Introduction

In many countries cotton (Gossypium spp.) is one of the most important fibre producing plants. Cotton crop not only provides fibre for the textile industry, but also plays a role in the feed and oil industries with its seed, rich in oil (18 – 24%) and protein (20 – 40%). An estimated 350 million people are engaged in cotton production either on-farm or in transportation, ginning, baling and storage. China consumes 40% of the world’s raw cotton. Australia and Egypt produce the best quality cotton in the world. Cotton is a major export revenue source for Burkina Faso, Benin, Uzbekistan, Mali, Tajikistan, Ivory Coast, Kazakhstan, Egypt and Syria. The world’s lowest cost cotton producers are Australia, China, Brazil and Pakistan.

The USA and Israel are two of the highest cost cotton producers in the world. World’s main cotton exporters are the USA, Uzbekistan, Brazil and Australia. World cotton demand has increased steadily since the 1950s at an average annual rate of growth of 2%.

In terms of global production, cotton is the foremost fibre crop. Present world production is some 25.5 million tons of seed cotton from 34.8 million ha. China, USA and India are the world’s major cotton producing countries, accounting for nearly 60% of the world production. Nearly 53% of cotton produced in the world is subsidized. Cotton producing countries that subsidize their domestic industry include the USA, China, Greece, Spain, Turkey, Brazil, Mexico, Egypt and India.

Cotton is grown in more than 100 countries accounting for 40% of the world fibre market. The cotton is raised in diverse climates such as tropical, sub-tropical and temperate climates.

The development of the crop is sensitive to temperature. Cool nights and low daytime temperatures result in vegetative growth with few fruiting branches. The crop is very sensitive to frost and a minimum of 200 frost-free days is required. The length of the total growing period is about 150 to 180 days. Depending on temperature and variety, 50 to 85 days are required from planting to first bud formation, 25 to 30 days for flower formation and 50 to 60 days from flower opening to mature boll. Cotton is a short-day plant but day-neutral varieties exist. However, the effect of day length on flowering is influenced by temperature. Germination is optimum at temperatures of 18 to 30 °C, with minimum of 14 °C and maximum of 40 °C.

Delayed germination exposes seeds to fungus infections in the soil. For early vegetative growth, temperature must exceed 20 °C with 30 °C as desirable. For proper bud formation and flowering, daytime temperature should be higher than 20 °C and night temperature higher than 12 °C, but should not exceed 40 and 27 °C respectively. Temperatures between 27 and 32 °C are optimum for boll development and maturation but above 38 °C yields are reduced. Strong and/ or cold winds seriously affect the delicate young seedlings and at maturity will blow away fiber from opened bolls and cause soiling of the fiber with dust. Continuous rain during flowering and boll opening will impair pollination and reduce fiber quality. Heavy rainfall during flowering causes flower buds and young bolls to fall.

Cotton is grown on a wide range of soils but medium and heavy textured, deep, well drained, fertile clayey, alluvial, chernozom and laterite soils with good water holding characteristics are preferred. Acid or dense sub soils limit root penetration. The pH range is 5.5 to 8 with 7 to 8 regarded as optimum. The crop is tolerant to soil salinity. The plant propagation is by seed. The plant density varies between 100,000 to 160,000 plants/ ha under high density and between 14,000 to 37,000 plants/ ha under low density population.

Adoption of drip irrigation and fertigation in cotton proved to be technically feasible and economically viable and beneficial in many ways in many countries. Drip irrigation in many diverse agro-ecological situations registered higher yield (15 to 30 %) besides saving in water (30 to 45 %) and improving lint quality in comparison to conventional furrow, overhead sprinkler and centre pivot sprinkler irrigation methods. Under Adana, Turkey agro-climatic conditions subsurface drip irrigated cotton raised on 11 ha registered seed cotton yield of 5.5 to 5.8 tons/ha (33% increase over furrow irrigated cotton) besides saving 30% water, 20% energy, 15% labor and 5% plant protection chemicals.

For high yields, the seasonal crop water requirements for cotton were estimated to be 350 to 900 mm/ ha under range of climatic conditions and varying length of growing season (150 – 210 days) with an average daily evapotranspiration rate of 4 to 8 mm/ day. Irrigation scheduling using either daily growing rate or leaf water potential measurements by pressure chamber enabled efficient use of water, fertilizer and energy inputs. Cotton is a heavy feeder of nutrients. The aim of the fertigation program is to cover the difference between crop demand and supply. The ability of drip system to apply nutrients by fertigation frequently according to crop developmental stages gives the grower the ability to react to the plant needs in the most efficient way.

