Effect of water management on dry seeded and puddled transplanted rice. Part 1: Crop performance

Field Crops Research 120 (2011) 112–122

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Effect of water management on dry seeded and puddled transplanted rice. Part 1: Crop performance Sudhir-Yadav a,∗ , Gurjeet Gill a , E. Humphreys b , S.S. Kukal c , U.S. Walia c a b c

The University of Adelaide, Adelaide, Australia International Rice Research Institute, Los Ba˜ nos, Philippines Punjab Agricultural University, Ludhiana, India

a r t i c l e

i n f o

Article history: Received 13 May 2010 Received in revised form 12 September 2010 Accepted 13 September 2010 Keywords: Establishment method Irrigation schedule Soil water tension Yield attributes Indo-Gangetic Plains

a b s t r a c t An alarming rate of ground water depletion and increasing labour scarcity are major threats to future rice production in north west India. Management strategies that reduce the irrigation amount and labour requirement while maintaining or increasing yield are urgently needed. Dry seeded rice (DSR) has been proposed as one means of achieving these objectives, but little is known about optimal water management for DSR. Therefore a field study was conducted on a clay loam soil in Punjab, India, during 2008 and 2009, to investigate the effects of irrigation management on the performance of puddled transplanted rice (PTR) and dry seeded rice. Irrigation scheduling treatments were based on soil water tension (SWT) ranging from ponding/saturation (daily irrigation) to alternate wetting and drying (AWD) with irrigation thresholds of 20, 40 and 70 kPa at 18–20 cm soil depth. Rainfall was above average and well distributed in 2008 (822 mm), and average and less well distributed in 2009 (663 mm). With daily irrigation, crop duration of PTR and DSR was the same. Shifting from daily irrigation to AWD delayed crop maturity by 8–17 d, and DSR was more affected than PTR, and more so in the drier year. Crop performance in terms of tiller density, leaf area index and growth rate was better in DSR than PTR with daily and 20 kPa irrigation scheduling. However, crop performance was poorer in DSR than PTR at higher (40 and 70 kPa) irrigation thresholds, more so in the drier year when DSR showed signs of severe iron deficiency which was not overcome with iron sprays. Yield components were similar in both establishment methods when irrigation was scheduled daily or at 20 kPa, but panicle density and the number of filled grains per panicle were significantly lower at 40 and 70 kPa in DSR than PTR. Each year, yield of DSR and PTR were similar when irrigation was scheduled daily or at 20 kPa. Yields of both PTR and DSR declined under higher water deficit stress (40 and 70 kPa irrigation thresholds), but more so in DSR, and more so in the drier year. There was a very large and significant decline in irrigation water input with irrigation at 20 kPa compared to daily irrigation in both establishment methods, but only a very small decline in irrigation amount when the threshold was increased from 20 to 40 and 70 kPa. Irrigation water use in DSR-AWD treatments was significantly lower than in respective PTR treatments (e.g. by 33–53% when irrigation was scheduled at 20 kPa). The results suggest the feasibility of reducing irrigation amount while maintaining yield by replacing PTR with DSR with AWD, provided that soil tension is kept lower than 20 kPa at 20 cm depth, but that this threshold needs to be tested over a wider range of seasonal and site conditions and varieties. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Rice (Oryza sativa), the staple food of half of the population of the world, is an important target for water use reduction because of its greater input water requirement than other crops. This is espe-

∗ Corresponding author at: School of Agriculture, Food and Wine, The University of Adelaide, Waite Campus, PMB 1, Glen Osmond, South Australia 5064, Australia. Tel.: +61 8 8303 7744; fax: +61 8 83037109. E-mail address: [email protected] ( Sudhir-Yadav). 0378-4290/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2010.09.002

cially the case in the north west Indo-Gangetic Plains (IGP) of India, where the production of rice and wheat is critical for food security of India. Here, overuse of ground water is a major threat to the sustainability of the traditional system of puddled transplanted rice (PTR) production (Humphreys et al., 2010). For example, Jeevandas et al. (2008) estimated a groundwater depletion rate of 77 cm year−1 in the Amritsar district of Punjab (India). Such an alarming rate of ground water decline is forcing researchers and farmers to consider approaches for increasing the water productivity of rice. The conventional puddled, hand-transplanted and flooded method of rice production not only uses a lot of water, it is also cumbersome and

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Table 1 Soil properties at the experimental site. Depth (cm)

