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Field evaluation of crop yield as affected by nonuniformity of sprinkler-applied water and fertilizers
Agricultural Water Management 59 (2003) 1±13
Field evaluation of crop yield as affected by nonuniformity of sprinkler-applied water and fertilizers Jiusheng Lia,*, Minjie Raob a
Department of Irrigation and Drainage, China Institute of Water Resources and Hydropower Research, Beijing 100044, China b Agrometeorology Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, China Accepted 19 August 2002
Abstract The determination of target uniformity for sprinkler irrigation system should consider the impacts of nonuniformity of water and fertilizers on crop yield. Field experiments were therefore conducted in north China plains to address the impacts of nonuniformly applied water and fertilizers on winter wheat yield. Irrigation water and fertilizers were applied through a solid set sprinkler system. Three experimental plots were used with seasonal Christiansen uniformity coef®cients (arithmetic mean of individual CUs) ranging from 62 to 82%. Each plot was divided into 3 m 3 m grids. Sprinkler water depth and concentration of fertilizer solution for each grid was measured both below and above the canopy for each individual irrigation event. The spatial distribution of soil moisture for each experimental plot was also measured periodically to determine irrigation times and amounts. On harvest, grain yield and total nitrogen content of plant stems were measured for each grid. The experimental results showed that the uniformity of fertilizer applied increased with sprinkler water uniformity. The distributions of both fertilizers and water applied through sprinkler system can be represented by a normal distribution function. Field experiments also demonstrated that the uniformity of sprinkler-applied water and fertilizers has insigni®cant effect on winter wheat yield for the studied uniformity range. The current standard for sprinkler uniformity (for example, the target CU is equal to or higher than 75% in China) is high enough for obtaining a reasonable crop yield in dry sub-humid regions. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Sprinkler irrigation; Fertigation; Uniformity; Winter wheat; Yield
* Corresponding author. Tel.: 86-10-684-15823; fax: 86-10-684-15823. E-mail address: [email protected] (J. Li).
0378-3774/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 2 ) 0 0 1 2 3 - 3
2
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
1. Introduction The relationship between crop production and evapotranspiration, called the crop water production function, is important to agronomists, engineers, economists, and water resource planners. This importance is currently accentuated due to competition among users, declining groundwater reserves, various legal institutions, and degradation in water quality. There are many factors affecting the crop production function. In addition to evapotranspiration or evapotranspiration de®cits, sprinkler uniformity also affects the crop water production function. Stern and Bresler (1983) evaluated the impacts of sprinkler irrigation uniformity on soil water variability and yield of sweet corn by ®eld experiments. Letey et al. (1984) provided a general method for analyzing the effect of in®ltration water uniformity on crop yield and concluded that ignoring irrigation uniformity leads to underestimates of the optimum irrigation amount. Warrick and Gardner (1983) attempted to combine the effects of irrigation application variability and soil spatial variability distributions using the joint probability distributions that can be determined by convolution or by Monte Carlo methods. Other researchers addressing the interaction effects of irrigation amount and the uniformity of irrigation or in®ltrated water on crop yield include Varlev (1976) and Seginer (1978, 1983). Recently, Mantovani et al. (1995) simulated the effects of sprinkler uniformity on crop yield by assuming a uniform sprinkler water distribution and a linear crop water production function. Li (1998) presented a model that relates yield response to evapotranspiration de®cits at special growth stages to evaluate the impacts of uniformity on crop yield. Comparing the reported simulation results with those obtained from ®eld experiments leads one to ®nd there exists signi®cant differences between them. Field experiments (Mateos et al., 1997; Li and Rao, 2000) showed that sprinkler uniformity had little effect on crop yield, but simulation (Mantovani et al., 1995; Li, 1998) suggested that crop yield increased clearly with increasing sprinkler uniformity. Further ®eld experimental studies are obviously necessary to verify and modify the existing simulation models. Sprinkler irrigation system can be used for fertigation, but we have little knowledge of the effects of fertigation on crop performance. The primary objectives of this research were to investigate the response of crop performance to nonuniformly applied water and fertilizers through ®eld experiments and to give recommendations for the design of sprinkler irrigation systems. 2. Materials and methods 2.1. Experimental field The experiments were conducted at the Experimental Station of Agrometeorology Institute, Chinese Academy of Agricultural Sciences in Beijing, north China plains. The experimental area, located in the temperate monsoon climatic zone, is in a dry sub-humid region with an annual mean precipitation of 550 mm. Between 70 and 80% of the precipitation occurs between July and September. An automated weather station was installed 80 m from the experimental ®eld to monitor wind speed and direction, air
