Unit 3 - Soil Fertility and Plant Nutrition | MSc Horticulture & Agronomy

Soil Fertility and Plant Nutrition

( HORSS-201 & AGRMI-202 )

UNIT III

Nutrient and nutrient water interaction. Balanced use of nutrients. Integrated plant nutrient supply and management.

Nutrient and Water Interaction

Overview

Nutrient and water interactions are fundamental in determining plant growth, nutrient uptake efficiency, and overall crop productivity. Water acts as the medium for nutrient transport in the soil and within the plant, while nutrient availability can influence plant water use and water-use efficiency.

Types of Interactions

1. Positive Interaction

Adequate water improves nutrient solubility and mobility in soil.
Improves nutrient uptake and transport within the plant.
Increases microbial activity for nutrient mineralization.

2. Negative Interaction

Waterlogging leads to denitrification (loss of nitrogen).
Drought limits root growth and nutrient uptake.
Excess irrigation causes nutrient leaching (especially N, K, B, S).

How Water Affects Nutrient Uptake

Nutrient Solubilization and Mobility: Most nutrients are absorbed by plants in dissolved form. Adequate soil moisture is essential for dissolving nutrients and making them available to roots.
Transport to Roots: Water movement in soil carries nutrients to root surfaces via mass flow and diffusion.
Soil Water Status:

Deficiency: Low soil moisture restricts nutrient solubilization and transport, leading to reduced uptake and possible deficiency symptoms.
Excess: Waterlogged or saturated soils can cause nutrient losses through leaching (especially nitrate) or denitrification (loss of nitrogen as gases), and can also lead to toxicities of certain elements like Fe and Mn.

Nutrient Cycling: Adequate water promotes microbial activity, which enhances nutrient mineralisation and cycling in the soil.

How Nutrients Affect Water Use

Plant Growth and Water Demand: High nutrient availability, especially nitrogen, promotes vigorous plant growth, which can increase water consumption and potentially intensify water stress if supply is limited.
Water-Use Efficiency (WUE): Balanced nutrient supply improves WUE, allowing plants to produce more biomass per unit of water used.

Nitrogen improves photosynthesis and canopy development, enhancing WUE.
Potassium regulates stomatal opening and improves drought resistance.
Calcium and Boron strengthen cell walls and improve tolerance to water stress.

Root Development: Proper nutrition encourages deeper and more extensive root systems, improving water uptake from the soil profile.

Nutrient-Water Interactions: Key Points

Nitrogen and Water: Nitrogen uptake is closely linked to water movement through the soil and plant. Drought reduces nitrate uptake, while adequate water enhances nitrogen use efficiency.
Other Nutrients: Potassium helps regulate stomatal opening, affecting plant transpiration and drought tolerance. In submerged soils (e.g., rice), iron and manganese become more available, while zinc and copper may become less available.
Soil Type and Structure: Soil texture and structure influence both water retention and nutrient availability. Sandy soils drain quickly, leading to potential nutrient leaching, while clay soils retain water and nutrients but may suffer from poor aeration.

Importance of Nutrient-Water Synchronization

Ensures optimal plant growth, yield, and quality.
Reduces environmental losses of nutrients (e.g., nitrate leaching).
Enhances fertilizer use efficiency (FUE) and water use efficiency (WUE).

Management Strategies

Irrigation Scheduling Based on Crop Demand

Avoid over- or under-irrigation.
Use drip or sprinkler systems for precision.

Fertigation

Application of nutrients through irrigation water.

Enhances uptake, reduces losses.

Mulching: Conserves moisture and improves nutrient retention.
Soil Moisture Monitoring: Tools like tensiometers help optimize irrigation timing.
Balanced Nutrition: Avoid excess or deficiency that affects root and shoot growth, and indirectly water uptake.

Summary Table: Effects of Nutrient-Water Interaction

Water Status	Nutrient Uptake	Plant Response
Adequate	Optimal	Vigorous growth, high yield
Deficient	Reduced	Deficiency symptoms, low yield
Excess	Leaching/toxicity	Poor growth, root damage

Balanced Use of Nutrients

Definition

Balanced use of nutrients refers to supplying all essential nutrients in the right proportions, based on crop needs, soil fertility status, and expected yield targets.

Importance of Balanced Nutrient Use

Prevents Deficiencies and Toxicities: Over-application or under-application of any nutrient can disrupt plant growth and reduce yield.
Optimizes Nutrient and Water Use Efficiency: Balanced fertilization ensures that all nutrients work synergistically, maximizing uptake and minimizing waste.
Reduces Environmental Impact: Prevents nutrient losses to the environment, such as nitrate leaching and phosphorus runoff, which can cause water pollution.
Improves Crop Yield & Quality: Ensures all nutrients are available for optimal growth.
Sustains Soil Fertility: Prevents mining of specific nutrients from soil.

Principles of Balanced Fertilization

Soil and Plant Testing: Regular analysis to determine nutrient status and guide precise fertilizer application.
Integrated Nutrient Management: Combining organic and inorganic sources to maintain soil fertility and structure.
Site-Specific Management: Adjusting fertilizer rates and timing based on soil type, crop, and local climate.
Monitoring Water Supply: Ensuring irrigation matches plant needs and nutrient application to prevent losses and maximize uptake.
Crop-Specific Requirements: Different crops have varying nutrient demands (e.g., potatoes require more K, while legumes require less N).
Growth Stage Consideration: N is critical during vegetative phase, P during root/flowering, K during fruiting.
Nutrient Interactions: Maintain correct nutrient ratios (e.g., N: P: K = 4:2:1 commonly used as a baseline).
Include Micronutrients: Fe, Zn, B, Mn, Cu, Mo – though required in small amounts, are vital for enzyme activity and plant metabolism.

