Assessment of drip and ¯ood irrigation on water and
fertilizer use ef®ciencies for sugarbeets
F. Cassel Sharmasarkar, S. Sharmasarkar
*, S.D. Miller,
G.F. Vance, R. Zhang
Department of Plant Sciences and Renewable Resources, College of Agriculture, University of Wyoming, P.O. Box 3354, Laramie, WY 82071-3354, USA
Accepted 7 February 2000
Abstract
Mismanagement of nitrogenous fertilizers has caused serious nitrate (NO3) contamination in
many ¯ood-irrigated regions of the western US. Low-volume irrigation practices, such as drip irrigation, can offer an alternative approach for controlling NO3leaching and agricultural water use.
The objectives of this study were to compare NO3movement through soils under ¯ood and drip
irrigation practices for sugarbeet production, and to evaluate the agronomic feasibility of implementing drip irrigation. A ®eld experiment was conducted during the sugarbeet (Beta vulgaris
L.) growing seasons of 1996 and 1997 in southeastern Wyoming, where NO3contamination is a
continued concern and sugarbeet is a major cash crop. Three drip irrigation regimes, corresponding to 20, 35, and 50% water depletion of ®eld capacity (designated as D1, D2, and D3, respectively), were compared against ¯ood irrigation. The irrigation plots were treated with 112, 168, and 224 kg N haÿ1(designated as F
0, F1, and F2, respectively). Sugarbeet (SB) yields and sugar contents under
drip irrigation were higher (3±28%) than those with ¯ood irrigation; yields and sugar contents for the drip systems were in the order of D1>D2>D3. For all of the irrigation applications, there was an increasing trend in yields with increasing fertilizer rates. Drip regime resulted in greater residual soil NO3(RSN) for both 1996 and 1997 seasons as compared to ¯ood practices. Values of RSN in
both years followed the trend: F2>F1>F0. Soil NO3in all three drip regimes was higher (1.6±2.4
times) than that with ¯ood irrigation. In the overall root zone, NO3concentrations between D1 and
D2 were comparable, whereas both of those levels were lower than D3. Greater NO3concentrations
with D3 were observed at all depths. The amount of applied irrigation water with the drip system was lower than that for ¯ood irrigation. Agronomic water use ef®ciency (WUE) and fertilizer use ef®ciency (FUE) for drip irrigation were always higher than those for ¯ood irrigation. In 1996, WUE and FUE maintained an order of D1>D2>D3. There was a decreasing pattern in FUE values with increasing fertilizer rates. The overall results indicated that SB production could be sustained
*Corresponding author. Present address: California State University, Department of Plant Science, H/S AS-72, 2415E. San Samon Avenue, Fresno, CA 93740-8033. Tel.:1-559-278-2904; fax:1-559-278-7413.
E-mail address: ssharmas@csuffesno.edu (S. Sharmasarkar).
with lower water and fertilizer use by using drip irrigation. Thep-values (0.05), based on bothF -test (pf) and two-tailed student's t-test (pt), suggested a signi®cant difference between the yield
means obtained under drip and ¯ood irrigation practices. As compared to the ¯ood irrigation, the leastp-values were obtained with D1 followed by D2 and D3, respectively, thus, con®rming that D1 was the most effective treatment. Thep-values for SB yields under comparative fertilizer treatments and same drip application showed no signi®cant difference between the means, thus, suggesting the feasibility of using lower fertilizer rate while sustaining the targeted yield under drip irrigation. The comparative estimation of water losses by drainage between ¯ood and drip irrigation suggested that the later practice reduced the quantity of water leaching beyond the root zone. Among the three drip treatments, the lowest drainage amount was observed with D1 as a result of its higher irrigation frequency and smaller quantity of water input during each application.#2001 Elsevier Science B.V. All rights reserved.
