Final answer:
Sod is the best option for covering a backyard with grass and dirt in squares as it comes pre-grown and is easy to establish. Soil, which makes up part of sod, contains inorganic matter, organic matter, water, air, and living organisms, with grasslands providing particularly fertile soil due to their high organic matter.
Step-by-step explanation:
If you are looking to cover the ground in your backyard with grass and soil in squares, the best option would be sod. Sod is pieces of earth that have grass growing on the top and soil attached to the roots on the bottom. It is pre-grown and can be laid down to quickly establish a new lawn. This compares to other materials such as gravel, mulch, and topsoil which serve different purposes: gravel for drainage or aesthetic paths, mulch for moisture retention and weed control, and topsoil as the uppermost layer of soil where plants primarily get their nutrients.
Understanding what sod is can be aided by knowledge of the soil's composition. Soil is not just 'dirt'; it consists of four major components including inorganic mineral matter, organic matter, water and air, and living matter. The organic material of soil is made up primarily of humus, which is critical for improving soil structure and supplying water and minerals to plants.
It's important to note that plant life, particularly types of grasses, contributes significantly to the organic matter content of soil. For instance, grassland soils have much thicker A horizons with high organic matter contents, making them more agriculturally productive.