Daily Furrow Irrigation in Orchards

R. G. Evans, E. L. Proebsting, M. 0. Mahan
Vol. 6 (2): March 1990, American Society of Agricultural Engineers - 0883-8542/90/0602-0175

Abstract

High frequency furrow irrigation can achieve tree growth and yield responses similar to trickle irrigation on sweet cherry trees. Daily surge flow furrow irrigations from 1982 through 1986 were scheduled based on daily pan evaporation. Application efficiencies were near 80% and soil erosion was minimal even though slopes were in excess of 3 %. This technique is potentially a low cost alternative to solid-set microirrigation or sprinkle systems in widely-spaced perennial crops. The method is limited to lands normally suited to surface irrigation, but requires automation and careful system management.

Introduction

Irrigation methods which replenish root zone soil water at a rate approximately equal to plant water use have been found to benefit apples, peaches, pears, citrus, tomatoes, and many other crops (Evans and Proebsting, 1985; Rodney et al., 1977; Hutmacher et al., 1985). High frequency irrigation methods that apply water on a daily or alternate-day basis have been found to improve water use efficiencies and yields on most soil types and conditions (Davis et al., 1980; Elfving, 1982). The degree of homogeneity, uniformity, and water holding characteristics of soil become much less significant under high frequency trickle and sprinkle irrigation than with traditional irrigation regimes (Phene and Howell, 1981; Stegman et al., 1980).

Since many deciduous orchards are surface irrigated, it would be advantageous to extend those benefits to these conditions. This requires the evaluation of management and design considerations of high frequency orchard furrow irrigation systems. Consequently, a project was established in 1982, and continued through 1986, to determine if high frequency surface irrigation systems could be managed to maintain fairly uniform soil water levels without overwatering. Success in meeting these objectives would suggest that the potential benefits commonly associated with trickle or micro-irrigation could also be realized in furrow irrigated orchards.

Materials and Methods

In the spring of 1982, a mature sweet cherry block on the Roza Unit of. the Washington State University, Irrigated Agriculture Research and Extension Center near Prosser, WA, was selected for study. The 24 rows of trees were planted in 1963 in a N-S direction with 20 trees per 183 m (600 ft) row. Trees were planted in a diamond pattern with 9.1 m (30 ft) between trees and 4.6 m (15 ft) between rows. There was approximately a 70% canopy coverage and no cover crop throughout the duration of the project. An agricultural research weather station is located about 100 m (328 ft) south of the block.

The plots were located on Warden fine sandy loam soils (coarse, silty, mixed, mesic Xerollic Camborthids) from 1 to 1.5 m (3 to 5 ft) in depth overlying somewhat impervious basalt bedrock. Field capacity is approximately 28% and the 15 bar (1500 kPa) tension soil moisture level is about 8% by volume. The soils have less than 10% clay and are easily eroded. The field has about a 3% slope to the south and a 5% cross slope to the west.

The 110 m x 183 m (360 ft x 600 ft) block had been surface irrigated with six furrows per tree row until the east 12 rows were converted to trickle in 1972. The west 12 rows continued under furrow irrigation. Tree performance parameters, as represented by tree growth and yields from the two halves, were compared in this study to assess the effectiveness of the furrow irrigation program. The project was conducted over several years to assess any potential carry-over effects from one year's treatments to the next.

In 1982 the furrow-irrigated area was converted to surge flow with only one irrigated furrow per tree row. The furrow was located about 0.75 m (2-5 ft) east of the trees, the same location as the trickle lines. Individual risers from a buried gravity pipeline system were controlled with 1.9 cm (3/4 in.) diameter electric solenoid valves and a commercially available sprinkle/trickle controller. Daily irrigations were imposed with the inflow rate to each furrow set at 0.38 L/s (6 gpm) for each surge, which is approximately the maximum nonerosive flow rate for existing soil and slope conditions.

Surged flow was on for 15 min and off for 45 min (15/45) for 1982 through 1985 (60-min cycle, 0.25 cycle ratio) with full advance being achieved in about 10 min on the wet furrows. Using the same projected canopy area criteria as for trickle, one surge was calculated to supply a gross application of approximately 0.58 mm (0.023 in.) of water. In 1986, due to controller difficulties, the cycles were changed to on for 20 min and off for 40 min (20/40, 60-min cycle, 0.33 cycle ratio). Short on times were selected to minimize runoff from prewetted furrows which were consistently near the basic intake rates. A single 20/40 surge supplied a gross amount of about 0.76 mm (0.030 in.) of water. The number of surge cycles and thus the gross application was varied each day to correspond to the previous day's pan evaporation assuming an 80% application efficiency and a 70% canopy. Surface evaporation effects were not considered in scheduling the surged irrigations.