Keywords:Drip irrigation; Water use; Drainage; Fertilizer management; Sugarbeet production
1. Introduction
Mismanagement of nitrogenous fertilizers has caused serious agricultural contamina-tion in many regions throughout the US (U.S. Department of Agriculture, 1991). High concentrations of NO3 in drinking water can cause health problems (Environmental Protection Agency, 1990). In the southeastern region of Wyoming, where sugarbeet (SB) production is intensive and fields are mainly flood irrigated, levels surpassing the critical EPA limit of 10 mg lÿ1 NO3-N have been detected in several well waters (Baker and Associates Consulting Engineers, 1989; Wyoming Hydrogram, 1995). A way of managing NO3 pollution is to introduce an alternative irrigation method that reduces chemical transport through soils, as well as agricultural water demand. A low-volume irrigation practice, such as drip irrigation, can offer such a technology (Bucks et al., 1982; Caswell, 1991).
Field studies are necessary to determine the efficacy of this new irrigation system in Wyoming, where flood (furrow) is the major irrigation practice. Benefits of drip irrigation have been documented by different researchers. In a study involving NO3 transport to groundwater, Geleta et al. (1994) compared drip and flood irrigation, and concluded that drip irrigation resulted in lower NO3-N loss. Based on a groundwater quality assessment research in the delta Wadi El-Arish area of Egypt, Bihery and Lachmar (1994) also recommended that flood irrigation practice be replaced by drip irrigation system, especially in arid environments. In another study comparing drip and flood irrigation practices, Roth et al. (1995) observed that reduced water use did not affect the yield and quality of orange fruits. Drip irrigation practices are widely used on coarse-textured soils, and for high-value crops in FL, CA, Europe and Israel where water is scarce or expensive (Gregory, 1990).
Many SB growing areas in Wyoming are characterized by semi-arid climate and sandy soils in which NO3 causes serious contamination problems. Sugarbeet is a major cash crop within the eastern Rocky Mountain region, including Wyoming, and contributes more than US$ 48 million in annual income to the state (Wyoming Agricultural Statistics
Service, 1998). Use of drip irrigation for SB production is yet to be tested in Wyoming. Therefore, the objective of this study was to compare drip and flood irrigation regarding water and fertilizer use efficiencies for SB production.
2. Materials and methods
A field experiment was conducted during the SB (Beta vulgarisL.) growing seasons of 1996 and 1997 (seeding: first week of April, harvesting: first week of October) at the Torrington Research and Extension Center (elevation>1200 m), located in southeastern Wyoming, where NO3contamination is a continued concern and SB is a major cash crop (Wyoming Agricultural Statistics Service, 1998). The soil is classified as Daily sandy loam (sandy, mixed, mesic, Torriorthentic Haplustoll) with less than 1% organic matter within the root zone. This soil series was formed predominantly in alluvium and wind-deposited and reworked sand which originated from noncalcareous sandstone.
The experimental design was a split-plot, where each irrigation plot was factorially arranged for three rates of post-emergence nitrogen (N) fertilizer (urea ammonium nitrate, UAN) applications: control (0 kg haÿ1), half-dose (56 kg haÿ1), and full-dose (112 kg haÿ1). Earlier in the season, a basal pre-plant dose of 112 kg N haÿ1 was also applied. Thus, a total quantity of 112, 168, and 224 kg N haÿ1, designated henceforth as F0, F1, and F2, respectively, was used during the growing season. Weeds were controlled with two post-emergence herbicide applications (Nortron: 2.13 kg haÿ1, and Betamix: 1.70 kg haÿ1). Additional plot care was ensured by hand-picking of weeds throughout the growing season. SBs were irrigated using two different methods: conventional flood and surface drip irrigation. Both flood and drip irrigation applications were initiated in July and continued until harvesting. Prior to irrigation treatment initiation, the soil profile was watered to field capacity with flood irrigation to refill a depth of 1.2 m and ensure moisture content homogeneity in the experimental field. Three irrigation regimes, corresponding to 20, 35, and 50% water depletion of field capacity (designated as D1: drip1, D2: drip2, and D3: drip3, respectively), were used for drip irrigation in 1996. Application of flood irrigation was maintained at 65% water depletion of field capacity in consistency with the local farming practices. Therefore, a total of four irrigation treatments was used for the field experiment. Eight SB rows (10 m length0.76 m standard spacing) were allocated for each irrigation treatment, separated by four furrows (10 m length0.76 m width) as bordering-buffer-zones to prevent the influence of one treatment on another. A spacing of 3 m was also maintained as a bordering-zone at both ends of the rows. Thus, the experimental plot area totaled 600 m2in which each of the four irrigation treatments covered an area of 150 m2and comprised three replicates.
