Puddling and N management effects on crop response in a rice-wheat cropping system

ELSEVIER

Soil & Tillage Research 36 ( 1995) 129-139

Puddling and N management effects on crop response in a rice-wheat cropping system G.C. Aggarwal *, A.S. Sidhu, N.K. Sekhon, K.S. Sandhu, H.S. Sur Deprtment

of Soils, Punjab Agricultural

University,

Ludhiana-141004,

India

Accepted 27 July 1995

Abstract Coarse-textured soils are puddled to reduce high percolation losses of irrigation water under rice (0ryz.a sutiuu L. ). This practice, however, reduces yield of succeeding wheat (Triticum aestivum L.) owing to deterioration in soil physical conditions. The 6 year field study reported in this paper evaluated the effects of puddling level and integrated N management on the development of subsurface compaction and growth and yield of rice and the following spring wheat grown in 1 year sequence on a sandy loam soil. Treatments were combinations of three puddling levels: low (one discing and one planking), medium (two discings and one planking), and high (four discings and one planking), and three nitrogen sources: ( 1) 120 kg N ha-’ from urea, (2) 60 kg N ha-’ from urea plus sesbania (Srshania oculeatu Pers. ) green manure, and (3) 60 kg N ha- ’ from urea plus 20 Mg ha- ’ farmyard manure. Percolation rate decreased from 14 mm day- ’ with low puddling to 10 mm day-’ with high puddling. with a corresponding reduction in irrigation water requirement of rice of about 20%. Bulk density profiles in the O-30 cm soil layer showed the formation of a compact layer at 15-20 cm depth, and bulk density increased with puddling level and cropping season. The impact of organic amendments in reducing bulk density was immediate, but the rate of increase in bulk density with time was the same in all the nitrogen sources. Organic amendments did not affect percolation rate and irrigation requirement of rice. Rice yields were not significantly affected by puddling and N source treatments throughout the study period. Residual effects of treatments on wheat yield were observed from the second season onwards. Interactive effects of puddling and N source on yields of rice and succeeding wheat were not significant. Yield differences in wheat between high and low puddling were 8% and 1 1% during the second and the fifth cropping season, respectively. This study indicates that medium puddling was optimum, as it reduced percolation without decreasing yield of succeeding wheat. Kewnrdv:

Bulk density:

* Corresponding

author

Elsevier Science B.V. SSDfOl67-1987(95)00504-8

Irrigation

water requirement;

Percolation

rate; Xylem

water potential;

Root growth

I.30

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et (II. /Soil

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1. Introduction Rice has become the major summer season (June-October) crop of north-western India. The area under lowland rice in the Punjab state increased from 0.29 million ha in 19651966 to 6.7 million ha in 1989-90, mainly at the cost of maize (Zea mavs L.). This can be attributed to fluctuations in maize yield and to higher economic returns from rice. This shift, however, has increased demands on irrigation water as water requirements of lowland rice on coarse-textured soils are very high (Prihar et al., 1976; Sandhu et al., 1980; Aujla et al., 1984). This is evidenced in the increase in the number of tubewells in Punjab from 16 932 in 1965-1966 to 740 000 in 1989-1990, with a resultant lowering of the ground water level. Another consequence of the shift from maize to rice has been a deterioration in soil physical conditions and resultant reductions in wheat yields following rice (Meelu et al., 1979: Sur et al., 198 1; Boparai et al., 1992). This decrease in wheat yield may be due to reduction in root growth and distribution under poor soil physical environment (Oussible et al., 1992). Reduced root growth limits water uptake and consequently plants may experience water stress and thus lower crop yield. Various tillage practices have been tested for decreasing percolation rates in these coarsetextured soils. Puddling with tractor mounted disc harrow-cultivators is the most common technique used by farmers. Puddling, in general, refers to the destruction of soil aggregates into ultimate soil particles at a moisture content near saturation. Prihar et al. ( 1976) reported that puddling with a local plough (single tine bullock driven plough) was as effective as mechanical puddling with a disc harrow, angular puddler or rotavator. Pate1 and Singh ( 1980) found that compaction accomplished by running of the roller was better than puddling in reducing percolation loss in loamy sand. Sharma and Bhagat ( 1993) showed that puddling was effective in reducing percolation losses when sand was less than 70%, and finer fractions were dominated by clay ( 13-20%). However, information on effect of puddling on percolation rate in rice and on yield in rice-wheat cropping system is lacking. Concern for conservation of non-renewable energy, minimizing pollution and sustaining crop production has resulted in emphasis on integrated nutrient management, especially in the developing world (Aggarwal and Singh, 1983; Morris et al., 1986, 1989; Yadvinder Singh and Bijay-Singh, 1991). Studies have shown that incorporation of organic materials in rice soils improves aggregation in puddled soils (Chaudhary and Ghildyal, 1969; Sahoo et al., 1970). However, the effects of organic material incorporation on the development of subsurface soil compaction is not clearly understood. Incorporation of organic materials as a supplement to inorganic fertilizers in rice may reduce me development of compact layers and may ameliorate the deleterious effects of puddling in rice on rooting, growth and yield of a succeeding wheat crop. The objectives of this long-term study were to evaluate the effects of puddling levels and integrated ( urea plus organic) nitrogen sources on ( 1) irrigation water requirement, growth and yield of rice, (2) development of subsurface compaction, and (3) growth, plant water status and yield of a following wheat crop. 2. Materials

