Effects of soil matric potential on potato growth under drip irrigation in ...

agricultural water management 88 (2007) 34–42

available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/agwat

Effects of soil matric potential on potato growth under drip irrigation in the North China Plain Feng-Xin Wang a,b,*, Yaohu Kang b, Shi-Ping Liu b, Xiao-Yan Hou a a b

Center for Agricultural Water Research in China, China Agricultural University, Beijing 100083, China Institute of Geographical Sciences and Natural Resource Research, Chinese Academy of Sciences, Beijing 100101, China

article info

abstract

Article history:

This research examines the affect of five soil matric potential (SMP) treatments [F1 (15 kPa),

Accepted 18 August 2006

F2 (25 kPa), F3 (35 kPa), F4 (45 kPa), F5 (55 kPa)] under drip irrigation conditions

Published on line 5 October 2006

conducted in the North China Plain. The temporal and spatial SMP changes observed in the soil profile along with changes in potato root growth suggest that tensiometers placed

Keywords:

immediately beneath the emitter (at 20 cm) can be effectively used in scheduling the drip

Drip irrigation

irrigation regimen. Although rain affected soil water distribution during the growing season,

Potato growth

the affects of SMP on potato growth were very clear. Crop evapotranspiration was highest

Soil matric potential

for F2, decreasing thereafter to F1, F3, F4, and F5. Other potato growth properties such as

Tensiometer

crop height, leaf and stem water content, tuber bulk rate and grade, as well as WUE (water use efficiency) and IWUE (irrigation water use efficiency) suggest that an SMP of 25 kPa was the most favorable setting for potato production, while 15 kPa was too high and 45 kPa lead to severe water stress. # 2006 Published by Elsevier B.V.

1.

Introduction

The land area devoted to potato cultivation has decreased worldwide over the last few decades (Fabeiro et al., 2001). Interestingly, it has increased gradually in China, accounting for some 4.72 million ha in 2000 (Ministry of China Agriculture, 2001). In North China, potatoes are generally planted in raised beds and furrow-irrigated. However, their yields fluctuate dramatically due to frequent droughts, poor irrigation management, and general water shortages. As such, farmers have been encouraged by the Chinese government to adopt drip irrigation methods in an attempt to stabilize production and minimize water waste. It is generally recognized that potatoes are sensitive to water stress (Stark and McCann, 1992; Lynch et al., 1995; Eldredge et al., 1996; Shock et al., 1998; Fabeiro et al., 2001). Ideal conditions for potato growth include high and nearly

constant soil water potential along with a high soil oxygen diffusion rate (Phene and Sanders, 1976). Research by a number of authors including Phene et al. (1989) have emphasized the importance of maintaining a relatively constant soil matric potential under high-frequency irrigation scheduling. Soil matric potential (SMP), especially in non-saline areas, is considered a better criterion for characterizing crop soil water availability than gravimetric or volumetric water content. Numerous studies using tensiometers to measure SMP and schedule irrigation have been reported (Phene et al., 1973; Phene and Beale, 1976; Phene et al., 1979; Klein, 1983; Hook et al., 1984; Phene and Howell, 1984; Hegde, 1987; Hegde and Srinivas, 1989; Lieth and Burger, 1989; Hodnett et al., 1990; Clark et al., 1996; Shock et al., 2000; Wilson et al., 2001). After comparing four irrigation-scheduling methods, Shae et al. (1999) suggested tensiometer-based methods produce yields

* Corresponding author at: Center for Agricultural Water Research in China, China Agricultural University, No. 17, Qinghua East Road, Haidian, Beijing 100083, China. Tel.: +86 10 62737874. E-mail address: [email protected] (F.-X. Wang). 0378-3774/$ – see front matter # 2006 Published by Elsevier B.V. doi:10.1016/j.agwat.2006.08.006


