Nutrient Cycling in Agroecosystems55: 159–164, 1999.© 1999Kluwer Academic Publishers. Printed in the Netherlands.

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Long-term effect of nutrient management and cropping system on cottonyield and soil fertility in rainfed vertisols

M.V. Venugopalan & R. PundarikakshuduCentral Institute for Cotton Research P.B. No. 2, Shankar Nagar (PO), Nagpur - 440 010, India

Received 26 May 1998; accepted in revised form 12 February 1999

Key words: Gossypium hirsutumL., Gossypium arboreumL., yield trends, farm yard manure, fertilizers

Abstract

The effect of different N, P and K combinations with and without FYM on cotton productivity and the changes insoil fertility of three rainfed cotton based cropping systems were analyzed through a field experiment, conductedfor 11 yr. Monoculture ofG. arboreum(Asiatic) cotton, out-yielded monoculture ofG. hirsutum(upland) cottonin 9 out of 11 yr. except in years of heavy rainfall.G. hirsutumcotton in rotation with sorghum produced 8% moreyield than monoculturedG. hirsutum. Significant responses to N and P application were consistently observed,while the response to K was inconsistent. Substituting half the N dose with FYM, gave 162 kg/ha and 222 kg/hamore seed cotton at low (N60 P13 K25) and high (N90 P20 K38) doses respectively. Also substituting half the Ndose with FYM built up soil organic C from 4.2 to 5.4 g/kg, and increased available P from 4.5 to 6.4 mg/kg. Thevariations in the performance of the cropping systems and the response to fertilizers could not be accounted for bytotal rainfall alone. However, there was significant positive correlation between cotton yield and post Septemberrainfall. Multiple regression equations were fitted to estimateG. arboreumandG. hirsutumyields based on themonthly distribution of rainfall.

Introduction

Rainfed cotton is cultivated in about 15.7 million ha,a third of which is in India (Hearn, 1994). Its lowproductivity is largely attributed to the quantity anddistribution of rainfall (Tripathi et al., 1990). AlthoughG. arboreum(Asiatic) cotton is better adapted to lowsoil moisture conditions, bothG. arboreumand G.hirsutum (upland) are widely grown under rainfedconditions. The present global yield of rainfed cot-ton, 391 kg lint/ha, which is only 45% of that of theirrigated cotton, needs to be upgraded and stabilized.

Low input sustainable production practices likecrop rotation and integrated nutrient management im-parted stability to irrigated cropping systems (Mitchellet al., 1991, Lal et al., 1994, Meelu, 1996). Suchpractices have not always produced the desired res-ults in rainfed crops in general, and rainfed cotton, along-duration crop, in particular (Katyal et al., 1997).However, Mannikar (1993) observed that applicationof FYM, imparted stability to rainfed cotton. Frye

and Thomas (1991) observed that long-term experi-ments are ideal for analyzing the interactions betweensoil, cropping systems, climate and management fordeveloping sustainable crop production practices.

Hence, the results of a long-term field experiment,being conducted at the Central Institute for Cotton Re-search, Nagpur, India, were used to analyze the impactof continuous use of single nutrients (N, P and K) andtheir combinations, with and without organic (farmyard) manure, on the cotton yield and soil fertilityunder three cotton based cropping systems.

Materials and methods

A field experiment was initiated in the monsoon sea-son of 1986 at the Central Institute for Cotton Re-search, Nagpur, India. The experimental site is amedium deep vertisol, with a pH of 8.1 (1:2 soil: waterratio), organic carbon of 4.20 g per kg soil, Olsen ex-tractable P of 4.5 mg per kg and 1N ammonium acetate

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Figure 1. Trends in the performance ofG. hirsutum(C1) andG.arboreum(C2).

Table 1. Monthly distribution of rainfall (mm)

Year June July August September Post-Sept∗

1986 201 252 296 114 125

1987 155 191 303 24 169

1988 211 295 446 303 79

1989 160 254 206 40 80

1990 241 228 334 99 90

1991 171 396 313 3 4

1992 95 276 346 120 61

1993 131 439 188 248 152

1994 127 761 315 317 230

1995 141 378 252 266 25

1996 16 403 194 155 120

∗Rainfall from 1st October till end of crop season (Jan/Feb).