and methods

A field experiment was initiated at Ludhiana (30”56’N, 75”52’E), India, in 1986 on a Fatehpur sandy loam soil (coarse loamy, calcareous, mixed, hyperthermic Typic Usto-

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& Tiflage Research

36 (1995)

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131

chrept), This soil contains 64% sand, 23% silt and 13% clay, is low in organic carbon (3.5 g kg- ‘), low in KMnO,-extractable N (156 kg N ha-‘), medium in 0.5 N NaHCO,extractable P ( 14.6 kg ha- ’ ) and medium in available K ( 150 kg ha- ‘). Gravimetric soil water contents at -0.033 MPa and at - 1.5 MPa are 12.9% and 5.7%, respectively. Maximum air temperature during six rice seasons ranged between 33.8 + 1.2”C (July) and 30.9 F 0.W (October), and minimum air temperature was between 26.3 &- 0.6”C (July) and 15.4 + 1.6”C (October). Maximum and minimum air temperatures during six wheat seasons ranged between 19.0 + 0.W (January) and 34.1 + 1.6”C (April) and 6.0 k 1.O”C (January) and 16.7 + 1.O”C (April). Mean per cent relative humidity during rice seasons ranged between 74.014.8 (July) and 60.4 k4.2 (October), and during wheat seasons between 62.0 &- 3.3 (November) and 78.6 f 8.3 (January). The experiment was a factorial arrangement of three puddling levels and three integrated nitrogen sources. Puddling level and integrated nitrogen source treatments were repeated every year in the same plots. Puddling levels accomplished with a 35 H.P. tractor were: ( 1) one run of a disc harrow followed by one planking (Low, L) ; (2) two runs of a disc harrow followed by one planking (Medium, M); (3) four runs of a disc harrow followed by one planking (High, H). Planking refers to one run of post-tillage packing and levelling of soil with a wooden plank. The three integrated nitrogen sources were: ( 1) 120 kg N ha-’ from urea (U); (2) sesbania, a leguminous crop, used here as green manure, containing 140 kg N ha-‘, plus 60 kg N ha-’ from urea (U+GM); (3) 20 Mg ha- ’ (dry weight basis) farmyard manure (FYM) containing 120 kg N ha- ’ (6 years average) plus 60 kg N ha- ’ from urea (U+FYM). Total N content of FYM and green manure was determined by micro-Kjeldahl method. The experiment was arranged in a split plot design with puddling level as main plot treatments and nitrogen sources as sub-plot treatments. Each treatment was replicated three times. Sub-plot size was 12 mX4.25 m. Sesbania was sown after wheat harvest in the last week of April, with an application of 13 kg P ha- ‘. The mean dry biomass of the g-week-old sesbania was 4.8 Mg ha -‘. The green manure was incorporated into soil by discing twice. The other plots were also disced twice, I day before puddling and transplanting rice. Puddling was done in standing water by different passes of tractor-mounted disc harrow followed by one planking. The 40-45day-old rice seedlings (cv. “PR-106”) were transplanted between 30 June and 17 July during the 6 year period. Farmyard manure at 20 Mg ha- ’ was surface applied 1 day after transplanting. Nitrogen (urea) was applied in three equal splits at transplanting, and 3 and 6 weeks after transplanting. An application of 13 kg P ha- ’ was made to U + FYM and U treatments only, as in U + GM plots, P had been applied before to the green manure crop. All plots received 25 kg K ha- ‘. During the first 2 weeks after transplanting the soil was kept ponded continuously. Ponded water level was recorded daily before applying measured amount of water, with a Parshal flume, to ensure 5 cm submergence. Afterwards, all the irrigations (each irrigation of 7.5 cm ) were timed 2 days after the drainage of the ponded water (Sandhu et al., 1980). The entire plot was flooded with irrigation water. Depth of applied water was also recorded with a hook gauge. Percolation rates were monitored from data on water levels and open pan evaporation. Percolation rates (PR) for various rice cropping seasons (1986-1988) were estimated by the sum of total irrigation water applied (I) and cropping season rainfall (P)

