Olanike Aladenola 1* and Chandra Madramootoo 1. leaf area index, stomatal conductance against CWSI resulted in highly significant

Transcription

1 Paper # NABEC/CSBE Effect of Different Water Application on Yield and Water Use of Bell Pepper under Greenhouse Conditions Olanike Aladenola 1* and Chandra Madramootoo 1 1* & 1 Department of Bioresource Engineering, McGill University Macdonald campus, Lakeshore road, Montreal Qc., Canada. Abstract. Application of proper quantity of water to crops at the right time is required for optimal yield. The effect of different water applications on yield and the stress threshold of greenhouse grown bell pepper (Capsicum annuum L.) cultivar red knight were tested. The study was conducted with four irrigation treatments using a randomized complete block design. Highest marketable yield was obtained with 1.2 Epan. A regression equation between crop water stress index (CWSI) and crop yield was developed. Regressions of leaf area index, stomatal conductance against CWSI resulted in highly significant polynomial curves with coefficients of determination (R 2 ) = 0.99 and 0.96 respectively. Thus, CWSI, LAI and stomatal conductance monitoring can be useful as a tool for precise irrigation scheduling and can be integrated into an agricultural water demand model. A Community of Keywords. Bell pepper, Greenhouse, Irrigation, Pan Evaporation. For presentation at NABEC-CSBE/SCGAB 2012 Joint Meeting and Technical Conference Northeast Agricultural & Biological Engineering Conference Canadian Society for Bioengineering Lakehead University, Orillia, Ontario July 15-18, 2012

2 Introduction Canadian vegetable growers reported sales of $659 million dollars in 2010 with two provinces - Ontario and Quebec accounting for more than 80% of the vegetable sales (Statistics Canada, 2011). Canada s high value vegetable production depends on irrigation to sustain their cultivation and maintain/improve yields. Improving the efficiency of irrigation which accounts for major water withdrawals for agriculture is important for securing current and future food supplies for the growing population (Johansson, 2000). Scheduling irrigation water is very critical for obtaining optimal vegetable yields (Madramootoo, 2006; Bernier et al., 2010). For instance bell pepper requires a constant and adequate water supply during the growing season because it is very sensitive to water stress, especially during the establishment period and fruit setting (Yildrim et al., 2012). Irrigation scheduling methods based on pan evaporation (Class-A pan, with pan coefficient) has been used extensively for several crops such as tomato (Imtiyaz et al., 2000), cucumber (Yuan et al; 2006, Wang et al., 2009), bell pepper (Sezen et al., 2006) because of their ease of application and higher degree of adaptability at the farmer s level ( Eliades, 1988; Locascio and Smajstrla, 1996; Sezen et al., 2006). However the effect of 1.2 Epan (T1), 1.0 Epan (T2), 0.80 Epan (T3), and 0.40 Epan (T4) evapotranspiration replenishment on yield and water use of green house grown bell pepper has not been tested. To achieve optimal crop production, irrigation management strategies need to be assessed taking into consideration that irrigation efficiency is achieved with increase in yield and/or water conservation. Irrigation scheduling can be improved by monitoring plant water status by infrared

3 thermometer, which is reported to be precise for determining water stress in crops and should be used for determining when to irrigate (Erdem et al, 2010). Leaves are the primary control interface involved in regulating water loss and understanding the relative influence of leaf transpiration is critical to accurate prediction of crop water use. Leaf surface area is one of the main factors affecting transpiration procedure. One of the criteria of defining the leaf surface area is the leaf area index (LAI) which is the as one-half the total green leaf area (all sided) per unit ground surface area (Chen & Black, 1992a). Also, many researchers agree on the LAI value as an important factor to specify the physiology of a plant. The objectives of this research therefore were to (1) determine the yield, water use and corresponding stress index values of greenhouse grown bell pepper using 1.2 Epan (T1), 1.0 Epan (T2), 0.80 Epan (T3), and 0.40 Epan (T4) replenishment of evapotranspiration. (2) determine the relationship between leaf area index, stomatal conductance and stress index values of bell pepper. Materials and methods Experimental design and irrigation treatments Bell pepper seedlings (cultivar red knight) were grown at the Greenhouse of McGill University Macdonald campus, Ste-Anne-de-Bellevue, QC, Canada in 16 pots in a completely randomized design with four treatments each replicated four times based on 120, 100, 80 and 40% replenishment of crop evapotranspiration (ETc) (Table 1). The treatments had different irrigation amounts which are designed to evaluate the crop's response to irrigation applications, as well as the different threshold of crop water stress index values to schedule irrigation for bell pepper. Irrigation interval was fixed for all treatments. Seeds were sown on 19th January and transplanted on 18th February, Irrigation was uniformly applied to all treatments at the beginning of transplanting until 24th March, 2011 (36 Days After Transplanting) based on 100% replacement of evapotranspiration losses for plants to be well established; thereafter variable irrigation