extractable K of 208 mg/kg soil. The region has adry, sub humid climate with a mean annual rainfall of1050 mm, received primarily through the south-westmonsoon from June–September. The actual amount ofrainfall received during the years of experimentationare depicted in Figure 1 and the monthly distributionis presented in Table 1. The treatments comprised ofthree cropping systems viz. monoculture of cotton(G. hirsutum) variety LRA 5166 (C1), monocultureof cotton (G. arboreum) variety AKH-4 (C2) and (G.hirsutum) – Sorghum (Sorghum bicolor) variety CSH-9 (two year) rotation (C3) as main plots and 13 nutrientcombinations in a split plot design (with fixed ex-perimental plots) with four replications. The sub plottreatments were:

T1: N 0 P 0 K0 (control)

T2: N60 P 0 K 0T3: N60 P13 K 0T4: N60 P 0 K25T5: N0 P13 K25 + 10 tonnes FYM/haT6: N60 P13 K25T7: N30 P13 K25 + 5 tonnes FYM/haT8: N90 P0 K0T9: N90 P20 K0T10: N90 P0 K38T11: N0 P20 K38 + 15 tonnes FYM/haT12: N90 P20 K38T13: N45 P20 K38 + 7.5 tonnes FYM/ha

Half the dose of N in treatments T7 and T13 andfull dose of N in T5 and T11 was supplied throughFYM, applied about 4 weeks before sowing (taking theaverage N content in FYM as 0.6%). The entire quant-ity of P and K along with half the quantity of N (exceptin T7 and T13) was basally applied and the remainingN was top dressed in two equal splits, at 45 (squar-ing stage) and 70 (flowering stage) days after sowing(DAS) in cotton and 30 and 60 DAS in sorghum. InT7 and T13, basal N dose was skipped and the en-tire fertilizer N was top dressed. The crops were sownwith the onset of monsoon in the last week of June,and raised using the recommended crop husbandrypractices.

Above ground dry matter from 10 randomly selec-ted plants was used to calculate the Harvest Index. Theproduce from the entire net plot (size of 21.6 m2) wasused to calculate seed cotton yield. Soil samples werecollected from 0–20 cm depth after the 5th and 10thcrop manually using a soil auger. Three samples drawnfrom each plot were thoroughly mixed and a com-posite sample was prepared. Composite samples fromall the 156 plots were air dried, powdered and sievedthrough a 0.2 mm sieve. These samples were analysedfor organic C using a modified Walkley and Blackmethod by heating the soil-dichromate-acid mixture at150 ◦C for 30 min. to ensure complete oxidation andfor Olsen’s extractable P using the procedures outlinedby Page et al. (1982).

Data pertaining to eleven years was analyzed usingstandard procedure of ANOVA for Long-Term Exper-iments and the treatment means were compared byDuncans Multiple Range Test (Gomez and Gomez,1984). Multiple regression analysis using monthlyrainfall distribution and total rainfall (during the cropseason) on the yield ofG. hirsutumandG. arboreumwas performed. Stepwise regression analysis was doneto retain the variables that had a significant contribu-tion to yield. Similarly, multiple regression using year

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Table 2. Effect of cropping system and nutrient combination on seed cotton yield and harvest index

Tr. Seed Cotton Yield (kg/ha) 1986–96 Harvest Index (%)

No. G. hirsutum G. arboreum Mean C3∗ G. hirsutum G. arboreum

T1 430 468 449h 489 27.6 27.8

T2 658 718 688g 780 27.1 32.6

T3 906 1042 974d 898 32.7 34.2

T4 647 827 737fg 694 29.5 34.6

T5 869 1060 951de 1018 32.9 36.9

T6 964 1084 1024cd 978 29.8 35.1

T7 1036 1194 1115bc 1140 31.8 36.2

T8 609 880 745fg 727 29.1 34.3

T9 1067 1187 1127bc 1105 33.5 35.7

T10 749 923 836ef 705 26.7 31.3

T11 1042 1121 1082bc 1212 34.5 35.2

T12 1131 1234 1183b 1114 34.7 34.4

T13 1345 1464 1405a 1374 31.0 37.1

Mean 879m 1016n 948 941 30.84 34.26

∗Sorghum-G. hirsutumrotationAny two means having a common letter are not significantly different at 5% level of significance.

of culture, post-September rainfall and total rainfall ontreatment wise yield was done to estimate yield trends.In C3, where cotton was sown in alternate years, meanseed cotton yield for 5 yr are provided for comparison.

Results and discussion

Effect of cropping systems

On an average, monoculture ofG. arboreum(C2)significantly out-yielded monoculture of (G. hirsu-tum (C1) by 15.6% (Table 2).G. arboreumhad ahigher harvest index, 34.3% as against 30.8% inG.hirsutum, implying a more efficient partitioning ofassimilates into the economic sink under rainfed con-ditions. G. hirsutumcotton in rotation with sorghum(C3) out-yielded monoculturedG. hirsutum(C1) by7.8%. Earlier, Ebelhar and Welch (1989) and Mitchellet al. (1991) observed reduced yields under continuouscotton compared to rotation with corn, under irrigatedconditions.

