Effect of Phosphorus and Irrigation Levels on Yield, Water Productivity, Phosphorus Use Efficiency and Income of Lowland Rice in Northwest Pakistan

Rice Science, 2013, 20(1): 61−72                                                                         Copyright © 2013, China National Rice Researc...
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Rice Science, 2013, 20(1): 61−72                                                                         Copyright © 2013, China National Rice Research Institute Published by Elsevier BV. All rights reserved DOI: 10.1016/S1672-6308(13)60109-2 

Effect of Phosphorus and Irrigation Levels on Yield, Water Productivity, Phosphorus Use Efficiency and Income of Lowland Rice in Northwest Pakistan Khalid USMAN (Department of Agronomy, Faculty of Agriculture, Gomal University, Dera Ismail Khan 29050, Pakistan)

Abstract: With decreasing availability of water for agriculture and increasing demand for rice production, an optimum use of irrigation water and phosphorus may guarantee sustainable rice production. Field experiments were conducted in 2003 and 2004 to investigate the effect of phosphorus and irrigation levels on yield, water productivity (WP), phosphorus use efficiency (PUE) and income of low land rice. The experiment was laid out in randomized complete block design with split plot arrangements replicated four times. Main plot consisted of five phosphorus levels, viz. 0 (P0), 50 (P50), 100 (P100), 150 (P150), and 200 (P200) kg/hm2, while subplots contained of irrigation times, i.e. 8 (I8), 10 (I10), 12 (I12), and 14 (I14) irrigation levels, each with a water depth of 7.5 cm. Mean values revealed that P150 in combination with I10 produced the highest paddy yield (9.8 t/hm2) and net benefit (1 231.8 US$/hm2) among all the treatments. Phosphorus enhanced WP when applied in appropriate combination with irrigation level. The highest mean WP [13.3 kg/(hm2·mm)] could be achieved at P150 with I8 and decreased with increase in irrigation level, while the highest mean PUE (20.1 kg/kg) could be achieved at P100 with I10 and diminished with higher P levels. The overall results indicate that P150 along with I10 was the best combination for sustainable rice cultivation in silty clay soil. Key words: irrigation level; phosphorus; phosphorus use efficiency; rice; water productivity; yield

Rice (Oryza sativa L.) is one of the most important food crops in Asia providing an average of 32% of total calorie intake (Belder et al, 2004). To keep up with population growth and demand for food, rice production must be increased by 56% over the next 30 years (Hossain, 1997). In Asia, irrigated rice accounts for about 50% of the total amount of water diverted for irrigation which in itself accounts for 80% of the amount of fresh water diverted (Guerra et al, 1998). Fresh water is becoming scarce due to population growth, increasing urban and industrial development and decreasing water availability for agriculture, particularly for rice as a paddy crop (Tao et al, 2006). It is estimated that 50% of the world rice production is affected by drought (Belder et al, 2004). Pakistan is moving rapidly towards water deficit as the regions having less than 1 000 m3 per capita per annum are considered water deficit countries. At present, 140 million populations growing at an annual rate of 2.5% is expected only 550 m3 per capita per annum by 2025, Received: 27 September 2011; Accepted: 29 December 2011 Corresponding author: Khalid USMAN ([email protected])

 

which is very low to fulfill the daily country requirements (Smil, 2005). Rice is the second major food crop after wheat in the country. It is grown on an area of about 2.88 million hectares and gives a total production of 6.88 million tons with an average yield of 2 387 kg/hm2 (MINFAL, 2010), which is very low compared to other rice producing countries. Irrigation and fertilizers are the vital and costly inputs in irrigated agriculture. The economic use of these inputs depends on achievement of the maximum yield per unit area. In Pakistan, rice is traditionally cultivated in flooded conditions whereas the scarcity of water threatens the sustainability of such conventional farming. Standing water in rice fields is not necessary because only maintaining the saturated soil conditions during the growing season may produce high yields and would also reduce the water input (Zulkarnain et al, 2009). Maximum yield of non-flooded cultivation of rice can be achieved by improving the water use efficiency (Xu et al, 2007). Researchers now face a challenge to produce high yield with less water, which can be achieved by increasing crop water productivity. Water

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conserving agronomic techniques is supposed to enhance water productivity and is, therefore, urgently needed for fully utilizing the available water for large area. This will also help increase in the rice area in country to save and improve water productivity. Yang and Zhang (2010) proved that proper crop management holds great promise to enhance harvest index and, consequently, achieve the dual goal of increasing grain yield and saving water. Almost the same or higher yield of rice grain could be achieved with water saving techniques compared with traditional flooded conditions and moreover 48.5% of irrigation water could be saved (Zhang et al, 2004). Phosphorus (P) availability may not be a problem if the soil shifted from waterlogged to aerobic condition (Zhang et al, 2004). The different irrigation levels may have variable effect on the transformation of soil phosphorus in this new rice cultivation system. Since phosphorus is essential for plant growth and promotes root development, tillering, early flowering, biomass and grain yield of rice, and performs other functions like metabolic activities, particularly in synthesis of protein, it may have positive effect on saving irrigation water (Tanwar and Shaktawat, 2003; Li et al, 2005). The study site, being calcareous, is generally deficient in P and its deficiency can reduce the crop yield by 10%– 15% (Gill et al, 2004). The deficiency of P is more critical on calcareous and alkaline soils, because on these soils, P is generally present in insoluble form of tri-calcium phosphate, thus its management becomes more important (Aziz et al, 2006). Non-flooded rice cultivation would save irrigation and increase paddy yield compared to flooded rice cultivation (Zhang et al, 2004). He et al (2004) reported that paddy rice could be successfully cultivated under aerobic condition and under sufficient P supply. Amiri et al (2009) reported that paddy rice had similar response to 5-day interval irrigation as that to throughout submerged irrigations. However, it remains a major challenge to reduce water input without compromising

yield and to optimize scarce water in rice production. Here, we study the interactions between irrigation and phosphorus levels and their effects on water productivity, phosphorus use efficiency, paddy yield and income and thus, providing an appropriate way to manage the water and phosphorus in the low land rice on a silty clay soil in an arid environment of northwestern Pakistan.

