When the pH of the growing medium is too acidic or too alkaline, the availability of micronutrients will influence the plant growth (Buechel, 2020).
At high pH, nutrient availability like P, N will be decreased because alkaline media convert the phosphate to unavailable forms, resulting in loss of ammonia, and precipitate the micronutrients, where iron, manganese, zinc, copper, and boron are not available for absorption. But when the pH is below 5.5, these elements are available to the plant (Azeez & Averbeke, 2012; Buechel, 2020).
The optimum pH is different from plant to plant, but generally, when the pH range is 5.5-7.0 the media will be suitable for cultivating most plants, while some plants will grow in more acid soil or may require a more alkaline level. In this research, DPLC has the most suitable pH (6.6) for watermelon and sweet melon growth. Dhen et al. (2018) showed usage of date palm residues as a growth medium instead of peat moss.
Electrical conductivity (EC) is a measurement of the solution's ability to conduct electricity. When EC is high that means there are salts in the solution. If no salts are present, then the EC will be low, which indicates that the solution is not a good conductor of electricity. The electrical conductivity is associating with some properties of the soil, which are soil texture, cation exchange capacity (CEC), drainage conditions, organic matter level, salinity, and crop productivity (Patel & Lakdawala, 2014). The optimum EC value of suitable growing media is between 0.7 mS/cm-1 to 1.9 mS/cm-1. The DPLC EC was 3.8 mS/cm-1, which was higher than the optimum values.
Water holding capacity is the ability of the growing medium to hold water against gravity to supply water for plant growth by the plant's root system (Richards
et al., 1986). Substrates differ in water holding capacity according to particle size and bulk density. The growing media should contain an air space of 10% to 30% of its volume, and 45% to 65% of media should contain water (Altland, 2006).
Rostami et al. (2014) showed that the water holding capacity of date palm waste that was used as growing media was 18.72%. Whereas in this study, the water holding capacity of DPLC was 12.65%, and because of this the recommendation was to mix the DPLC with some amount of organic compost to get high water holding capacity, where the water holding capacity of organic compost was 56.44%.
Plants need many nutrients to grow. These nutrients are divided into macronutrients and micronutrients based on the amount needed by the plants (Marschner, 1995).
The results of this thesis showed that level of some elements was higher in date palm leaves compost compared to peat moss, organic compost and WOM. The concentration of Na, Ca, Mg, P, Cu, Fe, Mn, Zn, So4 were higher than peat moss before cultivation.
According to a work carried out by Silva et al. (2007), the stable compost had a C/N ratio of approximately 17 or less. When the C/N ratio was more than 20, it might have damage effects on plant growth and seed germination (Ghehsareh et al., 2011).
If nitrogen was low and carbon was high in organic substrates this might cause a decrease in plant growth (Shirani & Ghehsareh, 2013). The results of this study showed that peat moss has a higher C/N ratio (42.25%) compared to date palm leaves compost (39.7%) and organic compost (19.3%). A high C/N ratio is an indicator of immature compost, which can cause a deficiency of ‘N’ in plants.
Rahbarian et al. (2014) got results that is similar to this study where they studied the effect of date palm peat and other growth media on plant growth. The results showed that there was no significant difference between date palm, peat moss, and other substrates. This means that date palm substrate can replace peat moss or any other growing media.
Ghehsareh (2011) indicated that there was no significant difference on the quantitative and qualitative indexes between the date palm and perlite as substrate on the growth parameters of the tomato such as fruit yield, plant height, and fruit number.
Dhen et al., (2018) pointed to the high porosity and low bulk density of palm peat, which means that will enhance plant growth.
Rostami et al. (2014) showed the importance of the media that has high water holding capacity, the substrate that has high moisture conservation will meet plant needs from water and nutrients by keeping the substrate wet until next irrigation, Also this will create a better condition for growth and that was the reason why date palm peat had a significant effect on the number of leaves.
In the present study, there was no significant difference between the four treatments by the plant height, the number of leaves, flowers and fruit size, and firmness for watermelon and sweet melon plants, which means the water and nutrient needs were sufficient in the four growing mediums for the plant.
