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Resolving the Edaphic Conflict in Rice-wheat system

Muhammad Farooq1 and Shahzad M.A. Basra2

1Department of Agronomy, University of Agriculture, Faisalabad-38040, Pakistan, e-mail: farooqcp@gmail.com
2
Department of Crop Physiology, University of Agriculture, Faisalabad-38040, Pakistan e-mail: shahzadcp@gmail.com

Abstract

Traditionally rice is transplanted in puddled flooded field and wheat is sown after pulverizing the soil. This reflects to a tillage conflict in traditional soil management for rice and its consequent deleterious effects for the succeeding wheat crop in the rice-wheat system. A study consisting of two experiments (both being exactly the same in design and implementation) was conducted to find out the best tillage method for rice establishment in rice-wheat rotation system. Rice cultivar Super-basmati was grown in summer and wheat cultivar Auqab-2000 in autumn after rice. Rice was grown in four treatments viz. transplanting in continuously flooded conditions (TRF), transplanting with intermittent flooding and drying (TRI), direct seeded using dry seeds (DSR) and direct seeded using primed seeds (DSP). Traditional puddling tillage was followed in TRF and TRI, while for DSR and DSP, dry tillage was followed. For the sake of convenience, the abbreviations of the rice treatments were used to indicate the same plots during the wheat crop. The greatest tiller number, fertile tillers, kernel yield, straw yield, and harvest index were observed for rice in TRI. TRI also gave a yield advantage of 5% over TRF. The performance of DSR was at the bottom in case of rice; however, it was better than DSP treatment. In wheat, crop following direct seeded rice was better than transplanting. This study suggests that intermittent irrigation in the traditional puddling tillage system and direct seeding of the primed rice seeds in dry tillage system are promising alternatives.

Key Words

Rice-wheat system, stand establishment, seed priming, tillage, yield, direct seeding

Introduction

Rice-wheat systems occupy 24 million hectares of cultivated land in Asia. Of this, 13.5 million hectares are in South Asia extending from the Indo-Gangetic Plains to the Himalayan foothills. Traditionally rice is transplanted after puddling and wheat is sown after pulverizing the soil. This reflects to an edaphic conflict in conventional tillage system for rice and its consequent deleterious effects on the soil environment for the succeeding wheat and other upland crops. As a management scheme for rice, soil puddling in advance of transplanting (i.e. paddy rice) is typically considered advantageous for achieving resource-use efficiency, yield stability, and high productivity, primarily by retaining water and nutrient resources while reducing weed pressure (Surendra et al. 2001). Evidence from several rice-based crop rotations, however, suggests a putative conflict between soil conditions created by puddling and performance of subsequent non-rice crops (Sharma and DeDatta 1985).

Late planting is the main limitation to wheat productivity in many areas of South Asia (Ahmed and Meisner 1996). At best, post-rice deep tillage is a partial solution for physical constraints to wheat performance because it does not alleviate poor tilth in the surface horizon. For most regions that utilize the rice–wheat cropping system, there is general consensus that wheat yields will increase if puddling operations for rice establishment are reduced or eliminated (Timsina and Connor 2001). Thus, direct seeded rice provides an option to resolve the edaphic conflict between rice and wheat crops in rice-wheat system. Direct seeding of rice facilitates timely establishment of rice and succeeding winter crops. Unlike puddled fields, direct seeded field soils do not crack and thus helps save irrigation water.

The present study was therefore conducted to compare the conventional puddling and dry tillage systems in the rice-write systems and to investigate the benefits associated with each system.

Methods

Two rice–wheat experiments were conducted in a farmer’s farm in the rice growing belt (31.45o N, 73.26o E, and 193 m) in 2005-06 and 2006-07. Experimental soil was sandy clay loam with pH 8.1, 0.30 mS cm-1 total exchangeable salts and 0.75% organic matter. The climate of the area is semi-arid with an average annual temperature of 27C and average annual rainfall of 1000 mm.

