8.간단관개.pdf499.5KB

  Rice (Oryza sativa L.) is one of the most important food crops in Korea. Rice production consumes upto 80% of the total irrigated fresh water resources in Korea (Choi et al., 2004). Generally, paddy field is maintained flooded during most of rice growing period except for midsummer drainage. This continuous flooding irrigation method showed the lower efficiency of water use for rice production due to water losses as a result of percolation and seepage (Bouman, 1994). To increase water productivity under increasing scarcity of water resources, intermittent irrigation has been developed as a water-saving technique and adopted in many countries such as China, Bangladesh, and India (Bouman and Tuong, 2001; Xiaoping et al., 2004).

  Different from ‘broken irrigation’ included in conventional irrigation regime, intermittent irrigation allows the paddy soil to dry out to some water potential before re-watering (Peng et al., 1994). Intermittent irrigation methods are focusing on saving water by reducing hydrostatic pressure and minimize water loss by seepage and percolation during the whole or specific growing period (Tuong et al., 2005).

  It has been reported that, when compared with continuously submerged conditions, application of intermittent irrigation can maintain or even increase grain yield because of the enhancement in root growth and grain-filling rate (Xiaoping et al., 2004; Zhang et al., 2009; Zhang et al., 2012). On the other hand, there are reports that intermittent irrigation reduces grain yield due to the loss of nitrogen, reduction in shoot biomass, and a shortened grain-filling period (Belder et al., 2004). The inconsistent response of rice yield, water inputs, and water productivity in intermittent irrigation is mainly due to environmental conditions, especially soil type, ground water level, rice variety, and soil water potential. So it is important how to control drought stress in the intermittent irrigation system (Choi et al., 1999; Tuong et al., 2005).

 Water productivity in rice cultivation depends not only on the amount of irrigated water but also the degree on soil water potential because rice is sensitive to water stress. Rice is one of the sensitive crops to soil water condition and particularly to soil moisture deficiency (Lu et al., 2000). The effect of a water deficit on grain yield depends on the duration and timing of such a deficit. Yield decreases markedly when plants suffer from water stress at panicle formation stage and at flowering stage due to decreasing number of grains (Tajima, 1995). 

  The intermittent irrigation technology has been researched extensively. However, the effect of intermittent irrigation on the yield, plant growth, and water use under wet-hillseeding cultivation methods remains to be elucidated. Therefore, this study was conducted in order to clarify the effects of intermittent irrigation in machine transplanting (TP) and wet-hill-seeding (WHS), as well as on crop growth and grain yield.

MATERIALS AND METHODS

  Field experiments were conducted at research filed of National Institute of Crop Science (NICS), Iksan, Korea (35˚56’ N, 126˚55’ E, altitude 3 m) during 2009 and 2010. The soil plowed layer was fine silty of Jeonbuk series of paddy soil and the physicochemical properties are analyzed according to RDA (2003). The experiments were arranged in split-plot design with three replications having unit plot size 8 m × 10 m (80 m²). Two cultivation methods, transplanting (TP) and wet-hill-seeding (WHS), and two irrigation regimes, conventional irrigation (CI) and intermittent irrigation (II), formed the treatment variables. Plastic waved panels and soil hill were installed in the field in order to hydraulically isolate the plots.

  The high-grain quality medium-late maturing Japonica rice variety Hopum was used in the studies. The field was plowed and harrowed followed by flooding for well puddling and proper leveling for TP and WHS. Pre-germinated rice seeds were directly seeded on 20 May in WHS plots, while 30-day old seedlings were transplanted by machine on 3 June both the study years. In TP, 3 ~ 4 seedling per hill were transplanted in planting density of 23.8 hills/m² (30 cm × 14 cm). In WHS, the seeds were dropped in hills on the puddle paddy surface with the same spacing to TP.

