Irrigation & Water Requirements of Vegetable Crops

Munish Sharma

Dept. of Soil Science

College of Agriculture

C.S.K.H.P.K.V.

Palampur (H.P.)

INTRODUCTION

• Crop water requirements refer to the actual water

needs for evapotranspiration (ET) which are related to

soil type and plant growth, and primarily depend on

crop development and climatic factors which are closely

related to climatic demands.

• Irrigation requirements are primarily determined by

crop water requirements, but also depend on the

characteristics of the irrigation system, management

practices, and the soil characteristics in the irrigated

area.

• Water is essential for vegetable crops. It is absorbed by

plant roots from the soil through processes of osmosis

and diffusion.

• Besides absorption of water and translocation of

nutrients from soil, water also influences the

photosynthesis, respiration, transpiration, nutrient

utilization and cell division.

• Thus the crop plants require water almost

throughout the growing season.

• The water requirement varies with crop species

and growth stage of the crop.

IRRIGATION

• The important sources of water to a crop are

mainly rainfall and irrigation.

• The uncertainty of uniformity and level of rainfall

increases the importance of irrigation in vegetable

production.

• Irrigation is likely to increase size and weight of

individual fruit and to prevent defects such as

toughness, strong flavor, poor tipfill and podfill,

cracking, blossom-end rot and misshapen fruit.

• On the other hand, it reduces soluble solids in

muskmelons and capsaicin in hot peppers if

applied during fruit development.

PERCENTAGE IRRIGATION OF WORLD

AMERICA 17%

EUROPE 9%

AFRICA5%

OCENIA1%

ASIA 68%

PROBLEMS IN IRRIGATION

• Scarcity of water: According to Population

Action International (PAI), severe water

scarcity or hydrological poverty is feared in

the world by 2025.

• In India only 34% of the water resources is

available to meet the increasing demands

of agriculture, industry and urban usage.

• The quality and availability of water are two

major factors that affects irrigation in

vegetable crops.

Water Demand in relation to Crops

• The water demand and response to

irrigation varies along with crop species.

• Shallow-rooted crops and crops with tap

root system such as potatoes and celery

require frequent, light irrigations.

• Deep-rooted crops and crops with fibrous

roots, can use water from a greater volume

of the soil profile and do not require

irrigation as frequently.

• Vegetable crops differ in their water requirements, andhave certain stages of growth when an adequate watersupply is critical.

• Adequate water is essential for good germination of allcrops.

• For flowering crops, such as beans, tomatoes, cucurbitsand maize, another critical period is at flowering, andthen also during the development of fruit and/or seed.

• For heading crops, such as lettuce and cabbage, themost critical period for water is at heading stage.

• An adequate supply of water is essential for root cropsonce the roots start enlarging.

Water Demand in relation to Soils

• Soil types differ in their ability to retain

water following rainfall or irrigation.

• Coarse textured soils (e.g. sands and

coarse sandy loams) held less available soil

moisture. So frequent and light irrigation are

required in such soils.

• Fine textured soils retain more available soil

moisture. So heavier and less frequent

irrigations are required in such soils.

Water demand in relation to

growing season• The water requirements of crops also vary

with the growing season.

• Warm season vegetable crops have higher

water requirement in comparison to the cool

season vegetable crops.

• This is mainly due to the high evapo-

transpiration demand in the warm season.

Irrigation and water requirement

under various conditions

1. Improving Stands

2. Rooting Depth

3. Critical Moisture Periods

4. Drought tolerance

Irrigation for improving stands

• Irrigation is a valuable tool in producing a

good, uniform stand which will help ensure

high yields.

• Good uniform stands mean uniform harvest

dates and greater production efficiency.

• Vegetable transplants also require good soil

moisture. A light irrigation will help in the

establishment of young transplants by

providing a ready supply of water to young,

broken roots.

• Most vegetables have small seeds that areplanted 15 cm deep or less. The upper layer ofthe soil can dry rapidly, leaving shallowly sownseeds susceptible to drying out.

• Without enough soil moisture, the seed is leftpartially germinated. When this happens, nostand or, at best, an incomplete stand will result.

• A light irrigation immediately after sowing shouldbe applied to settle the soil around the seedsand to begin seed germination.

• For larger seeded crops, it is desirable that

irrigation begins a few days prior to sowing.

• If seeds are slow in emerging from the soil due

to cool temperatures or slow germination, then

application of light irrigation is needed to

encourage emergence.

Irrigation in relation to rooting depth

• It is important that the soil profile be filled withwater during each irrigation event. Otherwise,frequent light irrigation events result in theformation of shallow root systems.

• Shallow root systems result in plants beingstressed even in short periods of water deficit.In addition, the plants with shallow rootsystems are more prone to lodging and nutrientdeficiencies.

• On the other hand, excessive irrigation canleach nutrients from the soil and encourage thedevelopment of diseases and nutrientdeficiencies.