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
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temperature, humidity and precipitation every 15 min during the irrigation. The soil was a clay loam with a bulk density of 1.4±1.5 g/cm3 and a ®eld capacity of 0.32 cm3/cm3. Winter wheat (Triticum aestivum L.) was sown on 5 October 1999 with row spacing of 25 cm and sowing rate of 127.5 kg/ha. Pest and disease control followed the standard practices in this area. Three plots, designed as high uniformity, medium uniformity and low uniformity (referred to as plots 1±3 below, respectively), were used in the experiments. Each plot was 15 m 15 m in size, and sprinklers mounted on the 180 cm height risers were installed at each corner of the plot. The central of 12 m 12 m in each plot was selected as the observed area to avoid interference between adjacent plots. 2.2. Water measurements The 12 m 12 m observed area in each plot was divided into a grid of 16 3 m 3 m subplots. Catch cans of 112.8 mm diameter and 250 mm height were placed at the center of each subplot on the ground surface to measure sprinkler water distribution below the canopy. Since the developing winter wheat canopy has a potential to affect the distribution of sprinkler water, catch cans were also located above the canopy. A total of 16 cans with the same size as those on the ground surface were also placed in the center of the 3 m 3 m grids. The top of the above canopy cans was 85 cm above the ground surface. The water collected in both above and below the canopy cans was measured 15 min after the designed amount of water was applied. Catch can data free of crop interference were used in this article. Christiansen uniformity coef®cient de®ned in Eq. (1) was used to calculate the uniformity of both daily and cumulative application depths (Christiansen, 1941). ! PN xj i1 jxi CU 1 100 (1) Nx where CU is Christiansen uniformity coefficient; xi is the ith water application depth; and P N xj is the sum of the absolute deviation from the mean, x, of all N observations. i1 jxi 2.3. Crop measurements One square meter of winter wheat for each subplot was harvested on 12 June 2000 and the dry grain yield was recorded. The yield at the position of ground can was represented by the yield of 1 m2 sample. Plant stems for each 3 m 3 m subplot were sampled when winter wheat was harvested. The sample was digested by H2SO4±H2O2 and the total nitrogen of the solution was determined by distillation method to obtain the total nitrogen content of the plant stems for each subplot. Christiansen uniformity coef®cients for total nitrogen content of plant stems were also calculated by using of Eq. (1). 2.4. Irrigation Soil water contents from 30 to 100 cm depth were measured weekly by a neutron probe with an interval of 10 cm, but the contents at top 30 cm were measured by a time domain
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J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Table 1 Summary of irrigation depth collected by above catch-cans (AW), Christiansen uniformity coefficients (CU) and date of each of the five irrigation events Plot 1
Plot 2
Date 30 13 28 11 30
AW (mm) a
March Aprila April May May
Totalb
CU (%)
Date
38.1 31.7 52.8 48.5 56.3
88 71 82 88 81
30 13 28 11 30
227.4
82c
Total
March April April May May
Plot 3 AW (mm)
CU (%)
Date
35.8 31.6 47.1 44.7 45.1
76 76 74 67 70
30 13 27 12 26
204.3
72c
Total
March April April May May
AW (mm)
CU (%)
34.2 44.0 45.6 46.0 42.6
59 65 60 69 57
212.4
62c
a
Fertigation applied. Total crop water use from other sources (rainfall, soil water and germination and frozen irrigation) was 193, 204, and 226 mm for plots 1±3, respectively. c Seasonal Christiansen uniformity coefficient, is defined as arithmetic mean of individual CUs during the whole irrigation season. b
re¯ectometry (TDR). Five neutron access tubes were installed in the diagonals for each plot. TDR sample was about 10 cm around the access tube. Soil water content for each plot was represented by the mean of the ®ve observed positions. Irrigation was applied when average soil water content within top 40-cm layer depleted to 65% of ®eld capacity (about 45 mm depletion). A total of ®ve irrigation events were used between 30 March and 31 May 2000. Irrigation dates, amounts and CU values are summarized in Table 1. Impact sprinklers with nozzle diameter of 4 mm, namely LEGO 80B2, were used in the experiments. Four sprinklers applied water to an experimental plot using a rotation angle of approximately 908 during irrigation. Sprinklers were operated at pressures of 150, 200 and 300 kPa for low, medium and high uniformity plots (plots 1±3), respectively. For all the experiments, the average application rate ranged from 8 to 14 mm/h, and no surface runoff was found in the experiments. 2.5. Fertilizer measurements Fertigation was conducted with the irrigation events of 30 March and 13 April 2000 (Table 1). For the fertigation on 30 March, ammonium carbonate (N content of 15%) was applied with a rate of 22.2 g/m2. For the fertigation of 13 April, ammonium sulphate (N content of 21%) and urea (N content of 45%) were mixed at a rate of 1 to 3 and applied with the rates of 4.4 and 13.3 g/m2, respectively. The duration of fertigation was determined by the rule of quarter-half-quarter (Burt et al., 1998). Electric conductivity (EC) of fertilizer solution caught in each can was tested by a portable conductivity probe as fertigation was completed. The relationships between concentration of fertilizer solution and EC were calibrated for the fertilizers used prior to fertigation and the following equations were obtained: C 1:11EC
