Rogozhina E. V.

All Russia Scientific and Research Institute of Floriculture and Subtropical Crops, Sochi, Russia, e-mail: RogojinaEW@yandex.ru

The potential activity of nitrogen fixation and carbon dioxide emission of soil under peach orchard in humid subtropics of Russia.

Seasonal dynamics of potential nitrogen-fixing activity and CO₂ emission in brown weakly unsaturated forest soils of the natural cenosis (beech-hornbeam forest) and peach orchard in the subtropical zone of Russia were studied. In general, the soils of these communities were characterized by high values of nitrogen fixation activity (NA) (from 1.7 to 77 µg C₂H₄ / (g h) during the year); the rate of CO₂ emission was changed from 38,8 to 150,8 mg CO₂/ kg of soil per day. The potential activity of nitrogen fixation in soils of different cenoses was comparable and depended largely on the acidity of the soil solution. Reduction of CO₂ emission by 33% in average was observed in soils of the agrocenosis.

Key words: peach agroecosystem, soil biological activity, potential nitrogen-fixing activity and carbon dioxide emissions brown unsaturated forest soils, the humid subtropics of Russia.

The environmental conditions of the black sea coast of Krasnodar region is favourable for growing such valuable southern fruit crops such as peach (Persica Mill), natural habitat area which is located in the foothill and mountain areas of North China, parts of Central China. Obtaining high yields of peach in the Big Sochi it is possible only under condition of application of a number of agronomic practices, including fertilizer application and repeated treatments with pesticides. As a result, the agroecosystem peach acrogenous experiences high load [10]. For resort zone of the black sea coast are particularly acute questions of ecologization of agricultural production (in particular horticulture), to solve which it is possible, including on the basis of monitoring the status of the biological component of soils.

There are many indicators used to determine the biological activity of the soil to determine the level of agrogene load (the activity of enzymes, the number of different groups of microorganisms, the species composition and biodiversity, etc.) [3;7]. The study of the intensity of the process of nitrogen fixation in soils and emission of CO₂ allows to characterize the functional activity of microbiocenosis. These processes depend on many environmental factors: abiotic (humidity and temperature, physical and chemical properties of the soil), biotic (biochemical processes, type of vegetation) and agrogenic (agrotechnical and reclamation measures) [8; 9]. As a result, nitrogen-fixing capacity of the soil and the intensity of CO₂ emissions varies depending on the vegetation period, the influence of agrotechnical methods of cultivation [4; 11], which makes it difficult to assess the degree of exposure to a particular factor. Therefore, to assess the degree of changes in the functional activity of soils at agrogana the cultivation required in the annual dynamics.

In connection with the foregoing, the goal of this research was the comparative study of potential nitrogen-fixing activity and emission CO₂ of soil agroecosystem peach orchard, annually exposed to complex agrochemicals.

The study was conducted during 2008 – 2010 In the period from February to October 2008 (4-time selection), and also in April and October 2010 selected and mixed soil samples of the upper root layer (10-20 cm), the most exposed to agrochemical. Fertilizer doses N₁₈₀P₉₀K₁₃₀ kg / ha of active substance and the application of a set of pesticides was carried out in spring and summer. The climate of the black sea coast of Krasnodar region is characterized as humid subtropical with an average annual temperature of 14.4 °C, rainfall of 1500 mm per year, falling predominantly (over 60 %) in autumn-winter period, with frequent dry periods in summer. And in 2008, air temperature and soil (respectively) in February amounted to +9,1°C and +5,5°C in may, increased to +16,7°C and +8,5°C in August, there was a temperature maximum (+26,7°C and +21,5°C) in October the temperature dropped to +16,3°C and +13,0°C. Field soil moisture of the forest over the study period varied only slightly (from 26% to 31%). Minimum values were determined for the soil peach orchard in August (19%). In other periods the soil moisture of the two cenoses were equal.

