Research Article
Effect of Different Irrigation Intervals to Drip Irrigated Dent Corn (Zea mays L. indentata) Water-yield Relationship
Department of Field Crops, Faculty of Agriculture, Harran University, 63040 Sanliurfa, Turkey
Annual water flow regimes of rivers determine the possibility of transforming from non-fed to irrigated agricultural practices. When the availability of water resources is a limiting factor, however, success in agriculture cannot be expected even though funds are available for agricultural applications. Development of irrigated agriculture depends not only on sufficient water being available but also the appropriate use of that water.
Salinity and alkalinity may occur if the irrigation programs are not applied properly. There has been recent research on water saving methods, such as irrigation of different parts of crop root area (Kang et al., 1997). Drip irrigation is one these methods and its use has been increasing due to water savings and its positive effects on crop yield. Drip irrigation provides the efficient use of limited water with increased water use efficiency. There has not been enough research to determine irrigation intervals with corn crop. It is possible to achieve optimum quality and quantity of crop production per unit area if a proper irrigation method is applied along with other agronomic activities. Thus, it is necessary to determine proper irrigation techniques and irrigation intervals for each microclimate and each crop species.
The goal of this research was to determine deficit irrigation effect on yield and how different irrigation intervals with drip irrigation affected water use-yield relationships in corn crop and to determine most efficient irrigation time intervals.
Corn responds to high annual water and is grown in irrigated areas (Musick et al., 1990). Decrease in production of corn crop depends upon cultivar used, rainfall and evaporation rate and soil hydraulic conductivity. It is reported that limited water application does not cause decrease in yield and water use efficiency is increased (Shaozhong et al., 2000). Kanber et al. (1990b) determined that the amount of irrigation did not cause increase in yield and indicated that excessive amount of water was unnecessary.
Lamm et al. (1993) reported that grain yield was 780 g m2 when supplemental irrigation of 75 mm to 324 mm rainfall was applied. Four rates of irrigation amount were applied equal to 20, 50, 80 and 110% of evaporation measured by lysimeter, respectively with three different soil series (Pullman, Ulysses and Amarillo) in an arid region. Yields were 389-804, 559-899 and 438-736 g m2 in Pullman, Ulysses and Amarillo series, respectively. Kanber et al. (1990a) found that annual water consumption and irrigation water requirement of second crop corn ranged from 474.2 530.9 mm and 290 427.8 mm, respectively. This study also indicated that annual crop response factor (ky) was 0.98 for second crop corn and the crop required irrigation five times at different crop growth stages.
Cetin (1994) reported maximum yield of 10.15 t ha1 for second crop corn with irrigation applied every five days interval. The yield decreased to 7.71 t ha1 with irrigation applied at 10 days interval. The amounts of irrigation water were 1303 and 970 mm, water consumptions were 1371 and 1037 mm and maximum monthly water requirements were in August with irrigation treatments of five days and ten days intervals, respectively.
This study was conducted during 1998 and 1999 at the Field Research Facility of the Faculty of Agriculture at Harran University, Sanliurfa, Turkey. The experimental field is located in Harran Plain (altitude:465 m; 37°08' north and 38°46'east) where the climate varies from arid to semi-arid. The texture of the soil of experimental field was clay. Field capacity of the soil was between 32.71 and 33.84% on dry basis (Table 1), permanent wilting point was between 21.18 and 22.55% and bulk density of the soil was between 1.37 and 1.41 g cm3 (Table 1). In the months of June, July and August for both treatment years, the temperatures were all above 40°C while the relative humidity was below 50%. Except August 1999, no rainfall was observed in July and September of the treatment years and the rainfall seen in June is fairly low. During the time period for the treatments, the weather conditions were hot, dry and the relative humidity was very low (Table 2).