0–10 10–20 20–30 30–45 45–60 60–90 90–120 120–150

Texture Sand %

Silt %

Clay %

42 46 48 46 46 22 18 12

20 16 16 14 14 38 40 42

38 38 36 40 40 40 42 46

laborious. In Punjab (India), where agriculture is highly dependent upon migrant labour, labour scarcity for rice transplanting is also now a major concern for the viability of PTR. Unreliable electricity supply to the farming sector due to high demand across different sectors is also adversely affecting the availability of water for puddled transplanted rice. Labour and water (electricity) shortage can lead to delayed transplanting, which can reduce rice yield and delay sowing of wheat, reducing wheat yield. Studies in the north west IGP have shown that rice can be successfully dry seeded into non-puddled soils, with or without prior cultivation (Hobbs et al., 2002; Qureshi et al., 2004). Dry seeded rice (DSR) provides an opportunity for earlier crop establishment to make better use of early season rainfall and to increase crop intensification in some rice based systems (Tuong et al., 2000). Dry seeding of rice in Australia, with or without cultivation, is extremely successful (Beecher et al., 2006). Dry seeding of rice has been shown to be more water efficient in Pakistan (Mann et al., 2004), with additional benefits from being labour- and cost-effective (Pandey and Velasco, 1999). Moreover, DSR is conducive to mechanization (Khade et al., 1993) which brings additional benefits to the cropping system. Studies in north west India (Singh et al., 2005; Bhushan et al., 2007; Choudhury et al., 2007) and Pakistan (Jehangir et al., 2005) have shown that DSR consumes less irrigation water than puddled transplanted rice. These findings are consistent with comparisons of PTR and direct-seeded rice (both wet and dry seeded) in the Musa Irrigation Scheme in Malaysia (Cabangon et al., 2002). Malik and Yadav (2008) suggested that DSR can give similar yield to that of puddled transplanted rice, provided effective weed management is achieved. However, in several studies in north west India, yield of DSR was lower than of PTR (Gupta et al., 2003; Qureshi et al., 2004; Malik and Yadav, 2008). The cause of the lower yield is generally unknown, but water deficit stress is one possible factor, as rice yield generally declines as the soil dries below saturation, with 10 kPa suggested as the safe threshold (Bouman and Tuong, 2001). Where water is readily available, and at low cost, farmers are unlikely to adopt water saving technologies unless these technologies give similar or higher land productivity. Therefore, a study was undertaken to analyse and compare crop performance, components of the water balance, and water productivity of dry seeded and puddled transplanted rice, for a range of irrigation schedules. This paper (part 1) presents the findings on crop development, growth, yield and irrigation amount, and provides insights into optimum irrigation scheduling for maximum yield. A detailed analysis of the components of the water balance and various measures of crop water productivity is presented in Part 2 (Sudhir-Yadav et al., 2011). 2. Materials and methods 2.1. Experimental site The study was carried out on the research farm of Punjab Agricultural University (PAU), Ludhiana, India (30◦ 54 N, 75◦ 98 E, 247 m

Texture class

Bulk density (Mg m−3 )

pH (1:2) in water

Clay loam Clay loam Clay loam Clay Clay Silty clay Silty clay Silty clay

1.59 1.70 1.73 1.53 1.55 1.55 1.56 1.67

8.0 8.3 8.2 8.2 8.2 8.2 8.2 8.3

ASL) during 2008 and 2009. The climate is sub-tropical with a hot summer, wet monsoon season (late June to mid-September) and a cool dry winter. Average annual rainfall is 734 mm, 85% of which falls during the monsoon. The soil is a mixed hyperthermic; Typic Ustochrepts with a clay loam topsoil (0–10 cm) with 0.5% organic carbon, slightly alkaline (pH 8.0), and medium amounts of alkaline KMnO4 -extractable N (139 ␮g g−1 ), 0.5 N NaHCO3 -extractable P (6.3 ␮g g−1 ) and NH4 OAc-extractable K (95 ␮g g−1 ). The subsoil is clay loam to 30 cm, overlying clay and silty clay. Selected soil properties at the time of sowing the first crop are shown in Table 1. There is a hard pan around 15–25 cm depth with a bulk density of 1.73 Mg m−3 . The depth to the ground water at the site was around 24 m and the quality was good for all crops (Table 2). The site was under a soybean–wheat cropping system for 5 years prior to establishment of the experiment. 2.2. Experimental design The experiment was laid out in 4 replicates in a split plot design with 2 establishment methods (dry seeding and puddled transplanting) in main plots and 4 irrigation schedules viz. (i) daily, and intermittent (AWD) irrigation when the soil water tension (SWT) at 20 cm depth increased to (ii) 20, (iii) 40 and (iv) 70 kPa in subplots. The daily irrigated treatments were topped up to 50 mm standing water depth. The amount of irrigation water applied to all AWD treatments was 50 mm at each irrigation. Sub-plot size was 9 m × 7 m. 2.3. Crop management The site was cultivated and laser levelled prior to establishment of the experiment. Prior to the first rice crop, there were 2 discings followed by planking for DSR or puddling for PTR. Prior to the second rice crop, the field was cultivated manually. In DSR plots, a pre-sowing irrigation was applied each year, and the crop was sown when the topsoil was at field capacity. Puddling for PTR was done using a power tiller (VST Shakti 130-DI) after 2 h of flooding the plots. After puddling, the crop was transplanted on the same day. The DSR was sown on 9th June in both years with the medium duration (144 d) variety ‘PAU-201 , by drilling the seed (40 kg ha−1 ) with a hand plough at a row spacing of 20 cm. On the same day, the seedbed for the transplanted treatments was sown. The PTR was transplanted on 5th and 6th July in 2008 and 2009, respectively, in rows 20 cm apart and plant-to-plant spacing within the row of 15 cm. All treatments received a basal fertiliser application (40 kg N ha−1 as urea, 13 kg P ha−1 as diammonium phosphate, 25 kg K ha−1 as muriate of potash and 15 kg Zn ha−1 as zinc sulphate) broadcast prior to sowing (DSR) or after puddling (PTR). A further 80 kg N ha−1 as urea was broadcast in 2 splits, 21 and 42 d after sowing/transplanting (DAS/DAT). Weeds in DSR were controlled by applying a pre-emergence herbicide (pendimethalin @ 75 g ha−1 ) 1 DAS, and a post-emergence herbicide (butachlor @

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Table 2 Irrigation water quality at the experimental site. CO3 2− (meq/l)

HCO3 - (meq/l)

Cl− (meq/l)

Ca2+ + Mg2+ (meq/l)

Residual NaHCO3

EC (ds m−1 )

