Indicator Of Nutrient Status Of Microbial Biomass Biology Essay

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Laboratory incubation experiment was carried out to study the changes in the microbial biomass nitrogen and microbial biomass carbon under waterlogged condition of paddy soil with the use of parthenium and chromolaena as green manure and their compost. Based on the content of total C of plant material organic material applied at the rate of 0.5, 1.0 and 2.0 per cent level of organic carbon. The increase in extractable C and N in Mandya soil alone treatment was 24.53 mg kg-1 soil at 60th day of flooding. On 120th day of flooding was 30.12 mg kg-1. Similarly with time, the EN values also increased in the control. Addition of organic C through different sources at 0.5, 1.0 and 2.0 per cent levels increased the EC and EN values. The highest EC value was recorded in Mandya soil the different EC value was noticed in T10: Mandya soil + Chromolaena compost @ 2.0 % C at 60 and 90 day was 107.92 and 132.73 mg kg-1 soil respectively. The EC: EN ratio in control was 13.59 and 7.43 in Mandya soil on 60th day and 120th day of flooding respectively. Biomass C content (BC) across different treatments at 60th day of flooding ranged from 65 to 286 mg kg-1 in Mandya soil. Lowest microbial biomass content was noticed in T5: Mandya soil + Parthenium green manure @ 0.5 % C among treatments which received organic carbon inputs.

Key words: Microbial biomass, Parthenium, Chromolaena, Compost, Nutrient

1. INTRODUCTION

Microbes are an integral component of a living soil. It is widely being recognized that the presence and abundance of microbial wealth make soils healthy in terms of growth enhancement and protection against pests and diseases. Adding of organic manures significantly increase the microbial density and diversity in soils. Sensitive changes in microbial biomass, quantum and characters of biomass that develops upon flooding, fertilization and residue management practices. Although microbial biomass, only accounts for about 1 to 3 per cent of the soil organic matter, it exhibits a rapid turnover and can be considered as a driving force of major nutrient cycles. Hence anattempt was made to assess the microbial biomass and major nutrients of paddy soil upon addition of parthenium and chromolaena as green manure and their compost under flooded condition.

2. MATERIAL AND METHODS

The soil used for these studies was Typic Rhodustalf collected at Mandya taluk, Mandya district, Karnataka. Soil samples were air dried, sieved (< 2mm) and analyzed for physico-chemical properties pH 6.47, EC 0.06 dSm-1, total organic carbon 0.47 %, NH4+-N 29.58 mg kg-1, NO3- N 6.08 mg kg-1, Brays-P 6.57 mg kg-1 and NH4OAc-K 62.37 mg kg-1. The soil (500 g) contained in polythene pots, appropriate amount of organic manures like, parthenium and chromolaena as green manure and their compost were added. Excess amount of water was added and mixed to create puddled conditions. At periodic intervals, destruction sampling was done at 60 and120 days after flooding for analyzing various microbial biomass and nutrient status of soil. For all measurements wet soil samples were taken. Results were expressed on oven dry weight basis after taking account of moisture per cent.

There are 13 treatments and 3 replications, T1: Mandya soil (MS) (Control), T2: MS+ Chromolaena as green manure @ 0.5 % C, T3: MS+ Chromolaena as green manure @ 1.0 % C, T4: MS+ Chromolaena as green manure @ 2.0 % C,T5: MS+ Parthenium as green manure @ 0.5 % C,T6: MS+ Parthenium as green manure @ 1.0 % C,T7: MS+ Parthenium as green manure @ 2.0 % C, T8: MS+ Chromolaena compost @ 0.5 % C, T9: MS+ Chromolaena compost @ 1.0 % C, T10: MS+ Chromolaena compost @ 2.0 % C, T11: MS+ Parthenium compost @ 0.5 % C, T12: MS+ Parthenium compost @ 1.0 % C and T13: MS+ Parthenium compost @ 2.0 % C.

The NH4+-N of soil extracted with 2 M KCl was estimated by subsequent steam distillation [3]. Phosphorus was extracted with 0.03 N NH4 F in 0.025 N HCl and estimated according to [2]. Potassium extractable with N, N NH4OAc and estimated by flame photometry was analyzed as available K [7].

