Advances in Applied Agricultural Sciences 2 (2014); 05: 10-26
Effect of Bio-Organic Fertilizers, Hoeing and Polyethylene Mulch on Weeds, the Citrus Nematode (Tylenchulus semipenetrans) and Yield of Mandarin Trees in Egypt
Hussein Fawzy Abouziena 1, Ahmed El-Sayed Ismail 2* and Sameir Mahmoud Radwan 3,4
1 Botany Dept., National Research Center, Dokki, 33 Al Behoos Street, Dokki, Cairo, Egypt, 12622. 2 Plant Pathology Dept., National Research Center, Dokki, 33 Al Behoos Street, Dokki, Cairo, Egypt, 12622. 3 Agric. Microb. Dept., National Research Center, Dokki, 33 Al Behoos Street, Dokki, Cairo, Egypt, 12622. 4 Present address: Soil Science Dept., College of Food and Agricultural Sciences, King Saud University, P.O. Box 2460 Riyadh 11451, Saudi Arabia.
Combined safety methods and bio-organic fertilizers for controlling weeds and the citrus nematode,Tylenchulus semipenetrans were designed to producing healthy food free from the biomagnifiedagrochemical residues in fruit yield of mandarin trees in Egypt. A field experiment was carried out to study the effect of hoeing, black and white polyethylene sheets 80µm and different composted plant wastes such as rice straw, maize stalks or crop weeds in the presence or absence of multi-biofertilizers and their interactions on controlling weeds, citrus nematode and fruit yield parameters of mandarin trees cv. Balady. The results revealed that Cynodon dactylon, Echinochloa colonum, Amaranthus retroflexus, Portulaca oleracea, Panicumrepens and Cyperus rotunduswere the dominant weeds in the citrus grove. Covering the soil with black plastic sustained the lowest weed density and reduced the number of citrus nematode and consequently produced the highest fruit yield/tree, followed by white plastic, then hoeing treatments. The use of either composted weeds under white plastic or composted chicken manure under black plastic in the presence of biofertilizer attained twice superiority for controlling the citrus nematode comparing to without biofertilizer application, while rice straw compost treatment under hoeing and at black plastic surpassed the others in one period for controlling the citrus nematode. Application of the biofertilizer with the different organic composts caused increase in the number and yield of fruits per tree. Generally, the association action between composted plant wastes and biofertilizer application increase the number and fruits yield under weed control treatments. Also, composted crop weeds recorded the greatest fruits yield under black plastic. The treatments of chicken manure and composted rice straw without addition of biofertilizer surpassed the chemical treatment in fruit yield by 34.9% and 14.0%, respectively. While application of maize stalks compost caused a reduction of the fruit yield by 8.1%, compared to inorganic treatment. The highest value of total soluble solids in fruits was observed with rice straw compost and biofertilizer under the white plastic. The most promising interaction treatment producing the highest safety fruits production of Balady mandarin was the associating weeds composted with biofertilizer or chicken manure under black plastic treatment.
Organic crop production, whether for export or local consumption, is increasing to avoid the residual effects of synthetic chemicals in foods, soil and water. Egyptian citrus, especially organic fruits, is exported to many countries. Organic farmers consistently ranked weed management as one of their most important production problems (Shrestha and Mizutani 2013). Also, the citrus nematode, Tylenchulus semipenetrans (Cobb 1913), is reported from more than 50% of the citrus-producing areas (Van Gundy,1986) and is associated with poor growth of young citrus trees planted in infested groves and with poor performance of mature citrus trees called “slow decline” and the life cycle of this nematode consists of several stages, with the complete cycle from egg to egg requiring four to eight weeks, nematodes emerge from eggs after having been second-stage juveniles for 12 – 14 days (Duncan and Cohn, 1990; Ismail et al., 1997). Moreover, citrus fruit quality and yield has been negatively correlated with T. semipenetrans and weeds infestation level (Tucker and Singh 1984; Nakhla et al., 1998; Abouziena et al., 2008).
Uncontrolled weeds in the citrus grove caused significant reduction in yield and fruit quality and decreased the yield/tree by 23% – 33% (Singh and Sharma, 2008) to 62% (Abouziena et al., 2008) compared with hoeing treatment. Chemical control of weeds in citrus was reported to affect various physical and chemical properties and quality of fruits (Mohanty et al., 2002). Also, nematicides have been used to control economically important plant-parasitic nematodes, but due to their toxic effects on beneficial soil microorganisms and environmental pollution, it is necessary to consider alternative control strategies. Economically and environmentally sustainable weed control alternatives, such as non-synthetic or natural mulch, can provide many benefits, including weed suppression and delayed weed seedling emergence (Bond and Grundy, 2001; Abouziena et al., 2008). Soil solarization technique developed by Katan et al. (1976) has been used as an alternative management tool in controlling the citrus nematode (Ismail et al.,1997) or the root-knot nematode (Di Vito et al., 2005) as well as polyethylene mulch can provide effective weed control (Abouziena et al., 2008; Ustuner and Ustuner, 2011). They reported that the greatest control (94%–100%) of weeds occurred with the plastic mulch. Linares (2006) grew annual and perennial cover crops to suppress weeds in citrus orchards, and he found that, in general, perennial and annual cover crop treatments did not affect soil pH, C and N contents, and C: N ratio during the initial 3 years of field studies, while T. semipenetrans did not reach high levels. Shrestha and Mizutani (2013) reported that larger fruit with lesser peel percentage, lower total soluble solids (TSS) and titratable acidity (TA) and higher TSS/TA ratio in fruit juice were obtained at using mulching system while conventional practice resulted in smaller fruit with higher peel percentage. The interaction between organic fertilizer and soil mulching had significant effects on fruit yields of peach, pear and olive (Abu Irmaileh et al., 2011).
