Sulphur is an important plant nutrient necessary to produce bountiful food crops. Grains, fruits and vegetables and pasture crops all need sulphur to sustain growth. Visual cues and soil tests can be used to identify potential sulphur deficiencies.
Historically crops got their sulphur from the environment via SO2 gas from industrial processes entering the sulphur cycle in large quantities. Today, crops aren’t receiving the necessary amounts of sulphur from the atmosphere alone. Why the change? Regulations altering the composition of fuels and other pollution controls improved air quality for humans but lowered the amount of sulphur compounds available in the atmosphere for plants.
Also impacting sulphur availability is the increasing scale of agriculture. More sulphur is removed from the soil as a result of an increase in agricultural production by increasing fertilizer use, intensifying cropping systems, promoting high-yield crop varieties, and improving irrigation.
Further, less sulphur is added to the soil due to the increasing proportions of high-analysis, sulphur-free fertilizers, such as urea, diammonium phosphate (DAP), and potassium chloride; decreasing use of traditional organic manures; and reduction in use of sulphur-containing fertilizers.
Soil Analysis: A number of chemical methods have been developed and tested for estimating the available sulphur status of soils. The important thing is the selected method should be accurate, precise, rapid and highly correlated with crop response to sulphur application. The most often used method in India and some other places involves extraction of soil sulphur with 0.15 percent solution of CaCl2. Soils containing less than 10 ppm sulphur are considered to be low or deficient in plant available sulphur by this method. Globally, monocalcium phosphate is also a popular extrant.
Plant Analysis: Plant analysis is carried out by standard analytical methods. Normally leaves of cereal plants containing less than 0.2 percent sulphur are considered to be deficient in sulphur and require sulphur application for optimal growth and yield production. The optimal sulphur concentration in growing plants is usually higher for legumes and cruciferous crops than for cereals.
Whenever the sulphur status of growing plants drops below the critical level required, visual symptoms of sulphur deficiency start appearing on the plant. The appearance of such symptoms indicates a serious condition because crop yields can decrease even without the appearance of such symptoms.
Sulphur deficiency symptoms in many ways resemble those of nitrogen - that is, the leaves become pale-yellow or light-green. Unlike nitrogen, sulphur -deficiency symptoms appear first on the younger leaves, and persist even after nitrogen application. In cotton, tobacco and citrus, some of the older leaves are affected first.
Plants deficient in sulphur are small and spindly with short and slender stalks, their growth is retarded, maturity in cereals is delayed, nodulation in legumes may be poor and nitrogen-fixation reduced, fruits often do not mature fully and remain light-green in color, forages contain an undesirably wide N:S ratio and thus have lower nutritive value.
When sulphur deficiency symptoms have been confirmed, soil application through a material containing readily available sulphur should be applied.
Banana: Young leaves show chlorosis (loss of green color resulting in pale yellow tissue) but as they age, the green color returns. Youngest uncurled leaves become yellowish-white as the deficiency progresses. If S-deficient conditions continue, chlorosis is clearer and pale stripes become visible between the veins. Growth is retarded and small fruits are produced.
Blackgram (Urid): Chlorosis starts from the tips of young leaves and spreads along the margin. Young leaves which emerge after onset of S deficiency are severely chlorotic. Stems become thin and woody. Plants have a bushy appearance.
Chickpea (Gram, Bengal gram): Sulphur deficient plants appear erect. There is premature drying and withering of young leaves. Eventually entire foliage (leaf mass) turns chlorotic. Nodulation and thus N fixation is severely restricted and so is the seed setting.
Coconut: Typical symptoms are yellowish-green or yellowish-orange leaflets. Leaves droop as the stem becomes weak. In older palms, leaf number and size are reduced. Sometimes an apron of dead fronds develops around the stem due to weakness of the rachis. Nuts may fall prematurely. The kernel (copra) is rubbery and of poor market quality.
Coffee: There is yellow discoloration on the youngest pair of leaves. A general chlorosis of mature leaves is characteristic with newer leaves smaller in size and usually more chlorotic than the mature leaves. Interveinal tissue can become severely chlorotic and give a mottled appearance.
Cotton: Persistent yellowing of new leaves and reddening of the petiole is visible. Older leaves may be affected first.
Cowpea (Lobia): Plants remain stunted with short internodes. Young leaves turn pale and their size is reduced. Flowering is delayed. New leaves are chlorotic and fail to expand. Number of pods and seed yield is low.
