Agropedology 2012,22 (2), J03-JJ4

Long term effect of nutrient management on soil quality and sustainable productivity under sorghum-wheat crop sequence in

Vertisol of Akola, Maharashtra

R. N. KATKAR\ V. K. KHARCHE\ B. A. SONUNE\ R. H. WANJARI2 AND MUNESHWAR SINGU2

I Department of Soil Science and Agricultural Chemistry, Dr PDKV, Akola- 444 J 04, India clndian Institute of Soil Science, Bhopal-462 038, India

Introduction

Abstract: A long term experiment was conducted with the objective of assessing the

impact of continuous application of chemical fertilizers and manures on properties of

soil, key indicators of soil quality and yield sustain ability under sorghum (Sorghum

vulgare) - wheat (Triticum aestivum) cropping sequence, The experiment was con­

ducted in randomized block design since 1988 on Vertisols at the same site and with the

same randomization at AkoJa in Central India as one of the centres of AICRP on Long

Term Fertilizer Experiment. The treatments comprised of differential fertilizer levels of

NPK, sulphur free and 37.5 kg sulphur ha- I with RDF, 2.5 kg zinc ha- l with RDF, only

recommended nitrogen and nitrogen and phosphorus, farmyard manure @ lOt ha- I to

sorghum crop only singly and in combination with 100% NPK to sorghum and only

100% NPK to wheat crop. The long term yield data from 1988 to 2007 of both the crops

was used to study sustainability yield index which were found to be relatively higher in

super optimal fertilizer dose (0.436) followed by 100% RDF + FYM (0.432) and

100% RDF + sulphur (0.421). Howev.er, the highest soil quality index was observed

under integrated nutrient management comprising of 100% NPK + FYM (2.45), fol­

lowed by only FYM (2.16) and 150% NPK ofRDF (2.15) while the lowest was in the

control (1.14) followed by 50% NPK of RDF (1.45) indicating considerable enhance­

ment in soil quality due to integrated nutrient management. Among the various treat­

ments' 100% RDF + FYM not only had the highest soil quality index but it was found as

the most promising approach from the view point of yield sustainability, maintaining

higher average yields under sorghum - wheat cropping sequence.

Additional key words: Soil quality, sustainability yield index. FYM, chemicalfertiliz­ers, cropping system

Soil is a key natural resource and soil quality is the integrated effect of management on most soil proper­

ties that determine crop productivity and sustainability. Growing of crops one after another without giving due consideration to nutrient requirement has resulted in de­cline in soil fertility (Ghosh et. ai. 2003). Soil quality

assessment has been suggested as an effective tool for

evaluating sustainability of soil and crop management practices (Hussain et. ai. 1999). Soil quality assessment is purpose'oriented and site-specific (Karlen et. al. 1994). For assessing the soil quality, indicators (soil properties) are usually linked to soil function (Doran and Parkin

1994). Improved soil quality often is indicated by in­creased infiltration, aeration, aggregate size and stabil­

ity, soil organic matter, microbial biomass and by de-

104

creased bulk density. A valid soil quality index is helpful

to interpret the data from different soil measurements and

shows whether management and land use are having the

desired results for producti vity and environmental pro­

tection. Maintaining the soil quality at desirable level is

very complex issue due to involvement of climatic, soil,

plant and human factors and their interactions.

There is an urgent need to adopt appropriate

soil and plant management practices so as to reduce soil

degradation and maintain soil quality at desired level. As

temperature increases and precipitation decreases, theoxi­

dation of organic matter becomes faster which leads to

unsustainable farming. Soil quality research has focused

on the linkages among management practices and ob­

servable soil characteristics, soil processes and perfor·

mance of soil functions. The recommended dose of NPK

fertilizers alone does not sustain productivity under con­

tinuous intensive cropping system (Yaduwanshi 2003)

whereas inclusion of organic manures improves physical

properties (Mandai et. al. 2003), the biological soil sta­

tus (Ghai et.aL 1988), soil fertility and crop yields

(Swarup 1987; Mandai et. aL 2003). Several chemical,

physical and biological indicators have been evaluated

in present study using the data collected from a long term

fertilizer management experiment on sorghum-wheat

cropping system and soil quality was evaluated.

