Wudpecker Journal of Agricultural Research Vol. 2(4), pp. 108 - 114, April 2013

ISSN 2315-7259 2013 Wudpecker Journals

Impact of rainwater management on growth and yield of rainfed lowland rice Tilahun-Tadesse F.1*, Nigussie-Dechassa R.2, Wondimu Bayu3, Setegn Gebeyehu4 1

2

Amhra Region Agricultural Research Institute, P.O.Box 08, Bahir Dar, Ethiopia. Haramaya University, Department of Plant Sciences, P.O.Box 138, Dire Dawa, Ethiopia. 3 ICARDA, Ethiopia. 4 Ethiopian Institute of Agricultural Research, Ethiopia. *Corresponding author: [email protected]. Accepted 22 March 2013

Continuous flooding of rice from emergence to maturity is believed to suppress rice growth and productivity. A field experiment was conducted in Fogera plain, northwestern Ethiopia, during the rainy season (June-October) in 2010 and 2011 to determine appropriate water management practices for rainfed lowland rice production. Ten water management treatments were studied in RCB design with three replications. The water management treatments included continuous flooding, draining water after every 15 days and re-flooding after one day, draining water after every 15 days and re-flooding after two days , draining water after every 15 days and re-flooding after three days , draining water after every month and re-flooding after one day , draining water after every month and re-flooding after two days , draining water after every month and re-flooding after three days , draining water after every one and a half month and re-flooding after one day , draining water after every one and a half month and reflooding after two days and draining water after every one and a half month and re-flooding after three days . Data on leaf area at heading, plant height, thousand seeds weight, and grain and aboveground biomass yields were collected and analyzed. Leaf area index (LAI), Crop Growth Rate (CGR), Net Assimilation Rate (NAR) and harvest index (HI) were computed. Results of the experiment indicated that with continuous flooding, LAI, CGR, NAR, plant height, number of productive tillers, number of filled spiklets, grain yield and biomass yield were highly depressed but improved when drainage and aeration were practiced. Compared to continuous flooding, a grain yield increment of 26 % was obtained due to draining and re-flooding the water from 15-days to one month interval. It is concluded that the productivity of rain-fed lowland rice was depressed in response to continuous flooding whilst it was enhanced in response to draining and re-flooding the water at least every month. Key words: Rain-fed, lowland, continuous, flooding, draining.

INTRODUCTION Rice (Oryza sativa L.) is the foremost staple food for more than 50% of the world’s population. It is estimated that by the year 2025, farmers in the world should produce about 60% more rice than at present to meet the food demands of the expected world population at that time (Thakur et al., 2011). Rice cultivation is a recent phenomenon in Ethiopia. The cultivation has started in a number of regions in the country and has been progressing steadily (MoARD, 2010). Generally, rice has great potential and can play a critical role in contributing to food and nutritional security, income generation, poverty alleviation and socio-economic growth of Ethiopia. The production of rice in Fogera Plain of northwestern Ethiopia has been increasing rapidly. The

number of farmers growing rice, area covered with rice, and its production has increased from year to year (Mulugeta, 1999; Tesfaye et al., 2005). A rain-fed lowland production ecosystem is the main feature of the area. For generations, rice has been regarded as an aquatic plant that grows better under continuous flooding (Kassam et al., 2011). However, according to Shi et al. (2002) and Nyamai et al. (2012) continuously flooded rice plant roots do not develop fully and are abnormal. The roots degenerate prematurely and become less functional and effective, taking up less soil nutrients and water. Moreover, under anaerobic soil conditions, the soil biota is less numerous and less diverse (Kassam et al., 2011; Nyamai et al., 2012). The aerobic bacteria and fungi that

