The Trials Of Ms Americana.rar

The Trials Of Ms Americana.rar

DOWNLOAD --->>> https://urlca.com/2t7Gh5

3. SALINE SOILS AND THEIRMANAGEMENT 3.1 Characteristics 3.2 Reclamation andmanagement 3.3 Crops in salinesoils 3.1 Characteristics 3.1.1 Measuring salinity status 3.1.2 Salinity and plant growthThe distinguishing characteristic of saline soils from theagricultural standpoint, is that they contain sufficient neutral soluble saltsto adversely affect the growth of most crop plants. For purposes of definition,saline soils are those which have an electrical conductivity of the saturationsoil extract of more than 4 dS/m at 25°C (Richards 1954). This value isgenerally used the world over although the terminology committee of the SoilScience Society of America has lowered the boundary between saline andnon-saline soils to 2 dS/m in the saturation extract. Soluble salts mostcommonly present are the chlorides and sulphates of sodium, calcium andmagnesium. Nitrates may be present in appreciable quantities only rarely. Sodiumand chloride are by far the most dominant ions, particularly in highly salinesoils, although calcium and magnesium are usually present in sufficientquantities to meet the nutritional needs of crops. Many saline soils containappreciable quantities of gypsum (CaSO4, 2H2O) in theprofile. Soluble carbonates are always absent. The pH value of the saturatedsoil paste is always less than 8.2 and more often near neutrality (Abrol et al.,1980). Physico-chemical characteristics in respect of a few typical saline soilprofiles are presented in Tables 5-8.Excess salts keep the clay in saline soils in a flocculatedstate so that these soils generally have good physical properties. Structure isgenerally good and tillage characteristics and permeability to water are evenbetter than those of non-saline soils. However, when leached with a low saltwater, some saline soils tend to disperse resulting in low permeability to waterand air, particularly when the soils are heavy clays. Leaching may also resultin a slight increase in soil pH due to lowering of salt concentration but salinesoils, as will be shown later, rarely become strongly sodic upon leaching ifthere is an adequate drainage system.In field conditions, saline soils can be recognized by thespotty growth of crops and often by the presence of white salt crusts on thesurface. When the salt problem is only mild, growing plants often have ablue-green tinge. Barren spots and stunted plants may appear in cereal or foragecrops growing on saline areas. The extent and frequency of bare spots is oftenan indication of the concentration of salts in the soil. If the salinity levelis not sufficiently high to cause barren spots, the crop appearance may beirregular in vegetative vigour.Moderate salinity, however, particularly if it tends to beuniform throughout the field, can often go undetected because it causes noapparent injuries other than restricted growth. Leaves of plants growing in saltinfested areas may be smaller and darker blue-green in colour than the normalleaves. Increased succulence often results from salinity, particularly if theconcentration of chloride ions in the soil solution is high. Plants insalt-affected soils often have the same appearance as plants growing undermoisture stress (drought) conditions although the wilting of plants is far lessprevalent because the osmotic potential of the soil solution usually changesgradually and plants adjust their internal salt content sufficiently to maintainturgor and avoid wilting.Symptoms of specific element toxicities, such as marginal ortip burn of leaves, occur as a rule only in woody plants. Chloride and sodiumions and boron are the elements most usually associated with toxic symptoms.Non-woody species may often accumulate as much or more of these elements intheir leaves without showing apparent damage as do the woody species. Table 5 CHARACTERISTICS OFTYPICAL SALINE SOILS* pHS - pH measured on soil saturatedpaste.Table 6 TYPICAL SALINE SOIL REPRESENTING ADDALA SERIES,IRAQ (Sehgal, 1980) Depth cm Mechanical Composition % pHs ECe dS/m Composition of the Saturation Extract me/l SAR Organic Matter % Clay beans atthe cool location to beets > onions > beans at the hotlocation.Table 15 RESPONSE OF THREE CROPS TO SALINITY IN SANDCULTURES AT TWO LOCATIONS Crop Solution salinity at which 25% yield reduction was observed dS/m Cool location Hot location Bean pods 4.0 3.0 Garden beetroots 11.1 6.6 Onion bulbs 12.5 3.3 In some parts of India rice is grown both duringthe rainy season (kharif) and during the dry season (rabi). Data in Table 16 arethe relative average yields of eight rice varieties grown in kharif and rabiseasons at four salinity levels (Murthy and Janardhan, 1971). The data clearlyindicate that the yield reduction with increasing salinity was much