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Factors affecting deepwater rice in the central plain of Thailand
Field Crops Research, 19 (1989) 263-283
263
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Factors Affecting D e e p w a t e r Rice in the Central Plain of Thailand D.W. PUCKRIDGE 1, H.D. CATLING 2, PRASAN VONGSAROJ a, SAMLEE BOONYAWIVATANA3, LAVAN NIYOMWIT3 and PONGMANEE THONGBAI 1
1International Rice Research Institute (IRRI), P.O. Box 9-159, Bangkok 10900 (Thailand) 2IRRI, P.O. Box 933, Manila (The Philippines) :~Dept. of Agriculture, Bangkhen, Bangkok 10900 (Thailand) (Accepted 13 June 1988)
ABSTRACT Puckridge, D.G., Catling, H.D., Vongsaroj, P., Boonyawivatana, S., Niyomwit, L. and Thongbai, P., 1989. Factors affecting deepwater rice in the central plain of Thailand. Field Crops Res., 19: 263-283. Deepwater rices from Thailand have been among the most promising lines tested in the deepwater areas of Africa, Burma, Indonesia, and Vietnam, and the effect of environmental factors and cultural practices on production in Thailand is relevant to those countries. In Thailand, approximately 800 000 ha of deepwater rice is grown in fields which are flooded to depths of 50 cm or more for over a month during the growing season. Most of this specially adapted rice is grown in three regions of the central plain. Dry seeds are broadcast on ploughed fields at the beginning of the wet season, and the crop grows under rainfed dryland conditions for about 3 months before floods arrive in July-August. The plants elongate to maintain foliage above the floodwater, which may be as deep as four m. The crop is harvested after the fields drain in December-January. Investigations were made to assess yields in farmers' fields, and to determine yield-limiting factors and crop responses to inputs. Farmers were interviewed to determine production practices, and fields were sampled to estimate yields. Samples from 30 fields gave an average yield of 2.18 t ha -1 (0.7-3.5 t ha -1) for the 1981/82 season, and from 63 fields in 1982/83 gave an average of 1.83 t ha 1 (0.1-2.9 t h a - 1). There were 32 different varieties. Maximum water depths ranged from 60 cm to 200 cm. Major pests were yellow stem-borers and rats. A multi-location factorial experiment with 13 sites tested the possibility of improving yields by nitrogen and phosphorus fertilizer, or by use of a herbicide spray to control broadleaved weeds. However, grain yields were increased by N only at four sites, by P at one site, and by herbicide spraying at one site. Major yield-limiting factors were drought and poor plant stands in the preflood period, and some flood damage. Better characterisation of the environment and of its interaction with genotypes is necessary before adequate prediction of performance and improvements in production will be obtained.
INTRODUCTION
Deepwater rice (Oryza sativa L. ), often called floating rice, is grown on approximately 11 million ha in valleys and deltas of South and Southeast Asia 0378-4290/89/$03.50
© 1989 Elsevier Science Publishers B.V.
264
where flooding to depths of from 50 to 400 cm occurs each year. The largest areas occur in northeastern India and Bangladesh, followed by Thailand, Vietnam, Kampuchea, and Burma. Deepwater rice has also been introduced into Africa, Indonesia and Mexico, and some of the most promising lines introduced into those countries, as well as into Burma and Vietnam, have been Thai (Escuro et al., 1982; Toure et al., 1982; Vo-Tong Xuan et al., 1982; Hille RisLambers, 1986). The work reported here has attempted to identify environmental factors and cultural practices which affect the yield of deepwater rice in Thailand, with the aim of extending this information to other areas where Thai germplasm has been successful. In Thailand, deepwater rice is grown on approximately 800 000 ha, 9% of the total wet-season rice area. Most of this naturally flooded area is located on the Central Plain, which stretches more than 400 km north from Bangkok and the Gulf of Thailand. Virtually all of the deepwater rice is grown in the five regions of the Central Plain shown in Fig. 1, but about 12 000 ha have been reported for northeast Thailand, and 9 000 ha in northern Thailand. Areas shown as having water depths greater than 50 cm but less than 100 cm can be defined as 'deep water', where mostly tall or submergence-tolerant varieties are grown, and areas with more than 100 cm of water as 'very deep water' where elongating or 'floating' rices are planted. The terms 'deep water' and 'very deep water' were defined by Khush {1984), while 'floating rice' is a commonly used term for elongating rices grown in more than 1 m of water. Some varieties can elongate enough to survive in 4 m of water. In this paper, deepwater rice is any rice adapted to water depths remaining over 50 cm for more than 1 month. In Thailand, dry seeds of deepwater rice are broadcast on ploughed fields at the beginning of the wet season, April-June. Soils of the central plains have mainly developed on marine and brackish water deposits, and a large part of the southern plain, particularly in the east, has acid sulphate soils with low productivity (Van der Kevie and Yenmanas, 1972 ). The majority of soils have clayey textures with a high content of fine particles. The northern flood plain has young alluvial soils of medium texture on riverine sediments. The rice grows under rainfed dryland conditions for about 3 months before the floods arrive in July or August. Researchers such as Takaya and Thiramongol (1982) and Kaida (1973) have reported on water depths and different types of deepwater rice in Thailand. The distribution was reassessed on an agro-ecological basis by Catling (1985). Floodwaters usually rise about 2-3 cm/day, but after heavy rains an increase of over 30 cm may occur within 24 h. Maximum water depths are attained in September or October, before flowering, and range from 60 to 150 cm over most of the area, but vary from year to year. In some parts, depths of over 300 cm occur. The crop is harvested after the fields drain in December-January. Thai experience could be useful in predicting the performance of Thai varieties introduced elsewhere, but there is little information available on pro-
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266 duction constraints in farmers' fields. Consequently, as a basis for research to develop new technology, it was considered necessary to determine farmer practices and current production levels in the deepwater rice areas, and to identify yield-limiting factors. This paper reports the results of surveys of farmers' agronomic practices in 1981, of sampling for crop yield in the two years 1981/ 1982 and 1982/1983, and of a multilocation experiment on the use of fertilizer and herbicides in 1982/1983. METHODS
Agronomic practices and crop yields In order to provide background information to a crop yield study, 20 farmers' fields were selected at random early in the growing season of 1981, and the farmers were questioned regarding their cultural practices, farm size, equipment, soil and flood conditions, pest problems, and methods of control of pests. Samples from these fields were subsequently included in the grain yield study. A concurrent survey of deepwater-rice areas by the Statistical Analysis Subdivision of the Department of Agriculture of Thailand obtained data from 307 farms. During the December-January harvest periods of 1981/82 and 1982/83, a total of 90 farmers' fields were sampled for yield in each of the main deepwater rice provinces. In each field, four separate 5-m × 5-m samples were harvested at random distances on a 100-m transect. Each harvested square was trimmed to ensure that no overlapping panicles outside the frame were harvested. Grain yields were standardized to 14% moisture content unmilled paddy. In each field 20 quadrats of 50 cm × 50 cm were taken at random to record the number of panicles. The panicles from four of these quadrats were collected for an estimate of mean panicle weight.