Materials and Methods

Field site, experimental layout and treatments A permanenl field experiment was laid out in 1988

at Research Farm, Department of Soil Science and Agricul­

tural Chemistry (20042' N, 77"04' E, 308 m above MSL), Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra.

The climate of the region is semi-arid tropical. The mean an·

nual rainfall is 805 mm. The soil of the experimental site be­

longs to Wardha series (Fine, smectitic, hyperthermic Typic

Haplusterts). The soil properties at the start of experiment had

210 mm m" AWC and547 mm hr' hydraulic conductivity. The soil has alkaline pH (8.1 ) . high CEC (48 c mol (p+) kg'), high

base saturation (98%), moderate organic carbon (4.6 g kg"), low P (8.4 kg ha"), high K (358 kg ha") and marginal available

S (11.8 mg kg") and available Zn (0.62 mg kg· ').

The experiment was laid out in randomized

block design with fourreplieations and twelve treatments

[T, : 50% recommended dose of N:P20

S:KP, T2: 100%

recommended dose of N:P,0 5:K20, T3: 150% recom-

R N. Katkar et al.

mended dose of N:Pps:KP, T4

: 100% recommended

dose of N:PzOs:K20 (S free), Ts: 100% recommended

dose of N:P20S:~O + 2.5 kg Zn ha·1, To: 100% recom­

mended dose of N:P20 s,T7

: 100% recommended dose

ofN, Tg : 100 % recommended dose of N:PzOs:K20 + 10

t FYM ha·1 (kharij), T9 : 100 % recommended dose of

N:P20S:K

20 + 37.5 kg S ha· I

, TIO: FYM only @ 10 t ha"

(kharij), Til: 75% recommended dose of N:Pps:KP,

Til: Control (no fertilizer and manure)). The Farmyard

manure was applied one month before sowing of sor­

ghum crop as per treatments. The recommended NPK

dose for sQrghum (Sorghum vulgare) was 100:50:40 and

for wheat (Triticum aestivum) as 120:60:60 N, P and K

kg ha-1• The half dose of N and full P and K was applied

at the time of sowing and remaining half N was applied

as urea after one month to sorghum and after 21 days to

wheat after sowing as per the treatments. Phosphorus was ap­

plied through diammonium phosphate to T, and T9 treatments

only. Nitrogen, P and K were applied through urea, single su­

per phosphate and muriate of potash respectively as per treat­

ments. Sulphur was applied as gypsum to each crop as per treat­

men!. Zinc application was done through zinc sulphate once in

every two years to sorghum crop only. Sorghum (cv CSH 9)

was grown as f'ainfed crop. The wheat (cv AKW 1071) crop

was sown in the month of November keeping a distance of

22.5 cm row spacing. Irrigations were applied to wheat crop at

critical growth stages considering the moisture availability.

Soil sampling and analysis

Soil samples were collected from 0 to 20 cm

soil depth after harvest of wheat in 2007 at the end of

nineteenth cropping cycle and were analysed for various

physical, chemical and biological parameters. The physi­

cal parameters included aggregate size distribution (Yoder

1936) and values were expressed as mean weight diam­

eter (MWD) after oven drying. Bulk density was deter­

mined by the core method (Blake and Hartze 1986).

Hydraulic conductivity was determined by constant head

method (Klute and Dirksen \986). Soil water retention

at permanent wilting point (PWP) and field capacity (FC)

were measured in pressure plate apparatus at 33 kPa and

1500 kPa. The difference between PWP and FC was cal­

culated as available water. A part of representative soil

sample of each soil sample were air dried. powdered and

passed through 0.2 mm sieve for determination of or-

Long term effect of nutrient management

ganic carbon by Walkley and Black's method (Jackson

] 967). Total nitrogen was determined by using micro­

processor based KEL PLUS digestion system and dis­tilled using KEL PLUS automatic distillation system

based on Principal of modified Kjeldahl method (Jack­

son 1967). Available P was determined by sodium bicar­

bonate extraction and subsequent colorimetric analysis

(Olsen et al. 1954). Available K was determined by neu­

tral ammonium acetate extraction and followed by emis­

sion spectrophotometry (Knudsen and Peterson 1982).