MATERIALS AND METHODS Experimental site Field experiments were conducted in 2003 and 2004 at Gomal University, Dera Ismail Khan, Pakistan (31º49′ N, 70°55′ E, 165 m elevation). The study area comes in an arid climate with low annual rainfall less than 200 mm, hot and dry summer with moderate spells of rain during monsoon season. The average groundwater table depth is about 7 m. Meteorological data for 2003 and 2004 growing season were collected from the Agricultural Research Institute, Dera Ismail Khan, Pakistan (Table 1). The rainfall was higher in 2004 (53.3 mm) than in 2003 growing season (29.7 mm). The other meteorological data such as temperature and relative humidity were almost identical for the two growing seasons. The initial soil chemical properties at the 0- to 20-cm soil depth of the experimental site were pH 7.8, organic matter 6.5 g/kg (gram per kilogram of soil), total N 0.3 g/kg, AB-DTPA extractable P 7.8 mg/kg, and available K 192 mg/kg. Textural analysis of this site was sand 150 g/kg, silt 450 g/kg and clay 400 g/kg. Organic matter was determined through wet oxidation based upon Walkley and Black method (Nelson and Sommers, 1982). Total N in soil was determined by the Kjeldhal method (Bremner and Mulvaney, 1982). Phosphorus content was measured by spectrophotometer and potash by flame photometer. The extractable phosphorus and potash in soil samples were determined by the AB-DTPA extractable method (Soltanpour, 1985). Soil pH was determined in soil-

Table 1. Meteorological data for 2003 and 2004 growing seasons collected from Agricultural Research Institute, Dera Ismail Khan, Pakistan. 2003 Month

 

May June July August September October Mean

Temperature (ºC) Max Min 41.0 23.0 39.0 26.0 38.0 27.0 36.0 25.0 36.0 24.0 30.0 19.0 36.7 24.0

Relative humidity (%) 72.0 78.0 79.0 83.0 82.0 81.0 79.2

Rainfall (mm) 0.0 39.5 46.0 42.5 50.0 0.0 29.7

Temperature (ºC) Max Min 36.0 20.0 42.0 25.0 37.0 26.0 37.0 27.0 36.0 24.0 33.0 17.0 36.8 23.2

2004 Relative humidity (%) 65.0 60.0 81.0 81.0 82.0 80.0 74.8

Rainfall (mm) 19.0 0.0 142.5 96.0 62.0 0.0 53.3

Khalid USMAN, et al. Water Productivity, PUE and Production of Rice in Response to Phosphorus and Irrigation

water suspension (1:5) with the help of pH meter (McLean, 1982). Details of soil analysis were reported earlier by Usman et al (2010). Experimental layout and treatments The experiment was laid out in a randomized complete block design with split-plot combined over years replicated four times. The sub-plot size was 3 m × 5 m. The subplots were separated by bunds (30 cm wide) in which polythene plastic sheets were installed down to 60–70 cm depth to avoid shallow seepage of water between plots. Phosphorus levels (0, 50, 100, 150 and 200 kg/hm2) were kept in main plots while different times of irrigations, viz. I8 (8 irrigations), I10 (10 irrigations), I12 (12 irrigations) and I14 (14 irrigations) were kept in sub-plots. The water depth for each irrigation treatment was 7.5 cm. In irrigation regime I8, the first irrigation was given 10 d after transplanting (DAT) and the remaining irrigations were given at a 10-day interval. In irrigation regime I10, first irrigation was given 8 DAT and the successive irrigations were given at an 8-day interval. In irrigation regime I12, the first irrigation was given 6 DAT and this interval (6 d) was kept constant up to the 8th irrigation and thereafter the interval was extended to 8 d and continued till the last irrigation. In irrigation regime I14, the first irrigation was given 5 DAT and the interval (5 d) was kept constant up to the 10th irrigation while later on extended to 7 d and maintained till the last irrigation. Crop management Phosphorus was applied to the soil at the time of seed bed preparation before transplanting. Besides Papplication, a common dose of nitrogen was also applied at the rate of 120 kg/hm2 as urea split in three equal doses at transplanting, tillering and 7 d before panicle initiation. The germinated seeds of adapted, non-aromatic coarse rice (IR6) were sown in well prepared seed bed. Healthy seedlings of 30-day-old were transplanted in the sub-plots maintaining row to row and plant to plant distance of 20 cm, each with two seedlings per hill. The crop was transplanted on 15 June during both years of experimentation. Data were recorded for number of panicles per m2, seed setting rate, sterility percentage, paddy yield, harvest index, water productivity (grain yield divided by total water input), phosphorus use efficiency [Phosphorus use efficiency is here denoted as (yield with P – yield without P) / amount of P applied], and net benefit. About 25 plants were monitored to determine number of

 

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panicles per m2, seed setting rate and sterility percentages. For paddy yield, central four rows were harvested from each subplot, tied into bundles, sun dried, threshed, cleaned and weighed with electronic balance. Data were also recorded on input cost like seed, fertilizer, insecticides, herbicides, and operational costs such as land preparation, irrigation, transplanting, harvesting and threshing (Table 2). Net benefit was determined by total cost of production and gross income. Input and output prices for 2003 and 2004 were calculated on 2003 and 2004 currency rates, respectively, in the prevailing market. Data analysis Data for each parameter over 2-year period were subjected to analysis of variance (ANOVA) using a randomized complete block design with split plot combined over years according to MSTATC (Steel and Torrie, 1980). Treatment means were compared using least significant difference (LSD) test at P ≤ 0.05.