and quality equivalent to those from reference treatments with significant savings in seasonal irrigation totals. Taylor (1965) presented appropriate ranges of potential for irrigation control for many crops and suggested that a SMP for maximum yield in potatoes was between 30 and 50 kPa. Epstein and Grant (1973) found that potato plants exhibited water stress when SMP levels dropped below 25 kPa. Experimental results from Lynch and Tai (1989) showed that marketable potato yield decreased as soil water potential decreased from 30 to 120 kPa. Maintaining an appropriate level of soil moisture is also a common concern for potato disease inhibition and tuber quality improvement. Lewis (1970) found that when soil was irrigated to maintain potentials greater than 13 kPa (10 cm depth), potato tuber infection was negligible. Lapwood et al. (1973) showed that maintenance of SMP between 15 and 20 kPa was required for good disease control, while Eldredge et al. (1996) showed that potato dark ends on silt loam soils could be reduced by increasing irrigation frequency such that the SMP was wetter than 60 kPa. In spite of the many experiments on the issue, it remains difficult to find a comprehensive optimum SMP threshold that could be used in direct drip irrigation scheduling. Since the partial soil wetting pattern under drip irrigation is quite different from sprinkler irrigation, potato yield may respond differently to SMPs when the crop is drip irrigated (Shalhelvet et al., 1983). Under drip irrigation, especially under highfrequency drip irrigation, it is possible to maintain a small wetted soil zone sufficient for crop water uptake while keeping a much larger zone dry. Because it is unreasonable to average the SMPs in the root zone and use the mean to characterize soil water availability, sensor placement of the index tensiometer is always a concern (Phene and Howell, 1984; Levin et al., 1985; Coelho and Or, 1996). Rain patterns can also influence the desired threshold of soil matric potential (Sammis, 1980). Other factors, such as the type of potato cultivar, soil type and meteorological conditions may also affect experimental results as researchers seek to find an optimum threshold soil matric potential for use in scheduling drip irrigation. The objectives of this study were: (1) to investigate the temporal and spatial variation of soil wetting affected by several targeted SMPs under drip irrigation conditions and offer some suggestions for tensiometer placement; (2) to evaluate the effects of SMP on potato growth; (3) to find an optimum threshold for SMP in scheduling drip irrigation for potato production.

2.

Materials and methods

2.1.

Experimental site

A field experiment was conducted at the Luancheng Agroecosystem Experimental Station, Chinese Academy of Sciences in Luancheng County, Hebei Province. Annual precipitation for the area is about 480 mm, concentrated between July and September. Precipitation is rather small during the spring and early summer. The dominant soil in the area is loam with an average bulk density of 1.53 g/cm3. The groundwater table is

35

approximately 28 m below the surface with a mineral content of less than 0.5 g/l.

2.2.

Experimental design and irrigation process

The SMP 20 cm immediately under the emitter was used as the target matric potential. There were five target matric potential treatments: 15 kPa (F1), 25 kPa (F2), 35 kPa (F3), 45 kPa (F4), 55 kPa (F5). All treatments were repeated three times on experimental plots following a complete randomized block design. Thin-wall drip tapes (Chapin Watermatics, Inc.) with a 20 cm dripper spacing, flow rate of 3.72 l/m h, and an operating pressure of 0.042 MPa were placed in the center of each of the raised beds. Each plot had one valve, one flow meter, and one pressure gauge to control operating pressure and measure irrigation quantity. Before the potatoes sprouted, all treatments plots were irrigated with the same quantity of water at the same frequency in order to ensure a uniform emergence rate. After that, irrigation was applied only when the SMP reached the targeted value. Irrigation amounts were determined and adjusted according to the targeted matric potential readings at a set time. Irrigation amount per time was equal for all the treatments during the same growing period (relatively constant between 3 and 6 mm).

2.3.

Agronomic practices

Each plot was 5.6 m wide and 6.0 m long with potatoes (Favorita) planted in the center of the seven raised beds. Crop spacing was 20 cm 80 cm. The applications of plant ashes and N, P, K fertilizers were 150, 105, 180 and 130 kg/ha, respectively. Paclobutrazol (Chemically known as ‘‘(2RS,3RS)1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)-pentan-3-ol’’) was sprayed at a rate recommended by the manufacturer to restrain excessive growth of breaches and leaves on May 15. The crop was planted on 8 March 2002 and emerged about four weeks later. They were harvested on 17 June 2002.

2.4.

