- Phosphorus is poorly absorbed at lower temperatures, which are often recorded in the initial periods of corn development
- The application of phosphorus in places with unregulated pH may not be very effective
There is little phosphorus from manure in the first year
It is assumed that with each tonne of crop (grain and straw), corn absorbs 8 – 12 kg of phosphorus (P2O5). Therefore, assuming a yield of 10 t/ha, we should ensure a supply of this ingredient at the level of 80 – 120 kg. The forecrop, the soil’s phosphorus content and the availability of the ingredient from the given natural fertilizers must also be taken into account. At the same time, soil pH is important. Generally, the highest availability of this ingredient is recorded in soils with a pH of 6.5 – 7. Its availability drops dramatically in acidic lands, where phosphorus is limited (similarly in alkaline lands).
It is estimated that a ton of manure contains 2.8 kg of P2O5. This means that with a dose of this fertilizer of 30 t/ha, we provide 84 kg of phosphorus. What is important here is how often manure is applied to a given site. In the first year after application, a maximum of 25% of phosphorus is available. This means that after such an application we can reduce the mineral phosphorus fertilization by 21 kg/ha (of course in the pure ingredient). If manure is applied systematically, a higher availability of this ingredient can be assumed. Thus, in the second year after application, phosphorus uptake is as much as 70%. Therefore, autumn application will be much more beneficial than spring application.
Therefore, if we plan a corn yield of 10 t/ha, with regulated pH, average phosphorus content and application of manure in spring, we give at least 80 kg of P2O5 (e.g. 170 kg of ammonium phosphate 18-46). However, if manure is not provided, fertilization must be increased. In turn, if manure is applied cyclically (regularly, at least every two years), phosphorus from mineral fertilizers can be further reduced. We give higher doses when this ingredient is administered by spraying (more on this later), we do not give natural fertilizers, and additionally, research shows that the soil is low in phosphorus.
Phosphorus is best administered precisely
Let us add here that in case of cold weather, deficiencies of this ingredient may occur anyway (even despite high doses of the ingredient). Lower P intake is observed when the temperature drops below 13 ºC. Therefore, we often observe discoloration resulting from the lack of phosphorus supply of corn in the initial stages of development, when the soil is often still relatively cool. However, these discolorations on plants are the result of problems with the root system – it is reduced. A sure remedy for this problem is the application of, for example, ammonium phosphate through the grain sifter. Spot fertilization (5 cm next to and the same amount below the seed) significantly reduces poor phosphorus nutrition and even stimulates the plant to root deeper (the roots’ natural desire for phosphorus). This is where the advantage of localized fertilization comes into play. In the case of classic spreader application, phosphorus granules can be placed at different depths. It may turn out that the root system will grow intensively in the first moments of development only until it encounters phosphorus, and then the dynamics will decline. Moreover, localized fertilization is recommended in soils with a pH lower than optimal for P uptake – then this ingredient is quickly available.
The dose of fertilizers must be individualized
Whether we decide on lower phosphorus fertilization should be dictated by knowledge of the soil content. If the results of soil tests clearly indicate low abundance of both of these ingredients, the higher of the recommended doses should be administered (according to the expected yield). However, if the abundance is at a good level, the lowest possible values from the recommended ranges can be adopted. Much also depends on the forecrop, the method of treating post-harvest residues and the possible application of natural fertilizers. Each situation is slightly different, and in order to optimize economically, all of the above factors must be taken into account.
Material protected by copyright – the rules for reprints are specified in the regulations.