RESULTS Number of panicles per m2 There were significant effects of year (Y), phosphorus (P), irrigation (I), Y × I, P × I, and Y × P × I interactions (Table 3). Higher panicle number per m2 (338.7) were recorded in 2004 compared with 336.5 recorded in 2003 (Table 4). The irrigation level I10 (10 irrigations) produced higher panicle number per m2 during each year as well as mean over years (346.3) compared to other irrigation levels. Mean values for phosphorus levels revealed that P150 produced the highest number of panicles per m2 (353.7) compared to the control having the lowest number of panicles per m2 (311.2). In P × I interaction, panicle number per m2 increased with increase in P level up to 150 kg/hm2, while irrigation impacted panicles per m2 up to I10. In higher order interactions i.e. Y × P × I, the highest number of panicles per m2 (362.0) was observed at P150 with I10 during 2004. Seed setting rate Seed setting rate was significantly affected by Y, P, I, Y × P, Y × I, P × I, and Y × P × I interactions (Table 3). Seed setting rate was higher in 2004 (80.8%) compared to 2003 (78.7%) (Table 5). The results further indicated that P150 and I10 produced higher seed setting rate in individual years as well as for the 2-year period compared to other P and irrigation levels, respectively.

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US$/hm2

Table 2. Break-up of total cost of production for crop seasons in 2003 and 2004. Year 2003

Treatment P

I

Input cost LR

Seed

Ploughing

IW

Fertilizer

Insecticide

Herbicide

TC

Harvesting

P0

Threshing

I8 45.8 4.2 21.0 30.0 65.4 18.1 22.2 33.3 41.7 33.3 I10 45.8 4.2 21.0 37.5 65.4 18.1 22.2 33.3 41.7 33.3 I12 45.8 4.2 21.0 45.0 65.4 18.1 22.2 33.3 41.7 33.3 I14 45.8 4.2 21.0 52.5 65.4 18.1 22.2 33.3 41.7 33.3 P50 I8 45.8 4.2 21.0 30.0 86.3 18.1 22.2 33.3 41.7 33.3 I10 45.8 4.2 21.0 37.5 86.3 18.1 22.2 33.3 41.7 33.3 I12 45.8 4.2 21.0 45.0 86.3 18.1 22.2 33.3 41.7 33.3 I14 45.8 4.2 21.0 52.5 86.3 18.1 22.2 33.3 41.7 33.3 P100 I8 45.8 4.2 21.0 30.0 107.1 18.1 22.2 33.3 41.7 33.3 I10 45.8 4.2 21.0 37.5 107.1 18.1 22.2 33.3 41.7 33.3 I12 45.8 4.2 21.0 45.0 107.1 18.1 22.2 33.3 41.7 33.3 I14 45.8 4.2 21.0 52.5 107.1 18.1 22.2 33.3 41.7 33.3 P150 I8 45.8 4.2 21.0 30.0 127.9 18.1 22.2 33.3 41.7 33.3 I10 45.8 4.2 21.0 37.5 127.9 18.1 22.2 33.3 41.7 33.3 I12 45.8 4.2 21.0 45.0 127.9 18.1 22.2 33.3 41.7 33.3 I14 45.8 4.2 21.0 52.5 127.9 18.1 22.2 33.3 41.7 33.3 P200 I8 45.8 4.2 21.0 30.0 163.8 18.1 22.2 33.3 41.7 33.3 I10 45.8 4.2 21.0 37.5 163.8 18.1 22.2 33.3 41.7 33.3 I12 45.8 4.2 21.0 45.0 163.8 18.1 22.2 33.3 41.7 33.3 I14 45.8 4.2 21.0 52.5 163.8 18.1 22.2 33.3 41.7 33.3 2004 P0 I8 46.7 5.0 21.7 30.7 66.7 18.3 22.3 35.0 43.3 36.7 I10 46.7 5.0 21.7 38.3 66.7 18.3 22.3 35.0 43.3 36.7 I12 46.7 5.0 21.7 46.0 66.7 18.3 22.3 35.0 43.3 36.7 I14 46.7 5.0 21.7 53.7 66.7 18.3 22.3 35.0 43.3 36.7 P50 I8 46.7 5.0 21.7 30.7 88.3 18.3 22.3 35.0 43.3 36.7 I10 46.7 5.0 21.7 38.3 88.3 18.3 22.3 35.0 43.3 36.7 I12 46.7 5.0 21.7 46.0 88.3 18.3 22.3 35.0 43.3 36.7 I14 46.7 5.0 21.7 53.7 88.3 18.3 22.3 35.0 43.3 36.7 P100 I8 46.7 5.0 21.7 30.7 110.0 18.3 22.3 35.0 43.3 36.7 I10 46.7 5.0 21.7 38.3 110.0 18.3 22.3 35.0 43.3 36.7 I12 46.7 5.0 21.7 46.0 110.0 18.3 22.3 35.0 43.3 36.7 I14 46.7 5.0 21.7 53.7 110.0 18.3 22.3 35.0 43.3 36.7 P150 I8 46.7 5.0 21.7 30.7 131.7 18.3 22.3 35.0 43.3 36.7 I10 46.7 5.0 21.7 38.3 131.7 18.3 22.3 35.0 43.3 36.7 I12 46.7 5.0 21.7 46.0 131.7 18.3 22.3 35.0 43.3 36.7 I14 46.7 5.0 21.7 53.7 131.7 18.3 22.3 35.0 43.3 36.7 P200 I8 46.7 5.0 21.7 30.7 153.3 18.3 22.3 35.0 43.3 36.7 I10 46.7 5.0 21.7 38.3 153.3 18.3 22.3 35.0 43.3 36.7 I12 46.7 5.0 21.7 46.0 153.3 18.3 22.3 35.0 43.3 36.7 I14 46.7 5.0 21.7 53.7 153.3 18.3 22.3 35.0 43.3 36.7 P, Phosphorus; I, Irrigation; LR, Land rent; IW, Irrigation water; TC, Transplanting charges; P0, No phosphorus; P50, 50 kg/hm2 P; kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Inputs were uniformly applied in both years, however, due to price variation cost of inputs varied accordingly.

