The Pro Farmer

How much fertilizer should i add to my plants

Healthy development of plants depends on proper nutrition. The nutrients that plants need are taken from the soil using their roots. If the soil does not have enough nutritional properties, additional plant nutrients should be mixed into the soil. However, if these materials are used together and properly with knowledge and technology, the expected yield can be achieved. Otherwise, irreversible problems begin.

Fertilizer is a substance that is mixed into the soil to provide the chemical ingredients necessary for nutrition to the plant. Fertilizers include foods that help plant growth. Hence, the types of fertilizer to be used, minerals and other chemicals in the content of the fertilizer are of great importance. Essential elements for plant development are phosphorus, nitrogen, potassium, magnesium, manganese, calcium, iron, sulfur, copper and zinc. The most important of which are phosphorus, nitrogen and potassium.

Commercial fertilizers contain mainly phosphorus, nitrogen and potassium, which are important for plant nutrition. Lack of nitrogen turns the plant yellow and prevents its development. Lack of phosphorus prevents the growth of roots and inhibits the ripening of the plant. Potassium deficiency weakens the plant stems and prevents fruit formation.

The plants uses the nutrients in the soil and empty them from their nutrients. So we need to add these nutrients all the time, using fertilizers.

Each soil contains some or none of these nutrients, but each soil or planting media, is different from the other. And also 10 plants consume more fertilizer than 5 plants, and full grown plants with fruits need more fertilizer than young small ones. So how can you know, how much fertilizer to add, if any?

With the soil water sampler/soil salinity tester/soil solution sampler/lysimeter, we can extract the solution that is around the plant’s roots enviroment and determine 7 things:

1. Does the plant have enough nitrogen (N) 2. Does the plant have enough potassium (K) 3. Does the plant have enough phosphoros (P) 4. Does the plant have enough oxygen (indication of over irrigation) (NO2) 5. Is the soil too salty for the plant (too much fertilizer), Which will make it difficult for it to absorb water (EC) 6. Another indicator for the salinity of the water, which will make it difficult to absorb water (CL) 7. Does the nutrients are easily absorbed fron the soil (PH)


With this device we can pump out of the plant roots zone, a sample of soil solution. The soil water consists of most of the dissolved nutrients, as well as salt that may accumulate, or be missing, in the soil. The user can analyze the sampled water content throughout the growing period.

The soil solution sampler is a 300mm length of 40mm diameter PVC electrical conduit with a ceramic cup glued to one end. A PVC plug seals the other end and two tubes travel from inside the soil solution sampler to the soil surface. The vacuum tube protrudes just inside the PVC plug and the extraction tube rests at the bottom of the ceramic cup. The sampler is buried at the depth of interest, in a place and depth where the plant roots are mostly active. The sampler must be tightly fited in the soil, and the ceramic cap has to be in full contact with the soil.

To retrieve a soil solution sample, a vacuum pump is used to vacate the soil solution sampler. By pulling the plastic syringe a vacuum power is created within the device The sampler is then left for solution to collect in the ceramic cup. The time taken for sufficient soil solution to collect in the ceramic cup depends on the soil tension. In heavy soil the wetting time is longer than in light soils. Normally 4-8 hours after the end of irrigation, The time depends on soil type and also the user’s convenience. 24 hours is usually long enough. The 1-way vacuum tube valve is then opened and a syringe with a filter is attached to the 4-way valve to extract the sample. From which the farmer can analyze the water.

It is Generally recommended to activate the soil water sampler soon after watering, when the soil is in Field Capacity.

Locate a healthy plant or row, with a developed canopy, a typical plant to represent most of the monitored field. The device should be inserted into the soil in an active root zone, the same as we do for Tensiometers. For best results and to get a better picture of the situation it is recomended to put two samplers in different depths, like 15cm and 30cm, or in a different place in the field for authentication.

The sampler stays permanently in the ground, and used each week or when needed.

In order to measure the solution of nutrients, PH level, salinity etc, in the growing medium in the pot, you need to water the pot and measure the runoff.
runoff is the excess liquid that comes out of the drain holes of the pot during irrigation.

After you collect the solution from the root’s zone its time to analyze it with the fertilizer test kits, and with the PH and EC meters.

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