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are able to fix nitrogen, solubilize phosphorus and provide other benefits to plants cannot function under such conditions; nor can mycorrhizal fungi provide their various services (Kassam et al., 2011). According to Rahman and Ando (2012), various kinds of water management methods such as mid-season drainage, delayed flooding, shallow water management, intermittent irrigation, alternate wetting and drying systems, etc should be practiced by farmers the adverse effects of continuous flooding on rice and making the roots of the plant healthy. Balasubramanian and Palaniappan (2007) reported that drainage at maximum tillering stage stimulates vigorous root growth of and checks the development of ineffective tillers. After conducting an experiment on three different rice water management systems (flooded, intermittent irrigation, and dry cultivation), Shi et al. (2002) concluded that under intermittent irrigation, where fields were irrigated after at least 3 days without ponded water, yields were 8 to 10% higher than under continuous flooded conditions. Drainage and intermittent irrigation implies that water is drained until the soil surface is exposed to air, after which irrigation water is reintroduced. McHugh, (2002) also found that grain yields were 6.7 tha-1 for alternate wet dry irrigation and 5.9 tha-1 for continuously flooded fields. Results of the study suggest that, by using alternate wet and dry irrigation practices, farmers can increase grain yields while reducing irrigation water demand. The rate of drainage and the interval between the cycles vary with soil characteristics and weather conditions (Yoshida, 1981). Farmers in Fogera plain have the experience of draining rice fields at some intervals (personal observation). However, impact of drainage and timing on the growth and yield of rain-fed lowland rice in Fogera plain has not been studied in detailed and there is no any recommendation in this regard. Therefore, this study was conducted to study and determine the appropriate water management practices for improved rice production in the Fogera plain of northwestern Ethiopia. MATERIALS AND METHODS Experimental site The study was conducted at Fogera plain in northwestern Ethiopia during the 2010 and 2011 cropping seasons. Fogera plain is located at 130 19’ N latitude, 370 03’ E longitude, and at an altitude of 1815 m above sea level. Based on ten years data (2001-2011), the area had mean 0 minimum and maximum temperatures of 13.5 C and 0 26.1 C, respectively during the main cropping season (June to October). Rainfall is uni-modal, falling from June to October, and amounts to 1205 mm. The soil is Vertisol with a clay content of 71.25%. It is slightly acidic (pH

5.90) and the 20cm soil horizon contains 0.22% total N, 12.64ppm available P (Olsen), 0.93cmol(+)kg1 exchangeable K, 3% organic carbon, and 52.9 cmol (+) kg-1 CEC. According to Bernard (1993), the total N and available P contents of the soil are medium, while the organic matter content is low. According to Roy et al. (2006), the exchangeable K content and CEC are high. Planting material A rice variety called X-Jigna was used as a test crop. The variety matures in 130 days, which means it takes medium time of maturity. It is also medium in height (102 cm). Treatments and experimental design The treatments consisted of the following 10 water management practices: 1) Continuous flooding (W1) 2) Draining water every 15 days and re-flooding after one day (W2) 3) Draining water every 15 days and re-flooding after two days (W3) 4) Draining water every 15 days and re-flooding after three days (W4) 5) Draining water every month and re-flooding after one day (W5) 6) Draining water every month and re-flooding after two days (W6) 7) Draining water every month and re-flooding after three days (W7) 8) Draining water every one and a half months and re-flooding after one day (W8) 9) Draining water every one and a half months and re-flooding after two days (W9) 10) Draining water every one and a half months and re-flooding after three days (W10). The experiment was laid in randomized complete block design with three replications. Gross and net plot sizes were 4 m x 5 m and 3m x 4m, respectively, with distances of 1m between adjacent plots and 2 m between adjacent blocks. Experimental procedures Soil analysis Composite soil samples were collected from each block from the depth of 0 to 30 cm before planting. The samples were air-dried, ground to pass through a 2 mm sieve. The samples were analyzed for selected physico-

