Irrig Sci (2005) DOI 10.1007/s00271-005-0005-9
O R I GI N A L P A P E R
Shuqin Wan Æ Yaohu Kang
Effect of drip irrigation frequency on radish (Raphanus sativus L.) growth and water use
Received: 16 May 2005 / Accepted: 28 June 2005 Springer-Verlag 2005
Abstract Irrigation frequency is one of the most important factors in drip irrigation scheduling, and a proper irrigation frequency can establish moderate moist and oxygen conditions in the root zone throughout the crop period. Field experiments on the effects of irrigation frequency on radish growth and water use were carried out in 2001 and 2002. The experiment included six irrigation frequencies: once every day, once every 2 days, once every 3 days, once every 4 days, once every 6 days and once every 8 days. There was no significant difference among the six treatments on radish development and yield, but significant differences in radish roots distribution and market quality were found. Radishes irrigated once every 3 days had well-developed roots throughout the crop period, the lowest cracking rate and the least number of radishes of Grade 3. The observation results of lysimeter in 2002 showed that radish evapotranspiration decreased as irrigation frequency decreased, and the general changing tendency of 2-day ET of high irrigation frequency was related to that of 2day evaporation. It is recommended that radish irrigation frequency should be once every 3 days and the irrigation amount should be estimated according to the evaporation of 20 cm diameter pan in the North China Plain.
Introduction Radish (Raphanus sativus L.) is an important root vegetable and is widely planted in China. It is a short Communicated by J. Ayars S. Wan Æ Y. Kang (&) Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographical Sciences and Natural Resource Research, Chinese Academy of Sciences, 11 A, Datun Road, Anwai, Beijing 100101, China E-mail:
[email protected] Tel.: +86-10-64856516 Fax: +86-10-64856516
duration crop with high growth rate and sensitive to water stress. The deficiency and overabundance of soil water do harm to its yield and quality (Singh and Cheema 1972; Park and Fritz 1982; Barker et al. 1983). Therefore, a frequent, uniform supply of water is extremely important for its growth, yield and quality. Drip irrigation, a modern irrigation method, can readily establish a nearly constant water regime in the root zone (Beese et al. 1982), and ensure plants growing under proper soil water for the optimum yield and size. Drip irrigation management is based on the frequent replenishment of water loss by evapotranspiration (ET). There is varying agreement over the effect of irrigation frequency on crop water use. Goldberg et al. (1971) indicated that the high irrigation frequency could reduce evaporation and deep percolation, and establish a favorable soil moisture and oxygen condition in the root zone throughout the crop period. Smasjtrla et al. (1985) pointed out that to minimize deep percolation and to maintain nearly constant high soil water potential, high frequency (multiple applications per day) irrigations should be recommended. Whereas some scholars figured out that practicing irrigation water management with minimal plant water stress by maintaining a high soil moisture content between irrigations can lead to significant deep percolation losses (Levin et al. 1979b). Meshkat et al. (2000) concluded that an excessively high irrigation frequency could cause the soil surface to remain wet and the first stage of evaporation to persist most of the time, and resulted in more water loss. Findings from Goldberg and Shmueli (1970) indicated that yields of cucumber (Cucumis sativus L.) and melon (Cucumis melo L.) planted in sandy soil would be reduced if irrigation frequencies were beyond one day. Bucks et al. (1974) experimented on clay soil showing that the yields of cabbage (Brassica oleracea L.) would drop by the increase in irrigation frequency. Results provided by Levin et al. (1979a) on the similar clay soil illustrated that different irrigation frequencies (once every day, twice every week and once every week) had no distinct effects on apple (Malus pumila Mill.) yield.
Radin et al. (1989) indicated that the relationship between water and cotton (Gossypium herbaceum L.) was highly dependent on the frequency of irrigation when the fruit load was heavy, but was generally independent of irrigation frequency before and after the period. Trials conducted by Oktem et al. (2003) suggested that among 2-, 4-, 6- and 8- irrigation frequencies, a 2-day irrigation frequency, with 100% ET water application was optimal for sweet corn (Zea mays L.) grown in semi-arid regions. Potato (Solanum tuberosum L.) was subjected to six irrigation frequency treatments (1-, 2-, 3-, 4-, 6- and 8irrigation frequencies) to evaluate the effects of several irrigation frequencies on potato yield, ET and water use efficiency (WUE) by Kang et al. (2004) and the results showed that potato yield, ET and WUE increased as irrigation frequency increased, and the highest yield, ET and WUE values were achieved with an irrigation frequency of once a day. The objectives of this study are: (1) to measure the effect of drip irrigation frequency on radish growth, yield, water use and WUE; and (2) to define the basis for irrigation scheduling of drip-irrigated radish and water resource planning in the North China Plain.
