INFLUENCE OF CONSERVATION FARMING ON CARBON STATUS AND MICROBIAL ACTIVITY OF CALCIC CHERNOZEMS IN ORENBURG REGION

ВЛИЯНИЕ ПОЧВОСБЕРЕГАЮЩИХ ТЕХНОЛОГИЙ НА УГЛЕРОДНЫЙ СТАТУС И МИКРОБНУЮ АКТИВНОСТЬ ЮЖНОГО ЧЕРНОЗЕМА ОРЕНБУРГСКОЙ ОБЛАСТИ 

D.A. Khoroshaev, V.O. Lopes de Gerenyu, I.N. Kurganova

Д.А. Хорошаев, В.О. Лопес де Гереню, И.Н. Курганова 

Institute of Physicochemical and Biological Problems in Soil Science of the Russian Academy of Sciences

(Russia, 142290, Moscow region, Pushchino, Institutskaya Str., 2/2) 

Институт физико-химических и биологических проблем почвоведения РАН

(Россия, 242290, Московская область, г. Пущино, ул. Институтская, 2/2)

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All conservation systems improved the quality of soils, led to accumulating of organic matter thereby reducing the CO2 concentration in the atmosphere and providing the prolonged mitigation of climate changes. The lowest content of microbial carbon and the minimal total C-CO2 losses from soils studied during 1-year incubation experiment was observed under the conventional tillage.

Все виды почвосберегающих технологий улучшают качество почв, приводят к аккумуляции органического материала и, тем самым, способствуют уменьшению концентрации СО2 в атмосфере и смягчению текущих изменений климата. Самое низкое содержание микробного углерода и минимальные потери C-CO2 из почв за 1 год инкубирования были обнаружены на варианте с применением традиционной вспашки. 

Introduction. Most agricultural activities, especially intensive tillage, lead to a strong decrease of soil organic C stocks and release CO2 into the atmosphere [4]. It has been estimated that croplands have a global potential to sequester soil C between 0,4 and 0,9 Pg C per year (1 Pg = 1015 g) due to improved agricultural management, restoration of degraded lands, extensive use of abandoned lands, and restoration of wetlands [8]. The use of no-tillage has both economic and ecological benefits compared with the conventional system of agriculture. Conservation systems (CS) in agriculture is based on the following principles: (i) minimization of tillage or no tillage; (ii) conservation of plant residues on the soil surface; (iii) the use of crop rotations, including cost-effective culture and culture, improve soil fertility; (iv) an integrated approach to pest and diseases; (v) growing of crops responsive to conservation farming. Conservation farming is successfully applied in the different climatic zones: from cold regions to the tropic and from arid regions to excessive wet areas. According to FAO statistics, more than 400 Mha over the world are cultivated by minimum tillage. The no-till technology are used for 100 Mha, 84% of which are located in the USA [9].

Today, No-till technology is most promising way for keeping of soil organic carbon and prolonged mitigation of climate changes. Exclude of plowing and the conservation of plant residues on the soil surface leads to conservation and more intensive recovery of soil fertility, improved soil structure, reduce wind and water erosion, increases the infiltration of rain water, accumulation of moisture in the soil and its more effective use by crops, creates favorable conditions for the soil microflora and invertebrates, increase crop yields due to the effect of the abovementioned factors. According to some studies [1, 10], No-Till technology causes the accumulation of soil organic carbon (SOC). Global warming potential (GWP) in humid climate reduces significantly after 10-20 yrs of No-till. Under dry conditions, the GWP due to No-Till use was higher than under humid climate and the decrease of GWP was observed only after 20 yrs of No-Till.

This study was aimed to estimate the influence of conservation farming on carbon status and microbial properties of Calcic Chernozems in Orenburg region.

Materials and methods. The effect of different tillage systems on organic and microbial C pools, C-mineralization rate, and total nitrogen (Ntot) was studied in field experiments which was established in Orenburg State Agrarian University (loamy Calcic Chernozems). The experiment has been running from 1992 and established the rotation of cereal crops. Five treatments were foreseen: (1) conventional tillage, CT, (2) subsurface tillage, ST; (3) minimal tillage, MT; (4) minimal tillage+ploughing, MT-P; (5) no-tillage+ploughing, NT-P.

Mixed soil samples were collected from a depth of 0-10 cm. Content of organic carbon (Corg) and total nitrogen (Ntot) were determined using CHNS element analyzer (Leco, USA). The rate of the SOC mineralization (Rmin, mg С/kg/day) was determined under laboratory conditions by the intensity of the СО2 emission from the soil with a moisture content of 70-75% of the water holding capacity (WHC) and a temperature of 22°С. The concentration of microbial carbon (Cmic) was determined by the substrate induced respiration method, SIR [2]. The content of the microbial biomass (Cmic, μg C/100 g of soil) was estimated according to the equation:

Cmic = 40,04VSIR + 0,37                                                                                  (1),

where VSIR is the rate of the substrate induced respiration (μg C/g soil per h).

To determine labile (Clab) and recalcitrant (Crec) pools of carbon, root-free soil samples (10 g) were wetted with distilled water to moisture corresponding to 75% of WHC and incubated at 22oC over 12 months. During the experiment, we kept the water content constant at 75-80% of WHC. CO2 released during the incubation was measured by infra-red analyzer LiCor-820 weekly during first 6 months and twice per month over the next 6 months of incubation experiment.

A first order two-component model [7] was used for the analysis of cumulative CO2-C evolution (Ccum, mg C/g of soil):

Ccum = α·Co·(1- e(-k1·T)) + (1- α)·Co·(1- e(-k2·T)),   0 ≤ α ≤ 1                     (2),

where Co is the initial amount of total C in the soil (μgС/g soil), α·Co and (1- α)·Co are the initial amount of C in the labile and recalcitrant pools, respectively (μgС/g soil), k1 and k2 are the corresponding mineralization rate constants for each C-pools, and T is the time (days).

Results and discussion. Conservation farming resulted in the increase in Corg and Ntot in topsoils by 9-30%. The most sensitive pool that reflects various alterations in the soil was microbial carbon. Under conservation technology it was 1,5-3 times higher in comparison with conventional system.

The ratio between Cmic and Corg is a very substantial ecological parameter characterizing the status and diversity of microbial community and the maturity of ecosystem [6]. The Cmic/Corg ratio depends on climatic conditions and land use changes. As a rule, it is significantly lower in the monoculture as compared to crop rotation, and in arable soils in comparison with soils under native vegetation [5]. Higher Cmic/Corg values are typical for mature ecosystems and attest to favorable nutritional conditions and higher diversity of the soil microbial community [3]. It was found that Cmic/Corg ratio was 0,9% under conventional tillage and 1,4-2,6% under conservation farming.

Due to the higher microbial activity in soils under conservation farming, the rate of C-mineralization was the highest under NT-P. Total C-CO2 losses (Ccum) from soils studied during 1-year incubation experiment varied between 0,69 and 1,46 g C/kg soil. The minimal loss of carbon was observed under the conventional tillage. The slowly decomposing fraction (recalcitrant, Crec) was the major pool in the total SOC and varied between 98,8% and 99,9% depending on treatments. We observed a clear tendency of increasing of the recalcitrant fraction in total organic carbon pool under the conservation tillage for soils studied

Conclusions. Conservation farming should be recommended for use in main agricultural regions of Russia to prolong the mitigation of climate changes after recultivation of current idle lands. All conservation technology improved the quality of soil and led to accumulating of organic matter. Besides, NT system reduced the expenses of diesel and cost of agricultural production thereby reducing GWP. 

The study was supported by the RFBR (project no. 18-04-00773a). 

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