partial root-zone drying

ISBN 978-92-9060-360-3Production Systems andthe Environment DivisionWorking PaperNo. 2008-2

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Partial root-zone drying:An alternative irrigationmanagement to improve the wateruse efficiency of potato crops

Adolfo Posadas, International Potato Center (CIP),Guliver Rojas, Escuela de Post Grado, UNALM, Lima, PerúMiguel Málaga, Escuela de Post Grado, UNALM, Lima, PerúVíctor Mares, International Potato Center (CIP)Roberto A. Quiroz, International Potato Center (CIP)

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Partial root-zone drying:An alternative irrigation

management to improve the wateruse efficiency of potato crops

Adolfo Posadas, International Potato Center (CIP),

Guliver Rojas, Escuela de Post Grado, UNALM, Lima, Perú

Miguel Málaga, Escuela de Post Grado, UNALM, Lima, Perú

Víctor Mares, International Potato Center (CIP)

Roberto A. Quiroz, International Potato Center (CIP)

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© International Potato Center (CIP), 2008

ISBN 978-92-9060-360-3

CIP publications contribute importantdevelopment information to the public arena.Readers are encouraged to quote or reproducematerial from them in their own publications. Ascopyright holder CIP requests acknowledgement,and a copy of the publication where the citationor material appears. Please send a copy to theCommunication and Public AwarenessDepartment at the address below.

International Potato CenterP.O.Box 1558, Lima 12, [email protected] • www.cipotato.org

Produced by the CIP Communication and PublicAwareness Department (CPAD)

Production CoordinatorCecilia Lafosse

Design and LayoutElena Taipe and contributions from Graphic Arts

Printed in Peru by Comercial Gráfica SucrePress run: 200November 2008

The Production Systems and the Environment Division Working Paper Series comprises preliminary research results published to encourage debate

and exchange of ideas. The series also includes documentation for research methods, simulation models, databases and other software. The views

expressed in this series are those of the author(s) and do not necessarily reflect the official position of the International Potato Center.

Comments are invited.

This series is available on the internet at www.cipotato.org

Partial root-zone drying: An alternative irrigation managementto improve the water use efficiency of potato crops

iii

Table of Contents Abstract ............................................................................................................................................................................iv Introduction.................................................................................................................................................................... 1

Physiological aspects ............................................................................................................................................ 2 Partial root-zone drying ....................................................................................................................................... 2 The water factor in potato................................................................................................................................... 3

Materials and methods ............................................................................................................................................... 4 Results and discussion................................................................................................................................................. 6

In-field PRD applicability ..................................................................................................................................... 6 Production effects.................................................................................................................................................. 7 Yield and WUE......................................................................................................................................................... 9 Quality........................................................................................................................................................................ 9 Growth parameters .............................................................................................................................................10

Conclusions...................................................................................................................................................................10 References .....................................................................................................................................................................10

iv

Abstract

Drought is a severe environmental stress that limits agricultural production. Vegetable crops,

including potato, have high water requirements and in most countries full or supplemental

irrigation is necessary for successful vegetable production. However, water availability for

agriculture is being reduced as a consequence of global climate change, environmental pollution

and growing demand for other uses. Therefore, great emphasis is placed on crop management

for dry conditions with the aim of increasing water use efficiency. To see how restricted irrigation

systems affect water use efficiency and yield of potato, an experiment was conducted in an arid

area in coastal Peru at the International Potato Center in Lima. Partial Root-Zone Drying (PRD), an

innovative irrigation system in which both halves of the root system are alternately dried and well

watered, was compared to conventional irrigation (CI) on an early potato cultivar (4 months)

grown in furrows in randomized plots. Plants were fully and uniformly irrigated for 60 days

following planting (pre-experimental period) and then treatments were applied up to the harvest

time. For CI every furrow was irrigated during each watering. The PRD system consisted of

alternately irrigating one of the two neighboring furrows during consecutive watering. CI and