Microbial biomass carbon measurements

Chloroform fumigation - extraction technique standardized for paddy soils [6] was employed for measuring biomass C content. Moist soil samples were divided into two portions. One portion was extracted with 0.5 M K2SO4 by shaking for 30 minutes and filtered. Other portion was fumigated with addition of 1 ml ethanol free chloroform [22] in 250 ml conical flask with stopper for 24 hours at 250C. Finally the fumigant was removed and then the samples were extracted with 0.5 M K2SO4 for 30 minutes and filtered.

The contents of organic carbon in the fumigated and non-fumigated K2SO4 soil extracts were measured by dichromate digestion [20] and EC values were calculated. EC value is the difference in C extracted from CHCl3 fumigated sample and C extractable from nonfumigated sample. From EC, biomass C content was calculated using the relationship biomass C in mg g-1 oven dry soil = 2.65 x EC where EC is also expressed in mg g-1 oven dry soil [17].

Microbial biomass N measurement

Microbial biomass N measurement after biocidal treatment with 0.5 M K2SO4. Total N in the K2SO4 extracts were measured after Kjeldahal digestion using 0.6 ml of 0.19 M CuSO4 and 10 ml concentrated H2SO4. After digestion it was allowed to cool and distilled with 25 ml of 10 M NaOH and distillate was collected in 5 ml of two per cent boric acid with a mixed indicator. Finally, distillate was titrated with 50 ml 1 M H2SO4 to faint pink colour [4]. EN was calculated by deducting quantity of N extractable with 0.5 M K2SO4 without CHCl3 treatment form the quantity of N extractable with 0.5 M K2SO4 after CHCl3 treatment. Biomass N in mg kg-1 oven dry soil = EN x 2.22 where EN is mg kg-1 oven dry soil [17].

3. RESULTS AND DISCUSSION

Microbial biomass properties

Data on chemical composition of organic materials used in the experiments are presented in Table 1. Highest carbon and nitrogen content was noticed in chromolaena followed by parthenium. Phosphorus content ranged from 0.63 to 1.93 per cent; lowest in parthenium and highest in chromolaena compost. Maximum K content was noticed in chromolaena compost (1.89 %) followed by parthenium compost (1.46 %). The C: N ratio showed wide variation among organic materials. It ranged from 15.50 (chromolaena compost) to 23.95 (parthenium).

Table 1. Biochemical composition of the organic manures

Parameters

Chromolaena

Chromolaena Compost

Parthenium

Parthenium Compost

Carbon (%)

39.30

20.47

38.32

19.32

Nitrogen (%)

1.90

1.32

1.60

0.99

Phosphorus (%)

0.69

1.93

0.63

1.03

Potassium (%)

1.08

1.89

0.98

1.46

C:N ratio

20.68

15.50

23.95

19.15

Cellulose (%)

18.76

11.92

12.04

6.79

Lignin (%)

11.36

5.20

26.63

6.63

Lignin : N ratio

7.04

3.93

14.02

6.69

Cellulose content was found to vary in the organic materials. Highest cellulose content was observed in chromolaena (18.76 %) followed by parthenium (12.04 %). Lignin content of the materials ranged from 5.20 per cent in chromolaena compost to 26.63 per cent in parthenium (Table 1). Lignin: N ratio was observed to be in between 3.93 to 14.02.

Quantity of soil microbial biomass is another soil quality parameter and increased to a great extent due to incorporation of organic carbon sources at 2.0 per cent C level. The organic load given to soils modified the properties of microbial biomass also. In control results in increase in EC: EN ratio, with time. Organic matter treated soils showed higher EC: EN ratio at 120th day of flooding, than at 60th day of flooding. Very high build up of microbial biomass C was noticed in both parthenium compost and chromolaena compost treated soils and BC contents of these treatments are very high on 120th day of flooding.

