Excessive use of nitrogen fertilizer in rice cultivation can trigger a series of adverse consequences. These not only impact rice growth and yield but also pose potential threats to the environment and human health. The following is a detailed analysis:

I. Soil Quality Deterioration

1. Soil Compaction and Hardening: Overapplication of nitrogen fertilizer leads to excessive nitrogen content in the soil, accelerating the decomposition of organic matter. This disrupts soil structure, resulting in compaction. Compacted soil hinders root growth, reduces soil aeration, and impairs water permeability, ultimately affecting rice’s normal development.

2. Salinity Accumulation: Excessive nitrogen fertilization can also cause salt buildup, particularly in poorly drained or frequently irrigated fields. Elevated soil salinity disrupts ion balance, increases soil osmotic pressure, and inhibits crop roots’ ability to absorb water and nutrients.

3. Soil Acidification: Long-term use of acidic nitrogen fertilizers (e.g., urea) gradually acidifies the soil. This fixes essential micronutrients like iron and manganese, reducing their availability and compromising crop uptake.

II. Increased Water Pollution

1. Nitrogen Runoff: Excess nitrogen can enter water bodies via surface runoff, escalating eutrophication risks. Eutrophicated water harms aquatic ecosystems and poses health risks to humans through the food chain.

2. Algal Blooms: Nitrogen-rich waters spur rapid proliferation of algae (e.g., cyanobacteria), forming algal blooms. These blooms degrade water quality, reduce transparency, and deplete dissolved oxygen, disrupting downstream ecological balance.

3. Groundwater Contamination: Nitrogen fertilizers may leach into groundwater systems, especially when applied excessively. Contaminated groundwater endangers sustainable use of freshwater resources and threatens human health through drinking water sources.

III. Ecological Damage

1. Biodiversity Loss: Degraded soil and water environments directly undermine ecosystem stability and biodiversity. Limited plant growth and imbalanced microbial communities erode natural ecological equilibrium.

2. Impaired Agroecosystem Functions: Overreliance on chemical fertilizers and pesticides weakens the self-regulating capacity of agroecosystems. Prolonged fertilizer use reduces soil fertility, diminishes biodiversity, and degrades ecosystem services.

3. Climate Change Impact: Agricultural activities, including nitrogen fertilization, contribute to greenhouse gas emissions (e.g., carbon dioxide). Excessive nitrogen use exacerbates global climate change trends.

Excessive nitrogen fertilization in rice farming has far-reaching negative impacts, including soil degradation, water pollution, and ecological damage. Rational nitrogen management, soil and water conservation, and eco-friendly practices are critical to ensuring food security and promoting sustainable agricultural development.