PRD were further divided into two treatments with different watering amounts, resulting in a

total of four irrigation treatments, ranging from CI1 with 100% of the water typically applied to

the potato crop in Lima, according to crop requirements; CI1/2 (50% of the amount of water

applied to CI1); PRD1 (same amount of water as CI1/2); and PRD1/2 that received half of the water

applied to PRD1. Fresh tuber yield was significantly higher for CI1 (45.1 t ha-1), followed by PRD1

(36.2 t ha-1), CI1/2 (33.9 t.ha-1) and PRD1/2 (31.0 t.ha-1). Water use efficiency (WUE) calculated for total

water use (pre-experimental and experimental periods) was similar for PRD1/2 (2.6 kg DM ha-1. m-3),

PRD1 (2.4 kg DMha-1. m-3), CI1 (2.3 kg DM.ha-1. m-3), and CI1/2 (2.2 kg DM.ha-1. m-3). However, WUE

calculated for water used during the experimental period showed larger differences as it was

higher for PRD1/2 (14.6 kg DM ha-1 m-3) followed by PRD1 (8.1 kg DM ha-1 m-3), CI1/2 (7.5 kg DM ha-1 m-

3), and CI1 (4.9 kg DM ha-1 m-3). Our results suggest that the PRD irrigation system might become

an alternative in large potato-producing areas in the world, where water is limiting and where

salinity might become a problem.

Keywords: PRD, irrigation system, WUE, potato.

C I P • P R O D U C T I O N S Y S T E M S A N D T H E E N V I R O N M E N T W O R K I N G P A P E R 2 0 0 8 -

P A R T I A L R O O T - Z O N E D R Y I N G : A N A L T E R N A T I V E 1

Partial root-zone drying: An alternative irrigation management to improve the water use efficiency of potato crops INTRODUCTION

Drought is a severe environmental stress that limits agricultural production in many agro-

ecosystems worldwide. Many vegetable crops, including potato, have high water requirements

and in most countries supplemental irrigation is necessary for successful vegetable production.

However, in many countries water availability for agriculture is being reduced as a consequence

of global climate change, environmental pollution and growing demand for other uses.

Therefore, great emphasis is placed on water management for dry conditions based on plant and

crop physiology, with the aim of increasing water use efficiency by major crops. Regulated deficit

irrigation (RDI) and partial root-zone drying (PRD) are two irrigation methods that attempt to

decrease the agricultural demand for water. PRD is an irrigation technique whereby half of the

root zone is irrigated while the other half is allowed to dry out. The treatment is then cyclically

reversed allowing the previously well-watered side of the root system to dry down while fully

irrigating the previously dried side. The PRD technique is rather simple, requiring only the

adaptation of irrigation systems to allow alternate wetting and drying of parts of the root zone

(Loveys et al., 2000, Stikic et al., 2003). However, important issues such as the growth stage at

which PRD should be applied to the potato crop to improve WUE without yield reductions remain

to be addressed (Liu, 2006a).

When PRD irrigation is applied to a crop, the normal root to shoot signaling system that operates

in water-deficient soils is altered, causing the drying half of the root system to release abscisic

acid (ABA) thus reducing stomatal aperture, whereas the fully hydrated roots maintain a

favorable water status throughout the aboveground parts of the plant. In other words, PRD

uncouples the biochemical signal in response to water stress from the hydraulic signal and

physical effects of reduced water availability (Bacon, 2003). This mixed root signals causes a

limited closure of stomata to restrict water vapor loss without a severe restriction of CO2 entrance.

The outcome is reasonably good yields with considerable water savings and higher water use

efficiency (WUE), which is of paramount importance in areas where water resources are limiting.