Total cost 315.0 322.5 330.0 337.5 335.8 343.3 350.8 358.3 356.7 364.2 371.7 379.2 377.5 385.0 392.5 400.0 413.3 420.8 428.3 435.8 326.4 334.0 341.7 349.4 348.0 355.7 363.4 371.0 369.7 377.4 385.0 392.7 391.4 399.0 406.7 414.4 413.0 420.7 428.4 436.0 P100, 100

Table 3. Analysis of variance (mean squares) of panicle number per m2, seed setting rate, sterility rate, paddy yield, harvest index (HI), water productivity (WP), phosphorus use efficiency (PUE), and net benefit (NB) as affected by year, phosphorus and irrigation levels. Panicle number Seed setting Sterility rate Paddy yield HI per m2 rate (%) (%) (kg/hm2) (%) Year (Y) 1 185.76** 172.02** 25.76** 2.07** 23.87** Rep (y*) 6 1.25 0.07 0.29 0.01 0.26 Phosphorus (P) 4/3+ 9 546.54** 185.99** 617.40** 27.96** 13.82** Y×P 4/3+ 0.76 0.69** 1.42** 0.02* 1.49** Error (a) 24/18+ 1.28 0.25 0.26 0.01 0.26 Irrigation (I) 3/3+ 3 476.83** 130.05** 395.69** 18.08** 16.59** Y×I 3/3+ 11.06** 0.69* 0.28 0.02 1.61** P×I 12/9+ 161.57** 3.49** 17.87** 0.33** 8.52** Y×P×I 12/9+ 3.30** 2.15** 0.48 0.01 1.70** Error (b) 90/72+ 1.16 0.19 0.48 0.01 0.28 * and **, Significant at the 0.05 and 0.01 probability levels, respectively. + , df for PUE; Rep (y*), Replication over year. Source

 

df

WP [kg/(hm2·mm)] 6.32** 0.04 45.13** 0.17** 0.02 153.34** 0.06* 0.56** 0.19** 0.02

PUE NB (kg/kg) (US$/hm2) 3.22 31 312.42** 0.45 218.41 256.05** 497 290.55** 2.99** 840.71** 0.27 184.85 153.91** 473 475.28** 0.62* 306.65 4.55** 9 279.68** 0.68** 179.01 0.16 370.83

Khalid USMAN, et al. Water Productivity, PUE and Production of Rice in Response to Phosphorus and Irrigation

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Table 4. Number of panicles per m2 of rice as affected by different levels of phosphorus and irrigation. Year

Irrigation level

2003

I8 I10 I12 I14 I8 I10 I12 I14 I8 I10 I12 I14

P fertilization P0

P50

P100

P150

P200

Mean

287.5 v 314.0 t 333.0 o 347.0 gh 337.0 kl 323.7 h 325.0 r 335.5 lmn 350.0 f 356.5 bc 355.6 c 344.5 b 315.0 st 334.0 no 347.5 g 355.0 cd 352.0 e 340.7 d 313.8 t 331.0 p 343.6 i 351.4 ef 345.5 h 337.1 f 2004 290.0 u 315.0 st 335.0 mn 348.0 g 340.0 j 325.6 g 328.0 q 338.0 k 354.0 d 362.0 a 358.0 b 348.0 a 316.0 s 336.0 lm 351.0 ef 358.0 b 354.0 d 343.0 c 314.0 t 334.0 no 343.0 i 352.0 e 347.0 gh 338.0 e 2003–2004 288.8 p 314.5 no 334.0 k 347.5 f 338.5 i 324.7 d 326.5 m 336.8 j 352.0 cd 359.3 a 356.8 b 346.3 a 315.5 n 335.0 k 349.3 e 356.5 b 353.0 c 341.9 b 313.9 o 332.5 l 343.3 h 351.7 d 346.3 g 337.5 c 2003 mean 310.3 328.6 343.5 352.5 347.5 336.5 b 2004 mean 312.0 330.8 345.8 355.0 349.8 338.7 a Phosphorus means 311.2 e 329.7 d 344.6 c 353.7 a 348.6 b Data in each category followed by the same letter (or no letter) indicate no significant difference at 5% level by the LSD test. P0, No phosphorus; P50, 50 kg/hm2 P; P100, 100 kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Table 5. Seed setting rate of rice as affected by different levels of phosphorus and irrigation.

%

P fertilization Mean P0 P50 P100 P150 P200 2003 I8 72.3 a 74.5 q 77.0 n 80.8 h 79.0 k 76.7 g I10 78.0 lm 80.0 ij 81.0 gh 84.0 b 82.4 e 81.1 b I12 77.0 n 77.5 mn 79.0 k 82.6 de 81.0 gh 79.4 d I14 75.5 op 76.0 o 77.5 mn 81.0 gh 78.2 l 77.6 f 2004 I8 75.0 pq 78.0 lm 79.0 k 83.0 cd 80.5 hi 79.1 e I10 81.5 fg 82.0 ef 82.5 de 85.0 a 83.5 bc 82.9 a I12 79.5 jk 80.0 ij 80.5 hi 84.0 b 82.5 de 81.3 b I14 75.8 o 78.0 lm 80.0 ij 83.5 bc 82.0 ef 79.9 c 2003–2004 I8 73.7 l 76.5 j 78.0 h 81.9 cd 79.8 f 77.9 d I10 79.8 f 81.0 e 81.8 d 84.5 a 82.9 b 82.0 a I12 78.3 h 78.8 g 79.8 f 83.3 b 81.8 d 80.4 b I14 75.6 k 77.0 i 78.8 g 82.3 c 80.1 f 78.7 c 2003 mean 75.7 i 77.0 h 78.6 f 82.1 b 80.1 d 78.7 b 2004 mean 77.9 g 79.5 e 80.5 c 83.9 a 82.1 b 80.8 a Phosphorus means 76.8 e 78.3 d 79.6 c 83.0 a 81.1 b Data in each category followed by the same letter indicate no significant difference at 5% level by the LSD test. P0, No phosphorus; P50, 50 kg/hm2 P; P100, 100 kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Year

Irrigation level

The highest mean seed setting rate at P150 and I10 were 83.0% and 82.0%, respectively. Mean values for P × I interaction revealed that P150 had the highest seed setting rate (84.5%) with I10 among all the treatments. The Y × P × I interaction showed that P150 in combination with I10 had higher seed setting rate during both the years, however, the highest seed setting rate (85.0%) could be achieved during 2004. Sterility Sterility rate in rice was significantly affected by Y, P, I, and P × I interaction (Table 3). Sterility rate was higher in 2003 (29.7%) than in 2004 (28.9%) (Table 6), which may be attributed to seasonal variation

 

between the two years. Mean values for P revealed that the highest and the lowest sterility rates were recorded in P0 (35.3%) and P150 (24.3%), respectively. The results also revealed that sterility rate was higher in 2003 than in 2004 at each level of P except at P200 which gave similar sterility rate during both the years. Mean values for irrigation revealed that I14 showed the highest sterility rate (32.7%), while I10 displayed the lowest (25.7%) among the irrigation levels. In P × I interaction, P0 × I14 showed the highest sterility rate (39.5%), whereas P150 × I8 showed the lowest (22.8%). Paddy yield The data presented in Table 3 indicated that paddy

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66 Table 6. Sterility rate in rice as affected by different levels of phosphorus and irrigation.

