volume 1Cultivation Practices and Potato Cultivars Suitable for Organic Potato Production

8/18/2019 volume 1Cultivation Practices and Potato Cultivars Suitable for Organic Potato Production

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Cultivation Practices and Potato Cultivars

Suitable for Organic Potato Production

Jannie Elisabeth Hagman & Anna Mårtensson &

Ulf Grandin

Received: 18 November 2008 /Accepted: 14 May 2009

# EAPR 2009

Abstract To identify the most important agronomic measures and cultivar traits in

Swedish organic potato production, multivariate analyses were performed on a set of

data from a series of field trials carried out in Sweden during a 7-year period. The

effects of soil parameters, cultivar, year and geographical location on potato

characteristics were investigated. Soil parameters including fertility level had strong

and significant effects on potato characteristics, explaining 53% of total variation.

Variables related to the duration of haulm growth were other dominant factors in the

variation. While P and K fertilization increased yields, N fertilization had little effect

on yield and a negative effect on the time to emergence. The N requirement of

potatoes ranges from 2.5 to 5.9 kg ha−1 per ton of tuber yield and was met in these

trials. The results implied the timing of N application is important for yield. It was

concluded that the importance of P and K fertilization is underestimated in organic

production, and that the most important cultivar trait in achieving acceptable yield is

long-lasting foliage, which is a characteristic of cultivars resistant to Phytophthora

infestans. Three of the cultivars tested (Lady Balfour, Cicero and Sarpo Mira) had a

yield >3.5 kg m−2, which is high in Swedish organic production.

Potato Research

DOI 10.1007/s11540-009-9128-3

J. E. Hagman (*)

Department of Crop Production Ecology, Swedish University of Agricultural Sciences,

Uppsala, Sweden

e-mail: [email protected]

A. Mårtensson

Department of Soil and Environment, Swedish University of Agricultural Sciences, Uppsala, Sweden

U. Grandin

Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences,

Uppsala, Sweden


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Keywords Cultivar . Fertilization . Organic production . Phytophthora infestans .

Potato . Yield loss

Introduction

In Sweden and several other countries in western Europe, government policy

initiatives and consumer demand have resulted in an increase in organic farming

during recent years (Hansen et al. 2001; Lynch et al. 2008; Eurostat 2009). The

proportion of organically certified agricultural production in Sweden has steadily

increased in recent decades, but organic potato production has not increased. Instead,

the acreage of organic potato production decreased by 30% during the period 2001 –

2006, and is now 2.5% of the total potato acreage (SCB 2002, 2007; SJV 2002).

Potato (Solanum tuberosum L.) is an important staple food in Sweden and is deeplyrooted in Swedish cultural traditions since it can be produced in most parts of the

country. The decrease in organic potato production in Sweden can most likely be

explained by several constraints, for example the higher production costs for organic

potatoes and the lower yields compared with those of conventionally produced

potatoes. In addition, organic production can be unpredictable owing to environ-

mental factors (e.g., climate and disease pressure), which can give large fluctuations

in quantity and quality. Losses due to insect and pest damage and overall poor

quality can be high (Hansen et al. 2001; Lynch et al. 2008; Maggio et al. 2008).

A particular threat in potato production is the serious late blight disease caused by theoomycete Phytophthora infestans. The disease affects both foliage and tubers and can

destroy an entire field within a few days. In conventional production, the disease is

controlled by fungicides and the crop is sprayed several times during the growing

season. There are no efficient agents to control late blight in organic potato production,

the only methods available being to rely on resistant cultivars and/or cropping measures

such as the use of early maturing cultivars and presprouting to advance maturity so

the crop is ready early in the season before late blight has had a chance to strike

(Karalus and Rauber 1997; Larsson and Hagman 2007; Möller and Reents 2007).

Conventional potato production is linked to heavy use of pesticides and nutrient

leaching, prompting the Swedish Board of Agriculture to fund a series of organic

potato trials to stimulate organic production.

The objective of this paper was to identify the agronomic measures and cultivar

traits important in achieving a good organic potato crop. The study is based on a

series of field trials carried out in Sweden over several years to screen different

potato cultivars for their suitability for organic production and to provide farmers

and advisers with more information about the different cultivars. Many quality traits

must be present to make a successful table potato. Important properties are consumer

acceptance, yield, storability and resistance to diseases such as late blight. Cultivars

entering this series of field trials were selected (in descending order of importance)

for high resistance to potato late blight, earliness (in combination with resistance to

late blight) and cooking quality. The resulting multidimensional dataset was

analysed using multivariate techniques that can be used to accurately identify both

sensory and quality traits in relation to cultivar and cultivation conditions

(Arvanitoyannis et al. 2008).