The microorganisms which develop after incorporation of fresh residues initially had very high quantities of nitrogen with respect to carbon demand. Initially when abundant supply of labile C compounds were present, microbes readily utilizes them, builds up biomass, and hence incorporates large amounts of N in their skeletal structure. As labile compounds are used up, gradually biomass C and N contents come down, releasing nitrogen to soluble pool. [18] observed that biomass of waterlogged soils actually possess high nitrogen concentrations. Certain anaerobic bacteria have narrow C: N ratio, whereas fungi, have wider C: N ratio of microbial biomass which confirm the dominance of bacterial population at the expense of fungi.

Table 2. 0.5 M K2SO4 extractable carbon (EC) and nitrogen (EN) (mg kg-1

oven dry soil) after chloroform fumigation under flooded condition

Treatments

60 DAF

120 DAF

EC

EN

EC:EN

EC

EN

EC:EN

T1 :MS alone

24.53

3.36

7.28

30.12

4.05

7.43

T2 :MS+ CG1

81.58

10.81

7.54

89.69

11.86

7.56

T3 :MS + CG2

85.31

11.10

7.68

91.70

11.83

7.75

T4 :MS+ CG3

92.83

11.81

7.86

101.38

12.86

7.88

T5 :MI+ PG1

77.61

10.36

7.49

87.94

11.71

7.50

T6 :MS+ PG2

90.56

11.59

7.81

103.08

13.11

7.86

T7 :MS+ PG3

96.11

12.01

8.00

105.56

13.32

7.92

T8 :MS+ CC1

89.56

11.84

7.56

112.27

14.77

7.60

T9 :MS+ CC2

97.75

12.12

7.74

122.08

15.61

7.82

T10:MS+ CC3

107.92

13.59

7.94

132.73

16.67

7.96

T11:MS+ PC1

81.13

10.81

7.50

84.99

11.24

7.56

T12:MS+ PC2

93.75

11.97

7.83

109.72

13.96

7.85

T13:MS+ PC3

101.64

12.64

8.04

114.55

14.56

7.90

SEm ±

4.13

3.92

9.31

3.02

LSD (P = 0.05)

12.07

11.98

27.05

5.81

DAF: Days after flooding

EC: Carbon extractable CHCl3 minus C extractable without CHCl3

EN: Nitrogen extractable after CHCl3 minus N extractable without CHCl3

In the present investigation, EC: EN ratios ranged from 7.50 to 7.96 on 120th day of flooding in organic manure applied soils (Table 2). Generally, EC: EN ratio of aerobically treated soils was reported to be smaller (10-12), than those under anaerobic conditions (14-20). EC: EN ratio in the soils ranged from 4 to 6, values smaller than those recorded in well drained paddy soil (9-22) [18] [8] [6] [17]. These findings suggest that during initial period, up to 60th day of flooding, microbes that are capable of thriving in oxygen depleted and ill drained conditions decompose added organic matter and may immobilize soils nutrients depending on the quality of the organic manure.

Addition of different levels of organic manures to soils showed highly significant changes in nutrient content of soil over control at 60 and 120 days after flooding. The observed increase in 2 M KCl extractable ammonical nitrogen content in control might be due to accumulation of ammonium as a consequence of N mineralization from native soil organic matter and due to lack of oxygen for nitrification (Table 4). [16] observed a positive correlation between ammonia production and organic carbon content of soils.

In case of soils with standing water, inactivation of aerobic bacteria causes an accumulation of NH4+-N [11]. N release rate from N rich organic material used in the experiment might be quick as explained by [21] and [10]. Increasing the level of carbon application via these high N materials further increased KCl extractable N content.

Table 3. Changes in the properties of microbial biomass (mg kg-1 oven dry soil) in the soil incorporated with different organic manures under flooded condition

Treatments

60 DAF

120 DAF

BC

BN

BC:BN

BC

BN

BC:BN

T1 :MS alone

65

7

9.28

79

9

8.77

T2 :MS+ CG1

213

24

8.88

226

26

8.69

T3 :MS + CG2

226

26

8.69

243

28

8.67

T4 :MS+ CG3

243

28

8.82

266

31

8.58

T5 :MI+ PG1

203

23

8.74

226

26

8.69

T6 :MS+ PG2

236

27

8.56

256

30

8.53

T7 :MS+ PG3

257

30

8.74

278

32

8.68

T8 :MS+ CC1

236

27

8.63

256

32

8.00

T9 :MS+ CC2

259

30

8.66

276

32

8.62

T10:MS+ CC3

286

33

8.60

307

35

8.77

T11:MS+ PC1

215

25

8.60

223

26

8.58

T12:MS+ PC2

247

28

8.82

265

31

8.54

T13:MS+ PC3

265

33

8.03

281

32

8.78

SEm ±

15.52

11.01

18.04

14.52

LSD (P = 0.05)