PRD has been successfully used in fruit-producing crops such as tomatoes, grapes, oranges, olive

trees, tomato, corn, cotton and others, but no extensive research has been conducted in root and

tuber crops, particularly in semi-arid environments where the water resource is scarce. The results

C I P • P R O D U C T I O N S Y S T E M S A N D T H E E N V I R O N M E N T W O R K I N G P A P E R 2 0 0 8 - 2

2 P A R T I A L R O O T - Z O N E D R Y I N G : A N A L T E R N A T I V E

in the former crops demonstrated that PRD has no major negative effect on the yield but

improves fruit quality with a reduction of more than 50% of the consumption of water (Loveys et

al., 2001).

Physiological aspects The first physiological response of plants to water deficit is stomatal closure, which slows down

the fall in plant water potential. Stomatal closure results from the regulation of osmotic pressure

in the guard cells, mediated by ABA released by roots in drying soil. Recent studies on progressive

root drying in potatoes have shown that root-sourced ABA reduces stomatal conductance (Liu et

al., 2005). This kind of communication is known as non-hydraulic or chemical signaling, which

differs from hydraulic signals, which are based on changes in the xylem sap tension (Stikic et al.,

2003). When the tips of young roots come into contact with dry soil, the release and high

concentration of ABA in the xylem prompts stomatal closure to reduce water loss and bud

growth, and prevent wilting (Zhang et al., 1989; Zhang & Outlaw, 2001; Khalil & Grace, 1993; Jia et

al., 1996). Besides the reduction of water vapor loss, stomatal closure brings about a series of

physiologic and metabolic adjustments that includes, among others, the decrease of

photosynthesis rate and alterations in translocation and distribution of photosynthates (Hanson

& Hitz, 1982; Kaiser, 1987). Waggoner in 1969 (cited by Harris, 1992) considered the possibility of

manipulating stomatal opening in potato in order to increase the yield per unit volume of

transpired water, although this increment would also mean a reduction in the yield per unit area.

Interestingly, Xu et al., (1998) stated that ABA stimulates tuber formation in potato whereas

Jackson (1999) has suggested that ABA participates in the control of tuber formation although its

direct effect is not totally clear yet. The effect of partial root-zone drying in tuber formation has

not yet been elucidated.

Partial root-zone drying PRD is based in the theoretical assumption that a small narrowing of stomatal opening may

reduce water loss substantially with a minimum effect on CO2 uptake and photosynthesis (Jones,

1992). It is known that when the root system is exposed to dry soil, it responds by sending ABA-

mediated chemical signals to the leaves to close stomata and reduce the water loss (Davies &

Zhang, 1991). On the other hand, plants with a good watering regime usually keep turgor and

their stomata wide open in response to hydraulic signal through xylem water pressure. Therefore,

it is expected that contradictory root signals brought about by PRD would cause a slight

reduction of the stomatal opening that would decrease the water loss substantially with only a

small effect on the photosynthesis rate, provided plant turgor is maintained by the watered


P A R T I A L R O O T - Z O N E D R Y I N G : A N A L T E R N A T I V E

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fraction of the root system. If this is achieved in practice, the WUE in terms of the carbon gained

per unit of water lost will be increased at a minimum cost of CO2 uptake and yield reduction. In

grapevine and other fruit-crops it has been demonstrated that the PRD has no effect on yield, but

it can improve quality, with a reduction of more than 50% of the consumption of water (Loveys et

al., 2001).

Besides the continuous chemical signaling that PRD stimulates (Stoll et al., 2000), this practice

induces the growth of secondary roots, which reduces the vulnerability to drought (Zhang &

Tardieu, 1996). A root system more widely distributed in the soil volume as a result of the lateral

dry-wet cycle can result in an improved uptake of nutrients and water by the root system (Kang et

al., 1998).