Available sulphur was determined after extracting with

CaCl2

and followed by spectrophotometry (Chesnin and

Yien 1951). Electrical conductivity and pH were deter­

mined using conductivity and pH meter. Microbial bio­

mass carbon (MBC) and nitrogen (MBN) determinations

were made by using chloroform fumigation and extrac­

tion technique (Jenkinson and Powlson 1976; Jenkinson

and Ladd 1981). The dehydrogenage activity (DHA) was

estimated by using tri-phenyl tetrazolium chloride

(Lenhard 1956), which was reduced to tripheny1

formazan.

For assessment of soil quality physical parameters

viz., bulk density, mean weight diameter, hydraulic con­

ductivity and available water capacity, chemical param­

eters viz .• soil pH. electrical conductivity, organic car­

bon, total N, available N, P, K, N03

- N and NH4- N and

biological parameters viz., microbial biomass carbon,

microbial biomass nitrogen and dehydrogenage activity

were used and the Principal Component Analysis (PCA)

was carried out. Minimum data set was retained based

on the factor loadings (Doran and Parkin 1994). These

parameters were called soil indicators. Key indicator approach was employed for assessing soil quality index. For calculating the suslainability yield index (SYI) (Singh et al. 1990; Sharma et at. 2004) the following equation was used.

6

SYI=

Ymax

Where, i = Average yield of the treatment.

6 = Treatment standard deviation.

Y max = Maximum yield in the

experiment over the years.

The soil parameters (physical, chemical and bio­

logical) which are most sensitive to management prac-

105

tices were determined. After determining the MDS of

indicators: every observation of MDS indicators was

transformed using linear scoring method (Andrews et al.

2002). Indicators were arranged in order depending on

whether a higher value was considered "good" or "bad"

in terms of soil function. For more is better indicators

each observation was divided by the highest value such

that the highest observed value received a score of 1.

For less is better indicators, the lowest observed value

was divided by each observation such that the lowest

observed value received the score of 1. Soil quality in­

dex (SQI) was determined by using the following equa­

tion (Sharma et al. 2004).

n

SQI = L (WjS)

i=1

Where, W = Factor loading derived from the PCA.

S = Score for subscripted variable.

Results and Discussion

Crop productivity

The yield data indicates that the different fertil­

izer treatments recorded significant increase in the grain

yield of sorghum over control (Table 1). The treatment

of 150% NPK (T,) recorded higher grain yield up to the

year 1997. However, 100% NPK + FYM (Tg) was supe­

rior in the subsequent years. The superiority of this treat­

ment involving integrated nutrient management compo­

nents may be due to adequate supply of secondary and

micronutrients through FYM. Moreover, inclusion of

sulphur (T9

) and zinc (T5)also increased the grain yield

to the extent of 14.11 and 8.48 per cent over sulphur free

(T4) and 100% RDF (T2

) respectively. Continuous crop­

ping without supplementing even with inorganic fertiliz­

ers (T (2) reduced the crop productivity considerably over

a period of20 cropping cycles. Application of only FYM

@ 10 t ha·1 before sowing of sorghum crop reduced the

yield to the tune of 60.4 per cent over 100% NPK and

could not sustain the crop productivity.

The grain yield of wheat (Table 1) showed that

the continuous cropping of sorghum-wheat sequence

without fertilizer application drastically decreased the

106

wheat productivity in the control plots indicating that

application of inorganic fertilizers to both the crops in

the sorghum-wheat cropping sequence is essential. High­

est grain yield of wheat was recorded with the applica­

tion of 150% NPK during initial nine years, but subse­

quently the treatment of 100% NPK + FYM shown its

superiority over 150% NPK. Application of N, K and P

dose through S- free fertilizer (DAP) caused significant

decline in the wheat yield as compared to nutrients sup­

plied through S containing fertilizers (SSP), This strongly

indicated the need of sulphur fertilization to the crops

R. N, Katkar et at,

grown in shrink-swell soils of central India. Application

of Zn @ 2,5 kg ha- I once in two years to sorghum crop

did not show much beneficial influence on the wheat pro­

ductivity as compared to 100% RDF. Use of FYM @ 10

t ha- ' alone could not sustain the high productivity and

yielded approximately one fourth of the produce obtained

with the application of 100% NPK treatment. Imbalanced

application of 100% N or 100% NP alone could not sus­

tain the wheat productivity, This resulted in gradual de­

crease in the yield over a period of cropping.

