Everything you need to learn about cultivating citrus organically. Learn about:- 1. Introduction to Citrus Fruit 2. Some Fundamentals of Organic Citrus Management 3. Nursery Techniques 4. Procurement 5. Planting Design and Planting Density 6. Planting and Orchard Establishment 7. Diversity Planting, Intercropping and Weed Control 8. Nutrient Management 9. Post-Harvest Handling 10. Insect Pests and Diseases.
Contents:
- Introduction to Citrus Fruit
- Some Fundamentals of Organic Citrus Management
- Nursery Techniques for Multiplication of Citrus Plants
- Procurement of Citrus Seeds and their Treatment
- Planting Design and Planting Density of Citrus Crop
- Planting and Orchard Establishment of Citrus Fruit
- Diversity Planting, Intercropping and Weed Control of Citrus Fruit
- Nutrient Management of Citrus
- Post-Harvest Handling of Citrus Fruit
- Insect Pests and Diseases in Citrus Fruit Crops
1. Introduction to Citrus Fruit:
Citrus fruits are most important fruits of the country, as these are very juicy, delicious to eat and have high vitamin C content. Citrus fruits in India are cultivated in an area of about 10,42,000 hectares with production of around 100,90,000 tons (2012-13). Citrus group of fruits comprise an array of various species and types.
However here, only most important commercial citrus fruits of the country are described:
1. Mandarins (Citrus reticulata) – Different types of mandarins are cultivated in India, such as, Nagpur mandarin, Kinnow mandarin, Khasi mandarin, Coorg mandarin etc.
2. Sweet oranges (Citrus sinensis) – Different sweet oranges being cultivated are Sathgudi, Mosambi, Hamlin, Jaffa, Pineapple, Red Blood etc.
3. Acid lime (Citrus aurantifolia) – This is popularly known as Kagzi lime or “Nimboo”.
4. Lemons (Citrus Union) – Most important lemons are Assam lemon, Nepali Oblong, Nepali Round, Eureka and Lisbon.
Cultivation practices of above citrus group crops under organic management are being described including nutrient management and pest and disease management
2. Some Fundamentals of Organic Citrus Management:
Organic citrus is still a niche subject and world over just 1-2% of the total area under citrus cultivation is being managed organically. Although some growers may attempt to plant a new orchard under organic right from beginning but most of the organic growers in India may be in the situation of converting an already existing plantation into organic.
The first and most important conversion step is the design of the organic orchard based on the ecological principles, that higher the diversity of species, higher the stability of the agro-ecosystem. The high degree of biodiversity creates the habitat for natural enemies of pests.
One of the most important tasks on the way to organic production is to find strategies on how to increase biodiversity:
1. Create a diverse mosaic of citrus units and other crops from an existing plantation. In case of large orchards of many hectare areas removing some rows of citrus trees and replacing with other fruits and diverse tree species can achieve this. In case of small farms, planting additional tree species around the existing plantations can create diversity.
2. Between the rows (in the alleyway) plan intercrop with pasture grasses, beans or other crops. However, this might be difficult in case of older plantations where the trees are adapted to a certain management; in such cases, a step-by-step procedure is recommended (introduction of new crops and elements year by year), because the root systems of the citrus trees have to adapt to new competition in the soil.
3. The density of existing plantations may be decreased to 8 x 8 m (156 trees per ha) if there is a too high density. High density plantings reduce ventilation and light interception and thus increase disease pressure. Lower density plantings are better adapted to the organic production system. High density plantings are ideally not suited to organic management.
Farmers who intend to plant a new citrus orchard have the advantage that right from the start they can create an optimal organic system.
This can be achieved by adopting following strategies:
1. Creating a diverse mosaic of citrus units with some diversity among the citrus species. Adequate space need to be assigned for ecological compensation such as cover crops in the alleyway and under the trees as well as hedges and wild flower fallow plots/border rows around and in the orchard;
2. Intercropping is the key for success in organic management with any crop, therefore for organic farmers it is essential not to rely on the citrus production alone and consider mixed crop model. Large numbers of studies have confirmed that mixed cropping have several advantages over mono cropping and the yields and profits are much higher in mixed crop systems.
