Agriculture for Engineers 4 (3+1)

Lesson 42. Fertilizer Application and Fertigation

42.2 METHODS OF APPLICATION

While selecting the method of application of manures and fertilizers to the nursery plants, nurserymen should consider the nutrients, their ability to be effectively absorbed, their effect on soil and environment, equipment availability and the relative cost involved. However, in general, fertilizers in the nursery are applied either as surface application, sub-surface application or as foliar sprays.

(a) Surface application: Band placement along the rows is the most commonly used method of fertilizers application by the nurserymen. It is an effective and efficient method for the application of nitrogen, since nitrogenous fertilizers move into the root zone with the downward movement of water. However, direct surface application is not suggested for applying phosphorous, potassium and other nutrient because they may get fixed on the exchange complex.

(b) Sub-surface application: Incorporation of the fertilizers into the soil by subsurface application is the most effective means of applying nutrients that are fixed (P, K etc.) on the exchange complex or are slow to move into the soil solution. Nurserymen can best incorporate these materials into the soil prior to planting the nursery crop.

(c) Foliar application: In general, nutrients can be applied through foliar means immediately after the symptoms have appeared. For nursery plants, foliar application of the nutrients is very effective as compared to soil application because through foliar means, nutrients are absorbed at a faster rate. Moreover, wastage of nutrients is also very less. For foliar application, the nutrients should be applied when there is sufficient foliage on the plant. The nutrient should either be applied in the morning or late evening hours. Similarly, it is always better to add some wetting agents like Tween-20, Triron-X-100 etc. in the spray solutions as these help to absorb the nutrients even more effectively. Borax is used for supplying boron, which is difficult to dissolve in fresh water. Therefore, one should use lukewarm water for this purpose.

(d) Top dressing: It implies to application of fertilizer in standing crop. Nitrogen and micronutrient fertilizers are administered to the plants using this method.

(e) Localized placement: In this technique, fertilizers are applied close to the seeds or plants. This technique is very much economic and less quantity of fertilizers is required for the purpose of applying the nutrients.

(f) Contact placement: In this technique, seeds and fertilizers are applied simultaneously at the time of sowing. To avoid salt injury, seeds and fertilizers are applied at different depths.

(g) Band placement: In this technique, the fertilizers are applied in band. This is especially useful in widely spaced crops like fruits and plantation crops in which by applying in band close to the root spread, the fertilizer saving is achieved.

(h) Row placement:  It consists of placing the fertilizer along the rows of crops. Fertilizer may be applied in one or both sides of the rows depending upon spread of the crops. This technique is suitable for application of fertilizer in vegetable crops.

(j) Pellet placement: In this technique, fertilizers are applied in pellet form. For making pellet, soil and fertilizers are mixed in the ratio of 1:10 and made into dough. Small pellets are made out of it and placed in root zone of plant.

(k) Other forms of application

• Starter solution: It is mild solution of NPK in the ratio of 1 : 2 : 1 used for soaking seed, dipping roots and spraying over seedlings for early start of the crop. Feeding starter solution, the seedlings establish early and start growth soon.
• Fertigation: Application of fertilizer along with irrigation water is called fertigation.
• Foliar spray: Mild solution of nutrient is applied over foliage.

42.3 FERTILIZER DOSE

Fertilizer dose is calculated based on requirement of crops/plants for its various physiological activities. While applying fertilizer, nutritional status of soil is taken into account. After deducting contribution of soil, rest amount is replenished externally using fertilizer. To ascertain this dose, following approaches are resorted.

42.3.1Maintenance Concept

     In this approach, whatever quantity of nutrient is removed by crop, it is supplemented by application of fertilizer to maintain original nutritional status of soil.

42.4 FERTIGATION

This term refers to supply of dissolved fertilizers to crops through an irrigation system. Continuous applications of small quantities of soluble nutrients overcome the problems of loss of fertilizers due to runoff of leaching, save labour and ensure uniform placement of nutrients around roots, in turn encouraging rapid and maximum uptake by plants. Fertigation offers a potential technique to reduce fertilizer wastage and increase fertilizer use efficiency. Fertigation became possible after development of micro irrigation systems. Fertilizers to be used and method of mixing with irrigation water should be selected with proper care. Only readily soluble fertilizer products can be used for this purpose. Specific soluble fertilizer formulations for particular crops are available in markets, which are costly but cost effective also. Uniformity of water application, which ensures even fertilizer distribution, method of injection, type of fertilizer and scheduling are significant factors to be considered. Fertilizer should be injected at scheduled times at optimum concentration with limited quantity of water to avoid leaching losses. Fertigation immediately before or after irrigation or heavy rains should be avoided. After injection of fertilizers, system should be run for 15-20 minutes to prevent any clogging of emitters. Fertigation is beneficial in fruit crops like mango, banana, grapes and papaya.