Jalpo potato discovery version

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JALPO POTATO DISCOVERY 2010

EDITION

It is the intention of the JALPO that the POTATO DISCOVERY should help the VIEWER to discover the most important factors which influence the production and development of the potato crop and to comprehend their interaction.

The JALPO accept no liability for any inaccuracies that might possibly be found or negative consequences of the use of information contained in the JALPO POTATO DISCOVERY.

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PRODUCTION

PLANT & TUBER RELATION

ECOPHYSIOLOGYSEED PREPARATION

SEED RATE AND CROP DENSITY

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The potato plant

Partitioning of CarbohydratesCarbohydrates are used for the haulm growth and tuber growth. Haulm is needed for photosynthesis and has to be kept functional for a sufficient period. In an efficient production the major part of the carbohydrates is used for tuber growth. A relation between haulm growth and tuber growth exists. A too abundant haulm growth delays tuber growth. It is avoided to build the "carbohydrate factory" larger than needed for production.

PARTITIONING CARBOHYDRATESRootsThe roots are essential for the uptake of water and nutrients from the soil.

ROOTS

The potato used for consumption is a tuber bearing herbaceous plant. Main plant parts are: haulm (foliage), tubers and roots.

Potato Plant

Foliage The main functions of the foliage (leaves and stems) are photosynthesis and respiration. The foliage is the "factory" of the plant in which the carbohydrates are produced. These carbohydrates are used for haulm- and tuber growth. The foliage is not suitable for consumption, but is occasionally used as cattle food or fuel.

HAULM (FOLIAGE)Tubers

The tubers are used for consumption and for reproduction.TUBERS

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Haulm The haulm consists of aerial and below soil level stems. The areal stems are in general hollow and triangular in cross section. The lower part of the stem is round and solid. The stolons and the roots grow on the below soil level stem parts. Mature leaves are compound, consisting of a petiole with terminal leaflet, lateral leaflets, secondary leaflets and sometimes tertiary leaflets. The foliage of the crop is the "carbohydrate factory". Green leaves intercept light and CO2 and water is converted in carbohydrates and water. Indicators for light interception are: stem density, the morphological growth of the stem, LAI and percentage ground cover.PHOTOSYNTHESIS & RESPIRATION

Stem density and crop density. Crop density is either expressed as number of main stems per m2 or as the number of plants per hectare. As a rule of thumb: the density for a consumption potato crop is 15 - 20 main stems per m2 or 35 000 - 40 000 plants per HA .A main stem is considered as a plant unit. From a seed 1, 2, 3, 4 or more main stems may develop and it is more accurate to express crop density as number of stems per hectare, than as number of plants per hectare. A stem is considered to be a main stem if it grows directly from the seed tuber. The lower lateral branches from the stem are called secondary stems. If a secondary branches off from the main stem, then this secondary stem may be considered as a main stem. Mainstem and secondary stem

Morphological growth of the stemApart from lateral branching a potato stem may develop apical branches several times during its growth according to a certain pattern, while the lower (first leaves of the plant) drop from the plant or turn yellow. In fact during the production season the older leaves at the lower part of the plant are replaced by new leaves at the top of the stem. Morphology haulmgrowth

During the first phases leave haulm growth is fast and later slower. Haulm growth at various phases of growth Consequently spraying schedules for late blight need to be adjusted to haulmgrowth.SPRAYING SCHEDULES

Percentage ground coverThis is an important crop characteristic since it indicates what percentage of the incoming solar irradiation is used for photosynthesis. Ground coverage with green leaves

Leaf area index-LAILeaf area index-LAI is the ratio of leaf surface over soil surface.LEAF AREA INDEX

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TU B ER Y IELD ESTIM A TIO N

Tuber yield estimationA basic formula for production is:

Foliage and productionA judgment of the foliage in terms of: crop density (stem density), light interception, the quality of the foliage as well as on a balanced plant growth is necessary to estimate yield.A balanced crop shows sufficient, but not abundant, haulm growth.

Production per day - bulkingIt is estimated that, once the full bulking has started, the daily increase in tuber yield (the bulking rate) is close to 700 kg per hectare per day.Thus each day that the foliage remains healthy green, is turgid and intercepts 100% of the incoming light, the yield increases with 700 kg per hectare. With long days and high light intensity in optimal conditions a producton of 1000 kg per hectare/hectare/day may be reached.

Balanced plant growthA balanced plant growth is needed to obtain optimum tuber growth. Haulm growth can neither be too abundant nor be too limited, but has to be adjusted to optimal production in the period available for production.

Calculations on potential yieldPotential yields can be calculated based on light interception. Such calculations allow comparisons between potential yield with actual yield.The gap between both the actual- and the potential yield is an indication for improvements to be made.

Tuber yield estimationPotential yield of a potato crop is estimated by judging a number of crop characteristics at a certain stage of the crop: • plant density • stem density • percentage soil cover (ridge size and ridge shape) • colour of leaves (nutrition) • ratio: haulm growth/tuber growth • growth stage of the crop in relation to the period still suitable for growth • presence of diseases and pests • availability of water

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Leaf Area IndexLeaf area index and light interception

Leaf area index ( LAI ) is the ratio of leaf surface over of soil surface. LAI is the figure that indicates from a plant, the number of layers that can be covered with leaves from that plant on the soil surface where the plant is growing.For example: a Leave Area Index of 3 means that with all the leaves of this crop the soil, on which it is growing, can be covered with three layers of leaves. Leaf area index is determined measuring the surface of all the leaves of a plant. The sum of these leave surfaces is divided by the surface of soil that a plant occupies.In a crop with a closed canopy and 40 000 plants per hectare, one plant occupies 2500 cm2 soil surface. With a LAI=3 the total surface of all the leaves of the plant then totals 7500 cm2). For the determination of the LAI the plant cannot be kept intact, while also the determination of the LAI is labour intensive. Leaf area index ( LAI ) and percentage of soil coverage with green leavesOften the more practical method to determine the leaf size as an indication for light interception is the determination of the percentage of soil coverage by green leaves. With a LAI of 3 almost 100% of the incoming light is intercepted and thus LAI = 3 corresponds with a soil coverage of 100%.

