Fertilizer Rate Calculation

During the cultivation of agricultural and horticultural crops, the lion’s share of the cost of the farmer falls on the application of fertilizers. Neither more nor less, but about 25%. Therefore, the urgent questions of each farmer before sowing –

How much and what kind of fertilizer to use this year?
How to correctly calculate the rate and form of fertilizer application?

Of course, agrochemical soil analysis will be the first thing to help. This is an important tool for calculating rates, as well as a method for choosing the fertilizers themselves. The resulting analysis must be deciphered and then a technological map should be created for the crops planned for sowing and yield calculation.

Such soil analysis must be performed by an accredited laboratory or specialized facility. For example, in the Kharkiv region, this may be the Scientific and Technical Center Institute of Soil Science and Agrochemistry. A.N. Sokolovsky.

After the analysis, a Research Protocol is issued, which indicates the following main macro indicators:

1. Nitrogen (N-NO3, NH4) in ammonium and nitrate form, mg/kg soil
2. Phosphorus (P2О5) including mobile forms, mg/kg soil
3. Potassium (K2O) mobile forms, mg/kg soil
4. soil pH

Further, the measurement results can be converted to more standard kilograms for calculations. Namely, from the established calculation that in the arable layer (up to 30cm) there is 3 million kg / ha of soil, we calculate:

• Nitrogen

(N-NO3 mg/kg+ NH4 mg/kg)*3,000,000 / 1000 = N-NO3, NH4 kg/ ha

Recalculation for phosphorus and potassium can be done through the coefficient of their use by a certain agricultural crop on a specific type of soil (see the norms of the coefficient in textbooks or on the Internet -resources). For example:

• Phosphorus

(P2O5 mg/kg*use factor)*3,000,000 / 1000 = P2O5 kg/ha

We calculate potassium in the same way:

• Potassium

(K2Omg/kg*utilization rate)*3,000,000 / 1000 = K2O5 kg/ha

IMPORTANT! Knowledge of the actual biochemical state of the soil will allow you to increase your yield by 30-50% at no extra cost.

Then, using the balance-calculation method, based on the coefficient of use of nutrients from fertilizers, we calculate the rate of the active substance using the formula:
N a.w = W l.w kg/ha – K e.f kg/ha / 10 *Cd
where,

• In kg/ha – nutrient removal by the planned crop (see norms on the Internet)
• Ke.f kg/ha – the amount of the element in the soil actually
• Coefficient of fertilizer use by plants (for nitrogen 50%, for phosphorus 15%, for potash 50%)

For the sample, we calculate nitrogen, for example, for corn (for corn, the removal N = 3.4 kg a.i. by-products):
H a.w = 340kg/ha – N-NO3, NH4 kg/ha / 10 * 0.5
And by analogy, do the calculations for phosphorus and potassium.

Next, pay attention to soil pH. If the indicator is normal (from 5.5 to 7.5 or 8), then any type and form of fertilizer can be used. An integrated approach and a correct mathematical calculation for the use of fertilizers will maximize yields at the lowest possible cost.

For a balanced plant nutrition and a high level of agricultural production, a clear understanding of the environment and separation in the application of fertilizers is important. Namely, taking into account such factors as:

• climatic characteristics of the region
• soil features
• changing nutritional needs of crops during different growth periods
• hereditary possibilities of bred varieties
• soil biochemical parameters.

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Literature:
Blog article by agronomist Dobrenky A.