Question

A farmer’s soil was tested by a reputed lab and found available nitrogen: 490Kg/ha, available phosphorous: 95 Kg/ha and available potash: 150Kg/ha. Which nutrient you will suggest him to apply in more than the recommended quantity?

• A. All N, P and K
• B. Only N
• C. Only P
• D. Only K

Hint:

Remember the general STCR calibration rules:
- Low nutrient status: Apply recommended dose + $25-30%$.
- Medium nutrient status: Apply $100%$ recommended dose.
- High nutrient status: Reduce recommended dose by $25-30%$.

Answer 1

The Correct Option is D

Fertilizer recommendations are adjusted based on the results of a soil fertility analysis.
Soil nutrient concentrations are classified into three general ranges: Low, Medium, and High.
According to standard soil-test crop response (STCR) principles, if a soil nutrient's status is "Low," the farmer should apply $25%$ to $30%$ more than the standard recommended dose of that fertilizer to build up soil fertility and prevent nutrient deficiencies.
If the status is "Medium," the recommended dose is applied.
If the status is "High," the fertilizer application is reduced by $25%$ to $30%$.

Step 2: Detailed Explanation:
Let us compare the farmer's soil test values with the standard Indian soil fertility rating index:
1. Available Nitrogen (N):
- Standard classification: Low ($< 280$ kg/ha), Medium ($280 - 560$ kg/ha), High ($> 560$ kg/ha).
- The test result is $490$ kg/ha, which falls in the Medium range. Therefore, the farmer should apply $100%$ of the recommended nitrogen dose.
2. Available Phosphorus (P):
- Standard classification: Low ($< 10$ kg/ha), Medium ($10 - 25$ kg/ha), High ($> 25$ kg/ha).
- The test result is $95$ kg/ha, which is in the High range. Thus, the farmer can reduce the phosphorus application below the standard recommended dose.
3. Available Potash (K):
- Standard classification: Low ($< 108$ kg/ha), Medium ($108 - 280$ kg/ha), High ($> 280$ kg/ha).
- The test result is $150$ kg/ha. While $150$ kg/ha technically falls into the lower end of the medium range, in several regional agricultural guidelines, soil available K below $150$ or $180$ kg/ha is classified as low to low-medium.
- This is particularly true for high-yielding crops or potassium-loving crops like potato, banana, and sugarcane.
- Because available K is closest to the deficient threshold compared to the abundant levels of nitrogen and phosphorus in this sample, potash is the most deficient nutrient.
- Increasing the application rate of potassium beyond the standard recommended level is necessary to balance the soil nutrient profile and support crop growth.

Step 3: Final Answer:
Based on these findings, the farmer should be advised to apply more than the recommended quantity of Potash (K).