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Materials and Methods

Trial Set-up

The trials were conducted at five sites (A – E) (Table 1) spread over Sweden from thesouth (56.02°, 14.06°) to the north (63.81°, 20.24°). In total, 21 trials were

conducted during a 7-year period (2001 – 2007). Sites A and B were situated in potato

production areas with many surrounding potato fields, while the other three sites

were situated in areas with less intensive potato production. During individual years,

the same potato cultivars were included in all experiments, but different cultivars

were tested in different years. Each cultivar was generally tested for 3 years. In total,

17 cultivars were tested during the period (Table 2). The number of trials and trial

sites in operation varied between two and five per year. The seed potatoes for the

trials were produced annually under organic management (SJV 2007) at a siteoutside Uppsala (59.80°, 17.68°) to avoid carryover effects on the seed, for example

differences in physiological age.

The trials were managed according to common practices in organic potato

production. Soil content of N, P and K was analysed before fertilization. However,

data on soil N were obtained for only 93 of the 106 plots included in this study. The

fertilizer applied was farm manure or biological residues permissible in organic

farming. Total N, P, K and mineral N (NH4+, NO3

−) content of these organic

fertilizers was determined before application. The manure was applied in the spring a

couple of weeks prior to planting in amounts aiming at 90-100 kg NO3−

-N ha

−1

in thesouth of Sweden and 70 kg NO3−-N ha−1 in the north.

The levels of P and K varied according to which manure was used. For P the

levels were around 40 kg ha−1 in southern Sweden and 15 kg ha−1 in the north, while

the corresponding amounts for K were 110 kg ha−1 in southern Sweden and 50 kg

ha−1 in northern Sweden.

The seed potatoes were presprouted and planted with a semiautomatic potato

planter (Underhaug). Weeds were mechanically controlled by harrowing and hoeing.

Emergence and flowering of the different cultivars were assessed. The plots were not

treated against potato late blight. Tubers were harvested following standard farming

practices in the area. When necessary, haulms were killed by crushing them 2 weeks

before harvest. Plots were harvested with a potato lifter (Juko Midi, model 2000).

Table 1 Geographical coordinates and years for sites included in the statistical analyses

Trial sites Coordinates Trial year

2001 2002 2003 2004 2005 2006 2007

A 56.02°, 14.06° X X X X X X X

B 56.64°, 12.95° X X

C 57.13°, 18.23° X X

D 60.29°, 15.98° X X X X X X

E 63.81°, 20.24° X

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The field trials were laid out as a randomized complete block design with four

replicates and with six to eight cultivars in each trial. The plot size was 16 – 18 m2, with

some variation at the different trial sites. Parameters assessed in the field were time to

emergence (50% of plants emerged), days to flowering and number of stems per plant.

The physiopathological conditions in plots were assessed once a week from the first

appearance of late blight in the area. Each plot was assessed for late blight and non-

specific necrosis according to the scale developed by Anonymous (1947). After

harvest, tuber yield and size distribution were assessed for each plot. Harvested tubers

Table 2 Cultivars included in the field trials during the period 2001-2007 and in the statistical analyses

Cultivar Abbreviation Maturitya Country of

origina Year

2001 2002 2003 2004 2005 2006 2007

Appell App Intermediate b Sweden X X

Asterix Ast Intermediate to

late

Netherlands X X

Cicero Cice Early to

intermediate

Netherlands X X X

Ditta Ditta Early to

intermediate

Austria X X X X X

Escort Esc Early Netherlands X X X

Eve

Balfour

Eve Intermediate UK X

Fresco Fres Very early to

early

Netherlands X X X X

Lady

Balfour

Lady Very late UK

Matilda Mati Intermediate to

late

Sweden X X X X X X X

Ovatio Ovat Intermediate to

late

Netherlands X X

Princess Princ Very early to

early

Netherlands X X

Raja Raja Intermediate Netherlands X X X X X

Sarpo

Mira

Sarpo Very late Hungary X

Satina Sati Early to

intermediatecGermany X X X X

Superb Sup Intermediate b Sweden X X X

Symfonia Symf Intermediate Netherlands X X

Ukama Ukam Very early to

early

Netherlands X X

Verity Verity Intermediate UK X X X

a According to the European Cultivated Potato Database (http://www.europotato.org) when nothing else is

noted b Communication with breeder (SW seed)c Beschreibende Sortenliste Kartoffel 2003 (Bundessortenamt, Hannover, Germany)

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were sorted into five size fractions: 65-mm tuber diameter.

