Influence of a six-year organic and inorganic fertilization on the diversity of the soil culturable microrgansims in the Indian mid-Himalayas

Applied Soil Ecology 120 (2017) 229–238

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Influence of a six-year organic and inorganic fertilization on the diversity of the soil culturable microrgansims in the Indian mid-Himalayas

MARK

⁎

Dibakar Mahantaa, , Ranjan Bhattacharyyab, Pankaj Kumar Mishraa, Kodigal A. Gopinathc, Chandrashekara Channakeshavaihd, Jeevanandan Krishnana, Arunkumar Rajae, Mangal Deep Tutif, Eldho Vargheseg, Brij Mohan Pandeya, Jaideep Kumar Bishta, Jagdish Chandra Bhatta a

ICAR-Vivekananda Parvatiya Krishi Anusandhan Sansthan, Almora, 263601, India ICAR-Indian Agricultural Research Institute, New Delhi, 110012, India Central Research Institute for Dryland Agriculture, Santoshnagar, Saidabad, Hyderabad 500059, India d Central Horticultural Experiment Station, ICAR-IIHR, Chettalli, Madikeri, 571248, Karnataka, India e Sugarcane Breeding Institute Research Centre, Kannur, 670002, Kerala, India f Indian Institute of Rice Research, Rajendranagar, Hyderabad, 500030, India g Indian Agricultural Statistical Research Institute, New Delhi, 110 012, India b c

A R T I C L E I N F O

A B S T R A C T

Keywords: Poultry manure Soil cracking Soil culturable microbial diversity index Soil temperature moderation Vermicompost

Industrial agriculture inputs can diminish soil microbial biodiversity. The use of organic soil amendments may foster beneficial microorganisms. Organic production systems have increased in recent years, but we know little about the effect of these production practices on soil culturable microbial diversity compared to inorganic fertilization. Therefore, the objective of our research was to evaluate the effect of two levels (high and low) of three organic amendments (poultry manure, vermicompost and cattle manure) versus inorganic fertilization (IF) on soil culturable microorganism diversity and selected soil properties after six years under a gardenpea (Pisum sativum var. hortense L.)-french bean (Phaseolus vulgaris L.) system in a sub-temperate soil of the mid-Himalayas. There was at least 31% greater population of beneficial microorganisms with application of high level (6 Mg ha−1) of poultry manure (PM6) than IF in the surface soil layer (0–15 cm depth). The highest soil culturable microbial diversity index was recorded with PM6 (0.562). Application of high level (6 Mg ha−1) of vermicompost (VC6) yielded the highest Trichoderma species count, and PM6 plots had similar values to VC6. The morning and afternoon surface soil temperature moderation during the coldest and hottest weeks with PM6 amendment was 0.50 and 1.73 °C higher over IF, respectively. The soil cracking surface area under PM6 was 112% less than IF (0.311 m2 m−2 area). Application of PM6 provided 38 and 29% higher gardenpea and french bean pod yields than IF, respectively. The soil organic carbon under PM6 in the surface layer was about 9% greater than IF. Soil organic carbon markedly influenced soil culturable microbial diversity, moderation of soil temperature and other soil properties. Thus, application at 6 Mg ha−1 poultry manure for each crop is recommended over inorganic fertilizer for higher soil culturable microbial diversity under gardenpea-french bean system in this region and similar agro-ecologies.

1. Introduction It is well known that inorganic fertilizers and pesticides degrade the environment and soil biodiversity. Food and environmental safety are often-cited reasons for popularity of organically produced foods (Bulluck et al., 2002). Hence, demand for organically produced food has increased manifold. The world organic market size reached $80 billion US dolar in 2014 from $15.2 billion US dolar in 1999 (Willer and

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Corresponding author. E-mail address: [email protected] (D. Mahanta).

http://dx.doi.org/10.1016/j.apsoil.2017.08.012 Received 25 April 2016; Received in revised form 6 June 2017; Accepted 22 August 2017 0929-1393/ © 2017 Elsevier B.V. All rights reserved.

Lernoud, 2016). Indian organic farming industry is estimated at $78 million US dolar and is almost entirely export oriented (Willer and Lernoud, 2015). A premium for organic production of 10–100% in India (Chadha and Choudhary, 2007; Mahanta et al., 2015) and 12–60% in different countries of world (Bulluck et al., 2002; Lohr, 1998) is often obtained. Most of the arable lands in the Indian Himalayas have not yet been exposed to inorganic fertilizer and pesticide application. Hence, these

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2. Material and methods

lands are organic by default (Saha et al., 2007). The livestock population per household in this region is higher than India’s average (Mahanta et al., 2013). These livestock and poultry are the main sources of biological wastes. The biological wastes will contribute substantial amounts of greenhouse gases. Hence, utilization of these wastes as organic manures is a better option. The biological wastes produced in this region are sufficient to fulfill the manure requirement of the organic growers. Since the organic food markets are also expanding rapidly in many countries, including India, it makes the Himalayan farmers to emerge as major suppliers of organic products with high price premiums. In addition, the use of organic soil amendments can foster beneficial microorganisms and improve soil properties. Furthermore, the amounts of soil nitrogen in plots under inorganic fertilizer have been negatively correlated with soil microbial population (Bulluck et al., 2002). In this study, three different organic amendments, i.e. cattle manure (CM), vermicompost (VC) and poultry manure (PM), were compared with inorganic fertilizers (IF) in a vegetable production system. Out of these three manures, CM is mostly used for vegetable cultivation. However, VC and PM are less frequently used, but slowly gaining importance in the sub-temperate Himalayas. Recently, the Himalayan states of India are providing subsidy for vermicomposting to popularize its use in organic farming (Anonymous, 2014; Venkatachalam et al., 2012). Despite an increase in organic production systems in recent years, little is known about the soil culturable microbial communities and their diversity in organic fields compared to inorganic fertilizer. Information on the impacts of organic production practices on crop productivity and soil properties are limited. Inadequate studies have been conducted to assess the impacts of soil amendments on soil organic matter (SOM), culturable soil microorganism population and crop yield in actual organic and conventional production systems in the field (Bulluck et al., 2002). Soil organic matter has a definite effect on strength and structural characteristics of soils and it can determine how soils respond to different management practices (Bhattacharyya et al., 2012a, 2012b). Certain soil physical factions (like soil cracking, soil temperature and bulk density) and SOM can influence the population of culturable microorganisms in soils. The development of new methodologies, such as the estimation of the culturable soil microbial diversity index may give us better insight into many of the soil biological processes (Murphy, 2014). Due to the complexity of soil function and origin of microbes, different microbes and their groups may respond to different sources and levels of nutrients. Hence, a single numerical value, i.e. soil culturable microbial diversity index, is thought to be useful to condense all the information. Many studies have assessed the impact of organic amendments on soil culturable microbial count and biomass (Prakash et al., 2007; Saha et al., 2008). However, few studies have observed the impact on functional groups or classes of soil culturable micro-organisms and their diversity index in the Himalayas. With the increasing organic vegetable production in the Indian midHimalayas, it is pertinent to think about if the organic amendments (CM, VC and PM) versus IF will affect the soil culturable microbial diversity index and other soil properties. Gardenpea and french bean are two important leguminous vegetables cultivated in the midHimalayas (Mahanta et al., 2013). Hence, it was hypothesized that different organic soil amendments would provide higher soil culturable microbial diversity index and better soil properties than inorganic fertilizers under a gardenpea-french bean system. To address that hypothesis, the objective was to determine the effects of organic amendments and inorganic fertilizers on soil culturable microbial population count, diversity index and selected soil properties under a gardenpeafrench bean system in the sub-temperate mid-Himalayas.

