Concept:Soil-borne diseases in the nursery are best controlled by removing or killing pathogens present in the soil before seedlings are planted.
Explanation:Mulching mainly conserves soil moisture and suppresses weeds.
It does not destroy disease-causing organisms in the soil.
Manuring improves soil fertility but does not kill soil pathogens.
Provision of shade controls light and temperature, not soil-borne diseases.
Heat treatment, such as soil steaming or solarisation, kills harmful fungi, bacteria, and nematodes.
Therefore, heat treatment is the effective nursery practice for controlling soil-borne diseases.
Answer:C. heat treatment