Growing sweetcorn for profit and sustainability 2014-2015 Season Guidelines Introduction Fresh, locally grown high quality sweetcorn is in constant demand within the UAE marketplace. The UAE s sandy soils are suitable for growing good quality sweetcorn when well irrigated. Careful selection of varieties, adoption of appropriate technology and good management of sweetcorn crops throughout the production cycle allow growers to maximise yields. This guide will show you the methods for profitable and sustainable production of sweetcorn, including a water efficient high technology drip irrigation system. Botany Sweetcorn (Zea mays var. rugosa) including popcorn are the only members of the Poaceae (Gramineae) family classified as vegetables. The distinct difference between sweetcorn and maize lies in the way sugar in the kernels are converted into starch. Maize kernels readily convert sugars into starch but this process is slower for sweetcorn. Consequently, maize kernels are bland to taste. Cross contamination Hybrid supersweet corn varieties must be planted a minimum of 200 m up wind of other corn to avoid contamination from crosspollination. When planting, it is important to take this aspect into consideration. Failing to do this will result in starchy kernels which are not sweet. When sequential planting is followed the planting gap between supersweet corn, normal sweetcorn and maize varieties should be between 14 and 21 days. Growing season Planting period: September to mid-february Harvest period: mid-november to late April Table 1: Sweetcorn growing season Month Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Sowing Harvest Growing period Sowing to harvest: 13 weeks Total crop cycle: 13 weeks Table 2: Sweetcorn growing period Week 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Growth stages S T/S H H Key to colours and symbols: S Sowing T/S Tasseling and silking H Harvesting Varieties The majority of sweetcorn varieties grown for the fresh market are now hybrid supersweet types which are twice as sweet as the traditional ones. Varieties differ in characteristics such as length of growing season, cob number, cob size and number of kernels per cob. Therefore, careful selection of hybrid supersweet types is important when growing for the fresh market. Selected varieties should be suited to local climatic conditions, have good pest and disease resistance and meet market needs. Communicate with your marketer and seed supplier to determine the most suitable variety for the UAE growing conditions and that gives you best returns. 1
Irrigation layout, plant density and expected yield In Abu Dhabi, sweetcorn has traditionally been planted in clusters of three plants per dripper with a between row spacing of 90cm resulting in a plant density of 6,600 with a typical yield of 2,500 kg/donum (Table 3). Optimal density sweetcorn is planted in single rows along the drip emitters at the same between row and closer within plant distance of 20cm. Higher yields from fewer plants are obtained because optimal density planting with even spacing better utilises light and nutrients with the added savings on expensive hybrid seed cost. Table 3: Plant arrangement and density Plant spacing (cm) Drip line and drip emitter spacing (cm) Plant density Plant arrangement Between rows Within rows Between lines Within lines Number of plants/do Potential marketable yield (kg/do) Recommended high density planting 90 20 90 20 5,000 3,000 Not recommended traditional planting 90 50 90 50 6,600 2,500 Figure 1. Optimal density planted sweetcorn with reduced spacing between plants Soil analysis and water quality requirements Sweetcorn is moderately tolerant to salinity and is more sensitive at the seedling stages. Prior to field preparation, soil and water samples should be taken and sent for analysis. An ADFSC extension engineer can assist with soil and water sampling techniques and help interpret results from the lab to grow the crop successfully. Once plants are fully established, a water salinity of between 1.1 and 1.7 ds/m (704 and 1088 ppm) may be used to grow the crop provided a leaching fraction of 15 to 20% is followed. Water salinity levels higher than 3.9 ds/m (2,500 ppm) will however severely restrict growth and impact yield by 50%. 2