Multi-location fertilizer and herbicide trial At the beginning of the 1982 wet season, 13 sites in farmers' fields were selected in deepwater areas of the central plain to assess responses to nitrogen and phosphorus fertilizers, and to herbicide for control of broadleaved weeds (Fig. 1 ). Samples of the surface soil (0-10 cm) from each site were collected for determination of pH (1:1 water), available phosphorus (Bray and Kurtz, 1945), and available nitrogen (Waring and Bremner, 1964). At each site a factorial trial with three factors in a randomized complete block was marked out after the rice was sown by the farmer. Plot size was 6 m × 6 m with three replications. Triple superphosphate was broadcast soon after rice emergence (either nil or 17.5 kg P / h a ) , and urea was broadcast at the onset of flooding, 6-12 weeks after emergence (either nil or 50 kg N / h a ) . The herbicide ioxynil/
267 2,4-D was applied 15-20 days after rice emergence for the control of broadleaved weeds (either nil or 1.0 kg a.i./ha). The sites were monitored for incidence of pests and diseases, with regular dissections of stems to assess stemborer damage by the method of Catling et al. (1984/85). Mean stem numbers were obtained 4-5 times during the period from preflood to harvest by taking 20 frame counts using 50-cm X 50-cm quadrats. At maturity a 1-m 2 sample was taken for yield components, and then the remainder of a 5-m X 5-m area of each plot was harvested for grain yields. The grain weight was standardized to 14% moisture content. RESULTS
Agronomic practices Some of the results from the 20-farmer survey in 1981 are shown in Table 1. Farm size ranged from 2.1 to 25.6 ha, but the larger farms were split up into many fields, with an average field size of about 2.4 ha. Sixteen of the farms were owned by the operator, and four were rented. Most soil preparation was done by contractors using 7-disc ploughs pulled by tractors of more than 65 horsepower. Only two of the farmers owned buffalo. Seven farmers owned small two-wheel tractors which were normally used for secondary tillage. Most fields were ploughed twice, but only occasionally was the second tillage used to cover the seed. Three of the farmers near Pitsanulok transplanted their crops. The rest of the fields were broadcast with dry seed, which was expected to germinate with the early rains. Broadcasting date ranged from mid-April to late June. Estimates of the maximum water depth in the previous year ranged from 30-340 cm. Both the shallowest and the deepest areas were in Pitsanulok province. The floods arrived from late June to early October depending on location and on distribution of rainfall. Floods are generally earliest in the southeast part of the central plain where rain tends to come earlier in the year. Farmers used herbicides only for broadleaved weeds. On the acid-sulphate soils of Nakhon Nayok and Prachinburi provinces, all farmers used some fertilizer and all included phosphate, but levels were low. Of the nine farmers who used fertilizer, four broadcast ammonium phosphate into standing water after arrival of the flood. Major pests were considered to be rats (listed by 16 farmers) and yellow stem borers (11 farmers), followed by crabs (5), brown plant hopper (3), and grasshoppers. Only three farmers used insecticides; stem borers cannot usually be controlled by chemicals. Additional data from the concurrent survey by the Statistics Sub-division are given in Table 2. More detailed information on methods, rice varieties and other aspects are given in the Thai-language report which was printed for local
268
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270 distribution (Anonymous, 1984 ). A total of 307 farm households growing deepwater rice were interviewed in the seven provinces shown.
Cropyields The average grain yields given in Table 2 for each province, derived from farmers' own records of area and production, ranged from 2.4 t / h a in Singburi to 1.2 t / h a in Prachinburi. The overall mean yield of 1.87 t / h a was very close to the 2-year average of 1.94 t / h a from sampling (Table 3). Crop sampling, however, also identified varieties. In 1981/1982 there were 18 different varieties in 30 fields, and in 1982/1983 there were 27 varieties in 63 fields. Mean yield was slightly higher in 1981/1982 than in 1982/1983. In 1981/1982 three fields gave samples averaging 3.5 t/ha, and two others more than 3.0 t/ha. The yields were a response by the varieties to the conditions under which they were grown, and do not necessarily show a difference in potential between varieties. Very low yield was often associated with very poor growing conditions such as drought and weeds, a n d / o r damage by rats, and in 1981 by ragged stunt virus infection. However, the high yields obtained by some varieties and in some locations indicate that the potential for deepwater rice is much higher than the average yields of approximately 1.9 t/ha. The distribution of varieties by location recorded during crop sampling in 1982/1983 is shown in Table 4. The provinces of Nakon Nayok, Ongkarak, Prachinburi and parts of Chachoengsao have acid soils and farmers there use different varieties than in other provinces. However, locality or district average water depth, topography, and farmer's preference also influence the distribution of deepwater rice varieties. The plain is generally very flat, but there is sufficient variation in local topography to make it worthwhile using varieties adapted to different water depths. Ten of the varieties were found in areas with maximum water depths greater than 150 cm, and most of these have good elongation capability. There is some overlap of varieties because maximum water depth varies from year to year, and farmers use a variety which can survive most years. However, as water gets very deep only a few varieties are suitable. Pin Gaew 56 was grown in three of the four fields with water depths expected to be greater than 200 cm. The month of maximum depth depends on location and is influenced by roads and water control schemes as well as the flow of water from the rivers. Harvest dates ranged from 30 November at P h a n o m Sarakam to 31 January at Bang Pa-In and Angthong. Fields drain at different times in different locations, and harvest date is affected by selection of varieties to mature just after the fields have drained. Chachoengsao and Prachinburi usually drain in early December. Yields were highest in Ang Thong province, and lowest in Suphanburi province where crops were severely affected by drought. Yields were also low on acid soils of Nakhon Nayok and Ongkarak.
271 TABLE 3 E s t i m a t e d yields of deepwater rices obtained from crop sampling on the central plain of T h a i l a n d Variety
1981/1982
1982/19831
Fields sampled
Mean yield { t / h a )
Fields sampled
Mean yield ( t / h a )
B a n Daeng Khao P u a n g Nak Puang T h o n g K h a o Nak Khao Tah Oht Khao Sa-art Khao Kwien Hak Pin Thong P i n Gaew 56 Khao M a Na Khao T a h Haeng K h a o P u a n g Glang H a Ruang Pan Thong Sang Kaset Ruang P r a T h a n Leb Mue N a h n g 111 Mali Luay Sam Ruang Garp Daeng Khao Sa Daeng No. 5 Nang Kiew J a m Pa Pey S a m Ruang Nak Chor Magawk Khao Kwien Hak Khao T h o n g Yawn Khao Mall Nak J a m Pa Nak P u a n g Malai Khao P u a n g H a h n g Moo
1 2 1 ---2 -3 -1 4 ----2 1 2 ---1 2 3 --1 1 1 1 1
3.53 3.48 2.77 ---1.64 -2.57 -1.02 3.04 ----1.25 2.48 2.11 ---0.69 2.03 1.51 --2.25 1.87 1.21 0.66 3.42
2 2 1 1 1 2 1 1 5 3 6 4 2 1 1 3 5 4 3 1 1 2 3 3 3 1 1 ------
2.89 2.86 2.78 2.66 2.60 2.51 2.44 2.40 2.36 2.34 2.30 2.23 2.18 2.15 1.96 1.49 1.45 1.42 1.42 1.39 1.35 1.09 0.96 0.95 0.88 0.59 0.06 ------
Number/Mean
30
2.18
63
1.83
~Varieties listed in order of yield.
In 1982/1983 from
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averaging
1.5 g t o 1.9 g / p a n i c l e
(overall mean 2.32 g). Seeds/panicle ranged from 36 to 173 (mean 88.7). I n 1 9 8 1 / 1 9 8 2 s t e m b o r e r s d a m a g e d o v e r 4 0 % o f t h e s t e m s s a m p l e d i n 12 (crop-cut)
fields. In the 24 fields sampled
age averaged
in 1982/1983
38%. For five of these, which included
(Table 4), stem dam-
the cultivars
Pin Gaew 56,
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274 Ban Daeng, Khao Sa-art and Mali Luay, where more than half of the stems were infested, yield losses of at least 20% are suspected.
Multi-location trial Site data for the multi-location trial with 13 sites established in 1982 are given in Table 5. The Ratchaburi site was abandoned after severe flood damage. Eight of the sites were affected by early drought. At Bang Pla Ma, drought continued through most of the preflood period, resulting in poor plant growth and low yields. The effects of fertilizer and herbicide treatments were limited at most sites by the growing conditions; consequently, treatments had no consistent effect on grain production, nor was there any correlation between grain yield and initial soil N or P content, or maximum water depth. Averages over all treatments (24 plots) of yield components from 1 m 2 and grain yields (25 m2/plot) are given in Table 6. Mean coefficients of variation were about 25% for yield components and 15% for grain yield. Sampling was very difficult, and a high variability between samples is common for deepwater rice as a result of field conditions (sequentially dryland, deeply flooded, and then drained) and growth habit, where very tall plants are moved by wind and water during flooding and then lie flat on the ground at harvest. However, yields calculated from panicle number and weight are mostly within 20% of measured yields, and the data show marked differences in components between sites. The extreme was Site 10, Ban Pong, which averaged only 24 panicles/ m 2, but compensated by very large panicles with an average weight of nearly 8 g. Weight per panicle tended to decrease as the number of stems increased from 60/m 2 to 120/m 2. Grain yield increased as dry weight increased to approximately 900 g / m 2. Harvest index was usually less than 0.2 if water depth was over 80 cm. The wide variation in early stem populations and the decline in stem number with time in samples from the farmers' fields adjacent to the experimental plots are shown in Fig. 2. In most cases the initiation of a rapid decline in stems coincided with the commencement of flooding. In nearly all fields the final number of stems was less than 100/m 2, irrespective of the initial population. None of the farmers' fields received fertilizer. Nitrogen topdressing increased yields at Sites 2, 4, 7 and 8. Yields at Bang Ban were 2.25 t / h a without N fertilizer, and 2.49 t / h a for 50 kg N / h a (P < 0.01 ); at Maharat yields were 2.13 and 2.37 t / h a ( P < 0 . 0 5 ) , and at Ban Sang 1.27 and 1.42 t / h a ( P < 0 . 0 5 ) . At Prachinburi, Amphur Muang, yields were 2.22 and 2.53 t / h a (P < 0.01) for nil and 50 kg N/ha, respectively. Measurements of yield components from 1-m 2 samples showed that the improved yield with N at Bang Ban was associated with increased total dry-weight and an increase in dry-weight per stem, but there were no significant differences between treatments for yield components at the other three sites where N increased yields.