3. Some months before planting citrus trees, organic growers can sow vigorously growing legumes (e.g. Sesbania, sunhemp, cluster bean etc.) and mulch them well before planting the citrus trees. This way the soil will be enriched with organic matter and nitrogen along with high degree of soil microbial activity.
Under Indian conditions, however, legume and green manure crops are most ideal intercrops. Intercropping with other high water and nutrient demanding crops may result in predisposing of citrus plantations to attack of various insect pests, nematodes and diseases, which within a few years results in early die back.
Therefore, plantations of mandarins and sweet oranges at a spacing of 8m x 8m and lime and lemons at a spacing of 6m x 6m may be adopted as mixed crop model using only leguminous and green manuring crops. Extra spaces available between the rows are to be utilized mainly for growing green manuring crops and legumes for ploughing back into the field or as mulch.
The requirements of nutrients as well as pest and disease management care of intercrops must be met at required time. Good air circulation, ample penetration of sunlight and low humidity will help in containing the multiplication of pests and diseases.
3. Nursery Techniques for Multiplication of Citrus Plants:
For multiplication of citrus fruit plants, seeds of appropriate rootstock cultivars are sown and grown into plants for budding with improved varieties.
Following rootstock varieties are generally used for different citrus fruits:
Nagpur mandarin – Rough lemon (Jambhiri), Rangpur lime, Alemow
Kinnow mandarin – Rough lemon (Jatti Khatti)
Darjeeling/Sikkim/Khasi/Coorg mandarin – Grown on their own roots as seedlings
Acid lime (Kagzi lime) – Grown mostly on their own roots as seedlings
Sathgudi sweet orange – Rough lemon and Rangpur lime
Mosambi – Rangpur lime
4. Procurement of Citrus Seeds and their Treatment:
Seeds need to be extracted from fully ripe fruits of the selected rootstock. In case of fruits in which plants are raised on their own roots, the seed of the scion variety itself is procured. After extracting seed, the mucilaginous layer on the seed needs to be removed by washing and rubbing in water or rubbing in wood ash and later seed is dried in shade.
After this seeds are treated with Trichoderma viride and Pseudomonas fluorescens @ 5-10 g/kg seed. In cases of seed borne disease prevalence, the seeds can also be treated with clove and cinnamon oil or any other seed treatment solution.
i. Media Preparation for Germination and Raising of Seedlings:
Media is prepared by mixing virgin soil, sand, FYM and vermicompost in equal quantities. This mixture is slightly moistened by water and spread on a concrete floor in the form of 15-18 cm thick layer and is covered with 100 gauge UV stabilized transparent polythene sheet in summer months (April-May) keeping ends of polythene sheets sealed.
In this way mixture is solar sterilized. In cases of heavy soil infestations, it may also be drenched with suspension of Trichoderma viride and Pseudomonas fluorescens @ 10 g each in 1 litre of water. After 1-2 days, this media can be used in plastic trays and polybags. In extreme cases the mixture can also be steam sterilized.
ii. Raising of Seedlings in the Primary Nursery:
Primary nursery is raised in plastic trays of the size 60 x 40 x 12 cm. After making holes in the bottom of tray to drain excess water, trays are filled with solar sterilized media and are kept at 1.5 feet height from the ground on cemented floor in a net house or green house, to check contamination. Seeds are sown at a depth of 1-1.5 cm with a spacing of 2.5 to 3.0 cm in the rows. After sowing light irrigation is given with water can.
iii. Transplanting of Seedlings in Secondary Nursery:
When seedlings are 4-6 inches tall having 8-10 leaves, these are transplanted in black polythene bags of 30 cm x 15 cm size having 2-4 holes at the bottom. These polybags are filled with solar sterilized media and are arranged in a net house or green house. While transplanting, to ensure uniform nucellar seedlings, avoid planting of too small or too tall seedlings. Also reject hook necked, bent or twisted taproot seedlings.
