WO2009057050A2

WO2009057050A2 - Crop irrigation system

Info

Publication number: WO2009057050A2
Application number: PCT/IB2008/054459
Authority: WO
Inventors: Alan Charles Hill; Dustin David Mills; Jeffrey Colin Smithers; Neil Louis Lecler
Original assignee: South African Sugar Association; University Of Kwazulu-Natal
Priority date: 2007-10-30
Filing date: 2008-10-29
Publication date: 2009-05-07
Also published as: WO2009057050A3

Abstract

One aspect of the invention concerns a crop irrigation system for irrigating, in irrigation cycles, a crop (14), typically sugarcane, planted in crop row sets (16.1, 16.2, 16.3) in a field (10). The system has at least one main irrigation supply line (18) connected to a supply of water for supplying irrigation water to a number of crop row sets. There is a lateral pipe (24) connected to the main supply line for each of the crop row sets as well as an associated control valve (22) for each lateral pipe. Emitters (26) extend transversely from each lateral pipe into spaced apart ground furrows (28) between the crop rows (12) of the associated crop row set. The respective control valves are operated sequentially, in an irrigation cycle, to direct water from the main supply line in turn into each associated lateral pipe for a predetermined period of time, such that the ground furrows of each crop row set are sequentially supplied with water for the predetermined period of time through their associated lateral pipes and emitters. In the preferred system, the control valves (22) operate automatically and are purely mechanical, requiring no electrical supply. Other aspects of the invention concern the control valve and the irrigation method.

Description

"CROP IRRIGATION SYSTEM"

BACKGROUND TO THE INVENTION

THIS invention relates to a crop irrigation system.

The performance of a crop irrigation system is dependent on water balance, irrigation uniformity and management of water application.

Water balance refers to the balance in any particular irrigation system between the irrigation water applied and other factors including free water evaporation from the plant and soil surfaces, transpiration from the plants themselves, surface run-off and deep percolation, i.e. percolation of the applied water through the soil to a level below the root zone of the plants. The efficiency of an irrigation system can in general be improved by reducing non-beneficial factors.

Irrigation uniformity refers to the evenness of irrigation water applications. It can have significant effects on irrigation performance because even if the timing and average magnitude of water applications is well matched to crop water demand and soil water storage capacity, non-uniformity can result in some areas of a field receiving relatively higher water applications and other areas receiving relatively lower water applications. Excessive runoff and deep percolation losses are likely in the areas which receive relatively higher water applications while reductions in crop yield can be expected in the areas receiving relatively lower water applications.

The traditional approach to dealing with a low level of irrigation uniformity is simply to increase the water application. However, reductions in crop yields can also occur in areas which receive excess water and thus the benefits of such an approach, especially on poorly drained fields, are doubtful. The present invention seeks to provide an irrigation system which allows for accurate management of water applications inter alia with a view to improving irrigation uniformity.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a crop irrigation system for irrigating, in irrigation cycles, crops planted in crop row sets in a field, the system comprising at least one main irrigation supply line, connected to a supply of water, for supplying irrigation water to a plurality of crop row sets, a lateral pipe connected to the main supply line for each of the crop row sets, an associated control valve for each lateral pipe and emitters extending transversely from each lateral pipe into spaced apart ground furrows between the crop rows of the associated crop row set, wherein the respective control valves are operable sequentially, in an irrigation cycle, to direct water from the main supply line in turn into each associated lateral pipe for a predetermined period of time, such that the ground furrows of each crop row set are sequentially supplied with water for the predetermined period of time through their associated lateral pipes and emitters.

Preferably the control valves operate automatically to direct water sequentially into each lateral pipe in turn. In the preferred embodiment a control valve at an upstream position in the main supply line initially directs water from the main supply line into its associated lateral pipe for a predetermined period of time and thereafter redirects water to an adjacent control valve at a downstream position in the main supply line in order for the latter control valve similarly to direct the flow of water into its associated lateral pipe for the predetermined period of time, and so on, whereby the ground furrows of each crop row set are sequentially supplied with water for the predetermined time period during an irrigation cycle. Other features of the irrigation system are described below and set forth in the appended claims.

