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Wheat irrigation scheduling under water shortage conditions

The proper irrigation scheduling is needed for the efficient use of water, seed, fertilizer and other inputs

By Dr. Shamsuddin Tunio
Associate Professor Department of Agronomy,
Sindh Agriculture University, Tandojam
Mar 26 - Apr 01, 2001

Wheat is the major food crop of Pakistan and covers the largest area under any other crop in the country. It is small grain cereal crop widely grown in temperate regions of the world, where there is low temperature and high rainfall, to supplement adequate soil moisture. However, wheat is winter annual grain grass of graminae family with erect growth habits.

Pakistan is the country, where subtropical arid and semi-arid climate exist throughout cultivated Indus plain except northern mountainous area with temperate climate. In Pakistan, winter hardly extends long but it took short period including months of November, December and January (about two and half and three months). Where the months of December and January are months of winter monsoon that does not exist in the Sindh province, which experienced very low rainfall and arid climate most of the time in the year.

Water is essential for plant growth and it serves many functions in living plants, which is a medium for supplying nutrients to plants. The annual availability of Canal water supplies can meet only little portion of the total water requirements, which put major constraints on potential crop production. The shortage of irrigation water may develop through a high degree of water losses, which are observed through primary, secondary and tertiary water transport or conveyance systems. The poorly managed farm irrigation applications is one of the root cause of water losses.

The water losses may greatly occurs at the level of mainstreams, barrages and canals due to siltation, breaches in the canal banks, over flow as well as evaporation, seepages and leakages through canals, water courses and channels. However, losses of water may also develop at the farmers fields due to poor farm management practices such surface run off, downward drainage, siltation of channels, percolation, leaching and evaporation of water through soil surface and transpiration from plants.

Over the past two decades, increase in agricultural productivity in Pakistan have been brought about largely by the spreading of high yielding yarieties, increased fertilizer use and greater availability of irrigation water. The effective management of water for crop production becoming ever more important and essential during water shortage. The efficiency of water use in crops is low under the existing irrigation practices. Therefore, proper irrigation scheduling is essential that can conserve water and improve irrigation efficiency. The increase of wheat production depends upon changes in management practices including high yielding varieties, good seed bed preparation, timely planting, better crop stand, effective control of weeds and pests, and more efficient use of fertilizers and irrigation water. Shortage of irrigation water particularly during critical stages of crop growth (milky and grain formation stages) significantly affect the crop yield.

Rainfall is among the major sources of water for crop production. There is great variability in rainfall. The shortage of water has developed due to low rainfall throughout the country and silting of reservoirs, and also use of water for generating electricity on hydel energy. However, in certain areas and/or years, total rainfall may exceed the crop water requirements but, requirements and the crops suffer due to drought stress conditions. Wheat yield may strongly correlated with winter rainfall especially January through March. The adequate water supply in March is critical to wheat crop. However, late irrigation at soft dough stage increased yield by 6%. Where seedling, tillering, pre-flowering and grain-development are critical stages during the crop life. The shortage of soil-moisture at such stages results in permanent reduction in yield.

Concept of Irrigation Scheduling

The proper irrigation scheduling is needed for the efficient use of water, seed, fertilizer and other inputs, and one must be aware of it. Irrigation scheduling is the process of determining when to irrigate and how much water to apply per irrigation. There are certain benefits of proper irrigation scheduling such as improved crop yield and its quality, water and energy conservation and lower production costs.

Irrigation schedules are designed to either fully or partially provide the irrigation requirement. For this purpose, several methods are used to determine when to irrigate by using plant indicators, soil indicators and water budget technique. To manage efficient use of water, irrigation scheduling of crop is necessary, which determines when and how much irrigation water to apply to a particular crop in existing agro-climatic conditions per irrigation. In practice, over irrigation is done by farmers due to lack of awareness about crop water requirements under the fixed interval system of water distribution. However, too much or too little water both directly reduce crop yield. Whereas, improved irrigation scheduling and irrigation practices could result in increased crop yield and reduce seasonal irrigation water requirements.

The real goal of irrigation use in soil is to supply sufficient water to keep the plant growth normal. However, for optimum yield of wheat, it is necessary to irrigate wheat crop at proper timings and proper stages of growth and maturity. The irrigation water should only be applied when it is needed to crop. Whereas in wheat crop, the time of irrigation application has great influence on the growth and reproductive phases, which ultimately affect yield potential in routine or newly evolved wheat varieties.

Irrigation is the application of water to soil for the purpose of supplying moisture essential for plant growth. Crop water use is expressed in acre inches, where an acre inch is the amount of water required to cover one acre of land with one inch of water. For normal wheat crop under optimum grown conditions, 4-6 irrigations are sufficient. First irrigation should be applied 3-4 weeks after sowing, and subsequent irrigation should be applied at 21 days intervals (Table 1).

