PARC || WRRI

At present the low water availability is one of the main constraints in increasing per acre yield and bringing more area under cultivation. The per capita availability of water has reduced from 5650 m3 in 1951 to 1200 m3 in 2003 against the international standard of 1500 m3. It will decrease to 800 m3 in 2025. Moreover, competition for water is also increasing with the rise in population, urbanization and industrialization. The domestic and industrial water uses will increase to 15% by 2025 of the available water resources against 3% in 2000. Agriculture is the major user of good quality water (93%) but its share is decreasing because of competing non-agricultural demands. The productivity of water is very low in Pakistan. Such as for cereal it is 0.13 kg m-3 of water in Pakistan against 1.56 kg m-3 in USA, 0.82 kg m-3 in China and 0.39 kg m-3 in India. This low water productivity is due to low water use efficiency as a result of conventional irrigation methods and poor agronomic practices. Under this situation there is need to utilize the available water more efficiently and wisely alongwith introducing innovative and high efficiency irrigation systems.

Sprinkler irrigation systems are labour, water and fertilizer efficient. Sprinkler irrigation systems are most desirable for soils with a high permeability and/or low water holding capacity. However, sprinkler irrigation systems require high pressure pumps. Water Resources Research Institute (WRRI) in collaboration with local pump industry developed multistage pumps which deliver discharge from 2 to 12 lps at a pressure upto 60 m. Different models of Chinese rainguns were tested and two models (PY1-30 and PY1-50) have been indigenized in collaboration with local industries. Different sizes of replaceable nozzles have also been developed to cover a range of pressure and discharge under different site-specific conditions. Diesel engine and tractor PTO driven (operated) raingun sprinkler irrigation systems were also developed. In a portable system, a high pressure pump is coupled with a prime mover (electric motor, diesel engine or a tractor) and is mounted on a two wheel trolley which can be moved from one location to another. In semi-portable, the pumping unit is fixed near a water source. The main delivery pipe may be fixed and laterals alongwith raingun are moved from field to field. This type of system is good for small farmers having an area of 2.5 ha.


Models of Raingun (PY1-20, PY1-30, PY1-40 and PY1-50)	Portable Raingun sprinkler irrigation systems

Trickle irrigation has great potential especially in water scarce areas and soils with undulating topography and poor water holding capacities. High initial cost of imported trickle irrigation equipment is considered to be the main limitation for large-scale adoption in Pakistan. So WRRI in collaboration with local industry developed low density polyethylene (LDPE) pipes (13 mm to 75 mm diameters) and their fittings. Various types of emitters; spiral, turbo and micro-tubing were tested. The micro tubing emitters performed better under local field conditions due to their easy installation, operation and maintenance. Application uniformity and pressure variation in locally developed trickle irrigation systems were evaluated. The discharge of the micro-tube emitter varied from 7 to 12 l h-1 under pressure of 15 to 19 m. The water application uniformity was above 85% showing satisfactory performance of the system.

A considerable area of the country is outside the Indus basin where rainfall is the only source of water for crops. In the rain-fed area, stochastic behavior of rainfall limits profitable crop production. The yields of major crops are 30 to 50% lower than the national average crop yields mainly because of lack of available soil moisture at the critical crop growth stages. The sowing of wheat crop is often delayed due to uncertain and scanty rains. Furthermore, water for agriculture is becoming scarce. It is likely that it will increasingly be used as supplemental/deficit irrigation rather than full irrigation. In rainfed areas where small quantity of water is available in the form of nullahs, ponds, reservoirs or wells, the sowing of crops at right times can be managed by applying small quantity of water through raingun sprinkler irrigation to moist the required depth of rootzone for seed germination. Similarly when the soil moisture depletion has reached more than 80%, the life saving irrigation can be applied with raingun sprinkler irrigation system. The benefits of supplemental irrigation with raingun sprinkler irrigation system were evaluated. The wheat grain yield increased from 1.4 to 1.7 ton ha-1 and straw yield from 1.3 to 2.9 ton ha-1 with the use of supplemental irrigation. The highest net benefit was achieved with application of 25 mm irrigation with sprinkler system at 75 % depletion of available water. The wheat crop yield increased 45 to 100% over rainfed with 10 to 25 mm supplemental irrigation.