Other best management practices include irrigation scheduling, protection of crop from pests & diseases, need based weed management, defoliation, harvesting and post harvesting operations to minimize yield losses.

Cotton Best Practices

Best Management Practices (BMPs) are the best recommended agronomic practices for growing a specified crop. These practices are based on research and experience and apply to cotton under the specified agro-ecological conditions.
The recommended BMPs are not the only way to grow cotton but are the best way determined by Netafim. The BMPs may change as additional proven research becomes available.
Agro-ecological situation
Climate
Conditions: Temperate, tropical and subtropical
Climatic requirement: Short day plant, frost free days 180 to 200. The crop is sensitive to low temperature and frost
Day length: 9 – 12 hours
Rainfall: 500 to 800 mm/annum
Relative humidity: 50 to 80%
Base temperature: 14 ºC
Optimum temperature: Germination 18 – 30 ºC; vegetative growth 20 – 30 ºC
Bud formation & flowering: Daytime 20 – 40 ºC; night time 12 – 27 ºC; boll development & maturity 27 – 32 ºC
Delayed germination causes seed rot and plant population. Strong winds affect young seedlings & fiber quality. Heavy rains & water logging during flowering and boll opening cause shedding of flower buds and young bolls, impair pollination and reduces fiber quality.
Soil
Soil suitability: Fertile, deep, well drained clayey, alluvial, chernozom & laterite soils with good water holding characteristics.
Soil pH: 6.5 to 7.5
Soil critical nutrient levels: 10 ppm NO3–N, 5 ppm P, 150 ppm K, 0.6 ppm Zn, 5 ppm Fe, 1 ppm Mn & 0.5 ppm B
Soil bulk density: 1.3 – 1.4 Mg/m3 favor better root penetration & proliferation and soil water air relations.
Groundwater table: Below 2.0 m
Critical soil salinity level (ECe): 7.7 dS/m above which yield decreases.
Soils to avoid: water logged soils
Crop rotation
Three-year rotation adequate to check weeds, diseases & pests and avoids yield losses.
Without proper rotation yield losses are up to 30 – 40% due to soil borne diseases such as verticillium wilt, root rot & seedling diseases.
Cereal grains such as wheat, oats, corn, sugarcane, rice, clover, sorghum, legumes, safflower are the best rotational crops.
Improved varieties
Several varieties with great differences in size, shape, colour, texture, cooking characteristics and taste are available depending on the country.
Important varieties: Several American and Egyptian hybrids.
Planting material
Seed
Spacing
Narrow spacing: 0.75 to 1.0 m x 0.08 to 0.10 m
Wider row spacing: 1.2 m x 0.6 to 0.75 m
Optimum plant density: Varies between 100,000 to 160,000 plants/ ha under high density and between 13, 888 to 37,000 plants/ ha under low density population
Seeding rates
Varies with cultivar, planting date, seed size and cost of production
For widely spaced crop: 3 to 5 kg/ ha and for narrow spaced crop 11 – 13 kg/ ha
Land preparation
Clod free seedbed with good tilth to express its lint yield potential, Subsurface drip irrigation (SDI) installation and optimal soil water air relations.
Destroy the hard pan if any using either chisel plough or a subsoiler to a depth of 35 – 40 cm.
Primary tillage by mould board plough or disc plough and secondary tillage by disc harrows, tyned harrows or rotavator to achieve proper tilth.
Compost to be applied: 15 – 20 tons/ ha if available
Planting for better stand, yield and quality
Poor plant stand registers low yield
Soil temperature at planting: 14°C
Planting depth: 2.5 to 5.0 cm
Weed control
Effective weed management and control in cotton is critical to maximize yields and harvest high quality lint.
Some weeds act as host crops for insect pests that can invade cotton which can be an important reason to keep weed numbers low.
Weeds compete mainly for light, water, nutrients and reduce seed cotton yields by 50 to 85% depending on the weed intensity.
Critical crop – weed competition period is initial 8 – 10 weeks.
Integrated weed control program involving crop rotation, manual weeding, good seedbed preparation, maintenance of optimum plant population, mechanical intercultivation and herbicide chemical applications.
Herbicides per hectare
Pre-plant application: Trifluralin 0.6 – 1.2 kg
Pre-emergence herbicides:
Fluometuron 0.8 – 1.6 kg
Diuron 1.0 kg
Prometryn 1.0 kg
Oxyfluorfen 0.57 kg
Post-emergence herbicides: Metolachlor 1.07 – 1.36 kg
Genetically modified varieties such as Roundup Ready® cotton enables growers to treat their cotton crop with an over the top application of Roundup Ready® herbicide, a Roundup® branded agricultural herbicide formulation specifically labeled for use with Roundup Ready cotton.
Roundup Ready herbicide is highly effective against the majority of annual and perennial grasses as well as broad-leafed weeds.
Irrigation system
Drip version: Surface or subsurface drip irrigation combined with fertigation
Drip products: DripNet PC, Tiran, Dripline 17009, Super typhoon and Python 22135
Dripline spacing: 2.0 m for narrow spacing with 1 lateral for every 2 rows and 1.2 to 1.8 m for wider row spacing with 1 lateral per each crop row or two crop rows.
Emitter spacing: 0.4 m to 0.75 m depending on soil texture
Emitter flow rate: 0.6 LPH, 1.0 LPH, 1.6 LPH and 2.0 LPH depending on soil texture
Crop water requirement & irrigation scheduling
Estimate crop water requirements as a product of daily reference crop evapotranspiration (ETo) by Penman-Monteith method and crop coefficient for a given day according to the plant developmental stages.
Begin with 0.4 Kc of daily ETo in the initial period, raise it to 0.7 to 0.8 at vegetative and square formation, 1.2 at flowering, boll formation and boll development stages, and decrease it to 0.7 at maturity of cotton.
Daily crop water requirement: 4 to 8 mm/ day
Seasonal crop water requirement: 350 to 900 mm under range of environments
Irrigation scheduling using daily growing rate and leaf water potential measurement by pressure chamber at 1.4 to 1.8 MPa enabled efficient use of water, fertilizer and energy inputs.

