrigation gave, in shallow gypsiferous soils, amoderate yield of 1.3 to 1.5 tonnes per hectare in the first year. An average yield of 0.5 to 1
tonnes per hectare was obtained on the sandy gypsiferous soils of the Euphrates Valley. As inthe case of vetches, it was noticed that few nodules were present on the root system in the firstyear of cropping with obvious signs of nitrogen deficiency on the plots receiving no nitrogenfertilizer (Mardoud 1980).
Broad beans
Broad beans (Vicia faba) are usually planted, under dry farming conditions, in the higher rainfallzone (350 to 500 mm as annual rainfall). Supplementary irrigation is required to obtain higheryields under lower rainfall conditions. Broad beans grown in irrigated fields of shallow and veryshallow gypsiferous soils of the Euphrates Valley gave a poor yield of 0.3 to 0.5 tonnes perhectare at first. Data on the performance of broad beans on deep gypsiferous soils are notavailable.
Trifolium
Trifolium (Trifolium alexandrinum) is an important fodder crop under irrigated agriculture. Matar(private communication) tested its tolerance to gypsum in pots, under greenhouse conditionswith ample K and P fertilization. Four successive cuts were harvested at the flowering stage.The effect of gypsum content was significant in the first cut, reducing the yield by more than 50percent where the gypsum content exceeded 20 percent (Table 4.2). The effect of gypsumbecomes much less in the following cuts. This significant reduction in yield could reflect thedelay in the seed emergence and stand establishment caused by the gypsum and calciumcarbonate contents. The total fresh weights of the four successive cuts demonstrates thattrifolium is quite tolerant to gypsum content in soils. Data on its performance on a field scale arenot available.
Table 4.2 EFFECT OF GYPSUM CONTENT OF SOILS ON YIELDS (FRESH WEIGHT INGRAMS) OF FOUR CONSECUTIVE CUTS OF TRIFOLIUM GROWN IN POTS (Matar,unpublished work)
Gypsum (%) No. of cuts Total weight
1 2 3 4
0 281.3 133.2 363.0 409.8 1187.2
5 281.6 161.8 316.1 414.5 1174.0
10 260.0 154.9 322.2 432.5 1169.7
20 233.8 143.9 292.6 375.6 1045.9
40 129.6 123.2 282.4 389.1 924.3
Alfalfa
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The performance of alfalfa (Medicago sativa) as a major crop on gypsiferous soils is quiteimpressive. High yields of irrigated alfalfa are recorded on the highly gypsiferous soils of theEbro Valley of Spain (Van Alphen and de los Rios Romero 1971). Amami et al. (1967) reportedyields of 10 tonnes per hectare of alfalfa on light textured gypsiferous soils containing 20 to 25percent gypsum in the root zone. Mardoud (1980) harvested 20 to 60 tonnes per hectare offresh fodder in the first and the second year of cropping. The yields were obtained where alfalfa
was grown in medium deep soils (less than 25 percent gypsum content in the first 45 cm of thesoil profile); and similar yields, 14 and 61 tonnes per hectare were also obtained in shallowergypsiferous soils (15 to 20 cm depth with 25 percent gypsum content). The performance ofvarious alfalfa cultivars tested on the shallow gypsiferous soils of the Euphrates Valley wassignificantly different. The result of variety trials is reported in Table 4.3.
Table 4.3 YIELDS OF ALFALFA GROWN IN SHALLOW GYPSIFEROUS SOILS1
1 15-30 cm deep with less than 25 percent gypsum
Variety Green production (tonnes per hectare) Number of replicates Sensitivity to frost
1st year 2nd year
ASR 13 32.320 66.820 3 Sensitive
ASR 11 32.250 51.130 3 Resistant
Selection 28.00 67.100 2 Resistant
Colient 26.260 65.940 3 Resistant
Heiroprovian 24.540 60.740 2 Resistant
Siwa 23.490 56.200 2 Resistant
Provience 22.950 59.320 2 Sensitive
Moaba 19.640 45.110 4 Resistant
Local 17.600 44.800 4 Sensitive
Europe 17.500 39.650 1 Sensitive
Lahonta 17.160 44.380 2 Resistant
Good performance of alfalfa is also reported by Vieillefon (1976) in Tunisia on soils containingmoderate amounts of calcium sulphate with little surface soil incrustation. Akramov (1981) whorecently studied the effect of alfalfa residues on reclaiming gypsiferous solonchaks, reports thatploughing-under of alfalfa and the addition of manure converted unproductive gypsiferous soils(with >40 percent gypsum) into productive ones. As well as performing well, alfalfa improvesstructure in gypsiferous soils and increases their productivity.