The information about pressure and discharge is pre-requisite for designing sprinkler and trickle irrigation systems. The raingun PY1-30 is mostly recommended for irrigation of crops due to its less pressure and energy requirements. The pressure and discharge relationship for PY1-30 have been developed. The system was operated with 6, 8, 10 and 12 mm diameter nozzles under 15 to 55 m pressure. The discharge of raingun increased with increase in pressure. The relationship was developed which is being used for designing of system. The use of PY1-30 raingun with 10-12 mm nozzles and working pressure of 34-40 m, an area of 0.21 to 0.26 ha can be irrigated at one setting with application rate of 2.94 to 3.86 mm ha-1. The area and application rate can be increased with PY1-50 raingun. At working pressure of 40 to 50 m, the area coverage is 0.43 to 0.50 ha with application rate of 4.11 to 5.03 mm ha-1 when nozzle diameter varied from 16 to 18 mm.

For trickle irrigation system, locally developed micro-tubing emitters are performing better. So these emitters were tested under pressure heads of 3 to 21 m for different lengths and diameters. The pressure-discharge relationship for micro-tubing emitters has been developed. The relationships are being used for designing of trickle irrigation system.

Border irrigation system for various stream sizes were tested at five locations under various agro-ecological conditions. Three unit stream sizes of 1, 2 and 3 lps, and three border lengths of 30, 60 and 90 meter were evaluated. The application efficiency of 90 % was achieved with stream size of 3 lps m-1 and laser leveled border of 60 m long. The increase in stream size increased the application efficiency mainly due to reduction in advance time and uniform leaching.

A thin layer of fresh water lies over saline water mostly in the centres of "DOABS". This fresh water needs to be skimmed without mixing of underlying saline water due to up-coning. As the skimmed water is in small quantities and can not be used for surface irrigation. A collaborative research project was undertaken in SCARP-II, where skimmed water was used through sprinkler and trickle irrigation systems. The four sprinkler and two trickle irrigation systems were installed for sugarcane, wheat, fodder and orchards (Guava and Citrus).

The farmers are in the process of increasing cropping intensity by using groundwater to an extent of around 50 % of total water use in agriculture. In the Indus basin the groundwater aquifers in around 60 % areas are of marginal to hazardous quality. A research study was conducted in the SCARP- II area to evaluate the changes occurred in the quality of groundwater with time. It was found that the quality of 12 % project area changed from very good ( <500 ppm; TDS) quality to marginal quality ( >1000 ppm; TDS) in 30 years (1965-1997) indicating deterioration of groundwater quality. The low quality water can be used for salt tolerant crops, trees and shrubs. A research study was undertaken in saline area of Sargodha district, in which irrigation was provided with marginal quality of groundwater (EC = 1.36 dS m-1, SAR = 9.2 and RSC = 2.1 meq l-1) to establish fruit trees. In another study, the barren and abandoned land was brought under cultivation using low quality water with integrated water management techniques, such as use of farm yard manure, green manuring, use of gypsum, and sulpher. The janter and kallar grass were grown along with Guava, Falsa and Ber plants.

Accurate measurement of irrigation water permits more intelligent use of this scarce natural resource. Different types of water measurement devices have been tested and evaluated for water measurement under different field conditions. A "V" notch is the standard water measuring device which is used where surface gradient is available. The "V" notch was used to calibrate cutthroat flume and broad-crested weir. The cutthroat flume can be used under free flow conditions. The broad-crested weir should be used under submerged conditions. The "H" type flumes can handle large and variable flows.

Dr. Muhammad Yasin	PSO/PL/Director	mywrri@yahoo.com
WRRI, NARC, Park Road, Islamabad. Ph. No. 051-9255022