0.0

3.8

0.8

3.8

0.0

0.51

150 g ha−1 ) 21 DAS. Weeds that escaped these treatments were removed manually at 45 DAS. In PTR, weeds were controlled by a post-emergence herbicide (butachlor @ 150 g ha−1 ) 15 DAT. Chlorpyriphos @ 50 g ha−1 , monocrotophos @ 50.4 g ha−1 and propiconazole @ 62.5 g ha−1 were used to control insects and diseases as recommended by PAU. In 2008, all DSR treatments were sprayed once with 1% ferrous sulphate solution (250 l ha−1 ) at 45 DAS. In 2009, the DSR-daily and 20 kPa treatments were sprayed twice at weekly intervals starting at 30 DAS. However, the DSR-40 and 70 kPa treatments, which exhibited more severe symptoms of iron deficiency, were sprayed thrice at weekly intervals starting at 30 DAS, and another four times at 3-d intervals starting at 67 DAS. For the first 42 DAS, the DSR was irrigated to keep soil water tension below 10–15 kPa at 10 cm soil depth to avoid water deficit stress during crop establishment. Thereafter, the irrigation treatments commenced in both PTR and DSR. The AWD irrigation treatments were scheduled on the basis of soil water tension measured using tube tensiometers with the ceramic cup at a depth of 18–20 cm. All PTR treatments were continuously flooded for the first 15 DAT prior to commencement of the irrigation scheduling treatments. The crop was harvested at 15–18% grain moisture content in all treatments each year. The land was fallowed between the two rice crops.

was determined. The number of filled florets (grains) and unfilled florets per panicle were determined in 10 randomly selected panicles from each plot at harvest. Floret fertility was calculated as the percentage of filled grain to the total number of florets per panicle. Average grain weight was determined from the weight of 1000 grains from the threshed grain sample for each plot and expressed at 14% moisture content. 2.5. Weather data Daily maximum and minimum temperature, sunshine hours and pan evaporation were measured at the PAU meteorological station, about 1.5 km from the experimental site. Rainfall was measured using an automatic rain gauge at the experimental site. 2.6. Statistical analysis All data were analysed by analysis of variance (ANOVA) using GenStat V.10. The comparison of treatment means was made by the least significant difference (LSD) at 5% level of probability (p = 0.05). 3. Results 3.1. Weather

2.4. Observations 2.4.1. Irrigation The plots were irrigated one at a time with groundwater via a piped irrigation system with a separate outlet to each plot. The volume of irrigation (I) water applied to each plot was measured with a Woltman® helical turbine meter and the depth of application was expressed in millimetres after dividing the volume by the area of the plot. The total amount of irrigation water was calculated from the sum of all irrigations, including pre-tillage and pre-sowing/transplanting irrigations. 2.4.2. Crop growth, yield and yield components Tiller density (no.m−2 ) was determined every fortnight by counting the number of tillers in a 1 m row (DSR) or 6 hills (equivalent to 0.9 m row length) within a row (PTR) at two fixed places in each plot. A Delta-T Sunscan® probe (SS1) was used for fortnightly in-field measurement of leaf area index (LAI), commencing 45 DAS. Measurements were made across five rows, with the probe parallel to the rows, at one fixed location in each plot. Plant samples were collected fortnightly from 0.5 m row length (DSR) or 3 hills (0.45 m row length) within a row (PTR) at two different places to measure dry matter accumulation after drying the plant samples at 60 ◦ C for 72 h. Grain yield was determined from an area of 25 m2 in the centre of each plot, which was harvested and threshed manually. Grain moisture content was measured for each plot using a moisture meter and yield was expressed as t ha−1 at 14% grain moisture. The fresh weight of straw was calculated after deducting grain yield from the bundle weight of each plot. Straw moisture content was measured by taking a small sample and oven drying at 60 ◦ C for 72 h and straw yield was expressed as t ha−1 at 0% moisture content. Harvest index was derived as the ratio of dry grain yield to total biomass at harvest. Panicle density was determined in 0.9 and 1 m row lengths in PTR and DSR, respectively, at the same locations where tiller density

The mean monthly maximum temperature was 4.6 and 5.6 ◦ C lower in June 2008 than the long-term average and the 2009 June mean, respectively (Fig. 1a), as a result of lower solar radiation in June 2008 (Fig. 1b). Total rainfall in June 2008 was much higher than long-term average and June 2009 rainfall (Fig. 1d). This all resulted in 51% less pan evaporation in 2008 than 2009 in June (Fig. 1b). In later months, mean monthly temperature and pan evaporation were similar in 2008 and 2009, and close to the long-term average, except in August 2008 when there was 19% less evaporation than in 2009, and which was also associated with much higher rainfall. The mean monthly sunshine hours were 42% and 19% less in June and July of 2008 than the long-term average. The monthly total sunshine hours in 2009 were similar to the long-term average except in August when it was 14% lower. The sunshine hours were 20% less during October (grain filling period) of 2008 than the long-term average and the 2009 amount. Total rainfall was 24% higher in 2008 (822 mm) than in 2009 (663 mm) (Fig. 1c); most of the 2008 rainfall was received in June and August, whereas much of the 2009 rain was received in the second half of July (Fig. 1d). 3.2. Irrigation As a result of the frequent rain for several weeks after sowing in 2008, the first irrigation of the 20, 40 and 70 kPa treatments did not start until 77, 80 and 82 DAS, respectively (i.e. around the time of maximum tillering). In 2009 the 20, 40 and 70 kPa treatments received their first irrigations 59, 62 and 65 DAS (active tillering stage). Each year, there was a significant interaction between establishment method and irrigation treatment on irrigation amount. In both years, the irrigation amount in all AWD treatments was much lower (by 50–80%) than in the daily irrigated treatments, and the amount of irrigation water applied to DSR with AWD was significantly lower than the amount applied to respective PTR treatments (Fig. 2a,b). Within establishment method, there were only relatively