Percentage soilcoverage

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TUBERS

The tuber can be considered as a part of the stem which is adapted for food storage and reproduction. The tuber may be regarded as an enlarged stolon.

The quality of potato tubers is a.o. determined by size, chemical composition. These are influenced by: variety, growing conditions (duration) and storage.SIZE OF TUBERSCHEMICAL COMPOSITION TUBERQUALITY FRESH POTATOESWASHING AND GRADING PICTURESQUALITY PROCESSED POTATOES

SkinThe skin of a mature tuber is almost impermeable to chemicals, gases and liquids and also provides good protection against micro-organisms and water loss.The rudiments of the scale leaves (the eyebrows) and of the buds (the eyes) in the axis of the scale leaves can still be seen on the skin. Each eye has more than one bud. The skin of the tuber has many lenticels. They may be considered as the stomata of the tuber.

Cross sectionIn cross section of the tuber the following zones are visible: Outer cork layer (periderm), inner storage parenchyma, outer storage parenchyma and vascular ring. The distance between the skin and the vascular ring is normally 0.5 cm, but the skin and the vascular ring are more or less in contact near the eyes and the stolon attachment.

Cross section tuber

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CROSS SECTION TUBER

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PARTITIONING CARBOHYDRATES

Growing pattern (partitioning of assimilates)Growing pattern

The growth of the potato crop shows a certain pattern. There are the following stages: pre-emergence/emergence -haulm growth - tuber growth.

Crop patternPlanting, emergence, haulm growth, tuber growth, maturity • From planting to emergence takes 2-4 weeks. • Tuber initiation starts 3 weeks after emergence. • At first tuber growth is slow and continues at a constant rate (bulking rate = 700-1000 kg/hectare/day) as long as the haulm is

active and green. • Tuber growth stops when 80% of the leaves are dead QUICK EMERGENCE

Short cycle crop and long cycle cropAs example a short cycle crop and a long cycle crop are given.

Long- and short cycle cropUntil the end of May the 'short cycle crop' yields 6.5 tonnes more than the 'long cycle crop'.Then the 'short cycle crop' matures, while the 'long cycle crop' continues to grow.Later in the season (end of July) the yield of the 'long cycle crop' is 7.5 tonnes higher than that of the 'short cycle crop'.Factors affecting the crop cycleAlthough there is an interaction between the factors which influence the crop cycle, each of them may have an effect of its own on

tuber growth and haulm growth.FACTORS AFFECTING HAULM GROWTH AND TUBER GROWTH

Growing pattern adapted to available growth periodThe growth pattern of the crop is adapted to the period available and the crop uses this entire period. If the cycle of the crop is shorter than the length of the available growing period, the yield is lower than would have been the case with a better utilization of the available period. If on the contrary the pattern is longer than the available season, too much carbohydrate is used for haulm growth and at harvest the crop is still immature.For a good yield a balanced plant growth is needed, with neither too much foliage nor too little foliage .

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CROP PATTERN

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LONG- AND SHORT CYCLE CROP

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FACTORS AFFECTING HAULM GROWTH AND TUBER GROWTHSeed age, variety, day length/temperature and nitrogen influence the relation between haulm growth and tuber growth.

Seed ageSeed age, physiological stage and seed vigour affects the growth of the plant. A crop grown from seed in the optimal physiological condition produces a vigorous crop.

SEED PHYSIOLOGY AND GROWTH PATTERNVarietyThere are early-, mid early-, mid late- and late maturing varieties. The first group of varieties matures in a relatively short production season (short cycle crops), whereas the late maturing varieties mature later and are better adapted to situations where the growing season suitable for production is longer (long cycle crops).

Temperature and day lengthTemperature and day length strongly influence the growing pattern of varieties. Short day stimulates tuber initiation and restricts haulm growth (initiation of short cycle crops)Relatively high temperature, combined with long day, tends to delay tuber initiation and to stimulate haulm growth.There is an interaction between day length and temperature with regard to tuber initiation of varieties.

High temperature delays tuber initiation more in long day than in short-day conditions.The short day conditions in the tropics allow, that at relatively high temperatures cultivars from temperate long day can be grown here in 120 days. Long cycle varieties (andigenum type) from the short day cool highlands conditions, are neither suitable for the high temperature tropics nor for the long day temperate climates.

Nitrogen, haulm growth and yieldNitrogen is not only a nutrient, but also acts as a growth regulator. In high doses it stimulates haulm growth, delays tuber growth and may delay the crop to mature in time.

At low nitrogen the haulm development is poor(LAI=lower than 3), tuber growth starts early, bulking rate is relatively low and if harvested before the first week of May the highest yields are obtained.At high nitrogen, the haulm growth is abundant, tuber growth starts late, bulking rate is high but maturity is late. The yield may be high if crop reaches to maturity.The high nitrogen crop is a risky crop since it takes a long time to mature. The medium nitrogen crop gives the highest yield if harvested between the end of June.

The medium nitrogen crop is considered to be the safest crop, since it still matures relatively early (end August) and yields high.

Hail and frostHail and frost affect potato yields. Yield reduction depends on severity of damage and the stage of growth when it occurs.There is an interaction between day length and temperature with regard to tuber initiation of varieties.

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SEED PHYSIOLOGY AND GROWTH PATTERN

Seed sprouting stagesSprouting methods

Seed tubers after the end of dormancy taken from the cold store (2-4 oC) and taken to higher ambient temperature start sprouting in about 1-2 weeks (Mini-sprouting of seed). When kept in dark conditions and in piles (bulk or bags) for longer time the sprouts will be long, weak and slender. By separating the bags to allow ventilation sprout growth is slower and sprouts are less weak.When pre-sprouted seed is required the seed is taken from the cold store 6-8 weeks from the store, if necessary the apical sprouts are removed and the seed is placed in thin layers in trays allowing the light to reach the spouts. The seed develops in this way firm and strong sprouts.