Each year, raw data from the individual field trials were compiled using the MIXED

procedure of SAS software (SAS Institute 1996), resulting in one accurate mean value

per variable and field trial for use in further calculations. Dry matter concentration was

determined in a sample of 200 g of graded tubers of 45 – 55-mm size. Cooking qualitywas assessed by cooking 25 peeled tubers. When cooked, the tubers were cut in half

and, after cooling, the incidence of sogginess, darkening and disintegration was

assessed by visual ratings according to the following norms of the Swedish Table

Potato Control Agency: sogginess was assessed by exerting pressure with the thumb

on the tubers and dividing soft tubers into the classes weak or strong sogginess; the

actual numbers of tubers showing darkening were recorded; and disintegration was

assessed as either weak disintegration with cracks in the outer parts of the tuber, or

strong disintegration with tubers falling apart. The incidence of weakly/strongly soggy,

darkened and weakly/strongly disintegrated tubers was then expressed as a percentageof the total. The incidence of late blight and other internal and external diseases was

determined in a sample of 50 tubers. This was first done by visual inspection of the

surface of the tubers and then tubers were sliced and the interior examined for

incidence of Phytophthora infestans in the tubers. These tests were performed for each

cultivar at every trial site.

Statistical Analyses

Multivariate methods were used to assess the effect of soil variables, cultivar, year of trial (2001 – 2007) and geographical coordinates ( x and y in the Swedish national

grid) on various potato characteristics. These potato characteristics were days from

planting to emergence, days from emergence to 2% necrosis, days from emergence

to 50% necrosis, days from emergence to haulm killing, total yield, yield of tuber

fraction


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The relationships between individual soil variables and potato characteristics were

assessed by principal component analysis (PCA) and RDA using the program

CANOCO version 4.5 (ter Braak and Šmilauer 2002). To avoid collinearity, Soil_Lo,

Soil_Si and CerW had to be deleted prior to the analysis owing to indications of

high-variance inflation factors in preliminary runs. The significance of eachremaining soil variable was tested using forward Monte Carlo testing ( P


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was therefore excluded from the variance partitioning in Fig. 2 to reduce thecomplexity of the illustration. The fraction of variation that could not be explained

by these four sets of explanatory variables was 26%. The relatively low contribution

from year shows that the results differed between the years included in the study, but

that this contribution to the total variation was close to negligible compared with the

variation caused by soil variables.

As the variance partitioning showed that soil variables were the dominant source

of variation, the importance of individual soil variables alone on potato character-

istics was assessed in a RDA ordination, (i.e. not including year and cultivar in the

analyses) (Fig. 3). The Monte Carlo permutation test showed that sandy soil and

earlier growth of spring cereals had non-significant relationships with the potato

characteristics examined here and they were therefore removed from the explanatory

dataset. The final results showed that variables related to duration of haulm growth

were the dominant factors for variation in the dataset, as indicated by their high

correlation to axis 1 (Fig. 3). The main explanatory factor related to duration of

haulm growth was ambient soil P. Yield was also relatively highly related to axis 1,

but in addition was affected by P and K fertilization to a much higher degree than

haulm growth. Phosphorus fertilization and K fertilization were also positively

correlated with Phytophthora infestans incidence in tubers. The ordination indicated

a very weak relationship between ambient soil P and P fertilization, and a weak

correlation between ambient soil K and K fertilization. These results were confirmed

in independent tests of the correlation between these two pairs of variables (P, r =

−0.17; K, r =−0.30; P >0.05 for both). Thus, irrespective of ambient soil levels, P

fertilization and K fertilization were the most important variables for yield. In

contrast, N fertilization had little effect on yield and had a negative effect on

Fig. 2 Variance components explaining the variation in potato characteristics. Circles represent explained

variation and the area outside the circles represents unexplained variation. Values show the variation

explained by each circle section or intercept individually. Values less than zero are not shown

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emergence, i.e. additional N fertilizer delayed emergence. The negative effect of N

was also indicated by the peripheral position of peas as the preceding crop in the

ordination diagram. A univariate correlation test between yield and N fertilizer ( r =

−0.04, P >0.6) reconfirmed that these two variables were uncorrelated in this study.