860 for ammonium carbonate solution
n 10; r 2 0:999
(2)
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
C 0:45EC
443 for ammonium sulphate solution
n 9; r 2 0:993
5
(3)
where C is the concentration of fertilizer solution (mg/l), ranging from 0 to 1800 mg/l; EC is the electric conductivity of fertilizer solution (ms/cm); n is the number of samples and r is correlative coefficient. Eqs. (2) and (3) were used to determine the concentration of fertilizer solution for each catch can and the amount of fertilizer applied for each subplot was determined from the concentration of fertilizer solution and the water volume caught in the catch can. Christiansen uniformity coef®cients for fertilizer solution and fertilizer amount were also calculated by using Eq. (1). 3. Results and analysis 3.1. Uniformity of fertigation Fig. 1 compares the cumulative frequency distributions between fertilizer applied and water depth for the fertigation on 30 March 2000. Fertilizer applied and water depth are normalized (value/mean) in the ®gure. The amount of fertilizer applied produced an approximately similar cumulative frequency distribution to water depth. Fig. 1 also indicates that both fertilizers applied and water depth can be represented by a normal distribution function. Examining the standard deviation values presented in Fig. 1, one can ®nd that fertilizer applied gave a lower standard deviation than water depth for medium and low uniformity experimental plots (plots 2 and 3). Fig. 2 compares Christiansen uniformity coef®cients (CU) for water application, concentration of fertilizer solution and fertilizer applied for the fertigation event on 30 March 2000. Fig. 2 indicated that a higher CU for water application produced a more uniform distribution of fertilizer. For example, as water application CU increased from 59% for plot 3 to 88% for plot 1, CU for fertilizer applied increased from 68 to 84%. There was a signi®cant difference for CUs of water application among the three experimental plots (88% for plot 1, 76% for plot 2 and 59% for plot 3), but the three plots produced an approximate CU value for concentration of fertilizer solution (83% for plot 1, 90% for plot 2 and 83% for plot 3). This suggests that water application uniformity have a little effect on CU for concentration of fertilizer solution. Examining Fig. 2 can also lead one to ®nd that CU for fertilizer applied was greater than CU for water application for medium and low uniformity plots (plots 2 and 3). 3.2. Effects of nonuniformity of sprinkler applied water and fertilizers on crop yield The cumulative frequency distributions of cumulative water depth during irrigation season and yield for the three experimental plots are illustrated in Fig. 3. One can ®nd from Fig. 3 that both cumulative irrigation depth and crop yield can be represented by a normal distribution function. Water application depth varied in a larger range than yield, especially for the low uniformity level plot (plot 3). Table 2 summarizes the mean and CU values for several components of yields. Analyzing the data indicated in Table 2, one can ®nd that yield components for all three
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J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Fig. 1. Cumulative frequency distributions for fertilizer applied and water depth measured above canopy for fertigation on 30 March 2000 for the three experimental plots. The lines represent normal distribution functions.
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
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Fig. 2. Comparison of Christiansen uniformity coefficients for water application, concentration of fertilizer solution and fertilizer applied for fertigation on 30 March 2000.
plots gave a CU value greater than 90%, even though the arithmetic mean of individual CUs of irrigation depth (seasonal CU) varied from 62 to 82% (Table 1). The relationships between crop yield and arithmetic mean of individual CUs and CU for cumulative irrigation depth during irrigation season are illustrated in Fig. 4. The data obtained from the ®eld experiments conducted in 1998±1999 (Li and Rao, 2000) are also shown in the ®gure. Fig. 4 clearly indicated that sprinkler uniformity CU has an insigni®cant impact on crop yield. Plant nitrogen uptake is mainly affected by the spatial distributions of water and fertilizer applied through sprinkler system. Fig. 5a and b shows Christiansen uniformity coef®cients for total nitrogen content of plant stem on harvest as function of CU for fertilizer applied on 30 March 2000 and of seasonal CU for water application. It can be seen from Fig. 5a that the uniformity for total nitrogen of plant stem increased with the uniformity for fertilizer applied. A greater value of seasonal uniformity coef®cient of water Table 2 Summary of mean and Christiansen uniformity coefficients (CU) for yield components of the three experimental plots Plot
Effective ears
Seeds per ear
Weight per 1000 grainsYield
Mean (ear/m ) CU (%)
Mean (g)
CU (%)
Mean (g)
CU (%)
Mean (t/ha)
CU (%)
350.5 324.1 371.7
49.6 48.8 50.5
95 93 94
48.2 48.1 46.1
96 97 95
6.98 6.43 7.02
94 93 94
2
1 2 3
91 94 92
8
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Fig. 3. Cumulative frequency distributions for cumulative irrigation depths during the irrigation season and winter wheat yields for the three experimental plots. The lines represent normal distribution functions.