Other Winter Crops
Other cereal crops can be grown on gypsiferous soils with success. Loomis (1944) shows thatthe yields of oats (Avena sativa) improved slightly in the presence of gypsum in a potexperiment.
4.3 Summer Crops
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Many summer crops can be grown on gypsiferous soils with various degrees of success. Theseinclude cotton, sugar beet, potato, groundnut, soybean, sesame, tomato and sunflower.
Cotton
Cotton is an important cash crop. Boyadgiev (1974) notes that crystallized gypsum particles insoils depressed the yield of cotton in the Euphrates Valley. Mardoud (1980) obtained goodyields of cotton (4 tonnes per hectare) in moderately deep gypsiferous soils (with 45 cm of soil,with less than 25 percent gypsum content), 1.94 tonnes per hectare in medium deep sandy soilswith 25 to 50 percent gypsum content in the root zone. Vieillefon (1976) found little effect ofgypsum on the performance of cotton in soils with medium calcium sulphate content at AinZerig. Minashina et al. (1983) observes that yields of cotton grown on grey-brown gypsiferoussoils fell by 16 percent in soils with 10 percent gypsum. A larger decrease in yield was observedin soils with higher gypsum levels. They also observe that the quality of the cotton fibredeteriorates as the gypsum content in the soil increases. Although the field observations in theEuphrates Valley gave promising yields of cotton, greenhouse and recent field studies byMinashina suggest that cotton is not always sufficiently tolerant to gypsum. More research isneeded to study the effect of gypsum on cotton cultivars in the various gypsiferous soil types.
Sugar beet
Limited work has been done on the suitability and tolerance of sugar beet (Beta vulgaris) ingypsiferous soils. Mardoud (1980) obtained 17.5 to 22.5 tonnes per hectare of autumn-grownsugar beet and 35 tonnes per hectare of spring-cultivated sugar beet in moderately deepgypsiferous soils in the Euphrates Valley. These yield levels are considered moderate.
Corn
Corn (Zea mays) is one of the main crops in the irrigated areas of the arid zone. The effects of
soil gypsum content on corn growth and nutrient composition has been studied by severalworkers, for example
Hernando et al. (1963, 1965). Growth of corn was reduced with the high gypsum levels. Theinteraction between gypsum content and soil moisture stress was found significant in its effecton corn growth and performance. Mardoud (1980) obtained 2 tonnes per hectare of corn seedsgrown in moderately deep gypsiferous soils of the Euphrates Valley. Some foliar symptoms ofmicro-element deficiences were noticed, however.
Soybean
Soybean (Glycine max) is strongly affected by the gypsum content of soils. On the sandy
gypsum soils of the Euphrates Valley (25 to 50 percent gypsum content) it gave very low yieldsof about 0.4 tonnes per hectare of grain seeds (Mardoud 1980). Soybean, grown in pots,however, showed a marked tolerance to gypsum. The effects of Rhizobium innoculation, offertilization and of the gypsum content in different gypsiferous soils on seed production were notstudied.
Groundnut
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Groundnut (Arachis hypogaea) is a good leguminous crop for light to medium textured soils.Yields of 1.25 to 1.42 tonnes per hectare of seeds have been obtained in the Euphrates Valleyon sandy gypsiferous soils, with 25 to 50 percent gypsum content (Mardoud 1980). In spite ofadequate P and K fertilization, groundnut grown in pots with 6 kg soil showed a gradualdecrease in fresh weight of tops as the gypsum content increased. The average yield of freshtops dropped by 35 percent at a gypsum content of 40 percent. The effect of gypsum content on
the yield of seed was more pronounced (Figure 4.1). There were no visual signs of nutrientdeficiencies on the plants. There were no nodules on the roots of plants grown in the gypsumtreatments.
Walker et al. (1976) found that application of gypsum to soils low in calcium increased thepercentage of oil in all peanut cultivars; while the nitrogen content of the seed was reduced.Davidson et al. (1983) reports that application of gypsum to groundnuts grown in Georgiaincreased germination and reduced aflatoxin contents by 40 percent.
