Fertigation makes it possible to apply nutrients very precisely according to the nutritional demands of the crop. This has dual benefits: on one hand it can increase the potential yield of a crop by means of precise and timely nutrient provision, and on the other hand it means that the amount of nutrients applied can be reduced due to the reduction of losses through leaching or volatilization. To maximize results, a grower needs to work consistentlywith WSFs throughout the irrigation cycle.
Before designing a fertigation programme, several parameters need to be taken into consideration:
- Soil: the soil analysis is a very important factor in determining the fertilization plan; knowledge of the nutrient levels in the soil means the grower can adjust the fertilization plan (adding or reducing nutrients). The pH of the soil makes it possible to predict which nutrients will be available in large or small quantities for the plant roots.
- Water: the water analysis is important as it informs the grower which nutrients the water will supply. The common nutrients in water are: Ca, Mg, and Cl. Knowing the pH levels of the water allows a grower to choose the best formula for his/her conditions. For example, if the pH levels of the water and the bicarbonates are high, the grower will choose fertilizers with an acidifying effect to neutralize the bicarbonates and to reduce the pH of the water. (More information is available in the ‘water quality’ section).
- Crop demand: knowing the nutrient demands of various crops during the growing cycle allows the grower to create an accurate fertilization plan that will result in an optimum yield.
To successfully grow crops, many variables must be taken into account:
Besides climatic conditions (temperature, humidity, light intensity, etc.), pH, and soil nutrient levels, another important factor is the quality of the water used for the irrigation of the crops. When we talk about the quality of irrigation water, we refer to nutrient levels, pH, salts (expressed as the conductivity: EC), and bicarbonates.
The plant receives macro and microelements via the irrigation water.
If the level of these nutrients and the requirements of the plant are known, we can determine the optimum fertilizer dosage and thus avoid overfertilization.
pH is the degree of acidity of the soil or water, expressed on a logarithmic scale from 0 to 14, with 0 being highly acidic and 14 being highly alkaline. A neutral pH is expressed as 7.
Each crop needs a certain pH level for growth and harmonious development. The pH of the irrigation water is as important as the pH of the soil in which the plants will grow. The vast majority of crops grow and thrive in an environment with a pH between 5.5 and 6.5. It is important to understand that the pH directly influences the absorption of essential nutrients for the plant’s growth and development. At high pH levels (above 7–7.5), the plant’s absorption of phosphorus, iron, boron, copper, and zinc will start to be inhibited. This is how plants suffer deficiencies, even when fertilizers are used to provide the necessary nutrients. If these parameters are not known, it can be tempting to apply greater quantities of fertilizers and thus increase the salinity (EC) around the roots. This can also cause other imbalances, forinstance by reducing the absorption of water and nutrients by the plant due to high osmotic pressure created around the roots by the increased presence of soluble salts.
Water hardness is a very important factor determining the quality of the water. Calcium (Ca) and magnesium (Mg) have a major role in the hardness of the water. To accurately check the pH of the water, the grower needs to perform an analysis of the water.
EC: salt concentration
EC is expressed numerically in mS/cm. In general, the EC in the solution used for the plant - the sum of the irrigation water EC and the water-soluble fertilizer EC - should not exceed 2–2.2. This value is recommended for soil-grown crops. Water-soluble fertilizers are basically salts. When they are dissolved in water, the salt concentration increases. In general, these values are expressed in grams per litre and are specified on the packaging.