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Fig. 2. Changes in number of stems/m 2 over time in farmers' yields adjacent to plots. Sites (numbered) are listed in Table 5. Stars show approximate date of onset of flood, and arrows time of maximum water depth. Thailand, wet season, 1982.
Nitrogen appeared to depress yield at Wang Noi, where yields were 1.43 t / h a for nil and 1.07 t / h a for 50 kg N / h a ( P < 0 . 0 1 ) . At Ban Pong (Site 10), application of P was associated with a 36% increase in both panicles/m 2 and total dry weight/m 2, but only at Site 13 did P application give a significant improvement in yield; this was at Pisanulok, where addition of P was associated with an increase in yield from 1.3 t / h a to 1.52 t / ha (P<0.01). Many farmers' varieties are considered unresponsive to fertilizer applications, even though vegetative responses to P, which give the plants a better chance of survival in years of high water levels, are commonly observed on the acid sulphate soils. Weeds recorded at each experimental site are listed in Table 7; other species may have been present outside the plot area (24 m × 36 m). Herbicide application was associated with a significant increase in yield only at Pitsanulok (Site 13) where the unsprayed plots yielded 1.30 t / h a and the sprayed plots 1.52 t / h a ( P < 0.01). The herbicide was applied 15-20 days after rice emergence, and was effective in controlling broadleaved weeds. Grasses were not controlled. The lack of response to herbicide at some sites may have been partly due to the encroachment of aquatic weeds onto sprayed plots later in the season, particularly Ipomoea aquatica. However, it appears that the severe environmental conditions were the dominant influence on production at several sites, with growth of both crop and weeds limited during much of the early part of the season.
278 TABLE 7 Weed species found in fields of a multi-location trial in deepwater rice, Thailand 1982 Site Number1
1
Soil pHbeforeflooding
4.7 4.5 4.3 4.4 4.8 3.8 4.3 4.6 4.7 5.7 7.0 5.0 4.9
Aeschynomene indica Aeschynomene aspera Alternanthera sessilis Amaranthus viridus Cyanotis axillaris Cyperus iria Cyperus procerus Cyperus rotundus Eclipta prostrata Eleocharis dulcis Fimbristylis dichotoma Fimbristylis miliacea Heliotropium indicum Ipomoea aquatica Ipomoea gracilis Melochia corchorifolia Pentapetes phoenicea Phyllanthus niruri Cynodon dactylon Echinochloa colona Hymenache pseudointerrupta Ischaemum barbatum Leersia hexandra Panicum cambogiense Panicum repens
Percent weedcover: Sprayed (20July) Unsprayed
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1Locationsas Table 5. aNot assessed. All of the sites were m oni t or ed for incidence of pests and diseases, and sites were visited 4-5 times. Before flooding there was minor damage to foliage from a leaf-eater complex of gryllids, hispa, flea beetle, whorl maggot, leaf-folder, thrip and leaf-miner; a few plants were damaged by gall midge. At Prajinburi (Site 8) 4.4% deadhearts were recorded in July, but the preflood overall average was only 0.8%. Yellow stem-borer built up rapidly in October, during late elongation and heading, to reach an average of 41% damaged stems and 4.1% whiteheads at harvest. R o o t - k n o t nematodes were found in several fields.
279 Thirty-eight percent of fields were affected by rice ragged stunt virus, but levels were less than in 1981; it was only severe at Ongkarak (site 6) where more than 5% of stems showed symptoms. During flooding, patches of stem-cutting by rats were noted in several fields. DISCUSSION Information from these studies reflects the fact that deepwater rice is grown in a very complex environment with many interacting factors. It has a long growing season of over 200 days, comprising an early rainfed period in which the crop is subjected to drought, followed by deep flooding, which gives a multitude of combinations which can affect growth and production. Positive or negative effects during the first part of the season can be nullified or reversed by events occurring in the later growth stages, so that the crop often appears unresponsive to treatments such as the application of fertilizer. The yield of deepwater rice is mainly determined by the number of panicles per unit area, a result of the production of stems in the pre-flood period, and the percentage survival of those stems during flooding. Pre-flood stem populations depend on of initial establishment, soil conditions, rainfall and nutrient effects on tillering and survival, and weed competition. Information on the dynamics of deepwater rice stem populations is sparse. Catling et al. (1982) reported maximum stand densities before flooding for local varieties in Bangladesh of about 220 tillers/m 2. The best fields in their study, which averaged over 3 t/ha, had a mean of only 109 panicles/m 2, a marked reduction from the initial stem population. For RD19, an upright, high-tillering modern variety of deepwater rice, Kupkanchankul et al. (1982) showed that it was possible to get up to 400 s t e m s / m 2 in early growth, with 220 paniclesff at harvest; for Leb Mue Nahng 111, a Thai traditional elongating deepwater rice, a high seed-rate of 600 seeds/m 2 gave 480 s t e m s / m 2 at 30 days after emergence (DAE)and 180 panicles/m 2 at harvest. However, for Leb Mue Nahng 111, 1/3 of the seed rate gave the same number of panicles and the same yield. Consequently, the decline in stem numbers from a high initial population is probably less important than the ability of plants to compensate for low initial plant populations by tillering. Field observations for our multi-location experiment indicated that initial establishment is reduced by sporadic rainfall after sowing, and that tillering is greatly reduced by drought conditions. It is for these reasons that farmers continue to use high seed-rates, even though experimental results have not shown significant yield differences between 60 and 120 kg of seed/ha (e.g., Sittyos and Kupkanchankul, 1983). The mean yields from both crop cuts and the multilocation trial were less than those obtained by crop-cut studies in Bangladesh by Catling et al. ( 1983 ), who reported a 4-year average yield of 2.3 t/ha. Thailand has a quite different system of deepwater rice farming from that of Bangladesh, particularly in crop-
280 establishment techniques. Flooding patterns also differ (Puckridge et al., 1988). In Bangladesh, land preparation consists of several passes with a plough, and up to eight harrowings with simple cattle-drawn implements to give a fine seedbed, whereas in Thailand farm size is larger, and a very rough seedbed results from one or two ploughings with tractor-drawn ploughs. In Thailand average seed rates are higher than in Bangladesh, and may compensate for the rough seedbed in plant establishment. Both cases show farmer adaptation to resources and environment. However, the distribution of yields between provinces suggests that adverse soil conditions are a main cause of lower yields in Thailand. Farmers' use of fertilizer is also a response to the environment. Although Khan and Vergara (1982) showed that application of basal N increased basal tiller number, generally the results from application of fertilizer to deepwater rice fields is unpredictable. Francis and Brackney {1982) pointed out that measurements of yield in deepwater rice fields have coefficients of variation of 30-40%; hence it is difficult to show yield differences. Also, fertilized plots are often more heavily damaged by rats than non-fertilized plots, leading to lower measured yield (Catling and Izlam, 1979). Fertilizer management in deepwater rice was reviewed by Puckridge and Thongbai (1988), who found that positive responses to N and P were most likely on acid sulphate soils such as those found in the Thai provinces of Prachinburi and Nakhon Nayok, in Kampuchea, and in Vietnam (Van Breemen and Pons, 1978). Many farmers in the eastern Thai provinces used fertilizer, whereas on the less-acid soils in the western part of the Central Plain fertilizer use was negligible. On acid sulphate soils, fertilizer affects both survival and productivity of a wide range of varieties (Wiengweera et al., 1988), but the farmers' practice of broadcasting into relatively deep water in these areas is less likely to improve survival than earlier application. Nitrogen-uptake studies have also shown that losses of N are small for deepwater rice on acid soils, with recovery of N in dry-matter of over 50% (Puckridge and Thongbai, 1988), hence the reasons for this practice need further examination, particularly in relation to other potential sources of N; for example, in flooded deepwater rice, the long submerged stems offer a larger biomass for colonization by aquatic microorganisms than rice in shallow-water fields. Kulasooriya et al. ( 1981 ) found a high rate of epiphytic N-fixing activity, mainly due to blue-green algae which they calculated could fix 10-20 kg N / h a per crop, and biological N sources may be partly responsible for the lack of N responses of the crop. Rainfall can be quite unevenly distributed in deepwater rice areas, and drought is quite common. In addition to affecting establishment and tillering, drought results in reduced height and internode elongation, so that the plants are more susceptible to submergence by rising flood water, and less responsive to fertilizer. From pot experiments, Vergara and Mazaredo (1979) found that, after 12 days of drought, the height of Leb Mue Nahng 111 following submer-