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
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Fig. 4. Crop yield as function of (a) arithmetic mean of individual CUs, and (b) CU of cumulative water depth during the irrigation season of winter wheat, for field experiments conducted in 1998±1999 and 1999±2000.
application also produced a more uniform distribution of total nitrogen content of plant stem (Fig. 5b). Fig. 5a and b also indicated CU for total nitrogen content of plant stem was greater than the CUs for water and for fertilizer applied for a given experimental plot. This may suggest that the uniformity for plant nitrogen uptake be higher than that for water and fertilizer applied. It should be noted that the initial distribution of nutrients in the soil might also affect the plant nitrogen uptake. Fig. 6 demonstrates the relationship between yield and fertilizer applied on 30 March 2000 at collector location above the canopy for three plots. The ®gure indicates fertilizer applied measured on a 3 m 3 m grid had little effect on crop yield even though yield increased slightly with fertilizer applied.
10
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Fig. 5. Christiansen uniformity coefficient for total nitrogen content of plant stem as function of (a) CU for fertilizer applied on 30 March 2000 and (b) arithmetic mean of individual CUs during the irrigation season of winter wheat.
Crop yield and its uniformity as function of CU for fertilizer applied on 30 March 2000 is presented in Figs. 7 and 8, respectively. The value of CU for fertilizer applied signi®cantly affects neither crop yield nor CU for crop yield. 4. Summary and remarks The ®eld experiments conducted in this study demonstrated that uniformity of sprinkled water and fertilizers measured on a 3 m 3 m square grid had little impact on crop yield. A possible explanation is that improvement of water uniformity through canopy interception (Li and Rao, 2000), redistribution of sprinkled water in the soil, rooting system of the wheat
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
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Fig. 6. Relationship between crop yield and fertilizer applied on 30 March 2000 for the three experimental plots.
12
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Fig. 7. Crop yield as function of CU for fertilizer applied on 30 March 2000.
reduced the negative in¯uence of nonuniformly applied water and fertilizers on yield. Stem¯ow redirects to the plant roots, which would also impact crop performance. Furthermore, a uniform precipitation of 65 mm during the growing season of 1999± 2000, accounting for approximate 15% of the crop water requirement of 420 mm, also reduced the negative effects of nonuniform water application on yield. Through ®eld experiments, Mateos et al. (1997) also demonstrated sprinkler irrigation uniformity has an unimportant impact on crop yield. Therefore, the current standard for sprinkler uniformity
Fig. 8. Christiansen uniformity coefficient for crop yield as function of CU for fertilizer applied on 30 March 2000.
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
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(for example, the target CU is equal to or higher than 75% in China) is high enough for obtaining a reasonable crop yield in dry sub-humid regions. Acknowledgements This study was ®nancially supported by the National Natural Science Foundation of China (no. 59979027 and no. 50179037). References Burt, C., O'Connor, K., Ruehr, T., 1998. Fertigation, Irrigation Training and Research Center, California Polytechnic State University, San Luis Obispo, CA, USA. Christiansen, J.E., 1941. The uniformity of application of water by sprinkler systems. Agric. Eng. 22, 89±92. Letey, J., Vaux Jr., H.J., Feinerman, E., 1984. Optimum crop water application as affected by uniformity of water infiltration. Agronom. J. 76, 435±441. Li, J., 1998. Modeling crop yield as affected by uniformity of sprinkler irrigation system. Agric. Water Manage. 38, 135±146. Li, J., Rao, M., 2000. Sprinkler water distributions as affected by winter wheat canopy. Irrig. Sci. 20 (1), 29±35. Mantovani, E.C., Villalobos, F.J., Orgaz, F., Fereres, E., 1995. Modeling the effects of sprinkler irrigation uniformity on crop yield. Agric. Water Manage. 27, 243±257. Mateos, L., Mantovani, E.C., Villalobos, F.J., 1997. Cotton response to nonuniformity of conventional sprinkler irrigation. Irrig. Sci. 17, 47±52. Seginer, I., 1978. A note on the economic significance of uniform water application. Irrig. Sci. 1, 19±25. Seginer, I., 1983. Irrigation uniformity effect on land and water allocation. Trans. ASAE 26, 116±122. Stern, J., Bresler, E., 1983. Nonuniform sprinkler irrigation and crop yield. Irrig. Sci. 4, 17±29. Varlev, I., 1976. Evaluation of nonuniformity in irrigation and yield. J. Irrig. Drain. Div. ASCE 102, 149±164. Warrick, A.W., Gardner, W.R., 1983. Crop yield as affected by spatial variations of soil and irrigation. Water Resour. Res. 19, 181±186.