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Fig. 1. Monthly mean maximum and minimum temperature (a), monthly mean sunshine hours (lines) and total pan evaporation (bars) (b), cumulative rainfall (c), and monthly total rainfall (d) at Ludhiana in 2008 and 2009, compared with long-term averages (1995–2009).

small differences in the amount of irrigation water applied to the 3 AWD treatments each year. In 2008, the amount of irrigation water applied was similar in the daily irrigated PTR and DSR treatments. However, in 2009, the irrigation input in daily-irrigated DSR was significantly higher (more than double) than in PTR. 3.3. Crop growth 3.3.1. Crop establishment, development and visual observations The plant stand and crop growth in all plots was good each year. For example, the coefficient of variation of biomass produc-

tion within treatments at each sampling date ranged from 5% to 19%, and was usually less than 15%. Plant density of DSR at 12 DAS was 165 plants m−2 in 2008 and 110 plants m−2 in 2009, compared with 33 seedlings m−2 in PTR. The seed to seed duration of the daily irrigated treatments of both DSR and PTR was similar each year (134-135 DAS). In 2008, maturity (15–18% grain moisture content) of all AWD treatments was delayed by 9–12 d compared to daily irrigation. In 2009, maturity of PTR-20 and 40 kPa was delayed by 8 d compared with the daily irrigated treatments, and all other treatments (PTR-70 kPa, DSR-20, 40 and 70 kPa) were delayed by 16–17 d.

Fig. 2. Irrigation water input (mm) in relation to different establishment methods and irrigation schedules in 2008 (a) and 2009 (b). Vertical bars are LSD (p < 0.05) for comparing all treatment combinations.

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Fig. 3. Effect of establishment method (a) and irrigation schedule (b) on periodic tillering pattern of rice in 2008. Vertical bars indicate LSD0.05 for comparing treatments within each date after observation. Table 3 Yield attributes of rice under different establishment methods and irrigation schedules. Establishment method (EM)

Irrigation scheduling (IS)

Yield attributes of rice Panicle density m−2

Florets panicle−1

Floret fertility %

Average grain weight (mg)

2008

2009

2008

2009

2008

2009

2008

2009

PTR

Daily 20 kPa 40 kPa 70 kPa Mean

392 351 303 290 334

387 357 319 291 339

169 180 167 176 173

162 156 138 128 147

67.6 71.6 66.3 62.6 67.0

91.1 88.1 85.7 84.5 87.3

26.5 25.2 23.5 22.7 24.5

24.4 24.2 23.4 22.5 23.6

DSR

Daily 20 kPa 40 kPa 70 kPa Mean

378 338 257 215 297

392 360 227 180 290

168 161 163 157 161

171 149 116 110 137

68.0 72.2 64.9 62.3 66.9

90.5 88.5 82.0 80.3 85.3

26.5 26.3 22.7 22.0 24.4

24.9 24.3 21.3 20.9 22.8

Mean of PTR and DSR

Daily 20 kPa 40 kPa 70 kPa

385 345 280 253

390 359 273 236

168 171 165 166

166 152 126 119

67.8 71.9 65.6 62.5

90.8 88.3 83.8 82.4

26.5 25.7 23.1 22.3

24.6 24.2 22.3 21.7

NS 21.2 42.7

20.7 12.7 18.9

6.2 NS NS

2.8 9.4 11.6

NS 4.9 NS

NS 3.4 NS

NS 2.5 NS

NS 1.2 NS

LSD0.05 EM IS EM × IS

Table 4 Effect of establishment method and irrigation schedule on yield and harvest index of rice. Establishment method (EM)

Irrigation scheduling (IS)

Rice yield (t ha−1 )

Harvest index

Grain yield

Straw yield

2008

2009

2008

2009

2008

2009

PTR

Daily 20 kPa 40 kPa 70 kPa Mean

7.12 7.38 6.32 5.40 6.56

8.18 7.94 6.53 5.69 7.09

9.73 8.40 8.20 7.32 8.41

9.35 9.03 7.91 6.86 8.29

0.39 0.43 0.40 0.39 0.40

0.43 0.43 0.41 0.42 0.42

DSR

Daily 20 kPa 40 kPa 70 kPa Mean

6.56 7.01 4.42 3.38 5.34

8.27 7.82 4.09 3.04 5.80

11.31 8.03 8.27 7.72 8.83

11.21 9.06 7.07 6.01 8.34

0.33 0.43 0.31 0.37 0.34

0.39 0.43 0.33 0.30 0.36

Mean of PTR and DSR

Daily 20 kPa 40 kPa 70 kPa

6.84 7.20 5.37 4.39

8.23 7.88 5.31 4.37

10.52 8.22 8.24 7.52

10.28 9.05 7.49 6.43

0.36 0.43 0.36 0.33

0.41 0.43 0.37 0.36

0.79 0.91 NS

NS 0.62 1.10

NS 0.87 NS

NS 0.44 0.56

0.037 0.048 NS

NS 0.026 0.053

LSD0.05 EM IS EM × IS

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Fig. 4. Effect of establishment method and irrigation schedule on tiller density at different growth stages in 2009. Vertical bars indicate LSD0.05 for comparing all treatment combinations.