Along the SB rows, furrow irrigation water was delivered from gated pipes connected to the main water supply. Furrows were fitted with flumes at the beginning and end of each row to calculate water flow rates. The furrows for flood irrigation were scheduled for 2 h bi-weekly watering at a rate of 7.00 l hÿ1. Flood irrigation (designated as Fl) was applied when the soil moisture reached a level of 65% water depletion of field capacity. The drip irrigation system consisted of PVC pipe laterals (19.05 mm i.d., 10 m length) and spaced at 0.76 m intervals. Each drip line was equipped with 20 emitters spaced at
0.55 m intervals. The drip water was supplied through a pump connected to the main water source. Each drip system was operated by a control valve at a discharge rate of 3.78 l hÿ1with an application efficiency of 92%. For D1, D2, and D3, water applications were scheduled to coincide with 20, 35, and 50% water depletion of field capacity, respectively. The water depletion, caused by evapotranspiration (ET), was replenished with irrigation water.
The amounts of water estimated to refill the plant-root zone to field capacity were computed using the following equations for drip irrigation: SWRCWUÿP; and DDWHCRZPwf. The soil water requirement (SWR) was calculated based on the crop water use (CWU) and precipitation (P). The CWU was determined from the moisture loss due to crop ET. Throughout the growing season at Torrington Research and Extension Center, daily P data were recorded and the sugarbeet ET values were calculated based on a modified Penman method (Doorenbos and Pruitt, 1977). The design depth (DD) indicated the water depletion level between irrigation events and was determined from soil water holding capacity (WHC), crop rooting depth (RZ), water depletion factor (f), and percentage of wetted soil surface (Pw) maintained at 70% according to a FAO guideline for drip irrigation (Vermeiren and Jobling, 1984). Each irrigation event for D1, D2, and D3 was scheduled at DD values calculated with 20, 35, and 50% water depletion of field capacity, respectively (fvalues). Irrigation water was applied when cumulative value of the daily SWR equaled DD for each drip regime. The range offvalues was consistent with the FAO guideline for drip irrigation (Vermeiren and Jobling, 1984). The DD with lower f value corresponded to a higher frequency of irrigation events and smaller quantity of water input during each application.
Once the comparative assessment of different drip and flood irrigation treatments was established in 1996, a similar experiment was repeated during the 1997 season using one drip irrigation treatment (analogous to D1 of 1996) along with flood irrigation for the purpose of verifying the patterns of our previous findings. The SBs from each plot were harvested in October and analyzed for yield and sugar content by the Holly Sugar Company, Torrington, Wyoming. Soil samples, collected from the rooting depth (0±45, 45±90, 90±135, 135±150 cm), were stored at 48C until analyzed. The samples were air-dried, finely ground (<2 mm), and analyzed for NO3 in 2 M KCl extracts using a Technicon Autoanalyzer (Keeney and Nelson, 1982). Soils were also analyzed for texture (Gee and Bauder, 1986), bulk density (Blake and Hartge, 1986), saturated hydraulic conductivity (Klute and Dirksen, 1986), water holding capacity (Klute, 1986), and pH (Schwab, 1992). The statistical analyses including the analysis of variance, descriptive statistics, andt-tests were conducted using a Statistical Analysis System (SAS, 1989) in order to compare any significant differences between the treatments.