more in thedry than in the wet season.Table 16 EFFECT OF SEASON ON THE RELATIVE RICE YIELDS(Murthy and Janardhan, 1971) Salinity of root zone dS/m (approximate range) Relative yield Wet Season Dry Season Control (non saline) 100 100 2-4 93 81 4-8 63 53 10-12 39 11 Note: Relative yields are comparable only withinthe same season.Sinha and Singh (1974, 1976) studied the effect oftranspiration rate on the accumulation of sodium and chloride ions near the rootsurface of maize and wheat crops under controlled conditions. Their studiesshowed that the sodium and chloride contents of the soil closely adhering to theroots were linearly related to the total amount of water transpired by theplants as well as the water transpired per unit root length. Based on thesestudies it was pointed out that the stress to which plants are subjected insaline soils would be determined by the evaporative demand during growth andcould be much greater than that indicated by the electrical conductivity of thebulk soil. These results explain the observed differences in plant responses tosalinity in different climatic conditions reported by several workers.Apart from the atmospheric evaporative demand, some workers(Hoffman et al., 1975) have shown that air pollution may increase theapparent salt tolerance of many crops. For example, with alfalfa, grown at ozoneconcentratons often prevalent in several agricultural areas, yields were highestat moderate salinity levels that normally reduced growth. Because some crops areaffected more by air pollutants when grown under non-saline than under salineconditions, they may appear more salt tolerant in air polluted areas.iii. Varietal differences in salt toleranceDifferences in varietal tolerance to salinity and otheradverse soil conditions have been known to exist for decades but it is only inthe latest decades that serious efforts have been initiated to exploit thegenetic potential of salt-tolerant crop varieties through different breedingprogrammes.Rice has long been grown in the coastal regions of India andother countries where salinity is a perpetual problem due to inundations fromthe sea, and intrusion of sea water through rivers, estuaries, etc. Screening ofa large range of rice germ plasm collected at different saline areas in Indialed to the identification of several genotypes that are extremely salt tolerant(Bhattacharya, 1976) (see Table 17).Table 17 SALT-TOLERANT RICE VARIETIES FROM DIFFERENT STATESIN INDIA (Bhattacharya, 1976)StateVarietiesAndhra PradeshMCM 1; MCM 2KeralaPokhaliMaharashtraKala Rata; Bhura RataOrissaSR 26 BWest BengalMatla, HamiltonTamil NaduPVR ICSSRI, CanningDamodar, Dasal, GetuThough most of these rice varieties are highlytolerant of salinity, all the varieties are tall indica and photosensitive typesand have a low yield potential compared to the dwarf high-yielding types. Inrecent years systematic breeding efforts have been made and some of the tolerantgenotypes used extensively in a hybridization programme with high yielding linesto act as donors for salinity tolerance. Some of the cultures which have nowbeen released for large scale cultivation in the saline areas possess goodagronomical traits in addition to tolerance to salinity.Apart from hybridization, mutation breeding approaches weretried and some promising cultures, Mut-1 (CSR4), evolved from the widelycultivated high-yielding variety IR-8 (Sinha and Borah, 1980). In recent yearsintensive efforts have been made at the International Rice Research Institute atLos Banos in the Philippines to breed varieties for tolerance to various adversesoil conditions and many advanced lines in IRRI’s breeding programme showtolerance for one or more adverse soil factors (Ponnamperuma, 1977; Ikahashi andPonnamperuma, 1978).Researchers at the University of California at Davis arebreeding barley for culture with sea water irrigation (Epstein, 1976). Lineshave been developed which survive and set seed (yields in the order of 1188kg/ha) under irrigation with undiluted sea water. Similar breeding is underwaywith wheat.The same researchers screened for salt tolerance in tomatocultivars with little success. However a wild tomato, Lycopersiconcheesmannii, collected from sites close to the shore on the GalapagosIslands was able to survive in saline culture equivalent in salinity to seawater. While the fruit of the wild species is too small for commercial use,F-progeny of crosses of the wild species and commercial cultivars includesegregates with acceptable fruit size (similar to cherry tomatoes) and toleranceto a salinity equivalent to one-third that of sea water (Epstein,1976).Shannon (1978) screened for salt tolerance 32 accessions oftall wheatgrass, Agropyron elongatum (Host) Blauv., a forage grass usedon the western rangelands of the United States. He classified plants