Trends in seed cotton yields, indicated that mono-culturedG. arboreumwas superior toG. hirsutumin9 out of 11 yr. except in years experiencing heavyrainfall (Figure 1). ThusG. arboreumis better adaptedto drier conditions. Wide annual variations in yield ofboth the species, shown in Figure 1 was not positivelycorrelated to total rainfall. However, there was a sig-nificant positive correlation between post-September

rainfall and yield with r values of 0.36 and 0.57 forG. hirsutumandG. arboreumrespectively, the latterbeing significant. Adequate rainfall during the post-September months when the crop enters the criticalboll development phase would have ensured sufficientsoil moisture. De Kock et al., (1993) reported thatmoisture stress during the boll development phaselimits cotton yields. Despite well distributed rainfall,cotton yields were low during 1994 and 1995, due toheavy damage by American bollworm (Helicoverpaarmigera).

Stepwise regression analysis indicated that theyields could be estimated using the equations:

G. arboreum:Y = 1289 + 1.93 X1 + 3.47 X2− 1.19 X3 (R2 = 0.859)

(0.52) (0.78) (0.29)

G. hirsutum:Y = 202 + 1.62 X1 + 2.11 X2 (R2 = 0.523)

(0.67) (1.01) (1)

where Y = seed cotton yield (kg/ha), X1 = totalJuly rainfall (mm), X2 = total post-September rainfall(mm), X3 = total rainfall (mm) during cropping seasonand figures in parentheses are SE of the coefficients.

Cropping systems did not significantly influencethe organic C or available P content of the soil (Table3).

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Table 3. Effect of cropping systems and nutrient combinationson organic C and available P

Tr. Organic C (g/kg) Available P (mg/kg)

No. After 5 yr After 10 yr After 5 yr After 10 yr

Nutrient combinations

T1 3.83g 3.64f 3.74cd 3.05e

T2 4.56de 4.71cde 3.78cd 3.39e

T3 4.27ef 4.82cde 4.40c 4.25d

T4 4.06fg 4.42e 3.75cd 3.15e

T5 5.26ab 6.18a 5.71ab 6.60ab

T6 4.29ef 4.89cd 3.97cd 4.59d

T7 4.72cd 5.43b 5.57ab 6.36abc

T8 4.20f 4.78cde 3.87cd 3.01e

T9 4.34ef 5.08bc 4.53c 4.50d

T10 4.00fg 4.58de 3.57d 3.09e

T11 5.51a 6.37a 6.19a 6.85a

T12 4.58de 5.12bc 5.35b 5.72c

T13 4.97bc 6.08a 6.01ab 6.55ab

Cropping systems

C1 4.42m 5.07m 4.65m 4.63m

C2 4.60m 5.11m 4.66m 4.72m

C3 4.51m 5.10m 4.64m 4.66m

Any two means within the same column having a common letterare not significantly different at 5% level of significance

Effect of nutrient combinations:

The pattern of response to nutrient combinations weresimilar in all the three systems and hence only theaverage response over C1 and C2 are discussed.

Mean seed cotton yield:Cotton responded signi-ficantly to N application alone up to 60 kg N/ha (T2)over control (T1), beyond which there was no fur-ther response at 90 kg N/ha (T8), in the absence ofP and K (Table 2). The response to P applicationwas significant up to 20 kg P/ha, while the responseto K application was not significant. The mean re-sponse to P i.e. N60 P13 (T3) over N60 (T2) andN90 P20 (T9) over N90 (T8) was 45.5 and 51.2% re-spectively. Earlier, Pundarikakshudu (1989) reportedsimilar response in rainfed cotton up to 18 kg P/ha ona vertisol.

Both G. hirsutum(C1) andG. arboreum(C2) re-sponded to a higher NPK dose and the mean increasein yield with N90 P20 K38 (T12) over N60 P13 K25(T6) was 159 kg/ha. Supplying half the N dose throughFYM benefited all three systems. The average re-sponse with N30 P13 K25 + 5 tonnes FYM (T7) overN60 P13 K25 (T6) was 7.7% and N45 P20 K38 + 7.5tonnes FYM (T13) over N90 P20 K38 (T12) was 18.7percent, the latter being significant.

Trend analysis:The trend in seed cotton yield inselected treatments are depicted in Figures 2 and 3.