The trickle-irrigated trees had four 3.8 Lph (I gph) emitters per tree. This permitted an application of approximately 0.028 mm (0.0011 in.) of water per hour. An application efficiency of 95% was assumed for the trickled trees. Emitters were approximately 1.5 m (4.92 ft) apart.

The individual furrows were reformed each spring. Leaves, twigs, and other vegetative matter which tended to make small dams were removed during the growing season as soon as they were observed. HS flumes (Gwinn and Parsons, 1976) with water level recorders (24-h charts) were placed at the top and tail ends of two furrows. The daily hydrographs were digitized and integrated using a computer. Inflow rates in furrows without flumes were periodically checked with portable 60 degree V-notch weirs. Starting in 1984, water applications to the trickle-irrigated trees were measured with 1.9 cm (0.75 in.) diameter totalizing municipal-type flow meters and volumes were recorded daily.

Table 1. Crop coefficients for estimating 100% ETa of mature sweet cherries from pan evaporation at Prosser, WA (pan coefficient is 0.80)

Month     Coefficient
-----     -----------
April        0.40    
May          0.60    
June         0.85    
July         1.00    
August       1.00    
Sept.        0.95    
Oct.         0.70    

Irrigation scheduling was based on daily replacement of pan evaporation times a crop coefficient to estimate crop evapotranspiration (ETa). The crop coefficients used to estimate ETa were empirically developed by the authors from several years of soil water and water application data in the trickle irrigated cherries (Table 1). The volume of applications were based on the projected area of the canopies. Applications were reduced to compensate for rain based on 70% effective precipitation.

In July 1984, five neutron meter access tubes were installed at the second tree in from the head and tail ends of each of four furrows. The tubes were placed in a line perpendicular to the furrow line about 45 cm (17.7 in.) north of the trees. The center tube was placed about 15 cm (5.9 in.) west, while the other four were equally split 60 and 90 cm (23.6 and 35.4 in.) on either side of the furrow. Soil water was monitored biweekly with readings in 15 cm (5.9 in.) increments to bedrock.

Results and Discussion

When water was first turned into the furrows in 1982, it took more than 24 hours for the water to reach the end of the row (183 m, 600 ft) at the low flow rates. In subsequent years, the inflow rates for the initial irrigation were increased by about 50% to hasten the wetting. However, once the furrows were wet, the water consistently reached the end of the row in 10 to 12 min on each surge for the rest of the season.

Measured advance rates in the wetted furrows were basically linear. This is consistent with data reported by Gerards (1978) on advance in continuous flow furrows irrigated the previous day, and by Walker et al. (1982), Allen (1980), Coolidge (1981), and others in surged flow. The linear advance also produces a nearly linear function for increased intake opportunity time from the top to the bottom of these furrows. Recessions were also linear and required 8 to 10 min to complete as would be expected on the 3% slope.

Soil water measurements at two points in the furrow showed that the soil water levels were generally higher at the head of the furrow than at the tail end in all years. Figure 1 presents data for a 10-week period in 1985. This shows a consistently higher, and not unexpected, soil water level at the head end compared to the tail end, and increased during the season. The imbalance in intake opportunity times accounted for an estimated 10 to 15% soil water difference. Infiltration contributions at the tail end during recession were not sufficient to offset the effects of greater water depth and somewhat greater intake opportunity times at the top.

Figure 1 omitted.

Figure 2 presents representative soil water profiles based on the readings from the five neutron meter access tubes at the top and bottom of the furrow for 1985 on the 100% Eta daily replacement schedule. These profiles indicate that the area was not greatly overwatered, adequate water was available and that deep percolation was not a large problem. These data clearly show that the spatial differences in water depths and opportunity times are important considerations in the management of high frequency furrow systems. Due to the inherent nature of surface irrigation, it is unlikely that these differences between the top and tail end of the rows could be eliminated. However, it should be possible to minimize these differences through the optimal selection of cycle times and/or cutback flow rates for various soil and slope conditions.

Figure 2 omitted.

Calculation of application efficiencies (AE) was based on the difference between inflow and outflow volumes divided by inflows for the surged furrows assuming no deep percolation or surface evaporation. It was assumed that soil water conditions during this time were representative, because the system had been operating since May each year. In all three years, measurable precipitation during August was minor and infrequent. There was no measurable precipitation in August 1984.

Figure 3 omitted.
Figure 4 omitted.
Figure 5 omitted.

Application efficiencies for the surged applications were generally above 70%, although daily values occasionally dipped as low as 50%. Low or extremely high daily efficiencies often occurred on weekends when the inflows were not adjusted for precipitation and/or climatic conditions were different than anticipated. High efficiencies during the end of August 1984 (> 95%) occurred during a relatively warm and windy period. These and other events imply that surface evaporation along the furrow had a more significant effect on the outflow than was included in the scheduling, resulting in relatively small outflow volumes. The average application efficiency during August over the three years was about 80%.