Sprouting in bags Sprouting in tray Pregerm sprouting method

Characteristics of sprouted seed 1.non sprouted seed non-dormant tubers - the eyes are 'closed':emergence is slow and growing sprouts are easily attacked by micro- organisms. 2.mini sprouted seed - tubers start sprouting with small sprouts (the eyes 'open' and greenish-yellow coloured buds are visible):emergence is faster. 3.pre-sprouted seed - under light conditions, tubers produce strong sprouts of 1-2 cm: pre-sprouted seed germinates quickly, roots develop early and the stems are vigorous. Sprouting stagesPre-sprouting leads to: an early crop, early emergence and early tuber initiation. A 10 days earlier emergence and tuber initiation can be expected. regular emergence and regular crop (= less subject to Rhizoctonia attack) a relatively high yield when the available growing season is short. early suppression of weeds by early canopy closure. an earlier crop that may escape virus or Late Blight infection. Sprouting and emergence

Example pre-sprouted crop:

A crop from pre-sprouted seed can be considered as a short cycle crop and a crop from mini-sprouted seed as a long-cycle crop. A crop from pre-sprouted seed is earlier, while the crop from mini-sprouted seed may mature later and continue to produce for longer.

Sprouting and crop cycle

Harvested until mid-July the 'pre-sprouted' crop in the given example, yields 4.5 tonnes of potatoes more than the 'mini-sprouted' crop. Then the 'pre-sprouted' crop matures, while the 'mini-sprouted' crop continues to produce. Finally the yield of the 'mini-sprouted' crop at late harvest is 3.5 tonnes higher.

PROFIT PRE-SPROUTING

SEED PREPARATION

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SPROUTING IN BAGS

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SPROUTING IN TRAY

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PREGERM SPROUTING METHOD

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SPROUTING STAGES

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SPROUTING AND EMERGENCE

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SPROUTING AND CROP CYCLE

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PROFIT PRE-SPROUTINGBudget: Pre-sprouted / mini-sprouted seed

Example pre-sprouted crop: A crop from pre-sprouted seed can be considered as a short cycle crop and a crop from mini-sprouted seed as a long-cycle crop. A crop from pre-sprouted seed is earlier, while the crop from mini-sprouted seed may mature later and continue to produce for longer.

Sprouting and crop cycle

Harvested until mid-June the 'pre-sprouted' crop in the given example, yields 4.5 tonnes of potatoes more than the 'mini-sprouted' crop. Then the 'pre-sprouted' crop matures, while the 'mini-sprouted' crop continues to produce. Finally the yield of the 'mini-sprouted' crop at late harvest is 3.5 tonnes higher.

The costs of pre-sprouting are € 0.06 higher than the costs of mini-chitting.The seed rate is 2000 kg per hectare.The price of the potatoes at early harvest is € 0.25 per kg and € 0.15 at late harvest.Partial Budgets

At early harvest for the extra investment in pre-sprouting the rate of return is 7.3This high rate of return for the higher sprouting costs certainly justifies the extra costs for pre-sprouting

At late harvest for the extra investment in pre-sprouting the rate of return is 0.25This low rate of return for the higher sprouting costs does not justify the extra costs for pre-sprouting

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ROOTSRoots and water use

Plants growing from tubers develop adventitious roots at the nodes of the underground stems and stolons. Plants grown from true seed develop a slender tap root from which lateral branches arise.

Uptake of water from ridges and from deeper soil layersThe roots are essential for the uptake of water and nutrients from the soil. Only part of the water needed is extracted from the ridge. The remaining part needed comes from deeper soil layers

Water use of single plantRooting depth and irrigation frequencyCompared to other crops, potato roots rather shallow (often no deeper than 40 to 50 cm).If, however, no obstructive layers or sharp transitions from one soil type to another occur in the soil profile, plants may root as deep as 1 m. When rooting is deep, irrigation can be less frequent than when rooting is shallow. For the growth of roots the presence of oxygen is essential. With too heavy irrigations in the early growth of the crop there will be a lack of oxygen and root growth is hampered. Compacted layers hamper root growth.

Rooting depth and soil conditions

Measures that can be taken to make conditions advantageous for deep rooting are:

• select fields with good physical soil properties • avoid too heavy irrigation in the early stages of crop growth • adequate soil tillage operations • avoid soil compacting

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WATER USE OF SINGLE PLANT

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ROOTING DEPTH AND SOIL CONDITIONS

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ECOPHYSIOLOGY

Production ProcessCrop production is a process and the tuber yield is high if: • the dry matter production per day is high • the production takes place over an extended period (number of days) • a large proportion of the dry matter is used for tuber growth (harvest index) • the growing pattern of the crop is adjusted to the length of the available growing period

Growing pattern and available growing periodYield is optimal when the growing pattern of the crop is adjusted to the length of the available growing period.

GROWING PATTERN-PARTITIONING ASSIMILATESHarvest indexThe ratio: total tuber production/total plant production

Dry matter contentIn a given period of time a certain quantity of dry matter is produced. Dry matter content is often inversely correlated with yield: Varieties with high tuber yield often have a relative low dry matter content; Varieties with high dry matter content often have a relative low tuber yield.

Tuber yield estimationAt any stage of the crop, the final crop yield can be fairly well estimated, by judging: tuber formation, condition of foliage, maturity stage of the crop and the expected time still available for production.

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Growing pattern (partitioning of assimilates)Growing pattern

The growth of the potato crop shows a certain pattern. There are the following stages: pre-emergence/emergence -haulm growth - tuber growth.

Planting, emergence, haulm growth, tuber growth, maturity • From planting to emergence takes 2-4 weeks. • Tuber initiation starts 3 weeks after emergence. • At first tuber growth is slow and continues at a constant rate (bulking rate = 700-1000 kg/hectare/day) as long as the haulm is

active and green. • Tuber growth stops when 80% of the leaves are dead QUICK EMERGENCE

Short cycle crop and long cycle cropAs example a short cycle crop and a long cycle crop are given.

Until the end of May the 'short cycle crop' yields 6.5 tonnes more than the 'long cycle crop'.Then the 'short cycle crop' matures, while the 'long cycle crop' continues to grow.Later in the season (end of July) the yield of the 'long cycle crop' is 7.5 tonnes higher than that of the 'short cycle crop'.Factors affecting the crop cycleAlthough there is an interaction between the factors which influence the crop cycle, each of them may have an effect of its own on

tuber growth and haulm growth.