%

P fertilization Mean P0 P50 P100 P150 P200 2003 I8 35.0 30.0 28.0 23.0 25.0 28.2 I10 30.0 27.5 25.5 24.0 23.0 26.0 I12 39.0 35.0 30.0 25.6 28.0 31.5 I14 40.0 37.0 33.0 26.0 29.5 33.1 2004 I8 34.0 29.0 27.0 22.5 24.5 27.4 I10 28.5 26.5 25.0 23.0 24.0 25.4 I12 37.0 34.0 29.5 25.0 27.0 30.5 I14 39.0 36.0 32.0 25.5 29.0 32.3 2003–2004 I8 34.5 d 29.5 f 27.5 g 22.8 k 24.8 i 27.8 c I10 29.3 f 27.0 g 25.3 hi 23.5 j 23.5 j 25.7 d I12 38.0 b 34.5 d 29.8 f 25.3 hi 27.5 g 31.0 b I14 39.5 a 36.5 c 32.5 e 25.8 h 29.3 f 32.7 a 2003 mean 36.0 a 32.4 c 29.1 e 24.7 h 26.4 g 29.7 a 2004 mean 34.6 b 31.4 d 28.4 f 24.0 i 26.1 g 28.9 b Phosphorus means 35.3 a 31.9 b 28.8 c 24.3 e 26.2 d Data in each category followed by the same letter (or no letter) indicate no significant difference at 5% level by the LSD test. P0, No phosphorus; P50, 50 kg/hm2 P; P100, 100 kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Year

Irrigation level

Table 7. Paddy yield as affected by different levels of phosphorus and irrigation.

t/hm2

P fertilization Mean P0 P50 P100 P150 P200 2003 I8 6.0 6.8 7.2 7.9 7.5 7.1 I10 7.5 8.1 9.0 9.7 9.3 8.7 I12 6.7 7.5 8.6 9.2 8.9 8.2 I14 6.4 7.1 8.2 9.0 8.8 7.9 2004 I8 6.2 7.0 7.5 8.0 7.7 7.3 I10 7.7 8.3 9.2 9.8 9.4 8.9 I12 6.9 7.6 9.0 9.4 9.2 8.4 I14 6.7 7.4 8.4 9.2 9.0 8.2 2003–2004 I8 6.1 k 6.9 i 7.4 h 8.0 f 7.6 g 7.2 d I10 7.6 g 8.2 e 9.1 c 9.8 a 9.3 b 8.8 a I12 6.8 i 7.5 g 8.8 d 9.3 b 9.1 c 8.3 b I14 6.6 j 7.3 h 8.3 e 9.1 c 8.9 d 8.0 c 2003 mean 6.6 j 7.4 h 8.2 f 8.9 b 8.6 d 8.0 b 2004 mean 6.9 i 7.6 g 8.5 e 9.1 a 8.8 c 8.2 a Phosphorus means 6.8 e 7.5 d 8.4 c 9.0 a 8.7 b Data in each category followed by the same letter (or no letter) indicate no significant difference at 5% level by the LSD test. P0, No phosphorus; P50, 50 kg/hm2 P; P100, 100 kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Year

Irrigation level

yield was significantly affected by Y, P, I, Y × P, and P × I interactions. Paddy yield was higher in 2004 (8.2 t/hm2) than in 2003 (8.0 t/hm2) probably due to more rainfall in 2004 (Table 7). Mean values for phosphorus revealed that there was significant increase in paddy yield with each additional increment of P, which peaked at 150 kg/hm2 (9.0 t/hm2), indicating maximum phosphorus absorption might have increased with further P application (200 kg/hm2), but the rate of dry matter partitioning to grain could not enhance accordingly. Similarly, I10 produced mean maximum paddy yield (8.8 t/hm2) compared with other irrigation levels. It is also evident from the results that paddy yield was

 

higher in 2004 at each level of P than in 2003 at the corresponding level of P. However, the highest paddy yield (9.1 t/hm2) could be achieved at 150 kg/hm2 in 2004. The P × I interaction showed the highest mean paddy yield (9.8 t/hm2) at P150 in combination with I10. Harvest index (HI) HI is the ratio of paddy yield to biological yield. The HI was significantly affected by Y, P, I, Y × P, Y × I, P × I, and Y × P × I interactions (Table 3). The HI was higher in 2004 (40.4%) than in 2003 (39.6%) (Table 8). Mean values revealed that the highest HI (41.0%) was obtained from P0, which decreased with increase in P level. The lowest mean HI (39.4%) was recorded

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Table 8. Harvest index as affected by different levels of phosphorus and irrigation.