Materials and methods Experimental site Field experiments were conducted at Luancheng Agroecosystem Station (LAES), Chinese Academy of Sciences. LAES is located in Luancheng County, Hebei Province (Latitude: 3753¢N; Longitude: 11441¢E; 50 m above sea level). Average annual precipitation is about 480 mm, mainly concentrated from July to September. The spring and early summer are normally quite dry. The dominant soil is silt loam with an average bulk density of 1.53 g/cm3, and organic matter content in the tillage layer is about 11.2%. Field soil water capacity (gravity content) is about 22.5%. The soluble mineral content of groundwater is less than 0.5 g/l. The water table is about 28 m deep and groundwater contribution to the root zone is therefore negligible. Experimental design The experiments included six irrigation frequency treatments in 2001 and a reference and six irrigation frequency treatments in 2002. The six irrigation frequency treatments in 2001 and 2002 were as follows: (1) once every day (F1), (2) once every 2 days (F2), (3) once every 3 days (F3), (4) once every 4 days (F4), (5) once every 6 days (F6), and (6) once every 8 days (F8). In 2001, the irrigation quantity for F1 was adjusted daily to maintain the soil matric potential at 20 cm depth immediately under drip emitter close to 25 kPa. Though the irrigation quantity for F1 was adjusted daily in 2001, when the daily ET was great, the daily irrigation
quantity could not completely meet radish water consumption. So in 2002, in order to determine irrigation quantity for F1 per day, a reference treatment (R) was devised. The R treatment was designed to control the soil matric potential at 20 cm depth immediately under drip emitter higher than 25 kPa. All the treatments were replicated three times and they followed a complete randomized block design. Each treatment plot was a submain unit of a drip irrigation system comprising a flow meter, a valve and a pressure gauge at the entrance of the unit to control the operating pressure and measure the irrigation volume. Thin-wall drip tape (Chapin Watermatics) with 0.3 m emitter spacing and a flow rate of 1.12 l/h at the operating pressure of 0.042 MPa was placed on the center of raised beds. Irrigation management In both years, irrigation for F1 was applied daily, unless the soil matric potentials of F1 were too high after rain. In 2001, the average irrigation quantity for F1 was about 2.5 mm per day and adjusted daily to maintain the soil matric potential at 20 cm depth immediately under drip emitter was close to 25 kPa. In 2002, the irrigation amount per day for F1 was equal to the ET value of the previous day of R treatment, which was measured by the lysimeter. The irrigation of R treatment was applied only when the soil matric potential at 20 cm depth immediately under drip emitter was close to 25 kPa, and the average irrigation amount was about 2.5 mm per time. In both years, irrigation amount for F2, F3, F4, F6 and F8 was the cumulative values of F1. Agronomic practices In 2001 and 2002, about 37.5 m3/ha well-rotted cow manure was uniformly applied to all plots before field was ploughed. About 34 days later, 1 kg carbamide and 1.25 kg compound fertilizer (monoammonia phosphate) were uniformly applied to each plot when the soil was bedded. The total applications of N, P2O5 and K2O were 182, 71 and 52 kg/ha, respectively. The soil was disced and bedded 0.8 m apart and 0.15 m high. Every drip irrigation plot contained seven beds, and the area of each plot was 5.6·6 m2. Radishes were double-row planted on each bed with row spacing of 0.3 m and interplant spacing of 0.25 m (Fig. 1). The two radish varieties are both planted in autumn, and most of their characteristics are alike. Seeds of radish cv. ‘Dahongpao’ and ‘Mantanghong’ were planted on July 31 and August 17 during 2001 and 2002, respectively. After emergence, seedlings were thinned to leave only one seedling at each location maintaining a plant population of approximately 100,000 plant/ha. Radishes were harvested on October 19 and November 9 in 2001 and 2002, respectively.