Growing pattern adapted to available growth periodThe growth pattern of the crop is adapted to the period available and the crop uses this entire period. If the cycle of the crop is shorter than the length of the available growing period, the yield is lower than would have been the case with a better utilization of the available period. If on the contrary the pattern is longer than the available season, too much carbohydrate is used for haulm growth and at harvest the crop is still immature.For a good yield a balanced plant growth is needed, with neither too much foliage nor too little foliage . HAULM GROWTH AND TUBER GROWTH RELATION

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Haulm growth and tuber growth relationRoot growth, haulm growth and uptake of water and mineralsAfter emergence the haulm and the roots develop simultaneously. If conditions are not favourable for root growth, also haulm growth is poor and thus the "starch factory" of the plant will not produce enough assimilates to obtain good yields. Adequate mineral and water supplies are needed for good functioning of leaves.

Relation tuber growth and haulm growthDuring a part of the growing season haulm growth and tuber growth proceed simultaneously. A too abundant haulm growth delays tuber initiation and delays crop maturation. Too little haulm growth may lead to an early maturity of the crop and if LAI is below 3 to a low bulking rate. Tuber growth starts slowly 3 weeks after emergence and continues at a constant rate during the bulking period.

Factors affecting haulm and tuber growthSeed physiology, external factors (day length and temperature) and Nitrogen influence the relation between haulm growth/tuber growth.

FACTORS AFFECTING HAULM AND TUBER GROWTH

Under favourable conditions during the bulking period growth rate is estimated to be 700 kg - 1000 kg potatoes per HA and per day.

DroughtDuring a draught period, the rate of bulking is low.After a drought period early in the season the plant may recover, but this is not the case if the drought period is more to the end of the season. Bulking rate and drought

Hail and frostHail attack cause haulm damage and yield reduction. Yield reduction is high if hail is severe and attack is later (plant cannot recover) in the season. After young plants are damaged by a night frost, these plants may recover.

HAIL AND FROST

Late blightIf the foliage dies due to late blight, the tuber growth stops and the yield of the crop is low.Other diseases causing an early dying (or destruction) of the foliage,which results in low yield, are Early blight

Late blight (or other foliar disease) and yield reduction

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HAIL AND FROST

Hail and night frostHail and night frost affect potato yields. The yield reduction will depend on: • the severity of the damage and • the stage of growth when damage occurred. Young plants may recover after damage and older plants may not.

HailThe example given shows that yield reduction is greater if the crop is attacked just after flowering rather than before flowering, because the later attacked crops do not recover.

Hail damage

Night frostIf night frost occurred in an earlier stage of growth the yield reduction is may be limited, but in case of a later attack later in the season the damage can be a disaster. Yield is low and quality is poor (small tubers, low dry mater, high sugar).In fields it is occasionally noticed that contrary to the majority of the older plants some of the younger plants have a reasonable re-growth

Frost damage

Risk for attack by nigh frost is reduced by: • to avoid soil tillage operations shortly before night frost is expected, • to cover of emerging plants by ridging, • to moisten the soil by irrigation shortly before low temperatures are expected.

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HAIL DAMAGE

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FROST DAMAGE

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LATE BLIGHT

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Seed preparationFor seed potatoes there are several treatments: sorting, sprouting, cutting, seed disinfection.

SortingPrior to selling seed lots or using them for planting, these lots have to be brought up to the minimum seed standards by sorting. Lots containing tubers infected with quarantine diseases (e.g. brown rot) should not be used as seed and be destroyed. Sorting should take place not earlier than a few weeks before the seed is sold or planted. Seed lots that have already reached the "normal sprouting stage" and have been prepared for selling/planting, should after sorting not be kept at high temperatures but temporarily be returned to the cold store in case there are doubts that the seed is being sold/planted within two weeks after sorting.

SEED QUALITY

Sprouting

Sprouting of seed accelerates the emergence of a crop. Especially when the available growing period is short or when there is a risk of Rhizoctonia, sprouting of the seed is recommended. In no case non-sprouted seed, which comes directly from the cold store, should be planted . Before it is planted the seed should at least be exposed to higher temperatures for a week.

SEED SPROUTINGCuttingIt may be considered cutting large tubers or tubers still in a physiological young stage.CUTTING OF SEEDChemical seed treatmentBefore storage and/or planting the seed may be treated with chemicals to reduce losses and/or to control diseases.

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Seed quality characteristicsEssential seed quality characteristics are:

1. Purity of the variety

The seed should be of the variety as which it is sold 2. Physiological stage

At planting time the seed should be in such a physiological stage that emergence takes place quickly. The period between planting and emergence is a delicate stage and should be kept as short as possible.

3. Seed sizeThe seed should be of the size specified.

4. Virus diseasesThe seed should have no higher percentage virus infested tubers than is justified for the purpose for which the seed is to be used: e.g. the production of table potatoes or seed.

5. Quarantine diseasesThe seed should be free of dangerous quarantine diseases, such as brown rot (Pseudomonas) and ring rot (Corynebacterium).

6. Diseases spread easily during the season when infected seed is plantedThe seed should not be infected with diseases that spread easily during the growing season and which may destroy the crop (e.g. Phytophthora infestance)

7. Diseases which negatively affect the quality of the potatoes when infected seed is plantedCommon scab, Rhizoctonia. Seed programs aim at the production of quality seed and at reducing the risks of spreading soil-borne and seed-borne diseases which negatively affect potato quality.

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SEED SPROUTING STAGESSprouting methods

Seed tubers after the end of dormancy taken from the cold store (2-4 oC) and taken to higher ambient temperature start sprouting in about 1-2 weeks (Mini-sprouting of seed). When kept in dark conditions and in piles (bulk or bags) for longer time the sprouts will be long, weak and slender. By separating the bags to allow ventilation sprout growth is slower and sprouts are less weak.When pre-sprouted seed is required the seed is taken from the cold store 6-8 weeks from the store, if necessary the apical sprouts are removed and the seed is placed in thin layers in trays allowing the light to reach the spouts. The seed develops in this way firm and strong sprouts.

