Broadcasting is uniformly distributing dry or liquid materials over the soil surface, usually before sowing. The fertilizer may be incorporated into the soil mechanically, or left on the surface to be washed in by rainfall or irrigation. Incorporation into the Ap horizon can be done with a harrow (2-3 cm depth), a cultivator (4-6 cm depth) or a plough (incorporation to plough depth). Broadcasting is the simplest and cheapest method and is best suited for high-speed operations and heavy application rates, especially before planting.
In order to achieve high efficiency, fertilizer may be applied in localized bands, at or just prior to planting. However, inaccurate band placement can leave large concentrations of soluble salts in the deposition zone, leading to decreased germination and plant emergence, because of severe plasmolysis. Fertilizer placed in a band below (5 cm) and to the side (5 cm) of the seed usually causes minimal damage during germination, and seedling roots develop normally. Within a short period (2 weeks) and if there is enough soil moisture, the salt in and around the band diffuses into a larger volume of soil, so that there is no longer any hazard to plants. The quantity of fertilizer that can be safely band-placed depends on the crop and the type of fertilizer used.
Fertilizer can be applied with the seed by a double-disc or similar drill that places the seed and fertilizer in a very narrow band. Band placement can be more efficient than broadcasting, especially where soil test levels are low, where early-season stress from cool or wet conditions is likely to limit root growth and nutrient uptake, and in soils likely to fix a large proportion of the added nutrient. Banding of fertilizer is widely practiced under no-till management.
Side or top dressing
Fertilizer is side- or top-dressed when it is applied after the crop has emerged, and/or when the dose is split between two or more applications. Split applications can be beneficial in some cases, especially for annual crops with a long growing period.
Split application is also recommended for crops growing on soils with low cation exchange capacity (CEC), where the nutrients can be lost through leaching following high rainfall or excess irrigation. Split application is also used in orchards and for other perennial crops, especially for alfalfa and grasses
Equipment for solid fertilizer application
Fertilizers can be applied manually, by trained workers who achieve approximately the correct amount and uniform application. It is typical in small plots in developing countries. A more advanced method consists uses small portable centrifugal distributors operated by hand.
Modern fertilizer spreaders range from simple centrifugal types with broadcasting widths of 24 m or more, to pneumatic spreaders in which each outlet accurately spreads over 2 to 3 m.
Wide-sweep or full-width distributors can be of the box type or centrifugal. In the drop or box-type distributor the fertilizer drops by gravity through a distributing device that uses slots, an endless chain, rotating plates or grids at the bottom of the box. This type of distributor suits both fine and granulated fertilizers, and applies a fairly exact pattern, limited to the distance between the wheels. The main disadvantage is the small working width - up to 5 m.
In the centrifugal, rotary or cyclone distributor, the fertilizer drops from a conical container onto a high-speed rotary disk with throwing bars. A baffle plate ensures that the fertilizer is spread in a semicircle, and only to the rear. The main advantage is the larger working width (12-14 m). The main disadvantages are that only granulated fertilizers can be spread; and they are harder to calibrate because heavier fertilizer particles are thrown further from the spreader. Another type of distributor is the row distributor, which uses pneumatic systems to give precise application in plant rows..