Soil moisture measurement and calculation

A set of 30 mercury column tensiometers was installed in one replicate of each treatment for observation of SMP. Sensor placements for all five treatments were the same (Fig. 1). Observations were made daily at 8:00 a.m. for each of the tensiometers. Once the potatoes emerged, the tensiometers under each drip emitter were observed every 2 h during the daytime to check matric potential in order to determine irrigation timing. In order to draw a soil water retention curve, the gravimetric soil water content of different soil layers was measured frequently during periods when the soil matric potential declined from the highest to the lowest, at a time interval of once every day or 2 days. The values were converted to a percentage volumetric basis by multiplying the respective values by the bulk density of the soil of the respective layer. Soil matric potentials were measured in a similar fashion. Crop evapotranspiration (ET) was estimated using the water balance equation below: ET ¼ I þ P DS R D

(1)

36


unsaturated hydraulic conductivity (mm/day) estimated according to Lei et al. (1988):

KðuÞ ¼ Ks

m u us

(3)

where Ks is the saturated hydraulic conductivity, us the saturated volumetric water content, m the regression coefficient, and u is the volumetric water content. u was derived from a soil water characteristic curve based on field measurements and expressed as u ¼ 0:3853 e0:01775cm

(4)

where cm is soil matric potential measured in situ as ‘kPa’ with a range of 1 to 55 kPa. Both Ks and us (0.713 (m/day) and 0.377, respectively) were measured using the method suggested by Lei et al. (1988) using soil obtained from a depth of 80 cm in the field where the experiment was conducted.

2.5.

Fig. 1 – Placement of tensiometers with a plane view.

where I is the irrigation amount, P the precipitation, DS the change in soil water content that occurred between planting and harvesting, R the surface runoff, and D is the downward flux below the crop root zone. To estimate DS, soil water content in the soil profile (down to 90 cm) just before planting and harvesting were determined by gravimetric measurements. Surface runoff was ignored because precipitation during the growing season was very small and there were separating strips that could limit possible runoff along the furrows. Deep percolation was estimated according to Darcy’s equation (Azevedo et al., 2003; Kang et al., 2003) as c cm1 þ1 D ¼ KðuÞ m2 Z2 Z1

(2)

where D is the deep percolation (mm/day), cm2 and cm1 are matric potentials at 90 and 70 cm, respectively, Z1 and Z2 are soil depths under the crop root zone (Z1 = 70 cm, Z2 = 90 cm), u is mean soil moisture content at Z1 and Z2, and KðuÞ is the

Potato growth property sampling

Root sampling was carried out just before harvesting. A hollow auger with an internal diameter of 0.055 m was used to take soil cores. Samples were collected at five points perpendicular to the drip line at 0, 10, 20, 30 and 40 cm such that the center of the standard potato crop was immediately under the dripper. Samples were extracted at 10 cm intervals to a depth of 90 cm. The same process was repeated at three different locations in each treatment plot. To reduce labor cost, samples of the same depth and horizontal distance for the same treatment were mixed. The samples were steeped and flushed prior to using a root scanner (CID201, CID Inc.) to measure root length as suggested by Zhang (1999). Dry root weight was measured indoors after the root samples were oven-dried at 75 8C. To determine water content of fresh leaves and stems, five potato plants in each treatment were cut from the stem base, parceled into plastic bags, and immediately sent to the laboratory where the leaves and stems were separated and their fresh weight measured. The samples were then ovendried to determine dry weight. Potato tubers of the same five plants were weighed for tuber growth analysis. In each treatment plot, 10 potato plants were chosen and marked to measure crop height. On June 13, 10 potato plants in every treatment plot were sampled for tuber grading, and the middle three rows of potatoes in each plot harvested for yield analysis.

3.

Results and discussion

3.1.

Total water received

Irrigation and rain amounts for each treatment during the growing season are shown in Fig. 2. Total rain for the period was 104 mm spread over 16 events. Two major rain events occurred in May when the potatoes were growing most rapidly. Rainfall was less then 5 mm for 12 rain events (23 mm in total), which is usually counted as ineffective rain. A major 25 mm rain occurred at the end of growing season when the


37

Fig. 3 – Soil matric potential for the soil depth of 20 cm immediately under emitter.

Fig. 2 – Cumulative amount of rain and irrigation during the growing season.

potatoes were in the late maturing stage and didn’t need much water. As such, nearly half of the rain (48 mm) contributed little to potato growth. Irrigation totals for F1, F2, F3, F4 and F5 were 153, 132, 111, 89 and 45 mm, respectively.