Implementation of PRD irrigation requires that the watering system allow a wet and dry cycle in

different areas of the root, independently if it is flood or pressurized irrigation (Loveys et al.,

2001). The cycling is essential for maintaining a constant emission of signals from the root to the

foliage, because a drought-primed root is not able to sustain its production of ABA for long

periods of time (Davies and Hartung, 2004). The alternating frequency is determined according to

the crop, soil type and environmental factors. The soil is a most important factor because texture

and structure influence the water infiltration rate and high levels of salts increase the effect of

water stress in plants (Kriedemann & Goodwin, 2004). Contrary to the conventional deficit

irrigation techniques, in which the watering schedule depends mainly on potential

evapotranspiration (ET), in PRD more emphasis is given to direct measures of the soil water

content in the root area. The frequency of irrigation in the PRD system varies according to

environmental conditions, but the watering volumes depend on the soil type and root depth,

without adjustments for environmental conditions. For the calculation of the real ET in the PRD

system, it is necessary to make an adjustment of the crop coefficient (kc), since, like in all methods

of deficit irrigation, this value is not similar to that of a regime of normal watering.

The water factor in potato Potato is a crop that is very sensitive to water deficit. Even in normal conditions of watering,

water stress happens during the noontime due to high transpiration rates (Harris, 1978; Kumar et

al., 2003) and short periods of water stress are usually caused by inadequate watering practices.

Although the high incidence of pests and diseases are partly responsible for low yields, the main

restrictive factor of yield and quality is water stress. It is considered that the world yield average

(20 t/ha) could be increased by approximately 50% by optimizing the water supply to the crop

(Kumar et al., 2003). This sensitivity to water stress makes potato a water-demanding crop,



requiring from 400 to 600 liters of water to produce 1 kilogram of tuber dry matter (Beukema &

Van der Zaag, 1979). Under field conditions, the water requirements vary between 350 to 500 mm

over the growing season, depending on the crop period, environmental conditions, soil type and

cultivar (Sood & Singh., 2003). Potato plants can respond with increments of up to 2 t/ha for each

2 cm of water lamina (Harris, 1978). The optimal yield is highly dependent on well-planned

watering with low volume and high frequency (Vayda, 1994; Wright & Stark, 1990).

The potato’s limited tolerance to drought is due to its comparatively shallow root system (50-60

cm) and the stomatal tendency to close (Harris, 1992; Kleinkopf & Westermann, 1981; and Bailey,

2000), which reduce leaf extension rates (Haverkort & MacKerron, 2000). Stomatal closure also

reduces CO2 uptake and photosynthetic activity, increases leaf temperature and photorespiration,

and is therefore negative for crop production (Egúsquiza, 2000). The longer the reduction of

stomatal opening lasts, the higher the reduction in yield (Martínez y Huamán 1993). When the

water stress is short, most of cells recover; but if it lingers, the plant withers (Beukema & Van der

Zaag, 1979). Thus, PRD may reduce water stress by decreasing vegetative development.

The critical period to water deficit in potato is during tuber development; achieving high yields

requires an adequate water supply from tuber initiation to maturity (Salter & Goode, 1967; Jensen

et al., 2000 and Egúsquiza, 2000) and even short episodes of water stress during this period can

cause significant reductions in yield and quality (Miller & Martin, 1987; Kumar et al., 2003) causing

chained, hollow and small tubers (Jensen et al., 2000).

Deficit irrigation techniques, intended to save water, produce results that are generally non-

profitable, since the reduction in the amount of applied water in the total root zone does not

compensate for the economic loss due to the reduction in yield and quality (Shock & Feibert,

2002). However, PRD represents an alternative to deficit irrigation techniques, and more

experimental tests on the potato crop are needed. Therefore, the objective of this initial study

was to test the effects of PRD on WUE and tuber production as compared to full irrigation, and

investigate its effect on morphological and physiological characteristics of the potato crop.