by abilityto recover from salt stress and identified seven tolerant genotypes from diversegeographic origins for continued selection.A long-term programme of evaluation and selection of avocadorootstocks for tolerance of salinity has resulted in the development of verysuccessful avocado orchards in regions with saline irrigation water in Israel(Kadman and Ben-Ya’Acova, 1976).Efforts are also being made in different parts of the world toinduce tolerance to salinity in other field crops. Rana et al. (1980)indicated the promising role of polyploid breeding in evolving crop varietiessuited to problem soils. It is apparent that breeding crop varieties tolerant tosalinity offers significant opportunities for better management of areas wheresalinity is a perpetual problem. Figure 10 Effect of increasingsalinity level on the chloride content of leaves of six citrus root stocks(Cerda et al., 1977)iv. Rootstocks and salinitytoleranceMost fruit crops are more sensitive to salinity than arefield, forage or vegetable crops (Figure 8h). Grapes, citrus, stone fruits, pomefruits, berries and avocados are all relatively sensitive to salinity. However,certain stone-fruits, citrus and avocado rootstocks differ in their ability toabsorb and transport sodium and chloride ions and have, therefore, differentsalt tolerance. Cerda’ et al. (1977) studied the effect of sodiumchloride in the irrigation water on the foliar contents of chloride and sodiumof six citrus rootstocks, viz., Sour orange (Citrus aurantium L.), Troyercitrange (Poncirus trifoliata x Citrus sinensis), Cleopatramandarin (Citrus reticulata Blanco), Allemow (citrus macrophyllaWester), Nanshodaidai (Citrus taiwanica) and Kinnow mandarin(Citrus nobilis Loureiro x Citrus deliciosa Tenore). Their resultsshowed that mandarin as a group was characterized by a marked capacity toexclude chloride ions while the sour orange and Troyer citrange varieties, ingeneral, accumulated high amounts of chloride ions (Figure 10). Similar resultswere earlier reported by Cooper (1961) and other investigators. Bernstein (1965)pointed out that for many fruit crops damage to the plants could be related tothe concentration of specific ions, e.g. chloride or sodium in the soil solutionand/or plant leaves rather than to the total soil salinity. Thus, the specificinjury symptoms appeared before any effect of total salt concentration wasobserved. For instance, a chloride level of 10 mmol/l in a saturated pasteextract is considered toxic to sensitive rootstocks although the same rootstockcan tolerate a higher total salinity if it is not due to chloride salts. Forthis reason, classification of fruit crops with respect to specific salinityaccording to varieties and rootstocks is important. Such a toleranceclassification was presented by Bernstein (1965) and is reproduced in Table18.Table 18 TOLERANCE OF FRUIT VARIETIES AND ROOT STOCKS TOCHLORIDE LEVELS (Bernstein, 1965) Crop Rootstock/Variety Limit of tolerance to chloride in soil saturation extract mmol/l Rootstocks Citrus (Citrus spp.) Rangpur lime, Cleopatra mandarin 25 rough lemon, tangelo, sour orange 15 sweet orange, citrange 10 Stone fruit (Prunus spp.) Marianna 25 Lovell, Shalil 10 Yunnan 7 Avocado (Persea americana Mill.) West Indian 8 Mexican 5 Varieties Grape (Vitis spp.) Thompson seedless, Perlette 20 Cardinal, Black rose 10 Berries (Rubus spp.) Boysenberry 10 Olallie blackberry 10 Indian Summer raspberry 5 Strawberry (Fragaria spp.) Lassen 8 Shasta 5 Most fruit crops are also sensitive to other toxicelements, particularly boron. This ion is present in most irrigation water andin saline soils. It is toxic to many plants at a concentration only slightly inexcess of that required for optimum growth. Small quantities of boron absorbedby the roots are accumulated by the leaves and values above 250 ppm result intypical leaf burns. A grouping of plants according to their relative toleranceto boron is presented in Table 45. The data show that fruit crops, in general,are more sensitive to boron in irrigation water and soils compared to fieldcrops. Significant reductions in yield of most field crops due to excess boronalone under field conditions have rarely been reported. 