Effectiveness of Phosphorus Fertilizers
The effectiveness of phosphorus fertilizers depends on:
- soil and climatic conditions;
- properties of fertilizers;
- zonal characteristics of soils;
- biological characteristics of crops;
- agrochemical methods for optimizing the application of phosphorus fertilizers;
- phosphate content;
- moisture availability.
Features of applying phosphorus fertilizers with regard to their solubility:
- water-soluble phosphates are applied on all soils, for all crops, and by various methods;
- the effectiveness of phosphates soluble in weak acids depends on soils; for example, on acid soils their effect is higher than that of superphosphates;
- sparingly soluble phosphorus fertilizers are effective on acid soils of the Non-Chernozem zone and on northern leached and degraded chernozems.
Numerous experiments comparing equivalent doses in different soil-climatic zones indicate that periodic (once every 3 years) application of phosphorus fertilizers to annual crops is, as a rule, more effective than annual application. Under perennial forage and fruit-and-berry crops, this practice is even more effective.
The concentration of hydrogen ions is important for phosphate uptake by plants: as a solution is alkalinized, phosphate forms change from dihydrogen orthophosphates H2PO4- to hydrogen orthophosphates HPO42- and orthophosphates PO43-. At the same time, the solubility of these forms also decreases, making phosphorus unavailable to plants.
On all soils, superphosphate and precipitated phosphate have a more stable effect on yield.
Effect of Soil Phosphorus Content on Effectiveness
Phosphorus fertilizers have a greater effect on yield on soils with low and medium mobile phosphorus content, whereas on soils with elevated and high content, the effect is weak or absent.
On sod-podzolic and gray forest soils, the optimal mobile phosphorus content by the Kirsanov method is 10–15 mg/100 g. This level of supply is considered sufficient to obtain, under normal climatic conditions and against the background of nitrogen-potassium fertilizers, high yields of field crops, for example, grain up to 5.5 t/ha, hay of perennial grasses 5.5–7.0 t/ha. The same value of optimal mobile phosphorus content by the Chirikov method is adopted for noncarbonate chernozems. On carbonate chernozems, chestnut, and serozem soils, the optimal content by the Machigin method is 3–4.5 mg/100 g.
When the mobile phosphorus content in sod-podzolic soils is 10–12 mg/100 g, yield increases from phosphorus fertilizer application are unstable, and at 15 mg/100 g the effect is, as a rule, absent. Complete abandonment of phosphorus fertilizers on such soils is inadvisable, since it leads to depletion of soils in mobile phosphates; therefore, fertilizer doses are applied that compensate for P2O5 removal by plants. Agrotechnically optimal can be considered the combination of applying sparingly soluble forms in the main fertilizer with row (starter) application of soluble forms.
Phosphorus fertilizers must be applied at high doses of nitrogen-potassium fertilizers to avoid imbalance in the ratio of elements (N:P:K).
The application of fertilizers on soils with low phosphorus content should ensure a gradual increase in content to the optimal level. For this, doses are calculated not only for the planned yield but also for increasing soil fertility. To increase the content of mobile phosphorus in soil by 1 mg/100 g, one can use the nutrient consumption rates developed by the All-Russian Research and Design-Technological Institute of Agricultural Chemistry.
Table. Nutrient consumption for increasing the content of mobile phosphorus in soil by 1 mg/100 g.
| Soils | Particle-size distribution | P2O5 consumption |
|---|---|---|
| Sod-podzolic | Sandy and sandy loam | 50-60 |
| Light and medium loamy | 70-90 | |
| Clayey and heavy loamy | 100-120 | |
| Gray forest | Sandy and sandy loam | 70-80 |
| Light and medium loamy | 90-110 | |
| Clayey and heavy loamy | 120-140 | |
| Podzolized and leached chernozems | Sandy and sandy loam | 80-90 |
| Light and medium loamy | 90-100 | |
| Clayey and heavy loamy | 100-120 |
Effect of Moisture Availability
Phosphorus improves root system development, thereby increasing plant resistance to drought and other unfavorable conditions.
The effectiveness of phosphorus fertilizers depends on moisture availability for crops. As climate continentality increases, which leads to reduced moisture availability, effectiveness decreases. However, phosphorus fertilizers promote economical use of moisture by plants, thereby mitigating the effect of moisture deficit.
Phosphorus fertilizers are more effective in areas of insufficient moisture and arid climate on southern and ordinary chernozems, chestnut and brown soils, and on poorly cultivated soils of other types. For example, on uncultivated sod-podzolic variants (1st–2nd class), they surpass nitrogen fertilizers in effectiveness.
Effectiveness of Phosphorus Fertilizers Depending on Soil Type
On chernozem soils, phosphorus fertilizers show good effectiveness, which is explained by sufficient soil nitrogen supply and development of plant root systems. Against a phosphorus-fertilized background, plants use 10–15% less water per unit of yield.
On gray forest soils, the effect of phosphorus decreases due to poorer nitrogen supply and mobility of organophosphorus compounds in them.
On sod-podzolic soils, phosphorus fertilizers show fairly high effectiveness provided they are used in combination with other fertilizers and with observance of agrotechnical and reclamation measures.
Phosphorus fertilizers are well absorbed by soil at application sites; phosphorus migrates little through the soil profile and is rapidly fixed by chemical absorption, especially on soils with high absorption capacity and base saturation degree. The danger of phosphorus leaching on such soils is almost absent.
Effect of Fertilizer Properties
To avoid nitrogen losses when applying phosphorus and nitrogen fertilizers, observe the following rules:
1. Alkaline forms of phosphorus fertilizers must not be mixed with ammonium forms of nitrogen fertilizers.
2. Dry superphosphate is mixed with ammonium nitrate before application, since their mixture becomes damp during prolonged storage.
3. Mixing superphosphate and ammonium sulfate leads to formation of gypsum; the mixture hardens during prolonged storage.
Mixing acidic superphosphate with nitrate fertilizers leads to the formation of free nitric acid, which quickly volatilizes:
Before application, the excess acidity of superphosphate, which negatively affects young plants, is eliminated by mechanical mixing with phosphate rock (up to 15%), dolomite flour (up to 10%), or lime.
Phosphorus from organic fertilizers (manure and composts) is assimilated by plants better than from mineral fertilizers.
References
1. Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Ed. by B. A. Yagodin. Moscow: Kolos.
2. Evtefeev Yu. V., Kazantsev G. M. (2013). Fundamentals of Agronomy: A Textbook. Moscow: FORUM.
3. Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Ed. by Mineev V. G. Moscow: Publishing House of VNIIA named after D. N. Pryanishnikov.