Identification of potential activity of nitrogen fixation was carried out by means of acetylindole on a gas chromatograph Crystal-2000 with a flame ionization detector. Determination of the CO₂ emissions of the soil was carried out using absorption [11] and titrimetric end - (weight of soil 100 g, 3 replications; incubation of soil samples brought water to 60% of the total moisture capacity, was carried out in sealed plastic bags for 1 day; absorbing CO₂ solution - 0.1 n NaOH; solution used for titration with 0.1 n HCl). Agrochemical parameters [1]: pH_sal – potentiometric; the content of humus – by Tyurin's method in the modification Orlov and quiet and scenic sur; mobile phosphorus and potassium by Oniani; nitrogen hydrolyzable – by Tyurin and Kononova, Ca²⁺ and Mg²⁺ – trilonometric; and humidity was determined by the weight method. Experimental results calculated on the absolutely dry soil (105°C, 8 h). Statistical processing of the results was performed using Statistica 6.0.

As a result of research, it was determined that in accordance with the established grades [5], soil peach orchard – brown weakly unsaturated forest, humus-poor, characterized by low provision hydrolizable nitrogen, medium, and high security movable potassium, the supply of the mobile forms of phosphorus – the middle. The acidity of samples changed in the range of 6.14 to 7.4 [Table.1].

Table 1. Agrochemical properties of brown weakly unsaturated forest soils (in the layer 10 – 20 cm) (average values)

Indicator	2008		2010
	Forest (background)	Peach	Forest (background)	Peach
pHsal	7,6	6,1	7,4	6,3
Humus, %	3,8	2,7	2,9	2,2
Nitrogen easily hydrolizable, mg/kg	37,0	69,0	63,0	72,0
Mobile phosphorus, mg/kg	268,0	429,0	330,0	410,0
Mobile potassium, mg/kg	178,0	480,0	Not det.	Not det.

The change in indicators of biological activity under the influence of the culture of the peach was evaluated at the background site (beech and hornbeam forest) soil which was characterized by a more alkaline reaction of the soil solution, a higher content of humus and less security hydrolizible nitrogen, mobile phosphorus and potassium [Table.1]. The soil of the beech-hornbeam forest (background site) in the summer-autumn period was characterized by high values of potential nitrogen-fixing activity (NA) (August 1,7; in October C₂H₄ 3,3 µg/(g h)), which was comparable with the values obtained for leached medium loam black earth in the forest steppe zone of Eastern Siberia (рН_Н2О=6,8) [9]. The intensity of the process of nitrogen fixation in brown weakly unsaturated forest soils had a large influence neutral reaction of soil solution (pH_КСl=7.3 in August and 7.6 in October). The level of nitrogen fixation of soil peach orchard of the same order with a background forest site (Fig.1).

Fig.1 Seasonal dynamics of CO₂ emissions (A) and the potential activity of nitrogen fixation (B) soil peach orchard (layer 0 – 20 cm, 2008, 2010)

The differences of NA compared to the forest (2.6 times higher in August and 1.4 times lower in October) was related, perhaps first with various security nitrogen-fixing microbial complex organo-mineral nutrition [9]. The decrease in NA in the soil of the peach orchard from may to October (Fig.1) correlated with soil acidity (pH_КСl=7.4 in may; 7,0 – in August, from 6.3 in October), what was stated earlier on other types of soils and other agricultural lands (r = – 0,74)[11].

The intensity of CO₂ emissions of forest soils is comparable to the values obtained for the loamy red soil (USA, GA) (pH _H2O =6,4) [2]. The maximum values during the vegetation period was in August (150,8 mg CO₂ /kg soil), in spring and autumn the differences are minor (in April – 105,2; in October – 109,5 mg CO₂ /kg soil). Emission of CO₂ from forest soils was greater than from soils of agrocenosis (peach garden) (in April and August, 2 times; in October 1.1%). More intense process of CO₂ emissions from soils with natural vegetation were also noted by other researchers [8; 10]. This was attributable both to differences in the speed of mineralization in the quality and quantity of organic matter and the inhibition of the process of chemical means of protection. The regularity of change of CO₂ emissions from soil of the peach orchard (an increase from may to October) may have been determined primarily by the decrease of pesticide load on soil microbiocenosis.