3.2.

Soil matric potential

SMPs for the 20 cm of soil right under emitters are shown in Fig. 3. Three major rain events disturbed the targeted potentials on the corresponding days. Other small rains had little effect. Except for the disturbance of the three major rains, the general trend was around the targeted potentials, especially for treatments F1, F2 and F3. Because the period from May 16 to June 7 was very dry, soil water distribution

before irrigation and after irrigation at the end of May served as the typical soil wetting pattern without rain for the different treatments (Fig. 4). The SMPs of the upper 50 cm layer were clearly affected by the targeted SMP, with higher targeted potentials having a higher mean SMP. SMP readings for the 30 tensiomenters in each treatment showed the most dramatic changes within 20 cm horizontal distance from the plants and within 30 cm of the soil surface (see Fig. 5, F2 as an example). This suggests that the process of soil water depletion by evapotranspiration and replenishment by irrigation or rain was most active in this zone. The same results were found in our previous drip frequency experiment (Wang et al., 2006). Tensiometers placed at 10 cm depth could be affected by tuber bulking, or accidentally destroyed during regular fieldwork, while those placed at 30 cm depth may not be sensitive to soil water replenishment and depletion (Fig. 5). As such, placement at 20 cm right under the emitter is best in characterizing soil water status.

Fig. 4 – Soil water distribution before irrigation on the irrigation day and 1 day after irrigation.

38


The SMP for the F1 treatment was the highest of all soil profiles, and showed the least variation in SMP. There are two possible reasons for this outcome. One is that very high hydraulic conductivity might occur at a high soil matric potential, where water leaving is quickly replaced by new water entering from other areas. The other occurs when the same amount of water is extracted under a higher SMP, because the reduction in SMP is always smaller than that of the lower one. In addition, the SMPs of F1 at soil depths of 50, 70, and 90 cm got higher during the growing season indicating some water infiltration into these soil layers. It is also reasonable to believe that deep percolation may have occurred. The other four treatments had nearly the same SMP at soil depths of 70 and 90 cm during the early two thirds of the growing season. In the later one third of the growing season, the F2 increased slightly while the F3 remained stable and both the F4 and F5 dropped gradually.

3.3.

Potato evapotranspiration

Potato evapotranspiration for the different treatments was quite small due to the very short growing period for potatoes (Table 1). We expected potato evapotranspiration to be closely related to SMP during the growing season. However, F2 that had the highest evapotranspiration among the five treatments, which was 48.6 mm (23.3%) more than the lowest value for F5. In contrast, F1 had highest irrigation, more depth percolation (14.7 mm), and less evapotranspiration than F2, which suggests that the F1 experienced somewhat waterlogged conditions. If so, fertilizers could have been leached out of the root zone and root activity restrained because of poor soil aeration; factors which would have affected plant performance and water uptake. ET values declined as SMP dropped from 25 to 55 kPa with the sharpest reduction (22 mm) occurring when the SMP dropped from 45 to 55 kPa. This suggests that potatoes sustain notable water stress at SMP values below 45 kPa.

Fig. 5 – SMP variations at 0, 10, 20, 30 and 40 cm horizontal distances from dripper and 10, 20, 30, 50, 70 and 90 cm depths for treatment F2.

3.4.

Potato growth

3.4.1.

Crop height

The crop height growing process is illustrated in Fig. 6. At the beginning of the growth period, crop heights for the five drip

Table 1 – Crop evapotranspiration calculation and some agronomic properties

DS (mm) D (mm) I (mm) P (mm) ET (mm) Potato yield (kg/ha) WUE (kg/ha mm) IWUE (kg/ha mm)

F1

F2

F3

F4

F5

46 15 153 104 196 22590 ab* 115 194

24 4 132 104 208 26660 a 128 155

23 0 111 104 192 23410 ab 122 126

11 0 89 104 182 20640 b 113 38

12 1 45 104 160 18980 b 119

DS is the change in soil water content that occurred between planting and harvesting, D the downward flux below the crop root zone, I the irrigation amount, P the precipitation, WUE ¼ potato yield=ET and IWUE is defined as in Eq. (6). * Difference among different treatments is significant by F-test (P < 0.05). Values in a row with the same letter are statistically homogeneous by Duncan’s test.

