|Soils, Crops and Fertilizer Use: A Field Manual for Development Workers (Peace Corps, 1986, 338 p.)|
NOTE: Before trying to diagnose hunger signs, read over the section in Chapter 7 on their usefulness and drawbacks.
Cereal Grains (Maize, Sorghum, Millet, Rice, Wheat): Young plants are stunted and spindly with yellowish-green leaves. In older plants, the tips of the lower leaves show yellowing first which progresses up the mid-rib in a "V" shaped pattern, the leaf margins remaining green. In some cases, there's a general yellowing of the lower leaves. In severe N hunger, the lower leaves eventually turn brown and die, starting at the tips. This "firing" can also be caused by drought which prevents N uptake. Maize ears are pinched at the tips.
Pulses and Pasture Legumes (Peanuts, Beans, Kudzu, etc.)
Many legumes like peanuts, cowpeas, mung beans, soybeans, and pasture legumes can fix all the N they need if the right strain of rhizobia bacteria is present. Others, such as beans, garden peas, and non-vining lima beans, are less efficient.
N-deficient legumes have pale green leaves with a yellowish tinge, starting first with the lower leaves. In severe cases, leaf drop may occur.
If an efficient N fixer like peanuts or soybeans shows N deficiency symptoms, check for adequate nodulation (refer to the section on pulses in Chapter 10).
Tomatoes first show stunted growth and loss of normal green color, first in the younger, upper leaves which stay small and thin. The whole plant gradually becomes light green to pale yellow. The veins begin to change from light green to purple, especially on the underside of the leaves. Stems may turn purple. Flower buds may turn yellow and drop off, and fruits are small.
Cucumbers and squash first show leaf stunting and a loss of deep green color. Stems are spindly, and fruits are light in color (cucumbers).
Potatoes have light green to yellowish-green leaves. In late stages, leaf margins turn yellow and tend to curl.
Other vegetables show a general leaf yellowing.
P hunger signs are most likely to occur during early growth. Mild shortages usually cause stunting without clear leaf symptoms. More severe shortages cause a purplish color starting at the tips of the lower (older) leaves which may even turn brown and die. Some varieties of maize and sorghum don't show a purplish color but rather a bronze coloration of the same pattern. Disregard purple stems.
In maize, a purplish color can be caused by either low temperatures or P shortage. Low temperatures make it more difficult for the roots to absorb P; however, the purpling can be caused by low temperature alone even when the plans 'e level of P is adequate.
In maize and sorghum, symptoms usually disappear once the plants reach 40-45 cm, but yields will be severely lowered. Maize ears from P deficient plants are somewhat twisted, have irregular seed rows, and seedless tips.
Pulses and Pasture Legumes: Hunger signs often aren't well defined. Plants lack vigor and have few side branches. Upper leaves become dark green but remain small. Flowering and maturation are retarded.
Leaves of most vegies first fade to a lighter color. In tomato and Crucifer Family plants (cabbage, turnip, etc.). a purple color develops on the undersides of the leaves or along the veins. (On tomatoes, this can be confused with deficiency).
Potatoes have smaller than normal leaves with a darker color than usual; leaves fail to expand normally. Tubers may have rusty brown lesions in the flesh.
Cereal Grains: Maize, sorghum, and millet, etc. rarely show symptoms the first several weeks of growth. The margins of the lower leaves turn yellow and die, starting at the tip. K-deficient plants have short internodes (distance between the nodes) and weak stalks. Maize stalks sliced length-wise often reveal nodes that are discolored and a darkish brown. Maize ears from K-deficient plants are often small and may have pointed, poorly seeded tips.
Pulses and Pasture Legumes: K deficiency is fairly easy to spot. In broad-leaved legumes like beans and cowpeas, early signs are irregular yellow mottling around the leaflet edges, especially in the lower part of the plant. This turns into a "firing" of the leaf margins that may move inward to cover half the leaf.
Tomatoes will grow slowly and have a dark blue-green color. The young leaves become crinkled; older leaves turn dark green and then develop a yellow-green color around the margins. Blotchy ripening of tomatoes can be caused by K deficiency.
Cabbage plants first show bronzing of the leaf edges which then turn brown and dry out.
Potatoes: The early appearance of unusually dark green, bluish-green, or glossy foliage is a dependable sign. Older leaves become yellowish and develop a brown or bronze color starting at the tips. A number of lower leaves nay dry up at the same time. Plants become stunted and seem to droop due to downward curling of the leaves. Tuber flesh turns dark when cooked.
Calcium deficiencies are very unlikely except in some vegetables and peanuts.
Maize leaf tips become stuck to the next lower loaf.
Beans: Ca hunger is moat likely to occur in combination with aluminum toxicity on very acid soils. Leaves stay green with a slight yellowing at the margins and tips. Leaves may pucker and curl downward.