281 gence was only 44% of the height of unstressed plants. In addition, it is during the rainfed period that weeds are competing most vigorously with the young rice plants. Farmers use 2,4-D for the control of broadleaf weeds, but little is done to control grass weeds. Grasses are considered by farmers to be of little importance after the arrival of floodwater, provided that the depth is greater than 60 cm. However, open areas are quickly colonized by aquatic weeds such as Ipomea aquatica which, if not controlled, can spread rapidly across the surface of the water and can almost eliminate a rice crop. It has been extremely difficult to demonstrate yield improvements from weed-control experiments, because of the irregular distribution of weeds from season to season, and the effect on experiments of other factors such as rats, drought, flood, and the high variability that occurs in deepwater rice fields. Latitude, the soil and water environments, land preparation, and varietal requirements in deepwater rice areas of Thailand are very similar to those of Kampuchea and Vietnam, and there can be a direct exchange of technology between these countries when improvements in production techniques are made. At present this is particularly relevant to Kampuchea, where most of the specially adapted deepwater rices were lost due to war and population dislocation from 1970 to 1979. Both Vietnamese and Thai deepwater rices have been introduced or are being tested as replacements in Kampuchea (Puckridge, 1986). Thai varieties have also been successful in Indonesia and Burma, and have been some of the most promising introductions into African and Mexican deepwater rice areas. However, the results of the studies reported in this paper indicate that better characterisation of environments, and better analyses of the interaction of deepwater rice genotypes with the environment, are necessary before adequate prediction of performance and improvements in production will be obtained. ACKNOWLEDGEMENTS Assistance in data collection and field supervision was provided by Raywat Pattrasudhi, Panatda Bhekasut, Kachon Petchrit, Malee Tanasate, Decha Tuna, Lek Chankasem, Somsak Luangsirirat and Hathairat Leuangsodsai. Administrative support was given by Chai Prechachat, Prayote Charoendham and Soonton Naka. Chemical analyses were by Chackrapong Chermsiri, and data analyses by Saowanee Pisitphan and Phannee Panichagoon. The valuable support of all these researchers is gratefully acknowledged. REFERENCES Anonymous,1984. Technologyuse in deepwaterrice production. Statistical Analysis Sub-division, Planning and TechnicalDivision,Department of Agriculture,Bangkok,Thailand, 63 pp. (in Thai).
282 Bray, R.H. and Kurtz, L.T., 1945. Determination of total, organic and available forms of phosphorus in soils.Soil Sci.,59: 39-45. C atling, H.D., 1985. An agro-ecological characterization of the deepwater areas in the Chao Phya Basin of Thailand with a subdivision into five regions (unpublished). International Rice Research Institute, P.O. Box 933, Manila, The Philippines. Mimeo, 27 pp. Catling, H.D. and Islam, Z., 1979. Effect of fertilizeron traditional deepwater rice varieties in Bangladesh. In: Proc. 1978 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines, pp. 157-164. Catling, H.D., Islam, Z. and Alam, B., 1982. Stand density in deepwater rice and its relation to yielding abilityin farmers' fieldsin Bangladesh. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 179-188. Catling, H.D., Hobbs, P.R., Islam, Z. and Alam, B., 1983. Agronomic practices and yield assessments of deepwater rice in Bangladesh. Field Crops Res., 6: 109-132. Catling, H.D., Islam, Z. and Pattrasudhi, R., 1984/85. Seasonal occurrence of the yellow stem borer Scirpophaga incertulas (Walker) on deepwater rice in Bangladesh and Thailand. Agric. Ecosystems Environ., 12: 47-71. Escuro, P.B., U Ohn Kyaw and U Aung Kha, 1982. Status of deepwater rice varietal improvement in Burma. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 87-96. Francis, P. and Brackney, C.T., 1982. Adaptability testing of traditional deepwater rices in Bangladesh. In: Proc. 1981 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines, pp. 157-167. Hille RisLambers, D., 1986. Trip report Mexico, 13-26 June 1986 (unpublished). IRRI, P.O. Box 933, Manila, The Philippines, 19 pp. Kaida, Y., 1973. A subdivision of the Chao Phraya delta in Thailand based on hydrographical conditions. Southeast Asian Stud., 11: 403-413. Khan, M.R. and Vergara, B.S., 1982. Varietal difference in nitrogen uptake and utilization in deepwater rice cultivars. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 315-320. Khush, G.S., 1984. Terminology for rice growing environments. In: Terminology for Rice Growing Environments. IRRI, P.O. Box 933, Manila, The Philippines, pp. 5-10. Kulasooriya, S.A., Roger, P.A., Barraquio, W.L. and Watanabe, I., 1981. Epiphytic nitrogen fixation on deepwater rice. Soil Sci. Plant Nutr., 27: 19-27. Kupkanchanakul, T., Vergara, B.S. and Kupkanchanakul, K., 1982. Effect of agronomic practices on tillering and yield of deepwater rice. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 373386. Puckridge, D.W., 1986. Report on visit to Kampuchea, October 30-November 6, 1986 (unpublished). IRRI, P.O. Box 933, Manila, The Philippines. Mimeo, 9 pp. Puckridge, D.W. and Thongbai, P., 1988. Fertilizer management in deepwater rice. In: Proc. 1987 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines. Puckridge, D.W., Panichagoon, P. and Thongbai, P., 1988. Analysis of floodwater patterns. In: Proc. 1987 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines. Sittyos, P. and Kupkanchanakul, K., 1983. The effect of three different seed rates on grain yield of deepwater rice by broadcasting. Deepwater rice planning meeting, March 1983. Rice Research Institute, Department of Agriculture, Thailand, p. 16. Takaya, Y. and Thiramongol, N., 1982. Chao Phraya Delta of Thailand. Asian Rice-land inventory: a descriptive atlas No. 1. Center for Southeast Asian Studies, Kyoto University, Kyoto, Japan. Toure, A.I., Choudhury, M.A., Goita, M., Koli, S. and Paku, G.A., 1982. Grain yield and yield
283 components of deepwater rice in West Africa. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 103-111. Van Breemen, N. and Pons, L.J., 1978. Acid sulphate soils and rice. In: Soils and Rice. IRRI, P.O. Box 933, Manila, The Philippines, pp. 739-761. Van der Kevie, W. and Yenmanas, B., 1972. Detailed reconnaissance soil survey of southern central plain area. Soil Survey Division, Department of Land Development, Bangkok, Rep. SSR89. Vergara, B.S. and Mazaredo, A.M., 1979. Effect of presubmergence drought on internode elongation of deepwater rice. In: Proc. 1978 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines, pp. 41-44. Waring, S.A. and Bremner, J.M., 1964. Ammonium production in soil under waterlogged conditions as an index of nitrogen availability. Nature, 201 (No. 4922 ): 951-952. Wiengweera, A., Puckridge, D.W. and Bhekasut, P., 1988. Testing deepwater rice for response to nitrogen and phosphorus. In: Proc. 1987 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines.