Sprouting in bags Sprouting in tray Pregerm sprouting method

Characteristics of sprouted seed 1.non sprouted seed non-dormant tubers - the eyes are 'closed':emergence is slow and growing sprouts are easily attacked by micro- organisms. 2.mini sprouted seed - tubers start sprouting with small sprouts (the eyes 'open' and greenish-yellow coloured buds are visible):emergence is faster. 3.pre-sprouted seed - under light conditions, tubers produce strong sprouts of 1-2 cm: pre-sprouted seed germinates quickly, roots develop early and the stems are vigorous. Sprouting stagesPre-sprouting leads to: an early crop, early emergence and early tuber initiation. A 10 days earlier emergence and tuber initiation can be expected. regular emergence and regular crop (= less subject to Rhizoctonia attack) a relatively high yield when the available growing season is short. early suppression of weeds by early canopy closure. an earlier crop that may escape virus or Late Blight infection. Sprouting and emergence

Example pre-sprouted crop:

A crop from pre-sprouted seed can be considered as a short cycle crop and a crop from mini-sprouted seed as a long-cycle crop. A crop from pre-sprouted seed is earlier, while the crop from mini-sprouted seed may mature later and continue to produce for longer.

Sprouting and crop cycle

Harvested until mid-July the 'pre-sprouted' crop in the given example, yields 4.5 tonnes of potatoes more than the 'mini-sprouted' crop. Then the 'pre-sprouted' crop matures, while the 'mini-sprouted' crop continues to produce. Finally the yield of the 'mini-sprouted' crop at late harvest is 3.5 tonnes higher.

PROFIT PRE-SPROUTING

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CUTTING OF SEED

In many countries seed cutting is practiced, especially if the seed size is large. This is done to: • economize on seed costs, • stimulate sprout growth if seed is still dormant, • increase stem number if seed is still in the early apical stage. Either plant cut seed directly in moist soil and cover immediately or cut seed prior to planting and store a few days

underconditions favourable for suberization (temperature about 15 C, relative humidity 85% and a sufficiently high oxygen

contentof the air.Seed pieces, either freshly cut and planted or properly healed before planting, can be just as productive and healthy aswhole small seed tubers. The desired seed piece size from the stand point of productivity and planter performance is:28 g and < 56 g.Soil conditions at planting are frequently favourable for suberization or healing of the cut surface so that freshly-cut

seedpieces can be planted directly after cutting. This requires that the cutting operation and the planting operations besynchronized to avoid holding unplanted cut seed pieces an extended length of time.It is safe to cut seed tubers some time ahead of planting if storage conditions promote healing of the cut surfaces.Wound healing is best accomplished by:1) holding the cut seed pieces 3 to 5 days at temperatures of 13-18 C,2) maintaining a relative humidity of at least 85 percent, and3) providing good ventilation.

Failure to provide any of these conditions can lead to seed piece decay. Seed cutting (drawing) Seed cutting

RisksThe percentage emergence may be lower if cut seed is used (due to seed piece decay). In general the percentage ofemergence is inversely proportional to the size of the cut tuber pieces.Another disadvantage of cutting may be the transmission of certain diseases by means of the knife: PVX, PVS, ring rot(Corynebacterium sepedonicum), brown rot (Pseudomonas solanaecearum), blackleg (Erwinia carotovora var.

atroseptica).The following measures are relevant to reduce risks:

• do not cut seed when there is a risk transmitting of dangerous diseases (contaminated lots). • periodically disinfect cutting tools in a 1% solution of calcium hypochlorite. • do not cut physiologically old seed. • do not use cut seed when soil temperature is high (e.g. 25 C). • do not cut seed of varieties susceptible to Fusarium and which are slow in wound healing. • cut seed pieces should not be exposed to hot sun or wind for even a short time or they will severely shrivel and may decay (keep cut seed in the shade).

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SEED CUTTING (DRAWING)

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SEED CUTTING

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SEED RATE AND CROP DENSITYCrop density:

The crop density is expressed as: • number of stems per m2 • number of plants per HA For table potatoes the density is 40 000 plants/HA or 15-20 stems per m2.For seed the density may be as high as 60 000 plants/HA or 30 stems per m2.

Seed rate:A stem density of 15 stems/m2 or 30 stems/m2 can be reached by planting different sizes of seed.

The seed sizes:(< 35 mm , 35-45 mm, 45-55 mm) are commonly used. Relation seed size and seed weight Seed Size

Stem density:The number of stems per m2 is a more accurate manner to express crop density than number of plants per hectare.Total yield increases until a density is reached of approximately 15-20 stems per m2. With a further increase of stem density the yield remains more or less the same, but the average tuber size decreases (relatively more small tubers). Graph: density-yield-tuber size

Seed sizes:The seed sizes are expressed in diameter: < 35 mm , 35-45 mm, 45-55 mm and > 55 mm.The same density can be reached with large sized seed and with small sized seed. The price of the different seed sizes determines the preference of the user:Producers of table potatoes have a certain preference for smaller sized seed, while seed growers often use their bigger sized tubers for re-multiplication as seed.Mini-tubers from rapid multiplication programs are often very small (e.g. 10-30 mm) and require special care in the first field multiplication (eg shallow planting, cover with perforated plastic).Size and vigour: The seed size not only has an effect on stem number, but also on the early development of the crop. Larger sized seed gives an early and vigorous crop. Mini-tubers(10-30 mm) from rapid multiplication programs, are slow in their early development and crops grown from these tubers require a relatively long growing Period.

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RELATION SEED SIZE AND SEED WEIGHT

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SEED SIZE

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GRAPH: DENSITY-YIELD-TUBER SIZE

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Crop establishment

During the cropping season the farmer makes many decisions with regard to the establishment of the crop and interferes in the crop growth continuously when needed. His actions are focused on good yield and good quality.

The timing of his work is extremely important.A one day delay in implementing a certain operation ( e.g. planting, spraying, irrigation, harvest) makes the difference between success and failure.

SOIL TILLAGE AND SEED BED PREPARATION

PLANTING AND RIDGING

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SOIL TILLAGE AND SEED BED PREPARATION

Soil tillage, seed bed preparation, planting and ridging aims at: • a quick emergence • a deep penetration of the roots • a good drainage • weed control • to prepare sufficient loose soil necessary for the formation of a ridge in which the new

growing tubers are well protected Soil levelingLeveling of soils is done to prevent water logging on lower spots after irrigation or intensive rain.

