Which factors are indicators of soil fertility?

The correct answer focuses on specific characteristics that directly impact soil fertility. Nutrient levels are crucial because they indicate the availability of essential elements such as nitrogen, phosphorus, and potassium, which are vital for plant growth. The organic matter content plays a significant role in improving soil structure, water retention, and microbial activity, which are all essential for nutrient cycling. Lastly, pH affects nutrient availability and microbial activity; certain plants thrive in specific pH ranges, and many nutrients become less accessible to plants under extremes of pH.

The other options provide information relevant to soil health and overall environmental conditions, but they do not specifically pinpoint indicators of fertility as clearly as nutrient levels, organic matter, and pH. For instance, soil color and texture can give clues about drainage and parent material, but they don't directly measure the nutrient status. Plant growth may indicate soil health but doesn't provide specifics on the fertility levels. Similarly, soil depth and temperature relate to some aspects of soil function but are not direct measures of fertility.