2.1. Site The field experiment was conducted during 2002 to 2008 at the research farm of ICAR-Vivekananda Parvatiya Krishi Anusandhan Sansthan, Almora. The farm is at Hawalbagh (29°36′N and 79°40′E and 1250 m above mean sea level) in the Indian Himalayan region in Uttarakhand state, India. The soil was a silty clay loam (Typic Haplaquept) with the following characteristics in 0–15 cm soil depth: pH 6.1 (1:2.5 soil:water suspension), soil organic C 11.3 g kg−1, available N 179.9 mg kg−1, 0.5 M NaHCO3 extractable P 6.79 mg kg−1 and 1.0 N NH4OAc exchangeable K 80.4 mg kg−1 soil. 2.2. Experimental details The experiment was conducted for six years with two leguminous vegetable crops- gardenpea and french bean. A factorial randomized complete block design (RCBD) with three replications and eight nutrient management practices was used. Two levels (low and high) of three organic amendments (poultry manure (PM), vermicompost (VC) and cattle manure (CM)) were evaluated with two additional treatments- inorganic fertilizer (IF – recommended NPK) and absolute control (Con) in a fixed plot. The low levels for PM, VC and CM were 3 Mg ha−1 (PM3), 3 Mg ha−1 (VC3) and 5 Mg ha−1 (CM5) and high levels were 6 Mg ha−1 (PM6), 6 Mg ha−1 (VC6) and 10 Mg ha−1 (CM10), respectively. The high levels of organic amendments were commonly used in this region. The low levels were included in the test as a consideration of the resource available to poor marginal farmers. The low and high levels of CM were relatively higher than other organic amendments (PM and VC) because of the lower nutrient status present in CM (Table 1). All organic amendments were added on a dry-weight basis. The recommended inorganic fertilizers rates for gardenpea and french bean under IF treatment were 20-26.2-33.3 and 50-30.641.7 kg ha−1 N-P-K, respectively, and were applied during sowing. The sources for N, P and K were urea, single superphosphate and muriate of potash, respectively. Gardenpea was sown (80 kg seeds ha−1) in the last week of October each year. The seeds were manually sown in row interval of 30 cm apart at about 5 cm depth. Pods were harvested manually. The last picking of pods was completed in the last week of April or first week of May in different years. After gardenpea harvest, french bean was sown in the fourth week of May. French bean was sown by hand (75 kg seeds ha−1) in row spacing of 40 cm apart to a depth of about 5 cm. French bean pods were harvested by picking and last picking was completed in the fourth week of August. Both crops were cultivated under irrigated conditions and hand weeding was also done for both crops for weed control. Maize-wheat system was cultivated in the land before the experiment on gardenpea-french bean system was conducted. 2.3. Organic amendment preparation from biological waste Poultry manure (PM) was collected from a nearby poultry farmhouse. The basic materials used for preparation of PM are poultry excreta, the spilled poultry feed and material used as bedding in poultry operations. Vermicompost (VC) and cattle manure (CM) were produced at the experimental farm. The details of the CM and vermicompost preparation are given by Mahanta et al. (2015) and Saha et al. (2008). All manures were applied manually 15 days before crop sowing. Each organic amendment was analyzed before application for different properties (Table 1). 2.4. Yield and economics Marketable green pods of gardenpea and french bean were harvested in different phases during harvesting period for pod yield 230

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Table 1 Properties of manures from biological wastes and Inorganic fertilizers. Particulars

Inorganic fertilizer (Urea, SSP, MOP)#

Manures from biological waste Poultry manure

Vermicompost

Cattle manure

poultry excreta + spilled feed + material used as bedding in poultry operations Mixture of small aggregates and powder > 2 mm

Crop residues + Cattle dung Powder < 2 mm

Cattle dung and urine + left over material of fodder + litter Small aggregates > 2 mm

Colour

Ashy grey

Black

Brownish black

Bulk density (Mg m−3)†

0.346

0.361

0.240

Water holding capacity (g kg−1)‡ pH§

936

1416

1703

7.93

7.66

7.76

C (g kg−1) N (g kg−1) P (g kg−1) K (g kg−1) C:N ratio Fe (mg kg−1) Mn (mg kg−1) Zn (mg kg−1) Cu (mg kg−1)

448 18.4 17.68 12.41 24:1 4124 393 345 71

322 12.6 5.98 5.88 26:1 10951 303 138 44

299 10.2 5.04 7.81 29:1 5421 345 298 59

Basic organic material Texture

No organic material Granular 1–2.8, 1–4 and 1–3.4 mm for urea, SSP and MOP fertilizer, respectively Crystal white, gray and pink for Urea, SSP and MOP fertilizer, respectively 0.816, 1.124 and 1.145 for Urea, SSP and MOP fertilizer, respectively – 9.53, 2.39 and 8.55 for Urea, SSP and MOP fertilizer, respectively – 460 for Urea 69.9 for SSP 500 for MOP – – – – –