4 was carried out once in three days until harvest. The soil is loamy sand (77% sand, 19% silt and 5% clay), low in organic matter, 1.40 g/cm 3 bulk density, 19% gravimetric moisture at field capacity and 7% at wilting point determined in the laboratory at 0.33 mbar and 15 mbar respectively. Automatic recorders were used to determine the daily values of greenhouse average temperature, relative humidity and vapour pressure deficit while Class-A evaporation pan (121 cm in diameter and 25.5 cm in depth) was used to determine evaporation during the growing season. Daily crop evapotranspiration was estimated using the pan evaporation data, pan factor and crop coefficient (Doorenbos and Pruitt, 1992). Yield data and water applied for each treatment were statistically analysed using PROC GLM in SAS. Analysis of variance (ANOVA) was conducted and significance of differences among treatments was tested using the Least Significant Difference (LSD) at 5% probability level. Treatment Trt 1 Trt 2 Trt 3 Trt 4 Table 1. Irrigation treatments. Crop Evapotranspiration (ETcrop) Irrigation at 120% of ETcrop Irrigation at 100% of ETcrop Irrigation at 80 % of ETcrop Irrigation at 40 % of ETcrop Measurements Photosynthesis rate and stomata conductance were measured using Li-6400 Portable Photosynthesis System (LICOR Ltd, USA). Leaf area index was measured during the growing period with LI-2000 plant canopy analyser while leaf/canopy temperature was measured using an infrared thermometer (Evett et al., 2000). Four infrared thermometer measurements were carried out when the plants covered about 80% of the pot area from the 14th April to 26th May, The temperature of the non-stressed plants (lower baseline, treatment 1) and fully

5 stressed (upper baseline, treatment 4) was determined from the canopy and ambient air temperature data. The air temperature was obtained from a Campbell scientific psychrometer installed about a meter above the crops while the leaf/canopy temperatures were obtained using Fluke infrared thermometry, model 572 set at emissivity of 0.95, at least two (east and west) viewing directions were considered and the average temperature value taken. The measurement time was between 11:30 am-2:00 pm because it is expected that during these hours, the sun will be striking on all the plants. The mean values of the crop canopy temperature were used for calculating crop water stress index (CWSI). The crops were irrigated manually for maximum and minimum plant water stress conditions. Treatment 4 which had the maximum water deficit was used to determine the fully stressed baseline while treatment 1 suggesting that the irrigation water applied was adequate to meet the full crop water requirements was selected in order to determine non-stressed CWSI baseline. The upper and lower limit values were obtained using the expression by Idso et al., (1981) (equation 1). (1) Where T c canopy temperature ( o C) T a air temperature ( o C) T nws non-water stressed canopy temperature ( o C) T dry water-stressed canopy temperature ( o C) Irrigation water use efficiency (IWUE) and water use efficiency Water use efficiency (WUE, kg/m 3 ) was calculated as the ratio between total yield harvested (kg/ha) and Crop evapotranspiration (ETc, m 3 /ha, as calculated using pan evaporation) and also from the ratio between marketable yield (kg/ha) and crop evapotranspiration (ETc). Irrigation

6 water use efficiency (IWUE) was also calculated as the ratio between total yield harvested (kg/ha) and total volume of water applied (mm). Results Effects of evapotranspiration on crop yield and quality The irrigation at 120% of crop evapotranspiration (ETcrop) (treatment 1) gave significantly highest total yields ( kg/ha), almost twice that obtained under 80% ETc but about 4 times greater than that obtained under very stressed conditions (40% ETc). The marketable yield under treatment 1 remained higher than that obtained in all the other treatments and this treatment gave a higher fruit quality in terms of firmness. Total yield was influenced by the irrigation treatment but this effect was not always significant. For instance, the total yield of treatments 1 and 2 were not statistically significantly different at an alpha level of 0.05 but there was a significant difference when yield from treatment 1 was compared with treatment 3 and 4. Total yield and marketable yield of treatment 4 (which represents a severe water stress condition) were evidently lower than those of the other treatments. The marketable yield from all the treatments is relative to the volume of irrigation water applied. Marketable yield vs. seasonal evapotranspiration (ET) Total water used by the crop for each irrigation treatment ranged between m 3 while ETc was approximately 295 mm for the entire growing season. The relationships of total yield and marketable yield vs seasonal evapotranspiration (ETc) gave a linear relationship similar to what has been found in many other crops such as green bean, sorghum, corn and sweet corn, (Farré and Faci, 2006; Oktem, 2008; Sezen et al., 2008). Treatment 1 (120% ET) gave the highest yield of kg/ha and treatment 4 (40% ET) gave the lowest yield kg/ha. In this experiment, a 20% increment in irrigation water in