39


Fig. 7 – Root weight density of different soil depth layer.

Fig. 6 – Potato height.

treatments were very close. As soil matric potentials became different, however, crop height varied significantly from: F2 > F1 > F3 > F4 > F5 (F-test, P < 0.05). Later in the growing period when paclobutrazol was being applied, crop height changed very slowly and soil matric potential seemed to have little effect on crop height.

3.4.2.

Water content of leaves and stems

It has been suggested that the relative water content (RWC) of some plant parts, especially the leaves, is a direct criterion for evaluating crop water status (Epstein and Grant, 1973; Riga and Vartanian, 1999; Viswanatha et al., 2002). In this paper, the water content of both leaves and stems (See Table 2) was used to compare the affect of SMP on water uptake by the plants. The results found that the water content of the F1 and F2 leaves and stems were always higher than that in the other treatments. The close water content in the F1 and F2 leaves and stems suggests that a SMP of 25 kPa was sufficient for water uptake, and that a higher SMP didn’t mean more water availability. Water content in the leaves and stems of treatments F3, F4, and F5 decreased as SMP declined, implying that potatoes in those treatments experienced some degree of water stress. This result also supports the contention that potato plants exhibit water stress when the soil water potential drops below 25 kPa (Epstein and Grant, 1973).

3.4.3.

Root weight density (RWD)

Both root length and weight density were measured. Regrettably, it was later discovered that the root scanner

Fig. 8 – Root weight density for different horizontal distance from crop base.

had not worked well. Therefore, the potato root distribution illustrated in Figs. 7 and 8 uses only RWD. RWD had a tendency to increase gradually as SMP dropped from 15 to 35 kPa in 0–30 cm soil layer, reaching a maximum in F3 and then declining as SMP decreased from 35 to 55 kPa. The exception observed in the F4 at 0–10 cm might be due to sampling errors. It is clear that most potato roots grew in the upper 0–40 cm soil layer, with only a few roots growing deeper than 40 cm. These results are similar to those of Lahlou and Ledent (2005) who found the average root length of the four potato cultivars whose root dry mass had been reduced by drought were all below 38.5 cm under wellirrigated and stressed conditions. The affect of SMP on RWD in the horizontal direction was similar to that vertically, with few roots extending more than 30 cm from the potato plant.

3.4.4.

Tuber growing process and tuber grading

For treatments F1, F2 and F3, potato tuber growth process was similar to a ‘S’ curve (Fig. 9). Tuber bulk rates increased slowly during the early growth stage, but increased quickly during the middle period before slowing down again as the plants approached maturity. Tuber bulking rates for the F4 and F5

Table 2 – Water content of leaves or stems (g/g) 8 May

F1 F2 F3 F4 F5

25 May

13 June

Leaves

Stems

Leaves

Stems

Leaves and stems

0.8679 0.8715 0.8628 0.8659 0.8542

0.9456 0.9373 0.9348 0.9292 0.9298

0.8507 0.8543 0.8521 0.8488 0.8411

0.9325 0.9306 0.9291 0.9193 0.9088

0.8925 0.8932 0.8846 0.8843 0.8459

40


Table 3 – Tuber grading Treatment F1 F2 F3 F4 F5

Marketable tubers per plant (number) 3.0 3.5 3.7 2.6 2.3

ab* ac a b b

Culls per plant

Total tubers per plant

2.2 NS 2.9 2.7 2.7 2.2

5.2 NS 6.4 6.4 5.3 4.5

Marketable tuber weight per plant (g) 311.3 385.9 355.5 271.2 225.6

ab* a ab b b

NS: difference among different treatments is not significant by F-test (P > 0.05). Difference among different treatments is significant by F-test (P < 0.05). Values in a column with the same letter are statistically homogeneous by Duncan’s test. *

treatments were very similar, especially during the middle and late periods. The rates were also higher than those for F1, F2 and F3 during the late period, although this might be explained by a compensation effect from the plant as soil water status became better with rain. The tuber bulking rate was most sensitive to water stress during the middle period. The mean tuber bulking rate for the different treatments followed as: F2 > F3 > F1 > F4 > F5. Tuber grading results are listed in Table 3. Treatments F2 and F3 had more marketable tubers per plant than did the F4 and F5. However, while the F3 had the most tubers, the difference among the F1, F2 and F3 treatments was not significant. The difference in both culls (tuber weight < 50 g) and total tubers per plant for the different treatments were also insignificant according to F-test results. Marketable tuber weight per plant (Tuber weight 50 g) was significantly affected by soil matric potential, with the F2 having a much heavier weight than the F4 and F5.