  Chemical fertilizers N, P₂O₅, and K₂O were applied as 90-45-57 kg/ha for both cultivation methods. Fertilizer N was applied three times at a ratio of 50-30-20% at land preparation, active tillering, and panicle initiation stage, respectively. Whole P₂O₅ and 70% K₂O were applied as basal and the remaining 30% of K₂O was applied at panicle initiation stage. Irrigation regime II was imposed 20 days after machine transplanting and 30 days after direct seeding to 2 weeks before harvest. For CI, irrigation water was applied as continuous flooding condition except midsummer drainage between maximum tillering stage and panicle initiation stage. Irrigation water for intermittent irrigation was applied when the soil died to field capacity moisture condition. The level of standing water for both irrigation regimes reached at a maximum of 7 cm depth.

  Evapotranspiration (EVT) was measured using a lysimeter of 30 cm diameter with the bottom set in the topsoil, in which some rice plants are growing. Percolation (DP) rate was measured using a cylinder with a cover, and evaporation was measured with the bottom set in the topsoil excluding rice plant by putting between rows and hills. A set of three cylinders was installed for three replications. Runoff (R) from a plot over a season was calculated by following equation:

 R = I + WL − EVT − DP

  where, R is the loss by runoff, I is the depth of irrigation, WL is the current water level, EVT is the amount of water lost due to evapotranspiration, and DP is the percolation loss. Meteorological data were recorded automatically by an AWS (automated weather system: Campbell Scientific Inc., US) that had been set up adjacent to the experimental field.

  At 30 days after transplanting, 10 hills having uniform growth were marked in each plot which was used for measuring for height for the whole growing period. Milled rice yield was measured from an area of 3.6 m² of each plot. The milled rice yield was calculated at 14% moisture level. When rough rice grain reached at proper maturity (around 18% moisture content) a randomly selected area of 0.45 m² was hand harvested to determine the yield components following standard procedures.

  Analysis of variance was performed using R v.2.11.0 (R Development Core Team, 2008). For mean comparison between the irrigation treatments and cultivation methods, Duncan’s multiple rage test was employed at 0.05 probability level.

Table 1. Physicochemical properties of the soil in experimental fields.

RESULTS AND DISCUSSION

Weather condition

  Figure 1 shows the seasonal changes in mean air temperature, precipitation, and sunshine hours during rice growth period in Iksan in 2009 and 2010. Weather conditions in the two study years were generally favorable to rice growth and grain production. The mean air temperature in 2010 was higher than in 2009. Effective precipitation from May to September in 2009 and 2010 were 445 mm and 504 mm, respectively. In 2009, precipitation in July was the highest for the year, but lower in following three months than the previous 10 years average. In 2010, there was no rain except a few days in June so that almost all the water needed in the field was supplied by irrigation. Precipitation in August was higher than the previous 10 years average, however the sunshine hour was similar during the ripening period.

Fig. 1. Monthly mean temperature, precipitation, and sunshine hours during rice growth period in Iksan.

Irrigation and water productivity

  The amounts of irrigation water in II plots were 22% and 24% lower than that in CI plots of machine transplanting and wet-hill-seeding cultivation, respectively (Table 2). In 2009, more water was irrigated than in 2010 due to the less precipitation. Machine transplanting consumed more irrigated water than wet-hill-seeding in both irrigation regimes. It has been reported that intermittent application of irrigation water saved 25 ~ 50% of the irrigation water as compared to the continuous submergence of fields, without any adverse effects on rice yields (Tajima, 1995; Zhang et al., 2009).

Table 2. The amount of irrigation water, milled rice yield, and water productivity for machine transplanting (TP) and wet-hill-seeding (WHS) as affected by irrigation methods in rice paddy field.

  Water productivity is defined as the amount of grain produced per unit volume of water input (Tuong et al., 2005). Different from Toung et al.(2005), the amount of milled rice yield (kg/10a) per irrigated water (mm) was used as water productivity in this study. The water productivities of intermittent irrigation in the present experiment were 0.73 in transplanting cultivation and 0.79 in wet-hill-seeding, which were similar to the result from Choi et al. (2004) in Korea. The water productivity was increased by 26% in machine transplanting plots and by 30% in wethill- seedling plots. Milled rice yields from II plots were slightly reduced; however the amount of irrigation water were much lower than CI plots. Therefore, the highest efficiency of water use was achieved in the II plots in wet-hillseeding.