The research efforts are made in the past for finding an optimum and practicable irrigation schedule for wheat. Yields are influenced by both the amount of water used and the frequency of irrigation. Many researchers consider crop growth stages for developing irrigation schedules for wheat (Table 2). Wheat growth stages are very sensitive to drought. For wheat crop under better soil conditions. 4-5 irrigation (21 acre inches) are sufficient. In this case, two approaches are used to irrigate wheat crop. One approach is to irrigate at definite crop growth stages and the other is to irrigate when the moisture is available to the crop is depleted, irrespective of growth, crop stage, until maturity. The stages like crown root initiation, tillering, booting, heading, milky and dough are critical ones. Such growth stages may appear as tillering (21 days after sowing), heading (50 days after sowing), milky (80 days after sowing) and dough (100 days after sowing).

The number of irrigation may be synchronized to such growth stages. There are reports that the highest wheat yields may be obtained from four irrigations: crown root initiations, booting, flowering and milky stages. Out of all stages, crown root initiation is most important stage for irrigation with regard to proper root development. Maximum yield of wheat may be obtained when supplement irrigation was applied at the crown root initiation. The available reports indicated that the cost critical stage for irrigation in wheat is crown root initiation. But, irrigations at CRI, maximum tillering, booting and grain filling may produce better yields. However, the largest yield decrease, associated with reduced number of grains per spike observed when water stress was given at tillering stage.

Table 1. Irrigation Frequency and scheduling in wheat

Irrigation Frequency

Days after sowing

Crop stages

1 - Irrigation

21

CRI (Crown Root Initiation)

2 - Irrigations

42

CRI + Tillering

3 - Irrigations

63

CRI + Tillering + Heading

4 - Irrigations

84

CRI + Tillering + Heading + Milky

5 - Irrigations

105

CRI + Tillering + Heading + Milky + Dough

6 - Irrigations

126

CRI + Tillering + Heading + Flowering +

 

Milky + Dough

 

Source: New wheat production technology, 2000-2001. Agriculture Extension Department, Sindh.

Table 2. Effects of irrigation schedulings on wheat yields

Irrigation scheduling

Crop growth stages

Yield

1.

3 Irrigations (Kalwar, 1993)

Crown root initiation (CRI), Heading (H) and Grain formation (GF).

Highest grain yield was obtained.

2.

6 Irrigations (Bhardwaj et al. 1973)

CRI, Late Tillering (LT), Flowering (F), Milk ripe and Jointing or dough stages

Reduced grain yield.

3.

6 Irrigations (Patel, et al. 1974)

CRI (21 days after Sowing), LTX (42 DAS), LJ (60 DAS), Flowering (80 DAS), Milk-ripe (95 DAS) and Dough-ripe (115 DAS).

The highest yield was produced with 6 irrigation than 5 or 4.

4.

4 Irrigations (Tomar and Singh, 1974)

Tillering, Pre-heading, milk-ripe and wax-ripe stages.

Yield increased with first two irrigations

5.

4 Irrigations (Malik. 1980)

CRI, Tillering, Flowering & Dough ripeness stages

Yield increased from 2.68-4.42 t/ha.

6.

6 Irrigations (Samo, 1980)

CRI, Tillering, Flowering grain formation and hardening stages.

Produced maxi- mum grain yield.

7.

4 Irrigations (Jana and Sen, (1981)

CRI, Tillering, Flowering & dough stages.

More grain yield (3.01 t/ha) was obtained with 1-4 irrigations

8.

2 Irrigations (Lomete et al. 1981)

CRI and booting stages

Yield increase of 1, 25-2.1 t/ha.

9.

3 Irrigations (Sexena and Singh, 1981)

Tillering, flowering & milk ripe stages

Yield was highest with 3 irrigations.

10.

1-2 Irrigations (Metha et al. 1982)

CRI, Tillering, flowering & dough stages.

Produced best yield when irrigated at CRI & flowering

11.

4 Irrigations (Muhiuddin et al. 1982)

Pre-sowing (PS), Jointing (J), Flowering (F) and PS + J + F

Highest grain yield was obtained

12.

3 Irrigations (Rao & Bhardwaj, 1982).

CRI, CRI + booting and booting

Highest yield was obtained

13.

4 Irrigations (Singh, et al. 1985)

CRI, Jointing, flowering and milk-ripe stages.

Produced aver- age yield of 3.2 t/ha.

14.

2+2 Irrigations (Singh, 1986)

CRI, Jointing, flowering and milk-ripe stages.

Yield increa- sed by 2+2 irrigations

15.

2+3 Irrigations (Qayyum and Kamal. 1987).

CRI, maximum tillering, booting & grain filling.

Produced higher yields.

Source: Through literature Review, Irrigation scheduling in wheat. Pakistan and India.