Before transplanting, seedling’s roots are dipped first in fresh water then in a suspension having 10 g each of Trichoderma viride and Pseudomonas fluorescens in 1.0 litre of water. Keep the seedlings suspended in this solution for 15-20 minutes before transplanting. In case of Khasi, Coorg, Darjeeling mandarins and acid lime, the seedlings when their stems attain the size of pencil thickness are dipped in above solution and then transplanted directly in the field.
iv. Selection of Mother Plants for Bud Wood and Scion Sticks:
In case of rootstocks for Nagpur mandarin, Kinnow mandarin and sweet oranges like Sathgudi, Mosambi etc. these need to be budded with their scions. It is important that selected mother plants for supply of bud wood are from pedigree plants having high productivity, best fruit size and fruit quality. Bud wood from such plants must be free from virus diseases and are certified.
If virus diseases are present in the mother stock, the disease can be eliminated by using in-vitro shoot tip grafting and then indexing. In this way virus free mother block is established. Budding is done in the season, when bark of the rootstock seedlings slips. At the time of budding, very small and very tall rootstock seedlings should be rejected. This will further enhance the numbers of nucellar rootstock seedlings.
In Maharashtra for Nagpur mandarin, budding is usually done in the months of November-January using T or shield budding methods. In case of Kinnow mandarin, the best time for budding is February-March or August- September months. The budded portion is wrapped with 100 gauze polythene strips. It is preferred to bud at a height of 9 inches from ground level to protect the budlings from foot rot infestation.
Protection of Budlings against Insect Pests and Diseases:
The budlings need to be protected against insect pests and diseases using botanical pesticides such as NSKE/neem oil or any other available formulation for insect pests and by using organic fungicides such as Bordeaux mixture, copper oxychloride or lime sulphur for control of diseases.
5. Planting Design and Planting Density of Citrus Crop:
A planting density, which permits optimal light penetration and aeration and provides adequate illuminated space for intercrops/green manures/cover crops is the fundamental requirement under organic management. Tree spacing for new organic oranges should be kept around 8 x 8 mt (156 trees per ha) and for limes and lemons at 6 x 6 mt.
Performing organic cultural practices becomes much easier in low density plantations and facilitate adequate space for cover crop and to care for it, to apply compost, to manage pests and diseases and to use mechanical devices for mowing and cutting of cover crops.
The spaces between the rows can be used to grow additional crops like legume vegetables, beans, soybean and medicinal/herbal plants such as Aloe Vera in the alleyway and on the borders. Aloe Vera is a shade tolerant and is being recommended for inter-planting among citrus and other fruit trees with success. While selecting an intercropping system it must be ensured that intercrop is compatible to the citrus orchard management situations.
6. Planting and Orchard Establishment of Citrus Fruit:
Generally for planting, pits of the size of 3 x 3 x 3 feet are dug much in advance before planting. It is appropriate to dip bare roots of budded plants or seedlings in solution containing Trichoderma viride and Pseudomonas Fluorescens @ 10 g each/litre of water. Also mix 50 g each of Trichoderma viride and Pseudomonas Fluorescens in 10 kg FYM that may be mixed in pit soil before planting. Best time of planting in all regions is after the onset of monsoon in June-July, to avoid mortality.
Maintaining permanent soil cover is a key to the success in citrus organic orchard management. Locally adapted leguminous crops such as clovers, fenugreek, green gram, cowpea, Sesbania etc. help restore degraded soils very fast and successfully suppress weeds, fix nitrogen and prevent erosion. To avoid competition between the cover crop and the citrus, selection of the cover crop and their field management is important.
A model developed by the Research Institute for Organic Agriculture (FiBL), Switzerland suggests:
i. Mulch the cover crops before the dry season to prevent competition e.g. for water.
ii. Reduce the percentage of living soil coverage to optimally adapt the soil cover system to the soil, the crop and the climate conditions.
One possible solution is the sandwich system, which is feasible in young plantations and in orchards with deep soils where tree roots are not too close to the soil surface. However, in orchards established under conventional system it would be harmful for the trees to change to a different cultivation system. In these cases a system with cover crops or organic mulches can be used. In such orchards, the traditional cover crop system is the suitable method.