Land preparation and pre-planting fertilising Thoroughly cultivate the area to be planted four weeks prior to the sowing date. Apply pre-planting fertilisers and well composted manure in a 30cm wide band along each drip line and mix thoroughly into the top 10 to 15 cm of the soil along this band. Fertilisers that should be incorporated into the soil at least two weeks prior to sowing are shown in Table 4. Table 4: Pre-planting fertilisers Pre-plant Composted manure (kg/do) Triple super phosphate (kg/do) Total application 2,500 50 Pre- and post-plant fertiliser applications provided are only a guideline. Fertiliser recommendations should be based on soil and 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 an appropriate fertiliser programme. These recommendations assume minimal residual nutrients from previous crops and current irrigation practices. As nutrients in soil and water levels vary, soil and irrigation water analysis should be conducted to fine tune fertiliser requirements for local conditions. It is important that an up-to-date salt content in the irrigation water is known to allow for sufficient leaching requirements. This should prevent salt build-up during the growing season which can affect the crop production. Sweetcorn performs well in deep, free draining soil containing plenty of organic matter. A properly composted manure provides organic matter to the soil to help with the retention of irrigation water and provide 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. Installation of new irrigation lines 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 sowing to ensure all drippers are working. This is ideally done as part of the pre-planting weed control. Sweetcorn growth stages To best manage your sweetcorn crop, it is important to recognise the different growth stages. Stress caused by nutrient and/or water shortages during the different stages of growth can affect yield. The three main growth stages are Stage 1 - from planting to tasseling, Stage 2 - from tasselling to end of silking and, Stage 3 - from end of silking to harvest. The grower will need to learn to recognise these stages. Stage 1 Approximately four weeks after emergence, the sweetcorn plant goes through rapid growth for 25 days. There is rapid stem elongation and ear size is determined. Any stress on the plant at this stage will permanently affect the ear development. Figure 2. Two plots of sequentially planted sweetcorn at early and late Stage 1 3
Stage 2 Following the rapid stem elongation of Stage 1, immature tassels will begin to emerge and the cob begins to develop. This indicates the crop is now in Stage 2 and preparing for pollination, which typically lasts between 5 and 10 days. Any stress at this stage will result in delayed silking and prevent kernel development. Sweetcorn is particularly susceptible to water stress during this time. Poor pollination will result in the kernel failing to develop and result in reduced tip fill, affecting the marketability of the produce. Figure 3. Sweetcorn at tasseling Figure 4. Sweetcorn in silking Stage 3 This stage lasts approximately 12 to 14 days after silking. Stress at this time affects kernel fill. Figure 5. Sweetcorn after silking Crop nutrition and application of soluble fertilisers through irrigation (fertigation) Leaching of nutrients, particularly nitrogen, into ground water sources can be minimised using fertigation, particularly in sandy soils. Successful sweetcorn growth with high yields can be achieved with smaller applications of fertilisers in the irrigation water throughout the season. Weekly fertigation, or preferably daily application is recommended. A weekly application schedule is presented in the table below and the dose can be split for daily application. Table 6: Recommended fertiliser rates (kg/do) for fertigation and trace element application for UAE sands 4
Growth stage, week after planting Notes: Ammonium sulphate Potassium nitrate Magnesium sulphate Trace element mix Chelated Fe (EDDHA) 1 2.0 2.0 1.0 0.3 0.3 2 5.0 3.0 1.0 0.3 0.3 3 5.0 4.0 1.0 0.3 0.3 4 7.0 5.0 2.0 0.3 0.3 5 7.0 5.0 3.0 0.3 0.3 6 9.0 7.5 3.0 0.3 0.3 7 9.0 7.5 3.0 0.3 0.3 8 9.0 4.0 2.0 0.3 0.3 9 6.0 12.0 2.0 0.3 0.3 10 6.0 12.0 1.0 0.3 0.3 11 5.0 4.0 1.0 - - 12 5.0 4.0 - - - Total 75.0 70.0 20.0 3.0 3.0 Fertigation should commence when sweetcorn plants are fully emerged Depending on soil and water analysis it may be necessary to supply other chelated trace elements Continue irrigation for 5 minutes after fertigation to flush remaining fertilisers in the irrigation lines The above schedule of weekly applications (Table 6) 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. Weekly or more frequent fertigation ensures that nutrient levels are maintained in the root zone of the crop throughout the growing and production periods. These recommendations are based on good irrigation practices. Avoid excessive irrigation which will leach nutrients away from the root zone. Crop water requirements The successful production of sweetcorn requires adequate supply of water at critical times during the development of the crop. Steady, even growth of plants is necessary for high quality and yields. Therefore, irrigation must be closely monitored to ensure soil moisture remains even during the cropping period. The most critical moisture period is two weeks before tasseling, during pollination through to harvest. Reductions in the availability of water to plants will result in poor tip fill and consequently the number of kernels filled. It is important to recognise when the sweetcorn plant is stressed from the lack of water. When leaves start to roll particularly in morning, this is a sign the plant is under stress and care must be taken to prevent this from happening. Conversely, excessive irrigation promotes root rot diseases and results in leaching of nutrients away from the root zone. Application of soluble fertilisers as fertigation can be carried out during a normal irrigation. 