None of the treatments had visual symptoms of nutrient deficiency in 2008, while in 2009, DSR-40 and 70 kPa showed severe iron deficiency symptoms (interveinal yellowing, stunted growth and seedling death) commencing around 30 DAS, and which persisted for most of the vegetative growth phase despite multiple iron sprays. Interveinal yellowing was also observed in DSR-20 kPa around 30 DAS which was overcome with 2 iron sprays. 3.3.2. Growth, yield components and yield—2008 In 2008, there was no significant interaction between establishment method and irrigation treatment on tiller density, total biomass (except at 120 DAS) or LAI at any stage. Tiller density and

LAI were significantly higher in DSR than PTR at all growth stages (except during the late grain filling stage, due to higher senescence and tiller mortality in DSR (45%) than PTR (27%)) (Figs. 3a and 5a). Biomass of DSR was also significantly higher than of PTR until anthesis (101 DAS), after which the growth rate of PTR exceeded that of DSR, so that at maturity total biomass was similar in DSR and PTR (Fig. 7a). Maximum tiller density (700 m−2 in DSR and 512 m−2 in PTR) occurred at around 77 DAS, at which time the AWD irrigation treatments commenced. After this, there was a consistent trend for lower tiller density, LAI and biomass with less frequent irrigation, mainly due to greater tiller mortality (Figs. 3b, 5b, 7b). From

118

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6

PTR

(a)

6

Daily 20kPa

DSR

5

Tillers m-2

5

Tillers m-2

(b)

4 3

70kPa

4 3

2

2

1

1

0

40kPa

0 30

45

60

75

90

105

120

30

45

60

75

90

105

120

Days after sowing

Days after sowing

Fig. 5. Effect of establishment method (a) and irrigation schedule (b) on periodic leaf area index of rice in 2008. Vertical bars indicate LSD0.05 for comparing treatments within each date after observation.

87 to 119 DAS or maturity, tiller density and biomass with daily irrigation were significantly higher than with irrigation at 40 and 70 kPa. During this period, biomass with irrigation at 20 kPa was also significantly higher than with irrigation at 40 and 70 kPa. There was a significant interaction between establishment method and irrigation schedule on panicle density. Panicle density declined with less frequent irrigation, but the decline was greater in DSR than PTR, resulting in significantly lower panicle density in DSR than PTR in respective 40 and 70 kPa irrigation treatments (Table 3). Panicle density was almost significantly lower (p < 0.14) in DSR-20 kPa and PTR-20 kPa compared with daily irrigation. There

PTR

6

Daily irrigation

PTR DSR

5

5

4

4

3

3

2

2

1

1

0

0 30

45

60

75

90

105

120

30

45

60

Days after sowing

75

90

105

120

Days after sowing

PTR

6

PTR

6

40 kPa

70 kPa

DSR

DSR 5

5

4

4

LAI

LAI

20 kPa

DSR

LAI

LAI

6

was no interaction between establishment method and irrigation schedule on the number of florets per panicle or floret fertility. The number of florets per panicle was significantly lower (by 7%) in PTR than DSR, while floret fertility was slightly but significantly reduced with irrigation at 40 and 70 kPa. There was a consistent trend for grain and straw yield to decline as the irrigation threshold increased from 20 to 70 kPa, with a greater decline in DSR than PTR (Table 4). The interaction between establishment method and irrigation schedule was not significant at p < 0.05 (significant at p < 0.15 for grain yield, p < 0.14 for straw yield). The higher grain yields of DSR and PTR with daily and 20 kPa

3

3

2

2

1

1 0

0 30

45

60

75

90

Days after sowing

105

120

30

45

60

75

90

105

120

Days after sowing

Fig. 6. Effect of establishment method on periodic leaf area index of rice at different irrigation schedules in 2009. Vertical bars indicate LSD0.05 for the comparison of establishment method within DAS.

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20

(a)

PTR

16

Biomass accumulation (t ha-1)

Biomass accumulation (t ha-1)

18

DSR

14 12 10 8 6 4 2 0

(b)

119

Daily

18

20kPa

16

40kPa

14

70kPa

12 10 8 6 4 2 0

30

45

60

75

90

105

120

135

150

30

45

Days after sowing

60

75

90

105

120

135

150

Days after sowing

Fig. 7. Periodic biomass accumulation (t ha−1 ) as affected by establishment method and irrigation schedule in 2008. Vertical bars indicate LSD0.05 for comparing treatments within each date after observation.

irrigation than at 40 and 70 kPa were largely due to higher panicle density, and to a lesser degree to higher grain weight. Straw yield with daily irrigation was significantly higher than in all AWD treatments, with no significant differences between AWD treatments. Thus maximum harvest index (HI) occurred with irrigation at 20 kPa, and HI of PTR was significantly higher than of DSR. 3.3.3. Growth, yield components and yield—2009 In 2009, there was a significant interaction between establishment method and irrigation schedule on tiller density and biomass throughout the season (except for biomass at 87 DAS), and on LAI up to 75 DAS. At the early tillering stage, tiller density and LAI were significantly higher in DSR than PTR when irrigation was scheduled daily or at 20 kPa, but the difference declined with time, and by maturity there was no significant difference between the two establishment methods (Figs. 4, 6). Conversely, tiller density was initially similar in DSR and PTR scheduled at 40 and 70 kPa, but by 116 DAS, tiller density was significantly lower in DSR than PTR. As in 2008, maximum tiller density was significantly higher in DSR-daily (630 tillers m−2 ) than PTR-daily (around 560 tillers m−2 ). Total biomass in daily irrigated DSR was significantly higher than in daily irrigated PTR throughout the season, except at 87 DAS (Fig. 8). At 20 kPa, total biomass in DSR was significantly higher than in PTR until late tillering, however, between late tillering and late grain filling, the growth rate of PTR-20 kPa was significantly higher than of DSR-20 kPa, leading to similar biomass at maturity. At 40 and 70 kPa, growth rates in PTR and DSR were similar until after maximum tillering. However, from anthesis to late grain filling, the growth rate in PTR was significantly higher than in DSR, leading

