Agronomy – timing of nitrogen application for crop nutrition When is nitrogenous fertilizer primarily required in field crops, based on plant physiology and nutrient uptake patterns? (Select the most appropriate stage and purpose.)

Introduction / Context:
Nitrogen is the key macronutrient driving vegetative growth in most crops. The agronomic question is about the correct timing and purpose of nitrogenous fertilizer so that plants develop strong stems and ample leaf area, which later supports flowering and yield.

Given Data / Assumptions:

• Crops exhibit distinct growth stages: establishment, vegetative, reproductive, and maturation.
• Nitrogen chiefly promotes leaf and stem (shoot) biomass and chlorophyll formation.
• Over-application late in the season can delay maturity or reduce quality.

Concept / Approach:
Nitrogen fuels cell division, chlorophyll synthesis, and photosynthetic capacity. Supplying it early (basal and early topdress) maximizes leaf area index, which in turn captures more solar energy to build carbohydrates for later reproductive sinks. Many region-specific recommendations split N between planting and early tillering or crown root initiation (for cereals) to match crop demand and minimize loss pathways (volatilization, leaching, denitrification).

Step-by-Step Solution:

Verification / Alternative check:
Field trials consistently show that adequate early N increases tiller number (in cereals), canopy cover, and photosynthetic rate, ultimately supporting higher grain or fruit yields when balanced with P, K, and S.

Why Other Options Are Wrong:

• Accelerating fruit formation: Too much late N can reduce fruit set and quality.
• Lessen excessive potash: Potassium issues are corrected by water management and balanced fertilization, not by extra N.
• None of these: Incorrect because early nitrogen is clearly beneficial.

Common Pitfalls:
Applying all N at once; splits are preferred. Ignoring soil organic N supply or residual N can lead to waste and environmental loss.

Final Answer:
during the early stage of growth to promote development of stem and leaves.