Essential Plant Nutrients

These are nutrients that are required for the entire plant growth cycle. Deficiency of any one of these nutrients will make plant have limited growth, affect flowering and or seed formation.

The essential plant nutrients are divided into two groups: macro nutrients and micro nutrients.

• Macronutrients are required by plants in relatively large quantities and include; Nitrogen (N), Phosphorus (P), and Potassium (K), Sulphur (S), Calcium (Ca), and Magnesium (Mg).
• Micronutrients (Trace elements) are required in small (or micro) amounts by plants. They include Manganese (Mn), Iron (Fe), Boron (B), Zinc (Zn), Copper (Cu), Molybdenum (Mo), etc.

Signs of nutrient deficiency in beans

1. Nitrogen

• Lower leaves become yellow and eventually die.
• Growth is stunted.
• Few flowers develop and pods fill poorly.

2. Phosphorus

• Beans usually take long to display symptoms and by the time a visual deficiency is recognized, it may be too late to intervene.
• Small, dark green upper leaves that turn purple and later die.
• Plants are stunted with thin stems and the number of flowers, pods and seeds are reduced, while seed and fruit development is poor or absent.

3. Potassium

• The tips and edges of older leaves appear burnt or scorched, and poor filling of pods.
• The leaf midrib usually remains green.
• Deficient plants stay small and weak, and their leaves later fall off.
• The pods are poorly filled.

4. Calcium

• Stunting in stems, flowers and roots.
• Leaves are curled or cupped with black spots and yellow margins.
• Pods wilt and seeds fail to develop.

5. Magnesium

• Older leaves have yellowing between the leaf veins but the veins remain green.

6. Boron

• Stems abnormally thickened.
• Longitudinal splitting of epicotyl.
• Death of growing points and inter-venial chlorosis on middle aged leaves.

7. Iron

• Yellowing occurs between the veins of the newest growth.
• The veins will remain green except in extreme cases.

8. Manganese

• Stunting and yellowing between veins of young leaves.
• Leaves gradually turn pale-green with darker green next to the veins.

9. Zinc

• Younger leaves first become mottled and show interveinal chlorosis, with browning of the older leaves.
• When deficiency is severe, the area between leaf veins will become light green and yellow near the leaf tips and outer edges.
• A general downward curl of the leaves also occurs and pod set will be poor.
• Plants tend to be stunted due to shortening of the internodes.

10. Molybdenum

• Early deficiency symptoms are similar to nitrogen deficiency.
• Affected plants become stunted and lack vigor.
• Leaves may turn brown along the margins.
• Deficiency leads to poor nodule formation.

Methods of managing soil fertility

• Practice minimum tillage. In a used field, spray with a non-selective herbicide (Glyphosate), after 14 days, make fallows or hole (basins) and plant with minimal disturbance of soil.
• Soil and water conservation: construct contour bunds and terraces on steep slopes, planting cover crops to limit loss of water and soil nutrients.
• Correct soil pH by liming: Beans grow well an optimum soil pH) ranges from 5.8 to 6.5 and are very sensitive to highly acidic (pH < 5,2) soils. Beans will also not grow well in soils that are compacted, too alkaline or poorly drained.
• Crop rotation: Beans should be grown in a rotation sequence of legume, cereals, root crops and back to legumes so as to reduce; the risk of depleting the soil of specific nutrients and to break disease and pest cycles
• Intercropping: Beans can be intercropped with cereals to manage soil fertility.
• Fallow management: for farmers with adequate land, fallowing or allowing the land to rest for at least 2 years to rejuvenate the soils is advisable. However, in case, of inadequate land, a rotation program should be observed to reduce pests and disease accumulation.