Importance of Humus in Soil Structure

Soil Organisms and Humus

• Soil organisms starve when humus decomposes, leading to soil that is no longer loose and nutrient-rich.
• The clumpy aggregate structure of glued soil particles breaks down, causing water- and nutrient-holding capacities, infiltration, and aeration to decline.
• Mineralization occurs, resulting in the loss of humus and topsoil collapse, leaving only minerals (sand, silt, clay) behind.

Importance of Humus to Topsoil

• Topsoil forms when detritus and humus additions are balanced against their breakdown and loss.
• Humus is critical for maintaining topsoil's structure, water-holding capacity, and fertility.

Fertilizers

• Fertilizers are materials that contain one or more necessary nutrients (nitrogen, phosphorus).
• Organic fertilizers, such as plant and animal wastes, support soil organisms and build soil structure.
• Inorganic fertilizers, which lack organic compounds, do not support soil organisms or build soil structure.

Soil Degradation

• Soil degradation occurs when soil's capacity to support plants and perform ecosystem functions is reduced.
• Soil degradation is a worldwide problem, affecting about 200 million hectares (38% of the world's cropland).
• Erosion is a major cause of soil degradation, particularly in areas where forests have been cleared.

Causes of Erosion: Deforestation

• Removing forests exposes soil, leading to increased runoff and nutrient leaching.
• Tropical soils, which lack nutrients due to leaching, are particularly vulnerable to erosion.

Conserving and Restoring Soil

• Healthy soils are essential for human societies, and sustainability requires reducing erosion and preventing degradation.
• Soil conservation techniques, such as contour plowing, shelterbelts, and no-till farming, can help reduce soil erosion.
• Public policies can also promote conservation or lead to disaster.

Techniques to Reduce Soil Erosion

• Contour plowing involves plowing and cultivating at right angles to the slope of the land, slowing downhill water flow.
• Shelterbelts are protective rows of trees and shrubs planted beside plowed fields, which protect soil from wind and erosion.
• No-till farming minimizes erosion by leaving the soil undisturbed, allowing detritus to maintain topsoil.

Restoring Soil Fertility

• Adding organic material, such as compost, manure, or green manure, can enhance soil fertility.
• Using synthetic inorganic fertilizers made of inorganic compounds can also improve soil fertility.
• Crop rotation and bioremediation can also help restore soil fertility.

Protecting Soil Health

• Soil health is critical for sustainable development, including food security and sustainable agriculture.
• Protecting soil health requires addressing urban soils, mining and waste degradation, and the effects of climate change on soil.