Office of Overseas Programming & Training Support (OPATS) Agriculture Soil and Water Conservation Training Package Session 1: Introduction to Soil

State of the World’s Soils

Human Population Projections; Food and Agricultural Organization, U.N.

What is Soil? Decomposed rock Decomposing organic material (especially plant material) Water Gases Living creatures: – Bacteria, single-celled organisms, fungi, insects and other arthropods, nematodes, earthworms, and other invertebrates

What Do Plants Need From Soil? Food (Nutrients) Water Space Stability Oxygen

Photosynthesis Plants combine carbon dioxide from the atmosphere and water chiefly through their roots to make the simple sugar glucose 2 6CO H 2 O C 6 H 12 O 6 + 6O 2 Captures sunlight and converts the light energy to chemical energy Energy is now in a form that living things can use

Respiration How living things, including plants, access stored energy captured by photosynthesis Combine oxygen atoms with glucose molecules, releasing energy and giving off carbon dioxide and water as byproducts C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Heat Note: Reverse of photosynthesis. A closed system. Atoms continually recycle.

Why Plants Need Oxygen in Soil Photosynthesis takes place in cells with structures called chloroplasts, parts that are green Leaves and green stems use oxygen for respiration that they produce themselves Root cells do not photosynthesize, but they respire, so they need to obtain oxygen from their environment, like animals

Plant Nutrients Secondary Macro Nutrients Primary Macro Nutrients Micro Nutrients

Role of Decomposers

Productive Soil = Good Micro-fauna Habitat Food Oxygen Water Living Space

Nitrogen: A Special Case Vital soil nutrient for plants, often in short supply 78 percent of atmosphere is made up of nitrogen, but it is inaccessible to plants in this form Special bacteria (nitrogen-fixing) are uniquely capable of absorbing the nitrogen and converting it into a form that plants can absorb Bacteria are found on roots of legumes like acacia, peas, beans, clover, and Leucaena

The Nitrogen Cycle

Importance of Soil Structure Soil needs to provide a good habitat for both plants and for soil organisms Water and oxygen Soil structure has to contain spaces to hold both water and oxygen

Soil Texture Soil particle size is a significant determinant of soil structure Gravel Sand Silt Clay

Soil Texture: Particle Size

Sandy Environment

Clay Environment

Soil Spaces

Soil Texture Triangle

Soil Mycelia (Fungal Threads)

Summarizing - Healthy Soils Must: Support both productive plant growth and micro-fauna Contain the 13 nutrients plants need Retain water and oxygen Provide stability so plants can take root Contain sufficient organic matter

To Create Productive Soils Over the Long Term: Pay attention to structure as well as fertility Applying fertilizer without paying attention to structure is only a quick fix at best Only by paying attention to soil health can we “enhance productivity in perpetuity without ecological harm.” ( M.S. Swaminathan)

Particle Size