263
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Factors Affecting D e e p w a t e r Rice in the Central Plain of Thailand D.W. PUCKRIDGE 1, H.D. CATLING 2, PRASAN VONGSAROJ a, SAMLEE BOONYAWIVATANA3, LAVAN NIYOMWIT3 and PONGMANEE THONGBAI 1
1International Rice Research Institute (IRRI), P.O. Box 9-159, Bangkok 10900 (Thailand) 2IRRI, P.O. Box 933, Manila (The Philippines) :~Dept. of Agriculture, Bangkhen, Bangkok 10900 (Thailand) (Accepted 13 June 1988)
ABSTRACT Puckridge, D.G., Catling, H.D., Vongsaroj, P., Boonyawivatana, S., Niyomwit, L. and Thongbai, P., 1989. Factors affecting deepwater rice in the central plain of Thailand. Field Crops Res., 19: 263-283. Deepwater rices from Thailand have been among the most promising lines tested in the deepwater areas of Africa, Burma, Indonesia, and Vietnam, and the effect of environmental factors and cultural practices on production in Thailand is relevant to those countries. In Thailand, approximately 800 000 ha of deepwater rice is grown in fields which are flooded to depths of 50 cm or more for over a month during the growing season. Most of this specially adapted rice is grown in three regions of the central plain. Dry seeds are broadcast on ploughed fields at the beginning of the wet season, and the crop grows under rainfed dryland conditions for about 3 months before floods arrive in July-August. The plants elongate to maintain foliage above the floodwater, which may be as deep as four m. The crop is harvested after the fields drain in December-January. Investigations were made to assess yields in farmers' fields, and to determine yield-limiting factors and crop responses to inputs. Farmers were interviewed to determine production practices, and fields were sampled to estimate yields. Samples from 30 fields gave an average yield of 2.18 t ha -1 (0.7-3.5 t ha -1) for the 1981/82 season, and from 63 fields in 1982/83 gave an average of 1.83 t ha 1 (0.1-2.9 t h a - 1). There were 32 different varieties. Maximum water depths ranged from 60 cm to 200 cm. Major pests were yellow stem-borers and rats. A multi-location factorial experiment with 13 sites tested the possibility of improving yields by nitrogen and phosphorus fertilizer, or by use of a herbicide spray to control broadleaved weeds. However, grain yields were increased by N only at four sites, by P at one site, and by herbicide spraying at one site. Major yield-limiting factors were drought and poor plant stands in the preflood period, and some flood damage. Better characterisation of the environment and of its interaction with genotypes is necessary before adequate prediction of performance and improvements in production will be obtained.
INTRODUCTION
Deepwater rice (Oryza sativa L. ), often called floating rice, is grown on approximately 11 million ha in valleys and deltas of South and Southeast Asia 0378-4290/89/$03.50
© 1989 Elsevier Science Publishers B.V.
264
where flooding to depths of from 50 to 400 cm occurs each year. The largest areas occur in northeastern India and Bangladesh, followed by Thailand, Vietnam, Kampuchea, and Burma. Deepwater rice has also been introduced into Africa, Indonesia and Mexico, and some of the most promising lines introduced into those countries, as well as into Burma and Vietnam, have been Thai (Escuro et al., 1982; Toure et al., 1982; Vo-Tong Xuan et al., 1982; Hille RisLambers, 1986). The work reported here has attempted to identify environmental factors and cultural practices which affect the yield of deepwater rice in Thailand, with the aim of extending this information to other areas where Thai germplasm has been successful. In Thailand, deepwater rice is grown on approximately 800 000 ha, 9% of the total wet-season rice area. Most of this naturally flooded area is located on the Central Plain, which stretches more than 400 km north from Bangkok and the Gulf of Thailand. Virtually all of the deepwater rice is grown in the five regions of the Central Plain shown in Fig. 1, but about 12 000 ha have been reported for northeast Thailand, and 9 000 ha in northern Thailand. Areas shown as having water depths greater than 50 cm but less than 100 cm can be defined as 'deep water', where mostly tall or submergence-tolerant varieties are grown, and areas with more than 100 cm of water as 'very deep water' where elongating or 'floating' rices are planted. The terms 'deep water' and 'very deep water' were defined by Khush {1984), while 'floating rice' is a commonly used term for elongating rices grown in more than 1 m of water. Some varieties can elongate enough to survive in 4 m of water. In this paper, deepwater rice is any rice adapted to water depths remaining over 50 cm for more than 1 month. In Thailand, dry seeds of deepwater rice are broadcast on ploughed fields at the beginning of the wet season, April-June. Soils of the central plains have mainly developed on marine and brackish water deposits, and a large part of the southern plain, particularly in the east, has acid sulphate soils with low productivity (Van der Kevie and Yenmanas, 1972 ). The majority of soils have clayey textures with a high content of fine particles. The northern flood plain has young alluvial soils of medium texture on riverine sediments. The rice grows under rainfed dryland conditions for about 3 months before the floods arrive in July or August. Researchers such as Takaya and Thiramongol (1982) and Kaida (1973) have reported on water depths and different types of deepwater rice in Thailand. The distribution was reassessed on an agro-ecological basis by Catling (1985). Floodwaters usually rise about 2-3 cm/day, but after heavy rains an increase of over 30 cm may occur within 24 h. Maximum water depths are attained in September or October, before flowering, and range from 60 to 150 cm over most of the area, but vary from year to year. In some parts, depths of over 300 cm occur. The crop is harvested after the fields drain in December-January. Thai experience could be useful in predicting the performance of Thai varieties introduced elsewhere, but there is little information available on pro-
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266 duction constraints in farmers' fields. Consequently, as a basis for research to develop new technology, it was considered necessary to determine farmer practices and current production levels in the deepwater rice areas, and to identify yield-limiting factors. This paper reports the results of surveys of farmers' agronomic practices in 1981, of sampling for crop yield in the two years 1981/ 1982 and 1982/1983, and of a multilocation experiment on the use of fertilizer and herbicides in 1982/1983. METHODS
Agronomic practices and crop yields In order to provide background information to a crop yield study, 20 farmers' fields were selected at random early in the growing season of 1981, and the farmers were questioned regarding their cultural practices, farm size, equipment, soil and flood conditions, pest problems, and methods of control of pests. Samples from these fields were subsequently included in the grain yield study. A concurrent survey of deepwater-rice areas by the Statistical Analysis Subdivision of the Department of Agriculture of Thailand obtained data from 307 farms. During the December-January harvest periods of 1981/82 and 1982/83, a total of 90 farmers' fields were sampled for yield in each of the main deepwater rice provinces. In each field, four separate 5-m × 5-m samples were harvested at random distances on a 100-m transect. Each harvested square was trimmed to ensure that no overlapping panicles outside the frame were harvested. Grain yields were standardized to 14% moisture content unmilled paddy. In each field 20 quadrats of 50 cm × 50 cm were taken at random to record the number of panicles. The panicles from four of these quadrats were collected for an estimate of mean panicle weight.
Multi-location fertilizer and herbicide trial At the beginning of the 1982 wet season, 13 sites in farmers' fields were selected in deepwater areas of the central plain to assess responses to nitrogen and phosphorus fertilizers, and to herbicide for control of broadleaved weeds (Fig. 1 ). Samples of the surface soil (0-10 cm) from each site were collected for determination of pH (1:1 water), available phosphorus (Bray and Kurtz, 1945), and available nitrogen (Waring and Bremner, 1964). At each site a factorial trial with three factors in a randomized complete block was marked out after the rice was sown by the farmer. Plot size was 6 m × 6 m with three replications. Triple superphosphate was broadcast soon after rice emergence (either nil or 17.5 kg P / h a ) , and urea was broadcast at the onset of flooding, 6-12 weeks after emergence (either nil or 50 kg N / h a ) . The herbicide ioxynil/
267 2,4-D was applied 15-20 days after rice emergence for the control of broadleaved weeds (either nil or 1.0 kg a.i./ha). The sites were monitored for incidence of pests and diseases, with regular dissections of stems to assess stemborer damage by the method of Catling et al. (1984/85). Mean stem numbers were obtained 4-5 times during the period from preflood to harvest by taking 20 frame counts using 50-cm X 50-cm quadrats. At maturity a 1-m 2 sample was taken for yield components, and then the remainder of a 5-m X 5-m area of each plot was harvested for grain yields. The grain weight was standardized to 14% moisture content. RESULTS
Agronomic practices Some of the results from the 20-farmer survey in 1981 are shown in Table 1. Farm size ranged from 2.1 to 25.6 ha, but the larger farms were split up into many fields, with an average field size of about 2.4 ha. Sixteen of the farms were owned by the operator, and four were rented. Most soil preparation was done by contractors using 7-disc ploughs pulled by tractors of more than 65 horsepower. Only two of the farmers owned buffalo. Seven farmers owned small two-wheel tractors which were normally used for secondary tillage. Most fields were ploughed twice, but only occasionally was the second tillage used to cover the seed. Three of the farmers near Pitsanulok transplanted their crops. The rest of the fields were broadcast with dry seed, which was expected to germinate with the early rains. Broadcasting date ranged from mid-April to late June. Estimates of the maximum water depth in the previous year ranged from 30-340 cm. Both the shallowest and the deepest areas were in Pitsanulok province. The floods arrived from late June to early October depending on location and on distribution of rainfall. Floods are generally earliest in the southeast part of the central plain where rain tends to come earlier in the year. Farmers used herbicides only for broadleaved weeds. On the acid-sulphate soils of Nakhon Nayok and Prachinburi provinces, all farmers used some fertilizer and all included phosphate, but levels were low. Of the nine farmers who used fertilizer, four broadcast ammonium phosphate into standing water after arrival of the flood. Major pests were considered to be rats (listed by 16 farmers) and yellow stem borers (11 farmers), followed by crabs (5), brown plant hopper (3), and grasshoppers. Only three farmers used insecticides; stem borers cannot usually be controlled by chemicals. Additional data from the concurrent survey by the Statistics Sub-division are given in Table 2. More detailed information on methods, rice varieties and other aspects are given in the Thai-language report which was printed for local
268
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270 distribution (Anonymous, 1984 ). A total of 307 farm households growing deepwater rice were interviewed in the seven provinces shown.