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chemical properties, namely, organic carbon, total N, soil pH, available phosphorus (P), available K, cation exchange capacity (CEC), and texture. Organic carbon content of the soil was determined by the volumetric method (Walkley and Black, 1984) as described in Food and Agriculture Organization of the United Nations (FAO) guide to laboratory establishment for plant nutrient analysis (FAO, 2008). Total soil N was analyzed by Micro-Kjeldahl digestion method with sulphuric acid (Jackson, 1962). The pH of the soil was determined using 1:2.5 (weight/volume) soil samples to water ratio using a glass electrode attached to a digital pH meter. Cation exchange capacity was measured after saturating the soil with 1M ammonium acetate (NH4OAc) and displacing it with 1M NaOAc (Chapman, 1985). Available P was extracted by the Olsen method (Olsen et al., 1954), and P analyzed using spectrophotometer. Particle size distribution was done by the hydrometer method according to FAO (2008). To determine exchangeable K in the soil, the soil samples were extracted with 0.5N ammonium-acetate at pH 7.0 and the exchangeable potassium was determined with a flame photometer according to Hesse (1971). Sowing and fertilizer application Rice seed was broadcasted at the rate of 140 kg ha-1. Fertilizers were applied to all plots equally at the rates of 69 kg N ha-1 and 23 kg P2O5 ha-1. Other agronomic management practices were practiced as per the recommendations. Data collection and measurement Data on leaf area at heading was measured and calculated following the method of Yoshida (1981): 2

Leaf area (cm ) = L × W × K Where; L is leaf length, W is maximum width of the leaf and K is a correction factor of 0.75. Leaf area index (LAI) was also calculated by employing the formula of Yoshida (1981):

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and Where; A is area of land, is change in Dry matter, is time variations in days, LA is total leaf area per unit area of land. -2 -1 CGR is expressed as g dry matter m land area day and -2 -1 NAR is expressed as g dry matter m leaf area day (Ahmad et al., 2009). Data on plant height, thousand seeds weight, and grain and aboveground biomass yields were collected from the net plot area at maturity. Data on plant basis were recorded from five randomly sampled plants within the harvestable area in each plot. Harvest index (HI) was calculated as the ratio of grain yield to aboveground biomass yield. Grain yield was adjusted to 14% moisture content. Statistical analysis The data were subjected to analysis of variance using SAS software (SAS Institute, 2003). Differences among treatment means were delineated using the least significant difference test at 0.05 alpha level. RESULTS Soil Organic carbon and total nitrogen contents of soils of both sites were found to be medium to high according to Landon (1991), showing considerable potential of the soil to supply N to plants through mineralization during the growing season. The CEC value of the experimental soil is high according to Hazelton and Murphy (2007), indicating high cation retention and exchange ability for good crop growth. The exchangeable potassium content of the soil is high according to Hazelton and Murphy (2007). Therefore, the nutrient could not have been a factor limiting plant growth and yield at the study sites. The total and available P contents of the soil were, however, medium. Therefore, nitrogen and phosphorus fertilizers were applied to all plots at equal rates of 69 kg -1 -1 N ha and 23 kg P2O5 ha , respectively. Effect of water management on the rice crop

Crop Growth Rate (CGR) and Net Assimilation Rate (NAR) for the duration from planting to heading were computed using the equations developed by Hunt (1978) as cited by Ahmad et al. (2009):

Water management significantly affected most of the rice yield components except number of unfilled spikeletes plant-1, 1000 seeds weight, and HI (Table 1). LAI, CGR and NAR significantly responded to water management

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Table 1. Mean squares of the analysis of variance for the effects of water management on rice growth and yield parameters at Fogera plain in 2010 and 2011.