3.3.3 Water managementi. Irrigation frequencyModifying water management through appropriate irrigationpractices can often lead to increased crop yields under saline soil conditions.Most plants require a continuous supply of readily available moisture to grownormally and produce high yields. After an irrigation the soil moisture contentis maximum and the salt concentration or the osmotic pressure of the soilsolution is minimal: favourable for crop growth. As the soil progressively driesout due to evapo-transpirational losses the concentration of salts in the soilsolution and, therefore, its osmotic pressure increases making the soil waterincreasingly difficult to be absorbed by the plants. Thus infrequent irrigationaggravates salinity effects on growth. On the other hand, more frequentirrigations, by keeping the soil at a higher soil moisture content prevent theconcentration of salts in the soil solution and tend to minimize the adverseeffects of salts in the soil. For these reasons crops grown in saline soils mustbe irrigated more frequently compared to crops grown under non-saline conditionsso that the plants are not subjected to excessively high soil moisture stressesdue to combined influence of excess salts and low soil water contents. Figure 11depicts changes in the total soil moisture stress to which the growing plantsare subjected in a non-saline soil compared to a saline soil. Several studieshave shown that growth of plants was reduced nearly proportionally to the areasunder the curves. Thus, when the areas under two such dissimilar stress curvesas A and B were equal, the growth of plants was found to be reduced to nearlythe same level. If the saline soils were irrigated infrequently plants would besubjected to very high soil moisture stresses with consequent yieldlosses. Figure 11 Changes in total moisturestress in a saline and a non-saline soil in the interval between twoirrigationsii. Irrigation methodIrrigation method can play an important role in controllingsalts in the root zone. It has been discussed that frequent irrigations arehelpful in saline soils in maintaining adequate availability of soil water.Sprinkler irrigation is an ideal method for irrigating frequently and with smallquantities of water at a time. Leaching of soluble salts is also accomplishedmore efficiently when the water application rates are lower than theinfiltration capacity of the soil and such a condition cannot be achieved byflood irrigation methods. In a field experiment (Nielsen et al., 1966) floodirrigation required three times as much water as sprinkling to reduce soilsalinity by the same increment. Sprinkler irrigation also has the advantage thatsmall local differences in the level of the field will not cause non-uniformwater application and salt leaching.In the trickle or drip irrigation method water is suppliedcontinuously at a point source and in the immediate vicinity of plant roots. Themethod is suitable for perennial or seasonal row crops; it has been foundparticularly useful when irrigating with water of high salinity. The method hasthe advantage that it keeps the soil moisture continuously high in the rootzone, therefore maintaining a low salt level. The roots of the growing plantstend to cluster in the high soil moisture zone near the tricklers and thereforeavoid the salts that accumulate at the wetting front. Results of field trials tocompare sprinkler and drip irrigation methods using water of two qualities arepresented in Table 19. The good quality water had an electrical conductivity of0.4 dS/m and the saline water an electrical conductivity of 3dS/m.Table 19 EFFECT OF IRRIGATION METHOD AND WATER QUALITY ONTHE YIELD OF TOMATOES, t/ha (Goldberg et al., 1976) Irrigation method Electrical conductivity of water dS/m 0.4 3.0 Drip 66.7 65.0 Sprinkler 52.0 39.2 The yield difference between the two methods ofwater application was greater when saline water was used. Further, the yieldobtained by the drip method with saline water was almost equal to that producedwhen the high quality water was applied by this method. A more favourabledistribution of salts in the soil profiles with drip irrigation in comparisonwith the sprinkler and furrow methods was also shown at the end of the growingseason on a sweet corn plot (Figure 12), although in the drip irrigation methodappreciable salt accumulation is likely to occur between the rows depending onthe inter and intra row space between the drip points. Although sprinkler andtrickle irrigation methods are highly efficient, both from the view of water useand salinity control, their high initial costs often preclude their use inregions where transport infrastructure and markets are not highlydeveloped.A soil factor of considerable importance in relation to growthof plants is the location of salts in relation to root zone or seed placement.Irrigation practices can often be modified to obtain a more favourable saltdistribution in relation to seed location or growing roots. It is well knownthat salts tend to accumulate in the ridges when using furrow type irrigation.The direction of movement of applied water and dissolved salts (arrows) is shownin Figure 13. With each irrigation salts leach out of the soil under the furrowsand build up on the ridges. Where soil and farming practices permit, furrowplanting may help in obtaining better stands and crop yields under salineconditions. Figure 12 Salinity profiles insweet corn under