How does excessive irrigation affect nitrogen in the soil?

Excessive irrigation can lead to nitrogen leaching, which means that the nitrogen in the soil is washed away and drains through the soil profile into groundwater or surface water. This occurs when the soil becomes saturated, and excess water moves downward, carrying soluble nitrogen compounds along with it.

In many agricultural settings, nitrogen is applied as a fertilizer to enhance crop growth. However, if the soil is overly saturated due to excessive irrigation, there is a high risk that this added nitrogen will not remain in the root zone where plants can access it. Instead, it will be lost from the soil, leading to nutrient deficiencies for crops and potential water quality issues downstream.

With regards to the other options, while they influence plant growth and soil quality, they do not directly relate to the primary mechanism by which excessive irrigation impacts nitrogen in the soil. Increasing nitrogen content is not a result of excessive irrigation, nor does it directly enhance soil acidity or reduce plant nutrient uptake in a manner specifically linked to nitrogen leaching like option C does. Thus, understanding the leaching process highlights how water management is crucial for maintaining nitrogen availability in agricultural soils.