†

Oven dry-weight basis. Water holding capacity was the moisture content at −0.33 bar pressure. § Manure:water = 1:5. # Urea, SSP (single superphosphate) and MOP (muriate of potash) are the fertilizers for N, P and K, respectively. ‡

et al., 2012). Culturable microbial population in the soil from different organic amendments and inorganic fertilizers treatments were enumerated by the soil dilution plate method (Seeley et al., 1991). Pikovskaya Agar (Pikovskaya, 1948), King's B Agar (King et al., 1954; Johnsen and Nielsen, 1999), Jensen N-free agar (Jensen, 1942), Nutrient agar (Seeley et al., 1991), Potato dextrose agar (Waksman, 1922), Kenknight agar (Seeley et al., 1991), Trichoderma selective medium (TSM) (Elad et al., 1981) and Fusarium specific media (Komada’s Medium) (Komada, 1975; Vanwyk et al., 1986) were used for recording population count of total phosphate solubilizing bacteria, fluorescent Pseudomonas spp., heterotrophic free living N2-fixing bacteria, total bacteria, fungi (Pencillium spp., Aspergillus spp. and other fungi), actinomycetes, Trichoderma spp. and Fusarium spp., respectively (Hazan et al., 2012; Seeley et al., 1991; Pikovskaya, 1948; King et al., 1954; Johnson and Nielsen, 1999; Jensen, 1942; Waksman, 1922; Elad et. al., 1981; Komada, 1975; Vanwyk et al., 1986). To suppress bacteria, streptomycin (30 ppm) was added to Potato dextrose agar, Kenknight agar and actinomycetes agar. In the conventional dilution-plate procedure, 1 g of soil was added to 10 ml sterile water and tenfold dilution were prepared. From the resulting suspension, 0.1 ml of respective appropriate dilutions were spread on the surface of respective medium plates containing 25 ml of medium. The plates were incubated at 28 °C for 48 h for bacteria and 3–7 days for fungal growth, and colony forming units were recorded. For the enumeration of phosphate solubilzing bacteria, appropriate dilutions were placed on Pikovskaya agar (Hi-Media, Mumbai) medium plates contained (g l‐1): Yeast Extract – 0.5; Dextrose – 10.0; Calcium phosphate [Ca3(PO4)2] – 5.0; Ammonium sulphate – 0.5; Potassium chloride – 0.2; Magnesium sulphate – 0.10; Manganese sulphate – 0.0001; Ferrous sulphate – 0.0001; Agar 15.0 and incubated at 28 °C for 72 h. After incubation, the formation of clear halo around the colonies was an indication of inorganic phosphate solubilization, were counted and expressed as colony forming unit (CFU) per gram of soil (Pikovskaya, 1948). Pseudomonas spp. were enumerated by placing an appropriate

estimation. After picking all marketable green pods, plants were harvested at ground level and weighed for stover yield estimation. Economic analysis of the data was done based on the prevailing cost of inputs/operations and price of produce. The cost of cultivation for growing crops involved the expenditure towards land preparation, seed and sowing, purchasing organic amendments and inorganic fertilizers and their application, spraying for pest control, irrigation, harvesting and threshing. Gross returns were worked out based on the price of main produce (pod) of the crops as follows: US $240, $280, $300, $300, $320 and $360 Mg−1 gardenpea pod in the year 2002–03, 2003–04, 2004–05, 2005–06, 2006–07 and 2007–08, respectively; US $400, $440, $480, $500, $500, $500 Mg−1 french bean pod in the year 2003, 2004, 2005, 2006, 2007 and 2008, respectively. Net returns were estimated by deducting total cost of cultivation from the gross returns, and the net returns per US$ invested {benefit-cost ratio – (B:C ratio)} was estimated by dividing the net returns with the cost of cultivation. 2.5. Soil sampling Soil samples were collected 15 days after completion of six cropping cycles from the 0–15 cm soil layer (surface layer) using a 5 cm diameter tube auger and bulked. The moist soil samples were sieved (using a 2 mm sieve) after removing the roots and plant materials. Portions of soil samples were air-dried and kept at room temperature. The remaining soils (< 2 mm) were instantly transported to the laboratory for soil microbial analysis. 2.6. Soil biological properties 2.6.1. Soil culturable microbial population count The soil culturable microbial populations were recorded through colony forming units (CFU) and were enumerated by the serial dilution plate count method. The plate count method for estimating CFU was used. The CFU method can count any number of culturable microbes using dilutions. The viable microorganisms were counted by the CFU method, as this method could exclude dead microbes and debris (Hazan 231

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22nd week of the year (27 May to 2 June; the hottest week of the season). The soil temperature moderation was estimated as variation of soil temperatures between amended and unfertilized control plots. Details regarding the measurement of soil crack surface area (SCSA) and soil crack volume (SCV) are given in Dasog et al. (1988) and Mahanta et al. (2013). The SCSA and SCV were estimated using the following equations (Bandyopadhyay et al., 2003):

dilutions on King’s B agar (Hi-Media, Mumbai) medium {containing (g l−1) Proteose peptone −20 g; MgSO4 −1.5 g; K2HPO4 −1.5 g; glycerol – 15 ml; Agar- 20 g and distilled water 1 l}. The pH was adjusted to 7.0 ± 0.2 with 1 N NaOH before autoclaving and incubated at 28 °C for 72 h. After incubation, the colonies were counted and expressed as colony forming unit (cfu) per gram of soil (King et al., 1954; Johnson and Nielsen, 1999). For the enumeration of free-living nitrogen fixers and actinomycetes appropriate dilutions were spread on Jensen's Medium {Ingredients (g l−1) – Sucrose 20.0; Dipotassium phosphate – 1.0; Magnesium sulphate – 0.5; Sodium chloride – 0.5; Ferrous sulphate – 0.1; Sodium molybdate – 0.005; Calcium carbonate – 2.0; Agar – 15.0 (Hi-Media, Mumbai)} and Kenknight and Munaiers medium Ingredients (g l−1): Dextrose – 1.0; Potassium Hydrogen Phosphate – 0.1; Sodium Nitrate – 0.1; Potassium Chloride – 0.1; Magnesium Sulphate – 0.1; Agar – 15.0; pH – 7.0 –7.2, respectively (Kenknight and Muncie, 1939; Jensen, 1942). Similarly, appropriate dilutions were spread on the medium of Nutrient agar, Potato dextrose agar, Trichoderma selective medium (TSM) and Fusarium specific media (Komada’s Medium) for enumeration of total bacteria, fungi (Pencillium spp., Aspergillus spp. and other fungi), Trichoderma spp. and Fusarium spp., respectively (Hazan et al., 2012; Seeley et al., 1991; Waksman, 1922; Elad et al., 1981; Komada, 1975; Vanwyk et al., 1986).

