Growing potatoes for profit and sustainability Season Guidelines

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1 Growing potatoes for profit and sustainability Season Guidelines Introduction There is constant demand within the UAE marketplace for locally grown potatoes with premiums being paid for specialty varieties. Potatoes (Solanum tuberosum) are a hardy and durable crop that can be easily grown with existing irrigation set up. The UAE s sandy soils are suitable for growing good quality potatoes. This guide will show you the methods for profitable and sustainable production of potatoes, including a water efficient high technology irrigation system. Growing season Planting: mid-october to mid-december Harvest period: Early February to mid- April Table 1: Potato growing season Month Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Planting period Harvest period Growing period Planting to harvest: weeks Total crop cycle: can take up to 20 weeks depending on variety Table 2: Potato growing period from Week Growth stage P H H H H H Key to colours and symbols: P Planting H Harvesting Varieties Varietal selection is important for the success of your crop. Selected varieties should be suited to local climatic conditions, have good pest and disease resistance and meet market needs, particularly relating to tuber size, shape and flesh and skin colour. Certified pest and disease free seed potato is available for purchase from ADFSC. The varieties selected are best suited to the local growing conditions, have good storage potential and offer best returns. Irrigation layout, plant density and expected yield Plant seed potatoes at 20 to 30 cm spacing within rows, and a between row spacing of 90 cm. Potatoes can be also be grown using 20 to 50 cm dripper spacing (Table 3). 1

2 Table 3: Plant arrangement and density Plant spacing Drip line spacing Plant density Plant arrangement Between rows (cm) Within rows (cm) Between lines (cm) within lines (cm) Number of plants per donum Potential marketable yield (kg per donum) Recommended high density planting ,500 3,000 to 4,500 Not recommended traditional planting ,850 1,000 to 2,000 Seed potatoes should be of uniform size with an average weight of 50 grams. They should be planted whole. Where larger seed potatoes are used they should weigh between 80 and 120 g. Cut sections between 40 and 60 g and dry them in a cool, well ventilated and shaded location for one to two days before planting. Each seed potato or cut section should have a minimum of between two to four eyes. For high density planting you need about 4,500 seeds per donum. Seed potatoes are ready for planting when three or four small white sprouts emerge from the eyes. All rotten or diseased tubers should be discarded to avoid the spread of disease into the crop. Care should be taken when storing and handling potatoes to make sure that seeds are not exposed to excessive heat or mechanical damage. Figure 1: Close spacing for high density potatoes Figure 2: High density potato crop Soil analysis and water quality requirements Prior to field preparation, soil and water samples should be taken and sent for analysis. Potatoes are moderately sensitive to salinity. The recommended salinity of irrigation water should not exceed 1.1 ds/m (700 ppm) if the potential yield of potato is to be realised. However, a water salinity of 3.9 ds/m (2,500 ppm) will reduce yield by about 50%. Your local ADFSC extension engineer can assist you with soil and water sampling techniques and help with the interpretation of results from the laboratory to grow the crop successfully. Potatoes are sensitive to chlorides generally found in the calcareous soils in the UAE. Fertilisation with chloride-free fertilisers will contribute towards increased yields and quality of tubers. Land preparation and pre-planting fertilising 2

3 Thoroughly cultivate the area to be planted four weeks prior to the planting date. Dig trenches along rows 20 cm deep and 30 cm wide. Add manure and pre-planting fertilisers (Table 4) and thoroughly mix into the soil at the bottom of the trench to a depth of 5 cm. Back fill the trench with 10 cm of soil then smooth to an even depth of 15 cm. This is to prevent fertilisers coming in contact with seed tubers and to protect them from high soil surface temperatures. The risk of damage to tubers increases in dry conditions, on light soils and where pre-sprouted seeds are planted. Table 4: Recommended rates of pre-planting fertiliser application for UAE sands Fertiliser Application rate (kg/donum) Composted manure 1,000 Ammonium sulphate 25 Triple super phosphate (TSP) 60 Potassium sulphate 26 Magnesium sulphate 5 Trace element mix (Fe, Mn, Zn, B, Cu, Mo) 1 Pre- and post-plant fertiliser applications provided are only a guideline. Fertiliser recommendations should be based on soil irrigation water analyses and experience of soil conditions in your local area. Contact your ADFSC extension engineer for assistance with testing water and soil on your farm and formulating fertiliser schedules. The recommendations above (Table 4) are for a typical sandy soil in Abu Dhabi. Growers may achieve a similar result if necessary, using N:P:K compound fertilisers that supply the same amounts of nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg). The composted manure provides organic matter to the soil to help with the retention of irrigation water and nutrients for a strong healthy root system. Organic material must be thoroughly composted to avoid the introduction of weed seeds, pests, diseases and seedling root burn. Poorly composted manure can cause scab in potatoes. Figure 3: Pre-planting fertiliser application Figure 4: Mixing fertilisers and back filling trenches Installation of new irrigation lines 3

