By Dr. V. Praveen Rao, (Director, Water Technology Centre)
A growing world population, climate change, declining ground water and the requirement for more food production in several parts of India is pressing irrigators to look for more efficient methods of irrigation than the traditional surface methods of furrow irrigation. Drip irrigation can be a viable alternative when water is limited or when irrigation capacity is insufficient for traditional methods.
Some research studies have revealed that drip irrigation can reduce irrigation water use for corn production by 35% to 55% compared with traditional surface irrigation methods.
And in fact, yield for over 30 crops is greater and often uses considerably less water under drip irrigation.
However, the irrigation system alone does not guarantee all the potential benefits. Adequate design and management are an integral element on the road to success.
Planning the system:
Dripper discharge rate is a system design characteristic and should be selected taking into account the infiltration rate of the soil. In drip irrigation, the dripper discharge rate should not create runoff within the immediate application area. The discharge rate affects the number and spacing of drippers along the lateral and the wetted volume, which in turn affect the system cost.
When planning a drip irrigation system, it is imperative to select drippers with the appropriate flow rate, considering the soil, crop and weather factors which deliver a wetted soil-volume sufficient to fulfil the plant’s evaporative demands without affecting crop yield.
Deficit irrigation or DI which is an optimization strategy that can be applied by different types of irrigation scheduling methods and whose application requires a thorough understanding of the yield response to limited water and of the economic impact of reductions in harvest. In other words, DI aims at stabilizing yields and at obtaining maximum crop water productivity rather than maximum yields in scarce water regions.
The saved water can then be used for other purposes or to irrigate extra units of land, has been considered worldwide as a way of maximizing water productivity by eliminating irrigation in sensitive growth periods that have little impact on crops. Total water application is therefore not proportional to crop water requirements throughout the growing cycle.
What did we do exactly?
A field experiment was conducted for two successive years during the monsoon season (June to October), under semi-arid climate conditions at the Water Technology Centre, Professor Jayashankar Telangana State Agricultural University in India. The total rainfall received was 555.1 mm in 2011 – 12 and 714.3 mm in 2012 – 13.
The soil was clay loam in texture, slightly alkaline in reaction, non-saline with 0.38% organic carbon, low in available nitrogen, medium in available phosphorus and high in available potassium.
The steady state infiltration rate was 23 mm hour and hydraulic conductivity was 25 mm hour.
The source of water was an open well. The irrigation water quality was found to be safe for irrigation of castor crop and safe for use by drip irrigation system.
There were eight surface drip irrigation treatment combinations with different emitter discharge rates (nominal values of 0.6, 1.0, 1.6 and 2.0 L/hour) and two water supply levels (100% and 75% of crop evapotranspiration).
- The experiment was laid out in a Randomized Block Design with three replications. A corn Hybrid of approximately 110-day relative maturity was planted in 0.8 m row spacing and 0.15 m plant to plant distance at a seeding rate to achieve a desired plant population of 83333 plants ha.
- The crop was fertigated with water soluble fertilizers up to 80 days after sowing.
- Other standard cultural practices for the region for herbicides and insecticides were used.
- The drip system consisted of 16 mm inside diameter heavy wall integral dripper lines (Netafim DripNet PC) with welded drippers (Netafim 875 Typhoon) with a nominal varying flow rates (0.6 to 2.0 L/hour).
- The dripper lines were laid out on soil surface along each crop row at 0.8 m spacing with emitters spaced at 0.3 m apart giving an application rate of varying between 2.5 to 8.33 mm/hour.
- Each plot was approximately 5.6 m wide and 10.0 m long, with seven dripper lines spaced at 0.8 m. Each plot had a common sub main at the inlet side of the plot and a common flush line and flush valve at the distal end of the plot
- Irrigation amounts were metered separately onto each plot using commercial grade flow accumulators with an accuracy of ±1.5%. Irrigation time was different for each treatment due to different flow rates and water supply levels.
Crop increase achievements:
Corn grain yields ranged from 9.14 to 12.87 tons/ha during the two years of the study and were considerably greater than typical commercial production levels of 6 to 7 tons/ha obtained by farmers in the region. Corn grain yield was significantly higher with water application equivalent to 100% ETc in comparison to 75% ETc in both the years. Further, grain yield tended to increase with a decrease in emitter discharge rates from 2.0 to 0.6 L/hour.
The consistent efficiencies obtained in the study are further evidence that 0.6 to 2.0 L/hour flow rates are appropriate for this soil type and climate for corn production.
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