Declining yield trends were observed in control (T-1), N60 (T2) and N60 K25 (T4) treatments (Figure2). The response to K application was enhanced inthe presence of P. Deletion of K tended to declinelong-term yield trends, while its inclusion (N60 P13K25) i.e. T6, helped to stabilize rainfed cotton yieldsat around 1000 kg/ha (Figure 2).

The magnitude of yield improvement with FYMover chemical fertilizers alone, i.e. N30 P13 K25 + 5tonnes FYM (T7) over N60 P13 K25 (T6) and N45P20 K38 + 7.5 tonnes FYM (T13) over N90 P20K38 (T12) increased with progressive applications ofFYM (Figure 3). This may be attributed to a gradualimprovement in soil fertility (Table 3), or due to animprovement in hydrophysical environment (Wani etal., 1994). After 8 years, a yield equivalent to that withN90 P20 K38 (T12) could be obtained with N30 P13K25 + 5 tonnes FYM (T7), thus facilitating an optionfor reducing chemical fertilizers.

There were tremendous annual variations, duringthe 11 years in the magnitude of response to nutri-ents, including FYM, resulting in high Coefficient ofVariation (CV) ranging from 23.1 to 29.6%. The treat-ments involving FYM i.e. T5, T7, T11 and T13 hadCV values of 25.0, 27.6, 24.8 and 29.3% respect-ively. Thus, FYM applicationper sedid not impartstability. Nutrient responses in rainfed cotton weremodified by other factors, presumably, distribution ofrainfall, stored soil moisture and pest damage. Mul-tiple regression analysis indicated that only 20–78%of the variation in the different nutrient treatmentscould be accounted for by years of culture (time trend),post-September rainfall and total rainfall during thecrop season. This analysis also indicated a signific-ant negative long-term trend in Control (T1) plots andpositive trends in T3 and T9 involving P and T7 andT13 involving combination of chemical fertilizers andFYM with the following estimated linear regressionequations:T1: Y = 746 - 3.82 X1 + 1.40 X2 - 0.40 X3 (R2 = 0.61)

(10.44) (0.59) (0.14)T3: Y=1536+17.80 X1+2.92 X2-0.92 X3 (R2=0.78)

(13.42) (0.77) (0.19)T7: Y=1438+66.3 X1+3.10 X2-0.99 X3 (R2=0.66)

(22.6) (1.29) (0.32)T9: Y=1389+45.92 X1+2.93 X2-0.79 X3 (R2=0.58)

(21.17) (1.21) (0.30)T13: Y=1513+72.02X1+3.25X2-0.83X3 (R2=0.54)

(38.57) (2.25) (0.56)

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Figure 2. Long term yield trends in selected inorganic nutrient treatments (vertical bars indicate SE).

where Y = yield, X1 = year of culture, X2 = postSeptember rainfall (mm), X3 = total rainfall (mm) andfigures in parentheses give SE of the coefficients.

Katyal et al. (1997) also observed that the responseof cotton to FYM had high annual aberrations and areless predictable, unlike short duration crops. Yet, sig-nificant positive gradients in treatments T7 and T13indicate that the combinations of FYM and fertilizerscan sustain productivity rise, without a decline in soilfertility (Table 3).

Soil fertility changes:Continuous application of 10(T-5) and 15 (T-11) tonnes FYM increased soil organicC from 4.2 g/kg initially to 5.26 and 5.51 g/kg in fiveyears respectively (Table3). It further increased by an-other 0.92 and 0.76 units respectively after another 5years.

Annual application of 13 kg P/ha was necessary tomaintain the available P content at approximately theinitial level (4.5 mg/kg). However, compared to T6,a significant build up in soil available P was noticeddue to continuous application of a higher level of Pi.e. 20 kg P/ha in combination with N and K (T-12) as

well as where inorganic P was applied in combinationwith FYM (T5, T7, T11 and T13). Nambiar (1995)also reported that P and FYM application improvedthe available P status in vertisols.

Conclusion

Based on the present investigation, it can be con-cluded thatG. arboreumwas more productive thanG. hirsutumunder rainfed conditions experiencing soilmoisture stress.G. hirsutumcotton in rotation withsorghum yielded higher than monocultured cotton.Substituting half the fertilizer N with FYM built upsoil organic C and available P, and could sustain higherproductivity levels besides offering options to reducechemical fertilizer dose. Annual application of 13 kgP/ha was necessary to maintain the available P contentat approximately the initial level.

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Figure 3. Long term yield trends in NPK and NPK + FYM treatments (vertical bars indicate SE).

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