In this study, Dracma hybrid corn (Zea mays L. indentata) was used as the crop material. The experiment was laid out in a randomized block design with three replications. Each plot consisted of four rows of 5 m in length. The plants were grown 70 cm apart between the rows with 20 cm spacing in each row. The seeds were sown on 21.06.1998 (Day Of Year (DOY:172)) in the first year and on 26.06.1999 (DOY:177) in the second year. At sowing, 80 kg ha1 pure N and P (20-20-0 composite) was applied to each plot and this was followed by 160 kg ha1 N as urea when the plant reached to 30-40 cm height. Ears from two rows in the centre of each plot (50 plants) were harvested manually. The data obtained from the experiments were analysed with analysis-of-variance (ANOVA) and least significant difference (LSD) tests (Cochran and Cox, 1957) using MSTATC statistical analysis software package.
Irrigation treatments: First irrigation water was applied to all treatments using a sprinkler irrigation system during the experiments in 1998 and 1999 to bring the soil water content in 0-90 cm soil depth up to level of field capacity. Irrigation treatments were started using drip irrigation system when the water content of soil decreased to 50% of available soil water.
Irrigation water was applied as 100% of evaporation of Class A Pan in the 2 day irrigation frequency (ID2 treatment), 90% of evaporation in the 4 day irrigation frequency (ID4 treatment), 80% of evaporation in the 6 day irrigation frequency (ID6 treatment) and 70% of evaporation in the 8 day irrigation frequency (ID8 treatment).
The amount of required irrigation water was determined by Class A Pan evaporation every day (Kanber, 1984). The total evaporation from Class A Pan was measured with a manual limnimeter which has 0.1 mm accuracy. These measurements were checked with the readings from the water flow meters mounted in every plot.
Table 1: | Some of chemical and physical properties of experimental field soil |
Table 2: | Monthly climate data during the growth period of corn in 1998 and 1999 in Sanliurfa |
: Data collected from Sanliurfa Meteorological Station |
Crop water consumption in the treatments was calculated using Eq. 1 (Garrity et al., 1982; James, 1988):
(1) |
where; ET is crop water consumption (mm), P is rainfall (mm), I is irrigation water (mm), R is surface runoff (mm), Dp is deep percolation (mm), ΔS is soil water content variation in crop root depth (mm).
In this study, deep percolation (Dp) and surface runoff (Rf) in Eq. 1 were assumed to be negligible because the amount of irrigation water was not increased to above the field capacity as a result of drip irrigation and deficit irrigation. It approached field capacity only at the 2 day irrigation frequency.
The amount of irrigation water was calculated using Eq. 2:
(2) |
where; I is the amount of irrigation water (mm), A is plot area (m2), Epan is cumulative water depth from Class A Pan based on irrigation frequencies (mm), Kcp is crop pan coefficient determined as 100% of total evaporation of Class A Pan in the 2 day irrigation frequency (Kcp1), 90% of total evaporation of Class A Pan in the 4 day irrigation frequency (Kcp2), 80% of total evaporation of Class A Pan in the 6 day irrigation frequency (Kcp3), 70% of total evaporation of Class A Pan in the 8 day irrigation frequency (Kcp4) and CAI is canopy area index which was assumed to be 1.
During the experimental period, the variation of soil water content at 0-30, 30-60 and 60-90 cm soil depths in each treatment plot was continuously determined by gravimetric method for calculating the actual evapotranspiration (ETa).
Total Water Use Efficiency (TWUE), defined as the ratio of grain yield per hectare to seasonal water consumption and Irrigation Water Use Efficiency (IWUE), defined as the ratio of grain yield per hectare to the amount of irrigation water, were calculated using the methodology provided by Tanner and Siclair (1983).