Figure 4.1 Effect of gypsum content on yield of groundnut tops and seed in a potexperiment
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Tomato
Field tomatoes (Lycopersicum esculentum) showed significant tolerance to gypsum. A yield of17 tonnes per hectare of fruit was obtained when tomato was grown in moderately deepgypsiferous soils in the Euphrates Valley (Mardoud 1980). In recent years, irrigation withsulphate-rich water has been of interest to many scientists studying the growth and yield of
tomato crops. Papadopulos (1984) found that the weight of fresh tomato fruit was decreased byabout 50 percent when irrigated with sulphate-rich water. Similarly, Russo (1983) found thattomatoes grown in gypsiferous-sodic soils gave low yields because they had a small fruitweight. Martinez et al. (1984) report that the total sulphur content in leaves and roots of tomatoplants is significantly increased as the S04 levels in the substrate increase. Increasing the levelo f NO3 in the growing medium increases tomato yields and the total sulphur accumulated in theleaves and roots decreases. However, at high levels of SO4 in the growing medium the additionof NO3 decreases the yield. That leads to the reasonable conclusion that the effect of SO4 is notion specific but is mainly an osmotic effect.
Potato
Potato (Solarium tuberosum) planted in the moderately deep gypsiferous soils of the EuphratesValley with less than 25 percent gypsum content in the top 45 cm gave a poor yield of 7.3tonnes per hectare of tuber. More research is needed to determine the tolerance of potatoes togypsum.
Sesame
Sesame (Sesasum orientale) crop grown in the gypsiferous soils of the Euphrates Valley gavean average yield of 1.8 tonnes per hectare (Mardoud 1980).
Sunflower
The only published work on the effect of gypsum content on sunflower (Helianthus annuus) performance is that of Mardoud (1980) who obtained 1.27 to 1.7 tonnes per hectare of seedgrains on sandy gypsiferous soils, containing 25 to 50 percent gypsum.
Other Summer Crops
Other summer crops for which data are available include:
Sorghum, an important crop for animal feed and human consumption yielded between 2.25 and3.9 tonnes per hectare in the medium deep gypsiferous soils of the Euphrates Valley. However,the yield dropped to less than 0.65 to 1.85 tonnes per hectare when grown in shallower soils (15
to 30 cm thickness with less than 25 percent gypsum content).
Onion, a sulphur-loving plant, yields about 24 tonnes/ha in the sandy gypsiferous soils of theEuphrates Valley. The cooking quality of the bulbs is, however, unsatisfactory and the taste isvery strong.
Figure 4.2 Effect of soil gypsum content on relative yields of leaves and roots of Burleytobacco
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American Burley, the irrigated broad-leaved tobacco, grown in pots with gypsum contentranging between 0 and 40 percent, is extremely sensitive to gypsum. The yield of leavesdropped by more than 95 percent when grown in soil containing 5 percent gypsum or more(Figure 4.2). Complex symptoms of various nutrient deficiencies appeared on the tobacco
leaves. Ryding (1978) found in greenhouse trials, that application of gypsum decreased theyield of flue-cured tobacco although the Ca content of leaves was increased.
4.4 Classification of Field Crops Based on Their Tolerance to Gypsum
The tolerance, yield and product qualities of many agricultural crops grown on gypsiferous soilsare not yet well known. As a first approximation, the main agricultural crops are classified below
into four main groups in relation to gypsum tolerance based on the available data. Thispreliminary classification should be considered a guideline only.
Group I: Tolerant to gypsum - agricultural crops which show tolerance to 40 percent of gypsumin soil without a significant decrease in yield: alfalfa, trifolium, wheat, barley, lentil, oats, tomatoand onions.
Group II: Semi-tolerant to gypsum - agricultural crops which show tolerance to 20 percent ofgypsum in soil without a significant decrease in yield. The yield may drop by about 50 percent athigher levels of gypsum (say 40 percent gypsum). This group includes: broad beans, sugarbeet, sorghum, corn, soybean and sesame.
Group III: Semi-sensitive to gypsum - agricultural crops which show tolerance of up to 10percent of gypsum without a significant drop in yield. Yields fall at higher levels of gypsum. Thisgroup includes: cotton, groundnut, potato and sunflower.
Group IV: Sensitive to gypsum - among the test crops, tobacco was sensitive to gypsum.