3.5.

Potato yield and water use efficiency (WUE)

Total potato tuber yields (including culls) are listed in Table 1. F2 had the highest yield, then decreasing in order from F3, F1, F4 and F5. According to F-test (P < 0.05) and Duncan’s test (P < 0.05), Treatment F2 had a significantly higher yield than treatments F1, F4 and F5. F3 also had a significantly higher yield than F5. Interestingly, yield differences between any two treatments such as F2 and F3, F3 and F1, F1 and F4, F4 and F5, F1 and F5, F3 and F4 were not significant. Clearly, tuber growth in treatments F4 and F5 were restrained to some extent by a soil water deficit, while tuber growth in F1 was restrained by soil water excess.

Regression analysis of targeted soil matric potential and potato tuber yield resulted in the following equation: y ¼ 0:7032x3 81:686x2 þ 2762:3x 2739:6 ðR2 ¼ 0:7657Þ

where y is the total potato tuber yield in kg/ha and x is the targeted soil matric potential as kPa. The WUE values for the different treatments are listed in Table 1. Interestingly, the results for F1 were even higher than that for F5 and quite different from the general rule which suggests that the lower the amount of water received the higher the water use efficiency (Fabeiro et al., 2001; Kashyap and Panda, 2003; Yuan et al., 2003; Onder et al., 2005). Obviously, WUE is not a good criterion for evaluating the effectiveness of irrigation in this experiment. Therefore, IWUE (similar to Bos’s definition (Bos, 1985)) was introduced as an additional factor and defined as: IWUEi ¼

Y i Yi1 Ii Ii1

(6)

where Yi and Yi1 are yield at irrigation levels Ii and Ii1, respectively. IWUE values for F1, F2, F3 and F4 are listed in Table 1. F2 had the highest IWUE and should be favored for irrigation practice. F1 had a negative value given the yield reduction when compared with F2. F3 had a higher IWUE than F4 implying that the irrigation increase for F3 was more worthwhile than that for F4. Given the WUE and IWUE analysis above, it appears that both F2 and F3 are good soil matric potential thresholds for favorable potato production, with F2 superior due to both higher WUE and IWUE values. This finding is also comparable to an early report on sweet corn (Phene and Beale, 1976).

4.

Fig. 9 – Tuber weight per plant.

(5)

Summary and conclusions

The rain pattern during the growing season in this experiment was typical for the North China Plain. Although the rain affected the targeted SMP readings at a depth of 20 cm, temporal and spatial changes in soil water in the observed profile suggest that a SMP 20 cm immediately under emitter can be used as an index for scheduling drip irrigation. Potato roots were concentrated within the first 40 cm from the soil surface and at a horizontal distance of 30 cm from the potato plants, further strengthening our suggestion for tensiometer placement.


The analysis of water content of the leaves and stems for the different treatments showed that a SMP of 25 kPa was high enough for water uptake, and that a higher SMP as in F1 did not mean more water availability for uptake. As SMP declined from 35 to 55 kPa, the water content of the leaves and stems became lower, and implying that potatoes in these treatments had undergone water stress to some extent. The possibility of both deep percolation and evapotranspiration implied that the F1 treatment had some redundancy in soil water, which possibly restrained water uptake by the roots. It was also found that the tuber bulking rate was most sensitive to water stress during the middle growth period, and that a SMP of 45 kPa or lower would lead to a sharp reduction in the tuber bulking rate. Culls and total tubers per plant were not affected by SMP according to F-test results. However, marketable tubers and marketable tuber weight were significantly affected by SMP, with treatments F2 and F3 having significantly more tubers and heavier weights than treatments F4 and F5. Total tuber yield for the different treatments followed from F2 > F3 > F1 > F4 > F5, with F2 having a significantly higher yield than F1, F4 and F5. Furthermore, F3 had a significantly higher yield than the F5. In terms of potato growth, WUE and IWUE results suggest that an SMP of 25 kPa is most favorable for potato production, while an SMP of 15 kPa is too high and an SMP of 45 kPa or more leads to notable water stress.

