Yield and Water Use Response of Watermelon Under Deficit Irrigation and Mulch
Objectives of Study
The general objective of the study is to evaluate the yield and water use response of watermelon (Citrullus lanatus) under different irrigation levels and different mulching materials.
The specific objectives are:
- To determine the yield of irrigated watermelon field under different irrigation levels and mulch
- To determine the water use efficiency of irrigated watermelon under different irrigation levels and mulch
- To determine the yield response factor (Ky) and crop coefficient (Kc) of watermelon under different irrigation levels and mulch
Crop Water Requirement
A proper understanding of soil-water-plant relationship is required in order to obtain reliable information on the irrigation water requirement of a given crop which forms the basis for appropriate and sustainable water resources management. Crop water requirement is defined as the depth of water needed to meet the water loss through evapotranspiration or consumptive use of a disease-free crop, growing in large fields under non-restricted soil conditions including soil water and fertility and achieving full production potential under the given growing environment (Doorenbos and Pruitt, 1977). Evapotranspiration as defined by Hansen et al., (1979) is the sum of two terms, transpiration which is the water entering plant roots and used to build plant tissue or being passed through leaves of the plant into the atmosphere, and evaporation, which is water evaporating from adjacent soil, water, or from the surfaces of leaves of plants. Weather parameters, crop characteristics, soil characteristics, management and environmental aspects are the major factors affecting crop evapotranspiration (Allen et al., 1998). All agronomic crops have similar water use pattern. However, crop water use can change from growing season to growing season due to change in climatic variables (air temperature, amount of sunlight, humidity, wind) and soil differences between fields-root depth, soil water holding capacities, texture, structure, etc. Knowledge of water use patterns during the different growth stages has a major influence on how an irrigation system is designed and managed. Failure to recognize the water use patterns of crop may result in poorly managed water applications.
Crop water use, also known as evapotranspiration (Et), is the water used by a crop for growth and cooling purposes. The term evapotranspiration refers to the rate of evapotranspiration of a disease-free crop growing in a field under optimal soil condition including, sufficient water and fertilizer, and achieving full production potential of the crop under the given growing environment (Doorenbos and Pruitt, 1977). The evapotranspiration process is composed of two separate processes: transpiration and evaporation. Transpiration is the water transpired or “lost” to the atmosphere from small openings on the leaf surfaces, called stomata. Evaporation is the water evaporated or “lost” from the wet soil and plant surfaces.
MATERIALS AND METHODS
The experiment was conducted during dry season from February to May 2012 at the Irrigation Research Farm of the Institute for Agricultural Research, Samaru-Zaria, Nigeria. The study area is located at 11°11’N and 7°38’E, with an altitude of 686 m above sea level and is located within the Northern Guinea Savannah ecological zone of Nigeria with a semi-arid climate. The area has three distinct seasons; a hot dry season which spans from March to May; a warm rainy season from June to early October, and the cool dry (harmattan) season which spans from November to February. The average relative humidity of the area is 36.0 % during the dry season and 78.5 % during the wet season, and the average minimum and maximum temperatures are 15.6 and 38.5°C, respectively. The on-set of rains in the area is in May, but effective rainfall begins in late June and falls till early October, with a peak in August. The mean annual rainfall depth is 1150 mm, with an average peak of 650 mm in August, as obtained from the Meteorological Office of the Institute for Agricultural Research (I.A.R). The cool-dry (harmattan) and hot dry seasons are the months for irrigation. (Igbadun 1997; Ramalan and Nwokeocha, 2000; Oiganji 2010).
The meteorological data for the period of the study was obtained from the Institute’s Meteorological station located at the Farm. The monthly maximum temperature ranged from 32-39°C, while minimum temperature ranged from 13-23.1°C. A total rainfall of 16.5 mm was received during the period of the experiment as presented in Appendix I.
RESULTS AND DISCUSSION
Fruit number and Yield
The effect of various treatments on watermelon fruit number and yield is shown in Table 4.1; the watermelon fruit yield per plot from each treatment was classified on the basis of weight sizes as small, medium and large with 0-2 kg, 2-4 kg and 4-6 kg respectively to see the contribution of each class to the total yield.