The comparison of water losses by drainage under flood and drip practices was also evaluated. For each irrigation treatment, the drainage (D) was estimated on a daily basis during the irrigation period (July±October) from the Darcy's law equation:
DqDtÿK(y)rHDt, where q is the water flux (cm dayÿ1), t is the time (day),
Kis the hydraulic conductivity (cm dayÿ1),yis the water content (cm3cmÿ3), andrHis the hydraulic head gradient. Daily water potentials (h) were obtained from tensiometer readings at 120 and 150 cm, thereby representing depths in and below the root zone, respectively. Water content and hydraulic conductivity values were calculated with the
soil water characteristic curves derived from field and laboratory measurements ofy,h, andKbefore the irrigation season. The hydraulic parameters characterizing they(h) and
K(y) relationships were estimated based on the Van Genuchten model (Van Genuchten, 1980) and presented in Cassel Sharmasarkar et al. (2000). For each irrigation treatment, the cumulative drainage during the irrigation season was determined from daily D
calculations.
3. Results and discussion
Soil physical and chemical properties are listed in Table 1. The soils in the SB root zone (0±150 cm) had neutral to alkaline pH conditions (6.63±8.00) and high sand contents (77±90%). The profile depths were characterized as sandy loams with high bulk density (1.69±1.86 g cmÿ3), moderate saturated hydraulic conductivity (20.2±37.1 cm dayÿ1) and low water holding capacity (0.27±0.21 cm3cmÿ3). An increasing pattern with depth was observed for all these soil parameters except for WHC, which was explained by increased soil particle size with depth.
The SB yields, and sugar contents during 1996 and 1997 growing seasons under flood and drip irrigation are presented in Table 2. The yields and sugar contents under drip irrigation were higher (3±28%) than those with flood irrigation. In a similar study with orange fruits, Roth et al. (1995) also observed that low water use with drip irrigation sustained the yield and quality of the fruit. The pattern of yields among different drip regimes in 1996 was: D1>D2>D3. For all of the irrigation applications, there was an increasing trend in yields with increasing fertilizer rates. Yields and sugar contents obtained with the D3 system were closer to those determined with flood irrigation. The SB yields and sugar contents in 1997 were lower than those obtained in 1996. This pattern, however, was consistent with the yields reported for SB production in Wyoming during these two growing seasons (Wyoming Agricultural Statistics Service, 1998). Our yields in both years were greater than the average SB production in Wyoming over the last 50 years. We observed similar trends in both 1996 and 1997 regarding greater efficacy of drip irrigation than flood irrigation. Further comparison of these two seasons regarding climatic conditions and yields has been discussed later.
Accumulations of RSN in the root zone at the end of growing seasons for flood and drip irrigation (D1) are shown in Fig. 1. Drip irrigation resulted in a greater RSN for both 1996 and 1997 seasons as compared to the flood irrigation practice. Thus, drip irrigated
Table 1
Selected properties of the sugarbeet soil studied under irrigation management practicesa
Depth (cm) pH Sand (%) Silt (%) Clay (%) BD
fields would have a greater potential for fertilizer curtailment for the next crop. In a study with different cropping systems, Geleta et al. (1994) found that drip irrigation caused lower NO3leaching when compared to flood irrigation. This trend was observed for all three fertilizer treatments. There was, however, an increase in the NO3concentrations with increasing rates of fertilizer, i.e. values of RSN in both years followed the trend: F2>F1>F0. It was noteworthy that both SB yields and sugar contents, as described earlier, and the RSN values for 1997 were lower than those for 1996.
Comparative soil NO3concentrations at various depths under different drip regimes and flood irrigation practices are presented in Table 3. Soil NO3 under all three drip irrigation regimes was higher (1.6±2.4 times) than that with flood irrigation. In the overall root zone, the concentrations between D1 and D2 were comparable, whereas the levels were lower than that for D3. Greater NO3concentrations with D3 were determined at all depths. For all four irrigation regimes, soil NO3concentrations decreased with depth. Lower NO3concentrations under flood irrigation could be due to greater solute leaching than with drip practice. A closer inspection of the 135±150 cm profile layer revealed that
Fig. 1. Residual soil NO3in the root zone at the end of the growing season with ¯ood and drip irrigation under different fertilizer treatments (F0, F1, and F2112, 168, and 224 kg N haÿ1, respectively).