Field evaluation of crop yield as affected by nonuniformity of sprinkler-applied water and fertilizers Jiusheng Lia,*, Minjie Raob a
Department of Irrigation and Drainage, China Institute of Water Resources and Hydropower Research, Beijing 100044, China b Agrometeorology Institute, Chinese Academy of Agricultural Sciences, Beijing 100081, China Accepted 19 August 2002
Abstract The determination of target uniformity for sprinkler irrigation system should consider the impacts of nonuniformity of water and fertilizers on crop yield. Field experiments were therefore conducted in north China plains to address the impacts of nonuniformly applied water and fertilizers on winter wheat yield. Irrigation water and fertilizers were applied through a solid set sprinkler system. Three experimental plots were used with seasonal Christiansen uniformity coef®cients (arithmetic mean of individual CUs) ranging from 62 to 82%. Each plot was divided into 3 m 3 m grids. Sprinkler water depth and concentration of fertilizer solution for each grid was measured both below and above the canopy for each individual irrigation event. The spatial distribution of soil moisture for each experimental plot was also measured periodically to determine irrigation times and amounts. On harvest, grain yield and total nitrogen content of plant stems were measured for each grid. The experimental results showed that the uniformity of fertilizer applied increased with sprinkler water uniformity. The distributions of both fertilizers and water applied through sprinkler system can be represented by a normal distribution function. Field experiments also demonstrated that the uniformity of sprinkler-applied water and fertilizers has insigni®cant effect on winter wheat yield for the studied uniformity range. The current standard for sprinkler uniformity (for example, the target CU is equal to or higher than 75% in China) is high enough for obtaining a reasonable crop yield in dry sub-humid regions. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Sprinkler irrigation; Fertigation; Uniformity; Winter wheat; Yield
* Corresponding author. Tel.: 86-10-684-15823; fax: 86-10-684-15823. E-mail address: [email protected] (J. Li).
0378-3774/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 2 ) 0 0 1 2 3 - 3
2
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
1. Introduction The relationship between crop production and evapotranspiration, called the crop water production function, is important to agronomists, engineers, economists, and water resource planners. This importance is currently accentuated due to competition among users, declining groundwater reserves, various legal institutions, and degradation in water quality. There are many factors affecting the crop production function. In addition to evapotranspiration or evapotranspiration de®cits, sprinkler uniformity also affects the crop water production function. Stern and Bresler (1983) evaluated the impacts of sprinkler irrigation uniformity on soil water variability and yield of sweet corn by ®eld experiments. Letey et al. (1984) provided a general method for analyzing the effect of in®ltration water uniformity on crop yield and concluded that ignoring irrigation uniformity leads to underestimates of the optimum irrigation amount. Warrick and Gardner (1983) attempted to combine the effects of irrigation application variability and soil spatial variability distributions using the joint probability distributions that can be determined by convolution or by Monte Carlo methods. Other researchers addressing the interaction effects of irrigation amount and the uniformity of irrigation or in®ltrated water on crop yield include Varlev (1976) and Seginer (1978, 1983). Recently, Mantovani et al. (1995) simulated the effects of sprinkler uniformity on crop yield by assuming a uniform sprinkler water distribution and a linear crop water production function. Li (1998) presented a model that relates yield response to evapotranspiration de®cits at special growth stages to evaluate the impacts of uniformity on crop yield. Comparing the reported simulation results with those obtained from ®eld experiments leads one to ®nd there exists signi®cant differences between them. Field experiments (Mateos et al., 1997; Li and Rao, 2000) showed that sprinkler uniformity had little effect on crop yield, but simulation (Mantovani et al., 1995; Li, 1998) suggested that crop yield increased clearly with increasing sprinkler uniformity. Further ®eld experimental studies are obviously necessary to verify and modify the existing simulation models. Sprinkler irrigation system can be used for fertigation, but we have little knowledge of the effects of fertigation on crop performance. The primary objectives of this research were to investigate the response of crop performance to nonuniformly applied water and fertilizers through ®eld experiments and to give recommendations for the design of sprinkler irrigation systems. 2. Materials and methods 2.1. Experimental field The experiments were conducted at the Experimental Station of Agrometeorology Institute, Chinese Academy of Agricultural Sciences in Beijing, north China plains. The experimental area, located in the temperate monsoon climatic zone, is in a dry sub-humid region with an annual mean precipitation of 550 mm. Between 70 and 80% of the precipitation occurs between July and September. An automated weather station was installed 80 m from the experimental ®eld to monitor wind speed and direction, air