According to another aspect of the invention there is provided a control valve for the crop irrigation system summarized above, the control valve comprising an inlet connectable to an upstream side of the main supply line, a first outlet connectable to a downstream side of the main supply line, a second outlet connectable to an associated lateral pipe, a valve closure movable between a first position in which it closes the first outlet and opens the second outlet and a second position in which it closes the second outlet and opens the first outlet, a timing chamber, a bleed line for diverting water flowing to the second outlet into the timing chamber, an expandable and contractible valve closure actuation chamber, means biasing the valve closure actuation chamber to a contracted state, and a timing chamber flow line leading from the timing chamber into the valve closure actuation chamber, wherein:

- the valve closure actuation chamber is coupled to the valve closure so as to move the valve closure from its first position to its second position when expanded and to move the valve closure from its second position to its first position when contracted;

- when the valve closure is in its first position and the valve actuation chamber is contracted a portion of the water flow to the second outlet is diverted through the bleed line into the timing chamber for accumulation therein;

- after a predetermined time, water accumulated in the timing chamber enters the valve closure actuation chamber through the timing chamber flow line with the result that the valve closure actuation chamber expands and moves the valve closure from its first position to its second position; and when the valve closure is in its second position, water can return from the valve closure actuation chamber to the timing chamber through the timing chamber flow line and bleed from the timing chamber through the bleed line, allowing the biasing means to contract the valve closure actuation chamber after depressurisation of the main line.

Further features of the preferred control valve, which is purely mechanical and requires no electrical supply, are described below and set forth in the appended claims.

According to a further aspect of the invention there is provided a method of irrigating, in irrigation cycles, a crop planted in crop row sets in a field, the method comprising the steps of supplying water to the crop row sets through at least one main irrigation supply line connected to a supply of water, providing a lateral pipe connected to the main supply line for each of the crop row sets, providing an associated control valve for each lateral pipe and providing emitters extending transversely from each lateral pipe into spaced apart ground furrows between the crop rows of the associated crop row set, wherein the respective control valves are operable sequentially, in an irrigation cycle, to direct a flow of water from the main supply line in turn into each associated lateral pipe for a predetermined period of time, such that the ground furrows of each crop row set are sequentially supplied with water for the predetermined period of time through their associated lateral pipes and emitters.

Further features of the method are described below and set forth in the appended claims.

The system, valve and method summarised above may advantageously be used in the irrigation of sugarcane. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 diagrammatically illustrates an irrigation system according to this invention, at the commencement of an irrigation cycle;

Figure 2 diagrammatically illustrates the irrigation system after a predetermined period of time has passed;

Figure 3 diagrammatically illustrates the irrigation system after a further predetermined period of time has passed;

Figure 4 illustrates the manner in which an emitter is connected to a lateral line in the system of Figures 1 to 3; and

Figures 5 to 8 illustrate sequential stages in the operation of a control valve used in the system of Figures 1 to 3.

DETAILED DESCRIPTION OF THE DRAWINGS

In Figures 1 to 3 a sugarcane field is indicated generally by the numeral 10. The field is planted with parallel rows 12 of crops 14. In the illustrated example there are three sets of such rows, designated 16.1 , 16.2 and 16.3 respectively. The numeral 18 indicates a main water supply line which is connected to a source of water (not shown) such as a reservoir. Water may be pumped from the source or may flow under gravity. The line 18 is located at a relatively high elevation in the field 10, with the ground falling generally in the direction 20. The water pressure in the main water supply line is relatively low. In this example the water pressure in the main water supply line 18, at the edge of the field, is in the range 5OkPa to 10OkPa and is typically about 7OkPa.

Control valves 22 are connected into the line 18 at spaced apart positions. Connected to each of the valves 22 is a lateral pipe 24 which runs downhill from the line 18 and which is buried in the ground. Emitters 26 are connected at spaced apart positions to each of the lateral pipes 24. The emitters extend from the associated lateral pipe 24 into ground furrows 28 between the crop rows 12. The furrows are typically land-planed, generally follow the contour of the field at a slope in the range 1 :100 to 1 :300. In this example the furrows have closed ends 28.1 as shown in Figure 4.