Table 2
Sugarbeet (SB) yields and sugar contents under ¯ood and drip irrigation practicesa
Parameters D1 (1996) D2 (1996) D3 (1996) Fl (1996) D (1997) Fl (1997)
SB (kg haÿ1)
F0 63862 59684 59331 57416 40795 37792
F1 67766 64061 62912 58491 44450 43275
F2 71402 66448 62948 60480 47191 45429
Sugar (kg haÿ1)
F0 10603 10355 9783 9460 5765 5307
F1 10749 10433 9932 9702 6363 6376
F2 10783 10946 10271 9982 6814 6367
aD: drip; D1: drip1; D2: drip2; D3: drip3; Fl: ¯ood; F
0, F1, and F2112, 168, and 224 kg N haÿ1, respectively. D1 (and also D), D2, D3, and Fl correspond to 20, 35, 50, and 65% water depletion of the ®eld capacity, respectively.
the flood irrigated soil had the lowest NO3concentration. This could be an indication of higher NO3leaching at this depth in the flood irrigated treatment as a result of greater drainage. Discussions on drainage have been presented later.
Water and fertilizer use efficiencies for different irrigation treatments are presented in Table 4. The amount of applied irrigation water (AIW) was lower for drip irrigation than that with flood irrigation. The AIW was a measure of the cumulative amount of daily SWR for the irrigation events applied throughout the growing season that had been determined from the ET andPvalues. The ET values were 810 mm (1996) and 532 mm (1997). The P values were 197 and 323 mm during the irrigation period of 1996 and 1997, respectively. Due to high precipitation events during the 1997 growing season, AIW for drip irrigation was less as compared to 1996 season. However, there was no appreciable difference between the quantities of water applied through flood irrigation in the 2 years. Flood irrigation was applied following the general practice in Torrington area. Drip, being a low-volume irrigation system, was monitored more intensively. Compared to 1996, the season of 1997 was a low-radiation and wet period. This could have caused lower SB yields and sugar contents in 1997 as shown earlier in Table 2. Sugar contents in 1997 under drip and flood irrigation diminished from 1996 nearly by 40 and 38%, respectively. During both years, for all of the irrigation applications, SB yields and sugar contents increased with higher fertilizer inputs. However, under the same drip practice, no significant difference in yields was observed for comparative fertilizer treatments. Statistical discussions have been presented later.
Table 3
Comparative soil NO3concentrations (mg kgÿ1) under different drip and ¯ood irrigation practicesa
Soil depth (cm) D1 D2 D3 Fl
0±45 44.3 41.8 51.6 24.2
45±90 22.3 14.2 35.1 12.2
90±135 12.1 19.7 26.1 10.5
135±150 6.28 7.4 11.6 4.9
Overall root zone 24.9 24.2 36.1 15.1
aResults are from full-dose fertilizer treatment in the end of 1996 growing season.
Table 4
Water and fertilizer use ef®ciencies for different irrigation treatmentsa
Treatments AIW (mm) WUE (kg haÿ1mmÿ1) FUE (kg haÿ1/kg haÿ1)
F0 F1 F2
D1 (1996) 640 106 570 403 319
D2 (1996) 640 99 533 381 297
D3 (1996) 640 96 530 374 281
Fl (1996) 1120 53 513 348 270
D (1997) 250 177 364 265 211
Fl (1997) 1115 38 337 258 203
Agronomic water use efficiency (WUE) was calculated as the ratio between SB yield and total irrigation water received by the crop during the growing season (Table 4). During both years, the WUE values for drip irrigation were always higher than those for flood irrigation. In 1996, WUE among different drip regimes maintained an order of: D1>D2>D3. The values for both irrigation systems were lower in 1997 mainly due to the decreased crop yield as compared to 1996. Trends in fertilizer use efficiency (FUE), defined as the amount of crop yield per unit fertilizer application rate, were similar to WUE with different irrigation regimes for both 1996 and 1997. There was a decreasing pattern in FUE values with increasing fertilizer rates. Greater agronomic efficiency of drip irrigation practices was also observed by Bucks et al. (1982) and Caswell (1991). When compared for different irrigation regimes, the yield-based values of WUE and FUE indicated that crop production could be sustained with lower water and fertilizer applications, as noted with drip irrigation.