4.5 Fruit and Forest Trees
In addition to the gypsum content of the surface layer and its distribution in the profile, manyworkers have found that the hardness and degree of cementation of the gypsic layer is of greatimportance to the success of fruit orchards and forest trees. A cemented layer at shallow depthimpedes the extension of the root system by mechanical resistance and consequently limits thegrowth and production. Kalashnikov and Romanov (1949) found, from some afforestationexperiments conducted on dark chestnut soils overlying gypsum, that the greater the soil depthabove the gypsum layer the more suitable the soils are for afforestation. They also found thatoak (Quercus) and pear trees, 13 to 15 years old, grew 3.5 to 5.0 metres high when the gypsumlayer was at 170 cm from the surface and 2 to 4 metres only when the gypsum layer was at 1.10
to 1.25 metres depth. Mardoud (1980) noticed that the roots of forest trees, such as pines(Pinus halepensis) and eucalyptus, grown in the Euphrates Valley of Syria could not penetrateany gypsic horizon containing more than 60 percent of gypsum. Their roots extend horizontallyand the trees showed signs of weak growth compared with trees grown in soils with no gypsichorizon. Other researchers report that several species were found resistant to gypsum and gavegood yields in highly gypsiferous soils. Van Alphen and de los Rios Romero (1971) cite that highyields of apricots (Amermeniaca vulgaris) were obtained in the Ebro Valley of Spain whengrown on gypsiferous soils with a gypsic layer at a depth of 30 to 60 cm. The average apricotyield obtained in the El Burgo de Ebro was in the order of 8 tonnes per hectare.
A good yield of palms was obtained in gypsiferous soils containing 50 percent gypsum in theoasis of Tozeur, Tunisia (Amami et al. 1967).
Minashina (1956) reported excellent growth of grapevines grown on gypsiferous soils of theKirovabad Massif, even in soils with a gypsic layer at shallow depth. But work carried out in theEuphrates Valley in Syria, has shown that grapevine tolerance to gypsum depends on thevariety grown. Except Muscat and Cardinal, all varieties tested gave a poor growth on themoderately deep gypsiferous soils of the Euphrates Valley (Mardoud 1980). More research isneeded to determine grapevine varieties and rootstocks tolerant to gypsum. In Spain, wineproduced from grapes grown on gypsiferous soils is of poor to medium quality, but table grapesare of good quality (Prof. Roquero, personal communication). In the Murcia area of Spain,
where the soils are highly gypsiferous with a marked petrogypsic horizon, apricots, peaches,pears, olives and grapes are extensively planted. The farmers are very satisfied with the highyields obtained. The peach varieties are grafted onto rootstocks tolerant to soils with a largecalcium content.
Observations on other fruit trees grown in the moderately deep gypsiferous soils of the
Euphrates Valley show that many species tolerate gypsum, including pomegranate (Punica granatum), peaches (Amygdalis persica), plums and figs (Ficus carica) and apricots. Pistachio(Pistacia vera) however shows poor adaptability to gypsiferous soil conditions. Only three of 46trees of local pistachio cultivars remained alive after four years.
Several papers have been published recently on the effect of high sulphate-rich waters on ionadsorption and fruit quality of lemon trees. Cerdá et al. (1982) and Fernandez et al. (1983)found that sulphate ions are not taken up as readily as other soluble ions such as chloride orboron; and never exceeded 240 mmole/kg of plant. These authors believe that some of thesulphate effects reported in the literature might not be the result of sulphate uptake but due tothe salinity of the soil solution. Rind thickness and rugosity were the only fruit qualitycharacteristics affected by the sulphate application. The effect of the gypsum content in soils on
the yield of lemon trees and other citrus varieties is not yet known.
Boukhris and Lossaint (1970, 1972) in a study conducted on the gypsiferous soils of Tunisia,found that resinous trees including Pinus halepensis and other oligophore trees absorb few ofthe ions present in gypsiferous soils and control their uptake of ions very efficiently. They arepoor in all mineral nutrients especially potassium and calcium. Constant Mg, S, N and Pcontents were observed in pines and other trees grown under the various climatic conditions ofthe gypsiferous soils of Tunisia. The low levels of nutrients in pines make them quite successfuland adaptable to all types of soil environments including gypsiferous ones. Wild (1974) founddwarfing of woody species, particularly of Colophospermum mopane, grown on a gypsumdeposit in Botswana. He attributed the dwarfing partly to the poor physical properties of thesecompacted and clayey soils.
The available information on the tolerance of various species of fruit trees and their rootstocksto the gypsum content of soils is still inadequate. Much more information is needed on theperformance and adaptation of various tree species to the gypsiferous soils, and on the effect ofgypsum on fruit yield and quality.