MATERIALS AND METHODS

A field experiment with the potato variety Única was conducted in an arid area in coastal Peru, at

the International Potato Center in Lima, where the average rainfall is 23 mm y-1. Soils were sandy

loams with good drainage. A complete randomized block design with five replicates was used to

compare four watering treatments (See Figure 1). The distance among plants was 0.30 m and



5

among furrows, 0.9 m. The conventional furrow irrigation scheme was used. The water was

siphoned into the furrows from the irrigation canals (see Figure 2) and the amount of water per

day-furrow was measured. In the PRD treatments, which consisted of alternately irrigating one of

the two neighboring furrows during consecutive waterings, the furrows with irrigation were

alternated each week. All plots were irrigated in the conventional way for 42 days after

emergence (60 days after planting), the stage at which the corresponding treatments

(experimental phase) were applied. We estimated the percentage of tubers formed during the

pre-experimental phase, when all plots were equally irrigated. This estimation was used for the

attribution of tuberization to each treatment and the calculation of WUE.

The experiment had four irrigation treatments, as follows: CI1 was the conventional way where

every furrow was irrigated during each watering cycle with 100% of the water typically applied to

the crop in Lima according with crop requirements; CI1/2 was similar to CI1 but received 50% of the

water lamina applied to CI1; PRD1 received the same watering lamina as CI1/2 in the alternate way

described above; and PRD1/2, which received half of the water applied to PRD1 in the same

alternate way.

Figure 1. Experimental techniques for testing the PRD irrigation on potato. In A, by using a plastic membrane. In B, by dividing manually the root system in two joined pots. In C, using PVC siphons in field plots.



RESULTS AND DISCUSSION

In-field PRD applicability Scientists at the International Potato Center have been evaluating different procedures for

applying the PRD technique on potato since 2003. Plastic membranes were placed vertically

underground (figure 1A) before crop planting, so that the roots would grow in both sides of the

membrane; however, results were not as expected as the membrane impeded the fertilization

work and caused high temperatures that damaged the roots. In another experiment, emerged

plants were transplanted into adjacent pots with half of the root system in each pot (figure 1B);

however potato roots are very fragile and were damaged by manipulation. The conclusion was

that the simplest way to apply and assess PRD on potato is by furrow cultivation as in normal field

conditions, and the use of PVC siphons (figure 1C) to accurately control the volume of applied

water on each treatment. Although the division of the root system or the applied water is not as

exact as in pots, PRD in the field creates a gradient of humidity, in which the roots that are in

touch with the driest area of the gradient are expected to produce the chemical signals. This

assumption is supported by fieldwork with PRD in corn (Kang & Zhang, 2004). Figure 2 shows the

water status of the soil in adjacent furrows during our experimental phase. The peaks in the

curves indicate the watering dates. In the CI treatments the humidity of the soil was similar in all

furrows as they simultaneously received the same amount of water. However, in the PRD

treatments the alternate furrow irrigation caused a distinct spatial and temporal pattern of soil

humidity among furrows.

An important difference between PRD in the field as compared to the response under controlled

conditions in which roots are divided in adjacent pots is that in pots the root half that is well

irrigated maintains constant a high water status of the plant (Stikic et al., 2003; Davies et al., 2000

and Dry et al., 2000) whereas PRD in the field causes periodic symptoms of water stress in the

plant. This seems to be associated to the unavoidable temporary water stress that happens in

potato during sunny days as pointed out by Kumar et al., (2003), and to the likelihood that PRD

brings about some degree of water stress due to the fact that the amount of water applied is

determined by relative soil water content and not by actual soil and leaf water potential.

Kriedemann & Goodwin (2004) pointed out that in PRD, as in any of water deficit irrigation

techniques, an adjustment of the crop coefficient (Kc) should be made.



7

Production effects Table 1 shows the results of all the response variables. The letters beside the numbers indicate

the statistical differences according to the Waller-Duncan test.