Main soil tillage operation The main soil tillage operation with a plough (chisel plough, disc plough, mould board plough) is down to a depth of 25-35 cm.

Objectives of the main soil tillageto loosen the soil, to break impermeable layers, to improve drainage, to bring organic matter into the soil . The main soil tillage operation is an efficient weed control method, when executed with an implement that turns the soil (mould board plough, disc plough).

Seed bed preparation, compacting and clods Seed bed preparation starts at right moisture content. Soil tillage in wet soils results in soil compaction and clod formation. Soil compaction leads to poor drainage and poor root development. Clods often remain in the ground until harvest. Under dry soil conditions it is difficult to break down the soil.Cultivate soils no deeper than the moisture content allows. About 10 cm of loose soil is needed to make a ridge.

For seed bed preparation pto-driven harrows give good results. A combination of planting and seed bed preparation in one

Operation is used to avoid soil compaction.Cover of tubers by a layer of soilCover of tubers by a layer of soil prevents greening, attack by insects (e.g. tuber moth) or fungi (e.g. Phytophthora infestans) and a high rise of temperature (secondary growth).Protective layer of soil

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PROTECTIVE LAYER OF SOIL

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PLANTING AND RIDGINGPotatoes on ridgesGrowing potatoes on ridges allows shallow planting, since later in the season a ridge is build to protect tubers with sufficient soil.

Newly grown potatoes are well protected by soil layer

The tubers are better drained if the crop is grown in ridges than when grown in flat soil.Growing of potatoes on ridges also facilitates surface (furrow) irrigation

Covering of tubers by a layer of soil protects tubers against:- greening- attack by insects (e.g. tuber moth)- attack by fungi (e.g. Phytophthora infestans)- high temperature (second growth)- physiological disorders (growth crack, hollow heart, etc.)

Covering of tubers by a layer of soil protecting the tubers, can be achieved by:- deep planting- making large and well shaped ridges- increasing row distance which facilitates the making of better ridges.

Planting depthThe planting depth determines the position of tubers growing in the ridge and influences the depth of the layer of earth protecting these tubers.

PLANTING DEPTH Row distance and ridge sizeWith increasing row distance it is easier to make a sufficiently large ridge in which the tubers are well protected.

ROW DISTANCE AND RIDGE SIZETime of ridging and re-ridgingIn many cases, soon after planting only a shallow ridge is made and the final ridge is then made at emergence or when plants are 15-20 cm high.A final ridge is already made at planting in case temperature is expected to be relatively high (>12-15 C) and herbicides with a residual effect are used.

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PLANTING DEPTH

With deep planting the tubers in the ridge are better protected by soil than with shallow planting.

Planting depth

Advantages and disadvantages of deep-, normal-, and shallow planting.

Deep

- tubers well covered by soil and well protected against direct light (greening of tubers)- tubers well protected against high temperatures (secondary growth)- tubers well covered by soil and well protected against tuber moth and late blight- difficult to lift potatoes with elevator digger- poor drainage after irrigation or rain

Normal

- tubers reasonably well protected by soil, but re-ridging may be needed- relatively easy to lift with elevator digger- drainage rather good after irrigation or rain

Shallow

- tubers insufficiently covered by soil- easy to lift with elevator digger- drainage good after irrigation or rain

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PLANTING DEPTH

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ROW DISTANCE AND RIDGE SIZEWith a wide row distance it is easier to make a sufficiently large ridge in which the tubers are well protected.

Row distance and ridge size

Row distance and canopy closure.At a row distance of 50 cm or 60 cm the crop canopy closes earlier than at a wider row distance (e.g. 90 cm). In regions where varieties are grown with long stolons and an abundant haulm development, the row distance is wide (e.g. 90-110 cm)

In areas where the potatoes have a relatively poor haulm growth and the ridging and re-ridging is done using manual tools, the row distance is often between 60 and 70 cm.

Row distance and mechanization.In Europe the row distance gradually increased from 65 cm to 75 cm. The reason was the introduction of mechanization, especially the complete harvesters. These harvesters require a more shallow planting, but a sufficiently large ridge to cover the tubers with soil remained relevant. With adaptation of the ridgers it was possible, at a row distance of 75 cm, to make a ridge in which the tubers are well protected. Narrow tractor tires were introduced to avoid soil compacting in the ridge.

Row distance: 90 cmExperiments showed that in good crops the yield with a row distance of either 65 cm or 75 cm is the same, but there is a tendency that row distance will further increase. With a row distance of 90 cm the total yield may decrease slightly, but the net yield can be higher. The reason is that with a wide row distance a larger ridge can be made in which tubers are better protected by soil and tuber quality improves. (Less: green potatoes, secondary growth, misshapen tubers). With the wider row distance there is less compacting within the ridge by the tractor wheels.

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ROW DISTANCE AND RIDGE SIZE

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FERTILIZATION OF POTATOES

Different Combination of Fertilizers used by farmers in Potato Crop are explained. There are number of more different combinations.

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Different Combination of Fertilizers used by farmers in Potato Crop

Combination No.

Fertilizer Basal/EU

No. of Bags (50 Kg)

Nutrients in KG Micro Nutrient Zn

N P K S

1 BASAL DOSE

DAP 18:46 2.5 23 58 -- -- --

Ammonium Sulphate 20%

3 30 -- -- 36 --

MOP60% 2 -- -- 60 -- --

Earthing Up DoseUrea 46% 1 23 -- -- -- --

Zinc 21% Zinc (chelated)

-- -- -- -- -- 15 Kg/ 0.5 Kg

Total 8.5 76 58 60 36 15/0.5 Kg

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Combination No.

Fertilizer Basal/EU

No. of Bags (50 Kg)

Nutrients in KG Micro Nutrient Zn

N P K S

2 BASAL DOSE

DAP 18:46 2.5 23 58 -- -- --

Ammonium Sulphate 20%

2 20 -- -- 24 --

MOP60% 2 -- -- 60 -- --

Earthing Up DoseUrea 46% 1.5 34 -- -- -- --

Zinc 21% Zinc (chelated)

-- -- -- -- -- 15 Kg/ 0.5 Kg

Total 8 80 58 60 24 15/0.5 Kg

Different Combination of Fertilizers used by farmers in Potato Crop…contd

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Combination No.