Table 1. Long term effects of various treatments on crop yield and sustainability yield index

Treatments Sorghum yield Wheat yield Sustainability yield (q ha-1) (q ha- 1) index

1988-89

TI 50 %NPK 15.80

T2 100 % NPK 23,95

T3 150 % NPK 31.30

T4 100 % NPK S free 21.95

Ts 100 % NPK + 2.5 kg Zn ha- I 23.85

T6 100 % NP 26.43

T7 100%N 21.18

Ts 100 % NPK + lOt FYM ha -I 25.73

T9 100 % NPK + 37.5 kg S ha -1

TID FYM only 10 t ha -I 15.35

Til 75 % NPK 18.45

TI2 Control 9.05

CD (p",0.05) 5.14

Sustainability yield index (SYl)

The sustainability yield index in respect of sor­

ghum and wheat was almost similar in the treatments of

100% NPK + FYM (0.432) and 150% NPK (0.436)

(Table 2). Application of only farmyard manure recorded

relatively lower SYI (0,055) as compared to use of

inorganics alone or in combination with FYM, Lowest

SYI (0.006) was noticed in control treatment. This fur­

ther justifies that, FYM alone or non-application of fer­

tilizers (Control) could not sustain the yields of sorghum

(Sorghum+wheat) 2007-08 1988-89 2007-08

26.25 6.52 14.40 0,176

38,71 10.16 27.32 0.331

46,12 12.87 32,16 0.436

34.67 12.04 24.01 0.314

39.98 11.64 28.07 0.353

27.63 10.84 14.35 0.226

21.69 9.06 10.26 0.159

50,84 13.28 34.41 0.432

39.36 25,73 0.321

15.84 6.26 3.01 0.055

30.98 10.26 18.91 0.246

1.92 2.45 0,56 0.006

2,18 2,72 2.03

and wheat in long run. Although 150% RDF recorded

higher SYI the need based use of rnicronutrients and sul­

phur would be more appropriate in the context of bal­

anced nutrition. However, use of either organic manure

@ 10 t ha", under nutrition at 50-75 % of the recom­

mended NPK or imbalanced supply of N alone or NP or

NPK (-S or -Zn) led to unsustainability and a gradual

reduction in productivity over period of cropping (Fig.

I). This may be ascribed to the decline in soil fertility

leading to nutritional deficiencies in crop plant.

Long term effect of nutrient management 107

0.5

0,45

0.4 -l

0.35 ~

0.3

>-V\

0,25

0,2

0,15

0,1

005 ..

0

100 % NPK 100 % NPK + 10 t 150 % NPK FYMonly 10 tJ ha Control FYM/ha

Fig. l.SustaiJmbility yield index (SYI)

Table 2. Long tenn effect of various treatments on soil chemical properties under sorghum-

Treatments pH EC carbon Total N Avail. nutrients (kg ha") S

T I -50 %NPK 7.94 0.281 4.32 0.043 186 16.21 309 36.06

T2 -100 % NPK 7.85 0.314 5.11 0.048 280 30.96 388 44.13

T) -150 % NPK 7.78 0.341 5.93 0.052 305 32.98 431 58.02

T4 -100 % NPK S free 7.85 0.293 5.10 0.048 267 29.11 371 33.38

Ts -100 % NPK + 2.5 kg Zn ha·1 7.83 0.324 5.15 0.049 282 29.07 386 48.61

T 6 -100 % NP 7.87 0.311 4.90 '0.046 260 29.83 339 40.54

T 7 -1OO%N 7.88 0.307 4.29 0.043 248 24.7 299 34.05

Tg -100 % NPK + 10 t FYM ha" 7.75 0.336 6.77 0.059 313 37.08 460 63.39

T9 -100 % NPK + 37.5 kg S ha·1 7.82 0.331 5.21 0.050 283 31.16 391 65.18

TlO -FYM only 10 t ha ·1 7.82 0.284 6.01 0.051 253 28.81 338 31.58

Til -75 % NPK 7.86 0.289 4.64 0.043 214 19.92 348 43.01

T 12 -Control 7.98 0.27 2.81 0.033 175 12.17 230 28.67

SE (rn±) 0.07 0.014 0.13 0.002 4.24 0.263 3.25 0.42

CD (p=O.05) 0.042 0.37 0.005 12.21 0.755 9.36 1.16

Initial value (1988) 8.05 0.30 4.6 0.044 120 8.4 358 11.8

Soil quality parameters candy highest soil organic carbon (6.77 g kg· l) and total

