What are the specific benefits of optimal NPK concentration for rice?

The specific benefits of optimal nitrogen (N), phosphorus (P), and potassium (K) concentrations for rice are mainly reflected in the following aspects:

1. Significantly Increased Yield: Rational application of nitrogen, phosphorus, and potassium fertilizers can significantly increase rice yield. Studies have shown that rice yields in the full-fertilizer (NPK) zone increased by 48.7%, 33.4%, 16.7%, and 8.2% compared to the no-fertilizer, nitrogen-deficient, phosphorus-deficient, and potassium-deficient zones, respectively. Nitrogen fertilizer has the greatest impact on rice yield, followed by potassium fertilizer, while the impact of phosphorus fertilizer is relatively small.

The recommended fertilizer application rates in the full-fertilizer (NPK) zone are:

Nitrogen (N): 225 kg/ha

Phosphorus (P₂O₅): 90 kg/ha

Potassium (K₂O): 90 kg/ha

2. Improve Rice Quality

The rational application of nitrogen, phosphorus, and potassium fertilizers can improve rice quality, such as increasing the head rice rate, reducing chalkiness, length-width ratio, and amylose content in polished rice. Nitrogen and phosphorus fertilizers can also increase the protein content of brown rice.

3. Improve Nutrient Absorption Efficiency

The combined application of nitrogen, phosphorus, and potassium fertilizers can significantly increase the total nutrient absorption of rice. However, it is important to note that excessive fertilization can lead to decreased nutrient utilization efficiency.

In the brown soil region of Liaoning, the apparent utilization rates of nitrogen, phosphorus, and potassium fertilizers were 27%, 14%, and 62%, respectively, with an average fertilizer utilization efficiency of only 34%, far lower than the national average of 40.2% for rice fertilizer utilization in 2020.

Based on the QUEFTS model, the nitrogen, phosphorus, and potassium required to produce 1 ton of grain per hectare of single-season rice are 14.2 kg, 3.9 kg, and 14.3 kg, respectively.

4. Enhance Plant Stress Resistance: The rational application of nitrogen, phosphorus, and potassium fertilizers can enhance the stress resistance of rice plants, such as improving root vitality, preventing leaf curling, and enhancing photosynthetic efficiency, thereby improving single-grain quality.

In arsenic (As) contaminated soils, the optimal NPK concentration combination can significantly reduce the physiological toxicity of arsenic to rice seedlings and reduce the accumulation of inorganic arsenic in roots and stems.

5. Optimize Soil Fertility: Long-term application of nitrogen, phosphorus, and potassium fertilizers can significantly improve soil fertility, increasing the concentrations of soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), and available potassium (AK). Compared with the application of inorganic fertilizers alone, the combined application of organic and inorganic fertilizers (NPK) can further improve soil fertility and rice yield.

General Recommendations: Nitrogen fertilizer (N): Generally recommended at around 200-250 kg/ha, the specific amount needs to be adjusted according to soil fertility and target yield.

Phosphate fertilizer (P₂O₅): Around 100-120 kg/ha, but the initial phosphorus content in the soil must be considered.

Potassium fertilizer (K₂O): Around 120-150 kg/ha, especially effective in potassium-deficient soils.

6. Reduce Environmental Pollution Rational fertilization can reduce the loss of chemical fertilizers in farmland soil, thus reducing environmental pollution. By optimizing the amount and ratio of fertilizers, excess nutrients such as nitrogen and phosphorus can be reduced, thereby reducing pollution to soil and water bodies.