132

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36 (19951 129-139

minus the cumulative open pan evaporation (PE) divided by the duration of crop growing season (d). viz., PR=

I+P-PE d

Rice was harvested from the inner 8 m X 3 m area between 10 October and 4 November over the 6 year period. Plant height and effective tillers per hill were recorded at harvest. Plant N content was determined by the micro-Kjeldahl method at 50days after transplanting in 1988, and 38 days after transplanting in 1989. Profile bulk density in each plot was determined from two spots by a core measuring 7 cm in diameter and 5 cm in height from depths of 0-5,5-lO, lO--15,15-20,20-25 and 25-30cmfrom 1987 to 1990after harvesting rice. Six cores were taken from each depth for every treatment. Wheat (cv. “HD 2329”) followed the rice crop. Wheat was sown in rows 22.5 cm apart from 1 November to 18 November over the 5 year period. Nitrogen at the rate of 120 kg ha-’ was applied in two equal splits, at sowing and 4 weeks after sowing before first irrigation; 26 kg P ha- ’ and 25 kg K ha- ’ were applied at sowing. Wheat was flood irrigated according to a irrigation water/open pan evaporation = 0.9 schedule (Prihar et al., 1974). Wheat received four irrigations, each of 7.5 cm at 30-40 day intervals, depending upon amount of pan evaporation and rain received. Xylem water potential of wheat under four treatments, i.e. low puddling plus urea (L-U), medium puddling plus urea (M-U), high puddling plus urea (H-U) and high puddling plus urea plus green manure (H-U + GM), was recorded between 13:00 h and 14:30 h on various days of the growth season with a locally fabricated pressure chamber. Wheat growth parameters such as plant height, number of tillers, above-ground plant biomass and yield components were recorded. Periodic data on plant biomass and number of tillers were recorded in 199 1. Root distribution in each plot was studied in L-U, M-U and H-U treatments in the inter-row space on Day 140 after sowing in 1989. Soil cores were drawn from the inter-row space at O-7.5, 7.5-15, 15-30, 30-60, 60-90 cm depths with a 7.5 cm diameter metallic tube. Five samples were drawn from each plot for studying root growth. The soil from each depth was washed over a 1 mm screen, and roots were oven dried at 65°C to a constant weight and weighed. The effects of puddling and N source were assessed by analysis of variance.

3. Results and discussion 3.1. Soil physical changes Bulk density of the O-30 cm soil layer increased with puddling level (Fig. 1) as well as the number of cropping seasons (LSD,,a, = 0.02). Bulk density profiles indicated the development of a compacted layer at the 15-20 cm depth. The bulk density of the compacted layer was 1.69 Mg m-s with low, 1.72 Mg mm3 with medium and 1.77 Mg me3 with high puddling level in 1987. The value increased to 1.76 Mg me3, 1.78 Mg rnp3 and 1.83 Mg m -’ in 1990 under the respective puddling treatments (Fig. 2). The compaction effect of puddling was partially counterbalanced by organic manure. Green manuring buffered changes in soil bulk density more than FYM (Fig. 2).

G.C. Aggarwui

et al. /Soil Bulk

1.3 01

density

1.4

Fig. 1. Effect of low and high puddling

& Tillage Research

1. 5

(averaged

36 (1995)

129-139

1.13

( Mg me3) 1.6 1

1.7

over N sources)

1.8

I.9 1 ,051 1990 NS

after 2 and 5 years on profile bulk density

Formation of the subsurface compacted layer possibly led to reduced percolation rates through soil. A similar observation was made by Sharma and DeDatta ( 1986). Percolation rates were lowest with high puddling level (Table 1) . Mean percolation rates were 14 mm day-‘, 12 mm day-’ and 10 mm day-r under low, medium and high puddling levels, respectively. The reduction in percolation lowered irrigation requirement of rice (Table 1). Mean irrigation water ( 1986-1989) applied was 1047 mm, 978 mm and 853 mm in low, medium and high puddling treatments, respectively (Table 1) . Nitrogen source had no effect on percolation rate and irrigation water applied. Interactive effects of puddling and N source on percolation rate and irrigation water applied were not significant.

