How do compost and farmyard manure improve garden soil?

Compost and farmyard manure are essential organic amendments that enhance garden soil through both nutrient provision and physical conditioning.

Farmyard Manure
Manure, consisting of animal excreta and bedding like straw, improves soil by supplying humus and organic substances. Its primary benefits are indirect:12
* Physical Structure: It increases the soil's capacity to absorb and store water, enhances aeration, and promotes the activity of beneficial soil organisms.12
* Protection: When incorporated into topsoil, it helps prevent erosion from heavy rain and reduces surface evaporation.12
* Nutrients: It provides essential plant nutrients, though these are often in slow-acting forms that require soil microbes to become bioavailable.12

Compost
Compost is a crumbly mass of decomposed plant material that acts primarily as a soil amendment.34
* Soil Structure: It improves aggregation, pore spacing, and water storage, with maximum benefits typically realized after several years of use.34
* Biological Health: It adds beneficial microbes to the soil.3
* Nutrient Release: While its nutrient content is relatively low, it provides a steady, slow release of nitrogen throughout the growing season, which reduces leaching.34