Fertigation
Apply mineral fertilizers based on the targeted yield, leaf analysis results, fertilizer experiment results, leaf deficiency symptoms, nutrient uptake, soil analysis results and nutrient recycling.
It is highly recommended to make soil analysis before the commencement of cropping season. According to our field experience, by using drip fertigation in many cases we can avoid P & K application and also reduce the N application dose in comparison to other irrigation systems.
Nutrient uptake per ton seed cotton yield: 46 kg N, 16 kg P2O5, 40 kg K2O per ton
Recommended nutrient dose per hectare: 250 to 300 kg N + 80 to 100 kg P2O5 + 125 to 250 K2O
For fertigation use water soluble fertilizers such as urea (46% N), potassium nitrate (13% N & 46% K2O), monoammonium phosphate (12% N & 61% P2O5) and ammonium nitrate (34% N).
Pests & Diseases
Important pests include aphids, jassids, white flies, mites, cut worms, plant bugs, leaf worms, cabbage looper, boll worms and boll weevils.
Important diseases include seedling diseases, root-knot nematode, leaf spot, bacterial blight, wilt and boll rots.
Detect outbreaks and identify problem areas by routine patrols.
Monitor economic threshold levels and take up appropriate plant protection measures.
Harvesting
– The development of the cotton plant and its maturity are determined primarily by temperature, water, nutrients, and sunlight.
– For a boll to fully mature, 900 to 950 DD60’s are required after pollination. Thus, under optimal conditions, during the early part of the fruiting cycle, a boll matures in 45 to 50 days after flowering.
– A sharp knife can be used to determine boll maturity. Mature bolls are difficult to cut in cross section with a knife without stringing the fiber.
– Boll maturation is also correlated with seed maturation. The seed coats of mature seeds are tan to brown as opposed to the white and pale color of immature seeds. Inside the mature seeds, tiny leaves are easily identified. Immature seeds contain gelatinous material instead of leaves.
– Green bolls that crack when firmly squeezed should open within seven days during warm, dry weather.
– For mechanical harvesting and to ensure good harvest without losses, apply chemical defoliants when a minimum of 75% bolls are open. Defoliation usually occurs within 7 – 10 days when plant conditions are favorable and temperatures are above 18 °C.
– Most cotton in Europe and in countries such as the USA, Australia and Israel is harvested mechanically, either by a cotton picker or by a cotton stripper.
– Cotton strippers are used in regions where it is too windy to grow picker varieties of cotton.
Seed cotton yield
Under drip irrigation and fertigation a good commercial seed cotton yield is 5 – 6 tons/ ha depending on length of growing season and variety.
Water utilization efficiency varying between 0.8 and 1.0 kg/ m3

FAQ’S

How much a drip irrigation system costs per hectare of cotton?