Acknowledgements This study is the part work of the Project 40125002 supported by National Science Fund for Distinguished Young Scholars and the Project 40071020 supported by National Science Foundation of China.

references

Azevedo, P.V., da Silva, B.B., da Silva, V.P.R., 2003. Water requirements of irrigated mango orchards in northeast Brazil. Agric. Water Manage. 58, 241–254. Bos, M.G., 1985. Summary of ICID definitions of irrigation efficiency. ICID Bull. 34, 28–31. Clark, G.A., Albregts, E.E., Stanley, C.D., Smajstrla, A.G., Zazueta, F.S., 1996. Water requirements and crop coefficients of drip-irrigated strawberry plants. Trans. ASAE 39 (3), 905–913. Coelho, E.F., Or, D., 1996. Flow and uptake patterns affecting soil water sensor placement for drip irrigation management. Trans. ASAE 36 (6), 2007–2016. Eldredge, E.P., Holmes, Z.A., Mosley, A.R., Shock, C.C., Stieber, T.D., 1996. Effects of transitory water stress on potato tuber stem-end reducing sugar and fry color. Am. Potato J. 73, 517–530. Epstein, E., Grant, W.J., 1973. Water stress relations of the potato plant under field conditions. Agron. J. 65, 400–404. Fabeiro, C., Martin de Santa Olalla, F., de Juan, J.A., 2001. Yield and size of deficit irrigated potatoes. Agric. Water Manage. 48, 255–266. Hegde, D.M., 1987. Effect of soil matric potential, method of irrigation and Nitrogen fertilization on yield, quality, and nutrient uptake and water use of radish. Irrig. Sci. 8, 13–22.

41

Hegde, D.M., Srinivas, K., 1989. Effects of soil matric potential and nitrogen on growth, yield, nutrient uptake and water use of banana. Agric. Water Manage. 16, 109–117. Hodnett, M.G., Bell, J.P., AH Koon, P.D., Soopamanien, G.C., Batchelor, C.H., 1990. The control of drip irrigation of sugarcane using ‘Index’ tensiometers: Some comparisons with control by the water budget method. Agric. Water Manage. 17, 189–207. Hook, J.E., Threadgill, E.D., Lambert, J.R., 1984. Corn irrigation scheduled by tensiometer and lambert model in the Humid Southeast. Agron. J. 76, 695–700. Kang, S.Z., Hu, X.T., Jerie, P., Zhang, J.H., 2003. The effects of partial rootzone drying on root, trunk sap flow and water balance in an irrigated pear (Pyrus communis L.) orchard. J. Hydrol. 280, 192–206. Kashyap, P.S., Panda, R.K., 2003. Effects of irrigation scheduling on potato crop parameters under water stressed conditions. Agric. Water Manage. 59, 49–66. Klein, I., 1983. Drip irrigation based on soil matric potential conserves water in peach and grape. Hortscience 18 (6), 942–944. Lahlou, Q., Ledent, J.-F., 2005. Root mass and depth, stolons and roots formed on stolons in four cultivars of potato under water stress. Eur. J. Agron. 22, 159–173. Lapwood, D.H., Wellings, L.W., Hawkins, J.H., 1973. Irrigation as a practical means to control common scab (Streptomyces scabies), final experiments and conclusion. Plant Pathol. 22, 35–41. Lei, Z.D., Yang, S.X., Xie, S.Z., 1988. Soil Water Dynamics. Tsinghua University Press, Beijing, p. 33. Levin, I., Sarig, S., Meron, M., 1985. Tensionmeters location in controlled automated drip irrigation of cotton. In Proceedings of the Third International Drip/Trickle irrigation Congress. Lewis, B.G., 1970. Effects of water potential on the infection of potato tubers by Streptomyces scabies in soil. Ann. Appl. Biol. 66, 83–88. Lieth, J.H., Burger, D.W., 1989. Growth of chrysanthemum using an irrigation system controlled by soil moisture tension. J. Am. Soc. Hort. Sci. 114 (3), 387–392. Lynch, D.R., Tai, G.C.C., 1989. Yield and yield component response of eight potato genotypes to water stress. Crop Sci. 29, 1207–1211. Lynch, D.R., Foroud, N., Kozub, G.C., Farries, B.C., 1995. The effect of moisture stress at three growth stages on the yield, components of yield and processing quality of eight potato cultivars. Am. Potato J. 72, 375–386. Ministry of China Agriculture, 2001. China Agriculture Yearbook, vol. 22. China Agricultural Press, Beijing, p. 251. Onder, S., Caliskan, M.E., Onder, D., 2005. Different irrigation methods and water stress effects on potato yield and yield components. Agric. Water Manage. 73, 73–86. Phene, C.J., Hoffman, G.H., Austin, R.S., 1973. Controlling automated irrigation with soil matric potential sensor. Trans. ASAE 16 (4), 773–776. Phene, C.J., Sanders, D.C., 1976. High-frequency trickle irrigation and row spacing effects on yield and quality of potatoes. Agron. J. 68, 602–607. Phene, C.J., Beale, O.W., 1976. High-frequency irrigation for water nutrient management in humid regions. Soil Sci. Soc. Am. J. 40, 430–443. Phene, C.J., Fouss, J.L., Sanders, D.C., 1979. Water-nutrient management of potatoes with trickle irrigation. Am. Potato J. 56, 51–59. Phene, C.J., Howell, T.A., 1984. Soil sensor control of highfrequency irrigation systems. Trans. ASAE 27 (2), 392–396. Phene, C.J., Allee, C.P., Pierro, J.D., 1989. Soil matric potential sensor measurements in real-time irrigation scheduling. Agric. Water Manage. 16, 173–185.