Plant growth was determined by measuring the biomass (Barrett et al., 2016).
Date palm peat was used as alternative growing media. Dhen et al. (2018) showed that the highest fresh and dry weights from lettuce that was grown in date palm peat media.
In this study, the results are in agreement with the previous studies, in which date palm leaves compost showed the highest fresh and dry weights for both watermelon and
sweet melon fruits when comparing with peat moss, organic compost, and WOM.
Although, the results of this work showed that there was no significant difference between the four substrates.
Water is one of the most important needs of the plant to carry out its vital processes, where the water deficiency has a direct effect on the plant growth by reducing the content of chlorophyll and carotene in the plant, as these pigments have a big role in the photosynthesis process. Therefore, the growing media may have a major role in determining the content of these pigments (Antolín et al., 1995).
Shahinrokhsar et al. (2007) showed that, there was no difference in chlorophyll content in strawberry plants that are grown in different types of the substrate, which is consistent with the results of this research. There was no significant difference between the DPLC, peat moss, organic compost, and WOM in chlorophyll and carotene content, but DPLC showed the highest amount of total chlorophyll and carotene in watermelon and sweet melon, while the lowest chlorophyll and carotene content was on WOM.
Soil is the first source responsible for providing the plant with the nutrients it needs, the source of minerals present in the plant tissues is the soil or the growing medium (Marles, 2017). In this study, no significant difference was found between the four substrates in terms of elemental content, and this is correlated with the absence of a significant difference between the four growing mediums in the concentration of the element in watermelon and sweet melon shoots and roots.
The TSS content of the fruit is usually used as an indicator of sugar content, but TSS content does not mean just the sugar content, where it is a measure of the carbohydrates, organic acids, proteins, fats, and minerals of the fruit.
The TSS content of the fruit is usually used as an indicator of sugar content, but TSS content does not mean just the sugar content, where it is a measure of the carbohydrates, organic acids, proteins, fats, and minerals of the fruit. TSS affected by many factors, according to Gungor and Yildirim (2013), the TSS content of the fruit was affected by different growing media, where the peat growing medium caused an increase in the amount of vitamin C.
DPLC showed the highest TSS content in watermelon fruits with 10.9 Brix, while peat moss has the highest TSS content in sweet melon fruits with 11.96 Brix.
But the result of this work indicated there is no significant difference in the growing media. This is in line with some previous studies that indicated there was no significant difference among the growing media in TSS contents of strawberry fruits (Ayesha et al., 2011).
Sugars are carbohydrate, which includes glucose, fructose, and sucrose. Some sugars can be as reducing agents. This can be used for the analysis of reducing sugars.
Reducing sugar, total sugar, and sucrose content in fruits are a part of TSS content.
Reducing sugars consists of glucose and fructose that are obtained from sucrose hydrolysis (Smri, 1997).
According to Ayesha et al. (2011) results, all growing media showed no significant difference in sugar content in the fruits in the results among each other.
This is in the line with the result of this thesis. There was no significant difference in total sugar, reducing sugar, and sucrose content in watermelon and sweet melon fruits among the four growing media.
Chapter 6: Conclusion
Many previous studies showed that date palm waste can be used as alternative growing media. The results of this thesis indicated that date palm leaves to compost, peat moss, organic compost, and WOM had characteristics very close to each other, and they have no significant differences in all characters in watermelon and sweet melon crop growth. DPLC could be a good new alternative growing media in some countries like UAE were extensive date palms cultivation is carried out. Also, date palm waste is one of the important environmental problems that is faced by UAE.
Because of the low cost and high availability of date palm waste in UAE, date palm leaves compost can replace another available growing substrate like peat moss, which may reduce the cost of using the imported expensive growing media. The exploitation of date palm waste is an excellent step in the agriculture waste management sector. It is recommended that this study in the future can be extended to different parts of date palm waste. Also, it is recommended that use DPLC in a mixture with other substrates to maintain the water holding capacity at the different point of negative pressure.
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