7. Diversity Planting, Intercropping and Weed Control of Citrus Fruit:
Creation of diversity is key to the success for effective management of insect pests and diseases. Plant one or two rows of nitrogen fixing trees/bushes other suitable plants all around the orchard and along the road/pathways. Growing flowering plants along the orchard border by arranging small plants towards the crop and taller plants towards border also helps in creating diversity and for survival of beneficial insects.
Organic citrus growers are required to learn to distinguish between desired and undesired cover plants and should resort to cover crop management instead of weed control. This can be achieved by sowing competitive cover crops (legumes and other desired plants) to suppress weeds and undesired plants.
Besides cover crops a large number of plants, known for their pesticide value (such asadathoda, Ipomea, Calotropis, nirgundi etc.) and insectary plants (such as mustard, sunflower, alfalfa, marigold, French bean, cowpea, maize, coriander, spearmint, peppermint, Ocimum etc.) can also be interplanted and used as green manure or mulch. Nitrogen fixing plants like Gliricidia, Leucaena leucocephala, perennial pigeon pea etc. can also be planted on borders.
Besides this undesired plants are best suppressed by:
i. Regular mowing the (leguminous) cover crops. Different types of mowers are available most of them operated by a power take off from the tractor. Specially constructed mowers for organic orchards permit mowing in the alleyway and under the trees with sensor controlled bat wings.
ii. Hand weeding if other plants begin to dominate cover crops or citrus trees.
iii. Mulching and traditional discing.
8. Nutrient Management of Citrus:
Cover cropping, green manuring, mulching and nutrient rich manure applications are the major source of nutrition for citrus plants. For consistent availability of nutrients during active growth period, flowering and fruiting, foliar feeding is also a good supplement.
While making the nutrient protocol, depending upon the irrigation facilities available and other environmental factors such as rainfall, temperature and evapo-transpiration rates, calculate the possible contribution through different on-farm processes of cover crop mowing, green manuring, mulching and compensate the gap with nutrient rich compost applications and repeated foliar feeding.
Cover crops and green manures account for the major share of biologically fixed nitrogen. The quantum of contribution can be calculated by assessing the biomass output per square meter. Harvest entire above ground cover crop biomass in one sq meter. Suppose it comes to 4 kg and the dry matter % of the biomass is 15% and the percentage of nitrogen in dry biomass is 2.5% then the net N- contribution by the cover crop will be 150 kg N/ha.
In cases where only 50% of the space is being utilized by cover crops then the net N contribution will be 75 kg/ha. Similarly take into account the dry biomass in the form of fallen leaves, discarded fruits, residue of intercrops etc. and calculate the N contribution that may be about 50% of the cover crops.
Based upon the age of the plant and productivity being expected determine the need for nutrients by taking into consideration soil test and leaf analysis reports and calculate the need to be compensated by manures and by foliar feeding.
For soil application FYM or compost is generally provided once (under rainfed conditions) or twice (under irrigated conditions) and concentrated manure mixture is provided twice or thrice. Treating with cow urine can further enrich well decomposed FYM or compost.
Methods for preparation of enriched FYM/compost, concentrated manure mixture and foliar feeding solutions are as follow:
i. Making Cattle Urine Enriched FYM/Compost:
Spread the FYM/compost on the floor on bright sunny day and allow it to dry in sun. In the evening spray 50 lit cattle urine per ton of compost and mix thoroughly. If available 1-2 kg of Cow pat pit per ton of compost may also be mixed with enriched FYM/compost.
ii. Concentrated Manure Mixture:
Mix 70 kg vermicompost/biodynamic compost with 10 kg de-oiled cakes (such as of castor, mahua, karanj etc.), 5 kg neem cake and 9 kg of poultry manure. In areas of phosphorus deficiency 2 kg of rock phosphate or bone meal may also be added to this mixture. Add 200 gm each of Azotobacter, PSB and KMB bio-fertilizer and 500 gm each of Trichoderma viride and Pseudomonas fluorescens in 5 lit of water and mix with the above manure mixture. Keep the manure mixture covered in a heap for 48 hrs for incubation and use for soil application. Using this mixture within 5-8 days of preparation gives best results.
iii. Foliar Feed Solution:
Feeding plants through foliage is an important strategy in organic farming. Vermiwash (5%), Panchagavya (3%) and farm made protein hydrolysate (4-5 ml/lit of water) are ideal inputs. Any one or combination of two or all can be used depending upon the requirement.