TWUE = (Ya/ETa)*100 IWUE = (Ya/I)*100 |
The water use-yield relationship was determined using the Stewart Model in which dimensionless parameters in relative yield reduction and relative water consumption are used (Doorenbos and Kassam, 1979):
(3) |
where, Ya is actual yield (t ha1), Ym is maximum yield (t ha1), Ya/Ym is relative yield, 1-(Ya/Ym) is decrease in relative yield, ETa is actual crop water consumption (mm), ETm is maximum crop water consumption (mm), ETa/ETm is relative crop water consumption, 1- (ETa/ETm) is decrease in relative crop water consumption, ky is yield response factor defined as decrease in yield with respect to per unit decrease in ET.
Water use-yield relationship: Yield, decrease in relative yield and decrease in relative water use, amount of irrigation, water saving rates and yield response factors for corn crop irrigated with drip irrigation system at different irrigation intervals are presented in Table 3. Seasonal water consumption of treatments (ETa) and the amounts of irrigation water was different in each treatment. Maximum seasonal water consumption (ETm) was 1292 mm and maximum amount of applied water was 1116 mm in 2 day irrigation treatment (ID2), minimum ETa was 909 mm and minimum amount of applied water was 814 mm in 8 day irrigation treatment (ID8) during the first year experiments.
In the second year, the values were 1306 mm as maximum Etm and maximum applied water was 1206 mm in ID2 treatment, minimum ETa was 923 mm and minimum applied water was 843 in ID8 irrigation treatment. Amount of applied water to other treatments ranged between these values.
Table 3: | Relationship between the decrease in relative water use and decrease in relative yield and yield response factor for corn crop irrigated by drip irrigation system |
Table 4: | Grain yield1 irrigated by drip irrigation at different irrigation frequencies and LSD groups |
1 : Grain yield is calculated at 15% kernel moisture, **: p<0.01, : There is no statistical differences among same letter at, 0.05 level according LSD test |
Table 5: | Total Water Use Efficiency (TWUE) and Irrigation Water Use Efficiency (IWUE) values for corn irrigated by a drip system at different frequencies |
Fig. 1: | Grain yield values at different irrigation frequencies in 1998 and 1999 |
The reason for this was existing water content in the soil before the first irrigation application and the climatical parameters.
The amount of applied water affected grain yield (Table 4). Grain yield increased with the amount of applied water and ETa increased as seen in ID2 treatment. Findings in the literature were in accord with the results obtained in this study, the rate of decrease in yield was not the same with respect to per unit decrease in water applied (Yaron, 1971).
Decrease in relative yield was 3.77% in 2 day irrigation treatment group in 1998. Maximum yield was found to be 14.07 t ha1 in 4 day irrigation treatment group in which the water saving rate was 11.64% (Fig. 1). The rates of the decrease in relative yield were 19.47% and 27.01% in 6 day and 8 days irrigation treatment groups in 1998.
In 1999, the rate if the decrease in relative yield was 7.82% in the 2 day irrigation treatment group in which the amount of water applied was the maximum, 1206 mm.
Fig. 2: | Irrigation water (I) and fresh ear yield (Ya) relationship. Vertical bars indicate standard errors of the mean |
Fig. 3: | Fresh ear yield (Ya) and seasonal water consumption (Eta). Vertical bars indicate standard errors of the mean |
Maximum yield, 13.30 t ha1, was obtained from 4 day irrigation treatment group which used 9.4% less water than ID2 treatment. This result was supported by Cetin (1994) who recommended ones irrigation every 5 day time interval for second crop corn. The rates of the decrease in relative yield were 15.41 and 28.35% in ID6 and ID8 treatment groups, respectively. Moreover, the rates of water saving were determined to be 22.33 and 30.09% for 6 day and 8 day irrigation treatment groups, respectively. Zhang and Davis (1990) reported that yield was reduced as the crops were under drought stress for a long time.
Increase water deficit resulted in decrease in crop yield. Crop roots take up nutrients and the water from upper parts of the soil under the conditions of low water stress or non-stress. When the crops experience the water stress, their roots penetrate deep in the soil to withdraw water and crop nutrients (Rhoads and Bennett, 1990). Better aeration in the root zone, better utilization of nutrients and efficient use of soil water by the crops might cause increased yield in ID4 treatment group compared to ID2 treatment group.