to significantly higher biomass in PTR during grain filling and at maturity. There was a consistent trend for higher tiller density, LAI and biomass with more frequent irrigation, throughout the season, in both establishment methods (Figs. 4, 6, 8). Significant differences started to appear earlier, during the tillering stage, than in 2008. After anthesis, total biomass in daily irrigated DSR was significantly higher than in all other treatments, and total biomass in daily irrigated PTR was significantly higher in all other treatments except for PTR 20 kPa. Total biomass in DSR-40 and 70 kPa was always significantly lower than in the other DSR treatments after early tillering. The same trends occurred in PTR. As in 2008, there was a significant interaction between establishment method and irrigation schedule on panicle density, with a consistent trend for panicle density to decline with less frequent irrigation, and greater decline in DSR than PTR (Table 3). Panicle density was again similar in DSR and PTR within daily or 20 kPa irrigation scheduling, and was significantly lower in DSR than PTR in respective 40 and 70 kPa treatments. There was a significant interaction between establishment method and irrigation schedule on the number of florets per panicle, which was significantly higher in DSR-daily than in all other treatments except PTR-daily. The number of florets per panicle declined with decreasing irrigation frequency, but more so in DSR. DSR irrigated at 40 and 70 kPa produced significantly fewer florets per panicle than in PTR 20 and 40 kPa, respectively. There were again small but significant declines in floret fertility and grain weight with irrigation at 40 and 70 kPa. The interaction between establishment method and irrigation schedule on both grain and straw yield was significant. Grain yield

Biomass accumulation (t ha-1)

22 PTR-Daily PTR-20kPa PTR-40kPa PTR-70kPa DSR-daily DSR-20kPa DSR-40kPa DSR-70kPa

20 18 16 14 12 10 8 6 4 2 0 45

59

74

87

102

117

at harvest

Days after sowing Fig. 8. : Periodic biomass accumulation (t ha−1 ) in respect of interaction of establishment methods and irrigation schedules in 2009.

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of PTR and DSR with daily and 20 kPa irrigation was similar and significantly higher than yield of all other treatments. Grain yield was significantly higher in PTR irrigated at 40 and 70 kPa than in DSR-40 and 70 kPa, respectively. The higher yields of DSR and PTR with daily and 20 kPa irrigation were largely due to higher panicle density and more florets per panicle, and to a lesser degree to higher grain weight (Table 3). The lower yields of DSR than PTR at 40 and 70 kPa were mainly due to lower panicle density, and to smaller degrees to fewer florets per panicle and lower grain weight. Straw yield of daily irrigated DSR was significantly higher than in all other treatments, with a similar trend in 2008. Straw yield declined significantly as the irrigation threshold increased from 20 to 40 to 70 kPa in both DSR and PTR. Straw yield of DSR irrigated at 40 and 70 kPa was significantly lower than straw yield of corresponding PTR treatments. Harvest index was significantly reduced by increasing the irrigation threshold above 20 kPa, and was significantly higher in PTR-40 and 70 kPa than in respective DSR treatments. 4. Discussion 4.1. Irrigation water All PTR treatments received less irrigation in 2009 than 2008, despite lower rainfall and poorer rainfall distribution, due to lower seepage and runoff losses (Sudhir-Yadav et al., 2011). In contrast, all DSR treatments received more irrigation in 2009 than 2008, largely due to the dry start to the season (almost no rain, much higher ET for the first 20 d after sowing) and much higher deep drainage in the second year without puddling (Sudhir-Yadav et al., 2011). The large irrigation water saving in all AWD treatments compared to continuously flooded PTR was consistent with the findings of many other studies of PTR with AWD reviewed by Humphreys et al. (2010), which found 15–40% saving of water applied with AWD compared to continuous flooding. In contrast, reports of the effect of irrigation management on irrigation water use in DSR in the region are lacking. Within AWD treatments, the irrigation water input was significantly higher in PTR than DSR, mainly due to use of the recommended practice of continuous flooding for the first 15 d after transplanting, and in 2009 also partly due to the greater frequency of irrigation of PTR-20 kPa than DSR-20 kPa (Sudhir-Yadav et al., 2011). 4.2. Crop performance 4.2.1. Effect of seasonal weather conditions on crop performance The trends in treatment responses were similar each year, however, the trends and interactions between establishment method and irrigation scheduling were far more pronounced in 2009. The main reasons for greater treatment effects in 2009 than 2008 were the prolonged dry spell during the early tillering stage and more poorly distributed rainfall between the end of the dry spell and harvest in 2009, meaning that the soil was drier in 2009 for longer periods. For example, between the date of transplanting and panicle initiation, soil water tension exceeded 15 kPa on only 3 d in all PTR and DSR AWD treatments in 2008, compared with 7–8 d in 20 kPa treatments and 12–17 d in 40 and 70 kPa treatments in 2009. The other main difference in crop performance between the two seasons was the much higher grain yield of the daily irrigated treatment in 2009. This was entirely due to higher floret fertility in 2009 (91%, compared with 68% in 2008), while the number of florets per panicle and panicle density were similar each year. The higher floret fertility in 2009 more than compensated for the lower grain weight that year, which was probably due to the much

higher number of grains m−2 among which the photo-assimilate was shared. The lower floret fertility in 2008 was probably due to lower radiation during anthesis, when there was considerable rain. While tillering was greater in the daily irrigated treatments in 2008 (10% higher maximum tiller density), tiller mortality was higher, leading to similar panicle density (380–390 m−2 ) each year. The trend for higher tillering in DSR in 2008 than 2009 was probably a result of the higher plant density that year. The higher tiller mortality with DSR in 2008 is consistent with other observations of the effects of high plant density on tiller mortality (Dingkuhn et al., 1990; Oka and Lu, 1995; Hasanuzzaman et al., 2009).