Cropyields The average grain yields given in Table 2 for each province, derived from farmers' own records of area and production, ranged from 2.4 t / h a in Singburi to 1.2 t / h a in Prachinburi. The overall mean yield of 1.87 t / h a was very close to the 2-year average of 1.94 t / h a from sampling (Table 3). Crop sampling, however, also identified varieties. In 1981/1982 there were 18 different varieties in 30 fields, and in 1982/1983 there were 27 varieties in 63 fields. Mean yield was slightly higher in 1981/1982 than in 1982/1983. In 1981/1982 three fields gave samples averaging 3.5 t/ha, and two others more than 3.0 t/ha. The yields were a response by the varieties to the conditions under which they were grown, and do not necessarily show a difference in potential between varieties. Very low yield was often associated with very poor growing conditions such as drought and weeds, a n d / o r damage by rats, and in 1981 by ragged stunt virus infection. However, the high yields obtained by some varieties and in some locations indicate that the potential for deepwater rice is much higher than the average yields of approximately 1.9 t/ha. The distribution of varieties by location recorded during crop sampling in 1982/1983 is shown in Table 4. The provinces of Nakon Nayok, Ongkarak, Prachinburi and parts of Chachoengsao have acid soils and farmers there use different varieties than in other provinces. However, locality or district average water depth, topography, and farmer's preference also influence the distribution of deepwater rice varieties. The plain is generally very flat, but there is sufficient variation in local topography to make it worthwhile using varieties adapted to different water depths. Ten of the varieties were found in areas with maximum water depths greater than 150 cm, and most of these have good elongation capability. There is some overlap of varieties because maximum water depth varies from year to year, and farmers use a variety which can survive most years. However, as water gets very deep only a few varieties are suitable. Pin Gaew 56 was grown in three of the four fields with water depths expected to be greater than 200 cm. The month of maximum depth depends on location and is influenced by roads and water control schemes as well as the flow of water from the rivers. Harvest dates ranged from 30 November at P h a n o m Sarakam to 31 January at Bang Pa-In and Angthong. Fields drain at different times in different locations, and harvest date is affected by selection of varieties to mature just after the fields have drained. Chachoengsao and Prachinburi usually drain in early December. Yields were highest in Ang Thong province, and lowest in Suphanburi province where crops were severely affected by drought. Yields were also low on acid soils of Nakhon Nayok and Ongkarak.
271 TABLE 3 E s t i m a t e d yields of deepwater rices obtained from crop sampling on the central plain of T h a i l a n d Variety
1981/1982
1982/19831
Fields sampled
Mean yield { t / h a )
Fields sampled
Mean yield ( t / h a )
B a n Daeng Khao P u a n g Nak Puang T h o n g K h a o Nak Khao Tah Oht Khao Sa-art Khao Kwien Hak Pin Thong P i n Gaew 56 Khao M a Na Khao T a h Haeng K h a o P u a n g Glang H a Ruang Pan Thong Sang Kaset Ruang P r a T h a n Leb Mue N a h n g 111 Mali Luay Sam Ruang Garp Daeng Khao Sa Daeng No. 5 Nang Kiew J a m Pa Pey S a m Ruang Nak Chor Magawk Khao Kwien Hak Khao T h o n g Yawn Khao Mall Nak J a m Pa Nak P u a n g Malai Khao P u a n g H a h n g Moo
1 2 1 ---2 -3 -1 4 ----2 1 2 ---1 2 3 --1 1 1 1 1
3.53 3.48 2.77 ---1.64 -2.57 -1.02 3.04 ----1.25 2.48 2.11 ---0.69 2.03 1.51 --2.25 1.87 1.21 0.66 3.42
2 2 1 1 1 2 1 1 5 3 6 4 2 1 1 3 5 4 3 1 1 2 3 3 3 1 1 ------
2.89 2.86 2.78 2.66 2.60 2.51 2.44 2.40 2.36 2.34 2.30 2.23 2.18 2.15 1.96 1.49 1.45 1.42 1.42 1.39 1.35 1.09 0.96 0.95 0.88 0.59 0.06 ------
Number/Mean
30
2.18
63
1.83
~Varieties listed in order of yield.
In 1982/1983 from
panicles were sampled
at 40 sites. Mean particle weight ranged
1.0 g t o 4 . 8 g, w i t h 5 0 % o f t h e s a m p l e s
averaging
1.5 g t o 1.9 g / p a n i c l e
(overall mean 2.32 g). Seeds/panicle ranged from 36 to 173 (mean 88.7). I n 1 9 8 1 / 1 9 8 2 s t e m b o r e r s d a m a g e d o v e r 4 0 % o f t h e s t e m s s a m p l e d i n 12 (crop-cut)
fields. In the 24 fields sampled
age averaged
in 1982/1983
38%. For five of these, which included
(Table 4), stem dam-
the cultivars
Pin Gaew 56,
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274 Ban Daeng, Khao Sa-art and Mali Luay, where more than half of the stems were infested, yield losses of at least 20% are suspected.
Multi-location trial Site data for the multi-location trial with 13 sites established in 1982 are given in Table 5. The Ratchaburi site was abandoned after severe flood damage. Eight of the sites were affected by early drought. At Bang Pla Ma, drought continued through most of the preflood period, resulting in poor plant growth and low yields. The effects of fertilizer and herbicide treatments were limited at most sites by the growing conditions; consequently, treatments had no consistent effect on grain production, nor was there any correlation between grain yield and initial soil N or P content, or maximum water depth. Averages over all treatments (24 plots) of yield components from 1 m 2 and grain yields (25 m2/plot) are given in Table 6. Mean coefficients of variation were about 25% for yield components and 15% for grain yield. Sampling was very difficult, and a high variability between samples is common for deepwater rice as a result of field conditions (sequentially dryland, deeply flooded, and then drained) and growth habit, where very tall plants are moved by wind and water during flooding and then lie flat on the ground at harvest. However, yields calculated from panicle number and weight are mostly within 20% of measured yields, and the data show marked differences in components between sites. The extreme was Site 10, Ban Pong, which averaged only 24 panicles/ m 2, but compensated by very large panicles with an average weight of nearly 8 g. Weight per panicle tended to decrease as the number of stems increased from 60/m 2 to 120/m 2. Grain yield increased as dry weight increased to approximately 900 g / m 2. Harvest index was usually less than 0.2 if water depth was over 80 cm. The wide variation in early stem populations and the decline in stem number with time in samples from the farmers' fields adjacent to the experimental plots are shown in Fig. 2. In most cases the initiation of a rapid decline in stems coincided with the commencement of flooding. In nearly all fields the final number of stems was less than 100/m 2, irrespective of the initial population. None of the farmers' fields received fertilizer. Nitrogen topdressing increased yields at Sites 2, 4, 7 and 8. Yields at Bang Ban were 2.25 t / h a without N fertilizer, and 2.49 t / h a for 50 kg N / h a (P < 0.01 ); at Maharat yields were 2.13 and 2.37 t / h a ( P < 0 . 0 5 ) , and at Ban Sang 1.27 and 1.42 t / h a ( P < 0 . 0 5 ) . At Prachinburi, Amphur Muang, yields were 2.22 and 2.53 t / h a (P < 0.01) for nil and 50 kg N/ha, respectively. Measurements of yield components from 1-m 2 samples showed that the improved yield with N at Bang Ban was associated with increased total dry-weight and an increase in dry-weight per stem, but there were no significant differences between treatments for yield components at the other three sites where N increased yields.