SCV =

SCSA =

3. Results and discussion 3.1. Yield and economics There was a significant response of both gardenpea and french bean crops to the addition of organic amendments and inorganic fertilizer (Table 2). There were significant differences among different organic amendments for pod and stover yield of gardenpea (probability level of significance of 0.0005 and 0.0039 for pod and stover, respectively) and french bean (p < 0.0001 for both pod and stover). Contrast analysis of PM vs VC, VC vs CM and PM vs CM revealed that poultry manure performed significantly better than vermicompost and cattle manure, except for pod and stover yield of gardenpea under CM. The high level of organic amendment provided significantly higher pod and stover yield (probability level of significance of 0.0056, 0.0028, 0.0083 and 0.0172 for gardenpea pod and stover, and french bean pod and stover, respectively) of both vegetable crops compared to the low level of organic amendment. The interaction between organic amendment and their levels for pod and stover yields of both crops were significant. The highest pod yields of gardenpea and french bean were recorded in plots under PM6, with the values being significantly higher compared to IF plots. Plots under PM6 produced 29 and 38% higher pod yield of gardenpea and french bean, respectively compared to IF plots. The stover yields of gardenpea and french bean under PM6 plots were 45 and 24% higher than IF plots, respectively. The increase in pod and stover yield under organic amendments, especially PM6 plots, might have been due to the significant improvement in soil health through improvement of culturable soil microbial population count and diversity (Fig. 1A–D and Table 5) and soil physico-chemical properties (Table 4) compared to IF plots. The higher culturable soil microbial diversity and population count with their a near infinite number of functions related to nutrient mineralization, plant disease control, production of organic substances, decomposition and so forth under PM6 plots might have favoured the yield of both legume crops. The Wilks’ Lambda multivariate analysis of variance clearly indicated that there were significant differences for the yield, soil physical and chemical properties, soil culturable microrgansim count and diversity (Table 3). In most of the cases and particularly for the high levels, all organic amendments were significantly superior to

(1)

s i=1

(5)

Significant differences (p < 0.05) among means of experimental results were evaluated by analysis of variance (ANOVA) and means were compared by Tukey's Honest Significant Difference (HSD) Test, using SAS 9.3 version. Multivariate analysis of variance (MANOVA) was also conducted to assess the significant difference for homogeneous groups of variables. Correlations between various parameters were done by using statistical package SPSS (Statistical Package for Social Science, SPSS Inc., Chicago, IL).

2.6.3. Soil culturable microbial dominance index The soil culturable microbial dominance index was estimated from the Simpson dominance index (C) using the following equation (Simpson, 1949):

∑ Pi 2

(4)

2.8. Statistical analysis

where, H = the Shannon diversity index for soil culturable microbial diversity, Pi = fraction of the entire population made up of microbial genus/group i, s = numbers of microbial genus/group encountered, ∑ = sum from species 1 to species s, loge = the natural logarithm.

C=

2 Cl

(3)

where, w, d and l indicate crack width, crack depth and crack length, respectively. The parameter, C is derived from d and w.

s i=1

∑

0.5 wdl ;

C = [(0.5w )2 + d 2]1/2

2.6.2. Soil culturable microbial diversity index Soil culturable microbial diversity was expressed using Shannon diversity index (H), that was the most common and most preferred index. This index could consider both richness and evenness of culturable soil microorganisms and provides equal weight to rare and common microbial genus/group. The soil culturable microbial diversity was estimated using the following equation (Shannon, 1948):

H = − Σ (Pi × log e Pi )

∑

(2)

The Simpson dominance index describes about the most common species in the community. The higher value of index indicates that very few species are highly dominant in the community of species. 2.7. Soil organic matter and structure Walkley-Black C was measured in all soil samples (Walkley and Black, 1934). The soil:water suspension of 1:2.5 was used for determination of soil pH. Surface soil bulk density (Mg m−3) was measured using a core sampler (7 cm diameter and 8 cm height). Soil moisture content at field capacity (0.03 MPa) was measured using a pressure plate apparatus. Digital soil thermometers were used to measure soil temperatures. Three temperature readings were recorded randomly from each plot and averaged. Soil temperature was measured during the coldest and the hottest weeks of the last year of the study following Mahanta et al. (2013). The morning temperature was recorded at 0645 hr and the afternoon temperature was measured at 1415 hr, during the second week of January (the coldest week of the winter season). Similarly, the morning temperature was recorded at 0500 and the afternoon temperature was measured at 1415, during the 232

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Table 2 Yield and benefit-cost ratio with probability level of significance for pooled and contrast analysis of gardenpea-french bean system under different nutrient managements. Nutrient source

PM† VC CM IF Con

Level of nutrient source

Low High Low High Low High – –

Pod yield (Mg ha−1)

Stover yield (Mg ha−1)

Gardenpea

French bean

Gardenpea

French bean

6.58b‡ 7.70a 4.78c 6.59b 6.04b 7.60a 5.96b 3.42d

10.26b 12.60a 6.58d 9.16c 8.93c 11.19b 9.14c 4.12e

2.73b 3.16a 2.07c 2.82b 2.53b 3.15a 2.56b 1.46d

6.00b 7.37a 3.65d 5.10c 5.00c 6.36b 5.10c 2.20e

4.38b 5.30a 2.34f 3.23e 3.49de 4.14bc 3.64cd 1.41g

interactions 0.0039 0.0028 < 0.0001

< 0.0001 0.0172 < 0.0001

< 0.0001 0.0310 < 0.0001

< 0.0001 0.0183 < 0.0001 < 0.0001 < 0.0001 0.1470 < 0.0001

< 0.0001 0.0093 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001

< 0.0001 0.8638 0.0014 < 0.0001 < 0.0001 < 0.0001 < 0.0001

Probability level of significance for organic amendments and levels with their Organic amendment§ 0.0005 < 0.0001 Level of Organic amendment# 0.0056 0.0398 Organic amendments × Level of amendments < 0.0001 < 0.0001 Probability level of significance for contrast analysis Control vs rest < 0.0001 IF vs Organic†† 0.0014 IF vs OrganicHigh < 0.0001 PM vs VC < 0.0001 VC vs CM < 0.0001 PM vs CM 0.0582 < 0.0001 IF vs PMHigh

< 0.0001 0.0170 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001

Net returns per US$ invested (B:C ratio) for gardenpea-french bean system

†

See Section 2.2 for treatment details. Means in the same column with different letters are significantly (Tukey’s HSD tests, P < 0.05) different. Organic amendment = Poultry manure (PM), vermicompost (VC) and cattle manure (CM) were three organic amendments used in the experiment. # Level of Organic amendment = High and low were two levels of organic amendments used in the experiment. †† Organic = All organic amendments in experiment; OrganicHigh = High level of three organic sources; PMHigh = High level of poultry manure. ‡ §

Fig. 1. Influence of organic amendments and inorganic fertilizer on the culturable soil microbial population (A, B and C), diversity and dominance (D). Bars with the same letter are not significantly different (Tukey’s HSD tests, P < 0.05). Error bars represent standard deviation. See Section 2.2 for treatment details.

