Performance of Okra(Abelmoschus esculentus L. Moench) under Different Irrigation Frequencies

Abstract

Introduction Okra (Abelmoschus esculentus L. Moench) is a perennial vegetable of African origin, with production areas expanding throughout the tropical, sub-tropical and warm temperate regions of the world (Benchasri, 2012). Okra is a versatile crop produced forits pods, leaves, seedoil and protein, gums, and fiber in different parts of the world (Lamont,1999). It is produced in Vilanculos primarily for the immature pods, though leaves are consumed to a limited extent in rural communities. Important attributes of okra pods are shape and color, earliness, and totalmarketable yield. Since okra is handharvested, plant height and architecture,as well as the absence of spines are important tofacilitate harvesting (Simonne, et al, 2012).Okra is not only reach in nutrients (fats, proteins, carbohydrates, minerals and vitamins), but it is also believed to have medicinal properties. The climate in much of Mozambique presents favorable conditions for the production of Okra (INE, 2011) and because of the growing preference for Okra among consumers in Mozambique, its area of production had rapidly expanded to every part of the country, mainly in the provinces of Tete, Manica, Sofala and Inhambane. Okra provides a good alternative or supplemental income for smallholder farmers (COSTA et al., 1981) and its production in the district of Vilanculos requires the application of considerable amount of irrigation water to improve productivity. Small farmers-led irrigation in Mozambique takes place in diverse forms, including bucket irrigation, sprinkler and drip systems, furrow and small pumped irrigation systems. However, Mozambique has limited access to raw water supplies and the country as a whole is extremely vulnerable (ranks 3rd amongst African countries) to extreme weather patterns (i.e. recurring droughts and flood events), which contribute to crop instability, food insecurity and malnutrition (USAID, 2010). However, information on watering (irrigation) frequencies for optimal growth and development of this valuable crop under the edaphic-climatic conditions in the district of Vilanculos is lacking. Climate-smart strategies to increase irrigation efficiency at small-farm level are essential in helping rural smallholders optimize production of okra and other vegetable crops under climate change. Materials and Methods 1. Geographical location The field experiment was carried out between October and December 2016 on the campus of the Universidade Eduardo Mondlane-Escola Superior de Desenvolvimento Rural (UEM-ESUDER) located in the coastal town of Vilanculo within the district of Vilanculos, Province of Inhambane in Mozambique at coordinates 21º59’30.6” S, 035º16’14.8” E. and an average altitude of 49m. The district of Vilanculosoccupies the northern part of the province of Inhambane, bordering the district of Inhassoro to the north, the district of Massinga to the south, the districts of Mabote and Funhalouro to the west and the Indian Ocean to the east (MAE, 2005). 2. Climatic condition The climate of the study area is Aw according to the Köeppen e Geiger, which corresponds to a dry tropical climate with two distinct seasons. A wet season spans from October to March, with an average annual precipitation of 1300 mm; and a dry season from April to September, with an average annual precipitation of 700 to 900 mm (MICOA, 2009 and MAE, 2005).Figure-1 illustrates the average temperature and precipitation patterns in Vilanculos. The driest month is July, which averages 17 mm of rainfall, and the month of February is the wettest with an average precipitation of 166 mm. On average, the temperatures are always high, with an annual average of 24oC. 3. Soils of the study area The soils in the district of Vilanculos are sandy and permeable in the coastal areas, and sandy-loam to loamy-clay in the interior. The study site was approximatively 10 km from the coastal line and its soils are predominantly sandy and permeable with low organic content (8.55%) and low water holding capacity (less than 5cm/m) (MAE, 2005; Maite, 2014). The growing season averages 120 to 149 days, and because of low precipitation and recurring drought periods during the growing seasons, the area’s potential for rain-fed agriculture is marginal (Mafalacusser, 2013.) Figure 1. Monthly temperature and precipitation patterns in the district of Vilanculo, Mozambique. Adapted from Climograma Vilanculos: https://pt.climate-data.org/location/52395/ 4. Experimental design The experiment was laid out on an area of 83.375m2 within which 3 blocks of equal sizes were setup, each block divided into 4 parcels of 4 m2 (2 m x 2 m) for a total of 12 parcels. The blocks were setup at 1m apart and the parcels within each block were spaced at 50cm. Treatments were then randomly assigned to each parcel, resulting in each parcel representing a unique treatment within each block. Table-1 describes the different treatments (irrigation frequencies) used in the experiment. Table 1. Treatments details: Four (4) treatments randomly assigned to the experimental blocks. IF1 Irrigate twice a day in the mornings (5-6 AM), and afternoons (4-5 PM) IF2 Irrigate once a day in the afternoons (4-6PM) IF3 Irrigate once a day in the mornings (5-6 AM) IF4 Irrigate twice a day in the mornings (5-6 AM), and afternoons (4-5 PM) at 1- day intervals. 