The two experiments were exactly the same in design and implementation in both years. They were laid out in a randomized block design with three replicates and plot sizes of 10 m x 7 m. Rice was grown in summer and wheat in autumn after harvesting rice. Rice cultivar Super-basmati was grown in four treatments: transplanted continuously flooded (TRF), transplanted with intermittent flooding and drying (TRI), direct seeded using dry seeds (DSR) and direct seeded using primed seeds (DSP). Traditional puddling tillage system was followed in TRF and TRI, while for DSR and DSP, dry tillage system was followed.

In the traditional puddling tillage system, four cultivations with a tractor-drawn cultivator followed by two plankings were given to achieve the desirable soil structure. Field was flooded with water and puddle conditions were created with the help of a tractor drawn cultivator in standing water. The puddle field was left for a day or so to settle soil particles. Three weeks old seedlings were transplanted in 20 cm apart hills.

In dry tillage system, soil was dry plowed and harrowed before sowing and sowing was done in moist seed bed (at field capacity). Seeds (dry and primed) were drilled in rows 20 cm apart at a rate of 60 kg ha-1. For priming, seeds were soaked in CaCl2 solution with osmotic potential of –1.25 MPa for 24 h and were then re-dried to their original weight.

In transplanted plots, irrigation water at the time of transplanting was maintained at 3-4 cm. In TRF, one week after transplanting a constant water depth of 5-6 cm was maintained to keep the field continuously flooded. While in TRI, irrigation was applied about every other day to keep the soil moist. In direct seeded treatments, irrigation water was applied at one week interval. In all the treatment, irrigation was withheld when the signs of physiological maturity appeared. The crop was harvested when panicles were fully ripened at an approximate moisture of 23%, and each plot was threshed separately.

After harvest of the rice crop, wheat variety Auqab-2000 was sown. For convenience sake, we use the abbreviations of the rice treatments to indicate the same plots during the wheat crop. The crop was harvested when spikes were fully ripened at approximate moisture of 20%, and each plot was threshed separately.

Crop was harvested when fully ripened to determine grain and straw yield, and harvest index. At harvest, data on plant height, tiller numbers, number of branches and kernels per panicle and 1000 kernel weight was taken following the standard procedures

Results

Different tillage systems significantly affected tiller number, fertile tillers, kernel and straw yield, and harvest index; however, there was no affect of tillage systems on plant height, panicle branches, kernel numbers and 1000-kernel weight (Table 1). The greatest tiller number, fertile tillers, kernel and straw yield, and harvest index were observed in transplanting with intermittent flooding and drying (TRI). The tiller number, fertile tillers, straw yield and harvest index in transplanting in continuously flooded soil (TRF) were similar to that of TRI (Table 1). While the least tiller number, fertile tillers, kernel and straw yield, and harvest index were observed in direct seeding using dry seeds (DSR).

Table 1. Effect of Tillage Systems and Rice seedling establishment methods on the agronomic traits and yield components of rice in rice-wheat system

Treatments

Plant height (cm)

Tillers
(m-2)

Fertile tillers
(m-2)

Branches/ panicle

No. of kernels/ panicle

1000 kernel weight (g)

Straw yield
(t ha-1)

Kernel yield
(t ha-1)

HI (%)

DSR

83.67

673 c

566 c

19.11

87.66

17.66

8.70 c

3.12 d

26.39 c

DSP

84.33

729 b

607 b

19.08

88.00

17.33

9.42 b

3.56 c

27.42 b

TRI

86.00

779 a

645 a

19.07

90.00

18.00

10.17 a

4.28 a

29.61 a

TRF

85.00

760 a

640 a

19.00

87.33

17.00

9.95 a

4.07 b

29.02 a

Means sharing the same letters in a column do not differ significantly at p=0.05
DSR = Direct seeding using dry seeds, DSP = Direct seeding using primed seeds, TRI = Transplanting with intermittent flooding and drying, TRF = Transplanting in continuously flooded soil