%

P fertilization Mean P0 P50 P100 P150 P200 2003 I8 40.0 g-k 40.4 d-i 39.3 l-q 40.7 d-g 40.6 d-h 40.2 bc I10 43.5 b 39.5 j-p 40.6 d-h 39.4 k-p 38.6 qrs 40.3 b I12 39.8 i-l 39.9 h-l 38.8 o-r 38.5 rs 38.5 rs 39.1 d I14 38.0 s 39.6 j-o 38.5 rs 38.8 pqr 39.0 m-r 38.8 d 2004 I8 40.8 def 40.9 de 42.1 c 40.8 def 40.7 dg 41.1 a I10 44.5 a 40.1 f-k 39.6 j-n 39.5 j-p 38.9 o-r 40.5 b I12 40.6 d-h 40.2 f-j 40.2 e-j 39.2 l-r 39.5 j-p 39.9 c I14 41.1 d 40.7 d-g 38.9 n-r 39.2 l-r 39.7 i-m 39.9 c 2003–2004 I8 40.4 bcd 40.7 bc 40.7 bc 40.8 b 40.6 bc 40.6 a I10 44.0 a 39.8 efg 40.1 de 39.5 gh 38.7 j 40.4 a I12 40.2 cde 40.1 def 39.5 g 38.8 ij 39.0 hij 39.5 b I14 39.6 fg 40.1 de 38.7 j 39.0 hij 39.3 ghi 39.3 b 2003 mean 40.3 b 39.8 cd 39.3 f 39.3 ef 39.1 f 39.6 a 2004 mean 41.7 a 40.5 b 40.2 bc 39.7 de 39.7 de 40.4 a Phosphorus means 41.0 a 40.2 b 39.7 c 39.5 cd 39.4 d Data in each category followed by the same letter indicate no significant difference at 5% level by the LSD test. P0, No phosphorus; P50, 50 kg/hm2 P; P100, 100 kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Year

Irrigation level

Table 9. Water productivity (WP) of rice as affected by different levels of phosphorus and irrigation.

kg/(hm2·mm)

P fertilization Mean P0 P50 P100 P150 P200 2003 I8 9.3 p 11.3 h 12.0 ef 13.2 ab 12.5 d 11.7 b I10 8.9 q 10.7 j 11.4 h 12.0 ef 11.9 fg 11.0 d I12 7.4 x 8.4 tu 9.6 o 10.1 lmn 9.9 n 9.1 f I14 6.1 6.8 z 7.8 w 8.2 uv 8.2 uv 7.4 h 2004 I8 10.3 kl 11.7 g 12.5 d 13.3 a 12.8 c 12.1 a I10 9.3 p 11.1 i 12.2 e 13.0 bc 11.7 g 11.4 c I12 7.7 w 8.5 st 10.0 mn 10.5 k 10.2 lm 9.4 e I14 6.4 7.1 y 8.0 v 8.8 qr 8.6 rs 7.8 g 2003–2004 I8 9.8 j 11.5 f 12.3 d 13.3 a 12.7 b 11.9 a I10 9.1 k 10.9 g 11.8 e 12.5 c 11.8 e 11.2 b I12 7.6 n 8.4 l 9.8 j 10.3 h 10.1 i 9.2 c I14 6.3 p 6.9 o 7.9 m 8.5 l 8.4 l 7.6 d 2003 mean 7.9 h 9.3 f 10.2 d 10.9 b 10.6 c 9.8 b 2004 mean 8.4 g 9.6 e 10.7 c 11.4 a 10.8 b 10.2 a Phosphorus means 8.2 e 9.4 d 10.4 c 11.1 a 10.7 b Data in each category followed by the same letter (or no letter) indicate no significant difference at 5% level by the LSD test. P0, No phosphorus; P50, 50 kg/hm2 P; P100, 100 kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Year

Irrigation level

from P200, probably due to higher yield of straw compared to grain yield. The results revealed that HI was higher at each level of P in 2004 than at the corresponding level of P in 2003. Mean values for irrigation revealed that I8 and I10 had higher HI than I12 and I14 ranging from 39.3% to 40.6%. In P × I interaction, the highest mean HI (44.0%) could be achieved from P0 × I10, while the lowest HI (38.7%) was obtained from P200 × I10 and P100 × I14. In Y × P × I interaction, the highest (44.5%) and the lowest HI (38.0%) were obtained from Y2004 × P0 × I10 and Y2003 × P0 × I14, respectively. These results suggest that the highest level of P or I affect HI negatively. In interaction, I10 performed better regarding HI with P0 compared with higher

 

levels of phosphorus. Water productivity (WP) WP was significantly affected by Y, P, I, Y × P, Y × I, P × I, and Y × P × I interactions (Table 3). The WP was higher in 2004 [10.2 kg/(hm2·mm)] than in 2003 [9.8 kg/(hm2·mm)] (Table 9). The mean values revealed that the highest WP [11.1 kg/(hm2·mm)] could be achieved from P150 compared to the control having the lowest WP [8.2 kg/(hm2·mm)]. Each level of P had the higher WP in 2004 compared to the corresponding level of P in 2003. Mean values for irrigation revealed that I8 had the highest WP [11.9 kg/(hm2·mm)] which decreased linearly with the increase in irrigation level.

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Table 10. Phosphorus use efficiency (PUE) in rice as affected by different levels of phosphorus and irrigation.

kg/kg

P fertilization Mean P50 P100 P150 P200 2003 I8 13.0 kl 12.5 lm 12.9 l 7.8 r 11.5 f I10 16.8 de 19.2 b 17.3 cd 11.8 no 16.3 a I12 15.6 g 17.5 c 16.5 ef 11.1 p 15.2 b I14 14.5 hi 15.0 h 14.9 h 9.0 q 13.3 d 2004 I8 12.0 mn 13.0 kl 12.0 mn 7.5 r 11.1 g I10 16.0 fg 21.0 a 16.7 e 11.8 no 16.4 a I12 14.5 hi 17.0 cde 16.7 e 11.3 op 14.9 c I14 13.5 jk 15.0 h 14.0 ij 8.5 q 12.8 e 2003–2004 I8 12.5 g 12.7 g 12.5 g 7.6 k 11.3 d I10 16.4 c 20.1 a 17.0 b 11.8 h 16.3 a I12 15.1 d 17.3 b 16.6 c 11.2 i 15.0 b I14 14.0 f 15.0 d 14.5 e 8.8 j 13.0 c 2003 mean 15.0 d 16.1 b 15.4 c 9.9 f 14.1 a 2004 mean 14.0 e 16.5 a 14.8 d 9.8 f 13.8 b Phosphorus means 14.5 c 16.3 a 15.1 b 9.8 d Data in each category followed by the same letter indicate no significant difference at 5% level by the LSD test. P50, 50 kg/hm2 P; P100, 100 kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Year