Shallow-Rooted

(down to 45-60

cm)

Intermediate

(90-120 cm depth)

Deep-Rooted

(deeper than 120

cm)

Cabbage,

cauliflower,

broccoli, Brussels

sprout, corn, onion,

garlic, lettuce,

parsley, onion,

radish, spinach

Beet, beans, carrot,

turnip, cauliflower,

cucumbers,

muskmelon, summer

squash, peppers,

brinjal, pea

Asparagus, artichoke,

tomato, sweet corn,

pumpkin,

watermelons, winter

squash, sweet potato

Irrigation in relation to critical moisture

periods

• Critical periods of water needs can best be defined

as that time when soil moisture stress can most

reduce yield in an otherwise healthy crop.

• This is not to say that it is the only time in the life of

the crop that moisture stress reduces yield. It is,

however, the time when moisture stress will exert

its greatest effect.

• Most vegetable crops are sensitive to drought

during two periods: during harvest and two to three

weeks before harvest

Crops Critical Period

Beet, carrot, radish, turnip Root enlargement

Cabbage, cauliflower, broccoli,

lettuce

Head development

Tomato, peppers, brinjal,

cucumber, melons

Flowering, fruit set and fruit

development

Beans, peas Flowering and pod development

Onion Bulb development

Potato Tuber initiation and tuber

development

Asparagus Fern development

Sweet corn Tasseling, silking and ear

development

Irrigation in relation to drought

tolerance

• Drought tolerance is an indication of a cropsability to withstand short periods of droughtwithout significantly reducing yield.

• Vegetable crops vary in their tolerance todrought depending on their physiology andwater requirements.

• Crops with higher drought tolerance can begrown where water available for irrigation islow and the crop can still give economicyield if supplement irrigation is provided atcritical stages of plant growth.

Low tolerance Medium

tolerance

High

tolerance

Summer squash,

cucumber,

radish, leek,

celery,

cauliflower,

broccoli

Turnip, tomato,

pumpkin, peppers,

eggplant,

sweet corn, carrot,

watermelon

Sweet potato,

asparagus,

parsnip

Water requirement for different groups

of vegetable crops

• Leafy vegetables

• Root, tuber, and bulb vegetables

• Fruit and seed vegetables

Leafy vegetables

• Cabbage, lettuce, and spinach are generally

planted at or near field capacity.

• Being shallow rooted, these crops benefit from

frequent irrigation throughout the season. Since

leaf expansion relates closely to water availability,

these crops, especially cabbage and lettuce, are

particularly sensitive to drought stress during the

period between head formation and harvest.

Overwatering or irregular watering can result in

burst heads.

• Broccoli and cauliflower are sensitive to drought

stress at all stages of growth, responding with

reduced growth and premature heading.

Root, tuber, and bulb vegetables

• In sweet potatoes, potatoes, carrots, and onions,

yield depends on the production and translocation

of carbohydrates from the leaf to the root or bulb.

• The most sensitive stage of growth generally

occurs as these storage organs enlarge.

• Moisture stress causes the formation of small,

woody, and poorly flavored roots. Uneven irrigation

can lead to misshapen or split roots in carrots,

secondary growth in Irish potatoes, and early

bulbing in onions.

Fruit and seed vegetables

• Cucumbers, melons, pumpkins andsquashes, lima beans, snap beans, peas,peppers, sweet corn, and tomatoes aremost sensitive to drought stress at floweringand during fruit and seed development.

• Fruit set on these crops can be seriouslyreduced if water is limiting. An adequatesupply of water during the period of fruitenlargement can reduce the incidence offruit cracking and blossom-end rot intomatoes.

Methods of irrigation

• Surface irrigation

• Drip or trickle irrigation

• Sprinkler irrigation

• Central Pivot System

Surface IrrigationSurface Irrigation

Surface IrrigationSurface Irrigation

Drip or Trickle Irrigation

Sprinkler IrrigationSprinkler Irrigation

Sprinkler IrrigationSprinkler Irrigation

Center PivotCenter Pivot System

Choice of Method

• The choice of method of irrigation depends

on following factors :

– natural conditions

– type of crop

– previous experience with irrigation

– required labor inputs

– costs and benefits.

Choice of Method

NATURAL CONDITIONS

• Soil type

• Slope

• Climate

• Water availability

• Water quality

Type of crop

• Surface irrigation can be used for all types

of crops.

• Sprinkler and drip irrigation, because of

their high capital investment per hectare,

are mostly used for high value crops.

• Drip irrigation is suited to irrigating

individual plants. It is not suitable for close

growing crops.

Previous experience with irrigation

• The choice of an irrigation method alsodepends on the irrigation tradition within theregion or country.

• Previous irrigation experience reveals theproblems regarding irrigation in the regionand helps in choosing better irrigationmethods based on local conditions.

• The servicing of the equipment may beproblematic and the costs may be highcompared to the benefits.

Required labor inputs

• Surface irrigation often requires a much

higher labor input - for construction,

operation and maintenance - than sprinkler

or drip irrigation.

• Surface irrigation requires accurate land

leveling, regular maintenance and a high

level of farmers' organization to operate the

system.

• Sprinkler and drip irrigation require little

land leveling; system operation and

maintenance are less labor-intensive.

Costs and benefits

• Before choosing an irrigation method, an

estimate must be made of the costs and

benefits of the available options.

• On the cost side not only the construction

and installation, but also the operation and

maintenance (per hectare) should be taken

into account.

• These costs should then be compared with

the expected benefits (yields).

Thank You