CHAPTER 3 THE EFFECT OF DIFFERENT IRRIGATION REGIMES ON GROWTH AND YIELD OF THREE HOT PEPPER (Capsicum annuum L.) CULTIVARS
A trial was conducted in the 2004/2005 growing season at the Hatfield Experimental Farm (Pretori) to investigate the effect of different irrigation regimes on the growth, yield and water-use efficiency of different hot pepper cultivars. The aim was to select cultivars that are efficient in water utilization. Treatments were arranged in a randomized complete block strip plot design, with irrigation regime assigned to main plots and cultivars to sub-plots. The three cultivars were Mareko Fana, Jalapeno and Malaga and the three irrigation regimes, based on the percentage depletion of plant available water (DPAW) to 0.6 m soil depth were 25D: 20-25% DPAW; 55D: 50-55% DPAW; and 75D: 70-75% DPAW. Treatments were replicated three times and drip irrigation was utilized. Growth analysis, soil water content and yield measurements were performed.
Fresh fruit yield increased by 77 % and dry fruit yield increased by 64 % by irrigating at 25D as compared to 75D. The significantly higher yield obtained by the 25D irrigation tratment is attributed to its positive effect on fruit number and top dry biomass production. Cultivar Mareko Fana (3.63 t ha-1) out-yielded Jalapeno (3.44 t ha-1) and Malaga (2.11 t ha-1) by 5 and 71 %, respectively in dry fruit yield. Higher fruit fresh yield was recorded for Jalapeno (29.28 t ha-1), followed by Mareko Fana (21.49 t ha-1) and Malaga (6.90 t ha-1). The significant yield differences among the varieties, despite the fact that comparable top dry matter yields were produced by all varieties, may be explained by the fact that the variety with highest yield (Mareko Fana) partitioned more of its assimilates (55%) to fruits, while the variety with lowest yield (Malaga) accumulated only 37% of its assimilates in fruit on average. Average dry fruit mass and succulence were significantly affected by cultivar differences, but not by irrigation regime. Fruit number per plant was significantly affected by irrigation regime and cultivar differences. Jalapeno, a cultivar that matured early and with high harvest index, gave higher water-use efficiency in terms of fresh- (40.4 kg ha-1 mm-1) and dry- (4.9 kg ha-1 mm-1) fruit yield. Specific leaf area (SLA), leaf area index (LAI) and fractional interception (FI) were significantly affected by the effect of the variety. Irrigation regime significantly affected FI, but did not affect SLA and LAI.
It was concluded that irrigating between 25D and 55D is necessary for optimum yields. Furthermore, the absence of interactions between irrigation regime and cultivars for most parameters suggests that the optimum irrigation regime for best hot pepper productivity could be applied across all varieties.
Key words: Hot pepper, irrigation regime, soil water depletion, water-use efficiency
Hot pepper (Capsicum annuum L.) is a high value cash crop, of which cultivation is confined to warm and semi-arid regions of the world, where water is often a limiting factor for crop production (Kramer & Boyer, 1995). A shallow root system (Dimitrov & Ovtcharrova, 1995), high stomatal density, a large transpiring leaf surface and elevated stomata openings, make hot pepper plants susceptible to water stress (Wein, 1998; Delfine et al., 2000). The conventional solution to water shortages has been irrigation. However, due to competing demands for water from other sectors and increasing investment cost for irrigation, the rate of irrigation expansion is constantly decreasing (Hillel & Vlek, 2005). Therefore, adoption of land, crop and water management practices that enhance water-use efficiency of a crop are indispensable (Howell, 2001; Passioura, 2006).
Currently, irrigation techniques like water-saving irrigation and deficit irrigation are being used to increase the efficiency of irrigation (Wang et al., 2002; Deng et al., 2006; Fereres & Soriano, 2007). The application of drip irrigation has enhanced the water-use efficiency (WUE) of crops as compared to the more traditional irrigation methods (Xie et al., 1999; Antony & Singandhupe, 2004). Furthermore, other cultural practices such as cultivar selection (Ismail & Davies, 1997; Steyn, 1997; Jaimez et al., 1999; Collino et al., 2000), plant population density (Tan et al., 1983; Taylor et al., 1982), and fertilization (Ogola et al., 2002; Rockström, 2003) are reported to influence plant responses to irrigation water application. For instance, treatments like N fertilization (Ogola et al., 2002), high planting density (Ogola et al., 2005), and cultivars with a rapid early growth habit (Lewis & Thurling, 1994) were reported to contribute to increased WUE of plants by reducing water loss through evaporation, while increasing the water loss through transpiration. Species or cultivar differences in physiological adaptation to water shortages can also be exploited to make informed decisions on what to plant, where to plant, when to plant and what irrigation and other cultural management to use. Generally, studies demonstrated that growth and production were positively correlated with water-use due to its effects on leaf area, harvest index, mean fruit size and fruit number per plant (Chartzoulakis & Drosos, 1997; Sezen et al., 2006.
