Soil for Horticultural Crops

Introduction

Soil is the natural medium for plant growth and forms the foundation of all horticultural crop production. It provides anchorage, nutrients, air, water, and favorable temperature for plant roots.

In horticulture — where crops like fruits, vegetables, flowers, and plantation crops are grown — soil management is more critical than in field crops because:

• Horticultural plants have longer life spans (e.g., mango, guava).
• Their product quality (taste, color, aroma) depends on soil health.
• They require precise drainage and fertility management for optimum yield.

Definition of Soil

• “Soil is a natural body consisting of mineral and organic constituents, formed under natural processes, and capable of supporting plant life.”
• According to Dokuchaiev (1883) — the father of soil science — soil is a dynamic natural body formed at the Earth’s surface due to the combined influence of climate, organisms, parent material, relief, and time.

Importance of Soil in Horticulture

• Physical Support: Roots anchor firmly and support the plant body.
• Nutrient Supply: Provides essential macro- and micronutrients.
• Water Reservoir: Stores and supplies water through capillary action.
• Air Supply: Roots need oxygen for respiration — well-aerated soil promotes healthy roots.
• Temperature Regulation: Soil temperature affects germination and microbial activity.
• Microbial Habitat: Soil microorganisms (bacteria, fungi) aid in nutrient cycling and decomposition.

Physical Properties of Soil

• Soil Texture

Refers to the relative proportion of sand, silt, and clay particles in the soil.

Note: Ideal soil for horticultural crops = Loam or Sandy loam (well-drained, fertile, medium textured).

Soil Structure

• Refers to how soil particles are arranged into aggregates.
• Good structure (crumb or granular) = easy root penetration, good aeration, and water movement.
• Poor structure (platy or blocky) = waterlogging and poor drainage.

Soil Depth

• Deep soil (≥1 m) is needed for perennial fruit trees like mango, citrus, and guava.
• Shallow soils restrict root growth and reduce yield.

Soil Porosity and Aeration

• Soils with 40–50% pore space are ideal.
• Poor aeration (in heavy soils) → root suffocation → diseases like root rot.

Bulk Density

• Indicates soil compaction.
• Ideal range: 1.2–1.4 g/cm³ for good root and microbial activity.
• Above 1.6 g/cm³ = compact, poor root growth.

Chemical Properties of Soil

• Soil Reaction (pH)

Soil pH determines nutrient availability.
Most horticultural crops prefer slightly acidic to neutral soils (pH 5.5–7.5).

Effects of pH Extremes:

• Acidic soils → deficiency of Ca, Mg, Mo; toxicity of Fe, Al.
• Alkaline soils → deficiency of Fe, Zn, Mn → chlorosis and poor fruiting.

Soil Salinity

• High salt concentration reduces water uptake and causes leaf burn.
• Crops like mango, citrus, banana are salt-sensitive.
• Salt-tolerant crops: ber, aonla, pomegranate.

Control Measures:

• Leaching with good quality water,
• Gypsum application,
• Organic matter addition.

Soil Fertility

Soil fertility depends on the availability of essential plant nutrients:

• Macronutrients: Primary: N, P, K. Secondary: Ca, Mg, S
• Micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl

6. Biological Properties of Soil

• Soil Organisms: Bacteria, fungi, actinomycetes, earthworms improve soil fertility.
• Decomposition: Converts organic residues into humus.
• Nitrogen Fixation: By Rhizobium, Azotobacter, Azospirillum.
• Mycorrhiza: Enhances phosphorus uptake in fruit crops.

• Soil Requirements for Major Horticultural Crops