Growth parameters Leaf Area Index Crop Growth Rate Net Assimilation Rate Plant height Number of productive tillers Number of unproductive tillers -1 Number of filled spiklets plant -1 Number of unfilled spikelets plant 1000 seeds weight Grain yield Biomass yield Harvest Index

Water management treatment 1.11* 67.196* 1.799* 36.099* 1157.856* 211.348* 280.3* 99.985NS 47.867NS 0.275* 11.232* 0.003NS

Error Mean Square 0.427 3.421 0.722 13.807 248.678 91.626 101.989 49.496 69.744 0.066 3.266 0.002

Table 2. Effect of water management on LAI at heading and Crop Growth Rate (CGR) of rice at Fogera in 2010 and 2011.

Water Management

Leaf Area Index

Continuous flooding Draining water every 15 days and re-flooding after one day Draining water every 15 days and re-flooding after two days Draining water every 15 days and re-flooding after three days Draining water every month and re-flooding after one day Draining water every month and re-flooding after two days Draining water every month and re-flooding after three days Draining water every one and a half months and re-flooding after one day Draining water every one and a half months and re-flooding after two days Draining water every one and a half months and re-flooding after three days CV (%)

2.7 A 4.7 A 4.2 A 4.1 ABC 3.8 A 4.2 AB 4.0 BC 2.9 ABC 3.6 AB 3.9 17.14

(Table 1). Lower LAI was recorded in the continuously flooded rice (W1) and in the rice which was drained every one and a half month and re-flooded after one day (W8). Rice in the other treatments had the highest LAI (Table 2). Similarly CGR and NAR were significantly lower in the continuously flooded rice and in the rice drained every one and half month and re-flooded after one day (Tables 2 and 3). Plant height varied with the variation in water management (Table 1). Statistically shorter heights, 88.2 cm and 89.1 cm, were obtained in response to W1 and W8 water management treatments, respectively (Table 3). Though numerically taller plant height (97 cm) was recorded with W2, heights in the other water management treatments were also in statistical parity with this value (Table 3). Significant differences were observed in the number of productive tillers m-2 due to the water management treatments (Table 1). Higher numbers of productive tillers m-2 were observed with all treatments except for W1 and W8 which gave the lowest numbers of productive tillers. The number of filled spiklets plant-1 showed statistical difference owing to the water management treatments (Table 1). The lowest numbers of filled spiklets plant-1, 99.7 and 102, were recorded to W1 and W8, respectively

C

CGR (g dry matter m -1 land area day ) E 7.5 A 21.4 AB 19.8 AB 19.5 D 12.4 CD 15.1 BC 18.2 E 8.7 D 13.0 D 15.0 12.28

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(Table 4). However, the other water management treatments resulted in statistically comparable numbers of filled spiklets plant-1 (Table 4). Results revealed significant differences in grain yield due to the different water management treatments (Table 1) where the lowest grain yields (2.77 and 2.78 t ha-1) were recorded for W1 and W8, respectively (Table 5). W2 and W7 resulted in the highest grain yield of 3.5 t ha-1. However, W3, W4, W5, and W6 resulted in grain yields that were in statistical parity with each other (Table 5). Above ground biomass yield also responded differently to the different water management treatments (Table 1) where the lowest biomass yields of 7.1 and 7.2 t ha-1, respectively, were recorded for W1 and W8. However, all other treatments produced aboveground biomass yields that were higher than the aboveground biomass yields obtained for W1 and W8 (Table 5). Discussion The results of this study revealed that continuous and prolonged flooding resulted in the lowest LAI, CGR, NAR and productive tillers. Consistent with the results of this

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Table 3. Effect of water management on Net Assimilation Rate (NAR) and plant height of rice at Fogera plain in 2010 and 2011.