Fertilizer Basal/EU

No. of Bags (50 Kg)

Nutrients in KG Micro Nutrient Zn

N P K S

3 BASAL DOSE

DAP 18:46 2.5 23 58 -- -- --

Urea 46% 1 23 -- -- -- --MOP 60% 2 -- -- 60 -- --Sulphur 80% WDG

-- -- -- -- 3 Kg --

Earthing Up Dose

Urea 46% 1.5 34 -- -- -- --

Zinc 21% Zinc (chelated)

-- -- -- -- -- 15 Kg/ 0.5 Kg

Total 7 80 58 60 3 Kg 15/0.5 Kg

Different Combination of Fertilizers used by farmers in Potato Crop…contd

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Crop care

During the cropping season the farmer makes many decisions with regard to the maintenance of the crop and interferes in the crop growth continuously when needed. His actions are focused on good yield and good quality. The timing of his work is extremely important. Crop maintenance (haulm growth and tuber growth) includes: irrigation, pest and disease control, rouging, weed control, haulm destruction and harvest.

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WATER USE AND IRRIGATIONWater useThe water use of a crop with a closed canopy is about 90% of the evaporation of an open water surface. The evaporation may be 3 mm - 8 mm per day, depending on climatic conditions.

The water used by a crop is replaced by rainfall or irrigation.An estimate on the irrigation frequency can be made using good weather observations. The need for irrigation can also be determined by estimating the soil water content by hand.

Rooting depthFor water supply of a crop it is important that the plants forms deep roots

ROOTING DEPTHIrrigation methodsIrrigation methods surface-, sprinkler- and micro-irrigation.

IRRIGATION METHODSDrought periodsA drought period at the early stages will stop the production of the crop for some time, but a late drought period towards the end of the season will lead to an early dying of the crop and results in low yield.

Soil crackingIt is essential to continue with irrigation until harvest, since with dry soils harvest is difficult and soils begins to crack. Through these cracks the tuber moth can reach the tubers.

Water surplusToo much water has negative effects: 1) wasting of water, 2) poor root development, 3) opening of lenticels, which allow micro-organisms to enter, 4) increased risks of tubers to be attacked by fungus and bacterial diseases.

Water quality Irrigation water should not contain too much salt and be free from dangerous bacterial diseases (e.g. Bacterial wilt).

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ROOTSRoots and water use

Plants growing from tubers develop adventitious roots at the nodes of the underground stems and stolons. Plants grown from true seed develop a slender tap root from which lateral branches arise.

Uptake of water from ridges and from deeper soil layersThe roots are essential for the uptake of water and nutrients from the soil. Only part of the water needed is extracted from the ridge. The remaining part needed comes from deeper soil layers

Water use of single plantRooting depth and irrigation frequencyCompared to other crops, potato roots rather shallow (often no deeper than 40 to 50 cm).If, however, no obstructive layers or sharp transitions from one soil type to another occur in the soil profile, plants may root as deep as 1 m. When rooting is deep, irrigation can be less frequent than when rooting is shallow. For the growth of roots the presence of oxygen is essential. With too heavy irrigations in the early growth of the crop there will be a lack of oxygen and root growth is hampered. Compacted layers hamper root growth.

Measures that can be taken to make conditions advantageous for deep rooting are:

• select fields with good physical soil properties • avoid too heavy irrigation in the early stages of crop growth • adequate soil tillage operations • avoid soil compacting

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WATER USE OF SINGLE PLANT

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Irrigation methods

• Main irrigation methods are: surface irrigation, sprinkler irrigation and micro irrigation.

Surface irrigationSince potatoes are mainly grown on ridges the main surface irrigation method used is furrow irrigation. The system is used when there is:- ample water supply- on medium to fine texture soils- on uniform sloping land with slopes ranging from 0-1%The water use efficiency is relatively low. The investment costs as well as operational and maintenance costs are medium.FURROW IRRIGATION

Sprinkler irrigationSprinkler irrigation is used where there is:- water scarcity- soils with low water holding capacity and high infiltration rate- irregular topography and soils too shallow to be levelledThe water use efficiency is relatively high. The investment costs and maintenance costs are relatively high.SPRINKLER IRRIGATION

Micro irrigationDrip irrigation is used where there is:- water scarcity- a very low water holding capacity of soils- a very high or low infiltration rate and drainage of excess irrigation water is difficult- water salinityThe water use efficiency is high. The investment costs are high.DRIP IRRIGATION

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Pest and disease control

During the growing season the major fungus diseases are late blight and early blight. An adequate spraying with protective fungicides against late blight also protects against early blight.

Late blight:For chemical control quite a number of effective fungicides is available. It concerns a.o. the groups of the dithiocarbamates zineb, maneb and mancozeb and the copper compounds, which are extensively used.At present new types of fungicides are being produced which are introduced as they are more friendly to the environment None of these products is able to effectively control late blight for more than six to eight weeks under severe disease pressure, which is considerably shorter than the growing season. Therefore it is essential to prevent early infections by removing infection sources and by an early start of spraying. Crops should be protected when conditions are favourable for Late blight CHEMICALS LATE BLIGHT EARLY BLIGHTLate blight favourable conditions:Late blight favourable conditions are marked by one or more of the following:

• night temperatures do not drop below 7 °C. • temperatures between 15 and 21 °C are the most favourable for lesion development and sporulation, whereas at temperatures

over 29 °C the pathogen does not develop. • leafwet periods (dew and rain) over 6 hours are favourable for new infections. • leafwet periods over 8 hours are very critical. • in case of a severe late blight crop infection, seed tubers may carry over a large amount of inoculum to their following growing

season. Massive late blight outbreaks will occur when conditions are favourable to disease development, hence start spraying earlier and more frequently. At times when conditions are favourable for the development of late blight crops should be protected with the fungicides.

