Soil degradation and declining fertility are concerns affecting:

The correct answer is: d) All of the above

Soil degradation and declining fertility are concerns affecting crop productivity, input costs, and environmental sustainability.

• Crop productivity: Soil degradation can reduce crop yields by up to 50%. This is because soil degradation can lead to a loss of nutrients, organic matter, and water-holding capacity.
• Input costs: Soil degradation can also increase input costs, such as the need for fertilizers, pesticides, and irrigation. This is because degraded soils are less able to support crops, and therefore require more inputs to produce the same yield.
• Environmental sustainability: Soil degradation can also have a negative impact on environmental sustainability. This is because soil degradation can lead to the loss of biodiversity, the contamination of water resources, and the emission of greenhouse gases.

Therefore, soil degradation and declining fertility are concerns affecting crop productivity, input costs, and environmental sustainability.