4.2.2. Establishment and irrigation treatment effects on crop performance The growth of DSR in terms of the rates of biomass production, tillering and development of leaf area when water was never limiting (the daily irrigated treatments) was better than in PTR in both years. These differences were probably due to the 3–5 times higher plant density in DSR than PTR. Many researchers have concluded that plant density is an important contributor to tiller density and yield of rice (TeKrony and Egli, 1991; Matsuo and Hoshikawa, 1993). Miller et al. (1991) found increasing tiller density with increasing plant density from 122 to 458 plants m−2 . Fagade and De Datta (1971) found that leaf area index increased with increasing plant density of rice. The slower early growth of PTR could also have been due to transplanting shock. Ros et al. (2003) found that severe damage of roots during transplanting affected both early seedling vigour and the subsequent growth rate. After maximum tillering, the greater tiller mortality and reduced the crop growth rate in DSR may have been the result of higher intraspecific competition for light, water and nutrients due to the higher plant density, especially in the AWD treatments (Dingkuhn et al., 1990; Oka and Lu, 1995; Boonjung and Fukai, 1996; Hasanuzzaman et al., 2009). The average tiller mortality in 2008 was 45% in DSR, compared with only 28% in PTR. In 2009, tiller mortality was 19–21% in all irrigation schedules of PTR while it was 26% in DSR-daily and highest at 34% in DSR-70 kPa treatments (Fig. 5). In 2009, the rates of biomass, leaf area and tiller production in DSR showed much greater sensitivity to the higher water stress irrigation scheduling treatments (40 and 70 kPa) than PTR. The lower tiller density in these treatments of DSR was probably due to both water deficit stress and iron deficiency. Symptoms of severe iron deficiency first appeared during the early tillering stage, and persisted despite many iron sulphate applications. Agboola and Fube (1983) observed significantly lower tiller density under iron deficient conditions on a sandy loam soil of south west Nigeria. Many authors have reported severe iron deficiency symptoms in DSR on flats and raised beds with AWD (Bouman et al., 2002; Sharma et al., 2002; Yadvinder-Singh et al., 2009; Jat et al., 2009). Kreye et al. (2009) found that micro-nutrient deficiency was a major cause of yield failure in aerobic rice. The absence of visual symptoms of iron deficiency in DSR in 2008 was probably because of the frequent and substantial rainfall between sowing and maximum tillering in that season which kept the soil closer to saturation. For example, from 27 DAS to panicle initiation (PI), soil water tension in all AWD DSR treatments exceeded 10 kPa on only 2–3 d in 2008, compared with 8–20 d in 2009. Yield attributes were affected by water stress treatments beyond 20 kPa. The lower yield of DSR under greater water deficit (40 and 70 kPa) was largely due to: (1) reduced panicle density, which was mainly due to less tillering in 2009 and higher tiller mortality in 2008, and (2) fewer florets per panicle in 2009, consistent with the greater water deficit stress prior to PI in that year.

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However, there were also small reductions in floret fertility (2009) and average grain weight (both years) as water deficit increased. Reduction in fertility (%) could be related to abnormal pollen development whereas reduction in grain weight is most likely caused by insufficient availability of assimilates in rice grown under higher SWT (Hossain, 2001; Castillo et al., 2006; Venuprasad et al., 2007; Zubaer et al., 2007). In a Sahelain environment deVries et al. (2010) observed more spikelets m−2 and less sterility with flooding up to PI followed by AWD (irrigation after ∼2 d) up to harvest than AWD throughout the season or AWD up to PI followed by flooding. 4.2.3. DSR vs. PTR The similar duration of DSR and PTR with daily irrigation, and the longer duration of DSR with AWD, is in contrast to anecdotal claims that the duration of DSR is shorter than of PTR in the IGP. In both years of our experiment, maturity was delayed with AWD by 8–17 d. In 2009, when the AWD thresholds were reached earlier (during active tillering), the delay in DSR-20 and 40 kPa was 9 d longer than in PTR with these irrigation thresholds. In Osaka (Japan), Kato et al. (2009) also found longer duration of DSR irrigated at 60 kPa (at 20 cm soil depth) than daily irrigated PTR, by 8–29 d. Reports of grain yield of DSR relative to PTR also show variable results. In our experiments, the grain yield of DSR was similar to that of PTR with an irrigation threshold up to 20 kPa. Bhushan et al. (2007) and Saharawat et al. (2009) also reported similar yields of conventional PTR and zero or reduced till DSR on a range of soils from sandy loam to clay loam. Singh et al. (2005) reported that, in weed-free situations, yield of DSR is better than that of PTR. In contrast, Choudhury et al. (2007) observed 27% lower yield of DSR when irrigated at field capacity than in PTR in sandy loam and loam soils. In farmer participatory trials, Ladha et al. (2009) also reported lower grain yield in reduced or zero till DSR compared with PTR. The variable performance of DSR relative to PTR could be due to many factors including soil properties (which primarily affect nutrient and water availability to the plants), water management, weed management, and soil pathogens. Cereal cyst nematode infestation has been reported to be a problem in dry seeded rice on the flat and on beds on some soils in north west India (Sharma et al., 2002; Yadvinder-Singh et al., 2008, 2009). At present there is poor understanding of the variable performance of DSR, and while there are published guidelines for DSR (Gopal et al., 2010), there is a lack of detail on some aspects (e.g. irrigation scheduling), nor are the guidelines tailored to site specific conditions. 4.3. Optimum irrigation scheduling for DSR and PTR Our results show that the performance of both PTR and DSR is very sensitive to water management, and that DSR is more sensitive than PTR to drying of the soil. In two seasons with average or above average rainfall, but with contrasting distribution, yield of both PTR and DSR was maintained with an irrigation threshold of 20 kPa, while greatly reducing irrigation input. However, whether this would be the case in much drier seasons is unclear, and further field and modelling studies are needed to define the safe threshold for all likely weather conditions. Furthermore, the safe threshold may vary with growth stage. The present study shows that panicle density was significantly lower (or almost significantly lower) in both PTR and DSR each year with an irrigation threshold of 20 kPa compared with daily irrigation, and that there were significantly fewer florets per panicle in DSR 20 kPa compared with daily irrigated DSR in 2009. These results suggest that a lower threshold may be beneficial prior to PI. The effect of irrigation threshold on floret fertility and grain weight was small, and our results suggest that a threshold of 20 kPa may be adequate after flowering.