Soil chemical attributes N (0.059 %) were recorded in the treatment of applica-

The soil organic carbon and total nitrogen of lion offann yard manure @ 10 tonnes ha" + 100% NPK

soil varied significantly with long-tenn application of (Tg). These values were enhanced by nearly 14 and 15

manure and mineral fertilization (Table 3). The signifi- per cent compared to super optimal dose of fertilizers

108 R. N. Katkar et at.

(150% NPK) and 100% RDF respectively. The organic tivity. Application of inorganic fertilizers slightly in-carbon content increased by 32 per cent in the treatment creased electrical conductivity of soil, but did not cross of farm yard manure @ 10 tonnes ha-t + 100% NPK as the safe limit of EC indicating no hazard of accumula-compared to only recommended dose of fertilizer in two tion of salts in the crop root zone due to inorganic fertil-decades. The increase in organic carbon over a period of izers. Long-term manuring and fertilization registered 19 years under integrated nutrient management over the significant increase in available P, K and S in the plots initial can be attributed to addition of farm yard manure under 100% NPK + farm yard manure @ 10 tonnes ha-I

which stimulated the growth and activity of micro-or- (Tg). The availability of N. P and K increased by 2.6, ganism and better root biomass. Vineela et al. (2008) 12.4 and 6.7 per cent in the treatment of INM as com-also observed that soil organic carbon levels increased pared to super optimal dose of fertilizers (150 % NPK). considerably due to long-term fertilization and/or ma- However, availability of N, P and K increased to the ex-nuring applied for 29 years in Vertisol and Alfisol under tent of 11.8, 19.7 and 18.5 per cent in the treatment of semi-arid climatic condition. Mandai (2011) also reported INM as compared to recommended dose of fertilizers about 15 per cent increase in soil organic carbon in the (100 % NPK). The increase in available N in ~PK + treatment of integrated nutrient management treatment farmyard manure may be through direct addition of or-compared to recommended dose of fertilizers in differ- ganic matter from farmyard manure in combination with ent cropping systems. The soil pH was not significantly 100% NPK which might have helped in multiplication influenced due to long-term fertilization and manuring. of soil microbes, ultimately enhancing the conversion of The continuous application of mineral fertilizers and organical~y bound N to mineral form (Tolanur and manures had significant effect on soil electrical conduc- Badanur 2003).

Table 3. Long tenn effect of various treatments on soil biological and physical properties under sorghum- wheat cropping sequence (after 19th cycle)

Treatments 5MBC 5MBN DHA NOrN NlL-N BD AWC MWD HC

(mg kg-I) (rq.;KgI) y-!glgbfh) (mg N lloog soil) (Mgrri1 ~emm·t) ~mm) (em hr- l)

T1 50 % NPK 187 12.36 37.32 3.32 3.07 1.37 17.62 0.772 0.281

TrlOO % NPK 214 14.95 41.95 4.76 4.48 1.30 19.86 0.926 0.482

T3 -150 % NPK 227 16.03 45.69 5.11 4.96 1.25 21.31 1.169 0.597 T4 -100 % NPK S free 208 13.86 41.06 4.69 4.42 1.31 19.32 0.908 0.463 Ts -100 % NPK + 2.5 kg Zn ha- I 217 14.3 43.14 4.85 4.67 1.30 19.97 0.955 0.493

T6 -100%NP 196 12_74 40.11 4.45 4.21 1.32 19.41 0.886 0.478

T7 -IOO%N 179 11.98 36.97 3.96 3.72 1.32 17.48 0_858 0.396 Tg -100 % NPK + lOtFYMha-1 247 17.53 49.78 5.64 5.78 1.23 21.95 1.412 0.711 T9 100 % NPK + 37.5 kg S ha -I 220 14.8 44.19 4.89 4.73 1.29 20.08 0.966 0.508 T 10 -FYM only 10 t ha· I 222 J5.18 45.08 3.97 3.76 1.24 21.59 1.254 0,603