Water Management Continuous flooding Draining water every 15 days and re-flooding after one day Draining water every 15 days and re-flooding after two days Draining water every 15 days and re-flooding after three days Draining water every month and re-flooding after one day Draining water every month and re-flooding after two days Draining water every month and re-flooding after three days Draining water every one and a half months and re-flooding after one day Draining water every one and a half months and re-flooding after two days Draining water every one and a half months and re-flooding after three days CV (%)

NAR (g dry matter -2 -1 m leaf area day ) C 2.8 AB 4.6 AB 4.7 A 4.8 BC 3.3 ABC 3.5 AB 4.6 C 2.9 ABC 3.6 ABC 3.9 22.07

Plant height (cm) B

88.2 A 96.4 A 96.5 A 95.7 AB 93.3 A 97.0 A 96.2 B 89.1 AB 92.8 AB 91.8 13.9

Table 4. Effect of water management on the number of productive tillers and filled spiklets of rice at Fogera plain in 2010 and 2011.

Water Management Continuous flooding Draining water every 15 days and re-flooding after one day Draining water every 15 days and re-flooding after two days Draining water every 15 days and re-flooding after three days Draining water every month and re-flooding after one day Draining water every month and re-flooding after two days Draining water every month and re-flooding after three days Draining water every one and a half months and re-flooding after one day Draining water every one and a half months and re-flooding after two days Draining water every one and a half months and re-flooding after three days CV (%)

study, Lin et al. (2011) and Thakur et al. (2011) reported that intermittent irrigation compared with continuous flooding promoted higher LAI. In this study compared to continuous flooding, a 33 to 74% increment in LAI was observed with all treatments except W8. Similarly Lin et al. (2011) reported a 5.7 to 11.4% increase in LAI with intermittent irrigation. Thakur et al. (2011) also reported a higher value of CGR with aerating rice fields by draining the flood water for some time as compared to continuous flooding. The results of this experiment also indicated that plant height was negatively affected by prolonged flooding. Similar to this observation, Thakur et al. (2011) stated that rice plants grown under alternate wetting and drying were 22 and 24% taller than rice plants grown under continuous flood. Tillering is the result of continuous root development (through adventitious roots) which under aerated soil moisture regime remained active, whilst under continuous flooding it degenerated significantly and became minimized and hampered (Thankur et al., 2011). The lower number of productive tillers in the continuous flooded rice in the current study could be associated with the lack of aeration and degeneration of the roots. In line with this result Thakur et al. (2011) reported doubling in

Number of -2 productive tillers m B 154.3 A 209.0 A 208.3 A 206.7 A 197.7 A 204.0 A 207.0 B 162.3 A 198.3 A 196.7 18.11

Number of filled -1 spiklets plant C 99.7 A 124.0 A 123.3 A 122.0 AB 117.7 A 122.7 A 120.7 BC 102.0 AB 119.3 ABC 116.3 19.06

the number of tillers under aerated rice field as compared to continuous flooding. Nyamai et al. (2012) also reported improved rice tiller growth with alternate flooding and drying as compared to continuous flooding. Zhang et al. (2010) and Thakur et al. (2011) reported that the percentage of filled grains significantly increased under alternate wetting and drying condition as compared to under continuous flooding, which is in agreement to the results of the current study. Some farmers in Fogera plain are aware of the negative impacts of continuous flooding on rice yield. In the current study, it was confirmed that prolonged flooding led to the production of lower rice biomass and grain yields. In support of this result, Zhang et al. (2010) reported a 6.6% increase in aboveground biomass yield with alternate wetting and drying compared to continuous flooding. In this study grain yield penalties of 26.3% and 25.9% were observed with W1 and W8 water treatments compared to W2 and W7 water management treatments. Consistent with this result, Nyamai et al. (2012) reported a 71% yield increase with alternate flooding and drying over continuous flooding. Similarly, Thakur et al. (2011) reported rice yield increase of 25 to 50% in a noncontinuous flooding water management. Lin et al. (2011) also reported a 10.5 to 11.3% grain yield increase under

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Table 5. Effect of water management on grain yield and above ground biomass yield of rice at Fogera plain in 2010 and 2011.