Peanuts: Light green plants with a high percentage of "pops" (unfilled pods).
Tomatoes: Blossom end rot is caused by calcium deficiency which is promoted by "feastor-famine" watering and severe pruning. The blossom end (bottom end) of the fruit becomes sunken and dark, eventually rotting.
Celery will develop brown, decaying areas in its heart leaves.
Carrot roots will have cavity spots.
Where to suspect deficiencies: Very acid soils or soils that have been limed with a material low in magnesium. High K applications encourage deficiencies.
Cereal Grains: A general yellowing of the lower leaves is the first sign. Eventually, the areas between the veins turn light yellow to almost white, while the veins remain fairly green. As the deficiency progresses, the leaves turn reddish-purple along their edges and tips, starting at the lower leaves and working upwards.
Pulses: Interveinal (between the veins) yellowing appears first on the older leaves and then moves upwards. Leaf tips show the first effects.
Vegetables: Cabbage, cucumber, watermelon, tomato, eggplant, and pepper are the most susceptible. Tomatoes get brittle leaves which may curl upwards (caused by other things too). The veins may stay dark green while the areas between turn yellow and finally brown.
Where to suspect: Volcanic soils; acid, sandy soils; where low-S fertilizers have been used exclusively for some time.
Cereal Grains: Cereals have relatively low S needs. Stunted growth, delayed maturity, and a general yellowing of the leaves (as distinguished from N hunger) are the main signs. Sometimes the veins may stay green which can be mistaken for iron or zinc deficiency; however, iron and zinc hunger are more likely in basic or only slightly acid soils.
Other Crops: Signs aren't easily recognizable in most crops. In beans,the upper leaves turn uniformly yellow.
Where to suspect: Soil pH above 6.8; where high rates of P have been applied, especially if locally placed near the row. Maize is very sensitive to Zn deficiency.
Cereals: Maize shows the most clearly recognizable zinc hunger signs of any crop. If severe, symptoms appear within 2 weeks of of emergence. A broad band of bleached tissue on each side of the mid-ribs of the upper leaves, mainly on the lower part of the leaves, is typical. Mild shortages may cause an interveinal striping similar to manganese and iron hunger. However, in the case of Fe and Mn shortages, the interveinal striping runs the full length of the leaf. Sorghum shows similar signs but with less interveinal striping, and the white band is more defined.
Pulses and Pasture Legumes: Interveinal yellowing of the upper leaves.
Where to suspect: Soil pH above 6.8; sorghum and legumes.
Cereal Grains: Sorghum is much more prone to iron deficiency than maize. Cereals show an interveinal yellowing that extends the full length of the leaf and occurs mainly on the upper leaves.
Pulses: Interveinal yellowing of the upper leaves which eventually turn uniformly yellow.
Where to suspect: Soil pH above 6.8; sandy or highly leached soils.
Cereal Grains: Very uncommon.
Peanuts: Yellowing between the veins of the upper leaves which eventually become uniformly yellow and then bronzed.
Beans: Plants are stunted, and upper leaves become yellow between the small veins and eventually take on a bronzed appearance.
Manganese toxicity occurs on very acid soils and is accentuated by poor drainage. Beans are very susceptible. Upper leaves show an interveinal yellowing which is easily confused with Zn or Mg deficiency, but Zn hunger is very unlikely under acid conditions.
Where to suspect: Acid, sandy soils or high pH soils. Boron is the most common micronutrient deficiency on most vegetables. Cereals rarely show B deficiency.
Peanuts: Foliage may be normal but seeds often have a hollowed out, brownish area in the meat, usually referred to as "internal damage".
Beans: Thick stems and leaves with yellow and dead spots; if less severe, leaves are puckered and curl downward; easily confused with leafhopper damage and virus attack.
Table beets. turnips. and root crops show dark spots on the root, usually at the thickest part; this is known as "brown heart". Plants are stunted with smaller than normal leaves which develop yellow and purple-red blotches. Leaf stalks show a lengthwise splitting. The growing point may die.
Sweet potatoes: Plants are stunted with short internodes and curled petioles (the leaf stems). The edible roots have surface cankers covered with a black exudate.
Lettuce shows malformation of the quicker growing leaves, death of the growing point, and leaf tip burning and spotting.
Where to suspect: Acid soils. Legumes, Crucifer family (cabbage, cauliflower, etc.).
Pulses, Pasture Legumes: Since Mo is needed by the rhizobia bacteria, Mo-deficient legumes often show signs of N hunger.
Cabbage, Cauliflower. Broccoli, etc.: Interveinal yellowing along with cupping of the leaf margins. Leaves have a whiplike appearance.
COPPER: Copper deficiency is very uncommon but is most likely to occur in peat soils. Tree fruits and pasture legumes (especially stylo) are the most susceptible. Symptoms are varied but partial dying back of terminal shoots in fruit trees is one sign.