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 the sweetcorn crop remain below the economic threshold and swift action is taken should they become a problem. Use of pest resistant varieties This ensures the 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 weeks. They protect the sweetcorn crop from numerous insect pests, such as aphids, thrips, and leaf miner and from birds. 5
Crop rotation Do not plant sweetcorn in fields cultivated with sweetcorn in the previous season. This will also minimise the risk of bacterial diseases such as bacterial wilt and fungal diseases such as damping-off. Rotate with a non-host crop such as alfalfa. Soil solarisation This should be carried out each summer prior to planting to help control soil-borne diseases, nematodes, crickets, cutworms and weeds. Companion crops Planting of squash and sunflowers in the vicinity of sweetcorn crops will help reduce aphid infestation. Figure 6. Sunflowers are used as companion crops to attract aphids Traps Placing coloured, light and pheromone traps around your sweetcorn crop will help control caterpillars and thrips. Removing and correctly destroying all crop residues immediately after harvest This helps prevent last season s pests re-infecting the new crop and will help to control bacterial soft rot, damping off, common smut, rust, mites, aphids, thrips and cutworms. Good weed management Sweetcorn crops should be weeded every 2 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. Crop monitoring Sweetcorn crops should be monitored for pests and diseases on a weekly basis. This is especially important during the early stages of growth when sweetcorn is 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. Thorough composting of all organic matter All manure put on the crop should be thoroughly composted to prevent pest and disease outbreaks, and weed infestation. 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. 6
Harvest stage Pre-harvest interval Pre-harvest interval (PHI) 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 may result in pesticide residues in the harvested produce, and render the crop unfit for human consumption and for sale. It is illegal to sell crops where the PHI has not been adhered to. Figure 7. Sweetcorn ready for harvest Field hygiene during harvest Good field hygiene is required to ensure your 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. For further details please consult your local ADFSC procurement officer. Figure 8. Harvesting sweetcorn Crop maturity, handling and storage The crop should be harvested when the kernels are fully developed, plump, and milky; the pollinated silks are dried and the husk remain tight and have a bright clean green appearance. The ear should still be firm and turgid. The farmer should cut a sample from the crop to be harvested to check if the cob is fully mature and free of insect and worm infestation before harvesting. He should also check whether the kernels are present to the tip. If there are too many missing kernels, the product cannot be sold as Class 1 (see ADFSC specification for more details). Once the kernels become dimpled or doughy the cob is over ripe and its value is lost. To further ensure maximum prices the stems should be cut neatly and not torn or ripped from the plant. Once harvested the cobs must be kept 7
in a cool shaded place for collection. Rapid removal of harvested cobs from the field helps towards increasing the shelf-life of sweetcorn. Sweetcorn should be packed gently into clean containers to reduce the risk of damage and contamination. They should never be dropped or thrown as this will reduce quality and value. To reduce risk of damage in transit, crates must be stacked safely and securely so they are not resting on the produce beneath. Grading For best price returns, ensure produce of different quality class grades and sizes are not mixed together as this will reduce the overall crop value. Grading should be done carefully and evenly and according to the current ADFSC specifications, which can be obtained from your local procurement officer. For further information and advice: Contact your local ADFSC office for professional advice from our experienced team of extension engineers. 8