The quantity and quality of water for crops, both are important

Apr 02 - 08, 2001

At present, non availability of sufficient irrigation water is burning problem all over in Pakistan. Kharif cropping season is near to start. Therefore, cultivation of drought resistant crops is today's need, for obtaining optimum crop production and to support economy of the country not so much, but as much as could be possible.

Pakistan is basically an agricultural country, and has developed an extensive irrigation system, with barrages and link canals. Its weather is generally hot (sometimes very hot) in the plains and moderate (sometimes very cool) in the hilly areas. Agriculture provides food and fibre for our growing population, as well as fodder for our domestic animals and raw material for most of our industries. It constitutes the largest sector of the economy of Pakistan. It accounts for 25% of the gross national product (GDP), which provides employment to about 54% of the labour force and supports directly or indirectly, about 70% of the population and contributes to 70% of the foreign exchange besides meeting the raw material requirement of the domestic industry to a large extent.

According to "Economy of Pakistan, 1948-68", the principal assets of Pakistan's agriculture are the fertile soil of the country as a whole, a generally favourable climate and an elaborate net work of irrigation. On the other hand, there are some liabilities which hamper growth and development. These are low productivity land caused by water-logging, salinity and soil erosion; primitive methods of cultivation; small and fragmented holdings; conservation and illiteracy of the cultivators which make extension work difficult; low income of farmers making investment for adopting improved agricultural practices difficult; land tenure problems; poor marketing facilities, inadequate transport, communication and market intelligence; and price fluctuation.

Except and or including above discussed yesterday's constraints, non availability of sufficient irrigation water is today's burning problem at all over Pakistan. No doubt, water is the most important plant nutrient and constitutes the greater part of plant weight, hence is absolutely essential for plant life. Apparently even dry plants contain an appreciable amount of water because water is basic need and works as the nutrient solvent. In fact, plants use more water than any other substance they absorb, therefore the water in sufficient quantity is vital necessity for all plants. The function of soil moisture in plant growth is very important. When soil moisture is not enough, drought condition prevails leading to ultimate death of the plant. The availability of nutrient is controlled by the moisture content of the soil. On the other hand, it is also true that excessive water quantity in the soil inhibits plant growth and makes drainage essential. Excessive moisture reduced the supply of oxygen, which actually needed for respiratory system of the plant. While excessive moisture may also delay flowering and can lead to poor pod/fruit formation and filling as well as reduce grain/seed quality.

The agriculture of Pakistan is characterised by two main cropping seasons, namely, the Kharif (summer crops) from April to September; and Rabi (winter crops) from October to March. Wheat is the main crop of Rabi season, while rice, maize, sugarcane and cotton are considered the major crops of Kharif. Mono cropping, sequence cropping, mixed cropping, inter-cropping and relay cropping systems are practiced by growers (farmers), especially those with small holdings, to maximise crop production per unit area. The cropping pattern is largely determined by water availability and the climatic conditions as adaptation of crops. However, present situation of irrigation water is widely being reported daily through TV, Radio as well as Print media. A lot of research has been carried out by various research workers, on different crops, for their requirements of irrigation water. The results so far achieved, according to their critical growth stages as well as cultivation season, are being summarised here under, as per recommendations by Bhatti and Soomro (Ref. Agricultural inputs and field crop production in Sindh, ARS, Hyderabad, 1996. Now it is upto the growers that what they want to cultivate and how they would try to fulfil the irrigation water requirements of their crops.

Kharif crops

Rice: Rice is one of the leading cash and foreign exchange earning food crops of the world, including Pakistan. It requires a constant and plentiful supply of irrigation water. It needs 46 acre inches as soaking dose 4-6 days before transplanting, 1-2 acre inches at the time of transplanting and 3-4 acre inches 7-10 days after transplanting to maturity of the crop. The reproductive stages from penicle initiation to flowering and grain formation are the critical stages. Any stress at this stage will affect the yield and grain quality. However, rice requires over all 60-70 acre inches irrigation water on the basis of varieties.

Maize: Maize is also one of the cereal crops. It is very efficient water user. It needs large quantities of irrigation water for high yield, because drought conditions lead to lower yields and lower quality grains. Maize requires 6-8 irrigations. First irrigation 3-4 weeks after sowing, remaining may be given at 10-15 days interval. The grain formation is critical growth stage. It is not important grain crop in Sindh, but is grown mostly as fodder crop and very rare as for grain.

Sorghum (Jowar): The major area of sorghum in Pakistan lies in Punjab, but the yield per hectare is higher in Sindh. The sorghum plants are drought resistant, but 3-4 irrigations (30-35,50-60 and 70- 80 days after sowing) are compulsory for better yield.

Millet (Bajra): The area under millet crop is highly variable, because it is dependent on the amount and time of the rainfall. It is mostly confined to the desert and mountain (Thar, Cholistan and Kohistan) area. 3-4 irrigations are sufficient for better yield, as recommended for sorghum.

Mungbean (Green gram): It does not require much irrigation due to short duration and drought tolerant crop. However, 3-4 irrigations are sufficient for getting good yield. Flowering and seed development stages are very critical.

Mash (Black gram): Irrigation requirements are same as for Mungbean.

Arhar (Pigeonpea or Red gram): Same as discussed for Mungbean.

Cowpea: This crop is grown as pulse, vegetable, fodder and green manure crop, hence is of economic importance, especially in Sindh. Irrigation requirements are same as of Mungbean crop.