so there was adequate depth for the roots. The topsoil of the inner tank was shaped to the same forms as field beds, and at the bottom of the inner tank, a pipe serving as a drainage outlet connected the tank to the outer tank. Four radishes were cultivated in each tank with a density of 100,000 plants/ha equal to the field. The drip tapes for the beds were installed across the lysimeters for irrigation. There was a moveable electric weighing system to weigh the lysimeters one at a time. The lysimeter in R was weighed every day, and others were weighed once every two days. Twenty centimeter diameter pan evaporation over canopy (EW20) and weather data
Fig. 1 Placement of tensiometers for each experimental treatment
In 2002, a 20-cm diameter evaporation pan was installed over radish canopy in plot R on September 15 (29 days after seeding). The starting height of the evaporation pan was 15 cm above the ground and was adjusted with the growth of radish. On October 17 (61 days after seeding), the pan reached height of 50 cm above the ground, and was kept at this height till the harvest of radish. Pan evaporation was observed at 8:00 AM daily. The meteorological data were obtained from LEAS weather station. Radish growth
Observation and equipments Soil matric potential In 2001, one set of mercury tensiometers with 30 sensors was installed in F1 treatment to observe soil matric potential distribution. In 2002, another six sets of mercury tensiometers were installed in F2, F3, F4, F6, F8 and R treatments. Each set of mercury tensiometer included 30 sensors and the sensors placement was the same for all treatments. There were five series of sensors in the vertical transect perpendicular to the drip tape at five horizontal distances (0, 10, 20, 30, and 40 cm) and six vertical soil depths (10, 20, 30, 50, 70 and 90 cm) (Fig. 1). After radish establishment, the tensiometer at 20 cm depth immediately under drip emitter in R treatment was observed every 2 h during the daytime in order to determine the irrigation time. Radish water use In 2002, for each treatment, one weighing lysimeter was installed in the center of one of the radish plots to measure water use of each treatment. Each lysimeter consisted of an inner tank for crop cultivation and an outer tank for protection and drainage reservoir. The volume of the inner tank was 0.36 m3 (0.8 m·0.5 m·0.9 m), and a filtering layer of coarse sand and gravel, 0.15 m thick, was overlain by a repacked soil profile of 0.7 m. The rooting depth of radishes is generally less than 0.3 m under drip irrigation
Three representative plants were randomly selected and fixed in one plot of each treatment for leaf area measurement at 10-day intervals during radish-growing season in 2001 and 2002. Three other representative plants were randomly selected and sampled in another plot of each treatment for dry mass (leaf and succulent root) investigation at 10-day intervals in 2001 and 2002. In 2001, root dry weight density for each treatment was obtained from soil cores extracted between rows with an auger (55 mm in diameter, 10 cm high with a volume of 237.46 cm3) at the leaf development stage (September 22) and at harvest (October 19). In each plot, the distances to the center of raised beds for sampling were 0, 7.5, 15, and 22.5 cm, and sample depths were 010, 1020, 2030, 3040 cm depth on September 22 and 010, 1020, 2030, 3040, 4060 cm depth on October 19. In 2002, radishes in the middle three rows of one plot of each treatment were harvested for analysis. Fresh fruit weight (g/fruit) for size categories were as follow: >500 g (Grade 2), 250500 g (Grade 1) and F3F6F8>F4F1
Fig. 7 The succulent root body expanding during radish growing periods for irrigation frequency treatments in 2001 and 2002 35
Radish root circumference (cm)
25
order and F3>F4>F2>F6>F8>F1 order in 2001 and 2002, respectively. In both years, the highest irrigation frequency (F1) resulted in the least LAI. It is because a high irrigation frequency (irrigating once every day) caused a very humid region in the root zone and reduced the oxygen diffusion into the soil, which affected the activity of crop enzyme, weakened crop photosynthesis (Pezeshki 1994; Liao and Lin 1994; Huang et al. 1994), and inhibited the development of leaf area. Succulent root development The growth response of radishes to the different irrigation frequency can be presented by tracking the development of circumferences of radish succulent roots. The circumference accretion versus time relationship for each treatment in 2001 and 2002 (Fig.7) were sigmoid shapes. During the early growing period, radish succulent roots were small and began to expand rapidly about 25 days after planted. At the late period (about 65–70 days after planting), root circumference accretion rates began to slow. 35
F1 30
11-Oct 21-Oct 31-Oct 10-Nov
Date
Date
F2
F3
F4
F6
F8
2001 30 25
20
20
15
15
10
10
5
5
0 0 12- Aug 22- Aug 1-Sep 11-Sep 21-Sep 1-Oct 11-Oct 21-Oct 6-Sep
Date
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F2
F3
F4
F6
F8
16-Sep 26-Sep
6-Oct
Date
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16-Oct 26-Oct 5-Nov 15-Nov
Accumulated dry mass of roots (g)
60
70
F1 50 40
F2
2001 60
F3
F4
F6
F8
50
F1
F2
F3
F4
F6
F8
16-Sep 26-Sep
6-Oct
2002
40
30 30
20 20
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0 0 17- Aug 27-Aug 6-Sep 16-Sep 26-Sep 6-Oct 16-Oct 26-Oct 6-Sep
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Fig. 8 Development of succulent root dry masses during radish growing periods for different irrigation frequency treatments in 2001 and 2002
16-Oct 26-Oct 5-Nov 15-Nov Date
cm3, respectively. It can be seen that the root dry weight density for F3 treatment kept high throughout the whole growing period.