The manner in which an emitter is connected to its associated lateral pipe is illustrated in Figure 4. Each emitter is a length of slender, flexible pipe which is connected transversely to the lateral pipe 24. In this example, where the emitter enters the associated furrow 28, it enters a short length of larger diameter pipe 32 which is partially buried in the ground, at the upstream end of the furrow, and which vents into the furrow. The vent pipe 32 serves to guide and protect the emitter and also to reduce the velocity of water entering the furrow through the emitter.

In other examples, the emitters 26 may enter the furrows directly with the vent pipes 32 being omitted.

Irrigation is carried out in cycles controlled by manual or automatic operation of an upstream valve (not shown) in the main supply line 18.

Figures 5 to 8 illustrate sequential steps in the operation of a control valve 22 during each irrigation cycle. The valve 22 has a housing 33 with an inlet 34 connected to an upstream section 18.1 of the line 18, a first outlet 36 connected to a downstream section 18.2 of the line 18 and a second outlet 38 connected to the associated lateral pipe 24. The lower end of the housing is closed by a plug 39. A valve closure 40 is attached by a rod 42 to a biasing means in the form of a weight 43 at the upper end of a flexible, typically rubber, boot 44 of bellows-like configuration which defines an expandable and contractible valve closure actuation chamber 46. The boot is connected to the upper end of the housing 33 which is closed by a plug 50 beneath the boot.

A bleed line 52 extends from the second outlet 38 into a timing chamber 54 having an air release valve 56 fitted to its upper end. A timing chamber supply line 58 extends from an elevated position in the timing chamber into the valve closure actuation chamber 46.

Figure 5 illustrates the situation shortly after commencement or initiation of an irrigation cycle. At this stage, the valve closure 40 has been biased downwardly by the weight 43 to seat on a valve seat 60, thereby closing the first outlet 36 and opening the second outlet 38, preventing flow through the valve from the upstream section 18.1 of the main line to the downstream section 18.2 thereof, but allowing flow into the lateral pipe 24 as indicated by the arrows 62.

Water accordingly flows through the associated lateral pipe 24 to the emitters 26 which in turn discharge into the vent pipes 32, the vent pipes leading the water into the furrows 28. The discharged water accordingly irrigates the furrows and the crop rows planted on either side thereof throughout the set 16.1 of crop rows 12. This is illustrated in Figure 1 where the numerals 59 indicate the irrigation taking place. At this stage there is no irrigation of the sets 16.2, 16.3 of crop rows.

Some of the water flowing to the second outlet 38 is diverted through the bleed line 52 into the timing chamber 54 where it accumulates. With passage of time, the water level in the timing chamber rises to the level of the timing chamber supply line 58, at which point the water can flow from the timing chamber into the valve closure actuation chamber 46. Accumulation of water in the latter chamber expands the boot, driving the weight 43 upwardly against its gravitational bias. Expansion of the boot, i.e. upward movement of the weight, is transferred through the rod 42 to the valve closure 40, which is accordingly lifted up.

The valve closure is seen in an intermediate position in Figure 6. At this moment, with the valve partially open and partially closed, it is possible for water entering the valve housing 33 through the inlet 34 to exit the housing through both the first and second outlets as shown by the arrows 63. As shown in Figure 7, further entry of water into the valve closure actuation chamber causes further expansion of the chamber 46 and, shortly thereafter, seating of the valve closure 40 on a seat 64. The first outlet 36 is now fully open and the second outlet is fully closed, i.e. water will now flow through the valve 22 from the upstream section 18.1 to the downstream section 18.2 of the line 18, as shown by the arrows 65, but flow to the lateral pipe is prevented. Irrigation to the set 16.1 of crop rows is accordingly terminated.

The water flows in the main supply 18 to the next control valve 42 which is, at this stage, in the Figure 5 position. The process described above is repeated and the next set 16.2 of crop rows is irrigated. This is illustrated in Figure 2 where the numeral 66 indicates, the irrigation taking place.

In Figure 3, the numeral 68 indicates the irrigation that takes place when the final control valve 22 is operative to direct water from the main supply line 18 into the associated lateral pipe 24.

