What plant population should warrant a replant in cotton cultivation?

In cotton cultivation, the decision to replant is often influenced by the established plant population, as it directly impacts the crop's potential yield and quality. A population of less than 20,000 plants per acre generally indicates that the cotton will struggle to achieve optimal growth, reducing its competitive ability against weeds and resulting in inadequate crop density for good pollination and fiber development.

Maintaining sufficient plant density is crucial for cotton, as it can influence factors like light interception, water usage efficiency, and nutrient uptake. A population lower than the threshold signifies that the plants may not adequately cover the soil, leading to increased weed pressure and adversely affecting the microclimate around the plants. As such, a planting density that falls below this mark could lead to a similar or lesser yield compared to alternatives or could necessitate additional control measures, further incentivizing farmers to consider replanting.

In the context of the other options, populations at 10K-15K or 15K-20K would similarly be inadequate for establishing a high-yielding crop, but the specified threshold of less than 20K encapsulates a broader economic decision. Thus, monitoring and the resultant decision to replant are fundamental to ensuring an effective crop establishment and optimizing harvest potential.