Water Management Continuous flooding Draining water every 15 days and re-flooding after one day Draining water every 15 days and re-flooding after two days Draining water every 15 days and re-flooding after three days Draining water every month and re-flooding after one day Draining water every month and re-flooding after two days Draining water every month and re-flooding after three days Draining water every one and a half months and re-flooding after one day Draining water every one and a half months and re-flooding after two days Draining water every one and a half months and re-flooding after three days CV (%)

intermittent water application (aerobic irrigation) compared to continuous flooding which they attributed to the increase in the number of grains per panicle with aerobic irrigation. Rice yield and yield components were depressed in response to prolonged flooding. This indicates that the flooded rice needs to be drained at least once in a month. Perhaps the most important principle of alternate flooding and draining is active aeration of the soil (Nyamai et al., 2012). With continuous flooding, the gas exchange between soil and atmosphere and the diffusion of oxygen dissolved in water is affected by having a water layer covering anaerobic soil during flooding (Lin et al., 2011). Rahman and Ando (2012) described that continuous flooding caused the soil to become increasingly anaerobic with low redox potential which led to adverse effects on root development and activity, such as reduction in the number and diameter of lateral roots, root respiration, root damage and rots. Kassam et al. (2011) also reported that rice plant roots that were grown under hypoxic soil conditions did not fully develop and were abnormal. The roots that grew degenerated prematurely, so that they became less functional and effective, taking up less soil nutrients and water as the roots died back (Kassam et al., 2011). According to Rahman and Ando (2012), at about the time of the 45th day before heading, the soil in a field under the flooded condition became short of oxygen, causing an abnormal fermentation of organic matter in soil and producing harmful organic acid or hydrogen sulfides, which consequently inflicted damages on roots. Thakur et al. (2011) in their study reported that the proportion of roots that were brown or black (nonfunctional and decayed) was found to be higher in continuously flooded plots compared with aerated rice fields. Chapagain and Yamaji (2010) also reported that before the flowering stage, the average proportion of whitish (functional) and black (non-functional) roots was 74:26 under alternate flooding and drainage management; conversely, in continuously flooded plots, it was 46:54. These adverse effects on roots caused

Grain yield -1 (t ha ) D 2.77 A 3.50 AB 3.47 ABC 3.43 ABCD 3.13 AB 3.47 A 3.50 D 2.78 BCD 3.03 CD 3.00 18.0

Above ground -1 biomass yield (tha ) B 7.1 A 12.8 A 13.1 A 12.6 A 10.8 A 11.8 A 12.5 B 7.2 A 10.6 A 10.4 16.43

reductions in stomatal conductance, photosynthesis, leaf longevity and yield. According to Thakur et al. (2011), rice soil aerating practice not only induces greater root growth, but also enhances root activity. Root systems in aerated rice enhanced nutrient uptake (Thakur et al., 2011) while continuously submerged paddy fields had impaired root development thus reduced nutrient uptake. Rahman and Ando (2012) suggested that supplying air into the soil by draining the flooded water at some intervals is the only method to make the roots healthy. Aerobic conditions are healthy for increased soil microbial activities, which further induced increased breakdown and subsequent release of nutrients available for plant uptake within the rhizosphere (Nyamai et al., 2012). Kassam et al. (2011) reported less numerous and less diverse soil biota under anaerobic soil conditions while greater populations of beneficial soil biota under aerated rice soil management conditions. Kassam et al. (2011) indicated that aerobic bacteria and fungi that are able to fix N, solubilize P, and provide other benefits to plants cannot function under continuously flooded conditions; nor can mycorrhizal fungi provide their various services. Conclusion In this study, it was observed that rice yield components and grain yields were depressed in response to continuous flooding. The rice crop performed better in growth and produced higher grain yields when the flood water was drained and the soil was aerated for one to three days. It could, thus, be concluded that rice fields need to be drained at least once a month for one to three days to enhance the yields of the crop and food security in the region. REFERENCES Ahmad A, Iqbal S, Ahmad S, Khaliq T, Nasim W, Husnain

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