Hot pepper cultivars show considerable biodiversity. Cultivars differ vastly in attributes such as growth habit, length of the growing season, cultural requirements, fruit size, pigmentation and pungency (Bosland, 1992). Most experiments on Capsicum species have been conducted in controlled glasshouse conditions (Chartzoulakis & Drosos, 1997; Kang et al., 2001; Costa & Gianquinto, 2002; Dorji et al., 2005). Field studies on the effects of water deficit on growth, yield and water-use of hot peppers are few and inconclusive with regard to the optimum irrigation amount, due to variation in cultivars and growing conditions (Ismail & Davies, 1997; Jaimez et al., 1999; Delfine et al., 2000). Furthermore, literature on the water requirements of different hot pepper cultivars under local conditions is lacking. It is also important to understand the response of hot pepper to different levels of water deficit in order to determine the extent to which hot peppers can withstand water deficits, while maintaining acceptable yield. The objective of this study was, therefore, to establish whether hot pepper response to irrigation regime is influenced by cultivar differences. The effect of different irrigation regimes on growth, yield and water-use efficiency was evaluated in the field, with the aim of selecting the cultivars that are more efficient in water utilization.
MATERIALS AND METHODS
Experimental site and treatments
A field experiment was conducted on the Hatfield Experimental Farm, Pretoria, South Africa (latitude 2545’ S, longitude 2816’ E, and an altitude of 1327 m.a.s.l.) during the 2004/05 growing season. The area has an average annual rainfall of 670 mm, mainly from October to March (Annandale et al., 1999). The average annual maximum air temperature for the area is 25 °C and the average annual minimum air temperature is 12 °C. The hottest month of the year is January, with an average maximum air temperature of 29 °C, while the coldest months are June and July, with an average minimum air temperature of 5 °C. The soil characteristics to 30 cm soil depth are predominately sandy clay loam with permanent wilting point of 128 mm m-1, field capacity of 240 mm m-1 and pH (H2O) of 6.5. The soil contained 572 mg kg-1 Ca, 79 mg kg-1 K, 188 mg kg-1 Mg and 60.5 mg kg-1 Na.
Treatments were arranged in a randomized complete block strip plot design, with irrigation regime assigned to main plots and cultivars to sub-plots. The three cultivars were Mareko Fana, Jalapeno and Malaga. The three irrigation regimes were: high irrigation regime (25D, maximum of 20-25 % depletion of plant available water, DPAW), a medium irrigation regime (55D, maximum of 50-55 % DPAW) and a low irrigation regime (75D, maximum of 70-75 % DPAW). The plant available water was determined to 0.6 m soil depth. The profile was refilled to field capacity each time the predetermined soil water deficit per treatment was reached for all treatments. Subplots were 5 rows wide and 2.4 m long, with inter-row spacing of 0.7 m and intra-row spacing of 0.4 m.
Six-week-old hot pepper seedlings of the respective cultivars were transplanted on November 11, 2004. Plants were irrigated using drip irrigation for 1 hour (12.5-15.5 mm) every other day for the first three weeks until plants were well established. Thereafter, plants were irrigated to field capacity, every time the predetermined soil water deficit per treatment was reached. Based on soil analysis and target yeild, 150 kg ha-1 N, 75 kg ha-1P and 50 kg ha-1 K were applied to all plots. The N application was split, with 50 kg ha-1 at planting, followed by a 100 kg ha-1 top dressing eight weeks after transplanting. Weeds were controlled manually. Preventive sprays of Benomyl® (1H – benzimidazole) and Bravo® (chlorothalonil) were applied to control fungal diseases, while red spider mites were controlled with Metasystox® (oxydemeton–methyl) applied at the recommended doses.
Soil water deficit measurements were made using a model 503DR CPN Hydro probe neutron water meter (Campbell Pacific Nuclear, California, USA), which was calibrated for the site. Readings were taken twice a week, at 0.2 m increments to a depth of 1.0 m, from access tubes installed in the middle of each plot (one access tube per plot) and positioned between rows.
