Soil Carbon Sequestration and Rhizospheric Microbial Population in Apricot Orchards Following Plastic Film Mulching Under Cold Arid Region

H. V. Sing

Research Report

Soil Carbon Sequestration and Rhizospheric Microbial Population in Apricot Orchards Following Plastic Film Mulching Under Cold Arid Region

H. V. Sing

Regional Agricultural Research sub Station, SKUAST-K, Kargil, India

Author

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International Journal of Horticulture, 2013, Vol. 3, No. 8 doi: 10.5376/ijh.2013.03.0008
Received: 31 Jan., 2013 Accepted: 07 Feb., 2013 Published: 18 Feb., 2013

This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Preferred citation for this article:

Singh H.V., 2013, Soil carbon sequestration and rhizospheric microbial population in apricot orchards following plastic film mulching under cold arid region, International Journal of Horticulture, 3(8): 35-41 (doi: 10.5376/ijh.2013.03.0008)

Abstract

The study of agricultural management practices on rhizospheric microbial population and phytomass carbon sequestration in apricot orchard in cold arid region is conducted. Plastic mulching conserved the soil moisture and stabilized rhizospheric temperature of apricot which enhanced the microbial activity in the rhizosphere and plant growth of apricot. Significantly higher soil moisture conservation (19.75) per cent in July, maximum microbial population of fungi (15.36 cfu/gx10_⁴ cfu/g soil) and bacteria (11.45 cfu/gx10_⁶ cfu/g soil) in month of September and enhances in plant growth (17.73) per cent at end of season recorded in red plastic mulch with mulch size 1.5 m x1.5 m. Active plant growth phase of apricot plant also influence the microbial activity. All the plastic mulch found better in producing phytomass than control. Increased plastic mulch increases microbial growth, plant biomass and carbon sequestration in cold arid region.

Keywords

Apricot; Carbon sequestration; Cold arid; Microbial population; Plant growth; Plastic mulch; Rhizosphere

Apricot (Prunus armeniaca L.) is a main grown horticultural crop in cold arid region of Ladakh. Kargil, is a district of Ladakh comes under cold arid region of Jammu & Kashmir and well known as bowel of sweetest apricot production in India. It receives little precipitation mostly in form of snow. Temperature ranges between -40℃ to 35℃. Relative humidity sometimes reaches below to 15%, which enhances the rate of soil water evaporation. This harsh climatic condition persists nearly for 5~6 months (November to April) and adversely affects growth of apricot plants. While optimum soil temperature and moisture is the prerequisite for increase plant growth (Stone et al., 1999) and microbial population (Ristaino et al., 1991). Application of plastic as mulch material in agriculture increasing day by days and play an important role to, conserve soil moisture (Strautina, 2004; Panigrahi et al., 2008), maintain soil temperature and reduce weed population (Minuto et al., 2002 ). Soil of cold arid region is having low carbon and deficient in nitrogen. Polythene mulching has proved its effectiveness in conserving the soil moisture and increasing the growth, yield and quality of citrus (Shirgure et al., 2005). There is strong evidence that agriculture can play a significant role in mitigate the increase of greenhouse gases in the atmosphere. Plants capture CO₂ through the process of photosynthesis, which is the source for all plant growth. Plant materials from roots and non-harvested residues are returned to the soil where they are decomposed over time by soil microorganisms (e.g. bacteria, fungi). The amount of carbon that resides in the soil is governed by the balance between the rate of carbon addition (mainly through plant sources) and the rate of carbon loss, mainly as CO₂ from decomposition. These processes of carbon input and output are governed by external factors such as climate and soil physical properties, but also by management practices (Paustian et al., 1998). Soil microbial communities are responsible for the cycling of carbon (C) and nutrients in ecosystems and their activities are regulated by biotic and abiotic factors such as the quantity and quality of litter inputs, temperature, and moisture. It is well established that extreme weather events both drought and freezing can have substantial direct effects on microbial physiology and the composition of the active microbial community, and nutrient flows (Schimel et al., 2007). Increase in frequency and intensity of drought in drier ecosystems creating a negative feedback on microbial decomposition and soil carbon loss as microbial respiration. The basic idea behind carbon sequestration is to use agricultural management practicesto increase the rate of carbon added to soil and/or reduce the rate of organic matter decomposition in soil, thereby increasing the storage of carbon in the soil and removing it from the atmosphere. Keeping the above facts in mind, an experiment was chalked out with the objective to manage the rhizospheric soil microbial community of apricot through polythene mulch and its role in plant growth of apricot and carbon sequestration in term of plant biomass production and carbon addition in the soil under cold arid condition.

