The Effect of Mulching on Soil Moisture Retention and Yield of Lettuce (Lactuca Sativa L.)
Abstract
An experiment was conducted to evaluate the effectiveness of different mulching materials on soil moisture retention and yield of lettuce at the greenhouse located at Luyengo campus of the University of Eswatini during the months of January and February, 2019. The treatments consisted of grass mulch (GM), Plastic mulch (PM), leaf debris mulch (LM), and no mulch (NM) which was used as a control. Each of the treatments had four replications. The organic mulch was applied at a thickness of 10 cm, and the plots for experiments were randomly selected. Each plant received 600 cm3 of water every 3 days using a homemade drip irrigation system (equivalent to 6 mm per irrigation circle). Data on soil moisture content was collected using the gravimetric method every 3 days (before irrigation).The growth parameters of the lettuce plants that were collected weekly were plant height, leaf number and leaf area. Both wet weight and dry weight yield were determined for each plot at the end of the experiment (six weeks after planting). Data collected was coded and entered into SPSS computer software. Data analysis was conducted using the analysis of variance (ANOVA) and the least significance difference (LSD) test to determine if means were significantly different. The results showed that GMtreatment had high mean moisture retention at 9.3%. It was followed by PMand LM at 8.9%. The lowest moisture retention was realized from the control (No mulching) at 7.9%.The differences in mean moisture retention was significant between NMand NM (p<0.05). The same pattern was observed for the growth parameters, where GNhad highest values and the control had the lowest values. The wet mass yield was highest for GM, at 164.7 g. The yield from LMwas 149.3 g.It was followed by PM at 141.3 g. The lowest yield was obtained from the control at 108 g. The difference in mean yields for GMand NMwere significant (p<0.05). They were not significantly different for all the other treatments (p>0.050. It was concluded from the experiment that grass mulching resulted in improved moisture retention and high yields.
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Introduction
Lettuce (Lactuca sativa L.)is one of the most commonly used as salad vegetable. It belongs to the daisy family, Asteraceae. Lettuce probably originated from Asia, where it was grown for centuries and its early forms were used in Egypt around 4500BC [1]. Lettuce is a cool season crop grown for its tender head and leaves, but sometimes for its stem and seeds. It is rich in vitamins A and C and minerals like calcium. Lettuce is the dominant cultivated salad vegetable, which is commercialized worldwide. It is the most popular salad vegetable with the highest consumption rate and economic importance throughout the world). Farmers need to be educated for its production technology including judicious water management [2]. Water use efficiency is crucial and should be promoted in agricultural production [3]. A way of doing this is through mulching, which involves covering of the soil surface with crop residue (s) or other material such as paper or polyethylene film. Straw mulch helps to retain soil moisture, reduce temperature, conserves soil, control weeds and increase soil fertility. Mulches increase the soil moisture in the root zone and significantly decrease soil temperature. This provides a stable environment for seedling establishment and growth than soil that is not mulched. In addition, mulches increase the infiltration and storage of water in the soil and improve structure and macro-porosity of the soil along with reducing runoff and evaporation losses [4]. Water is essential for the sustenance of all forms of life. In the Kingdom of Eswatini, water utilization is expected to stimulate the economic development of the country through agricultural production. In the past few years, water availability has been scarce resulting to uneven water distribution across the country with high costs and worse, some water source went dry due to drought. This predicament has created a drive to conserve water in the country. Improving water efficiency is an ongoing goal in agricultural production, especially in area where water sources are limited and regulated. Farmers are adopting new strategies of conserving the little water they have for their production, especially vegetable production. That’swhen the need of other possible ways of water conservation through the use of mulch was considered, but there is still uncertainty of which mulch material is more effective, hence this study. Mulching benefits the soil in many ways which subsequently enhance the growth of the plants in that particular soil. Mulching offers tremendous potential for increased crop production through its marked effects on the soil environment which increase crop growth and yield [5]. Mulches are beneficial in soil and water conservation, modification of soil temperature and the temperature just above the ground, preserving and improving soil physical and chemical properties, suppressing weed growth and enhancing biological activities in the soil. Mulching improves the soil moisture regime by reducing losses caused by surface run-off and evaporation. It insulates and protects soil from drying and hard-baking effects caused by evaporation of water from soil exposed to hot sun and winds. Mulched soils absorb water faster than soils of the same type without mulch. Under mulch, the soil moisture is conserved because of reduced evaporation, improved infiltration rate, and the suppression of unnecessary plant growth [6].
The build-up of a large and active soil microbial biomass is critically important for sustaining the productivity of soils inorganic farming systems [7]. Soil microbes, the living part of soil organic matter, function as a transient nutrient sink and are responsible for releasing nutrients from organic matter for use by plants. Mulching enhances microbial activities in the soil, which is essential in nutrient recycling [8].
The effect of mulch on crop yield is an integrated effect of many factors and it is difficult to attribute the yield increments to anyone variable on its own [9]. Crops perform well when there is adequate soil moisture, nutrients and or optimum temperature. The presence of mulch enhances all the conditions mentioned above but mulch alone cannot provide adequate nutrients that the crop requires for development. The objective of this study was to determine the effect of mulching on soil moisture retention and the yield of lettuce.
Conclusion
Mulching of the soil resulted in improved growth and yield of lettuce. The performance of lettuce under all the three treatments (GM, PMand LM) was higher than of the control (NM). The differences in mean values for all the parameters (except for mean leaf numbers) were significant for GMand NM. They were not significant for all the other treatments. Based on the findings of this study, it is concluded that mulching has a positive effect on soil moisture retention and yield of lettuce. Grass mulch should be adopted as a moisture conservation measure that would result insignificant increase in the yield of lettuce.
