Fertigation in fruit crops
A. K. Goswami, A. Nagaraja, Madhubala Thakre and Jai Prakash
IARI, New Delhi-110012

Fertigation is a term specially coined to describe the supply of dissolved mineral fertilisers to tree roots via irrigation water, generally as continual or very frequent doses throughout the growing season. In this system fertilizer solution is distributed evenly in irrigation. The availability of nutrients is very high therefore the efficiency is more. The use of fertigation is gaining popularity because of its efficiencies in nutrient management, time, labour and potentially a greater control over crop performance. One of the major factors to promote modern fertigation was the development of micro irrigation system which includes drip, Jet and sprinklers. This has facilitated more widespread adoption of fertigation, especially for perennial fruit crops. In this method liquid fertilizer as well as water soluble fertilizers are used and fertilizer use efficiency is increased. The concept has been around for many decades, but recently fertigation has been more widely adopted, and it is now quite common on permanent plantings of fruit trees. One implication of fertigation is that the fertility of the soil becomes less important to the health and productivity of the crop, which relies far more on the provision of nutrients to the root zone via fertigation. When combined with an efficient irrigation system both nutrients and water can be manipulated and managed to obtain the maximum possible yield of marketable production from a given quantity of these inputs. Often, solid fertiliser applications are causing more management constraints rather than the horticultural requirements of the crop. Continuous small applications of soluble nutrients overcome many problems, save labour, reduce compaction in the field and the fertiliser being placed around the plant roots uniformly and allow for rapid uptake of nutrients by the plant.

Fertilisers used in fertigation

Fertigation can be achieved by using single or multiple nutrient fertilizers in their solid or liquid form. The fertiliser products which can be used are limited to those that are readily soluble. Method of fertilizer application is primarily depends upon the place of occurrence of feeder roots. Feeder roots are fine roots which are primarily responsible for nutrient and water absorption. Many commercially formulated soluble fertilisers nowadays available to growers. These fertilizers are crops specific, or their combinations can be used depending on the crop cycle. They have the advantage of being stable and highly soluble, dissolving rapidly and providing a balance of nutrients so only one product is handled at a time. However, they are generally more expensive per unit of nutrient than are standard fertilisers. The ideal fertilizer for fertigation should posses the following quality:

1. Fully soluble.
2. Quick dissolution in irrigation water.
3. Fine grained product.
4. Insoluble of non-clogging mineral and bacterial type.
5. High nutrient content in the standard solution
6. No chemical interaction between fertilizer and irrigation water.
7. It should have minimum content of conditioning agents.

Forms of Fertilisers

Agricultural grade fertilisers are generally not suitable for use in fertigation systems because of the amount of impurities present, which may be insoluble and lead to dripper blockages. For this reason technical grade fertilisers are normally required in fertigation systems because they have fewer impurities and proportionally higher levels of the desired mineral nutrients. Single, double and triple-strength superphosphate and rock phosphate are unsuitable for use in fertigation systems. Fertilisers suitable for use in fertigation systems come as technical grade salts (e.g. potassium sulphate), acids (e.g. nitric acid), bases (e.g. potassium hydroxide), polymers (e.g. polyphosphate) or chelates (e.g. iron EDTA). They are almost exclusively injected into the irrigation water already in solution (i.e. pre-dissolved in water). The amount of each fertiliser that can be completely dissolved in a given volume of water is different and highly dependent on the temperature of the water. Less of a given fertiliser can be dissolved in cold water (i.e. less than 5°C) than can be dissolved in warm water (i.e. more than 15°C). There are guides and charts available on the amount of various fertilisers that can be dissolved in a given volume of water as a function of the temperature of that water.

In conclusion, the synergism and combination of water and nutrient leads to an efficient use of both by the plants. Fertigation is sophisticated and efficient method of applying fertilizers, in which the irrigation system is used as the carrier and distributor of the nutrients. Using fertigation to manage crop performance needs to be based on a good knowledge of when and to what extent each mineral nutrient is taken up by the crop's roots and how it affects crop growth, development, and yield. Undoubtedly fertigation potentially offers many advantages over conventional approaches to managing a crop's fertiliser needs. While fertigation is an exciting and potentially profitable addition to horticultural production systems, it also requires significant investment in equipment, advanced management skills, constant monitoring and an understanding of the specific crop's nutrient needs. When the advantages of fertigation are exploited and the disadvantages are minimized, fertigation can be a very efficient method of fertilization.

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