233

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significantly higher population than VC. The interaction between organic amendment and their levels of different culturable soil microorganisms was significant. Phosphate solubilizing bacteria, Pseudomonas, N-fixing bacteria, Penicillium, Aspergillus, total bacteria, fungi and actinomycete population were highest under PM6 plots (Fig. 1A–C). The above culturable soil microbial population under CM10 plots were very close to PM6 plots. The highest population count of these microorganisms under PM6 plots and similar values under CM10 plots might be due to higher soil organic C concentrations (Table 4). Larkin et al. (2006) indicated that soil organic C concentrations had the most direct influence on microbial characteristics, as higher SOC levels could support greater microbial population. The soil microbial responses to PM6 application might also be due to either better soil physico-chemical characteristics (Table 3 and 4) or the introduction of microorganisms in the PM (Jangid et al., 2008). Jangid et al. (2008) also reported higher bacterial populations in PM amended soils. All organic amendments significantly increased Trichoderma and decreased Fusarium population compared to IF plots (Fig. 1B). Further, the vermicompost amendment provided significantly higher Trichoderma and lower Fusarium population compared to PM and CM. The interaction between organic amendment and their levels for Trichoderma and Fusarium population counts was significant. Plots with VC6 had the highest Trichoderma and lowest Fusarium population. Amendment of PM6, CM10, and the lower level of VC had similar population counts of Trichoderma compared to VC6 plots. Similarly, PM6 plots had similar population of Fusarium as the VC6 plots. Vermicompost contains the excreta and cocoons of earthworm. It also contains enzymes, vitamins, antibiotics and other plant growth hormones. Since the cast is produced after proper digestion of organic materials inside the gut of earthworms, the nutrients become water soluble. Due to the above factors, the population level of Trichoderma spp. probably increased manifold in the vermicastings (Vijayan et al., 2009) compared to other nutrient sources. Fusarium species is known as one of the most pathogenic genus of fungi (Swer et al., 2011). In this study, it was also one of the dominant genus isolated from the IF plots (Fig. 1B). Similarly, Abawi and Widmer (2000) observed a decrease in pathogenic fungi with application of organic amendments. Trichoderma species possess diverse metabolic activity and are aggressive in nature, which makes them necrotrophic to other fungi and helps in playing key roles in suppressing Fusarium species (Mahanta et al., 2013). Hence, the population of pathogenic Fusarium showed the lowest level where the highest population of Trichoderma was observed, i.e. in VC applied plots in this study. The soil culturable microbial diversity index mostly represents the richness of soil culturable microbial functional group and their evenness, while the dominance index describes the most common soil culturable microbial genus in the community. The diversity of microorganisms is critical to the functioning of the ecosystem, because there is the need to maintain ecological processes such as decomposition of organic matter, nutrient cycling, soil aggregation and controlling pathogens within the ecosystem. The functional diversity is very important in ecological assessments of microorganisms within the ecosystem, mainly because little is known about the relationship between the structural and functional diversity of these microorganisms. The functional microbial diveristy is likely to be more important than straight microbial diversity in promoting crop growth, as the microbes under the same functional group will perform the similar function. Hence, more emphasis is given on consortia of functional microorganisms instead of a single microorganism in the present study. The present study reflects the effect of different treatments on culturable microbial diversity of functional soil microorganisms. There were no significant differences among different organic amendments and their different levels for soil culturable microbial diversity and dominance index. However, the interaction between organic amendments and their levels of application was significant. Application of either 6 Mg ha−1 PM or 6 Mg ha−1 VC or 10 Mg ha−1

Table 3 Probability level of significance for multivariate analysis of variance in different group of variables under gardenpea-french bean system with different nutrient managements. Multivariate analysis of variance

Yield†

Soil physical property

Soil chemical property

Soil culturable microrgansim count and microbial diversity

Wilks' Lambda

< 0.0001

< 0.0001

< 0.0001

< 0.0001

† Yield = Yield group of variable includes pod and stover yield of both gardenpea and french bean; Soil physical property = Soil physical property group of variable includes soil temperature moderation during coldest and hottest week of the year, soil crack surface area and volume, water holding capacity and bulk density; Soil chemical property = It includes soil organic carbon and pH; Soil culturable microorgansim count and microbial diversity = It includes soil culturable microorganism count of phosphate solubilizing bacteria, Pseudomonas spp., N2-fixing bacteria, Penicillium spp., Aspergillus spp., Trichoderma spp., Fusarium spp., total bacteria, total fungi, total actinomycete, Shannon soilculturable microbial diversity index and Simpson soil culturable microbial dominance index.

the IF plots (Table 2, 4 and 5) for the yield, soil physical and chemical properties, soil culturable microrgansim count and microbial diversity and dominance. In the manure treated plots, there could be an uninterrrupted and controlled delivery of nutrients due to their slow release compared to the rapid solubility of inorganic fertilizers (Mahanta et al., 2013). It is often assumed that a synchrony exists between crop nutrient uptake and release of nutrient from organic amendments becasue the same factors control the processes of organic matter decomposition, nutrient demand and net primary productivity (Mahanta et al., 2013). Additionally, organic manures also provide growth promoting substances (Mahanta et al., 2015) and micronutrients (Table 1). The poor performance of VC6 plots compared to PM6 might be due to lower C and other nutrient concentrations in the former (Table 1). Although the C and other nutrient concentrations are low in CM (Table 1), the similar response of CM10 plots for pod and stover yield compared to PM6 plots might be due to the compensation with the higher application level (10 Mg ha−1). The high level of organic amendments provided significantly higher net returns US$−1 invested (B:C ratio) than inorganic fertilizer (Table 2). There were significant differences observed among the different organic amendments, between the two levels of amendments and the interaction of the above two factors for B:C ratio. Application of the high level of PM (i.e. PM6) recorded the highest B:C ratio of 5.30 for gardenpea-french bean system, which was significantly higher than other sources and levels. Despite the input cost under PM6 of $81 higher than IF plots, the highest B:C ratio was due to 1.7 and 3.5 t ha−1 gain in pod yield of gardenpea and french bean, respectively (Table 2). This increase in pod yield nullified the input cost and enhanced B:C ratio under PM6 plots and hence it was economically more sustainable. 3.2. Soil culturable microbial population and diversity Organic amendments significantly influenced microbial populations of Pseudomonas, phosphate solubilizing bacteria, N-fixing bacteria, Trichoderma, Aspergillus, Fusarium, total bacteria, fungi and actinomycete compared to inorganic fertilizer (Fig. 1A–C and Table 5). The higher microbial population in plots under organic amendments was most likely due to the existence of organic carbon (Table 1) that acts as an energy source for microbes in soil. This quickly soluble organic carbon as source for energy was lacking under the IF plots. There was no significant difference among different organic amendments for phosphate solubilizing bacteria and total bacteria (Table 5). Poultry manure amendment clearly dominated over both VC and CM for Penicillium, total fungi and actinomycete population (Table 5 and Fig. 1B and C). Amendment of PM and CM provided significantly higher population of Pseudomonas and N-fixing bacteria than VC (Table 5 and Fig. 1A). For Aspergillus, the PM amendment provided 234