Referring again to Figure 7, after the control valve has terminated water flow to the second outlet 38, i.e. water flow to the lateral pipe has finished, water can bleed back to the outlet 38 through the bleed line 52, as indicated by the arrow 68. The water pressure in the timing chamber 54 and valve closure actuation chamber 46 drops, as does the water level in the chambers. However, the valve closure 40 remains in the Figure 7 position as a result of the force exerted on its underside by the pressure of water flowing through the housing 33 from the section 18.1 to the section 18.2 of the line 18, i.e. the pressure of the water in the line 18. At the end of an irrigation cycle, the supply line 18 is closed by operation of an upstream supply line control valve (not shown), resulting in depressurisation of the line. The weight 43 now resets the valve closure 40 to the position seen in Figure 5. Figure 8 also illustrates the situation at the end of the irrigation cycle, with the main supply line control valve closed, water having bled out of the chambers 46 and 54 and the valve closure 40 having been reseated on the valve seat 60 by the weight 43, ready for the next irrigation cycle.

In each case, the design is such that during each irrigation cycle, irrigation of each set of crop rows takes place for a predetermined period of time, i.e. the time for which the second outlet 38 remains open to allow water to flow through the lateral pipe. This period of time is selected to provide uniform irrigation of the furrows 28, typically with a low quarter distribution uniformity value DU_(q > 0.75. This may for instance be of the order of 40 minutes.

The furrows are short in length compared to furrow lengths used in conventional surface irrigation practice. With the relatively low pressure in the main supply line 18, the emitter flow rates are also relatively low. The emitter flow rate may for instance be around 151/min but this value can be increased in sandy soils with relatively high infiltration rates or reduced in clay-type soils with relatively low infiltration rates.

The furrow length is dependent on soil conditions and will typically be less in sandy soils than in clay-type soils. The furrow length is typically in the range 20m to 50m and is preferably 30m or less. The width of each furrow may, for example, be of the order of 150mm. The furrow depth may also be about 150mm and the furrow slope is, as indicated above, typically in the range 1 :100 to 1 :300. Smaller slopes can be used where land smoothing is of a high standard and/or soil infiltration rates are relatively low.

In a practical design the main supply line 18 may be made of a low cost pipe such as low class PVC (polyvinyl chloride), and may be buried. The lateral pipes may also be of a low cost pipe, such as LDPE (low density polyethylene). The lateral pipes may be made of various smaller diameter sections connected together and may have a length up to about 80m. The diameters of the main supply pipe and lateral pipes will typically be varied as necessary to suit the natural field slopes and design flow rates, in order to ensure generally even pressures throughout the system.

The emitters are typically lengths of polypropylene pipe of 10mm diameter. Once again the lengths and diameters of the emitters may be varied as necessary to ensure even water flows into the furrows. The pipes 32 may be of PVC (polyvinyl chloride) or LDPE and have a diameter of about 50mm.

It is advantageous that all piping, except possibly for portions of the emitters, are buried at a suitable depth in the soil to protect the pipes and allow normal traffic to take place in the field without unduly disturbing the irrigation system.

The system described above also allows the water supply to be at a relatively low pressure compared to conventional irrigation systems using overhead sprinkler systems or even drip irrigation systems.

It will be understood that the control valves 22 should ideally operate in a fully automatic manner. It is perceive that by automating and controlling the supply of water to the short furrow sets it will be possible to reduce operational and labour overheads and to improve irrigation efficiency. Automation also facilitates night-time irrigation cycles with associated reductions in pump discharge rates and associated costs. Simulations with surface irrigation simulation software have shown that for soil types ranging from sands to clays, simulated low quarter distribution uniformities (DUι_q) in excess of 0.75 can typically be achieved, in the described short furrows, for most soil types. The relatively small and short furrows which are used can lead to mainly sub-surface lateral water flow and reduced evaporation losses.