1 Results and Discussion

1.1 Effect of plastic mulch on rhizosphere soil moisture and temperature

Effect of plastic film mulch on rhizosphere soil moisture per cent of apricot at eight inches depth was recorded and results presented in (Figure1) clearly indicates that all mulched treatments significantly showed higher soil moisture and conserved better rhizosphere soil moisture than without mulched treatment. Increased in size of plastic mulch proportionally increases in soil moisture conservation and higher moisture per cent was recorded with large mulch size (1.5 m×1.5m) in all the colors of plastic mulch. Pooled analysis of both the years indicated that red colour plastic film with size of 1.5 m×1.5 m conserved maximum soil moisture and it was 19.75%, 15.27% and 14.38% in the month of July, September and November respectively, which were significantly higher than other treatments. In general maximum rhizosphere soil moisture was recorded in red colour plastic film followed by black, blue and transparent with mulch size of 1.5 m×1.5 m, while in without mulch treatment only 4 to 5% soil moisture was recorded. Gomeh et al (1999) reported that distribution of soil moisture increased under plastic mulch treatment more than in bare soil. Mahapatra et al(1999) in the experiment on tomato at Bhubaneswar observed that plastic mulch was found better in conservation of soil moisture than without mulched plots. Variations in soil moisture conservation due to different colours of plastic because of different colours of plastic intercept solar radiation of different wave length. While increased size directly increases soil moisture due to its large coverage area. Variation in maximum and minimum soil temperature from July to November was significantly less in all mulched treatment than control (Figure 2). It varied from 18℃ to 30℃ in mulched while variation in rhizosphere soil temperature was 13℃ to 38℃ in control treatment. Higher soil temperature variation coupled with less soil moisture per cent restrict the plant growth.

Figure 1 Effect of different plastic film much on soil moisture

Figure 2 Effect of different plastic film much on soil tempareture

1.2 Effect on rhizospheric microbial population

Total fungal population 10_⁴cfu/g rhizosphere soil was recorded clearly indicates that plastic mulch had positive effect on fungal population. Pooled analysis of both the years indicated that significantly higher fungal population (15.36×10_⁴ cfu/g, 14.24×10_⁴ cfu/g, 14.91×10_⁴ cfu/g and14.11×10_⁴ cfu/g) rhizosphere soil were recorded in red, blue, black and transparent respectively with 1.5 m×1.5 m size plastic mulched treatment in the month of September (Figure 3). However, only 3.48×10_⁴ cfu/g rhizosphere soil recorded in without mulched treatment. Total fungal population increased up to September and then sharply decreased in the month of November in all the treatment including control. Reduction in fugal cfu/g rhizosphere soil was recorded with reduced mulch size in all mulched treatment. Similar trend in bacterial population was also recorded with colour and size of plastic mulch (Figure 4). Increased size of mulch increases in cfu/g of bacterial population in all the mulch treatments. Pooled data indicated that higher bacterial population 9.22×10_⁴cfu/g, 4.75×10_⁴ cfu/g, 5.85×10_⁴ cfu/g and 5.10×10_⁶cfu/g rhizo-sphere soil recorded in treatments of red, blue, black and transparent plastic mulch respectively with size of 1.5 m×1.5 m in month of July. While in control treatment bacterial population in the month of July was only 0.65×10_⁶cfu/g rhizosphere soil. The bacterial population increased to 11.45×10_⁶cfu/g, 7.04×10_⁶cfu/g, 9.15×10_⁶cfu/g, 5.98×10_⁶cfu/g and 0.93×10_⁶cfu/g rhizosphere soil with red, blue, black, transparent with maximum size used plastic mulch and control treatment respectively in September month.