Relationship between the amount of irrigation water, seasonal water consumption and grain yield: Second order polynomial relationship was found between the amount of water applied (I) and grain yield (Ya) in both years from the regression analysis. The equation for the relationship was Y = -0.0048I2+10.562I-4389.2 with R2 = 0.82 in 1998 and the relationship was explained by the equation Y = -0.0056I2+12.344I-5471.2 with R2 = 0.97 in 1999 (Fig. 2).
A linear relationship was found between seasonal water consumption (Eta) and grain yield (Ya) in both years. The equations for the relationship were Ya = 0.981ETa+137.8 (R2 = 0.92) and Ya = 0.8028ETa+257.85 (R2 = 0.63) for 1998 and 1999 experiments, respectively (Fig. 3). A linear relationship have been reported between crop yield and seasonal water consumption (Mogenson et al., 1985; Musick et al., 1994).
Water use efficiencies: Total Water Use Efficiency (TWUE) and Irrigation Water Use Efficiency (IWUE) were different based on the treatments and years (Table 5). TWUE were 1.05, 1.15, 1.10 and 1.13 kg m3 for the treatments ID2, ID4, ID6 and ID8, respectively in the first year while the values were 0.94, 1.15, 1.02 and 1.03 kg m3 for the treatments ID2, ID4, ID6 and ID8, respectively, in the second year. It was observed that TWUE was increased as the amount of irrigation water increased in both years. IWUE values were ranged between 1.21 and 1.43 kg m3 for the first year and the values were between 1.07 and 1.22 kg m3 in the second year. IWUE values of 1.9 kg m3 (Lyle and Bordovsky, 1995) and 1.25-1.46 kg m3 (Musick and Dusek, 1980) were reported. In a different study conducted in Cukurova regions, IWUE value of 1.38-1.80 kg m3 and TWUE values of 0.87-3.19 kg m3 were stated (Koksal, 1995). In addition, IWUE values of 1.02-2.43 kg m3 and TWUE values of 0.22-1.25 kg m3 were reported in a study conducted in Cukurova region by Gencoglan (1996). Furthermore, IWUE values of 0.57-0.795 kg m3 were found for corn crop in Harran Plain conditions (Cetin, 1994). The findings obtained in this current research are in good agreement to those values reported in the previous literature for corn crop.
Crop response factor (ky): Crop response factor, ky, indicates the relationship between the decrease in relative water use and the decrease in relative yield. It shows the sensitivity of yield with respect to the decrease in water use. In other words, it explains the decrease in yield caused by per unit decrease in water use. Adjusted yield (Yadj) was calculated using water consumption and yield relationship when maximum water consumption and maximum yield was not obtained. Adjusted yield values were used to determine relative decrease in yield.
Crop response factor was 0.90 (ID6 and ID8) for the first year and were 0.88 (ID6) and 0.93 (ID8) for the second year in the experiments (Table 3). Based on the research results, 11.64% water savings in irrigation water and 5% less ETa resulted in maximum 14.07 t ha1 yield in ID4 treatment group in the first year. For the same treatment group in the second year, 9.4% water savings and 11% less ETa resulted in maximum 13.30 t ha1 yield. These results were in accord with the findings reported in the previous literature. For instance, ky value of 1.25 (Doorenbos and Kassam, 1979) was reported for total growing season of corn crop. In addition, ky values of 0.97 (Yildirim et al., 1996), 0.98 (Kanber et al., 1990a) and 0.85 (Koksal, 1995) were found under the application of equal water limiting conditions during the growing season of corn crop.
In conclusion, based on the results obtained from this research, an irrigation time interval of 4 day, with 90% ET water application by a drip system, could be recommended for corn in semi-arid regions similar to that in Turkey where the research was conducted.