Soil Fertility and Nitrogen Testing

Soil Fertility

• Soil fertility refers to the soil's ability to provide essential nutrients and support plant growth.
• Healthy soil contains a balance of nutrients, water, air, and organic matter.
• Factors affecting soil fertility are nutrient content (nitrogen, phosphorus, potassium), soil pH, organic matter, and soil structure.
• Soil structure is the soil particles' arrangement, affecting water retention, root penetration, and aeration.
• Healthy soil is vital for crop production and sustainable agriculture.

Determination of Nitrogen in the Soil Using a Soil Testing Kit

• Materials: Soil test kit, distilled water, and a measuring spoon.
• Prepare the Soil Extract by collecting a soil sample, drying it if necessary, adding the recommended amount of soil to a test tube and adding distilled water and shaking well.
• Add Reagents: Use the provided reagent to react with the nitrogen compounds in the soil, and wait for the color to develop.
• Compare with Colour Chart by matching the color in the test tube with the kit's reference chart, and read the nitrogen level.

How to Reduce Nitrogen Levels

• Soil Amendments such as gypsum or sulphur can reduce nitrogen levels by promoting chemical reactions.
• Some plant species, such as grasses and certain cover crops, absorb high amounts of nitrogen.
• Adjust fertilizer application rates based on soil tests to avoid over-fertilization.

How to Increase Nitrogen Levels

• Growing leguminous crops helps increase nitrogen levels in the soil.
• Applying nitrogenous fertilizers, like urea and LAN, enriches the soil.

How to Reduce Phosphorus Levels

• Avoid using fertilizers that contain phosphorus for several seasons.
• Grow crops that are known to absorb high amounts of phosphorus (grasses and legumes).
• Apply soil amendments like lime or gypsum.

How to Increase Phosphorus Levels

• Use phosphorus-rich fertilizers, such as triple superphosphate (bone meal, rock phosphate).
• Add organic matter such as compost or manure that release phosphorus as they decompose.
• The soil should have a pH between 6.0 and 7.0 as phosphorus availability is optimal, use lime to raise pH or sulfur to lower it.

How to Reduce Potassium Levels

• Grow crops like alfalfa, sugar beets, and potatoes which are known to absorb high amounts of potassium.
• Avoid potassium-based fertilizers in soils with high potassium levels.
• Apply calcium-based soil amendments like gypsum or lime.

How to Increase Potassium Levels

• Applying potassium-rich fertilizers like potassium sulphate (K₂SO₄) or potassium chloride (KCI) aids potassium levels.
• Incorporating organic materials such as compost, well-rotted manure, or wood ash into the soil.
• Keeping an optimal soil pH of usually between 6.0 and 7.0, using lime to raise pH or sulfur to lower it, if necessary helps potassium quantity

Steps for Determining Potassium in Soil Using a Biological Soil Testing Kit

• Preparation of Soil Sample: Collect representative samples from multiple points.
• Mix the soil: Combine the samples and allow them to air dry.
• Extraction of Potassium from the Soil: Biological testing kits extract potassium using a specific solution, following kit instructions.
• Adding Reagents: Add a reagent that reacts with potassium, potentially causing a color change based on potassium levels.
• Reading the Results: Compare the color of the sample with the provided color chart.

Nitrogen Fixation in Legumes

• Legumes fix nitrogen from the air using rhizobia bacteria, converting atmospheric nitrogen (N₂) into ammonia (NH₃).
• Nodule formation is when Rhizobia bacteria, invade the legume's root hairs and stimulate the formation of root nodules to serve as habitat for the bacteria.
• Nitrogen fixation is when Rhizobium bacteria use nitrogenase to convert N₂ into NH₃, and symbiotic relationships enable energy exchange.
• In return for nitrogen, the plant provides bacteria carbohydrates for energy in an anaerobic environment inside the nodules.
• Ammonia utilisation is when ammonia quickly turns into Ammonium (NH₄), further processed into nitrate (NO₃) amino acids.
• Legumes absorb these nitrogen compounds and use them to build proteins, DNA, and other essential molecules.
• Legume-rhizobia relationships enrich the soil, support sustainable farming, boost plant growth, and reduce environmental impact thus reducing the need for synthetic fertilizers.
• Examples of nitrogen-fixing legumes include beans, lentils, soybeans, peas, and alfalfa.