French bean: Plants have short internodes, fewer and smaller leaves. The entire foliage appears pale green. Growth is poor and yield is low.
Greengram (Moong): Plants are stunted, branching is poor and they have a bushy appearance. Flowers are drastically reduced and pods have shrunken seeds.
Groundnut: Young plants are smaller than normal, pale and more erect from the petiole than normal plants giving the trifoliate leaves a “V” shaped appearance. Older leaves may remain green. In new leaves, area around the main vein may be pale. Nodulation and pod formation is restricted and maturity of seeds is delayed.
Horsegram (Kulthi): The entire leaf turns pale followed by interveinal (area between the veins) chlorosis of leaflets of young leaves. Under severe deficiency, symptoms spread from young to middle leaves.
Linseed: Yellowing, curling and premature drying of tips of young terminal (top most) leaves is evident. Chlorosis gradually spreads on old leaves. The stem remains slender with poor branching. Number of floral buds is reduced and most of these fail to open.
Maize: Yellowing between the veins along the entire length of the leaves is seen especially in younger, upper leaves. In later stages, reddening at the base of the stem and along the leaf margins may occur.
Oilpalm: Seedlings have small pale-green to almost white fronds and show some interveinal streaking while older leaves develop necrotic spots (dead tissue) followed by terminal necrosis.
Pea: Young leaves turn pale followed by chlorosis of interveinal areas first on young leaves and then on middle and old leaves. Root nodulation and hence N fixation, flowering and yield is reduced.
Pigeonpea (Arhar): Young and middle leaves turn yellow, branching, leaf size and flowering are suppressed. Flowers lack normal yellow color and shed early. Pod formation and seed development is retarded.
Pineapple: Leaves first become yellowish-green. Later, margins of the older leaves become pinkish red and such discoloration spreads to all the leaves. In the end, neither flowers nor fruits are formed.
Potato: There is pronounced inward curling of youngest leaves along with considerable yellowing of the stems. General yellowing of the plant is observed.
Rapeseed Mustard: Cupped leaves and a reddening of the underside of leaves and stem is observed. Flowers abort prematurely resulting in poor pod formation. Sulphur deficiency reduces oil content in seeds and thus lowers the economic yield. This holds true for all oil crops.
Rice: Initially the leaf sheath and then the leaf blade become yellowish. The whole plant may look chlorotic at tillering stage. Plant height and number of tillers are reduced. Panicles are fewer, shorter and bear fewer spikelets/grains than normal plants.
Rubber: The entire leaf may turn yellowish-green, is reduced in size and has typical brown necrotic spots at the tip and sometimes all over the surface. Leaves of young shoots are first to be affected.
Sesame: Growth is retarded, leaves are smaller and fully emerged leaves first turn pale and then golden yellow. Number of flowers and pods, hence yield is reduced.
Sorghum: Blades of young leaves are shorter and more erect than usual. At first, these turn pale green while older leaves remain green. In very severe deficiency, older leaves also turn pale green.
Soybean: New leaves continue to remain pale-yellowish green. Size of leaves and length of internodes is reduced. Chlorosis starts from leaf margins and spreads inwards. Under severe deficiency, the entire plant may turn yellow leading to premature leaf fall, reduced flowering and fruiting.
Sugarcane: Younger leaves develop a uniform yellowish-green color. Later, younger and older leaves show a faint purplish tinge. Stems are thinner and taper towards the tip.
Sunflower: Leaves and inflorescence (flowers) become pale. Plants are markedly smaller with shorter internodes than normal. Number and size of leaves remain small.
Tea: Sulphur deficiency is known as “tea yellows”. Leaves of S deficient bushes turn yellow, are reduced in size, the internodes are short and the entire plant appears shrunken. Under severe deficiency, leaves may curl up and their edges and tips turn brown. Axial buds produce dwarf yellow leaves.
Tobacco: Older leaves are affected first. New leaves are uniformly pale yellow-green and this condition extends to the whole plant with time. Leaves are smaller and internodes are shorter than normal.
Tomato: Plants are smaller and lighter green in color than normal. Yellowing may occur in various plant parts. In the case of severe deficiency, petioles and stems show a marked reddening.
Wheat: General yellowing of the plant is observed which is usually more prominent between the veins. Older leaves remain green.