This is very variable and depends on the following factors: Conveyance of water from source to the field: Normally this is the most expensive component of the irrigation system. It depends on the distance and elevation the water has to be conveyed by the pipelines. Peak crop water demand: Amount of water we need to apply to meet the peak crop evapotranspiration requirements during the cotton crop peak demand. This is a function of prevailing climate conditions, crop canopy cover and efficiency of the irrigation system. Other considerations: The land topography (flat or undulated) of the design area; the soil texture which determines the emitter spacing, for example sandy soils require closer emitter spacing and clayey soil require wider emitter spacing that will have a significant impact on the system cost per unit area.

Why choose drip and not sprinkler irrigation method?

The drip technology proved itself to be technically feasible and economically viable under range of environments besides increasing seed cotton yields and lint quality improvement. Drip technology also allows significant saving in water, fertilizers, labor and energy required for pumping water. In the long run, economic calculation shows that drip is the most suitable system for modern agriculture with higher economic returns.

Should I use subsurface or surface drip system?

Subsurface drip irrigation in cotton has shown to have many agro technical advantages besides regular drip system features: The driplines are protected from agro-machinery damage, it permits using a thin wall dripline that effect significantly the cost, applying the water and the fertilizers directly to the root zone and performing all the crop agro machinery actions such as spraying of plant protection chemicals and mechanical harvesting without interfering with the day to day irrigation system protocols.

What is the life of the drip system and after how many years I have to renew it?

The accumulated field experience revealed that cotton raised under subsurface drip irrigation system can continue up to ten and/ or more years before the field is renewed. During the renewal of the field for new plant crop, all the hydraulics (pipes, pump filters, etc.) remain intact the field for further use and only the dripline must be replaced which represents around 35 – 40% of the total system cost per unit area.

Does Bt cotton offer benefits to small growers in developing countries like India & China?

Yes, insect protected cotton is especially important in developing countries where small farmers may have less access to machinery and crop inputs, or must apply pesticides with hand sprayers under difficult conditions. Chinese farmers who used Bt cotton applied 80 percent less insecticide than farmers who planted non-Bt varieties.

Does Bt cotton provide economic benefits to farmers?

The National Center for Food & Agricultural Policy concluded that Bt varieties required an average 3.9 fewer insecticide sprays for bollworm/ budworm, cost $15.4 per acre less for insect control, yielded 37 pounds more lint per acre and resulted in $40.0 more profit per acre.

Is Bt cotton safe for soil organisms as the cotton plants degrade after harvest?

Impacts of Bt proteins have been investigated on a wide variety of terrestrial and aquatic invertebrates, including earthworms, collembola, daphnids, insect predators and parasites, spiders and honey bees. Even though test populations were exposed to levels 500 to 1,000 times greater than concentrations measured in the field, in most cases no adverse effects were observed.

What do you think about the possibility to say something about Roundup Ready (RR) cotton or generally about herbicides resistance?

Effective weed management and control in cotton is critical to maximize yields and harvest high quality lint. Some weeds act as host crops for insect pests that can invade cotton which can be an important reason to keep weed numbers low. Roundup Ready® cotton enables growers to treat their cotton crop with an over the top application of Roundup Ready® herbicide, a Roundup® branded agricultural herbicide formulation specifically labeled for use with Roundup Ready cotton. Roundup Ready herbicide is highly effective against the majority of annual and perennial grasses as well as broad-leafed weeds; it is the only glyphosate product registered for use over the top of Roundup Ready cotton. With the combination of Roundup Ready cotton and Roundup Ready herbicide growers gain superior weed control, plus a number of other environmental and crop management benefits such as the opportunity to reduce cultivation and residual herbicide use.