Tn -75 % NPK 192 13.34 38.81 4.08 3.84 1.35 17.93 0.829 0.310

TI2 -Control 139 8.86 32.51 3.22 2.94 1.38 15.86 0.737 0.239

SE (m±) 10.37 0.7 0.61 0.23 0.2 0.018 0.65 0.042 0.031

CD (£=0.05) 29.49 1.95 2.23 0.66 0.56 0.053 1.83 0.122 0.089

2[ 5.47

~ I

I ~

Long term effect of nutrient management

Availability of P increased to the extent of 91 per cent in the plots under NPK (T

2) compared to 50 %

NPK treated plots (T,). It was found higher by 6.5 % in the plots under J 50 % NPK (T J) compared to NPK treated plots (T). The maximum build-up of soil P was observed under NPK+ farmyard manure (Tg ). This might be at­tributed to build up of P in soil by its addition every year and solubilization of native P in the soil through release of organic acids from farmyard manure (Tolanur and Badanur 2003). Reddy et al. (2000) also reported that combined use of manure and fertilizers P proved better than their application in a Vertisols. The finding corrobo­rates with the results reported by Verma et at. (2005). The increase in P concentration and application of or­ganic manure suggests that organic manure is responsible for maintaining the greater concentration of Olsen P in the plots that received organic manure in a Vertisol (Singh et al. 2007). The organic manures are known to decrease P adsorption / fixation and enhance P availability in P fixing soils (Reddy et al. 1980 and Sharply et at. 1984).

The highest available K was observed in the plots under NPK + farmyard manure and the lowest un­der control. The higher available K was by 18.6 per cent as compared to NPK treated plots. Continuous cropping without addition of K and imbalanced fertilization (N and NP) reduced the availability of K as compared to initial soil K status. This might be due to continuous omission of K and! or imbalanced fertilization in crop nutrition which caused mining of its native pools that also caused reduction in crop yields (Subehia et al. 2005). The potassium showed negative balance in the treatment of only NP and N (-2859 and -2127 kgha", respectively). The available S was found highest (65.18 mg kg") in the plot under 100% NPK+ S followed by the treat­ment of INM (Ta)'

Increase in available K might be due to the di­

rect addition to the available K pool of the soil besides

reduced K fixation and release of K due to the interac­

tion of organic matter with clay (Sharma et al. 2001). This has been further reflected in sustained crop productivity over long-term cropping period of 19 years recorded at ad­equate and balanced supply of plant nutrients to the intensive cropping sequence (Ta)' The available sulphur was found sig­nificantly highest in the treatment of 100 % NPK + 37.5 kg S ha ·1 followed by farm yard manure @ 10 tonnes ha" + 100%

NPK and super optimal fertilizer dose.

Soil biological attributes

The application of NPK + farm yard manure @

109

10 tonnes ha· 1 recorded significant increase in soil bio­

logical properties viz., soil microbial biomass carbon

(SMBC), soil microbial biomass nitrogen (SMBN) and

dehydrogenase activity (OHA) to the extent of 8.8,9.3,

and 9.0 per cent as compared to J 50 % NPK through

chemical fertilizers without organics (Table 3). However,

5MBC, 5MBN and OHA was increased by 15.4, 17.2

and 18.4 per cent in the treatment of INM as compared

to recommended dose of fertilizers (100 % NPK).

This can be ascribed to direct addition of or­

ganic matter through farmyard manure and increase in

root biomass which helped in growth and development

of soil microorganisms causing beneficial effect on

5MBC, 5MBN and OHA. Application of farm yard ma­

nure at 10 tonnes ha" (only to sorghum) significantly in­

creased 5MBC, 5MBN and DHA over control which

might be due to a steady source of organic carbon to sup­

port the microbial population (Bhattacharyya et al. 2008).

The lowest value of 5MBC was observed in the control

obviously due to unfavourable environment arising out

of depletion of nutrients due to continuous cropping with­

out any fertilization or manuring (Fig. 2). ,------------------~---~-~--.