4 Existing irrigation systems can be adapted to the new layout by attaching new drip lines at the required spacing to the existing underground sub-mains or lateral water pipes. Existing outlets that do not align with the new spacing should be blocked off. In some situations farmers may choose to install new sub-mains or lateral pipes to facilitate the new drip line layout. Always test the irrigation system and dripper prior to transplanting to ensure all drippers are working. This is ideally done as part of the pre-planting weed control. Growing stage Planting Disease free seed potatoes of uniform size should be planted whole. Seed potatoes should be planted as follows: 1. Place potato seeds at the bottom of the prepared trenches cm apart 2. Backfill the trench to the original soil level 3. Place the irrigation line along the planting row Figure 5: Seed potatoes Crop nutrition and application of soluble fertilizers through irrigation (fertigation) Weekly fertigation is recommended according to the following schedule. Table 5: Recommended rates (kg/donum) for fertigation fertiliser and trace element application for UAE sands Growth stages in weeks Ammonium sulphate Potassium nitrate Magnesium sulphate Calcium nitrate Trace element mix Chelated Fe (EDDHA) At emergence Week Week Week Week Week Week Week Week Week Total Notes: Apply trace elements via fertigation at first irrigation Calcium nitrate should be applied separately from other fertilisers to prevent precipitates forming in the fertigation tank and clogging the drip lines. 4

5 The above schedule of weekly applications (Table 5) is only a guideline for the sandy soils typically found on Abu Dhabi farms. The exact fertiliser recommendations should be based on soil fertility levels and irrigation water conditions in your area. Contact your ADFSC extension engineer for assistance with testing water and soil on your farm. Weekly or more frequent fertigation ensures that nutrient levels are maintained in the root zone of the crop throughout the important growing and production periods. These recommendations are based on good irrigation practices. Excessive irrigation will leach nutrients away from the root zone Crop water requirements Irrigation is important as potatoes have a shallow sparse root system. Therefore, irrigation must be closely monitored to ensure soil moisture remains even in the beds during the whole cropping period. Until foliage emerges from the soil, the young plants need minimum water. Potatoes require even moisture availability to achieve rapid healthy growth. It is essential that the soil is kept constantly and uniformly wet to a depth of at least cm during the early vegetative growth phase until tuber formation. Excessive irrigation can promote tuber rots and results in leaching of nutrients from the root zone. Care should be taken during tuber initiation and formation as irregular irrigation can result in tuber cracking and over irrigation can lead to disease development. If soil dries after tubers have formed, a second growth will initiate when soil gets moist again. This will cause knobbly potatoes and multiples. Alternate wet and dry conditions can also cause hollow heart, or cavities near the middle of the potato. Application of soluble fertiliser as fertigation can be carried out during a normal irrigation. Continue irrigation for 5 minutes after fertigation to flush the system. Hilling The new potato will grow above the seed piece so hilling up is necessary to provide sufficient friable soil to create the correct conditions for tuber formation and to protect the new potatoes from sun exposure and turning green. Green tubers contain the toxic chemical solanine and eating these can cause sickness. After two weeks from planting, first hilling should be carried out when the plant stems are between 15 and 20 cm high. The second hilling is done when the stems are between 10 and 15 cm above the first hill. The hilling procedure involves gathering soil from between the rows to cover the stems. Figure 6: Hilling Figure 7: Potato field after hilling Plant protection Many pest and disease problems can be avoided through Integrated Pest Management (IPM) procedures. The following will help to ensure any pests in your potato crop remain below the economic threshold and swift action is taken should they become a problem. Use of pest resistant varieties This ensures your crop has natural resistance to pests and diseases, minimising the need for expensive chemical control. Row covering Covers should be put up immediately after planting and left for 2-3 weeks. They protect your potato crop from numerous insect 5