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Table 4 Effects of organic amendments and mineral fertilization on soil physical and chemical properties. Nutrient source

PM† VC CM IF Con

Level of nutrient source

Low High Low High Low High – –

Soil temperature moderation during extreme week of the year (°C) Coldest week of morning

Hottest week of afternoon

0.97ab§ 1.40a 0.42c 1.03ab 0.67bc 0.97ab 0.90b –

3.07ab 3.80a 1.20c 2.87ab 1.50bc 3.13ab 2.07b –

SCSA‡ (m2 m−2 area)

SCV (cm3 m−2 area)

BD (Mg m−3)

WHC (cm 15 cm−1 soil layer)

Soil pH

Soil organic carbon (g kg−1)

0.179 cd 0.147d 0.201c 0.172 cd 0.182 cd 0.199c 0.311b 0.423a

199c 175c 219c 195c 186c 206c 324b 401a

1.367c 1.343d 1.373b 1.363c 1.370bc 1.360c 1.377b 1.410a

4.30abc 4.89a 4.27abcd 4.79ab 4.21bcd 4.70abc 4.09 cd 3.67 cd

7.01a 7.20a 6.66ab 6.73ab 6.65ab 6.72ab 5.64c 6.11bc

12.3ab 12.6a 11.7c 12.2b 11.9bc 12.4ab 11.6c 9.5d

0.1734 0.8670 0.7588

0.4347 0.6202 0.0652

0.8001 0.3584 < 0.0001

0.2273 0.0311 0.1009

0.7959 0.8534 0.2133

< 0.0001 < 0.0001 < 0.0001 0.2380 0.5018 0.5955 < 0.0001

0.0001 0.1327 0.0395 0.1201 0.6853 0.2348 0.0111

< 0.0001 0.0017 < 0.0001 0.5444 0.4948 0.2072 < 0.0001

0.0015 < 0.0001 < 0.0001 0.0078 0.9403 0.0067 < 0.0001

< 0.0001 0.1720 0.0489 0.1791 0.6000 0.3948 0.0765

Probability level of significance for organic amendments and levels with their interactions Organic amendments 0.0441 0.1632 0.0115 Level of Organic amendments 0.7106 0.5669 0.3431 Organic amendments × Level 0.0010 0.0004 0.1230 of amendments Probability level of significance for contrast analysis Control vs rest < 0.0001 IF vs Organic# 0.9485 IF vs OrganicHigh 0.0485 PM vs VC 0.0041 VC vs CM 0.5173 PM vs CM 0.0154 IF vs PMHigh 0.0187

< 0.0001 0.2380 0.0202 0.0033 0.4870 0.0137 0.0080

< 0.0001 < 0.0001 < 0.0001 0.0369 0.7381 0.0191 < 0.0001

†

See Section 2.2 for treatment details. SCSA = Soil crack surface area; SCV = Soil crack volume; BD = Bulk density; WHC = Water holding capacity. § Means in the same column with different letters are significantly (P < 0.05) different. # Organic = All organic amendments in experiment; OrganicHigh = High level of three organic sources; PMHigh = High level of poultry manure. ‡

crops (Fig. 2A and B). Application of PM significantly moderated extreme soil temperatures compared to VC and CM (Contrast analysis of PM vs VC and PM vs CM in Table 4). Thus, PM6 application has a greater potential to adapt climate change for both crops. All organic amendments significantly reduced the soil cracking surface area (SCSA) and soil cracking volume (SCV) compared to the IF plots and the lowest value was recorded with PM6 for both parameters. Poultry manure significantly reduced SCSA compared to VC and CM amended plots (Table 4). The decrease in SCV under PM6 plots was about 85% compared to the IF plots (324 cm3 m−2 surface area). The plots under PM6 had 1637 cm2 m−2 less SCSA than IF (3111 cm2 m−2 surface area) plots. Higher soil water contents under PM6 plots (compared to IF plots) resulted in lowest SCV and SCSA meassurments (Table 4). The effect of PM application on SCV and SCSA reduction may be attributed to a greater root biomass and thus more C inputs compared to the IF plots (Cairns et al., 1997). The higher number of roots produced (as root production is directly proportional to above ground biomass) due to PM application might have reduced the shrinkage process by anchoring the soil mass and thus reducing the crack width. Mahanta et al. (2013) observed the reduction in SCSA by reducing soil crack width in a similar situation. All high levels of organic amendments significantly decreased the surface soil BD compared to IF plots. There was neither difference among organic amendments nor with their levels observed for BD. Organic amendments of PM6 significantly decreased BD compared to the rest of the sources and levels of nutrients, including the IF plots (Table 4). The surface soil BD (1.34 Mg m−3) under PM6 was 0.03 Mg m−3 lower than IF plots. The increase in SOC (Table 4) content with PM6 plots resulted in lower soil BD in the 0–15 cm layer. All organic amendments significantly enhanced the WHC compared to the IF plots (Table 4). The interaction between organic amendments and their levels for WHC was significant. The PM6 treatment (4.89 cm WHC 15 cm−1 soil depth) showed a gain of 20% moisture holding capacity in the surface soil layer over IF plots. Reduction of surface soil BD and