300

250

::;- 200 ~ .. !. 150

~ I '" 100 l

i 501

247

214 227 222

139

100 IINPK 150 II NPK 100 IINPK + 10 FYM only 10 ~ Co""ol tFYWha ha

Fig. 2. Soil microbilli biom'lss c,lI'bon(Sl\IBC)

The soil microbial biomass nitrogen decreased at 100% NP and 100% N to the tune ofl7.6 and 24.8 per cent as compared to 100% NPK (T

2) indicating neces­

sity of balanced fertilizer application for enhancing soil microbial activity. It was further observed that combined use of farm yard manure @ 10 tonnes ha" with 100% NPK increased microbial biomass nitrogen by 17.3 per cent compared to only NPK indicating enhanced effect of organics in microbial growth. Higher soil organic car­bon, more root proliferation and additional supply ofN through farmyard manure to microorganisms might be responsible for increasing the level of 5MBN (Verma

110

and Mathur 2009). Applications of farm yard manure @ 10 tonnes

ha· 1 + 100 % NPK recorded significantly higher dehy­drogenase activity (49.78 )lg/g/24 hr) compared to all other treatments (Fig. 3). The increase in DHA due to INM was 18.6 and 8.9 per cent over 100% :-JPK and 150% NPK respectively through mineral fertilizers. The results are in line with the findings reported by Bhattacharyya et £If. (2008). The addition of farm yard manure coupled with mineral fertilization exerted a stimu­lating influence on the preponderance of bacteria (Selvi et al. 2004). It was significantly higher in the plots under 100% :-.IPK (41.95 )lg/g/24 hr) and 100% NP (40.11 Ilg1 g/24 hr) compared with 100% N (36.97 )lg/g/24 hr), suggesting balanced application of nutrients is essential. Jain et al. (2003) also reported significant increase in DHA due to balanced nutrient supply.

60

49.18 so 4$.6, 45.08

41% i. 4(} .c: ~ 31.51

~ 30 .. 2-«

ZO ::c 0

10

l00"!,NPK 1SO%NPK 100'4NPK+l0 FVMonly10tl CanIrol tFVMlhlt h.

Fig. 3 Dehydrogennse assay (DH.-\')

Soil physical attributes

Application of NPK + farm yard manure @ 10

tonnes I ha recorded significant decrease in bulk density

as compareq to 100% NPK and 150 % NPK through

chemical fertilizers without organics (Table 3). This can

be ascribed to direct addition of organic matter through

farmyard manure and increase in root biomass which

helped in growth and development of soil microorgan­

isms causing beneficial effect on improvement in mean

weight diameter, available water capacity and hydraulic

conductivity.

Soil quality assessment

The soil quality was assessed by proper selection of indicators and seventeen soil parameters were used for Principal Component Analysis. The PC 1 and PC 2 which explained about 5% of the variability within the

R. N. Katkar el al.

measured data were retained. Highest weighted variables (Table 4) under PC) included bulk density, available water capacity, mean weight diameter, hydraulic conductivity, organic carbon, total nitrogen and dehydrogenase assay. A correlation matrix for the highly weighted variables under PCI was run separately (Table 5). It was assumed that the variables having the highest correlation sum best represented the group. Hydraulic conductivity, dehydrogenase assay and organic carbon were retained in the minimum data set. The hydraulic conductivity provides good aeration in the soil which was improved due to organic carbon enhanced by regular use as well as better root growth. The hydraulic conductivity and organic carbon helped in augmented growth of the microbes in the soil which are indicated by the dehydrogenase assay. These soil indicators were regressed as independent variables with grain yields of sorghum, wheat and total productivity as dependent variable. The coefficient of determination (R2) of soil indicators with yield of sorghum, wheat and total productivity were 0.572, 0.514 and 0.550 respectively indicating their per cent contribution in productivity of sorghum. wheat and total productivIty (Table 6).

Table 4. Results of Principal Component Analysis (PCA) of soil parameters

Sr. Soil parameters Factor loadings

No. PCI PC2

1

2 Available water capacity 0.786 0.329

3 Mean weight diameter 0.874 0.242

4 Hydaulic conductivity 0.811 0.405

5 pH -0.408 -0.!70

6 EC 0.237 0.519 7 Org. carbon 0.856 0.444

8 ToraiN 0.755 0.494

9 Avail. N 0.567 0.660

10 AvaiL P 0.669 0.645

11 Avail. K 0.577 0.750

12 iXvail. S 0.228 0.869

13 5MBC 0.683 0.447

14 5MBN 0.7 0.485

15 DHA 0.785 0.531

16 NOrN 0.447 0.683

17 NH4-N 0.493 0.724

* 15 % variation from highest factor loading.