Yield, growth, stomatal conductance, and other tree response data for the 100% ETa trickle- and surge-irrigated cherry trees showed that the surged trees behaved normally under both systems in all three years. In fact, relative to the trickled trees, the surged trees produced quite similarity to what they have historically produced under conventional surface irrigation. There were no significant differences in favor of either irrigation technique or tree location. However, results show that high frequency furrow irrigation systems can be managed to obtain crop production similar to those resulting from traditionally more efficient systems.

A discontinuous blue-green algae developed in the bottoms of the furrows each year. Portions of the algae were continuously breaking free and re-exposing the soil, which seemed to offset any potentially negative impacts on infiltration due to sealing effects. Although soil erosion was not monitored, the algae may have reduced soil erosion since there was very little sediment movement even with the 3% slope. In fact, the water was usually much cleaner when leaving the field than when it was applied at the top. The results of this study also imply that high frequency furrow systems could be an alternative to microirrigation systems on widely-spaced crops, but would be limited to lands normally suited to surface irrigation. It should be noted, however, that a high frequency irrigation program may not be possible under some canal delivery procedures where water is not available every day and/or portions of each day. In addition, many farm delivery systems are not designed to facilitate this type of scheduling.

A buried, gravity pressure pipeline system for a high frequency daily surge flow furrow irrigation system would basically be a two pipe layout as with any piped surge flow system. The expense for automation with commercially available surge flow equipment would be expected to be reasonable for an orchard or vineyard since a relatively large area could be irrigated at once. Individual furrow risers would be located only every 3 to 5 m (10 to 16 ft), corresponding to row spacing.

Table 2. Yield comparison data between the 100% ETa trickle and daily surge flow irrigated trees for 1986

                      Trickle                 Surge               
                      -------                 -----               
Yield (per tree)      138.0 kg (304.2 lb.)    173.0 kg (381.4 lb.)

Fruit weight *        72.g (0.25 oz)          7.9 g (0.28 oz)     

Soluble solids (%)    15.5                    14.5                

Firmness **           722                     691                 

% Bruising            69                      80                  

----------                                                        
 * Individual cherry weight                                       
** Relative measure from momentum transfer generator based on     
   dropping cherries on a tightly stretched membrane              

Conclusions and Recommendations

Both conventional, continuous flow and surge flow furrow irrigation techniques could be expected to work well in meeting the objectives of this experiment. Surge flow was utilized primarily because of commercial availability of equipment and the ability to use high flow rates because of leaf and other residue in the furrows.

Compared with yields from trickle irrigated trees, this study shows that satisfactory tree performance can be obtained under high frequency furrow irrigation. There was no significant difference between the treatments or with location in the field. This indicates that high frequency furrow systems are horticulturally feasible.

Daily surged furrow application of water can be managed based on pan evaporation or other scheduling technique in approximately the same manner as a solid set trickle irrigation system. The head of the furrow received an estimated 10 to 15% more water than the tail end primarily due to increased opportunity times. Soil erosion was not a problem in this study even though the slopes were in excess of 3%.

High frequency (daily) surge flow furrow irrigation requires automation and, fortunately, the necessary equipment is commercially available. As with any water application system, high frequency furrow irrigation requires careful management and routine maintenance.

In many ways, the management of these furrow systems is quite similar to a microirrigation system since water applications are on a daily replacement basis. Leaves, grass, and small branches have to be periodically cleaned out of the furrows. Flow rates, runoff, and soil moisture levels should be monitored fairly frequently.

Irrigating a single furrow per tree row with high frequency surface irrigation systems can be an efficient irrigation technique on widely-spaced crops. The results of this study show that high frequency, furrow irrigation technology can be managed to maintain fairly uniform soil water levels without overwatering, and to obtain good tree performance.

The general benefits of high frequency irrigation can potentially be extended to many crops which cannot presently justify the expense of a pressurized solid-set system. However, its application is limited to lands which would normally be suitable for surface irrigation. Further investigations are needed to examine optimal cycle times and or cutback flow rates for various soils and slope configurations to minimize runoff and minimize soil water differences between the top and tail end of the furrows.

References

Allen, J.L. 1980. Advance rates in furrow irrigation for cycled flow. M.S. thesis, Utah State University, Logan.

Bishop, A.A., W.R. Walker, N.L. Allen and G.J. Poole. 1981. Furrow advance rates under surge flow systems. ASCE J. Irr. and Drainage Division 107(IR3): 257 -264.

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