Although specific mention has been made of irrigation of sugarcane, it is also envisaged that the irrigation system described above will be suitable for a wide range of crops and soils, and that water applications of as little as 10 mm to 20mm per irrigation application may be used without compromising distribution uniformity or application efficiency. Because most water movement will primarily take place beneath the surface of the soil, it is expected that evaporation losses may be considerably reduced, even with frequent watering, compared to conventional irrigation systems.

Also, although Figures 1 and 2 show only a single main supply line 18 supplying the illustrated three crop row sets 16.1 , 16.2 and 16.3, it will be understood that in larger fields there may be multiple main supply lines supplying water to different groups of crop row sets.

Although the control valves 22 described above are fully automatic it should be understood that it would also be possible to use manually controlled valves to supply water to the lateral pipes, emitters and furrows for the predetermined time period. It is however recognised that manual control valve operation introduces the possibility of human error, and may preclude night-time operation.

As an alternative to the purely mechanical control valves 22 described above it would also be possible to make use of electronically controlled, electrically powered valves to achieve automation. The provision of the necessary power supply and electronic controls would however involve additional complexity and cost as well as introducing the possibility of electrical failure, tampering and/or cable or battery theft. The preferred control valves 22 described above, which do not require any electrical supply, avoid such potential problems.

Claims

1.

A crop irrigation system for irrigating, in irrigation cycles, crops planted in crop row sets in a field, the system comprising at least one main irrigation supply line, connected to a supply of water, for supplying irrigation water to a plurality of crop row sets, a lateral pipe connected to the main supply line for each of the crop row sets, an associated control valve for each lateral pipe and emitters extending transversely from each lateral pipe into spaced apart ground furrows between the crop rows of the associated crop row set, wherein the respective control valves are operable sequentially, in an irrigation cycle, to direct water from the main supply line in turn into each associated lateral pipe for a predetermined period of time, such that the ground furrows of each crop row set are sequentially supplied with water for the predetermined period of time through their associated lateral pipes and emitters.

2.

A crop irrigation system according to claim 1 wherein the control valves operate automatically to direct water sequentially into each lateral pipe in turn.

3.

A crop irrigation system according to claim 2 in which a control valve at an upstream position in the main supply line initially directs water from the main supply line into its associated lateral pipe for a predetermined period of time and thereafter redirects water to an adjacent control valve at a downstream position in the main supply line in order for the latter control valve similarly to direct the flow of water into its associated lateral pipe for the predetermined period of time, and so on, whereby the ground furrows of each crop row set are sequentially supplied with water for the predetermined time period during an irrigation cycle.

4.

A crop irrigation system according to any one of the preceding claims wherein the ground furrows have a length in the range 20m to 50m.

5.

A crop irrigation system according to claim 4 wherein the ground furrows have a length of 30m or less.

6.

A crop irrigation system according to any one of the preceding claims wherein the water supply pressure in the main supply line is in the range 5OkPa to 10OkPa.

7.

A crop irrigation system according to claim 6 wherein the water supply pressure in the main supply line is about 7OkPa.

8.

A crop irrigation system according to any one of the preceding claims wherein the main supply line is located at a relatively high elevation in the field and the lateral pipes extend downhill from the main supply line.

9.

A crop irrigation system according to any one of the preceding claims wherein the main supply line is buried in the ground.

10.

A crop irrigation system according to any one of the preceding claims wherein the lateral pipes are buried in the ground.

11.

A crop irrigation system according to claim 10 wherein the emitters comprise lengths of pipe of smaller diameter than the lateral pipes, the emitters extending below ground level from the lateral pipes to upstream ends of the furrows.

12.

A crop irrigation system according to claim 11 wherein the emitters extend from the lateral pipes into larger diameter vent pipes which are partially buried in the ground and which extend into the upstream ends of the furrows.

13.

A crop irrigation system according to any one of the preceding claims wherein the furrows have a slope in the range 1 :100 to 1 :300.

14.