Soil Water Content in Adjacent Furrows CI1 Soil Water Content in Adjacent Furrows CI½

Soil Water Content in Adjacent Furrows PRD1

Furrow Furrow Furrow Furrow

Furrow FurrowFurrow Furrow

Soil Water Content in Adjacent Furrows PRD½

Figure 2. Water content of the soil in adjacent furrows during the experimental phase.



Table 1: Potato responses under CI and PRD watering regimes.

WUEi: Water use efficiency at irrigation technique level (ratio between total dry weight in tubers and the volumen of applied water); WUEet: Water use efficiency at crop level (ratio between total dry weight in tubers and the evapotranspiration demand); CT: commercial Tubers; NCT: Non commercial tubers; HI: harvest index (ratio between tubers dry weight and plant dry weight); PI: Production Index (ratio between stems and leaves dry weight and plant dry weight); A/S: Aerial and subterranean relation (ratio between stems and leaves dry weight and stolons, roots and tubers dry weight); EC: electric Conductivity; nsad: no statistical analysis done; ns: no significant.

VARIABLE CI1 CI

1/2 PRD

1 PRD

1/2 Signif.

Fresh Tuber Yield (t/ha) 45.1 a 33.9 bc 36.2 b 31.0 c < 0.05

WUEi (kgdm/m3/ha) Total growth period 2.3 a 2.2 a 2.4 a 2.6 a ns

WUEet (kgdm/m3/ha) Total growth period 5.5 a 5.1 a 6.1 a 6.5 a ns

WUEi (kgdm/m3/ha) Experimental period 4.9 7.5 8.1 14.6

WUEet (kgdm/m3/ha) Experimental period 8.6 9.1 11.9 14.2

Tuber growth (t/ha) during exp period 38.3 28.8 30.8 26.4

Adjusted WUEi (kgdm/m3/ha) exp period 4.2 6.4 6.9 12.5

% Dry Matter in tubers 22.1 b 22.5 b 22.9 ab 24.1 a < 0.05

% CT weight 98.1 a 96.3 a 97.5 a 96.4 a ns

Chip color (grades del 1 al 5) 1.75 1.50 1.50 1.25 nsad

Chip Oil (%) 34 a 34 a 32 a 29 a ns

Number of stems per plant 1.5 1.8 1.8 1.7 nsad

Number of stolons per plant 22.0 a 22.2 a 20.4 a 22.3 a ns

Number of CT per plant 8.1 a 8.0 a 7.7 a 7.4 a ns

Number of NCT per plant 3.5 a 2.7 a 3.8 a 4.0 a ns

Leaf dried weight (g/plant) 29.6 a 22.5 b 22.6 b 22.5 b < 0.05

Steam dried weight (g/plant) 21.3 a 18.5 a 20.9 a 18.0 a ns

Stolon dried weight (g/plant) 4.4 b 4.8 b 5.8 a 4.7 b < 0.05

Root dried weight (g/plant) 0.8 a 0.6 b 0.5 b 0.5 b < 0.01

Tuber dried weight (g/plant) 274.9 a 200.4 b 204.8 b 182.5 b < 0.01

Relation A/S 0.32 a 0.27 b 0.29 ab 0.30 ab ns

HI 0.66 b 0.74 a 0.70 ab 0.72 a ns

PI 0.34 a 0.28 b 0.31 ab 0.32 ab ns

Fresh Foliage weight at harvest (kg/plant) 220.0 a 166.2 a 189.8 a 182.2 a ns

Root concentration (dm2) 5.1 9.5 11.2 11.1 nsad

Root Expansion (dm2) 19.8 22.8 23.2 24.8 nsad

EC soil (dS/100g) 0.67 0.34 0.62 0.32 nsad



9

Yield and WUE Significant differences in tuber yield were found among treatments. Highest fresh tuber yield was

obtained under CI1, which was significantly superior to all other treatments. However, it is

interesting to see that yields under CI1/2 and PRD1/2, which received the same total amount of

water (pre-experimental irrigation + experimental irrigation), did not differ. This seems to indicate

that PRD (applied during the experimental phase) had no negative effect on tuber growth as

yield in both cases were determined by total water applied, not by the watering regime. This is

further corroborated by the fact that the treatment with the lowest yield was PRD1/2, which

received the least water, both as total as well as during the experimental phase. These results are

in agreement with reports that water stress slows the vegetative development and reduces tuber

yield (Harris, 1992; Kumar et al., 2003; Jensen et al., 2000; Miller & Martin, 1987; Salter & Goode,