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance
found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural
lime, and is usually the principal cause of hard water. It is commonly used medicinally as a
calcium supplement or as an antacid, but excessive consumption can be hazardous.
that becomes important at high use temperatures.[8]
It also routinely used
as a filler in thermosetting resins (sheet and bulk molding compounds)[8]
and has also been mixed with ABS, and other ingredients, to form some
types of compression molded "clay" poker chips. Precipitated calcium
carbonate, made by dropping calcium oxide into water, is used by itself
or with additives as a white paint, known as whitewashing.
Calcium carbonate is added to a wide range of trade and do it yourself adhesives, sealants, and decorating fillers.[7] Ceramic tile adhesives
typically contain 70 to 80% limestone. Decorating crack fillers contain
similar levels of marble or dolomite. It is also mixed with putty in settingstained glass windows, and as a resist to prevent glass from sticking to
kiln shelves when firing glazes and paints at high temperature.
In ceramics / glazing applications, calcium carbonate is known as
whiting,[7] and is a common ingredient for many glazes in its white
powdered form. When a glaze containing this material is fired in a kiln,the whiting acts as a flux material in the glaze. Ground calciumcarbonate is an abrasive (both as scouring powder and as an ingredient of
household scouring creams), in particular in its calcite form, which has
the relatively low hardness level of 3 on the Mohs scale of mineralhardness, and will therefore not scratch glass and most other ceramics,
enamel, bronze, iron, and steel, and have a moderate effect on softer
metals like aluminium and copper. A paste made from calcium carbonate
and deionized water can be used to clean tarnish on silver.[9]
[edit] Health and dietary applications
500-milligram calcium supplements made from calcium carbonate
Calcium carbonate is widely used medicinally as an inexpensive dietarycalcium supplement or gastric antacid.[10] It may be used as a phosphate
binder for the treatment of hyperphosphatemia (primarily in patients with
chronic renal failure). It is also used in the pharmaceutical industry as aninert filler for tablets and other pharmaceuticals.[11]
Calcium carbonate is known among IBS sufferers to help reduce
diarrhea. Some individuals report being symptom-free since startingsupplementation. The process in which calcium carbonate reduces
diarrhea is by binding water in the bowel, which creates a stool that is
firmer and better formed. Calcium carbonate supplements are often
combined with magnesium in various proportions. This should be takeninto account as magnesium is known to cause diarrhea.
Calcium carbonate is used in the production of toothpaste and has seen a
resurgence as a food preservative and color retainer, when used in or
with products such as organic apples or food.[12]
Excess calcium from supplements, fortified food and high-calcium diets,
can cause the milk-alkali syndrome, which has serious toxicity and can
be fatal. In 1915, Bertram Sippy introduced the "Sippy regimen" of hourly ingestion of milk and cream, and the gradual addition of eggs and
cooked cereal, for 10 days, combined with alkaline powders, whichprovided symptomatic relief for peptic ulcer disease. Over the nextseveral decades, the Sippy regimen resulted in renal failure, alkalosis,
and hypercalcemia, mostly in men with peptic ulcer disease. These
adverse effects were reversed when the regimen stopped, but it was fatalin some patients with protracted vomiting. Milk alkali syndrome
declined in men after effective treatments for peptic ulcer disease arose.
During the past 15 years, it has been reported in women taking calcium
supplements above the recommended range of 1.2 to 1.5 g daily, forprevention and treatment of osteoporosis, and is exacerbated by
dehydration. Calcium has been added to over-the-counter products,
which contributes to inadvertent excessive intake. Excessive calciumintake can lead to hypercalcemia, complications of which include
vomiting, abdominal pain and altered mental status.[13]
As a food additive it is designated E170[14]; INS number 170. Used as an
acidity regulator, anticaking agent, stabiliser or colour it is approved for
usage in the EU,[15]
USA[16]
and Australia and New Zealand.[17]
It is usedin some soy milk products as a source of dietary calcium; one study
suggests that calcium carbonate might be as bioavailable as the calcium
in cow's milk .[18]
Calcium carbonate is also used as a firming agent in
many canned or bottled vegetable products.
[edit] Environmental applications
In 1989, a researcher, Ken Simmons, introduced CaCO3 into theWhetstone Brook in Massachusetts.[19] His hope was that the calcium
carbonate would counter the acid in the stream from acid rain and save
the trout that had ceased to spawn. Although his experiment was asuccess, it did increase the amounts of aluminium ions in the area of the