Statistical parameters for SB yields under different irrigation and fertilizer applications are listed in Table 5. Covariance, a measure of the average of the product of deviations of data points from their respective means, ranged from ÿ3.68107 to 6.11107 for different comparative treatments. The positive and negative covariance numbers suggested associations of large values of one data set with the large values and small values, respectively, from the other data set. Thep-values (0.05), based on bothF-test (pf) and two-tailed student'st-test (pt), suggested that there was a significant difference between the yield means obtained under drip and flood irrigation practices. As compared to the flood irrigation, the leastp-values were determined with D1 followed by D2 and D3, respectively, thus, confirming our previously noted observation about D1 being the most effective treatment. High mean square (MS) values were typically observed for the parameters with significant difference between the yield means, and vice versa.
The p-values for SB yields under comparative fertilizer treatments (F0, F1, F2) and same drip application (D1) were higher than 0.05 and showed no significant difference between the means, thus, suggesting the feasibility of using lower fertilizer rate while sustaining the targeted yield under drip irrigation (Table 5). Ther2(correlation coefficient
Table 5
Statistical parameters for sugarbeet yields under different irrigation and fertilizer treatmentsa
Treatments Cov. (107) MS (108) r2 pf pt
D1 vs. Fl (1996) ÿ1.38 10.6 0.04 0.002 0.003
D2 vs. Fl (1996) 2.01 5.52 0.15 0.01 0.01
D3 vs. Fl (1996) 0.94 3.98 0.02 0.03 0.03
D vs. Fl (1997) 1.64 0.57 0.23 0.05 0.05
D vs. Fl (1996±1997) 6.11 6.76 0.24 0.04 0.04
D1: F0vs. F1(1996) 2.18 0.23 0.16 0.66 0.67
aCov.: covariance; MS: mean square;r: correlation coef®cient;p
fandptarep-values based onF-test and two-tailed student'st-test, respectively.
square) values for yields under these comparative fertilizer treatments were generally high (up to 0.97) indicating linear relationships between two sets of data, albeit with some exceptions; thep-values, however, were greater than 0.05, regardless of ther2values.
The comparison of water losses by drainage between flood and drip irrigation is presented in Fig. 2. The cumulative drainages under the three drip practices at the end of the growing season were more than three times lower than that observed with flood irrigation. The cumulative drainage increased linearly for the drip treatments indicating small and regular water losses. The drainage curve under flood practices followed a step-like pattern with each step reaching a plateau. The rising part of the curve was suggestive of high drainage period after irrigation events, and the plateau was due to minor water loss occurring subsequently. This was a characteristic feature of high irrigation intervals with flood practices. These results, coupled with the higher soil NO3 concentrations observed with drip irrigation at the end of the growing season, suggested that the amount of leaching beyond the root zone was reduced with the low-volume practice. Among the drip treatments, the water loss by drainage followed the trend: D1<D2<D3. The lowest cumulative drainage found with D1 was explained by the higher irrigation frequency with smaller water amount, which favored a more efficient use of water in the coarse-textured soil.
4. Summary and conclusions
In an experimental study conducted in a SB field, soil NO3 distribution and crop production were compared under drip and flood irrigation practices. Higher residual NO3 concentrations were observed around the root zone for drip irrigation. Drip irrigation was characterized by a smaller amount of water applied to the soil system. The SB yields and sugar contents were not affected by the reduced water application, and resulted in higher yields under drip irrigation practices. Drip irrigation also enhanced water and fertilizer use efficiencies. Comparing the three drip treatments, a higher irrigation frequency was Fig. 2. Cumulative water losses by drainage during the 1996 growing season under ¯ood and drip irrigation practices.
found to be more efficient for SB production. The water losses by drainage were considerably reduced with the low-volume irrigation practice. This study shows that drip irrigation can be used for SBs with effective fertilizer and water management plans for sustaining water quality and agricultural productivity.
Acknowledgements
The research was funded by grants from Wyoming Agricultural Experiment Station (U.S.D.A.) and Wyoming Water Resources Center (U.S.G.S.).
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