Cotton: Cotton is alone fibre crop of Pakistan. It is also most important cash and foreign exchange earning crop. It requires 7-8 irrigations (at least 80 cm) to get an acceptable yield. The first irrigation is to be given 35-40 days after sowing (DAS) and subsequent irrigations should be applied at 15 days interval. The most critical stages for irrigation are early flowering to first boll opening and maturity.

Sugarcane: Sugarcane is also one of the major crops. The highest acreage is in Punjab but yield is higher in Sindh. The crop requires 30-33 irrigations at 15 days interval during winter and weekly in summer (a total of 96 acre inches).

Sunflower: Sunflower has gained higher popularity and acreage, among the new oilseed crops introduced for boosting edible oil production. The important features of this crop are short growing period, high yield potential and wide range of growing season viz. autumn, spring and winter. It fits well in different cropping patterns, low irrigation water requirements, wide adaptability to soil and moisture conditions. Its seed contains high oil (over 40%) of good edible quality and meal of good quality free from toxic compounds. 3 irrigations are necessary. The 1st irrigation should be given 30-35 DAS, 2nd at start of flowering and 3rd just after petal fall.

Soybean: It requires 5-7 irrigations from sowing to maturity. Irrigation at pod filling stage is very necessary, drought at this stage will reduce yield drastically.

Groundnut (Peanut): This crop requires 30 acre inches during 5-7 irrigations. The first irrigation should be given 25-30 DAS and subsequent at 15-20 days intervals. The critical stage is seed development.

Sesame: The sesame is cultivated throughout Pakistan as irrigated as well as un-irrigated crop. It requires 3-4 (21 acre inches) irrigation at 30 days interval.

Caster: Caster is grown under arid conditions, mostly as rainfed crop. Under irrigated conditions, it needs 5-7 (20 acre inches) irrigation at 30 days interval.

Guar (Cluster bean): It is a very important drought resistant Kharif legume of Barani and irrigated areas. However, if irrigation is available, then 20-25 cm per hectare, in the course of 2-3 irrigations increase the yield.

Moth: Moth is also important drought tolerant crop, cultivated as rainfed. Irrigated crop requires 2-4 irrigations.

Sesbania (Janter or Danicha): This crop is widely grown in all over Pakistan as main Kharif fodder and as green manure crop. It adds about 80 kg/ha nitrogen in the soil, therefore also used as rotation crop for maintaining the soil fertility. This crop requires 4-6 irrigations. First 2-3 irrigations at weekly and following should be applied fortnightly.

Rabbi crops

Wheat: Wheat is a staple food of more than one third of the world population. The major area in Pakistan lies in Punjab, but the yield per hectare is slightly higher in Sindh. 5-6 irrigations (21 acre inches) are sufficient, for normal wheat crop, under optimum soil conditions. First irrigation should be given 3-4 weeks after sowing. Out of all stages, crown root initiation (CRI) is the most important stage for irrigation, in view of nutrient availability and root development. Other critical stages are tillering, heading, milky and dough 21, 50, 80 and 100 days after sowing (DAS) respectively.

Barley: Barley is drought tolerant crop. It does not require much irrigation. However, 3-4 irrigations are recommended for maximum yield per unit area. First irrigation is to be given at 35 DAS. The irrigation at actively tillering increases the yield.

Gram (Chickpea): About 81% of gram area in Pakistan lies in Punjab followed by NWFP and Sindh, but the yield is highest in Sindh. No irrigation is required if planted after rice as Dobari crop. In case of irrigated crop, only one irrigation is required at pre-flowering stage. Heavy pre-sowing irrigation is better than light pre-sowing irrigation.

Lentil (Masoor): One irrigation at pre-flowering is adequate, but in light soil, it requires two irrigations. However, no irrigation is required for Dobari or Bosi crop.

Grasspea (Matter): Two irrigations are sufficient under irrigated conditions, but no irrigation is required for Dobari or Bosi crop.

Rapeseed and Mustard: 3-4 irrigations may be given to Toria and Sarsoon, 1-2 irrigations to Jambho or Taramira at 25-30 days intervals. Seed development stage is critical for irrigation. No irrigation is required for Dobari or Bosi crop.

Safflower: It is sensitive to heavy irrigations, especially in later growth stages. However, 56 irrigations are required under irrigated conditions.

Linseed: 4-5 irrigations are enough. First irrigation 30 DAS and subsequent doses at 20-25 days intervals should be given. No irrigation is required, when it is grown as Dobari crop.

Lucerne (Alfalfa): Lucerne is very important leguminous fodder, grown as a subsequent crop. 2 light irrigations in a week after sowing are helpful. It requires 10-15 irrigations in year, with an interval of 7-10 days during summer and 15-20 days in winter months. The yields are decreased with delay in irrigations.

Berseem: First 2 irrigations should be light and within a week. The following irrigations should be given at 10-15 days intervals.

Senji: It is one of the fodder crops, needs 2-3 irrigations during entire cropping period.

It should be kept in mind that water in larger quantities, as well as unfit water of different types must not be used for irrigation purpose. Only the water, that may be fit for the purpose, should be used in required quantity with suitable methods and time. Otherwise any problem in the crop as well as to the soil may occur due to its poor quality, pollution or so.

*Assistant Professor (Plant Pathology); Sindh Agriculture University, Tandojam