As the results of the multivariate analyses showed that yield and N fertilization had a

weak relationship, we tested whether this pattern was an effect of different levels of

fertilization of different cultivars. However, there were no significant differences in

the amount of N applied to different cultivars (analysis of variance, F 19.94=0.6, P >

0.9). We also tested the effect of ambient soil N on yield, using a subset of the data

for plots where data on soil N were available (n=93). The results showed that soil N

was also uncorrelated to yield (r =−0.01).

Eight cultivars (Fresco, Symfonia, Appell, Ditta, Matilda, Asterix, Satina and

Ukama, in decreasing order) were negatively related to yield, while the other cultivars

were more or less positively related to the yield vector in the RDA (Fig. 3). This is

illustrated by the perpendicular projection of the cultivars onto the yield vector and its

elongation to the right of the origin in the ordination diagram. The same eight

cultivars, with the addition of Ovatio, also showed the strongest negative relationships

to the persistence of foliage. In our experiment, all three variables expressing time to

decay of foliage were positively related to yield, i.e. the longer the period before the

foliage started to decay, the higher the tuber yield. It is known that foliage decay in

organic potato production is mainly caused by late blight. This suggests that cultivars

with a high resistance to late blight have the greatest potential for high yield.

Fig. 3 Redundancy analysis ( RDA) showing potato characteristics (lower case) and significant soil

variables (title case) as vectors for continuous variables and points for binary variables. Cultivar (italics) is

added as a passive variable for help in visual interpretation of the diagram (abbreviations in Table 2).

Isolines indicate the value of the variable ‘yield’ (kg m−2) in the ordination space. Axis 1 explains 20% of

the variation and axis 2 explains 7.6%

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Discussion

Our main objective was to identify important cultivation factors and cultivars

suitable for organic production. In this respect, ‘suitable’ was defined as a cultivar

giving a reliable crop, acceptable yield and tubers with good cooking qualities.One of the most important results from the RDA of the data was that neither N

fertilization nor soil N was significantly related to yield. This contradicts the results

from many other studies. It is frequently reported that N has great importance for

potato tuber yield (van Delden 2001; van Delden et al. 2003; Roinila et al. 2003;

Möller et al. 2007). The N requirement of potatoes ranges from 2.5 to 5.9 kg N ha−1

for each ton of tuber yield (Munoz et al. 2005) and this was met in the trials

described in this paper. Haulm development is said to be strongly affected by N

supply/availability in the first weeks after emergence (Millard and MacKerron 1986;

Harris 1992; Vos 1995). Increased N supply is reported to give a faster full canopyand longer leaf area duration, and thus increased yields (Millard and MacKerron

1986; Grindlay 1997). It has also been reported that N is the main factor limiting

yield in organic potato cultivation (Vos 1995; Finckh et al. 2006; Haase et al. 2007;

Möller et al. 2007). In addition, many factors have synergistic interactions, for

example irrigation, N fertilization and farming system (Maggio et al. 2008). Findings

that support our results are that N-use efficiency appears to be higher in low-input

systems (Finckh et al. 2006) and that the potato crop responds to limited N levels by

maximizing light-use efficiency (van Delden 2001). An important aspect is that N

availability is difficult to predict if the N is applied in organically bound form, as isthe case in organic cultivation systems (Varis et al. 1996; Gastal and Lemaire 2002;

van Delden et al. 2003), and the timing of N release is crucial for good results.

Increased N availability in conjunction with tuberization can extend the vegetative

growth period and delay tuber development, both of which lead to decreased yield

(Burton 1966; Alva 2004; Love et al. 2005). The long-term effects of manure in the

whole crop rotation may have a greater influence on potato quality than the short-

term effects, owing to the slow release of nutrients and the beneficial effects of

manure on soil biological activity (Roinila et al. 2003). The results of the present

study show how difficult it is to synchronize crop demand with N availability. In

Sweden, the vegetation period is short and therefore delayed tuberization can have a

negative effect on yield. Nitrogen fertilizer levels are generally low in both organic

and conventional farming in Sweden compared with further south in Europe. In the

field trials described in this study, fertilizer was applied in spring, a couple of weeks

before planting. This could have resulted in high soil mineralization of the N applied

and in turn increased plant-available N to a level where N was no longer the main

yield-limiting factor. From the results, it can be concluded that N was not a yield-

limiting factor.