1.60

I 1987

, 1988

I 1989

I

I 1990

1988

1

1989

Fig. 2. Development of subsurface ( 15-20 cm) compact layer as affected by (a) puddling sources) and time, (b) N source (averaged over puddling levels) and time.

1990

(averaged

over N

I34

G.C. Ag,qurwal

Tablr I Effect of puddling Year

and nitrogen

Puddling Low

1986 1987 1988

1986 1987 1988 1989 Mean

U, Urea: GM.

& Ti/lage

source on percolation

Research

rate and irrigation

level

Nitrogen

Medium

Percolation (mmday-‘) 14.4 18.3 9.7 14.1 Irrigation IO00 1320 870 1000 1047

et al. /Soil

High

Urea

rate 11.6 17.7 7.8 12.4 water (mm) 890 1320 740 960 978

green manure;

FYM

10.0 14.3 5.1 9.8

3.0 3.0 I.0 1.8

790 1140 690 790 853

SO NS

manure.

129-139

water applied to rice source UfFYM

Percolation rate (mm day-‘) 11.2 13.9 17.8 18.0 7.6 7.6 12.2 13.1 Irrigation water (mm) 890 950 1300 1330 500 510 920 960 903 938

60 90 65

farmyard

36 (1995)

Puddling

X N source interaction

Il.3 14.6 8.9 11.6

NS NS NS NS

850 1160 510 880 850

NS NS NS NS

was not significant

3.2. Rice growth and yield

(NS). NS

Puddling treatments did not affect grain and straw yields of rice significantly. Grain yield of rice in 1990 was very low (data not recorded), owing to decreased number of filled spikelets resulting from excessive rains, cloudy weather and strong winds during the early grain filling stage. Mean ( 1986-1989, 1991) rice grain yield under low, medium and high puddling was 5.7 Mg ha- ‘, 5.8 Mg ha- ’ and 5.9 Mg ha- ‘, respectively (Table 2)) and mean rice straw yield was 13.1 Mg ha-‘, 13.6 Mg ha-’ and 13.6 Mg ha-’ under low, medium and high puddling, respectively. Plant height and number of effective tillers were not affected by puddling treatment. Development of a compacted layer at 15-20 cm depth did not affect rice growth and yield probably because water availability to rice was not limiting. Moreover, rice has a shallow root system. About 90% of total root length of Table 2 Effect of puddling

level and nitrogen

Treatment Puddling Low Medium High J-SD,,, in, Nitrogen source U+FYM U+GM U LSD,om,

source on grain yield (in kg ha-‘)

of rice in different

years

1986

1987

1988

1989

1991 d

Mean

6650 6920 7090 NS

6560 6890 6890 NS

4590 4580 4650 NS

5950 5800 6160 NS

4870 4950 4510 NS

5720 5830 5860 NS

6610 6990 7050 NS

7320 6140 6880 NS

4420 4860 4530 NS

6390 5420 6110 NS

SllO 4730 4500 NS

5970 5430 5810 NS

’ Data of 1990 not recorded. U, Urea; GM, green manure;

FYM.

farmyard

manure. Puddling

X N source interaction

was not significant

(NS).

G.C. Agqmval Table 3 Effect of puddling years Treatment Puddling Low Medium High LSD,,, 05, Nitrogen source U+FYM U+GM u LSD,,,m,

level and nitrogen

et al. /Soil

& Tillage Research 36 (1995)

129-139

13s

source in rice on grain yield (in kg ha- r ) of succeeding

wheat in different

1986-1987

1987-1988

1988-1989

1989-1990

1990-1991

Mean

4150 4230 3980 NS

4880 so30 4510 171

4670 4830 43.50 283

3890 3970 3.530 265

4120 4120 3650 211

4340 4440 4000 148

4220 3990 4150 NS

4700 4890 4830 NS

4860 4510 4480 310

4010 3720 3660 285

4470 3700 3760 214

4450 4160 4180 127

U, Urea; GM, green manure; LSD,,,,,,, for years is 224.

FYM,

farmyard

manure.