  The field-level water productivity varies widely ranging from 0.1 to 2.2, and most of the data were less than 1.4 (Tuong et al., 2005). Increasing in water productivity of those experimental data was resulted from decreasing water input rather than increasing yield. However, higher water productivities over 1.4 with relatively high yield were achieved by combination of factors such as hybrid rice, clay soil, and shallow ground water table in China (Bouman and Tuong, 2001; Tuong et al., 2005).

Crop growth and yield

  Plant height and culm length were higher in machine transplanting plots (Table 3). For each cultivation method, plant height, culm length, and panicle length did not differ significantly among the plots exposed to different irrigation regimes (Table 3). However, tiller numbers at heading stage in II plots were higher than plants in CI plots in both irrigation methods. Choi et al. (2004) also reported the tendency of increase in tiller number affected by water depth during sallow intermittent irrigation. Reduction in the number of tiller under the CI regime was mainly attributed to less oxygen supply that inhibits tillering and growth of tiller buds.

Table 3. Comparison of plant height and tiller number at heading stage, and culm and panicle length at ripening stage as affected by irrigation methods in rice paddy field.

  Milled rice yield in machine transplanting plots showed more milled rice yield than wet-hill-seeding (Table 4). Among the yield component, spikelet number per panicle was thought to be the major factor for the yield difference. CI and II plots for each cultivation method were not significantly different in milled rice yield, but the yield from II showed 1 ~ 2% lower than that from the CI plots. Panicle number, spikelet number per panicle, ripened grain ratio, and 1,000-grain weight from CI and II plots in each cultivation method showed no significant differences.

Table 4. Effect of intermittent irrigation on grain yield and yield components of different cultivation methods.

  Reduction in milled rice yield in the present experiment is relatively less than the number of intermittent irrigation experiments that reviewed by Bouman and Tuong (2001). Grain yield normally decreased by 0 ~ 12% when the soil is kept just at saturation, whereas yield reductions of 10 ~ 40% occur when soil water potentials at 10 ~ 20 cm depth are allowed to reach −10 to − 30 kPa before re-applying water. Lu et al. (2000) and Choi et al. (2006) reported that the panicle number and spikelet number per panicle were significantly decreased when soil water potential drops below −10 kPa. These significant differences caused grain yield decreasing and the results imply that the irrigation regimes affect on all reproductive stages of the crop growth. So the duration of drainage or re-watering timing is important to avoid water stress in intermittent irrigation.

Milled rice quality

  Table 5 shows the head rice quality as affected by irrigation regimes. Head rice ratio, protein and amylose content in machine transplanting plots showed no significant difference from wet-hill-seeding. However, a little higher ratio of head rice in machine transplanting plots than wethill- seeding was resulted from the significant lower ratio of broken rice. The head rice ratio in the CI and II plots for each cultivation method were not significantly different. Chalky rice from CI plots in machine transplanting showed higher than that in II plots, however, II plots showed contrary results in wet-hill-seedling plots. Chalky rice is occurred when grains are exposed to high temperatures during development (Yamakawa et al., 2007) and less tiller number is seemed to reduce chalky grain in deep irrigation system (Hayashi et al., 2011). To understand different effect of irrigation regimes on chalky rice, it is supposed to check the weather condition and plant growth status together. Protein and amylose content showed no significant differences between CI and II. Above results were similar to the report from Zhang et al. (2009) that post-anthesis AWD regime applied during grain filling of rice can increase milled rice yield and quality by enhancing the grain-filling rate and grain weight of later flowering inferior spikelets.

Table 5. Effect of intermittent irrigation on physicochemical characteristics of milled rice of different cultivation methods.

  In conclusion, intermittent irrigation could save water input and increase water productivity without any significant negative impacts on rice growth, milled rice yields and quality. The intermittent irrigation practice is thought to be appropriate water management technique in watershort and even in abundant or adequate regions.