Planting and Cultivation
Quick, even emergence and good early crop growth are essential in the quest for good yields of quality potatoes.Where grass is ploughed up it is recommended that grass is burned off in advance of ploughing using Glyphosate. Deep cultivation (down to approximately 25 cm) is an essential start to seedbed preparation.
The aim of subsequent cultivations is to provide a fine seedbed with 12 - 15 cm of clod free tilth. Loose cloddy seedbeds will dry out, causing slow growth, irregular emergence and low stem counts. Wait until soils are dry enough, and then use an appropriate implement for cultivation. Cultivating soils that are not dry often results in compaction, and damage to soil structure. This restricts the rooting capacity and subsequent yield of the potato plant.
Ploughed ground is usually cultivated with a heavy tine cultivator prior to bed tilling and ridging. Bed tilling and ridging involves cultivating the soil to a depth of 15 -18 cm, and leaving it in large ridges between 175 – 185 cm in width.Stone separation is the process of removing stones and clods from the formed ridges, and burying them between alternate rows. This substantially reduces tuber damage during harvesting, and greatly increases harvester output.
The ridges should have been adequately cultivated prior to stone separation to ensure there are no excess clods to be removed. Soils need to be dry to ensure good separation whilst also avoiding damage to soil structure.
Varieties for salad potato production
There are two main types, round/oval and long oval, but a feature of potatoes for salad production is that they tend to produce large numbers of very uniform tubers. Another essential feature of salad potatoes is that they are capable of producing tubers with a good skin finish.
Breeders are now focussing their efforts on breeding salad varieties and currently around 25 varieties are available for commercial production. The majority of these are round/oval. A key feature of which variety is grown is to have a secure market outlet.
Shortlist of varieties
|Maris Peer||Second early||White tubers with cream flesh. The market leader for salad production, mainly as the variety is off patent and seed costs are lower.||-|
|Gemson||Second early||White tubers with white flesh. Very high tuber numbers and yield. Very good all-round disease resistance||Grampian growers|
|Jester||Second early||White skin with creamy white flesh.||Greenvale AP|
|Perline||First early||Pale yellow skin and flesh.||KWS|
|Picollo Star||Second early||Creamy skin and flesh. Good all round disease resistance except tuber blight||Branston|
|Bambino||Maincrop||White skin with creamy white flesh. Good all round disease resistance||Cygnet PB|
|Corolle||First early||Pale yellow skin and flesh. Reasonable disease resistance||Germicopa|
|Vizelle||Maincrop||Extremely high tuber numbers. Very susceptible to TRV spraing||Cygnet PB|
|Charlotte||Second early||Yellow tubers with yellow flesh. The most popular long oval variety for salad production, in part because it is off-label but also because it has good flavour||-|
|Jazzy||First early||Cream skin and light yellow flesh. Very high yielding||Meijer|
Almost all salad varieties have susceptibility to foliage or tuber late blight.Further information on most varieties can be found at the AHDB potato variety database (http://varieties.ahdb.org.uk/) or on the individual Breeder/Agent website.
Seed rate and quality parameters
To ensure that salad crops only produce progeny tubers in the correct size range, usually 25-42mm or 25-45mm, it is critical that both seed rate and seed spacing are considered carefully.
The seed rate for a salad crop is considerably higher than for other ware potato crop types or even seed production. Seed rate guidance will be provided for most varieties still under breeder control. Seed rate recommendations depend on how prolific in developing progeny tubers a variety is as well as the seed tuber count (usually expressed as no. seed tubers/50kg). As a guide, seed rates can range from 50,000/ha for seed with a 400 tubers/50kg count up to 105,000/ha for seed with a 2000 tubers/50kg count. Using the correct seed rate for the size of seed tuber supplied is very important.
For round/oval salad varieties, a target of 1 million progeny tubers per hectare is appropriate. For long oval salad varieties, such as Charlotte or Jazzy, it may be difficult to produce more than 600-700,000 tubers/ha
Even spacing is also important to ensure even competition between plants and thus an even size distribution of progeny tubers. To improve accuracy of spacing during planting, seed for salad production should be supplied in 5mm or 10mm bands, for example 30-35mm, 35-45mm, 40-45mm etc.
Larger, specialised salad producers are now growing salad crops using quad planting (2 rows per drill) or in 3 rows per bed to ensure uniform emergence and crop development. Other key features of uniform emergence are to plant healthy seed and/or use an appropriate fungicide seed tuber treatment and to plant at even depth into a fine seed-bed.
Salad potatoes are only marketable when virtually blemish free. Thus risks affecting quality should be considered before planting. As salad crops are mostly short season crops, risks from many tuber diseases are lower, unless harvesting is delayed. Nonetheless, checking variety susceptibility to disease on a variety database (e.g. AHDB variety database - https://potatoes.agricrops.org/) is worthwhile when staring to grow a new variety.
Perhaps the most important blemish risk to salads is common scab. Since even small levels of scab can have a major impact on marketability, even varieties with moderate resistance (ratings of 6 or less) should be considered a risk. Scheduled irrigation is an effective way to prevent common scab infection during the critical 2-4 weeks after tuber initiation (see section on Irrigation).
Some salad varieties have specific disease risks and these should be considered when growing salads. For example, many varieties are susceptible to foliage and tuber blight and an effective late blight fungicide programme is required on salads (see section on Blight). The variety Charlotte is susceptible to black dot and where harvest is delayed perhaps as a result of slow skin set, black dot may be a risk on progeny tubers. Where the risk of black dot is considered high, the use of an in-furrow fungicide treatment (e.g. Amistar) is advisable. Seed tubers can carry tuber disease and good practice is to wash a sample before planting. Where disease is present that can affect the crop (for example black scurf, black dot) application of an appropriate seed tuber fungicide treatment should be considered.
Tuber blemishes can also come from damage during harvesting and handling. As harvesters lifting small tubers usually require at least one narrow web (e.g. 25mm), stone separation to remove stones larger than 25mm will be required. This should reduce damage from stones on the harvester and ensure a fine tilth in the seed-bed.
Soil type and texture for salad potato production.
Field selection is important when producing salad potatoes. Soil texture, access to irrigation and soil fertility all need to be carefully assessed prior to planting.
The ideal site should be free from volunteers, be in soil index 3 for both phosphorous (P) and potassium (K), it should also have access to irrigation and should also be free draining eg, sandy clay loam with a low stone content. The soil texture pyramid (below) is a useful guide in helping to assess the texture of the soil. To use the table you will need a sample of the soil which you then wet and carefully rub between your fingers. You then try to assess the soil into one of the categories on the table.
Soil texture pyramid.
While most soils are capable of growing salad potatoes heavy clay soils or soils with abrasive sand characteristics should be avoided. Clay soils can be moisture retentive and can cause difficulty at stone separation and harvest while soils with high or abrasive sand content can scuff the skins at harvest.
All stones greater than 30mm will need to be removed so as to avoid damage at lifting, therefore web size and star settings will need to be changed from maincrop to achieve this. Sites with sharp flinty stones should be avoided as these types of stones are more likely to cause damage.