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
3
temperature, humidity and precipitation every 15 min during the irrigation. The soil was a clay loam with a bulk density of 1.4±1.5 g/cm3 and a ®eld capacity of 0.32 cm3/cm3. Winter wheat (Triticum aestivum L.) was sown on 5 October 1999 with row spacing of 25 cm and sowing rate of 127.5 kg/ha. Pest and disease control followed the standard practices in this area. Three plots, designed as high uniformity, medium uniformity and low uniformity (referred to as plots 1±3 below, respectively), were used in the experiments. Each plot was 15 m 15 m in size, and sprinklers mounted on the 180 cm height risers were installed at each corner of the plot. The central of 12 m 12 m in each plot was selected as the observed area to avoid interference between adjacent plots. 2.2. Water measurements The 12 m 12 m observed area in each plot was divided into a grid of 16 3 m 3 m subplots. Catch cans of 112.8 mm diameter and 250 mm height were placed at the center of each subplot on the ground surface to measure sprinkler water distribution below the canopy. Since the developing winter wheat canopy has a potential to affect the distribution of sprinkler water, catch cans were also located above the canopy. A total of 16 cans with the same size as those on the ground surface were also placed in the center of the 3 m 3 m grids. The top of the above canopy cans was 85 cm above the ground surface. The water collected in both above and below the canopy cans was measured 15 min after the designed amount of water was applied. Catch can data free of crop interference were used in this article. Christiansen uniformity coef®cient de®ned in Eq. (1) was used to calculate the uniformity of both daily and cumulative application depths (Christiansen, 1941). ! PN xj i1 jxi CU 1 100 (1) Nx where CU is Christiansen uniformity coefficient; xi is the ith water application depth; and P N xj is the sum of the absolute deviation from the mean, x, of all N observations. i1 jxi 2.3. Crop measurements One square meter of winter wheat for each subplot was harvested on 12 June 2000 and the dry grain yield was recorded. The yield at the position of ground can was represented by the yield of 1 m2 sample. Plant stems for each 3 m 3 m subplot were sampled when winter wheat was harvested. The sample was digested by H2SO4±H2O2 and the total nitrogen of the solution was determined by distillation method to obtain the total nitrogen content of the plant stems for each subplot. Christiansen uniformity coef®cients for total nitrogen content of plant stems were also calculated by using of Eq. (1). 2.4. Irrigation Soil water contents from 30 to 100 cm depth were measured weekly by a neutron probe with an interval of 10 cm, but the contents at top 30 cm were measured by a time domain
4
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Table 1 Summary of irrigation depth collected by above catch-cans (AW), Christiansen uniformity coefficients (CU) and date of each of the five irrigation events Plot 1
Plot 2
Date 30 13 28 11 30
AW (mm) a
March Aprila April May May
Totalb
CU (%)
Date
38.1 31.7 52.8 48.5 56.3
88 71 82 88 81
30 13 28 11 30
227.4
82c
Total
March April April May May
Plot 3 AW (mm)
CU (%)
Date
35.8 31.6 47.1 44.7 45.1
76 76 74 67 70
30 13 27 12 26
204.3
72c
Total
March April April May May
AW (mm)
CU (%)
34.2 44.0 45.6 46.0 42.6
59 65 60 69 57
212.4
62c
a
Fertigation applied. Total crop water use from other sources (rainfall, soil water and germination and frozen irrigation) was 193, 204, and 226 mm for plots 1±3, respectively. c Seasonal Christiansen uniformity coefficient, is defined as arithmetic mean of individual CUs during the whole irrigation season. b
re¯ectometry (TDR). Five neutron access tubes were installed in the diagonals for each plot. TDR sample was about 10 cm around the access tube. Soil water content for each plot was represented by the mean of the ®ve observed positions. Irrigation was applied when average soil water content within top 40-cm layer depleted to 65% of ®eld capacity (about 45 mm depletion). A total of ®ve irrigation events were used between 30 March and 31 May 2000. Irrigation dates, amounts and CU values are summarized in Table 1. Impact sprinklers with nozzle diameter of 4 mm, namely LEGO 80B2, were used in the experiments. Four sprinklers applied water to an experimental plot using a rotation angle of approximately 908 during irrigation. Sprinklers were operated at pressures of 150, 200 and 300 kPa for low, medium and high uniformity plots (plots 1±3), respectively. For all the experiments, the average application rate ranged from 8 to 14 mm/h, and no surface runoff was found in the experiments. 2.5. Fertilizer measurements Fertigation was conducted with the irrigation events of 30 March and 13 April 2000 (Table 1). For the fertigation on 30 March, ammonium carbonate (N content of 15%) was applied with a rate of 22.2 g/m2. For the fertigation of 13 April, ammonium sulphate (N content of 21%) and urea (N content of 45%) were mixed at a rate of 1 to 3 and applied with the rates of 4.4 and 13.3 g/m2, respectively. The duration of fertigation was determined by the rule of quarter-half-quarter (Burt et al., 1998). Electric conductivity (EC) of fertilizer solution caught in each can was tested by a portable conductivity probe as fertigation was completed. The relationships between concentration of fertilizer solution and EC were calibrated for the fertilizers used prior to fertigation and the following equations were obtained: C 1:11EC
