Land is said to be a fixed asset in Agriculture. This means that

Land is a fixed asset in agriculture because its features and topography are fixed. This means that the physical characteristics of the land, such as its shape, elevation, and natural resources, do not change over time. For example, the land will always have the same soil type, slope, and water availability.

Option A: its features and topography are fixed (Correct)

Option B: soil nutrients and its vegetative cover can be replaced - This option is incorrect because while soil nutrients can be replenished through fertilization and crop rotation, this does not change the fact that the land itself remains unchanged in terms of its features and topography.

Option C: its size remains fixed over time - This option is incorrect because land can be expanded or reduced through processes such as land reclamation or subdivision.

Option D: its micro organic composition is constant over time - This option is incorrect because the micro organic composition of the land can change over time due to natural processes and human activities.

Therefore, the correct option is A: its features and topography are fixed.