CHAPTER 1
Transformation of Phosphorus in Soils of Agroecosystems in Long-Term Experiments: Sustainability Challenges of Phosphorus and Food
RAFAIL A. AFANASâEV, GENRIETTA E. MERZLAYA, and MICHAIL O. SMIRNOV*
Pryanishnikov All-Russian Scientific Research Institute of Agrochemistry, d. 31A, Pryanishnikova Street, Moscow 127550, Russia
ABSTRACT
In field experiments with the long-term systematic application of fertilizers (prolonged trial), new regularities of the dynamics of the mobile phosphorus content in soils of various agroecosystems have been established. It is shown that the increase in the content of mobile phosphorus in different soils occurred only in the first rotation of crop rotations. In the future, despite the positive balance of phosphorus, the content of its mobile forms did not increase or even had a tendency to decrease due to the transition of phosphorus to an inactive state. In the case of a negative balance, the content of mobile phosphorus in soils was compensated by the reserve of inactive phosphates. Thanks to these processes of phosphate transformation in agricultural ecosystems supported the ecological balance, protecting against loss of phosphorus with surface and subsurface runoff of the element in the external environment and, thus, reduces the risk of water body eutrophication. The influence of phosphorus fertilizers on the biodiversity of soil microflora is also established. The dynamics of mobile phosphorus in various soils revealed in long-term field experiments can serve as a model of phosphorus transformation, which entered the soil from fertilizers in production conditions.
1.1 INTRODUCTION
The content of mobile phosphorus in soils in the years of intensive chemicalization was directly related to the level of fertilizer application. If in Russia in 1965, before the beginning of intensive chemicalization, the application of mineral fertilizers (NPK) per 1 ha of arable land per year averaged 20 kg of active substance, then for five years their use increased: in 1966â1970 up to 28 kg/ha, in 1976â1980 up to 65 kg/ha, and in 1986â1990 up to 99 kg/ha. With the increase in the use of minerals, including phosphorus, fertilizers in the country increased soil fertility, in particular the availability of their mobile phosphates. Thus, during the period from 1971 to 1999, the share of arable land with a low content of mobile phosphorus decreased from 52% to 22% with a corresponding increase in the share of medium and well-endowed soils (Sychev and Mineev, 2011).
However, increasing the content of mobile phosphorus in soils is not the only effect of the intensive use of phosphate fertilizers. A significant part of the phosphorus applied in excess of phosphorus removal by crops passed into inactive forms, creating a reserve of phosphorus nutrition of plants (Cook, 1970; Black, 1973; Ginsburg, 1981). According to Sychev and Shafran (2013), for 25 years it was applied over the removal of about 300 kg/ha of phosphorus, which remained in the soil. This amount of phosphorus is sufficient to produce 2 t/ha of grain crops for 25â30 years if you do not apply phosphorus-containing fertilizers.
Since 1995, when the balance of phosphorus in the countryâs agriculture began to develop with the excess of removal over the application, there has been a certain tendency to reduce mobile phosphates in arable soils, although not as obvious as previously expected. At the same time, the regularities of the transformation of phosphate fertilizers have not been sufficiently studied. This, in particular, is evidenced by the statement of one of the leading experts in this field of knowledge K. E. Ginzburg: âThe absorption capacity of soils with respect to phosphates confuses our calculations about increasing the content of mobile phosphates in the soil, since when soluble phosphates are applied into the soil, an unknown, but a significant part of them passes into poorly soluble and less accessible forms for plantsâ (Ginsburg, 1981, p 124). Long-term dynamics, the nature of the transition of mobile phosphorus in soils in inactive forms can be traced by the example of long-term field experiments with fertilizers, which is the subject of this work.
1.2 METHODS
The research method is based on the generalization of the materials of long-term field experiments, as well as the results of their own research. The authors analyzed the impact of the systematic use of high doses of organic and mineral fertilizers, including phosphorus, on the change in the content of mobile phosphorus in various soils: sod-gleyic clay loam (Lithuania), sodpodzolic clay loam (Moscow region), sod-podzolic sandy loam (Smolensk region), sod-podzolic loamy sand (Belarus), and ordinary chernozem (Stavropol region).
The economic balance of phosphorus on the main variants of field experiments is calculated taking into account the applied amount of phosphorus on rotations of field crop rotations and the influence of the long-term systematic application of phosphorus fertilizers on the content of mobile phosphorus in soils is shown.
Determination of the content of phosphorus mobile forms in various soils was carried out according to the methods adopted in agrochemistry (Agrochemical Methods of Investigation of Soils, 1975). The main methods for determining the content of mobile phosphorus were: EgnerâRima methodâextraction from soil with 0.04 n solution of calcium lactic acid, CH3CHOHCOO)2Caâą5H2O at pH 3.5â3.7; Kirsanov methodâextraction from soil with 0.2 normal solution; HCl and Machigin methodâextraction with 1% solution (NH4)2CO3. Methods for determining the content of mobile phosphorus are specified in the description of the research results.
1.3 DISCUSSION
In a field experiment in the Lithuanian Scientific Research Institute of Agriculture (Plesyavichius, 1982), the research was conducted to study the efficacy of continuous application of mineral fertilizers on drained sodgleyic clay loamy soil. In the variant with the application of the rotation N225P324K350 with an annual application of phosphorus fertilizer on average in seven deployed to the nature of the fields of crop rotation at the economic balance of phosphorusâ68 kg/ha in the first rotation and 73 kg/ha in the second; the amount of mobile P2O5 (by EgnerâRome) at the end of the rotation was 42 an...