860 for ammonium carbonate solution
n 10; r 2 0:999
(2)
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
C 0:45EC
443 for ammonium sulphate solution
n 9; r 2 0:993
5
(3)
where C is the concentration of fertilizer solution (mg/l), ranging from 0 to 1800 mg/l; EC is the electric conductivity of fertilizer solution (ms/cm); n is the number of samples and r is correlative coefficient. Eqs. (2) and (3) were used to determine the concentration of fertilizer solution for each catch can and the amount of fertilizer applied for each subplot was determined from the concentration of fertilizer solution and the water volume caught in the catch can. Christiansen uniformity coef®cients for fertilizer solution and fertilizer amount were also calculated by using Eq. (1). 3. Results and analysis 3.1. Uniformity of fertigation Fig. 1 compares the cumulative frequency distributions between fertilizer applied and water depth for the fertigation on 30 March 2000. Fertilizer applied and water depth are normalized (value/mean) in the ®gure. The amount of fertilizer applied produced an approximately similar cumulative frequency distribution to water depth. Fig. 1 also indicates that both fertilizers applied and water depth can be represented by a normal distribution function. Examining the standard deviation values presented in Fig. 1, one can ®nd that fertilizer applied gave a lower standard deviation than water depth for medium and low uniformity experimental plots (plots 2 and 3). Fig. 2 compares Christiansen uniformity coef®cients (CU) for water application, concentration of fertilizer solution and fertilizer applied for the fertigation event on 30 March 2000. Fig. 2 indicated that a higher CU for water application produced a more uniform distribution of fertilizer. For example, as water application CU increased from 59% for plot 3 to 88% for plot 1, CU for fertilizer applied increased from 68 to 84%. There was a signi®cant difference for CUs of water application among the three experimental plots (88% for plot 1, 76% for plot 2 and 59% for plot 3), but the three plots produced an approximate CU value for concentration of fertilizer solution (83% for plot 1, 90% for plot 2 and 83% for plot 3). This suggests that water application uniformity have a little effect on CU for concentration of fertilizer solution. Examining Fig. 2 can also lead one to ®nd that CU for fertilizer applied was greater than CU for water application for medium and low uniformity plots (plots 2 and 3). 3.2. Effects of nonuniformity of sprinkler applied water and fertilizers on crop yield The cumulative frequency distributions of cumulative water depth during irrigation season and yield for the three experimental plots are illustrated in Fig. 3. One can ®nd from Fig. 3 that both cumulative irrigation depth and crop yield can be represented by a normal distribution function. Water application depth varied in a larger range than yield, especially for the low uniformity level plot (plot 3). Table 2 summarizes the mean and CU values for several components of yields. Analyzing the data indicated in Table 2, one can ®nd that yield components for all three
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J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Fig. 1. Cumulative frequency distributions for fertilizer applied and water depth measured above canopy for fertigation on 30 March 2000 for the three experimental plots. The lines represent normal distribution functions.
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
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Fig. 2. Comparison of Christiansen uniformity coefficients for water application, concentration of fertilizer solution and fertilizer applied for fertigation on 30 March 2000.
plots gave a CU value greater than 90%, even though the arithmetic mean of individual CUs of irrigation depth (seasonal CU) varied from 62 to 82% (Table 1). The relationships between crop yield and arithmetic mean of individual CUs and CU for cumulative irrigation depth during irrigation season are illustrated in Fig. 4. The data obtained from the ®eld experiments conducted in 1998±1999 (Li and Rao, 2000) are also shown in the ®gure. Fig. 4 clearly indicated that sprinkler uniformity CU has an insigni®cant impact on crop yield. Plant nitrogen uptake is mainly affected by the spatial distributions of water and fertilizer applied through sprinkler system. Fig. 5a and b shows Christiansen uniformity coef®cients for total nitrogen content of plant stem on harvest as function of CU for fertilizer applied on 30 March 2000 and of seasonal CU for water application. It can be seen from Fig. 5a that the uniformity for total nitrogen of plant stem increased with the uniformity for fertilizer applied. A greater value of seasonal uniformity coef®cient of water Table 2 Summary of mean and Christiansen uniformity coefficients (CU) for yield components of the three experimental plots Plot
Effective ears
Seeds per ear
Weight per 1000 grainsYield
Mean (ear/m ) CU (%)
Mean (g)
CU (%)
Mean (g)
CU (%)
Mean (t/ha)
CU (%)
350.5 324.1 371.7
49.6 48.8 50.5
95 93 94
48.2 48.1 46.1
96 97 95
6.98 6.43 7.02
94 93 94
2
1 2 3
91 94 92
8
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Fig. 3. Cumulative frequency distributions for cumulative irrigation depths during the irrigation season and winter wheat yields for the three experimental plots. The lines represent normal distribution functions.