The plant height, spikelets numbers, number of grains per spike and 1000-grain number were not affected by different rice tillage system (Table 2). However, tillers numbers, straw and grain yield and harvest index were affected significantly. The greatest tiller numbers, fertile tillers and straw yield were observed in DSR treatment, which was similar to DSP treatments. However, the greatest grain yield and harvest index were observed in DSP treatment that was similar to DSR treatment (Table 2). Although, number of tillers, fertile tillers, straw yield and harvest index were similar in both transplanting treatments (TRI and TRF), the grain yield was higher in TRI treatment.

Table 2. Effect of Rice seedling establishment methods on the agronomic traits and yield components of wheat in rice-wheat system

Treatments

Plant height (cm)

Tillers
(m-2)

Fertile tillers
(m-2)

Number of spikelets per spike

No. of grains/ spike

1000 grain weight (g)

Straw yield
(t ha-1)

Grain yield
(t ha-1)

HI (%)

DRS

92.11

588 a

443 a

15

49.33

33.67

9.54 a

4.43 a

31.71 a

DRP

91.66

585 a

441 a

16

47.00

32.33

9.47 a

4.46 a

32.01 a

TRI

92.33

528 b

425 b

17

47.00

34.00

9.27 b

3.98 b

30.03 b

TRF

93.00

518 b

420 b

15

48.33

33.00

9.15 b

3.84 c

29.56 b

Means sharing the same letters in a column do not differ significantly at p=0.05
DSR = Direct seeding using dry seeds, DSP = Direct seeding using primed seeds, TRI = Transplanting with intermittent flooding and drying, TRF = Transplanting in continuously flooded soil

Discussion

There exists a conflict between the conventional rice tillage system (where transplanting is done in continuously flooded conditions) and subsequent wheat crop. Although conventional system has yield advantage for rice (Table 1) but the yield of subsequent crop is reduced (Table 2). Transplanting with intermittent irrigation to avoid the continuous flooding showed higher grain yield than traditional transplanting in continuously flooding (Table 1), which may be attributed to aerobic soil conditions during the aerobic period of this technique (McHugh et al. 2003), which promoted the root growth and subsequently the nutrient and water uptake, and ultimately enhanced the rice growth and development. The number of tillers and fertile tillers were lower in wheat crop following the transplanting treatments, although the problem was less severs with intermittent irrigation (Table 2). This might be the result of poor germination and subsequent stand establishment due to inadequate seed–soil contact in cloddy post-rice soil (Ringrose Voase et al. 2000). Intermittent irrigation in the transplanting system and direct seeding of the primed rice seeds are the promising alternatives for improving the performance and sustainability of rice-wheat system.

References

Ahmed SM and Meisner C (1996) Wheat research and development in Bangladesh. Bangladesh–Australia Wheat Improvement Project, CIMMYT-Bangladesh, Dhaka, 201 pp.

McHugh OV, Steenhuis TS, Barison J, Fernandes ECM and Uphoff NT (2003) Farmer implementation of alternate wet-dry and nonflooded irrigation practices in the System of Rice Intensification (SRI). In: Bouman BAM, Hengsdijk H, Hardy B, Bindraban PS, Tuong TP and Ladha JK. Water-wise rice production Proceedings of a thematic workshop on water-wise rice production, 8-11 April 2002 at IRRI headquarters in Los Baos, Philippines.

Ringrose Voase AJ, Kirby JM, Djoyowasito G, Sanidad WB, Serrano C, Lando TM (2000) Changes to the physical properties of soils puddled for rice during drying. Soil and Tillage Research 56, 83–104.

Surendra S, Sharma SN and Prasad R (2001) The effect of seeding and tillage methods on productivity of rice–wheat cropping system. Soil and Tillage Research 61, 125–131.

Timsina J, Connor DJ (2001) Productivity and management of rice–wheat cropping systems issues and challenges. Field Crop Research 69, 93–132.

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