The watermelon fruit yield obtained from small class ranges from 1.52 t/ha to 6.67 t/ha. The least yield values was obtained from treatment irrigated with 100% replacement of moisture depleted and rice straw mulch (I100 MRS), while the highest value recorded was obtained from treatment with 50% replacement of moisture depleted and black polyethylene mulch (I 50 MBP). For the medium class size the fruit yield obtained ranged from 19.64 t/ha to 19.64 t/ha, the highest fruit yield was obtained from treatment with 50% replacement of moisture depleted and black polyethylene mulch (I 50 MBP) while the least yield was obtained from treatment irrigated at 25% replacement of moisture depleted and no mulch (I 25 MNO). For the large class classification, watermelon fruit yield obtained ranged from 0 t/ha to 32.18 t/ha with the highest yield recorded at treatment irrigated with 50% replacement of moisture depleted and black polyethylene mulch while the least was treatment irrigated at 25% replacement of moisture depleted and no mulch. The total net harvested fruit yield of 12.07% was obtained from 0-2 kg classified as small, 35.68% obtained from 2-4 kg classified as medium and 52.25% of total net harvest was obtained from 4-6 kg classified as large. The large size attracts higher profit to farmers as they are found to be more attractive to customers while small size attracts less profit as some of the fruits may not be ripe for consumption. The number of fruit per ha ranges from 5333/ha to 20444/ha with the highest number of fruit obtained from the treatment irrigated with 50% replacement of moisture depleted and black polyethylene mulch while the least was obtained from treatment irrigated with 25% replacement of moisture depleted and no mulch.
SUMMARY, CONCLUSION AND RECOMMENDATIONS
A field experiment was conducted in 20011/2012 dry season at the Institute for Agricultural Research (I.A.R) farm, Samaru, Zaria. The experiment was used in determining the effects of irrigation levels and different mulch materials on fruit yield, crop water use and irrigation water applied. Other parameters obtained from the study was crop water use efficiency, irrigation water use efficiency, yield response factor and crop coefficient of watermelon crop grown under surface irrigation. The experiment was laid out in randomized complete block design (RCBD) with 12 treatment: consisting of four irrigation levels and three mulching material.
The maximum fruit yield was obtained when the watermelon crop was irrigated at irrigation at 50% replacement of moisture depleted and black polyethylene mulch (I50MBP) with 57.39t/ha, while the lowest was at irrigation with 25% replacement of moisture depleted and no mulch (I25MNO) with 7.29t/ha. The maximum marketable yield is at I50MBP with 53.48t/ha while the least is at I25MNO with 4.7t/ha. The highest seasonal water use was obtained at I100MNO with 373.72mm and the least is at I25MBP with 119.65mm. The highest irrigation water applied is at I100MNO with 462.01mm and the least is at I25MBP with 152.49mm. The highest crop water use efficiency and irrigation water use efficiency is at I50MBP with 347.39kg/ha-mm and 268.55kg/ha-mm respectively while the least was at I25MNO for crop water use efficiency with 33.56kg/ha-mm and at I100MNO for irrigation water use efficiency with 32.09kg/ha-mm.
The Ky values obtained were 1.3895 for MNO, and no relationship for MRS and MBP. The Kc values ranges from 0.42-0.55 for initial stage, 0.5-1.01 for development stage, 0.69-1.09 for mid season stage, 0.41-0.87 for late season stage.
The total yields for watermelon with MRS were 28.55 t/ha, 40.35 t/ha, 38.83 t/ha and 26.49 t/ha with 100%, 75%, 50% and 25% replacement of moisture depleted, respectively. With MBP the total yields were 28.8 t/ha,40.53t/ha, 58.49 t/ha and 17.15t/ha with 100%, 75%, 50% and 25% replacement of moisture depleted, respectively. And for treatment with MNO the total yields were 14.94 t/ha, 21.33 t/ha, 23.38 t/ha and 7.38 t/ha with 100%, 75%, 50% and 25% replacement of moisture depleted, respectively. However, irrigating watermelon crop with application depth of 50% replacement of moisture depleted at each irrigation and mulching the field with black polyethylene mulch gave the highest fruit yield while irrigation with 25% replacement of moisture depleted and MNO gave the least yield.
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