45.56

32.08

53.63

42.08

DAF: Days after flooding BC: Biomass Carbon BN: Biomass Nitrogen

N mineralization has shown that it is the form of N and C [19] and C to N ratio present in the material is important. N mineralization from different organic materials also depends on certain biochemical compounds and their ratios [13] in upland soils. [1] showed that lignin: nitrogen (L: N) ratio is the best index, among C: N, polyphenols: N predict N release pattern in the soils.

Table 4 Changes in the ammonical N, P2O5 and K2O content of soil (mg kg-1)

during decomposition of added organic manures under flooded

condition

Treatments

NH+4 -N

P2O5

K2O

60 DAF

120 DAF

60 DAF

120 DAF

60 DAF

120 DAF

T1 :MS alone

49.63

54.84

7.52

5.26

74.29

79.81

T2 :MS+ CG1

51.61

54.84

17.96

16.50

78.63

85.60

T3 :MS + CG2

53.73

59.09

18.56

18.75

82.16

88.34

T4 :MS+ CG3

55.10

63.60

19.63

24.34

91.00

98.34

T5 :MI+ PG1

49.74

55.78

19.02

17.36

76.53

82.58

T6 :MS+ PG2

51.00

57.38

18.03

18.72

78.00

84.51

T7 :MS+ PG3

52.23

59.38

19.22

19.63

81.39

86.36

T8 :MS+ CC1

58.75

66.74

18.53

19.65

96.74

108.56

T9 :MS+ CC2

61.34

71.84

19.63

21.62

98.63

110.57

T10:MS+ CC3

71.03

83.71

20.84

21.00

99.99

112.74

T11:MS+ PC1

56.34

62.71

20.96

22.60

92.72

100.53

T12:MS+ PC2

59.09

66.07

21.63

22.64

93.38

105.99

T13:MS+ PC3

62.74

70.46

21.39

21.50

95.34

109.74

SEm ±

12.58

16.87

3.90

3.00

12.04

15.34

LSD (P = 0.05)

35.87

46.35

10.13

9.07

34.57

42.65

DAF: Days after flooding

Persual of the data presented in Table 4 indicated an increase in Brays-P content upon submergence. According to [15] in general the increase in P availability under submerged conditions may be due to, reduction of ferric phosphates present in soil, release of occluded phosphate and phosphate sorbed in amorphous iron and manganese oxides following soils reduction, increase in pH of acid soils, desorption following reduction of Fe (III) oxides, desorption by clays and aluminium oxides following pH increase and solvent action of inorganic and organic acids on soil phosphates.

Simultaneously some inorganic P may be released from mineralization of organic P pools of soils and applied organic manures during the incubation process. High available P content noticed in compost treatment compared to green manure treatments in both soils may be due to the release of organic P, because composts are enriched with rock phosphate

Data on available potassium content of flooded soils indicated a slight increase with time (Table 4). NH4OAc extractable potassium shows highly significant variation over control upon addition of different levels of organic manure at 60 and 120th days after flooding. These findings are in line with the results of [15] and [9]. Among all the organic treatments, major increase in available K content was noticed. It is believed that K present in plant residues could be extracted with water as K will not be a structural constituent in residues unlike C, N, P and S. Therefore major portion of K is liberated to soil solution immediately after flooding [5] [12]. Highest and lowest available K contents were observed among various treatments depends mainly on K content of the organic manures and rate of incorporation of material.

Conclusion

In soils under flooded condition, addition of organic C significantly increased microbial biomass C and N contents. The increased microbial biomass also increases the availability of ammonical nitrogen, phosphorus and potassium in soils. The increase in biomass contents varied with the nature of organic manure added, rate of C application and the duration of decomposition process.

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