SPM BIOLOGY F5 C3 EXPT 3.1 To Study Effects of N : P : K Ratios on Plant Growth

Experiment Objective and Setup
📌 The experiment aims to study the effects of varying Nitrogen (N), Phosphorus (P), and Potassium (K) ratios on the growth of maize seedlings, requiring approximately one month to complete.
🧪 A complete Knop's solution contains all necessary macronutrients (N, P, K, Mg, S) and micronutrients (trace elements) required for healthy plant growth.
💧 The procedure requires using 250 ml of solution per bottle, ensuring the volume is kept constant across all setups.

Variables and Controls
⚙️ The manipulated variable is the NPK ratio within the different culture solutions (A through E).
📏 The responding variable involves observing plant growth parameters such as height, leaf color, root length, and stem strength after one month.
⚫ Black paper is used to cover the bottles to prevent the growth of green algae, which would compete for nutrients.

Experimental Conditions and Observations
🌿 Culture Bottle A (Complete Solution): Seedlings showed healthy growth as all macronutrients (N, P, K) and micronutrients were present, supporting the hypothesis (NPK ratio of $1:1:1$).
❌ Culture Bottle B (Control): Contained only distilled water, resulting in no growth and eventual death due to the complete lack of macronutrients.
🟡 Culture Bottle C (Nitrogen Deficiency): Showed chlorosis (leaves turning yellow) because Nitrogen is vital for chlorophyll synthesis; growth was also stunted as N is needed for protein synthesis.
🔴 Culture Bottle D (Phosphorus Deficiency): Leaves turned dark green with reddish dots; roots showed expanded growth, as Phosphorus is essential for healthy root development.
📉 Culture Bottle E (Potassium Deficiency): Resulted in yellowing of the leaf edges (marginal chlorosis) and stunted growth, eventually leading to the plant's death.

Key Procedures and Insights
🌬️ An air pump must be connected to provide oxygen to the roots for respiration since dissolved oxygen in water is insufficient.
🔄 The Knop solution must be replaced every week to ensure consistent nutrient levels, replacing absorbed nutrients except for the deliberately omitted ones in test groups.
✅ The initial hypothesis, stating that corn seedlings undergo healthy growth in a complete Knop solution with an NPK ratio of $1:1:1$, was accepted based on the results from Culture Bottle A.
🔬 Nitrogen is required for chlorophyll and protein synthesis, Phosphorus for root development, and Potassium as a cofactor for enzymes and for protein synthesis.

📸 Video summarized with SummaryTube.com on Feb 05, 2026, 14:34 UTC