CM provided significantly higher soil culturable microbial diversity index (0.562, 0.510 and 0.557, respectively) in the surface soil layer compared to IF (0.325) plots (Fig. 1D). The highest value of soil culturable microbial dominance index was recorded in the IF plots (0.881), followed by the control plots (0.876). The lowest value was recorded with the CM10 (0.770) plots. The soil culturable dominance index value under PM6 (0.772) and VC6 (0.798) were very close to CM10 plots. The soil diversity of culturable microorganisms in the organic amended soils were probably enhanced due to easily available C contents and improvements in soil structure in the surface soil (Table 1 and 3). Application of either 6 Mg ha−1 PM or 6 Mg ha−1 VC or 10 Mg ha−1 CM can be regarded as an excellent way to harbour higher soil culturable microbial diversity. Jangid et al. (2008) also reported higher soil culturable microbial diversity with organic manure application. Higher soil culturable microbial dominance index value under the IF and control plots indicated the presence of more dominant species (such as Fusarium spp.) than other species in this plot (Fig. 1B). 3.3. Soil organic matter and structure The high level of organic amendments significantly moderated the extreme soil temperature compared to the IF treatments (contrast analysis of “IF vs OrganicHigh” in Table 4). The interaction between organic amendments and their levels for soil temperature moderation was significant during both the coldest week in the morning and hottest week in the afternoon. The temperature moderations were 0.50 and 1.73 °C higher under PM6 than IF plots during the mornings of the coldest week and the afternoons of the hottest week, respectively. The higher soil temperature moderation in plots under PM6 might be due to significantly higher water holding capacity (WHC) under PM6 compared to the IF plots (Table 4). The increased stover yield (Table 2) might have enhanced soil moisture through the shadow effect of more canopy coverage. The soil temperature moderation had a very good correlation (R2 = 0.8489 and 0.8362) with gain in pod yield of both 235

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Fig. 2. Relationship between (A) coldest week soil temperature moderation and gain in gardenpea pod yield; and (B) hottest week soil temperature moderation and gain in french bean pod yield.

Table 5 Probability level of significance for nutrient source, level of nutrient sources and contrast analysis of gardenpea-french bean system under different nutrient management practices. PSB†

Pseudo

Nf Bact

Probability level of significance for organic amendments and levels Organic amendments 0.5768 0.1943 0.2268 Level of organic 0.2309 0.1207 0.1166 amendments < 0.0001 < 0.0001 < 0.0001 Organic amendments × Level of amendments Probability level of significance for contrast analysis Control vs rest < 0.0001 < 0.0001 IF vs Organic‡ < 0.0001 < 0.0001 IF vs OrganicHigh < 0.0001 < 0.0001 PM vs VC 0.1317 0.0089 VC vs CM 0.6020 0.0469 PM vs CM 0.3040 0.4063 IF vs PMHigh < 0.0001 < 0.0001

< 0.0001 < 0.0001 < 0.0001 0.0046 0.0497 0.2090 < 0.0001

Pen

Asp

Trich

Fus

Bact

Fung

Actin

Div

Dom

with their interactions 0.0740 0.1523 0.0161 0.3094

0.6705 0.8308

0.0562 0.6354

0.4290 0.8597

< 0.0001 0.4688

0.0009 0.5158

0.7442 0.4886

0.7146 0.4454

< 0.0001

< 0.0001

< 0.0001

< 0.0001

0.0353

< 0.0001

< 0.0001

0.0282

0.0325

< 0.0001 < 0.0001 < 0.0001 0.0094 0.6642 0.0226 < 0.0001

< 0.0001 < 0.0001 < 0.0001 0.0177 0.3681 0.1008 < 0.0001

< 0.0001 < 0.0001 < 0.0001 0.0252 0.0006 0.0755 < 0.0001

< 0.0001 < 0.0001 < 0.0001 0.0040 0.0001 0.0783 < 0.0001

< 0.0001 0.0416 0.0219 0.3127 0.5901 0.1322 0.0140

< 0.0001 < 0.0001 < 0.0001 < 0.0001 0.1328 < 0.0001 < 0.0001

< 0.0001 0.0004 < 0.0001 0.0493 0.0281 0.0004 < 0.0001

0.0018 0.0002 < 0.0001 0.2428 0.2816 0.9221 0.0002

0.0021 0.0004 < 0.0001 0.2630 0.2324 0.9359 0.0003

† PSB = Phosphate solubilizing bacteria; Pseudo = Pseudomonas spp.; Nf Bact = N2-fixing bacteria; Pen = Penicillium spp.; Asp = Aspergillus spp.; Trich = Trichoderma spp.; Fus = Fusarium spp; Bact = Total bacterial population count; Fung = Total fungal population count; Actin = Total actinomycete count; Div = Shannon soil microbial diversity index; Dom = Simpson soil microbial dominance index. ‡ Organic = All organic amendments in experiment; OrganicHigh = High level of three organic sources; PMHigh = High level of poultry manure.

that of IF plots. Organic amendments recorded 1.01-1.56 units higher soil pH values than IF plots in the surface layer. Mahanta et al. (2013) also reported that organic amendment neutralized soil pH by enhancing soil buffering capacity. The leaching of nitrate formed through nitrification of N fertilizer might have been the cause of the acidification under IF plot. Soil organic C concentrations decreased from the initial levels due to growing of gardenpea and french bean for six years in unfertilized control plots. The higher levels of all organic amendment treatments significantly added more SOC compared to the IF plots (Table 4). Plots under PM6 treatment (12.6 g C kg−1) contained ∼8.8% higher organic C in the surface soil layer compared to IF plots. The orgnic C increase in plots under organic farming can be attributed to higher inputs of organic C compared with no external carbon addition under the IF treatment (Table 1). Increased SOC contents under organic farming is also due to the protection of the organic matter within soil aggregates and effective metabolic activities (Bhattacharyya et al., 2010). A near perfect relationships for pod yield of both crops (Fig. 3), soil culturable microbial diversity index, soil culturable microbial dominance index (Fig. 4A), soil cracking surface area and the moderation of soil temperature during the coldest week of the year (Fig. 4B) with SOC indicated that alterations of these parameters were heavily dependent upon changes in SOC. All soil properties were influenced by the oxidizable SOC contents, except soil pH (Table 6). This indicates that SOC is one of the most important soil properties contributing to climate resilient production of gardenpea-french bean system in the mid-Himalayas.