Spraying schedules for late blight controlUntil recently, the most common rule for chemical late blight control was: "Start spraying against late blight when the leaves of the plants within the row touch and repeat spraying every 7 days when conditions for late blight are favourable and every 10 days when conditions for late blight are not favourable".With the presently more aggressive populations of P. infestans this rule of thumb has become obsolete.In stead of 7 days the generation time of the pathogen is now 4 days. Hence, spraying should be done when conditions for late blight development are favourable and intervals may be as short as 4 days.The start of the sprayings against Late bight is influenced by:

• infection pressure • susceptibility of the cultivar grown • growth of the plants • the existing weather conditions Infection pressure

If infection in the area is low and when there is no risk of infections from oospores start spraying later. Use of a, for the local conditions, adequate disease- forecasting-system is very useful.

Susceptibility cultivarSusceptible cultivars are to be sprayed more frequently than cultivars with a higher level of resistance. For a susceptible and a more resistant cultivar the interval may respectively be 4 and 10 days.

Growth of the plantsCrops with fast growing haulm need more frequent sprays than when growth is slow. Leaves that developed after the last spray are unprotected. With fast growing haulms, fungicides with a systemic component are recommended.

Weather conditions In periods that conditions are favourable for Late blight spraying is frequent. Efficiency of chemical control interacts with rain. Some hours of dry weather are necessary to allow the chemical to stick to the leaves.INTERACTION WITH RAIN

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Information on fungicidesFungicides are subdivided into different groups: contact fungicides, preventive fungicides, curative fungicides, systemic fungicides and translaminar fungicides.

Contact fungicides

Contact fungicides are fungicides which act against the pathogen on the surface of the plant. In the past contact fungicides were synonymous with preventive fungicides. Preventive fungicides are acting against the fungus before entering the plant tissues. At present there are preventively acting products which are transported to higher plant parts. These products are excreted on the surface of these higher (or newly formed) plant parts and give protection.

Systemic products

Systemic products are transported inside the tissues of the host. In most cases this transport is upward.

Curative productsCurative products are products which act against the growing parts of the fungus which are mainly inside the host tissues. Curative products are therefore also systemic products. A number of modern contact fungicides are transported systemically as well, but do not act against the fungus inside the leaf.

Translaminar products

Translaminar products are considered to have a limited transportation within leaves (about a diameter of 1 cm or less from where a droplet of fungicide has been deposited). Their application is to cut down infections up to 24 hours old. However, with a higher concentration of the same product, this period is extended to at least 2 to 3 days. The difference between trans-laminar and systemic is not a clear one and may depend on the concentration (or better the amount) of the concerned component applied.

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EARLY BLIGHTControl of Alternaria includes:

SanitationIt is recommendable to reduce the build-up of inoculum in field soils by removing the affected crop residues.

FertilizationIt has been experienced that a good control of early blight was obtained by fine tuning the fertilization with especially micro-elements such as manganese, zinc, boron and iron. The effects of such treatments surpassed those of chemical control.

ResistanceRelatively little work has been done on breeding for resistance to early blight:1) early blight is by breeders often not considered as an important disease, 2) breeding is not easy and testing is complicated. The resistance reaction depends amongst others on age and on environmental conditions. As a consequence early varieties show more pronounced symptoms in the field while late varieties have a tendency to escape from the most severe stages of the disease. Hence, results coming from field trials should be looked at with caution.

FungicidesA proper timing of the application of fungicides is a necessitySpraying before the onset of secondary spore flights often does not pay off as the resulting lesions are relatively few and the primary flights are very irregular in time. In most cases, the appropriate time for the first spray is at the onset of the secondary spore flights (monitored by spore traps).A second good solution is to spray for the first time around flowering time or when the first lesions are found in own or neighbouring fields. In general no more than two or three sprays should be given at ten day intervals. In case early blight appears late during the growing season there is no need for control as only mild yield losses are to be expected.Most contact fungicides controlling late blight are effective against early blight. If contact fungicides are preventively sprayed to control late blight, they will also control early blight reasonably well, as spraying intervals for late blight control are shorter than those for early blight.From the old low cost fungicides are chlorothalonil, triphenyl-tin-hydroxide and the dithiocarbamates maneb and zineb and combined formulations the most effective. From the newer fungicides is Tanos (famoxadone, cymoxanil) very effective and Shirlan (fluazinam) less effective than needed. Unfortunately these compounds are not effective against the fungus already penetrated in host tissues. It should be noted that systemic fungicides controlling late blight do not necessarily control early blight, as is the case with metalaxil and cymoxanil which are ineffective against the early blight fungus.

Tuber attackControl of tuber infection is mainly through agricultural measures: • tubers should be well suberized (mature) at lifting which makes them less prone to wounding, • tops should be burnt or removed before harvesting, • tubers should be handled as carefully as possible, • lifted tubers should not be left unshielded in the field, • infected tubers should be stored as cool as possible to limit lesion development and decay. Temperature should be at least below 10 °C.

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INTERACTION WITH RAIN

Weather conditions and applicationDry period after treatment

An indication of the effect of a dry period following treatment with a late blight spray can be summarized in a diagram. Depending on the weather conditions, a dry period of 1.5 - 7 hours after application is sufficient for a good protection.

Dry period and blight control

Spraying of dry leavesIn case dry leaves are sprayed the chemical gives a good protection if the leaves can dry after application. A dry period of 1-7 hours is needed for good protection.Under strong drying conditions crops are dry within one hour after spraying, while under poor drying conditions (cloudy, high relative humidity and no wind) drying may take 6-7 hours.

Spraying of wet leavesWhen wet leaves are sprayed the chemical runs of the leaves. Only some protection can be expected under strong drying conditions.

Rain after application • small amounts of rain e.g. a light shower of < 3 mm does not wash off the product

to such an extend that the treatment is useless. • if rain starts within 1.5 hours after spraying and showers exceed 4 mm application

can be considered as useless. • the expectation of rain is no reason to delay spraying in case spraying capacity is

limited.

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Dry period and blight control

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Diseases caused by fungi, bacteria, nematodes, phytoplasms

The potato is affected by quite a number of diseases and pests, but only a limited number are spread both worldwide and have a major impact on its productivity. In the context of this programme only the diseases will be dealt with which have a major and worldwide impact or are a threat with respect to potato production.

It concerns the following diseases/pests: • Fungi • Bacteria • Nematodes • Insects • Phytoplasms • Virus diseases • Weather, temperature

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