Compaction of soil in a garden has which of the following effects on plants?

Compaction of soil significantly influences the physical properties of the soil, which in turn affects plant health and growth. When soil is compacted, the particles are pressed tightly together, which leads to a reduction in the amount of pore space available. This means there is less air in the soil, resulting in decreased aeration.

Aeration is essential for plant roots as they require oxygen to conduct respiration, a process critical for growth and energy production. With reduced aeration due to compaction, roots may struggle to obtain the oxygen they need, leading to stunted growth or even root death.

Moreover, compaction impairs the soil's ability to absorb water, drastically decreasing infiltration. Instead of water percolating through the soil profile where it can be utilized by plant roots, water tends to flow over the surface of the compacted soil, increasing runoff. This not only leads to water loss (as it does not reach the plants) but can also cause erosion and nutrient loss from the soil.

Thus, the correct understanding of the impact of soil compaction is that it decreases aeration, decreases infiltration, and increases runoff, all of which are detrimental to plant health and garden productivity.