Irrigation level

Almost similar trend was observed in Y × I interaction. However, the highest WP [12.1 kg/(hm2·mm)] was noted in 2004 with I8. In P × I interaction, there was declining trend for WP under each category of P level with increasing irrigation level. The highest [13.3 kg/(hm2·mm)] and the lowest values [6.3 kg/(hm2·mm)] were recorded from P150 × I8 and P0 × I14, respectively. The higher order interactions revealed that WP increased with increase in P up to 150 kg/hm2 and diminished with further P supply under each category of irrigation level during both the years. The highest WP [13.3 kg/(hm2·mm)] was obtained from Y2004 × P150 × I8, whereas the lowest WP [6.1 kg/(hm2·mm)] was obtained from Y2003 × P0 × I14. Phosphorus use efficiency (PUE) PUE had significant response to Y, P, I, Y × P, Y × I, P × I, and Y × P × I interactions (Table 3). Higher PUE was recorded in 2003 (14.1 kg/kg) than in 2004 (13.8 kg/kg) (Table 10). Mean values for P levels revealed that the highest PUE (16.3 kg/kg) was achieved at P100, while the lowest value (9.8 kg/kg) was recorded at P200. The PUE was higher for each level of P in 2003 than that for the corresponding level of P in 2004 except for P100. Mean values for irrigation levels showed that the highest PUE (16.3 kg/kg) could be achieved with I10, while further increase in irrigation level resulted in lower PUE. The highest PUE with I10 was realized during both years. In P × I interaction, PUE was the highest (21.0 kg/kg) with P100 × I10 among all the combinations. In higher order interactions i.e. Y × P × I, PUE was the highest (20.1 kg/kg) in Y2004 × P100 × I10. There was increase

 

in PUE with increase in P level up to 100 kg/hm2 and irrigation level up to I10, any further increase in either P or I level would result in lower PUE. Net benefit (NB) The Y, P, I, Y × P and P × I interactions had significant effect on NB (Table 3). Higher net benefit was recorded in 2004 (982.1 US$/hm2) compared with 2003 (954.2 US$/hm2) (Table 11). Mean values for P revealed that the highest NB (1 107.0 US$/hm2) was obtained from P150 compared to the control having the lowest NB (792.8 US$/hm2). In Y× P interaction, the highest NB (1 113.8 US$/hm2) could be realized with P150 during 2004. Mean values for irrigation levels revealed that NB was the highest (1 091.7 US$/hm2) with I10, and diminished with further irrigation levels. The NB had the highest response to P150 in combination with I10 and displayed maximum NB (1 231.8 US$/hm2) among all the combinations. In contrast, local practice of submerged irrigation in combination with P fertilization (60–90 kg/hm2) had much lower economic return (301.7 US$/hm2).

DISSCUSION The higher yield and yield attributes such as panicle number per m2 , seed setting rate and paddy yield recorded in 2004 compared with 2003 may be attributed to more favorable environmental conditions such as higher rainfall. In interaction, P150 × I10 proved to be the best combination regarding higher yield and yield attributes along with higher net economic return. Other researchers also reported that proper combination of P

Khalid USMAN, et al. Water Productivity, PUE and Production of Rice in Response to Phosphorus and Irrigation Table 11. Net benefit (NB) of rice as affected by different levels of phosphorus and irrigation.

69 US$/hm2

P fertilization Mean P0 P50 P100 P150 P200 2003 I8 678.4 797.5 843.3 939.2 836.7 819.0 I10 919.2 1 006.7 1 127.5 1 229.2 1 120.9 1 080.7 I12 783.8 892.6 1 061.7 1 132.5 1 055.0 985.1 I14 729.2 828.4 979.1 1 100.0 1 022.5 931.8 2004 I8 706.9 818.7 880.3 942.0 870.4 843.6 I10 949.3 1 027.6 1 155.9 1 234.3 1 146.0 1 102.6 I12 808.3 903.3 1 115.0 1 160.0 1 104.9 1 018.3 I14 767.3 862.4 1 007.3 1 118.9 1 064.0 964.0 2003–2004 I8 692.6 m 808.1 k 861.8 j 940.5 h 853.5 j 831.3 d I10 934.3 h 1 017.2 f 1 141.7 b 1 231.8 a 1 133.4 b 1 091.7 a I12 796.0 k 897.9 i 1 088.3 d 1 146.2 b 1 080.0 d 1 001.7 b I14 748.2 l 845.4 j 993.2 g 1 109.5 c 1 043.3 e 947.9 c 2003 mean 777.6 h 881.3 f 1 002.9 d 1 100.2 b 1 008.8 d 954.2 b 2004 mean 808.0 g 903.0 e 1 039.6 c 1 113.8 a 1 046.3 c 982.1 a Phosphorus means 792.8 d 892.1 c 1 021.3 b 1 107.0 a 1 027.5 b Data in each category followed by the same letter (or no letter) indicate no significant difference at 5% level by the LSD test. P0, No phosphorus; P50, 50 kg/hm2 P; P100, 100 kg/hm2 P; P150, 150 kg/hm2 P; P200, 200 kg/hm2 P; I8, 8 irrigations; I10, 10 irrigations; I12, 12 irrigations; I14, 14 irrigations. Year

Irrigation level

and irrigation enhanced panicle number per m 2 (Khunthasuvon et al, 1998). Asif et al (1999) reported that P application of 90 kg/hm2 significantly enhanced seed setting rate. Less number of irrigations probably caused shortage of water for rice plants, which resulted in higher sterility rate compared to higher irrigation levels. These results suggest that I10 and P150 interaction was quite favourable and positively affected yield attributes probably due to post-flowering wetting and moderate soil drying which held great promise to improve grain filling of inferior spikelet through elevating cytokinin levels in the rice shoot (Thomas et al, 2003; Zhang et al, 2010). The results suggest that excess irrigation water increased sterility rate, whereas it declined with each additional increment of P up to 150 kg/hm2, however, further increase in P again increased sterility rate. The results indicate that rice grown without P fertilizer produced higher sterility rate compared with P treatments (Alam et al, 2009). The data indicate that yield increased initially up to certain level and maximized at P150 and then declined at P200. Similar trend was observed for irrigation levels. This suggests that P and irrigation levels follow Liebscher’s version of the law of diminishing returns: all production factors are most efficiently used when they are all at their optimum levels (de Wit, 1992). Thus 150 kg/hm2 P was the most suitable level to optimize paddy yield. The possible reason for higher paddy yield with I10 compared to higher irrigation levels may be due to secretion of oxygen by rice roots, which reduced P adsorption and increased P desorption/release in the rhizosphere, compared to the anaerobic bulk soil

