Abiotic Diseases

Failure of nodulation or nodule function because of various edaphic factors leads to severe nitrogen deficiency in lentil on fields low in inorganic nitrogen. Lack of efficient strains of Rhizobium leguminosarum, waterlogging, excessive heat and deficiencies of such essential nutrients as phosphorus, potassium, sulfur, calcium, cobalt, copper and molybdenum can cause nitrogen deficiency by adversely affecting the process of symbiotic nitrogen fixation. Plants infested with such insects as Sitona sp., whose larvae damage nodules, increase the nitrogen deficiency in lentil on nitrogenpoor soils.

Symptoms: The whole plant becomes light green, lower (older) leaves become yellow and dry to light brown (Fig. 41) and the stem remains short and slender.
        At an advanced stage, the plant is defoliated and flowering and pod growth are very much reduced (Fig. 42). Plants tend to mature earlier than healthy plants.

Control: The most effective control is by correction of the edaphic conditions that impair biological nitrogen fixation. Top dress with inorganic nitrogen fertilizer at a rate of 15-20 kg N/ha until symbiotic nitrogen fixation can function at optimum level.
         A foliar spray of nitrogen fertilizer at a concentration of about 0.5% N is effective if there is adequate foliar surface.

Fig. 41

Fig. 42

Phosphorus deficiency is generally encountered on sandy or eroded soils or soils with extremes of pH. Lentils grown on soil with less than 4.0 ppm of available P may develop deficiency symptoms. Phosphorus deficiency is accentuated under drought conditions. Under high production environments, intensive cropping without the use of phosphatic fertilizers can lead to the development of phosphorus deficiency.

Symptoms: Plants become dark green with red or purplish discoloration on soils amply supplied with available nitrogen. The leaflet size is reduced and branching is severely curtailed. Older leaves sometimes become yellowish and dry to greenish brown or black (Fig. 43).
        On soils deficient in available nitrogen, phosphorus deficiency results in the development of typical nitrogen deficiency symptoms (Fig. 42).
        Flowering, podding and maturity are delayed and podding is sparse.

Control: By the time typical symptoms of phosphorus deficiency are observed, it is generally too late to correct the deficiency. However, if foliage development is adequate, foliar fertilizer application can help. A 1-2% solution of triple superphosphate is recommended.
        Preventive measures include application of P₂O₅ at 40-50 kg/ha as single or triple superphosphate, placed in a band beside or below the seed on soils low in available phosphorus.

Fig. 43

Like phosphorous deficiency, zinc deficiency is common on eroded soils or soils with excessively high pH. Use of high concentration macronutrient fertilizers in intensive cropping systems, without application of zinc-bearing substances, can lead to zinc deficiency, particularly when high rates of phosphatic fertilizers are used. In lentils grown on soils with an available dithizone-extractable) zinc content of less than 0.5 ppm, deficiency commonly appears.

Symptoms: The symptoms are generally localized on older leaves. The interveinal tissue develops yellowing and necrosis in small patches on the leaflets, which quickly enlarge (Fig. 44).
        The leaflet size and internodal length are considerably reduced so that plants have a rosette appearance in the field. Under low temperature conditions, the plants may develop conspicuous purplish discoloration on the leaflets.

Control: Correct the deficiency with a foliar application of 4-5 kg zinc sulphate with 2-2.5 kg lime per hectare.
        Use a zinc-containing foliar fertilizer formulation available in the market.
        Preventive measures include using zinc sulphate at 15-25 kg/ha as a soil application on soils with a low available zinc content.

Fig. 44

This deficiency generally occurs in fields with soils that are acidic or low in available potassium. The soils of most of the lentil-growing areas in the Indian subcontinent and West Asia and North Africa are adequately supplied with available potassium; hence deficiency is rarely observed.

Symptoms: At the early stages of deficiency, the lower (older) leaves show development of chlorosis at the tips of leaflets (see Fig. 41). As the deficiency advances, these tissues become necrotic, although the rest of the leaflet remains green. Nodulation is sparse.
        Advanced deficiency of potassium under low nitrogen conditions in the soil leads ultimately to conspicuous nitrogen deficiency symptoms and reduced growth.

Control: A foliar spray of potassium-bearing inorganic fertilizers (potassium nitrate or potassium sulphate) as a 0.3-0.5% solution will help alleviate the deficiency.
        Preventive measures include use of potassium fertilizer (K₂O) at 40-50 kg/ha on soils low in available potassium.

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