Data on plant growth were collected at 15 to 25 day intervals. The fractional canopy interception (FI) of photosynthetically active radiation (PAR) was measured using a sunfleck ceptometer (Decagon Devices, Pullman, Washington, USA) a day before harvest. The PAR measurement for a plot consisted of three series of measurements in rapid succession. A series of measurements consisted of one reference reading above the canopy and ten readings below the canopy. The difference between the above canopy and below canopy PAR measurements was used to calculate the fractional interception (FI) of PAR using the following equation (Jovanovic & Annandale, 1999):Eight plants from the central two rows were reserved for yield measurement. Fruits were harvested three times in a season. On the final day of harvest, the whole aboveground part of plants was removed and separated into fruits, stems and leaves. Samples were then oven dried at 75 °C for 72 hours to constant mass and the dry mass determined. Leaf area was measured with an LI 3100 belt driven leaf area meter (Li-Cor, Lincoln, Nebraska, USA) and leaf area index was calculated from the leaf area and ground area from which the samples were taken. Specific leaf area was calculated as the ratio of leaf area to leaf dry mass.
Water-use efficiency was calculated for top dry matter, fresh fruit mass and fruit dry mass from the ratio of the respective parameter mass to calculated total evapotranspiration using eq. (3.2). Succulence, a quality measure for fresh market peppers, was calculated as the ratio of fresh fruit mass to the dry fruit mass.
Data were analyzed by using the Mixed Procedure of SAS software Version 9.1 (SAS, 2003).
Treatment means were separated by the least significance difference (LSD) test at P 0.05.
style= »color: #0000ff; »>DECLARATION
LIST OF FIGURES
LIST OF TABLES
LIST OF SYMBOLS AND ABBREVIATIONS
CHAPTER 1 GENERAL INTRODUCTION
1.1 Botany and ecology of hot pepper
1.2 Irrigation, irrigation scheduling and deficit irrigation
1.3 Justification of the study
1.4 Objectives of the study
CHAPTER 2 LITERATURE REVIEW
2.1 The role of water in plant production
2.2 Water availability for crop production in semi-arid and arid regions
2.3 Increasing water-use efficiency
2.4 A brief description of the Soil Water Balance model
2.5 Water requirements of peppers and water stress effects on peppers
2.6 Planting density effect on growth, yield and water-use of plants
CHAPTER 3 THE EFFECT OF DIFFERENT IRRIGATION REGIMES ON GROWTH AND YIELD OF THREE HOT PEPPER (Capsicum annuum L.) CULTIVARS
3. 1 INTRODUCTION
3.2 MATERIALS AND METHODS
3.3 RESULTS AND DISCUSSION
CHAPTER 4 RESPONSE OF HOT PEPPER (Capsicum annuum L.) CULTIVARS TO DIFFERENT ROW SPACINGS
4.2 MATERIALS AND METHODS
4.3 RESULTS AND DISCUSSION
CHAPTER 5 EFFECTS OF ROW SPACINGS AND IRRIGATION REGIMES ON GROWTH AND YIELD OF HOT PEPPER (Capsicum annuum L. CV ‘CAYENNE LONG SLIM’)
5.2 MATERIALS AND METHODS
5.3 RESULTS AND DISCUSSION
CHAPTER 6 FAO-TYPE CROP FACTOR DETERMINATION FOR IRRIGATION SCHEDULING OF HOT PEPPER (Capsicum annuum L.) CULTIVARS
6.2 MATERIALS AND METHODS
6.3 RESULTS AND DISCUSSION
CHAPTER 7 SWB PARAMETER DETERMINATION AND STABILITY ANALYSIS UNDER DIFFERENT IRRIGATION REGIMES AND ROW SPACINGS IN HOT PEPPER (Capsicum annuum L) CULTIVARS
7.2 MATERIALS AND METHODS
7.3 RESULTS AND DISCUSSION
CHAPTER 8 THERMAL TIME REQUIREMENTS FOR THE DEVELOPMENT OF HOT PEPPER (Capsicum annuum L.)
8.2 MATERIALS AND METHODS
8.3 RESULTS AND DISCUSSION
CHAPTER 9 CALIBRATION AND VALIDATION OF THE SWB IRRIGATION SCHEDULING MODEL FOR HOT PEPPER (Capsicum annuum L.) CULTIVARS FOR CONTRASTING PLANT POPULATIONS AND IRRIGATION REGIMES
9.2 MATERIALS AND METHODS
9.3 RESULTS AND DISCUSSION
CHAPTER 10 PREDICTING CROP WATER REQUIREMENTS FOR HOT PEPPER CULTIVAR MAREKO FANA AT DIFFERENT LOCATIONS IN ETHIOPIA USING THE SOIL WATER BALANCE MODEL
10.2 MATERIALS AND METHODS
10.3 RESULTS AND DISCUSSION
CHAPTER 11 GENERAL CONCLUSIONS AND RECOMMENDATIONS
11.1 GENERAL CONCLUSIONS
11.2 GENERAL RECOMMENDATIONS
11.3 RECOMMENDATION FOR FURTHER RESEARCH
LIST OF REFERENCES
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