Figure 3 Effect of different plastic film much on fungal population

Figure 4 Effect of different plastic film much on bacterial population

Apricot plant growth phase also influenced both microbial (fungi and bacteria) growth. Figure 5 clearly showed that microbial population positively correlated with soil moisture in the rhizosphere and different growth phase i.e. observed months. Fungal and bacterial populations start increasing from July and reached maximum in September and reduced in November month.

Figure 5 Soil moisture influence microbial population during different plant growth phage

In general all microbial population (fungi and bacteria) increased with mulch treatments. Maximum population of both the organisms had reached in the month of September and drastically reduced in month of November during both the years. This is might be due to rhizosphere microbial population very much influenced by plant root exudates and during July to September apricot plants were in active growth phase and more foliage were noted during this period. Drastic reduction in microbial population in November month may be due to senescence of apricot plant and defoliation started due to cold temperature. Devay (1995) observed that mulching of soil with plastic film increases the populations of beneficial bacteria and fungi.

Red colour plastic mulch had higher microbial population of both fungi and bacteria are due to one or more reasons. Different colour of plastic mulch absorbed with different wavelength of solar radiation which may be beneficial for microbial growth directly or due to better root growth in apricot plants. Besides this, soil moisture per cent and temperature in red colour plastic mulch may be conducive for microbial growth and sporulation as well as apricot root growth under cold arid conditions. Increased size of plastic mulch had increases microbial population than the without mulch treatment as well as with their respective small size. It is also due to increased mulch conserved the soil moisture per cent for log duration which ultimately provide conducive environment to microbial growth.

1.3 Effect on plant growth

Significant increased in apricot plant growth percent over control treatment was observed in end of the season during both the years. Pooled analysis showed that maximum 17.73% increase in trunk girth of apricot was recorded in the treatment of red colour plastic mulch with 1.5 m×1.5m size followed by blue, black and transparent where per cent growth were 11.48%, 7.00% and 6.33% respectively (Figure 6). In control treatment only 1.68% trunk growth was recorded. In general, increased size of plastic mulch increases per cent plant growth of apricot. Paries et al (1994) also reported on the basis of four years of research result on walnut plant, mulching with black polythene sheet increased stem growth than un-mulched walnut stem. Rubauskis (2004) observed that mulching with irrigation can influence the productivity of apple and plum trees.

Figure 6 Effect plastic mulch on growth of apricot plant

Colour of plastic mulch had different effect on plant growth. Maximum with red followed by blue, black and transparent while minimum growth of apricot plant was recorded in without mulch treatment. Similar observations had been reported by Almasoum (1998) in case of tomatoes. He observed that the highest yield (67%) was with the red mulch. Copper (1999) also reported, increase in average fruits of tomatoes with red color plastic mulch than black colour mulch. Variation in growth of apricot plants trunk with different colour of plastic mulch is due to the passing ability in different wave length ranges of infrared radiation.

1.4 Effect on carbon sequestration

Plant materials from leaves, roots and non-harvested residues are returned to the soil where they are decomposed over time by soil microorganisms (e.g. bacteria, fungi) and soil fauna, with carbon returned to the atmosphere as CO₂. However portions of this decomposing organic matter can reside in soil for decades or centuries, in stable forms that confer much of the natural fertility of soils. The amount of carbon that resides in the soil is governed by the balance between the rate of carbon addition (mainly through plant sources) and the rate of carbon loss, mainly as CO₂ from decomposition. The basic idea behind carbon sequestration is to use management to increase the rate of carbon added to soil and/or reduce the rate of organic matter decomposition in soil, thereby increasing the storage of carbon in the soil and removing it from the atmosphere.