1967; Wright & Stark, 1990). However, Liu et al. (2006b) found no difference in potato tuber yield

between full irrigation and PRD (70% of water applied to full irrigation from tuber initiation to

maturity) in a field experiment, which suggest that PRD could be an effective strategy to improve

WAE while sustaining yields provided PRD is optimized in terms of the timing of application and

shifting and volume of irrigation water (Shahnazari et al., 2008)

No differences in WUE were evident, either calculated on the basis of applied water (WUEi) or

evapotranspired water (WUEet) when the assessment was based on total water applied.

However, when the same analysis was based on water applied during the experimental phase,

differences between treatments in WUEi and WUEet were evident, PRD producing increased

efficiencies inversely related to water volume used.

Quality Although it is well known that water stress increases the number of small tubers (Kumar et al.,

2003), in the present work, the weight percentage of CT was near 100% in all treatments with no

significant differences among treatments. Also, no differences were found in the quality for

industry variables tested, although the PRD1/2 treatment produced tubers with higher % DM that

led to processed chips of better coloration and less absorbed oil. It is known that water stress

tends to improve the quality of chips due to the higher % DM in tubers that gives chips a clearer

and more uniform color (Kumar et al., 2003; Jensen et al., 2000).



Growth parameters Most of the plant growth parameters analyzed, such as number of stems per plant, number of

stolons per plant, number of commercial tubers per plant, steam dried weight were not affected

by treatments. Also, no clear trend in harvest index and other variables was found. However, leaf

dry weight was significantly higher for CI1, suggesting a trend to a higher aerial development in

plants well supplied with water.

CONCLUSIONS

As might be expected, tuber yield was related to the amount of water received by the crop.

However, the ratio of relative yield attained (percentage of yield relative to maximum attained

yield) to relative total water (percentage of total water applied relative to maximum total water)

was higher for both PRD treatments compared to CI treatments. Since WUE was higher for PRD

treatments during the experimental phase (when water supply was critically linked to

tuberization), we think that the overall results have been negatively affected by the lengthy and

liberal water application during the pre-experimental period. As to tuber quality, it was improved

by PRD. In future field work, PRD will be applied much earlier and at lesser levels than in the

present case. Also, water cost scenarios will be included in the analysis. Another issue that might

be relevant to be considered is the potential effect of PRD on soil pathogens. More controlled

indoors experiments already in course will assess physiological responses (ABA, leaf turgor, leaf

expansion, reflectance, photosynthesis, root growth, tuberization dynamics) to PRD.

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CIP’s MissionThe International Potato Center (CIP) seeks to reduce poverty and achieve food security ona sustained basis in developing countries through scientific research and related activities onpotato, sweetpotato, and other root and tuber crops, and on the improved management ofnatural resources in potato and sweetpotato-based systems.

The CIP VisionThe International Potato Center (CIP) will contribute to reducing poverty and hunger; improvinghuman health; developing resilient, sustainable rural and urban livelihood systems; andimproving access to the benefits of new and appropriate knowledge and technologies. CIPwill address these challenges by convening and conducting research and supportingpartnerships on root and tuber crops and on natural resources management in mountainsystems and other less-favored areas where CIP can contribute to the achievement of healthyand sustainable human development.www.cipotato.org

CIP is supported by a group of governments, private foundations, and international andregional organizations known as the Consultative Group on International AgriculturalResearch (CGIAR).www.cgiar.org

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