6 pests, such as whitefly, potato leafhoppers, thrips, mites and aphids and the diseases they carry, such as potato yellow vein, leafroll and mosaic virus. Crop rotation Do not plant potatoes in fields cultivated with potatoes, tomatoes, capsicum, eggplant and chilli in the previous 5 years or in fields cultivated with fodder crops such as Rhodes grass in the previous 2 years to avoid white grubs. This will also minimise the risk of fungal and bacterial diseases such as bacterial and fungal wilt, black scurf, black dot and nematodes. Rotate with a non-host crop such as corn, onions, carrots, beans and cabbage. Soil solarisation This should be carried out each summer prior to planting to help control soil borne pathogens such as fungal wilt, damping off, powdery scab, pink rot, nematodes and white grub. Companion crops Planting of coriander in the vicinity of your potato crops will help to repel a number of insect pests such as potato beetle and whitefly. Plant certified seed Plant only certified disease-free potato seed to avoid infection with potato leafroll virus, mosaic virus, blights, black scurf and smut. Traps Placing coloured, light and pheromone traps around your potato crop will help control whitefly, leafhoppers, cut worms and potato tuber moth. Removing and correctly destroying all crop residues immediately after harvest This helps prevent last season s pests re-infecting your new crop and will help to control early and late blights and bacterial wilt. Good weed management Potato crops should be weeded every 2-3 weeks after removal of Agrile row covers. This is especially important during the early stages of growth when canopy cover is less developed and the crop cannot compete with weeds. Weeds should be manually removed. This can be combined with hilling. Crop monitoring Potato crops should be monitored for pests and diseases every 3-4 days. This is especially important during the early stages of growth when potatoes are more susceptible to pests and diseases. Consistent monitoring enables a swift and effective response should an outbreak occur, which will minimise crop damage and expense. Prompt harvesting after canopy has dried off Harvest tubers 5 to 10 days after cutting the foliage or after foliage has dried off to prevent diseases such as black scurf. Thorough composting of all organic matter All manure put on the crop should be thoroughly composted to prevent pest and disease outbreaks. In the event of a pest or disease outbreak please contact your nearest ADFSC extension engineer to correctly identify the pest or disease and provide recommended control measures. Harvest stage Pre-harvest interval (PHI) Pre-harvest interval is the time between the last pesticide application and harvests of the treated crop. The PHI varies between different types of pesticides and must be adhered to for all crops. Failure to adhere to the PHI will result in pesticide residues in the harvested produce, which will render the crop unfit for human consumption and for sale. It is illegal to sell crops where the PHI has not been adhered to. 6

7 Field Hygiene during harvest Good field hygiene is required to ensure you crop is free of contaminants. This is essential for the crop to be sold in the market. Good hygiene practices must always be adhered to when harvesting fresh vegetables. Crop maturity, handling and storage The growing time to maturity for potatoes varies between 90 and 140 days depending on variety. As the crop matures the foliage changes in colour from bright green to yellow. However, as this colour change may also be caused by a number of pests and diseases, crops must be sampled to verify whether they have reached maturity. To do so, sample tubers from several representative plants within the crop. The skin of mature tubers should be firm and not easily removed when pressure is applied through light rubbing. Once potatoes are mature they must be cured to harden the skin so they can be stored. Gradually reduce irrigation to kill off the foliage. Irrigation should not be completely discontinued as sufficient moisture is required in the soil to prevent tuber dehydration and erosion of the hills, exposing the tubers to greening and sun damage. Cut foliage after one week of reduced irrigation. Harvest can begin once the skin of potatoes is judged to be suitable for market quality requirements which is generally five to ten days after foliage removal. Potatoes harvested before full maturity are prone to bruising and skin flaking during post-harvest handling and shrinkage in storage. Care must be taken to avoid any mechanical damage when harvesting potatoes using digging tools or damage from finger nails. The use of cotton gloves for harvesting potatoes will minimise this. Potatoes should be harvested in the coolest part of the day and immediately transferred to a cool shaded location for short-term storage. They should be packed as to avoid heat and sun damage. This is especially important during late season harvesting when air temperatures and intensity of the midday sun will dramatically reduce quality. Potatoes should be free from rots, blemishes, cuts and mechanical damage and be correctly cured so they are not green or soft. To reduce risk of damage in transit potatoes should be packed carefully. Potatoes bruise easily and should never be dropped or thrown as this will reduce quality and value. Crates must be stacked safely and securely so they are not resting on the produce beneath. Figure 8: Packing potatoes in the pack house Grading To ensure potatoes get the best price, grade them according to the current ADFSC specifications. These can be obtained from your local procurement officer. 7

8 For further information and advice: Contact your local ADFSC office for professional advice from our experienced team of extension engineers. Figure 9: Packed potatoes ready for distribution to retailers 8