5. Soil preparation and planting Soil preparation consisted of removing natural vegetation from the experimental site with a manual hoe without revolving the top soil, and the soil surface was raked and leveled prior to subdivision of the experimental area into parcels, blocks and replications for the study.Seeds of okra (Abelmoschus esculentus L. Moench) variety Clemson Spineless, were soaked in water for 24 hours to stimulate germination, and then sown by placing two (2) seeds in each planting hole at an approximate depth of 5cm in each parcel. Fifteen (15) days following the emergence, the seedlings were thinned by removing the least developed plant in each planting hole, leaving only one (1) okra seedling per hole in each treatment. The seedling selection criteria was based on height, and the number of developed leaves. 6. Soil fertilization Organic fertilizer in the form of bovine manure was applied seven (7) days prior to sowing and 15 days after seedling emergence, at the rate of 15 tons/ha each. All plants received the same fertilizer application. 7. Irrigation A hand-held irrigation bucket was used for applying water to the experimental plots, a watering scheme consistent with the most popular irrigation system among smallholders in the study area. All parcels were uniformly irrigated with 13 liters of water, starting from one (1) day prior to seeding until fifteen (15) days after seeding when the okra plants developed up to three (3) fully expanded leaves. Starting from day-15 through the end of the experiment, plants in each parcel were irrigated according to the established watering schedule (Table-1.) 8. Pests/Weed Control Weed control was manual and continuous throughout the study, by hand plucking at the onset of their appearance to avoid perturbation of soil and plants. The most common weeds were amaranthus, commelina benghalensis and cyperus esculentus species, with amaranthusandcyperus esculentus being the most dominants.Observed pests were acarids and caterpillars, and these were treated with pesticides Cipermetrina 25% E.C. and Fords. The occurrence of fungi during the experiment was sparse, but fungi was treated with the fungicide Bravo. Data Collection 1. Pre-harvest Data Pre-harvest plant parameters consisted of plant height and stem diameter. Plant height was determined by measuring the height of the primary stem of random sample of plants in each treatment from the base at soil surface to the apex, using a metric ruler. At the same time, stem diameter was measured with a digital Caliper, within 300mm at 5 cm above the soil surface. Growth Rate of okra plants was determined from height measurements and expressed as Absolute Growth Rate (AGR), based upon increments of measured plant heights between sampling dates (i.e. Height at day2- Height at day1) over the time-period (number of days) between measurement dates. 2. Post-harvest Data Post-harvest data included Fruit Length, Fruit Diameter, and Fruit Weight. Okra fruits were harvested twice; the first harvest took place 90 days after seeding, and the second harvest 8 days later, or 98 days after seeding. Harvest data were from random fruit samples under each treatment for both harvests. A graduated metric rulerwas used to measure fruit length, while fruit diameter was measured with a digital Caliper within at 5 cm from thebase of each fruit, and fruit weight was determined by weighing sample fruits per treatment from each harvest, with a digital scale equipped with a high precision strain gauge sensor system. Data Analyses All data collected from the experiment were analyzed with the statistical software SPSS(v.20, IBM SPSS Chicago). Analyses of Variance (ANOVA) were performed to determine differences between treatments, followed by mean comparisons based on Tukey HSD (α = 0.05). Homogeneity of the variances was verified through the test of Levene (α = 0.05), and graphical illustrations were produced with the Microsoft Excel program. Result and Discussion 1. Plant Height The different irrigation treatments had no significant effect on plant height at each sampl

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