Sprinkler and Drip Irrigation Questions and Answers

Answer: A

The discharge depends on operating pressure and nozzle geometry.

A sprinkler nozzle behaves like an orifice: \(q = C_{d}A\sqrt{2gh}\), where the area and discharge coefficient come from the nozzle's size and shape and \(h\) is the operating pressure head. So the flow rate is fixed by pressure and nozzle geometry.

The distribution pattern and application rate are results of the discharge, the spacing and the sprinkler's motion, not causes of the discharge. Nozzle angle affects the throw distance, not the flow rate.

Answer: D

The lateral spacing is 20.0 m.

A sprinkler's application rate is its discharge spread over the area it serves, sprinkler spacing times lateral spacing:

\[ \begin{aligned} q &= 1.3\ \text{L/s} = 4.68\ \text{m}^{3}/\text{h} \\ S_{l} S_{m} &= \frac{q}{I} = \frac{4.68}{0.0117} = 400\ \text{m}^{2} \\ S_{m} &= \frac{400}{20} = 20\ \text{m} \end{aligned} \]

The discharge given is already the actual sprinkler discharge, so the key does not apply the coefficient of discharge or the uniformity coefficient again. The distractors come from doing so: multiplying the area by 0.9 gives 18.0 m, by 0.8 gives 16.0 m, and by both (0.72) gives 14.4 m.

Answer: A

The emitter is an orifice type.

Emitter discharge follows \(q = k P^{x}\), where k is the emitter constant and x the emitter exponent that identifies the flow regime. Solve for x:

\[ \begin{aligned} 4 &= 0.3 \times 110^{x} \\ 110^{x} &= 13.33 \\ x &= \frac{\ln 13.33}{\ln 110} = \frac{2.590}{4.700} \approx 0.55 \end{aligned} \]

An exponent close to 0.5 means fully turbulent flow, which is the behaviour of orifice emitters. Long-path emitters run partly laminar, with x of about 0.7 (1.0 for fully laminar flow). Pressure-compensating emitters are designed for x near 0, so that discharge hardly changes with pressure. In the standard classification by flow regime, an exponent of 0.5 points to the orifice class.

Answer: B

Trickle irrigation is also known as drip irrigation.

In drip (trickle) irrigation, water is delivered at low pressure through a network of pipes and emitters that release it drop by drop, or as a slow trickle, directly at the root zone of each plant. It gives water use efficiencies of about 90% and is widely used for orchards, vegetables and sugarcane.

Sprinkler irrigation sprays water over the crop like rain. Surge irrigation is a surface method in which water is released into furrows in intermittent surges. Neither is another name for trickle irrigation.

Answer: C

The keyed answer is that overlap increases with an increase in the wind velocity.

Wind distorts and shortens the wetted pattern of a sprinkler, carrying spray downwind and leaving the upwind side dry. To keep the application uniform, the sprinklers are set closer together in windy conditions; design guides reduce spacing from about 65% of the wetted diameter in calm air to 50% or less in strong wind, which means more overlap.

Raising or lowering the sprinkler head changes the wetted diameter but is not the condition the overlap is designed for, and calm air allows the widest spacing, the least overlap.

Answer: A

The best method is sprinkler irrigation.

Sandy soil drains quickly and undulating land cannot be levelled cheaply. Water spread over the surface would sink in near the channel and never reach the far end, and on slopes it would run off and erode. A sprinkler system sprays water like rain at a rate below the soil's intake rate, so it needs no land levelling and loses little to deep percolation.

Free flooding and furrow irrigation are surface methods that need fairly level land and a less permeable soil. Subirrigation needs a natural or artificial water table close to the root zone, which sandy uplands do not have.

Answer: B

The method to encourage is the sprinkler method.

Rajasthan is mostly arid and semi-arid, with sandy soils that lose water quickly by deep percolation. A sprinkler system applies water like light rain only where it is needed, and saves a large part of the water that flood irrigation wastes, which is why the state promotes it with subsidies along with drip irrigation.

Wells, ponds and tubewells are sources of irrigation water, not ways of applying it economically. Drawing more from them does nothing to conserve water.

Answer: C

The best method where water is scarce is drip irrigation.

Drip irrigation delivers water slowly, drop by drop, through emitters placed at the root zone of each plant. Almost no water is lost to runoff, deep percolation or evaporation from wetted ground, so its application efficiency is the highest of all methods, around 90 percent.

Sprinkler irrigation also saves water, but loses more to evaporation and wind drift. Check flooding and furrow irrigation are surface methods that need far more water.

Answer: C

Statement I is true but Statement II is false.

Statement I: fertigation, applying soluble fertilizer through the irrigation water, usually drip, puts nutrients directly in the root zone in the right amounts at the right time. It is regarded as the most advanced and efficient way of using fertilizers, with high nutrient use efficiency.

Statement II is false: fertigation applies fertilizer in small, frequent doses matched to the crop's needs at each growth stage, not in large doses, and the schedule is tailored to each crop rather than uniform for all crops.