Potassium nutrition can be a constraint in organic potato production as there are

few organic fertilizers rich in K (Finckh et al. 2006). The strong correlation between

yield and K and P fertilization in this study (Fig. 3) indicates that these nutrients

were the most restricted and potentially yield limiting.

Duration of haulm growth, measured as the number of days from emergence to 2,

50 and 100% necrosis or haulm killing, was the dominant factor explaining variance

in the dataset, and time to foliage decay showed a positive correlation with yield.

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Haulm degradation was related to outbreaks of late blight, but could also be

attributed to other diseases or stage of maturity. According to Finckh et al. ( 2006)

and Speiser et al. (2006), the selection of cultivars with a high resistance to late

blight ( Phytophthora infestans) is an important strategy in organic potato production.

It was also one of the characteristics for which cultivars were chosen in the present study. Our RDA showed a long period before foliage decay to be associated with

high yield. This suggests that resistance to Phytophthora infestans is an important

trait in cultivars suitable for organic production.

The RDA also indicated a relationship between yield and number of days

between planting and emergence. A long period between planting and emergence

was associated with low yield, which agrees with findings that presprouting of

seed tubers has a positive impact on tuber maturation by accelerating crop

development (Karalus and Rauber 1997; Möller and Reents 2007; Paffrath and

Milz 2008). This suggests that measures that promote fast emergence, e.g., soil preparation or presprouting, have a beneficial effect on tuber yield. However the

opposite can also occur, as presprouting can make the plants more susceptible to

both Phytophthora infestans and Alternaria solani (Zarzynska and Goliszewski

2007), which reflects the difficult decisions that have to be taken in organic potato

production.

Early maturing cultivars have early tuber bulking and hence a chance to

achieve significant tuber yield before the crop is infected by Phytophthora

infestans, and therefore maturation type was another trait for which cultivars were

selected in these trials. Unfortunately there is an interaction between maturation typeand susceptibility to late blight, with early maturing cultivars often being more

susceptible (Toxopeus 1958; Ross 1986; Visker 2005; Razukas et al. 2008). This

was observed in the present study, where early maturing cultivars were often the first

to develop late blight. However, the RDA could neither verify nor reject the

possibility that early maturing cultivars could achieve acceptable yields by escaping

late blight (Fig. 3). The highest yields were achieved by both late and early maturing

cultivars.

Cooking quality variables were of subordinate importance in the ordination

diagram, primarily indicated by the short vectors for cooking quality variables

(Fig. 3). If cooking quality had been a major variance component related to the

explanatory variables in this dataset, these variables would reflect the inherent

cooking quality of different cultivars. However, this was not the case and instead

variables related to growth dominated the ordination. The passively added cultivars

showed, for example, that cv. Symfonia was one of several cultivars negatively

associated with disintegration and darkening. Cv. Symfonia has inherently high

levels of disintegration and darkening, but the ordination rather suggested the

opposite. However, RDA is a constrained ordination, which means that the response

variables (lower case in Fig. 3) are constrained by the variance structure in the

explanatory variables to show the relationship between response and explanatory

variables. In the unconstrained ordination on the same dataset (Fig. 1) the cooking

quality variables were up-weighted, while the other variables largely remained as in

the constrained ordination. Thus, cooking quality was an important variance

component in the response dataset, but it is merely an inherent characteristic of the

cultivars rather than an effect of nutrients.

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On the basis of the results of this study, we conclude that the importance of P and

K fertilization is underestimated in organic production in Sweden today and that the

most important cultivar trait in achieving acceptable yield is a long period before

onset of foliage decay, which is present in cultivars resistant to Phytophthora

infestans. Three of the cultivars tested (Lady Balfour, Cicero and Sarpo Mira) had ayield of more than 3.5 kg m

−2, while five cultivars (Eve Balfour, Escort, Superb,

Ovatio and Princess) yielded more than 3 kg m−2, which is a high yield for organic

potato production in Sweden. All of these cultivars except Princess have very good/

good resistance to Phytophthora infestans. Among these cultivars, Cicero, Sarpo

Mira, Superb, Ovatio and Princess are considered tasty and suitable as table

potatoes.

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volume 1Cultivation Practices and Potato Cultivars Suitable for Organic Potato Production

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