J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
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Fig. 4. Crop yield as function of (a) arithmetic mean of individual CUs, and (b) CU of cumulative water depth during the irrigation season of winter wheat, for field experiments conducted in 1998±1999 and 1999±2000.
application also produced a more uniform distribution of total nitrogen content of plant stem (Fig. 5b). Fig. 5a and b also indicated CU for total nitrogen content of plant stem was greater than the CUs for water and for fertilizer applied for a given experimental plot. This may suggest that the uniformity for plant nitrogen uptake be higher than that for water and fertilizer applied. It should be noted that the initial distribution of nutrients in the soil might also affect the plant nitrogen uptake. Fig. 6 demonstrates the relationship between yield and fertilizer applied on 30 March 2000 at collector location above the canopy for three plots. The ®gure indicates fertilizer applied measured on a 3 m 3 m grid had little effect on crop yield even though yield increased slightly with fertilizer applied.
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J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Fig. 5. Christiansen uniformity coefficient for total nitrogen content of plant stem as function of (a) CU for fertilizer applied on 30 March 2000 and (b) arithmetic mean of individual CUs during the irrigation season of winter wheat.
Crop yield and its uniformity as function of CU for fertilizer applied on 30 March 2000 is presented in Figs. 7 and 8, respectively. The value of CU for fertilizer applied signi®cantly affects neither crop yield nor CU for crop yield. 4. Summary and remarks The ®eld experiments conducted in this study demonstrated that uniformity of sprinkled water and fertilizers measured on a 3 m 3 m square grid had little impact on crop yield. A possible explanation is that improvement of water uniformity through canopy interception (Li and Rao, 2000), redistribution of sprinkled water in the soil, rooting system of the wheat
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Fig. 6. Relationship between crop yield and fertilizer applied on 30 March 2000 for the three experimental plots.
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J. Li, M. Rao / Agricultural Water Management 59 (2003) 1±13
Fig. 7. Crop yield as function of CU for fertilizer applied on 30 March 2000.
reduced the negative in¯uence of nonuniformly applied water and fertilizers on yield. Stem¯ow redirects to the plant roots, which would also impact crop performance. Furthermore, a uniform precipitation of 65 mm during the growing season of 1999± 2000, accounting for approximate 15% of the crop water requirement of 420 mm, also reduced the negative effects of nonuniform water application on yield. Through ®eld experiments, Mateos et al. (1997) also demonstrated sprinkler irrigation uniformity has an unimportant impact on crop yield. Therefore, the current standard for sprinkler uniformity
Fig. 8. Christiansen uniformity coefficient for crop yield as function of CU for fertilizer applied on 30 March 2000.
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(for example, the target CU is equal to or higher than 75% in China) is high enough for obtaining a reasonable crop yield in dry sub-humid regions. Acknowledgements This study was ®nancially supported by the National Natural Science Foundation of China (no. 59979027 and no. 50179037). References Burt, C., O'Connor, K., Ruehr, T., 1998. Fertigation, Irrigation Training and Research Center, California Polytechnic State University, San Luis Obispo, CA, USA. Christiansen, J.E., 1941. The uniformity of application of water by sprinkler systems. Agric. Eng. 22, 89±92. Letey, J., Vaux Jr., H.J., Feinerman, E., 1984. Optimum crop water application as affected by uniformity of water infiltration. Agronom. J. 76, 435±441. Li, J., 1998. Modeling crop yield as affected by uniformity of sprinkler irrigation system. Agric. Water Manage. 38, 135±146. Li, J., Rao, M., 2000. Sprinkler water distributions as affected by winter wheat canopy. Irrig. Sci. 20 (1), 29±35. Mantovani, E.C., Villalobos, F.J., Orgaz, F., Fereres, E., 1995. Modeling the effects of sprinkler irrigation uniformity on crop yield. Agric. Water Manage. 27, 243±257. Mateos, L., Mantovani, E.C., Villalobos, F.J., 1997. Cotton response to nonuniformity of conventional sprinkler irrigation. Irrig. Sci. 17, 47±52. Seginer, I., 1978. A note on the economic significance of uniform water application. Irrig. Sci. 1, 19±25. Seginer, I., 1983. Irrigation uniformity effect on land and water allocation. Trans. ASAE 26, 116±122. Stern, J., Bresler, E., 1983. Nonuniform sprinkler irrigation and crop yield. Irrig. Sci. 4, 17±29. Varlev, I., 1976. Evaluation of nonuniformity in irrigation and yield. J. Irrig. Drain. Div. ASCE 102, 149±164. Warrick, A.W., Gardner, W.R., 1983. Crop yield as affected by spatial variations of soil and irrigation. Water Resour. Res. 19, 181±186.