Long rerm effect of nutrient management

Table 5. Correlation matrix (Pearson's coefficients) under PC's with high factor loadings

PC 1 Variables BD AWC MWD HC OC Total N

BD -0 .. 886 -0.901 -0.927 -0.87 -0.863

AWC -0.886 0.863 0.921 0.898 0.913

MWD -0:901 0.863 1 0.926 0.896 0.871

HC -0.927 0.921 0.926 0.92 0.929

OC -0.870 0.898 0.896 0.92 0.951

Total N -0.863 0.913 0.871 0.929 0.951

DHA -0.867 0.904 0.882 0.933 0.958 0.964

14 6.335

Avail.K Avail.S

Avail. S 0.821

sum 1.821

Table 6. Results of multiple regressions of total soil parameters and soil indicators

GoallFunction

Sorghum yield

Wheat yield

Total productivity

Total soil parameters

0.988**

0.98-3**

0.986**

** -Denotes significance at I % level of significance

Soil indicators 0.572**

0.514**

0.550**

III

DHA

-0.867

0.904

0.882

0.933

0.958

0.964

Soil quality index (SQI) Table 7. Long term effect of various treatments on soil

The significantly highest soil quality index was

observed in the treatment of 100 % NPK + FYM (2.45)

than all other treatments followed by FYM only (2.16)

and 150% NPK (2.15). Control plot recorded lowest soil

quality index (1.14) (Table 7 & Fig. 4). The soil quality

index was found to decrease in the order ofNPK>NI?N>

control indicating less aggregative effect of these treat­

ments. Increasing the fertilizer levels also helped in main­

taining the higher soil quality index (1.45 to 2.15). Sharma

et al. (2004) also reported that increasing levels fertiliz­

ers enhanced the soil quality index. It could be noticed

that the balanced application of nutrients helped in im­

proving the soil quality as compared to imbalanced use

of nutrients.

quality index

Treatments

TI 50%NPK T2 100 % NPK T3 150% NPK

T4 100 % NPK S free T~ 100 % NPK + 2.5 kg Zn ha-1

T6 100 % NP T, 100% N

Ts 100 % NPK + to t FYM ha'!

T9 100 % NPK + 37.5 kg S ha,1

TIO FYM only \0 t ha'!

Til 75 %NPK

T!2 Control

CD (2:;:;(}.O5)

Soil quality index

1.45 1.86 2.15

1.82

1.90

1.80

1.58

2.45

1.93

2.16

1.55

0.089

112

l.> US

2.45

2.16

j 2 186

I I ~lS " I 15 . 1.14 a

, 1 I

I '" 0.>

0 l00lloNPK l~'!.NPK l00%NPK+l0 FYMonIyl0U ConIroI

tFYMlh. h.

Fig. 4. Soil quality index

Conclusions

The results suggest the contribution of impor­

tant soil quality attributes like hydraulic conductivity,

organic carbon and dehydrogenase is governing the soil

quality in VertisoL The soil parameters have beeJ:! identi­

fied as the most sensitive which respond to management

and can be regarded as the important soil quality indica­

tors in Vertisols.

Integrated use of inorganic fertilizers and or­

ganic manure found better under the long term which

sustained crop productivity and enhanced soil quality in

sorghum- wheat cropping sequence grown on Vertiso!.

Organic manures (FYM) along with recommended dose

of fertilizers found to be viable options in increasing soil

organic carbon, nutrient turn over, enhancing microbial

biomass, thereby improvement in availability of nutri­

ents in soil, maintenance of soil quality and achieving

the sustainable productivity of sorghum and wheat for

long run in rainfed as well as irrigated moisture regimes.

Acknowledgements

The authors are thankful for financial help from

AICRP on Long Term Fertilizer Experiments, Indian In­

stitute of Soil Science (ICAR), Bhopal.

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Received: January 2012 Accepted' October 2012