A crop irrigation system according to any one of the preceding claims wherein each control valve comprises an inlet connected to an upstream side of the main supply line, a first outlet connected to a downstream side of the main supply line, a second outlet connected to an associated lateral pipe, a valve closure movable between a first position in which it closes the first outlet and opens the second outlet and a second position in which it closes the second outlet and opens the first outlet, a timing chamber, a bleed line for diverting water flowing to the second outlet into the timing chamber, an expandable and contractible valve closure actuation chamber, means biasing the valve closure actuation chamber to a contracted state, and a timing chamber flow line leading from the timing chamber into the valve closure actuation chamber, wherein:

- after a predetermined time, water accumulated in the timing chamber enters the valve closure actuation chamber through the timing chamber flow line with the result that the valve closure actuation chamber expands and moves the valve closure from its first position to its second position; and

- when the valve closure is in its second position, water can return from the valve closure actuation chamber to the timing chamber through the timing chamber flow line and bleed from the timing chamber through the bleed line, allowing the biasing means to contract the valve closure actuation chamber after depressurisation of the main line.

15.

A crop irrigation system according to claim 14 wherein the valve closure actuation chamber is in the form of an expandable, bellows-like boot.

16.

A crop irrigation system according to claim 15 wherein the biasing means comprises a weight attached to the boot in order to apply a gravitational force tending to contract the boot.

17.

A crop irrigation system according to any one of the preceding claims when used to irrigate sugarcane.

18.

A control valve for a crop irrigation system according to any one of claims 1 to 13, the control valve comprising an inlet connectable to an upstream side of the main supply line, a first outlet connectable to a downstream side of the main supply line, a second outlet connectable to an associated lateral pipe, a valve closure movable between a first position in which it closes the first outlet and opens the second outlet and a second position in which it closes the second outlet and opens the first outlet, a timing chamber, a bleed line for diverting water flowing to the second outlet into the timing chamber, an expandable and contractible valve closure actuation chamber, means biasing the valve closure actuation chamber to a contracted state, and a timing chamber flow line leading from the timing chamber into the valve closure actuation chamber, wherein:

after a predetermined time, water accumulated in the timing chamber enters the valve closure actuation chamber through the timing chamber flow line with the result that the valve closure actuation chamber expands and moves the valve closure from its first position to its second position; and

when the valve closure is in its second position, water can return from the valve closure actuation chamber to the timing chamber through the timing chamber flow line and bleed from the timing chamber through the bleed line, allowing the biasing means to contract the valve closure actuation chamber after depressurisation of the main line.

19.

A control valve according to claim 18 wherein the valve closure actuation chamber is in the form of an expandable, bellows-like boot.

20.

A control valve according to claim 19 wherein the biasing means comprises a weight attached to the boot in order to apply a gravitational force tending to contract the boot.

21.

A control valve according to any one of claims 18 to 20 when used in the irrigation of sugarcane.

22.

A method of irrigating, in irrigation cycles, a crop planted in crop row sets in a field, the method comprising the steps of supplying water to the crop row sets through at least one main irrigation supply line connected to a supply of water, providing a lateral pipe connected to the main supply line for each of the crop row sets, providing an associated control valve for each lateral pipe and providing emitters extending transversely from each lateral pipe into spaced apart ground furrows between the crop rows of the associated crop row set, wherein the respective control valves are operable sequentially, in an irrigation cycle, to direct a flow of water from the main supply line in turn into each associated lateral pipe for a predetermined period of time, such that the ground furrows of each crop row set are sequentially supplied with water for the predetermined period of time through their associated lateral pipes and emitters.

23.

An irrigation method according to claim 22 wherein the control valves are operated automatically without any electrical supply.

24.

An irrigation method according to either one of claims 22 or 23 comprising the further step of burying the main supply line in the ground.

25.

An irrigation method according to any one of claims 22 to 24 comprising the further step of burying the lateral pipes in the ground.

26.

An irrigation method according to any one of claims 22 to 25 wherein the emitters comprise lengths of pipe of smaller diameter than the lateral pipes, the method comprising the steps of arranging the emitters below ground level to extend from the lateral pipes to upstream ends of the furrows.

27.

An irrigation method according to claim 26 comprising the steps of providing vent pipes of larger diameter than the emitters, partially burying the vent pipes in the ground such that they extend into the upstream ends of the furrows, and arranging the emitters to discharge into the vent pipes.

28.

An irrigation method according to any one of claims 22 to 27 wherein the crop is sugarcane.