Factors Affecting Nitrogen Fixation

• The rate of nitrogen fixation directly relates to the plant's growth rate.
• Drought, low temperatures, limited nutrients, and disease can reduce nitrogen fixation as environmental conditions.
• The legume-rhizobia is sensitive to salt or osmotic stress

Soil Conservation

• Soil conservation prevents or reduces soil erosion and depletion, improving soil quality and crop yields.
• Soil conservation is important because it improves crop yields, maintains soil fertility, protects water quality, mitigates climate change and preserves biodiversity.
• Healthy soils provide a natural sink for atmospheric carbon dioxide, helping mitigate climate change.
• Afforestation involves planting forests where they did not exist, reducing wind erosion.
• Debris captures water, roots bind the soil and prevents soil erosion.
• Good agricultural practices include observing optimal stocking rates to prevent overgrazing and soil compaction.
• Crop rotation reduces soil nutrient depletion and minimizes soil-borne diseases.
• Contour plowing is done across a slope and catches water in furrows, reducing runoff and erosion.
• Minimum tillage is when seedbeds are prepared without disturbing soil structure, reducing soil erosion, and preserving soil moisture.
• Zero tillage avoids plowing, planting seeds directly into undisturbed soil with crop residues.

Drainage

• Drainage is the artificial removal of surplus water from the surface and groundwater
• Soil drainage increase air supply for root respiration, reduces root diseases and provides useful microorganisms.
• Poor soil drainage signs in areas with waterlogging, moss growth, yellowing leaves, standing water, wilting plants and stunted growth.
• Surface drainage involves digging broad ditches or trenches with gentle slopes.
• Broad ditches are built at depths of 1-2 m and distance of 50-100m apart.
• Open ditch method offers low cost construction, but come with the disadvantages of potentially causing soil erosion, disturbing movement of farm equipment and occupying the space around crops
• Subsurface drainage uses perforated pipes underground, which does not interfere with field operations and encourages leaching.

Irrigation

• Irrigation is the controlled application of water to crops during the growing season.
• Irrigation ensures adequate moisture and improves crop quality.
• There are surface, sub-surface and over head irrigation methods
• Surface irrigation systems such as furrow dig trenches, flood divided land into earth walls.
• Sub-surface irrigation system are perforated pipes laid under the ground, such as in trickle or drip irrigation
• Overhead irrigations deliver water from above the crop.

Sprinkler Irrigation

• Sprinkler irrigation pumps water, under pressure, through pipes and releases it through rotating sprinklers.
• Has the advantage of controlling water applied and having uniform water distribution
• Center pivot irrigation is used on towers that rotates and delivers water through the crops
• Uses automated system programs and covers large area, however it is significantly expensive due to the required equipment costs
• Micro-jet irrigation systems delivers water dirctly and requires low pressure
• Micro jets systems provide efficiency, versatility and accommodate spray patterns and plant layouts.
• Micro Jet Irrigation System components are a Water source, Pump, Main line, Filter, Control valves, distribution and micro jets

Installing a Sprinkler Irrigation System

• Firstly, you must plan the system, gather materials and finally prepare the plan.
• Install materials by digging sprinkler heads to the appropiate measurements.
• Then you must correctly install the valve, and connect with main water line for appropiate support
• Make sure connections are secure and check that connections are properly made.
• Be sure to connect the controller to the main water line for appropiate measurements
• Test the system so the system is working properly, and cover the pipes for easy maintenence

Installing a Drip Irrigation System:

• To install a drip system, you must firstly plan the system, determine the plant size and the appropriate location to deliver water.
• Make sure to also design a layout to provide spacing
• Lastly, install and prepare the pressure regulator to ensure safety. Be sure to unroll and secure to appropriate tubing.
• Test the system by burying the tubing to determine the correct water level.
• By setting a timer, water is continuously delivered to the source for consistent watering.

This lesson covers soil fertility, its importance, and the factors that affect it. It also explains how to determine the Nitrogen content in the soil using a soil testing kit. This involves preparing the soil extract, adding reagents, and comparing the resulting color with a chart.