Approaches to Improve Balanced Use

Integrated Nutrient Management (INM) – combines chemical, organic, and biological sources.
Fertigation – precision application of nutrients via irrigation.
Split Application – especially for N to match crop uptake and reduce losses.
Use of Slow-Release and Controlled-Release Fertilizers – to provide nutrients steadily.
Awareness and Training of Farmers – to reduce misuse and promote scientific methods.

Tools for Balanced Nutrient Use

Soil testing – primary tool to understand fertility status.
Leaf/tissue analysis – to correct mid-season deficiencies.
Fertilizer recommendation charts/kits – region and crop specific.
Decision Support Systems – ICT tools and mobile apps for precise nutrient advice.

Imbalanced Use: Consequences

Type	Effects
Excess Nitrogen	Lush vegetative growth, delayed flowering, pest/disease susceptibility
Low Potassium	Weak stems, poor fruit quality, low drought resistance
High Phosphorus	Induces micronutrient deficiencies (Zn, Fe)
Ignoring Micronutrients	Poor yield even with adequate macronutrients

Integrated Plant Nutrient Supply and Management (IPNS/IPNM)

Definition and Concept

Integrated Plant Nutrient Supply and Management (IPNS/IPNM) is a holistic approach that optimizes soil fertility and plant nutrition by judiciously combining all available sources of plant nutrients—chemical fertilizers, organic manures, crop residues, green manures, and biofertilizers—to sustain high crop productivity while minimizing environmental degradation. The goal is to maintain or adjust soil fertility and nutrient supply at optimum levels for long-term productivity, profitability, and sustainability.

Objectives of IPNS

Sustain or enhance crop productivity.
Maintain soil fertility over the long term.
Minimize nutrient losses to the environment.
Improve nutrient use efficiency (NUE).
Reduce dependence on chemical fertilizers.

Key Principles of IPNS/IPNM

Balanced Use of Nutrients: Integrates mineral fertilizers with organic and biological sources to meet crop requirements and improve soil health.
Site-Specific Management: Considers local agro-ecological conditions, soil type, cropping system, and climate to tailor nutrient management strategies.
Nutrient Cycling and Recycling: Emphasizes the recycling of crop residues, use of green manures, and on-farm/off-farm organic wastes to enhance nutrient availability and reduce reliance on external inputs.
Sustainability: Aims to prevent soil nutrient mining, maintain soil organic matter, and reduce nutrient losses to the environment (e.g., runoff, leaching).
Integration with Farming Systems: Focuses on nutrient management at the cropping system or farm level rather than for individual crops or fields.
Enhancement of Soil Biological Activity: Promotes practices that support beneficial soil microorganisms, improving nutrient mineralization and availability.

Components of IPNS/IPNM

Chemical Fertilizers: Provide concentrated and immediately available nutrients but must be used judiciously to avoid environmental harm and soil degradation.
Organic Manures: Include farmyard manure, compost, green manure, and vermicompost; improve soil structure, water retention, and microbial activity while supplying nutrients gradually.
Biofertilizers: Microbial inoculants that enhance nutrient availability and biological nitrogen fixation.

Rhizobium, Azospirillum, Azotobacter (N fixation)
PSB (Phosphate Solubilizing Bacteria)
VAM (Vesicular Arbuscular Mycorrhiza) for P and micronutrients.

Crop Residues and Green Manures: Recycling of plant materials and incorporation of leguminous crops enrich the soil with nutrients, especially nitrogen and organic matter.
Nutrient Management Tools: Use of soil and plant testing, leaf color charts, and precision agriculture techniques to monitor and adjust nutrient applications.
Soil Amendments: Lime in acidic soils and gypsum in sodic soils to correct pH and improve nutrient availability.
Legume Inclusion in Cropping System: Biological nitrogen fixation and organic matter addition through legume crops.

Advantages of IPNS/IPNM

Enhances crop productivity and profitability by ensuring a continuous and balanced nutrient supply.
Improves soil health, structure, and biological activity, supporting long-term agricultural sustainability.
Reduces the risk of environmental pollution from nutrient runoff and leaching.
Increases nutrient use efficiency and resilience of cropping systems to climate variability.
Adapts to diverse farming systems, including irrigated and rainfed agriculture.

Implementation Strategies

Crop Rotation and Intercropping: Enhances nutrient cycling and minimizes pest/disease incidence.
Minimum Soil Disturbance: Conservation tillage and permanent soil cover reduce nutrient losses and enhance soil fertility.
Split Fertilizer Application: Applying fertilizers in multiple doses according to crop growth stages improves uptake and reduces losses.
Context-Specific Recommendations: Adjusting nutrient management based on soil testing, crop needs, and local conditions.
Soil and Plant Testing: Determines nutrient status and guides fertilizer use.
Balanced Fertilizer Application: Based on crop requirement, soil test, and yield targets.
Integrated Use of Inputs: Combining organic and inorganic sources for complementary effects.
Site-Specific Nutrient Management (SSNM): Tailoring nutrient applications to specific field conditions.

Challenges in Implementation

Lack of awareness among farmers.
Inadequate availability of quality organic manures and biofertilizers.
Regional variation in soil types and cropping systems.
Need for strong extension support and training.

Summary Table: Components and Roles in IPNS/IPNM

Component	Role/Benefit
Chemical Fertilizers	Immediate nutrient supply, yield increase
Organic Manures	Soil health, structure, slow nutrient release
Biofertilizers	Biological N fixation, P solubilization, sustainability
Crop Residues/Green Manures	Nutrient recycling, organic matter addition
Precision Tools	Site-specific, efficient nutrient management

Soil Fertility and Plant Nutrition- Click here for Notes of all units

Want a PDF of all the notes? Send a DM to me: https://www.instagram.com/puspendrps