Fig. 3. Relationship of soil organic carbon (SOC) with gardenpea and french bean pod yield.

increase in SOC content under PM6 might have improved soil aggregation and WHC compared to IF plots. All organic amendments significantly improved soil reaction (pH) compared to IF plots (Table 4). The high level organic amendments enhanced soil pH more than the low level amendments. Poultry manure significantly improved soil pH compared to the other organic amendments. Application of IF (5.64) provided 0.46 units less soil pH value than the initial level. Plots with PM6 had 1.56 units higher soil pH than 236

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Fig. 4. Relationship of soil organic carbon (SOC) with (A) soil microbial diversity index and soil microbial dominance index and (B) soil cracking surface area and moderation of soil temperature during the coldest week of the year (Mod CWM).

Table 6 Pearson correlations among soil physical, chemical and biological properties in gardenpea-french bean cropping system.

GPY FBY PSB Pseudo NFB Bact Penic Asper Tricho Fusar Fungi Actin WHC BD SCSA SCV SOC pH

GPY†

FBY

PSB

Pseudo

NFB

Bact

Penic

Asper

Tricho

Fusar

Fungi

Actin

WHC

BD

SCSA

SCV

SOC

pH

1.00

– 1.00

0.89** 0.84** 1.00

0.87** 0.83** 0.98*** 1.00

0.87** 0.83* 0.98*** 0.96*** 1.00

0.91** 0.89** 0.95*** 0.91** 0.87** 1.00

0.85** 0.80* 0.94*** 0.88** 0.96*** 0.88** 1.00

0.87** 0.83* 0.99*** 0.98*** 0.98*** 0.92** 0.94*** 1.00

0.58 0.51 0.87** 0.85** 0.82* 0.81* 0.82* 0.87** 1.00

−0.47 −0.39 −0.80* −0.87* −0.80* −0.66 −0.73* −0.83* −0.94** 1.00

0.80* 0.77* 0.94*** 0.92** 0.96*** 0.88** 0.95*** 0.97*** 0.87** −0.83* 1.00

0.79* 0.79* 0.90** 0.84** 0.87** 0.93** 0.91** 0.90** 0.85** −0.68 0.92** 1.00

0.87** 0.82* 0.99*** 0.94** 0.95** 0.95** 0.97*** 0.97*** 0.89** −0.78* 0.94** 0.92** 1.00

−0.87** −0.84** −0.97*** −0.94** −0.90** −0.99** −0.90** −0.95*** −0.88** 0.73* −0.90** −0.95*** −0.97*** 1.00

−0.78* −0.76* −0.89** −0.93** −0.80* −0.90** −0.70 −0.88** −0.81* 0.76* −0.79* −0.79* −0.84** 0.91** 1.00

−0.76* −0.73* −0.88** −0.94** −0.80* −0.86** −0.68 −0.88** −0.80* 0.77* −0.78* −0.76* −0.81* 0.88** 0.99*** 1.00

0.91** 0.90** 0.89** 0.90** 0.79* 0.95*** 0.74* 0.85** 0.69 −0.57 0.75* 0.78* 0.86** −0.92** −0.93** −0.91** 1.00

0.56 0.55 0.77* 0.84** 0.79* 0.66 0.66 0.83** 0.76* −0.87** 0.84* 0.68 0.69 −0.70 −0.80* −0.82* 0.62 1.00

† GPY = Gardenpea pod yield (Mg ha−1); FBY = French bean pod yield (Mg ha−1); PSB = Total phosphate solubilizing bacteria {colony forming unit (CFU) g−1soil)}; Pseudo = Pseudomonas species {(CFU) g−1soil}; NFB = Nitrogen fixing Bacteria {(CFU) g−1soil}; Bact = Total bacterial population count {(CFU) g−1soil}; Penic = Peniciliium species {(CFU) g−1soil}; Tricho = Trichoderma species {(CFU) g−1soil}; Asper = Aspergillus species {(CFU) g−1soil}; Fusar = Fusarium species {(CFU) g−1soil}; Fungi = Fungal population count {(CFU) g−1soil}; Actino = Actinomycete population count {(CFU) g−1soil}; WHC = Water holding capacity (cm 15 cm−1 soil layer); BD = Bulk density (Mg m−3); SCV = Soil crack volume (cm3 m−2); SCSA = Soil crack surface area (m2 m−2); SOC = Soil organic carbon content (g kg−1). * = p < 0.05. ** = p < 0.01. *** = p < 0.001.

4. Conclusions

culturable soil microorganisms in a gardenpea-french bean rotation in the mid-Himalayas and similar agro-ecologies. Further study should be done to investigate the unculturable most representative fraction of soil microorganisms.

The diversity of culturable functional soil microorganisms is critical for functioning different processes ecological balance. The functional microbial diveristy is likely to be more important than straight microbial diversity in promoting crop growth, as the microbes under the same functional group will perform the similar function. Organic amendments clearly favoured the soil culturable microorganisms and their diversity compared to application of inorganic fertilizers (IF) to the leguminous vegetable system in the mid-Himalayas. Among organic amendments, the high level of poultry manure (PM6) (i.e. amendment of 6 Mg ha−1 poultry manure) was outstanding for soil culturable microbial diversity and soil temperature moderation. Although vermicompost performed better for enhancing Trichoderma population and suppressing disease causing Fusarium species in soil, its ability to improve the status of other culturable soil microorganisms was lower than poultry manure. Amendment of PM6 considerably enhanced soil organic C compared to IF treatments. Soil organic C played an important role for enhancing soil culturable microbial diversity and producing climate resilient leguminous vegetable production in the midHimalayas. Thus, the application of 6 Mg ha−1 PM to each crop can provide climate resilient production with a higher diversity of

Acknowledgments The authors are thankful to Mr. Laxmi Datt Malkani and Mr. Sanjay for maintaining the field experiment over the years and estimating the soil organic carbon, respectively and Dr Henry Allen Torbert, USDAARS National Soil Dynamics Laboratory, Auburn, USA for editing the manuscript. The authors gratefully acknowledge ICAR-VPKAS, Almora, Uttarakhand, India for providing the necessary field and laboratory facilities during the course of the investigation. References Abawi, G.S., Widmer, T.L., 2000. Impact of soil health management practices on soilborne pathogens, nematodes and root diseases of vegetable crops. Appl. Soil Ecol. 15, 37–47. Anonymous, 2014. Promotion of Organic Farming and Soil Health Management – 2014–15 Agenda. Directorate of Agriculture, Dehradun, Uttarakhand, India. Bandyopadhyay, K.K., Mohanty, M., Painuli, D.K., Misra, A.K., Hati, K.M., Mandal, K.G.,

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