7 treatment 1 increased marketable yield by 28% although it had no appreciable effect on the total yield. This may, however, be considered a reasonable value for commercial bell pepper while a 20% or more decrease (treatment 3) had a had a negative effect on the yield and also the quality of the bell peppers (fruits were smaller and firmness was reduced)(table 2). Treatments Yield (kg/ha) Table 2. Yield and water use efficiency Marketable yield (kg/ha) Volume of water applied(m 3 ) IWUE (kg/ m 3 ) WUE (kg/ m 3 ) Trt Trt Trt Trt Crop water use efficiency (WUE), and irrigation water use efficiency (IWUE) were correlated with irrigation water applied (Figure 1). The maximum WUE and IWUE was obtained in Treatment 1 which indicated that water was used most effectively in this treatment, while minimum WUE and IWUE were in Treatment 4. Differences between WUE and IWUE could be due to decreasing applied irrigation water and yield in the other treatments in conformity with other researches (Babik and Elkner, 2002; Gutezeit, 2004). Irrigation under Treatments 1 and 2 significantly increased WUE and IWUE. The higher temperature due to lower water application resulted in low WUE and IWUE under Treatments 3 and 4 (Table 2). Also, it was observed that increased irrigation to 120% ETc would increase bell pepper WUE and IWUE.

8 Figure 1. The effects of irrigation on WUE and IWUE. Relating CWSI with yield, leaf area index and stomatal conductance The CWSI values for the irrigation treatments 1, 2, 3 and 4 are 0.1, 0.3, 0.7 and 1.0 respectively. CWSI values of each treatment were also compared with yield, leaf area index (LAI), transpiration and stomata conductance. In most cases, as the crop water stress increases, the yield is expected to decrease. Figures 2a & b show the curvilinear relationship between the CWSI value and the yield -marketable and total yield (excluding the data from treatment 4 for marketable yield). The relationship may be used to predict yield where the CWSI is known. The relationship between CWSI and leaf area index (LAI) showed that LAI values increased with increasing irrigation water thereby decreased with increasing CWSI and resulted in a decline in yield (Figure 3). This result agrees with many studies for other crops (Turner et al.,

9 1986; Wanjura et al., 1995; Yazar et al., 1999). Water status interacts with stomatal conductance, the transpiration rate decreased with increasing stress, as shown by the increasing stomata conductance and higher CWSI values( Figure 4). This was similar to results found in other crops (Leinonen et al., 2006; Zia et al., 2011).The strong correlation between CWSI and LAI, transpiration and stomatal conductance is an indication of their potential suitability for scheduling irrigation. Figure 2a. Total yield versus CWSI

10 Figure 2b. Marketable yield versus CWSI Figure 3. Relationship between leaf area index (LAI) and CWSI

11 Figure 4. Stomatal conductance and CWSI Discussion Total fruit yield was highly influenced by the total volume of irrigation water applied. The treatment with minimum irrigation water applied had the lowest production. The relationship between the yield and the irrigation water applied was linear, but the functions of yield and CWSI, irrigation water applied and WUE and IWUE were second degree polynomials. The water use efficiency (WUE) and irrigation water use efficiency (IWUE) increased with the increase in irrigation water applied. The CWSI obtained is in agreement with other studies (Alderfasi and Nielsen, 2001; Mehmet et al., 2005; Gontia and Tiwari, 2008). Lowest yield was obtained in Treatment 4 with least irrigation water because of the water stress experienced by the bell pepper. Yields in trt 1>trt2>trt3>trt4 showing that bell pepper is highly sensitive to water stress.

12 However no statistical significance was found between the yields of treatment 1 (120%) and treatment 2 (100% ETc) at an alpha of 5% using SAS software. The marketable yield is considerably higher when bell pepper receives water at 120% ETc. Highest water use efficiency (WUE) and irrigation water use efficiency (IWUE) values were also obtained with this treatment, while the lowest WUE and IWUE values were obtained from treatment with 40% ETc. This finding indicated that WUE and IWUE values increased with the increasing irrigation water and ETc. These results further revealed that the most appropriate irrigation program for fresh market bell pepper with higher marketable yield and WUE under greenhouse condition is when water is applied at 120 % ET and CWSI of 0.1.The CWSI gives a better understanding of the vulnerability and high sensitivity of bell pepper to water stress. The strong relationship between LAI, stomatal conductance and CWSI is an indication of their potential suitability for determining when to irrigate. Conclusion Irrigation timing of bell peppers in the greenhouse might be determined by CWSI values of However further studies are still required to determine the irrigation level that will achieve highest statistically significant irrigation water use efficiency.the equation Y= (CWSI) (CWSI) from the correlation between yield and CWSI can be used for yield prediction. Regressions of leaf area index, stomata conductance against crop water stress index resulted in highly significant polynomial curves with coefficients of determination (R 2 ) = 0.99 and 0.96 respectively. The strong correlation between CWSI and LAI, transpiration and stomatal conductance is an indication of their potential suitability for scheduling irrigation and can thus be integrated into an agricultural water demand model. CWSI can predict when to irrigate, but cannot provide information on how much to irrigate. Hence, it should be used as an adjunct to soil moisture sensors and/or evapotranspiration methods for irrigation scheduling.

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