275
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277 No. of stems/m ~ 300
250
T
20C
15C
/_ 12
\
\
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5C
M
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I d
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Dote of stem count
Fig. 2. Changes in number of stems/m 2 over time in farmers' yields adjacent to plots. Sites (numbered) are listed in Table 5. Stars show approximate date of onset of flood, and arrows time of maximum water depth. Thailand, wet season, 1982.
Nitrogen appeared to depress yield at Wang Noi, where yields were 1.43 t / h a for nil and 1.07 t / h a for 50 kg N / h a ( P < 0 . 0 1 ) . At Ban Pong (Site 10), application of P was associated with a 36% increase in both panicles/m 2 and total dry weight/m 2, but only at Site 13 did P application give a significant improvement in yield; this was at Pisanulok, where addition of P was associated with an increase in yield from 1.3 t / h a to 1.52 t / ha (P<0.01). Many farmers' varieties are considered unresponsive to fertilizer applications, even though vegetative responses to P, which give the plants a better chance of survival in years of high water levels, are commonly observed on the acid sulphate soils. Weeds recorded at each experimental site are listed in Table 7; other species may have been present outside the plot area (24 m × 36 m). Herbicide application was associated with a significant increase in yield only at Pitsanulok (Site 13) where the unsprayed plots yielded 1.30 t / h a and the sprayed plots 1.52 t / h a ( P < 0.01). The herbicide was applied 15-20 days after rice emergence, and was effective in controlling broadleaved weeds. Grasses were not controlled. The lack of response to herbicide at some sites may have been partly due to the encroachment of aquatic weeds onto sprayed plots later in the season, particularly Ipomoea aquatica. However, it appears that the severe environmental conditions were the dominant influence on production at several sites, with growth of both crop and weeds limited during much of the early part of the season.
278 TABLE 7 Weed species found in fields of a multi-location trial in deepwater rice, Thailand 1982 Site Number1
1
Soil pHbeforeflooding
4.7 4.5 4.3 4.4 4.8 3.8 4.3 4.6 4.7 5.7 7.0 5.0 4.9
Aeschynomene indica Aeschynomene aspera Alternanthera sessilis Amaranthus viridus Cyanotis axillaris Cyperus iria Cyperus procerus Cyperus rotundus Eclipta prostrata Eleocharis dulcis Fimbristylis dichotoma Fimbristylis miliacea Heliotropium indicum Ipomoea aquatica Ipomoea gracilis Melochia corchorifolia Pentapetes phoenicea Phyllanthus niruri Cynodon dactylon Echinochloa colona Hymenache pseudointerrupta Ischaemum barbatum Leersia hexandra Panicum cambogiense Panicum repens
Percent weedcover: Sprayed (20July) Unsprayed
2
3
4
X
×
X
X
5
6"
7
8
9
X
10 11 12 13
× ×
×
X
X × ×
× ×
×
X × X X
×
X
X
X ×
× X
X X
X X X
X X X
X
X
X X X
X X X
X X X
X X
X
X X X
X
X
X X X
X X X
X
X
X X X
X
X
X
X
X
X
X
X
X
X
X
X
X × X
14 5 44 3 27 38 64 12
X
7 19 32 46 95 21 35 31 53 95
1Locationsas Table 5. aNot assessed. All of the sites were m oni t or ed for incidence of pests and diseases, and sites were visited 4-5 times. Before flooding there was minor damage to foliage from a leaf-eater complex of gryllids, hispa, flea beetle, whorl maggot, leaf-folder, thrip and leaf-miner; a few plants were damaged by gall midge. At Prajinburi (Site 8) 4.4% deadhearts were recorded in July, but the preflood overall average was only 0.8%. Yellow stem-borer built up rapidly in October, during late elongation and heading, to reach an average of 41% damaged stems and 4.1% whiteheads at harvest. R o o t - k n o t nematodes were found in several fields.
279 Thirty-eight percent of fields were affected by rice ragged stunt virus, but levels were less than in 1981; it was only severe at Ongkarak (site 6) where more than 5% of stems showed symptoms. During flooding, patches of stem-cutting by rats were noted in several fields. DISCUSSION Information from these studies reflects the fact that deepwater rice is grown in a very complex environment with many interacting factors. It has a long growing season of over 200 days, comprising an early rainfed period in which the crop is subjected to drought, followed by deep flooding, which gives a multitude of combinations which can affect growth and production. Positive or negative effects during the first part of the season can be nullified or reversed by events occurring in the later growth stages, so that the crop often appears unresponsive to treatments such as the application of fertilizer. The yield of deepwater rice is mainly determined by the number of panicles per unit area, a result of the production of stems in the pre-flood period, and the percentage survival of those stems during flooding. Pre-flood stem populations depend on of initial establishment, soil conditions, rainfall and nutrient effects on tillering and survival, and weed competition. Information on the dynamics of deepwater rice stem populations is sparse. Catling et al. (1982) reported maximum stand densities before flooding for local varieties in Bangladesh of about 220 tillers/m 2. The best fields in their study, which averaged over 3 t/ha, had a mean of only 109 panicles/m 2, a marked reduction from the initial stem population. For RD19, an upright, high-tillering modern variety of deepwater rice, Kupkanchankul et al. (1982) showed that it was possible to get up to 400 s t e m s / m 2 in early growth, with 220 paniclesff at harvest; for Leb Mue Nahng 111, a Thai traditional elongating deepwater rice, a high seed-rate of 600 seeds/m 2 gave 480 s t e m s / m 2 at 30 days after emergence (DAE)and 180 panicles/m 2 at harvest. However, for Leb Mue Nahng 111, 1/3 of the seed rate gave the same number of panicles and the same yield. Consequently, the decline in stem numbers from a high initial population is probably less important than the ability of plants to compensate for low initial plant populations by tillering. Field observations for our multi-location experiment indicated that initial establishment is reduced by sporadic rainfall after sowing, and that tillering is greatly reduced by drought conditions. It is for these reasons that farmers continue to use high seed-rates, even though experimental results have not shown significant yield differences between 60 and 120 kg of seed/ha (e.g., Sittyos and Kupkanchankul, 1983). The mean yields from both crop cuts and the multilocation trial were less than those obtained by crop-cut studies in Bangladesh by Catling et al. ( 1983 ), who reported a 4-year average yield of 2.3 t/ha. Thailand has a quite different system of deepwater rice farming from that of Bangladesh, particularly in crop-
280 establishment techniques. Flooding patterns also differ (Puckridge et al., 1988). In Bangladesh, land preparation consists of several passes with a plough, and up to eight harrowings with simple cattle-drawn implements to give a fine seedbed, whereas in Thailand farm size is larger, and a very rough seedbed results from one or two ploughings with tractor-drawn ploughs. In Thailand average seed rates are higher than in Bangladesh, and may compensate for the rough seedbed in plant establishment. Both cases show farmer adaptation to resources and environment. However, the distribution of yields between provinces suggests that adverse soil conditions are a main cause of lower yields in Thailand. Farmers' use of fertilizer is also a response to the environment. Although Khan and Vergara (1982) showed that application of basal N increased basal tiller number, generally the results from application of fertilizer to deepwater rice fields is unpredictable. Francis and Brackney {1982) pointed out that measurements of yield in deepwater rice fields have coefficients of variation of 30-40%; hence it is difficult to show yield differences. Also, fertilized plots are often more heavily damaged by rats than non-fertilized plots, leading to lower measured yield (Catling and Izlam, 1979). Fertilizer management in deepwater rice was reviewed by Puckridge and Thongbai (1988), who found that positive responses to N and P were most likely on acid sulphate soils such as those found in the Thai provinces of Prachinburi and Nakhon Nayok, in Kampuchea, and in Vietnam (Van Breemen and Pons, 1978). Many farmers in the eastern Thai provinces used fertilizer, whereas on the less-acid soils in the western part of the Central Plain fertilizer use was negligible. On acid sulphate soils, fertilizer affects both survival and productivity of a wide range of varieties (Wiengweera et al., 1988), but the farmers' practice of broadcasting into relatively deep water in these areas is less likely to improve survival than earlier application. Nitrogen-uptake studies have also shown that losses of N are small for deepwater rice on acid soils, with recovery of N in dry-matter of over 50% (Puckridge and Thongbai, 1988), hence the reasons for this practice need further examination, particularly in relation to other potential sources of N; for example, in flooded deepwater rice, the long submerged stems offer a larger biomass for colonization by aquatic microorganisms than rice in shallow-water fields. Kulasooriya et al. ( 1981 ) found a high rate of epiphytic N-fixing activity, mainly due to blue-green algae which they calculated could fix 10-20 kg N / h a per crop, and biological N sources may be partly responsible for the lack of N responses of the crop. Rainfall can be quite unevenly distributed in deepwater rice areas, and drought is quite common. In addition to affecting establishment and tillering, drought results in reduced height and internode elongation, so that the plants are more susceptible to submergence by rising flood water, and less responsive to fertilizer. From pot experiments, Vergara and Mazaredo (1979) found that, after 12 days of drought, the height of Leb Mue Nahng 111 following submer-
281 gence was only 44% of the height of unstressed plants. In addition, it is during the rainfed period that weeds are competing most vigorously with the young rice plants. Farmers use 2,4-D for the control of broadleaf weeds, but little is done to control grass weeds. Grasses are considered by farmers to be of little importance after the arrival of floodwater, provided that the depth is greater than 60 cm. However, open areas are quickly colonized by aquatic weeds such as Ipomea aquatica which, if not controlled, can spread rapidly across the surface of the water and can almost eliminate a rice crop. It has been extremely difficult to demonstrate yield improvements from weed-control experiments, because of the irregular distribution of weeds from season to season, and the effect on experiments of other factors such as rats, drought, flood, and the high variability that occurs in deepwater rice fields. Latitude, the soil and water environments, land preparation, and varietal requirements in deepwater rice areas of Thailand are very similar to those of Kampuchea and Vietnam, and there can be a direct exchange of technology between these countries when improvements in production techniques are made. At present this is particularly relevant to Kampuchea, where most of the specially adapted deepwater rices were lost due to war and population dislocation from 1970 to 1979. Both Vietnamese and Thai deepwater rices have been introduced or are being tested as replacements in Kampuchea (Puckridge, 1986). Thai varieties have also been successful in Indonesia and Burma, and have been some of the most promising introductions into African and Mexican deepwater rice areas. However, the results of the studies reported in this paper indicate that better characterisation of environments, and better analyses of the interaction of deepwater rice genotypes with the environment, are necessary before adequate prediction of performance and improvements in production will be obtained. ACKNOWLEDGEMENTS Assistance in data collection and field supervision was provided by Raywat Pattrasudhi, Panatda Bhekasut, Kachon Petchrit, Malee Tanasate, Decha Tuna, Lek Chankasem, Somsak Luangsirirat and Hathairat Leuangsodsai. Administrative support was given by Chai Prechachat, Prayote Charoendham and Soonton Naka. Chemical analyses were by Chackrapong Chermsiri, and data analyses by Saowanee Pisitphan and Phannee Panichagoon. The valuable support of all these researchers is gratefully acknowledged. REFERENCES Anonymous,1984. Technologyuse in deepwaterrice production. Statistical Analysis Sub-division, Planning and TechnicalDivision,Department of Agriculture,Bangkok,Thailand, 63 pp. (in Thai).
282 Bray, R.H. and Kurtz, L.T., 1945. Determination of total, organic and available forms of phosphorus in soils.Soil Sci.,59: 39-45. C atling, H.D., 1985. An agro-ecological characterization of the deepwater areas in the Chao Phya Basin of Thailand with a subdivision into five regions (unpublished). International Rice Research Institute, P.O. Box 933, Manila, The Philippines. Mimeo, 27 pp. Catling, H.D. and Islam, Z., 1979. Effect of fertilizeron traditional deepwater rice varieties in Bangladesh. In: Proc. 1978 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines, pp. 157-164. Catling, H.D., Islam, Z. and Alam, B., 1982. Stand density in deepwater rice and its relation to yielding abilityin farmers' fieldsin Bangladesh. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 179-188. Catling, H.D., Hobbs, P.R., Islam, Z. and Alam, B., 1983. Agronomic practices and yield assessments of deepwater rice in Bangladesh. Field Crops Res., 6: 109-132. Catling, H.D., Islam, Z. and Pattrasudhi, R., 1984/85. Seasonal occurrence of the yellow stem borer Scirpophaga incertulas (Walker) on deepwater rice in Bangladesh and Thailand. Agric. Ecosystems Environ., 12: 47-71. Escuro, P.B., U Ohn Kyaw and U Aung Kha, 1982. Status of deepwater rice varietal improvement in Burma. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 87-96. Francis, P. and Brackney, C.T., 1982. Adaptability testing of traditional deepwater rices in Bangladesh. In: Proc. 1981 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines, pp. 157-167. Hille RisLambers, D., 1986. Trip report Mexico, 13-26 June 1986 (unpublished). IRRI, P.O. Box 933, Manila, The Philippines, 19 pp. Kaida, Y., 1973. A subdivision of the Chao Phraya delta in Thailand based on hydrographical conditions. Southeast Asian Stud., 11: 403-413. Khan, M.R. and Vergara, B.S., 1982. Varietal difference in nitrogen uptake and utilization in deepwater rice cultivars. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 315-320. Khush, G.S., 1984. Terminology for rice growing environments. In: Terminology for Rice Growing Environments. IRRI, P.O. Box 933, Manila, The Philippines, pp. 5-10. Kulasooriya, S.A., Roger, P.A., Barraquio, W.L. and Watanabe, I., 1981. Epiphytic nitrogen fixation on deepwater rice. Soil Sci. Plant Nutr., 27: 19-27. Kupkanchanakul, T., Vergara, B.S. and Kupkanchanakul, K., 1982. Effect of agronomic practices on tillering and yield of deepwater rice. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 373386. Puckridge, D.W., 1986. Report on visit to Kampuchea, October 30-November 6, 1986 (unpublished). IRRI, P.O. Box 933, Manila, The Philippines. Mimeo, 9 pp. Puckridge, D.W. and Thongbai, P., 1988. Fertilizer management in deepwater rice. In: Proc. 1987 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines. Puckridge, D.W., Panichagoon, P. and Thongbai, P., 1988. Analysis of floodwater patterns. In: Proc. 1987 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines. Sittyos, P. and Kupkanchanakul, K., 1983. The effect of three different seed rates on grain yield of deepwater rice by broadcasting. Deepwater rice planning meeting, March 1983. Rice Research Institute, Department of Agriculture, Thailand, p. 16. Takaya, Y. and Thiramongol, N., 1982. Chao Phraya Delta of Thailand. Asian Rice-land inventory: a descriptive atlas No. 1. Center for Southeast Asian Studies, Kyoto University, Kyoto, Japan. Toure, A.I., Choudhury, M.A., Goita, M., Koli, S. and Paku, G.A., 1982. Grain yield and yield
283 components of deepwater rice in West Africa. In: Proc. 1981 Int. Deepwater Rice Workshop, 2-6 November 1981, Bangkok, Thailand. IRRI, P.O. Box 933, Manila, The Philippines, pp. 103-111. Van Breemen, N. and Pons, L.J., 1978. Acid sulphate soils and rice. In: Soils and Rice. IRRI, P.O. Box 933, Manila, The Philippines, pp. 739-761. Van der Kevie, W. and Yenmanas, B., 1972. Detailed reconnaissance soil survey of southern central plain area. Soil Survey Division, Department of Land Development, Bangkok, Rep. SSR89. Vergara, B.S. and Mazaredo, A.M., 1979. Effect of presubmergence drought on internode elongation of deepwater rice. In: Proc. 1978 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines, pp. 41-44. Waring, S.A. and Bremner, J.M., 1964. Ammonium production in soil under waterlogged conditions as an index of nitrogen availability. Nature, 201 (No. 4922 ): 951-952. Wiengweera, A., Puckridge, D.W. and Bhekasut, P., 1988. Testing deepwater rice for response to nitrogen and phosphorus. In: Proc. 1987 Int. Deepwater Rice Workshop. IRRI, P.O. Box 933, Manila, The Philippines.