drip, sprinkler and furrow irrigation methods (Goldberg et al.,1976) Figure 13 Direction of salt flowand salt accumulation in furrow irrigation. The zone of maximum saltaccumulation is in the top of the ridges Figure 14 The pattern of saltbuild-up depends on bed shape and irrigation method. Seeds sprout only when theyare placed so as to avoid excessive salt build-up around them (Bernstein etal., 1955)Certain modifications of the furrow irrigationmethod including planting in single/double rows or on sloping beds, are helpfulin getting better stands under saline conditions. Typical patterns of saltaccumulation under different types of beds are shown in Figure 14. With doublebeds, most of the salts accumulate in the centre of the bed leaving the edgesrelatively free of salts. Sloping beds may be slightly better on highly salinesoils because seed can be planted on the slope below the zone of saltaccumulation.iii. MulchingDuring periods of high evapotranspiration between the twoirrigations and during periods of fallow there is a tendency for the leachedsalts to return to the soil surface. Soil salinization is particularly high whenthe water table is shallow and the salinity of groundwater is high. Anypractices that reduce evaporation from the soil surface and/or encouragedownward flux of soil water will help to control root zone salinity. Sandovaland Benz (1966) and Benz et al. (1967) studied soil salinity changes as effectedby bare fallow and straw mulch on fallow over a three years period. Theirresults showed that on bare fallow a soil mulch should be maintained to inducesalinity reduction. Under straw mulch there was a significant reduction in soilsalinity which resulted in an increased wheat yield of 25 to 50 bushels perhectare in an area where the normal wheat yields were about 62 bushels perhectare. Fanning and Carter (1963) reported significant reduction in root zonesalt concentration of plots where cotton-burr mulch had been applied at the rateof 90 tons per hectare. These workers also reported that periodic sprinkling ofmulched soils resulted in greater salt removal and therefore higher leachingefficiency than did flooding or sprinkling of bare soil (Carter and Fanning,1964).iv. Other practicesCrops vary not only in their tolerance to salinity but also intheir water requirements, optimum growth season, rooting depth and moistureextraction pattern and cultural requirements. Thus, in the absence of properwater and soil management practices, salinity of the soil may be affecteddifferentially under various crop rotations. Cropping sequences which includecrops such as rice, berseem and those requiring frequent irrigations reducesalinity effectively, where drainage is adequate. Therefore knowledge of theexpected salt balance of the root zone under various crop rotations will beextremely helpful in planning the best cropping sequences during and afterreclamation (Massoud, 1976).Changes in the micro relief in the order of a few centimetrescan result in increasing the salt content on the raised spots and betterleaching in the dips. Proper land shaping before cropping can help to correctthese elevation differences. Land levelling that results in the formation ofshallow profiles or an exposure of an impervious layer close to surface mayenhance salinization. Since this operation is executed at an early stage in newsurface irrigation projects, it should be carefully evaluated as a possiblecause of salinization.Tillage is another mechanical operation that is usuallycarried out for seed bed preparation and soil permeability improvement but if itis improperly executed it might form a plough layer or turn a salty soil horizonand bring it closer to the soil surface. Proper monitoring of changes in thesoil will help the timely adoption of corrective mesures for the control ofsalinity that might otherwise be accentuated. 3.3.4 Nutrient availability and uptake byplantsApart from the effect on water availability to plants and thepossible toxic effect of some constituents, excess neutral soluble salts insoils may also interfere with the normal nutrition of crops in saline soils. Ata given level of salinity, growth and yield of crops are likely to be depressedmore when nutrition is disturbed than when it is normal. At moderate saltconcentrations in the soil solution, plants generally try to exclude unwantedions, as far as possible, and promote the uptake of nutrients. With increasingsalt concentration, the uptake of sodium and chloride ions increases sharply.This luxury consumption of ions is essential for the plants to compensate forthe increased outside osmotic pressure but is responsible for growthretardation. Excessive uptake of certain ions, in turn, often results in reduceduptake of some essential plant nutrients causing nutrient imbalances anddeficiencies. Thus, although