(a) State three functions of nitrogen in crop plants. (b) Mention four effects of excess soil nitrogen and three effects of nitrogen deficiency on plants. (...

(a) Three functions of nitrogen in crop plants

• It is a major component of proteins, enzymes and protoplasm needed for growth.
• It is a constituent of chlorophyll, giving leaves their green colour for photosynthesis.
• It promotes vegetative growth, producing healthy leaves and stems.

(b) Four effects of excess soil nitrogen

• Excessive vegetative (leafy) growth at the expense of flowering and fruiting.
• Delayed maturity of the crop.
• Weak, succulent stems that lodge (fall over) easily.
• Increased susceptibility to pests and diseases; scorching of plants at very high levels.

Three effects of nitrogen deficiency

• Yellowing of leaves (chlorosis), beginning with the older leaves.
• Stunted growth and small leaves.
• Reduced yield and premature shedding of leaves.

(c) Three other ways (apart from lightning) by which nitrogen is added to the soil

• Fixation of atmospheric nitrogen by nitrogen-fixing bacteria (e.g. Rhizobium in legume root nodules).
• Application of nitrogenous fertilizers (e.g. urea, sulphate of ammonia).
• Addition of organic manure and decayed plant and animal remains.

(d) Six soil micronutrients

1. Iron (Fe)
2. Manganese (Mn)
3. Zinc (Zn)
4. Copper (Cu)
5. Boron (B)
6. Molybdenum (Mo)

(Chlorine, Cl, is also acceptable.)