Method of Application:
Enriched FYM/compost and concentrated manure mixture are applied mixed together in a ring or in square format in 20-30 cm deep trench dug with in the foliage periphery but about 1 meter away from the tree trunk. After application cover the trench first with soil and then by dry or wet biomass as mulch. Drench the mulched ring with Jivamrit mixed with water.
Crop wise recommendations for nutrient application, keeping in view that biomass recycling and mulching are being followed as a general rule, are described separately under each crop category.
9. Post-Harvest Handling of Citrus Fruits:
Success in post-harvest management through organic methods can be achieved only when management of insect pests and diseases has been done very efficiently at pre-harvest stage. Effort needs to be made that fruit, which has been grown through organic cultivation methods, has least infestation of insect pests and diseases. This is very important as in organic post-harvest management no fungicides can be used.
In a citrus pack house, the sequence of events can be (i) receiving in the pack house (ii) de-greening if required (iii) dumping and trash removal (iv) sorting including removal of diseased and small fruits (v) washing and rinsing (vi) waxing (vii) drying (viii) sizing (ix) carton filling and labeling (x) palletizing (xi) pre cooling and storage and (xii) container loading.
Details of these operations are given below:
i. De-Greening of Fruits:
Usually Ambia crop of Nagpur mandarin and Mosambi fruits need to be de-greened. Since de-greening is done by using ethylene gas for which special permission will be required from certification body. De-greening is done in a closed chamber at 27- 29°C and 90-95% RH. Concentration of ethylene gas and timing will depend upon the extent of green colour on fruits. However, 5-10 ppm ethylene gas up to 48 hrs was found optimum for Mosambi fruits.
ii. Management in the Pack House:
Earlier wet dumps were integral part of packing houses which have now been discontinued because wet dumps help in spread of decay pathogens through bruises and wounds on fruit surface.
Thus instead of using wet dumps, a padded hopper is provided and the fruits are carried to inspection roller by an elevated roller. In some cases fruits from plastic crates are put directly on the Inspection Roller-cum-Conveyor. At this stage fruits are sorted out manually and puffy, blemished, deformed, scarred or having pest or disease injury are eliminated.
iii. Washing and Cleaning:
Dust and adhering mould is eliminated by high pressure nozzles and disinfection is done with a spray of water containing chlorine (80-100 ppm) with nylon brushes with varying contact time. Fruit is then rinsed with clean water.
iv. Removal of Excess Water:
Excess water on surface of fruit is eliminated by moving the fruits on sponge roller belt where excess water is absorbed. This is an important step as success of wax treatment depends up on how effectively the excess water has been eliminated.
v. Waxing:
Wax coating is very important in citrus fruits as it provides gloss and shine to the fruit and increases its market value, protects fruits from water loss and it also acts as a carrier for added extracts of botanicals or oils for controlling diseases. Wax coating is applied with traversing automatic nozzles and soft brushes.
Only organic waxes, like natural carnauba wax is allowed in coating of organic fruits.
vi. Drying the Wax Coating:
The wax coating on the fruits needs to be dried in the dryer tunnel in packing line at a temperature of 30-35°C. It must be ensured that heaters etc. are effective so that drying is proper and appropriate.
vii. Sizing and Grading of Fruits:
Sizing or grading is done by using roller sizers. Various sizes are suggested for Nagpur mandarin, Kinnow mandarin, Mosambi and acid lime. The roller sizers are adjusted to achieve grading according to requirement.
viii. Packing:
In case of large size fruits, the number of fruits in a 10 kg cardboard box will be less and in case of small sized fruits, the number of fruits in CBF box will be higher. Usually 2 piece, telescopic, corrugated fiber-board boxes of 3 ply, treated with wax are used. A box of size 45 cm x 24 cm x 18 cm having 10 kg capacity is very common and acceptable.