Puddling

X N source interaction

was not significant.

transplanted rice is in the top 20 cm of soil (Sharma et al., 1987). If nutritional and water requirements of the crop are met in the zone above the compact layer, the crop would not be affected. Rice growth and yield (Table 2) were also unaffected by N source treatments. Interactive effects of puddling and N source on rice grain and straw yield were not significant. Mean plant height averaged 1.05 m and the number of effective tillers averaged 10.1 per hill. Mean rice straw yield under U + FYM, U + GM and U nitrogen treatments was 13.1 Mg ha-‘, 13.5 Mg haa’ and 13.6 Mg ha- r , respectively. This indicates that 60 kg ha- ’ urea could be replaced by either 4.8 Mg ha-’ GM or 20 Mg ha-’ FYM. Similar results were obtained by Yadvinder-Singh and Bijay-Singh (1991). Plant N concentration under U +GM, U+FYM and U treatments averaged 1.52%, 1.47% and 1.53%, respectively, during 1988,and 2.28%, 2.17% and 2.56%, respectively, during 1989. On the basisof total amount of nitrogen added through organic and inorganic sources,nitrogen useefficiency (kg grain per kg N applied) by rice indicates organic manuresas lessefficient sourcesof N comparedwith fertilizer urea. Kundu et al. ( 1993) alsofound that efficiency of Giliricidia sepiumJacq.and Sesbaniacannabina (Retz) Pers.N wasabout67% and45%, respectively, that of urea N. However, this conclusionis offset if residualeffects on the following wheat crop are considered.In our study, for example, wheat yield was favoured by FYM application to the preceding rice (Table 3). 3.3. Wheat growth and yield Wheat growth characterswere significantly depressed(P < 0.05) in the highly puddled treatment in 1988-1989; low and medium puddling treatmentswere similar in thesecharacteristics. Plant height at 120 days under high and low puddling was0.90 m and 0.96 m, respectively, and numberof spikesunder thesetreatmentsaveraged359 m-* and422 m-‘, respectively. Wheat grain yield components,i.e. numberof grainsper ear, 1000grain weight and grain weight per ear, however, were not affected by puddling level. Adverse effects of high puddling on wheat growth in 1990-1991 were observedthroughout the season(Table

136 Table 4 Effect of puddling 1991

G.C. A,q~mwd

level and nitrogen

Treatments

Plant dry weight Puddling Low Medium High LSD,,o,, Nitrogen source U U+GM U+FYM LSD,ow, No. of tillers m-’ Puddling Low Medium High LSD,o,,,, Nitrogen u U+GM U+FYM L%,o,,

et ul. /Soil

& Tillage Research

36 (1995)

source in rice on seasonal changes in growth

129-139

of succeeding

wheat in 1990-

Days after sowing 27

54

68

83

100

122

18.3 16.6 16.0 NS

96.1 97.3 80.4 7.5

162.3 140.1 116.2 13.1

349.8 347.9 271.3 16.2

562.4 544.8 495.2 36.8

1068.6 956.4 921.7 NS

16.5 14.8 19.6 I .08

86.7 65.9 121.3 11.4

124.2 126.3 168.0 12.5

294.4 279.3 395.2 25.7

467.8 503.3 631.2 22.8

864.3 914.2 1168.2 212.6

292 272 248 21.8

399 398 324 25.2

399 398 324 25.2

-a -

257 242 313 17.7

321 347 453 20.9

321 347 453 20.9

-

(g m ’f

” Not recorded.

4). Plant dry matter and tillering under high puddling as compared with low puddling ranged between 72% and 88%, and 81% and 94%, respectively, on different days. Differences in dry matter owing to puddling increased with crop age. Plant dry weight and tillering were significantly more with U + FYM as compared with other N source treatments (Table 4). Leaf water potential of wheat was affected by puddling and N source of preceding rice. Xylem water potential (@) of wheat was more negative under high puddling than under low puddling throughout the cropping season in 1988-1989 and 1989-1990 (Fig. 3). More negative 4x with increase in puddling may be partially due to reduced wheat root growth and consequently less water uptake. Root mass at 6-15 cm and 15-30 cm soil depths under high puddling was 67% and 53%, respectively, of the root mass under low puddling (Table 5). It could also be partially due to decreased infiltration and consequent low soil water content with greater puddling. Green manuring ameliorated the adverse effect of puddling on I,!JX.$x under H-U + GM treatment was comparable with I@ under L-U treatment (Fig. 3). Treatment effects on $x were not significant in the 1990-1991 season. Grain and straw yields of wheat were significantly affected by puddling and N source treatments imposed on preceding rice crop (Table 3). However, the interactive effect of