Dry mass accumulation Figure 8 indicates the succulent roots dry masses accretion versus time relationships were double-sigmoid shapes in 2001 and 2002. At first, the dry masses of succulent roots for each treatment accumulated slowly, and began to increase rapidly on September 12 and October 2 in 2001 and 2002, respectively. About half a month later, the dry masses accumulated slowly again. The slowly growing stage lasted about 10 days, and then the dry masses increased dramatically again before harvest. It is obvious that radishes were harvested early in the harvest season in 2001. Root distribution Figures 9 and 10 illustrate the roots dry weight density for the six treatments on September 22 and October 19 in 2001, respectively. On September 22, most of radish roots of each treatment developed in the soil 15 cm horizontally to the center of raised beds at the depth of 020 cm. The highest irrigation frequency treatment (F1) led to the lowest roots dry weight density, about 150·106 g/cm3, and the lowest irrigation frequency treatment (F8) resulted in the highest roots dry weight density, about 1,100·106 g/cm3. The roots dry weight density for F2, F3, F4 and F6 treatments were about 420, 840, 710 and 620·106 g/ cm3, respectively. When harvested (on October 19), the roots dry weight density for most treatments (except F1 and F3) was less than that on September 22, but the spatial distributions of roots were similar. Most of radish roots developed in the soil 15 cm horizontally to the center of raised beds at 020 cm depth. The roots dry weight density for F1, F2, F6 and F8 treatments were about 450·106 g/cm3, and that for F3 and F4 treatment was about 850 and 650·106 g/
Fresh root yields and market quality The highest yield was recorded at F2 in 2001 and F3 in 2002, and followed a F2>F3>F6>F4>F8>F1 order in 2001 and F3>F4>F2>F6>F8>F1 order in 2002 (Table 2). However, according to the statistical analysis, the differences in average root fresh weight and yield among the six irrigation frequency treatments in both years were not significant. Among all the six treatments in 2002, F3 had the lowest cracking rate (1.3%) and the fewest radishes (1.4%) of Grade 3 (W EW20 (185 mm)> F2 (177 mm) F3 (177 mm) > F4 (169 mm) > F8 (165 mm) > F6 (149 mm) order. The highest ET (F1) was 23 mm (14%) more than the lowest value (F8). The seasonal cumulative ET for F1 was even higher than the cumulative pan evaporation. It infers that F1 (irrigating once every day) may cause more water loss.
Table 2 Yield and market quality of radish as affected by irrigation frequency in 2001 and 2002 Average fresh root weight (g) 2001 F1 F2 F3 F4 F6 F8 2002 F1 F2 F3 F4 F6 F8
Yield (Mg/ha)
488.1a 506.3a 502.8a 496.9a 498.5a 492.5a
48.8a 50.6a 50.3a 49.7a 49.9a 49.2a
449.9a 473.7a 481.5a 475.0a 469.4a 459.1a
45.0a 47.4a 48.2a 47.5a 46.9a 45.9a
Rate of cracking (%)
Fresh root weight distribution
5.6a 5.1a 1.3b 7.8a 6.7a 7.1a
W>500 g Grade 2
250 g