Soil C levels are fundamentally determined by the balance between organic matter inputs, primarily as plant residues, roots, and root exudates, and organic matter losses due to decomposition, erosion, and leaching. Bacteria and fungi generally comprise 90% of the total soil microbial biomass, and they are responsible for the majority of soil organic matter (SOM) decomposition. Since soil microbial communities are key regulators of SOM dynamics and nutrient availability and very much influenced with different agricultural management practices. Results of this study clearly showed that plastic mulched treatments enhanced apricot plant biomass and rhizosphere microbial population. All the mulched treatment had significantly higher phytomass carbon than control (Figure 7; Figure 8). Enhancement in Apricot plant phytomass carbon was doubled in the second year and it was significantly higher in all plastic mulched treatment. Higher phytomass carbon 0.92 mg/h was recorded with red colour plastic mulch with size of 1.5 m×1.5 m and which was increased to 1.75 mg in second year. While 0.47 mg/h phytomass carbon was recorded in without mulched treatment. Total plant biomass positively correlated with carbon sequestration (Figure 9). Kumar et al (2009) reported fro Ladakh that Willow and poplar have been found to sequester more than 75 000 tonnes of carbon. Every year these plantations are contributing 400 tonnes of leaf litter to the ground, which is one of the best sources of soil organic carbon Blagodatskii et al (2008) reported that in soils with great annual input of plant material, more microbial biomass is formed per unit of organic matter and quantity of microbial biomass per unit of humus characterizes the intensity of the carbon turnover in soil. The total biomass and total organic carbon has been determined and compared with Allometric model. Their study revealed that Allometric model based on theoretical model can success used to determine the tree biomass by non-destructive method (Chavan and Rasal, 2010).

Figure 7 Sequestered carbon (tonnes) through living biomass during first year

Figure 8 Sequestered carbon (tonnes) through living biomass during second year

Figure 9 Total plant biomass and carbon sequestration

2 Materials and Methods

Study was conducted in the experimental field of apricot orchards with 5~6 years old plants from July to November (active period for plant growth) for two consecutive years at Regional Agricultural Researchsub Station, SKUAST-K, Kargil. The apricot plants were plastic film mulched with different colors and size to conserve the soil moisture required to enhance plant growth (Table 1). Thirteen treatments viz four color of plastic film namely red, blue, black and transparent with three size each i.e. 1.5 m×1.5 m, 1.0 m×1.0 m and 0.5 m×0.5 m respect- tively along with control, where plants were kept without mulch. Experiment was laid out in randomized block design with three replications. The thickness of each color of plastic film was 300 micron.

Table 1 List of treatments

Plastic film in different color and size spread over soil around the apricot plant in the month of July of each year of experimentation making a hole in centre. Edges of each plastic film were covered with soil so that plastic sheet should not replaced by wind. Data regarding rhizosphere soil moisture (%) and temperature were recorded using soil moisture meter in three months i.e. July, September and November after 15 days of irrigation for both the years. Three spots were selected randomly at eight inches distance from trunk of each plant making a hole of eight inches depth and soil moisture was recorded from these collected samples. Microbial population of fungi and bacteria cfu/g soil were recorded from rhizosphere soil collected from eight inch depth and eight inches distance from trunk of each plant. Soil microbial count in term of colony forming unit (cfu/g) of rhizosphere soil of each treatments was done by following dilution plating and culturing methods. This method has generally used to estimate the number of microorganisms in the rhizosphere soil. One gram of the soil sample was transferred into a McCartney bottle containing 9 mL of sterile water which was regarded as the stock suspension, from which serial dilutions were prepared using sterile water. One ml of each dilution was plated in triplicate. Nutrient agar (Difco) known to support the growth of most bacteria (Davies et al., 1980) and actinomycetes was used for their count. Meanwhile, potato dextrose agar (Difco) containing 64 mg/L penicillin G was used for fungal estimation. Plates with microbial colonies of between 30 and 300 were selected for enumeration and the numbers of colonies were multiplied by the dilution factors. Plant growth parameters of apricot i.e collar diameter, canopy spread and biomass weight due to pruning was recorded to calculate the addition of carbon in the soil.

Total sequestered carbon stock of apricot was analyzed through non-destructive, morphometric measurements and algometric equations relating to total ground biomass, carbon percentage and density of the wood of the plants studied. The model developed by Brown et al (1989) to estimate above ground biomass has been used in present investigation. Total ground biomass was determined through combined analysis of above ground biomass (AGB), below ground biomass (BGB) and tree canopy biomass values measured. AGB was morph- ometrically measured with volume of the above ground plant and wood density. The standard average value 0.6 gm/cm3 were taken as wood density. BGB was calculated with the formula given by MacDicken (1997).

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