Boxes must have 5% ventilation holes besides hand holes. Placement of fruits inside the boxes is done manually by placing accurately sized fruits to immobilize the fruits inside the box. Also wax coated dividers are used which act as cushioning material.
ix. Pre-Cooling:
After labeling the boxes, the Nagpur mandarin, Kinnow or Mosambi are pre-cooled.
Appropriate temperatures for pre-cooling and storage are given below:
Loading the Refrigerated Van/Container:
The boxes are loaded in the container, and it is to be ensured that the boxes are braced in such a way that there is no movement. Temperature and humidity need to be maintained inside the container.
10. Organic Management of Insect Pests and Diseases in Citrus Fruit Crops:
Pest management in Citrus fruits under organic management is an integrated approach and forms an integral part of overall management approaches combining cultural, mechanical and biological strategies in first place and using botanical and organically acceptable chemicals only as last resort.
First and foremost strategy for organic pest management in Citrus fruits is creation and maintenance of diversity, which includes permanent diversity plantation on boundary and internal bunds, and seasonal diversity through cover crops, intercrops, flowering plants and trap crops.
Permanent diversity plantation includes plantation of 2-3 varieties of citrus between main variety, nitrogen fixing plants like Gliricidia, Leucaena leucocephala etc. or some other fruit plants like custard apple or ber etc. on borders and pesticidal value plants such as Adathoda, Ipomea, Calotropis etc. randomly in between border plantation and aromatic grasses such as lemon and citronella grass on bunds. Seasonal diversity includes intercrops and cover crops. Some flowering trap crops such as marigold, maize and Hibiscus can also be planted along the borders.
Second strategy involves manipulation of cultural practices to ensure a balance in natural processes, which in turn keep the pests below the economical threshold limit.
A. Cultural Strategies:
1. Planting of disease free and resistant cultivars.
2. Proper spacing, mulching and green manuring and adequate use of organic manures and proper irrigation.
3. Avoid high density planting.
4. Frequent growing of legume cover crops and their mowing with soil.
5. Keeping soil covered with living vegetation and or crop residue.
6. Adequate use of organic manures followed by biomass mulching and drenching with fermented dung-urine slurry (such as Jivamrit).
7. Frequent application of bio-fertilizers especially the mycorrhiza and PGPRs.
8. Frequent drenching of tree basins (at least once a year) with Trichoderma viride, T. harzianum and Pseudomonas Fluorescens.
9. Do not allow cultivation of Murraya koenigii (curry leaf) plants in and around citrus plantations.
B. Ecological Strategies:
1. Ensure natural habitat and survival conditions for natural pest enemies such as pest predators, parasites and pathogens.
2. Do not uproot weed plants those are growing naturally and act as nectar source for natural enemies.
3. Due to enhancement of biodiversity by the flowering plants, number of parasitoids and predators (natural enemies) will also increase due to availability of nectar, pollen and insects etc. The major predators are a wide variety of spiders, ladybird beetles, long horned grasshoppers, Chrysoperla, earwigs, etc.
4. Collect egg cards of beneficial insects for release such as Trichogramma, Chrysoperla, Telenomus etc. which are available from state Bio-control Labs.
5. Install 4-5 pheromone traps for monitoring and 10-12 traps for mass trapping of moths.
6. Set up yellow pan water trap/sticky traps 15 cm above the canopy for monitoring whitefly and blue sticky trap for thrips @ 10-15 traps/acre.
7. Set up light traps 1 -2 trap/acre 15 cm above the crop canopy for monitoring and mass trapping of insects. Light traps with exit option for natural enemies of smaller size should be installed and operate around the dusk time (6 pm to 10 pm).
8. Grow flowering plants along the orchard border by arranging small plants towards the crop and taller plants towards border. Important insectary plants that can be planted as intercrops also include mustard, sunflower, alfalfa, marigold, carrot, French bean, cowpea, maize, spearmint, peppermint, coriander, Ocimum etc. After flowering these plants can be used as green manure/mulch.
Keep on monitoring pest- defender ratio. If pest defender ratio is 2:1 then no need to worry.