 

(Zhang et al, 2004). The results indicate that P application below or above 150 kg/hm2 is neither productive nor economical. Similarly, irrigation below I10 may cause water scarcity while irrigation above I10 would induce higher moisture stress. Water stress inhibits the growth and photosynthetic abilities of crop plants through disturbing the balance between the reactive oxygen species and the antioxidant defense, causing accumulation of reactive oxygen species which induce oxidative stress to proteins, membrane lipids and other cellular components. Water stress also affects photochemical and enzymatic activities in crop plants. Consequently, the stressful situations lead to lower paddy yield. Therefore, I10 is the optimum level of irrigation for enhancing paddy yield. The possible reason for higher paddy yield with P150 × I10 might be due to more panicles, higher seed setting rate, and larger biomass, which ultimately increased the rice yield (George et al, 2001). Farmers normally use higher irrigation level than I10, which is not only expensive but may have environmental consequences besides lower paddy yield. There is sufficient saving of water, land, and environment in addition to higher crop productivity on sustainable basis if efficient use of irrigation water is coupled with an optimum dose of P (Sovuthy et al, 2003; Zhang et al, 2004; Iqbal, 2004; He et al, 2004; Li, 2005; Yang and Zhang, 2010). Water is saved by 24.5% to 50.3% compared to conventional irrigation system (Yang et al, 2007). Amiri et al (2009) suggested 5-day interval irrigation instead of submerged irrigation. The local practice of submerged irrigation in northwestern Pakistan in combination with P fertilization (60–90

70

kg/hm2) had lower mean grain yield of 2.4 t/hm2 (MINFAL, 2010) compared to our recent yield of 9.8 t/hm2 obtained from P150 × I10. Thus in view of the above discussion, it can be concluded that submerged irrigation is neither productive nor economical. In other words, the transfer of dry mater to grain formation was the highest at P150, while this rate was either limited or slowed down with P200 perhaps due to sink limitation. Proper crop management holds great promise to enhance HI and, consequently, achieve the dual goals of increasing grain production and saving water (Yang and Zhang, 2010). These results suggest that WP increases with P level up to certain extent and then declines. Irrigation levels are negatively correlated with WP, indicating that WP decreases with increase in irrigation level. P150 in combination with I8 was optimum to achieve higher WP. Phosphorus plays a key role in enhancing water productivity under limited water supply. A suitable P level is not only water saving, but also a promising means for higher paddy yield. This may be due to better root growth and development resulting in improved moisture utilization and higher crop yield (Malik et al, 2006; He, 2010). Excessive use of irrigation water resulted in lower WP and lower paddy yield (Zhu et al, 1994; Yang et al, 2001, 2007; Tao et al, 2006). The rice crop could be grown in aerobic as well as anaerobic soil conditions with reduction of only 11% in grain yield (He et al, 2004). In general, P fertilizer enhanced water productivity when applied in suitable combination with irrigation level probably due to high yield and low seepage and percolation losses (Kundu et al, 2008). I10 was the best irrigation treatment for obtaining the highest PUE. However, P level could be increased up to 150 kg/hm2 in combination with I10 for higher paddy yield. The results also indicate that the highest P level in combination with the highest irrigation level resulted in the lowest PUE during each year as well as for the 2-year period. This may be associated with lower crop yield leading to lower PUE (Fageria and Barbosa Filho, 2007). The overall results indicate that P application at 100 kg/hm2 along with I10 was the best combination for obtaining the highest PUE. These results suggest that excessive use of irrigation water with either the lowest or the highest P application could not result in satisfactory economic return. Similarly, no P or too much lower P application with limited irrigation water resulted in lower net benefit. Therefore, judicious use of irrigation water in combination with suitable P level would be the best management option

 

Rice Science, Vol. 20, No. 1, 2013

to optimize water and phosphorus use efficiencies and enhance paddy yield and economics on a silty clay soil in an arid environment of northwestern Pakistan. This strategy would also ensure environmental safety and sustainable production of rice crop despite lower cost of production, because it will reduce soil and water pollution through substantial reduction in percolation and seepage water from rice field. In contrast to optimum use of water and P, heavy irrigation along with overdose of P and subsequent run off from paddy field may cause eutrophication, which leads to a severe reduction in water quality that disrupts normal functioning of the ecosystem, causing a variety of problems (Smith et al, 1999).

CONCLUSIONS This study evaluated five phosphorus (0, 50, 100, 150, and 200 kg/hm2) and four irrigation levels (8, 10, 12, and 14 irrigations) for yield, water productivity (WP) and phosphorus use efficiency (PUE), and eco-nomics of coarse rice on a silty clay soil in northwestern Pakistan. The P at 150 kg/hm2 produced the highest number of panicles per m2, seed setting rate, paddy yield, WP, and net benefit, as well as the lowest sterility rate. The highest PUE could be achieved at 100 kg/hm2. The irrigation level I10 had the highest number of panicles, seed setting rate, the lowest sterility, the highest paddy yield, net benefit and PUE. The highest WP could be achieved from I8. Phosphorus fertilizer improved water productivity when applied in proper combination with irrigation level. However, excessive use of P and irrigation resulted in lower PUE, WP, paddy yield and income besides unnecessary economic costs. The study indicates that P at 150 kg/hm2 in combination with I10 would be the optimum management practice to utilize resources more efficiently for enhancing paddy yield and income on sustainable basis.

ACKNOWLEDGEMENT The authors thank Gomal University, Dera Ismail Khan, Pakistan for partial support.

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