42


Riga, P., Vartanian, N., 1999. Sequential expression of adaptive mechanisms is responsible for drought resistance in tobacco (Nicotiana tabacum). Aust. J. Plant Physiol. 26, 211–220. Sammis, T.W., 1980. Comparison of sprinkler, trickle, subsurface, and furrow irrigation methods for row crops. Agron. J. 72, 701–704. Shae, J.B., Steele, D.D., Gregor, B.L., 1999. Irrigation scheduling methods for potatoes in the Northern Great Plains. Trans. ASAE 42 (2), 351–360. Shalhelvet, J., Shimshi, D., Meir, T., 1983. Potato irrigation requirements in a hot climate using sprinkler and drip methods. Agron. J. 75, 13–16. Shock, C.C., Feibert, E.B.G., Saunders, L.D., 1998. Potato yield and quality response to deficit irrigation. Hortscience 33 (4), 655–659. Shock, C.C., Feibert, Erik, B.C., Saunders, L.D., 2000. Irrigation criteria for drip-irrigated onions. Hortscience 35 (1), 63–66. Stark, J.C., McCann, I.R., 1992. Optimal allocation of limited water supplies for Russet Burbank potatoes. Am. Potato J. 69, 413–421.

Taylor, S.A., 1965. Managing irrigation water on the farm. Trans. ASAE 433–436. Viswanatha, G.B., Ramachandrappa, B.K., Nanjappa, H.V., 2002. Soil-plant water status and yield of sweet corn (Zea mays L. cv. Saccharata) as influenced by drip irrigation and planting methods. Agric. Water Manage. 55, 85–91. Wilson, C.R., Pemberton, B.M., Ransom, L.M., 2001. The effect of irrigation strategies during tuber initiation on marketable yield and development of common scab disease of potato in Russet Baurbank in Tasmania. Potato Res. 44, 243–251. Wang, F.X., Kang, Y.H., Liu, S.P., 2006. Effects of drip irrigation frequency on soil wetting pattern and potato growth in North China Plain. Agric. Water Manage. 79, 248–264. Yuan, B.Z., Nishiyama, S., Kang, Y., 2003. Effects of different irrigation regimes on the growth and yield of drip-irrigated potato. Agric. Water Manage. 63, 153–167. Zhang, X.Y., 1999. Crop Root System and Soil Water Utilization. Meteorological Press, Beijing, p. 5.