Thus established at this stage, the differences of nitrogen fixation capacity of the soil natural cenosis (beech-hornbeam forest) and farming peach, did not have a clear connection with pesticide load. The decrease in NA in the soil of the peach orchard from may to October were correlated with the acidity of the soil solution. Reduction of CO₂ emissions compared to the background site from 10 % in October to 50 - 55 % in April and August, respectively, showed inhibition in all the periods of vegetation of plants.

REFERENCES

1. Agrokhimicheskie metody issledovaniya pochv (Agrochemical Methods for Soils Investigation), Moscow: Nauka, 1975.

2. Ananiev, N. D., Spatial and temporal variation in microbial metabolic coefficient in soils / N. D. Ananiev, E. V. Blagodatskaya, T. S. Demkina // Soil Science, 2002, №10, pp. 1233-1241.

3. Malyukova, L.S., Influence of long application of fertilizers on the biological activity of tea plantation soils [Text] / L. S. Malyukova, E. V. Rogozhina, D. V. Strukova, // Agrochem. Vestnik, 2012, № 2, pp. 15-17.

4. Malyukova, L.S., Effect of different types and doses of mineral fertilizers on the respiratory activity of the soil of tea plantation / L. S. Malyukova, V. V. Kerimzade, A. V. Velikiy/ Fruit and berry-culture of Russia: collection of scientific works VSTISP, Moscow, 2015, T. 43, pp. 132-138.

5. Malyukova, L.S., Metodiheskie rekomendatsii po kompleksnoi pochvenno-rastitelnoi diagnostike mineralnogo pitanija chaya (Guidelines on integrated soil and plant diagnosis of mineral nutrition of tea) [Text] / L. S. Malyukova, N. V. Kozlova // Sochi: GNU VNIITS and SK RAAS, 2010. - 37 s.

6. Mineev, V.G., Praktikum po agrokhimii (Practical Work on Agricultural Chemistry), Moscow: MGU, 2001.

7. Rogozhina, E.V., Group composition and functional activity of the complex culture of tea rhizosphere microorganisms in the conditions of subtropical Russia / E.V. Rogozhina , L. S. Malyukova // Collection of scientific. tr. VNIITsiSK. Vol. 42. T. 2. "Subtropical crops and southern gardening." Sochi, 2009. pp. 111-118.

8. Chemitdorzhieva, E. O., Features of carbon dioxide emissions from muchnistokarbonatnyh chernozems Tugnui basin Zabaikalye / E. O. Chemitdorzhieva, G. D. Chemitdorzhieva // Agrochemistry, 2010, №11, pp. 45-49.

9. Schott, P. R., Biologicheskaya fiksatsiya azota v odnoletnih agrotsenozah lesostepnoi zoni Zapadnoi Sibiri (Biological nitrogen fixation in annual agrocenoses forest-steppe zone of Western Siberia): Abstract. Dis. ... With Dr.'s. Science / Peter Schott Reingoldovich. Barnaul: GNU ANIISKH SB RAAS, 2007. - 39 s.

10. Januszewski, E. B., The role of biologically active substances in improving environmental sustainability agrobiocenosis planting peach / E. B. Januszewski // Collected scientific. tr. VNIITsiSK. Vol. 42. T. 2. "Subtropical crops and southern gardening." Sochi, 2009. pp. 169-174.

Rogozhina, E.V., Estimation of Рotential Nitrogen-Fixing Activity of Agrophytocenoses Soils of the Subtropical Zone of Russia / E. V. Rogozhina, N. V. Kostina, L. S. Malyukova // Moscow University Soil Science Bulletin, 2011. Vol. 66, № 1. pp. 32-35.