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5. Conclusion The similar yields of dry seeded rice (DSR) and puddled transplanted rice (PTR) irrigated daily or when soil water tension increased to 20 kPa clearly demonstrate the feasibility of DSR with frequent AWD in north west India. However, rainfall was average or above average each year, therefore the number of drying events in the AWD treatments was limited relative to the situation in drier years. The results hint that a threshold of 20 kPa prior to panicle initiation might be too high in drier years, and this needs further investigation. Dry seeded rice irrigated when soil water tension had increased to 20 kPa at a soil depth of 18–20 cm resulted in significant saving (33–53%) of irrigation water in comparison with PTR with the same irrigation scheduling, while maintaining yield. As the threshold for irrigation increased to 40 and 70 kPa, yield of both DSR and PTR declined, but the decline was greater in DSR. The relative decline in yield of DSR was greater in the second year, when severe iron deficiency symptoms persisted, despite several sprays of iron sulphate. These results suggest that there are factors in addition to iron deficiency leading to lower yields of DSR than PTR irrigated at higher soil water tensions. Further evaluation under a wider range of environmental conditions (e.g. soil texture, climate, watertable depth) and varieties, is needed to develop irrigation scheduling and other management guidelines for DSR, tailored to site conditions. This should include studies on the level of water deficit stress to which DSR can be safely exposed at different growth stages. Acknowledgment This work was supported by the Australian Centre for International Agricultural Research (ACIAR) and the John Allwright Fellowship fund. We thank Sandeep Singh for his hard work and commitment while providing technical assistance in the project. References Agboola, A.A., Fube, H.N., 1983. Effect of iron on yield and performance of upland rice (var OS6 ) in south west Nigeria. Nutr. Cycling Agrosystems 4, 119–126. Beecher, G., Dunn, B., Mathews, S., Thompson, J., Singh, R.P., Humphreys, L., Timsina, J., O’Keefe, K., Johnston, D., 2006. Permanent beds for sustainable cropping. IREC Farmers’ Newslett. No. 171. Bhushan, L., Ladha, J.K., Gupta, R.K., Singh, S., Tirol-Padre, A., Saharawat, Y.S., Gathala, M., Pathak, H., 2007. Saving of water and labor in a rice–wheat system with no-tillage and direct seeding technologies. Agron. J. 99, 1288–1296. Boonjung, H., Fukai, S., 1996. Effect of soil water deficit at different growth stages on rice growth and yield of upland conditions 2. Phenology, biomass production and yield. Field Crops Res. 48, 47–55. Bouman, B.A.M., Tuong, T.P., 2001. Field water management to save water and increase its productivity in irrigated lowland rice. Agric. Water Manage. 49, 11–30. Bouman, B.A.M., Hengsdijk, H., Hardy, B., Bindraban, P.S., Tuong, T.P., Ladha, J.K., 2002. Water-wise rice production. Proceedings of the International Workshop ˜ on Water-wise Rice Production, 8–11 April 2002, Los Banos, Philippines. International Rice Research Institute, 356 p. Cabangon, R.J., Tuong, T.P., Abdullah, N.B., 2002. Comparing water input and water productivity of transplanted and direct-seeded rice production systems. Agric. Water Manage. 57, 11–31. Castillo, E.G., Tuong, T.P., Singh, U., Inubushi, K., Padilla, J., 2006. Drought response of dry seeded rice to water stress timing and N-fertilizer rates and sources. Soil Sci. Plant Nutr. 52, 496–508. Choudhury, B.U., Bouman, B.A.M., Singh, A.K., 2007. Yield and water productivity of rice–wheat on raised beds—results from a field experiment at New Delhi, India. Field Crops Res. 100, 229–239. deVries, M.E., Rodenburg, J., Bado, B.V., Sow, A., Leffelaar, P.A., 2010. Rice production in less irrigation water is possible in Sahelian environment. Field Crops Res. 116, 154–164. Dingkuhn, M., Schnier, H.F., De Datta, S.K., Wijangco, E., Doerffling, K., 1990. Diurnal and development changes in canopy gas exchange in relation to growth in transplanted and direct-seeded flooded rice. Aust. J. Plant Physiol. 17, 119–134. Fagade, S.O., De Datta, S.D., 1971. Leaf area index, tillering capacity and grain yield of tropical rice as affected by planting density and nitrogen level. Agron. J. 63, 503–506.

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