G.C. Afixnrwal

& Tillqe

et al. /Soil

-1 .o-

Reseurch

36 (1995}

129-139

137

1988-89

-2.5I %O

90 Days

Fig. 3. Xylem water manuring in preceding urea: 0. high puddling

Table 5 Rooting protile Soil

I 110

100 after

120

, 130

sowing

potential of wheat during 1988-1989 and 1989-1990 as affected by puddling and rice (0, low puddling plus urea; CI. medium puddling plus urea; X , high puddling plus urea plus green manure). Vertical bars indicate LSD,,,,,.

of wheat

depth

at grain

filling

Root

mass

stage in 1989 (kg ha

as affected

by puddling

in preceding

green

plus

rice

’)

(cm) Low

Medium

High

LSD,,,,,,,

15-30 30-60

1,190 90 48

2010 15 44

60-90 90- 120 O-120

I4 IO 2352

12 10

145.5 45 43 I5 8

46 15 NS NS NS

O-15

Measurements

from

urea

treatment

2151 only

1566

138

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er ul. /Soil

& Tillage Research

36 (1995)

129-139

puddling and N source treatments was again not significant. Mean wheat straw yield under low, medium and high puddling treatments was 6.5 Mg ha ‘, 6.5 Mg ha ’ and 6.0 Mg ha ‘, respectively. The effects on grain yield are shown from the second season onwards (Table 3 ) Grain yield with low and medium levels of puddling was statistically the same as or greater than with high puddling level. The differences in grain yield are attributed primarily to the differences in number of effective tillers per unit area. Our results agree with those of Oussible et al. ( 1992)) who attributed reduction in wheat grain yield owing to subsurface compaction to reduction in number of shoots per unit area rather than reduction in the number of kernels per spike or kernel weight. Differences in grain yield owingg to low and high puddling increased with time. For example, yield reduction with high puddling compared with low puddling was about 8% during the second cropping season ( 19861987), but increased to about 11% during the fifth cropping season ( 1989-1990). The combination of FYM with urea applied to rice produced higher wheat yields than urea alone or urea+GM, in three ( 1988-1989 to 1990-1991) out of five cropping seasons. Pooled (over years) analysis showed that wheat yield under U +FYM treatment was significantly higher than yield under urea alone and urea+ GM treatments, but wheat yield under the two latter treatments was statisticahy the same (Table 3). Grain yield differences again were due to differences in effective tillers per unit area rather than spike weight, number of grains per spike or 1000 grain weight. In 1988-1989, the U+FYM treatment produced 427 tillers m -’ as compared with 373 with U+GM treatment and 397 with U treatment (LSD,, ,,5 = 32 tillersm -*). The organic carbon content of soil in November 1990 was 0.53%, 0.4 I % and 0.43% in U + FYM, U and U + GM plots, respectively. This could be the reason for the higher wheat yield in U + FYM treatment. Like grain yield, straw yield was consistently reduced with the high puddling level from the second cropping season onward. The U + FYM treatment produced consistently higher straw yield (6.7 Mg ha- ’ ) than U + GM (6.2 Mg ha- ’ ) and U (6.1 Mg ha ‘) treatments after the second cropping season. Straw yield was affected by both plant height and number of tillers, and thus plant weight per unit area. For example, in 1988-1989, plant dry weights with low, medium and high puddling levels were 833 g rn- ‘, 843 g rn-’ and 724 g mm-“, respectively (LSD,,,,, = 69 grn-‘). Similarly, plant dry weights with U, U + GM and U + FYM treatments were 786 g rnp2, 760 g mm-’ and 855 g m -?, respectively (LSD,, 05 =61 gm-‘).

4. Conclusions Irrigation of rice on coarse-textured soils can be reduced by repeated puddling. Integrated (organic and inorganic) nitrogen management neither reduced irrigation needs of rice nor improved its yield. Intensive puddling, however, reduced growth and yield of succeeding wheat by increasing the bulk density of a subsurface compacted layer. Incorporation of green manure as the urea substitute in the rice crop decreased the bulk density of the subsurface compacted layer. Farmyard manure as substitute for urea in rice ameliorated the residual adverse effects of high puddling on wheat yield owing to factors other than compaction or N nutrition. Incorporation of organic amendments during a rice crop would benefit crop yields in a rice-wheat cropping system on a sustained basis.

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et (11. /Soil

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139

Acknowledgements The authors are grateful to Dr. Pradeep K. Sharma, Soil Physicist, H.P.K.V.V. India, for valuable suggestions and comments.

Palampur,

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