the available status of a nutrient in a soil mightnot be in a deficient range per se, its application might compensate for thedecreased uptake by plants resulting from the antagonistic effect of excessuptake of certain ions. Results of several studies tend to show thatdeficiencies of the elements K and Ca appear to play an important role in theobserved growth depressions in many saline soils (Finck, 1977). Properfertilization of soils of low or medium salinity should serve to:- supplement nutrients that are present ininsufficient amounts;- supplement nutrients that, although present in sufficientamounts, are not taken up in adequate amounts due to antagonistic effects, e.g.K or Ca; and decrease the uptake of harmful ions, e.g. K against Na or phosphateagainst chloride (Rankovitch and Porath, 1967; Chhabra et al.,1976).High salinity may interfere with the growth and activity ofthe soil’s microbial population and thus indirectly affect thetransformation of essential plant nutrients and their availability to plants.Reduced symbiotic N fixation due to the toxic effect of salts on rhizobia hasbeen reported (Bernstein and Ogata, 1966; Bhardwaj, 1975). Graham and Parker(1964) observed that normal rhizobia associated with pea can tolerate a maximumsalinity up to 4.5 dS/m. Other factors likely to influence the N-fertilizationof crops grown in saline soils include high leaching losses of N asNO3, decreased nitrification rates due to high salinity and thedirect toxic effect of ions such as chloride on the bacterial activity. In manysaline soils, water tables close to the surface can greatly modify thenutritional needs- of crops. Studies brought out that it was possible tocompensate for high water tables by applying N fertilizers to cereals (Figure15), sugarbeets, potatoes, etc. Figure 15 Schematic diagramshowing the effect of fertilization for correction of an unbalanced andinsufficient nutrient supply to plants in saline soils; the columns indicate theplant contents (Nutrient supply without fertilization) (Finck, 1977) Figure 15 Schematic diagramshowing the effect of fertilization for correction of an unbalanced andinsufficient nutrient supply to plants in saline soils; the columns indicate theplant contents (Nutrient supply with fertilization) (Finck, 1977)There have been only a limited number of studies on the effectof salinity on the nutrition of crops in respect of micronutrients. A disturbedbalance in the uptake and composition of major nutrients is bound to influencethe plant composition of micronutrients. Besides the generally known toxiceffects of boron there is a need to understand better the behaviour of Fe, Mn,Zn, Cu, etc., in relation to soil salinity particularly with a view toestablishing limiting values - so far only developed for normal soils. Figure 15schematically demonstrates how a well-adjusted fertilization could improve theyields of crops (Finck, 1977).Figure 16 shows the inverse relationship observed betweenavailable soil phosphorus and the chloride content of wheat straw in pot studies(Singh et al., 1979). Fine and Carson (1954) observed that the application of Pincreased yields of crops markedly and alleviated salt injury symptoms in oatsand barley. They observed a 400 percent increase in yield with a saline soil inspite of its having high available P. Ferguson and Berlin (1963) reported thatmuch higher responses of applied phosphorus occurred on a moderately saline thanon a non-saline soil of comparable available P status. Dregne and Mojallali(1969) reported that the beneficial effect of applied P to wheat and barleycrops was limited up to an ECe of 9 dS/m. These observations show that higherplant responses to applied P occur on moderately saline than on non-salinesoils. Responses to applied P-fertilizers in saline soils cannot be explained onthe basis of soil test values alone as the saline soils, even when containinghigh amounts of extractable P have shown positive responses to appliedphosphorus. This is because in saline soils the availability of P is more afunction of plant root length and area (which is restricted due to salinity) andthe negative effect of excess chlorides on P absorption by roots. Application ofjudicious quantities of P-fertilizers in saline soils helps to improve cropyields by directly providing phosphorus and by decreasing the absorption oftoxic elements like Cl. Figure 16 Effect of available soilphosphorus on the chloride content of wheat straw (Singh et al., 1979)On moderately saline soils, the application of potassicfertilizers may increase the crop yields (Dregne and Mojallali, 1969) either bydirectly supplying K or by improving its balance with respect to Na, Ca and Mg.However under high salinity conditions it is difficult to exclude Na effectivelyfrom the plant by use of K-fertilizers. 2b1af7f3a8