Soil Science and Plant Nutrition
Soil science and plant nutrition tests soil properties, nutrient functions, deficiency diagnosis, fertilizer calculations and irrigation/fertigation decisions. For horticulture, fertilizer scheduling and soil health are high-yield areas.
Core rules
- Soil texture differs from structure; pH 6.0–7.0 is generally favourable; EC indicates salinity; organic carbon and CEC affect nutrient holding.
- There are 17 essential elements, including C, H, O, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo, Cl and Ni.
- Mobile nutrients such as N, P, K and Mg show older-leaf symptoms; immobile nutrients such as Ca, Fe and B show young-leaf symptoms.
- Fertilizer grade is N–P₂O₅–K₂O; urea is 46% N, SSP is 16% P₂O₅ and MOP is 60% K₂O.
- Fertigation splits N and K; phosphorus needs care because of precipitation in irrigation lines.
Worked example
Recommended N = 120 kg/ha. Urea required = 120 ÷ 0.46 = 260.9 kg/ha. If 50% is basal and 50% at 30 days, apply about 130.4 kg urea per split. Reason: fertilizer grade is the nutrient fraction, not pure element.
Traps
- Treating P₂O₅ as P; convert using 0.44 (P/P₂O₅).
- Assuming urea is 100% N.
- Reading pH 5 as twice as acidic as pH 6; it is 10 times the H⁺ activity.
- Confusing deficiency with toxicity.
- Ignoring soil test values and crop stage.