Therefore, the objective of this study was to investigate the effect of some waste plant material composts as organic fertilizers and white and black polyethylene mulches as physical methods as well as organic manures i.e. farmyard manure or chicken manure in the presence or absence of multi-biofertilizer in comparison with hoeing, on the T. semipenetrans(Cobb, 1913) (the citrus nematode), the dominant weeds as well as on the quality and quantity of mandarin fruits.
Materials and Methods
A field experiment was carried out in sandy soil naturally infested with T. semipenetrans and different weed species in a private Balady mandarin (Citrus reticulate Blanco) orchard, 18-year old and budded on Sour orange (Citrus aurantium L.), located at El-Salhia District, Sharkia Governorate, Egypt to study the effect of some nonchemical control treatments i.e. hoeing as mechanical treatment, white or black plastic mulch (80 µm) as physical treatments and some composted plant wastes i.e. rice straw, maize stalks and crop weeds as well as farmyard manure or chicken manure as organic fertilizers in the presence or absence of multi-biofertilizer (containing of some microorganisms such as strains of phosphate dissolving bacteria i.e. Bacillus megaterium var. phosphaticum, Azotobacter spp., Azospirillum spp. andPseudomonas spp.) and their interactions on the weeds, T. semipenetrans and fruits yield of balady citrus during two successive seasons.
The trees were spaced 5 × 5 m apart and an experimental area was irrigated by flood irrigation system under a split-split plot design with four replicates. Irrigation and other agricultural practices were applied as recommended. The soil texture of the experimental site was sandy soil (72.6% sand; 24.2% silt and 3.2% clay) with 0.23% organic carbon, pH 8.1, E.C. 0.64 dsm–1, and 1.79% CaCO3, 0.04% N, 0.001% P, 0.027% K, 0.62 ppm Zn, 0.5 ppm Mn, 3.6 ppm Fe and the water holding capacity was 18.6%. Composts were added once a year in mid-February, while inorganic nitrogen treatment was applied three times/year i.e. mid-February, mid-May and mid-August for each season. Chemical analysis of the used artificial composts and organic manures was presented in Table 1.
Preparation and application of bio-fertilizer
Highly efficient strains of phosphate dissolving bacteria i.e. Bacillus megaterium var. phosphaticum, Azotobacter spp., Azospirillum spp. andPseudomonas spp. were grown in nutrient broth for 48 h. at 30°C in a rotary shaking incubator (Saber,1998). Liquid broth cultures initially containing 7×107, 6×107, 5×107and 3×107viable cell/ml of each strain; respectively. In bio-fertilization treatments, 100 ml of each tested microorganisms suspension were added to each tree with organic composts. In each season, all the treatments were added to the soil tree canopy on the peripheries of the treated trees particularly in the irrigated root zone.
The main plots were assigned for hoeing, white and black polyethylene treatments. The subplots were assigned for the different compost treatments as well as inorganic fertilizer. Mulches were applied to plots during the first week of March each year, while after winter cultivation; the application of composts and the first application of chemical fertilizer were applied in the third week of February.
The nematode extraction and assessment:
Soil and root samples for nematode assay of each treatment were sampled once before the treatments application as zero days, after that all treatments were applied and sampled 2,4 and 7 months after application. All samples were taken at 30 cm depth beneath tree canopy as three cores. Nematodes in an aliquot of 200 g soil were extracted by the sieving and decanting technique where, 2 deep basins, 25 to 30 cm diameter, two 20 cm diameter sieves made with wire mesh of 240 and 350 meshes per in, equivalent to an aperture size of 63 µm and 45 µm, respectively; a small pan about 15 cm diameter and 5 cm deep, and 250 ml-beakers for the residue from each of the sieve used according to Barker (1985). Also, nematodes in aliquot of 5 g roots from each sample were determined using the incubation method of Southey 1986, where in this method when roots are stored moist or in shallow water,
Migratory endoparasites tend to leave them, the roots are put into containers such as plastic dishes and kept at about 20 to 25ºC for five days. Percentage nematode reductions in either soil or
Table 1. Chemical analysis of the used artificial composts and organic manures.
Organic carbon %
Amount N addition:
a- Off year (g tree-1year-1)
b– On year (g tree-1year-1)
roots (% efficiency) were determined according to Handerson and Tilton formula (Werner, 1981) as follows:
PTA and PTB = Population in the treated trees after and before application, respectively.
PCB and PCA = Population in the check trees before and after application, respectively.
The plots were visually rated for weed control percentage 5 months after the mulch treatments application by using a scale of 0 (no effect on weeds) to 100 (complete weed control) according to Frans et al., (1986), where weeds counts were recorded per square meter randomly in each plot 5 months after treatment application in both years, then individual weeds were identified, dried and their dry weights were determined. These values were transformed to arcsine before analysis to improve the homogeneity of the error variance
Yield and yield components assessment of mandarin trees:
At harvest time in both seasons, number of fruits and yield per tree were recorded. Samples of 10 fruits from each tree were randomly taken to determine length, diameter and weight of fruit. TSS was analyzed as described by the Association of Official Agriculture Chemists (1995).
All data from the two seasons were combined and analyzed statistically by using the Fisher,s Least Significance Differences (LSD) according to Gomez and Gomez (1984).
Results and Discussion
Effect of treatments on weeds
The results indicated that Cynodondactylon (L.) Pers., Echinochloa colonum (L.) Link, Amaranthusretroflexus L., Portulaca oleracea L., Panicumrepens L. andCyperus rotundus L. were the dominant weeds in the Balady mandarin orchard.
Effect of hoeing, whiteand black plastic mulches on weeds:
Table 2. Effect of nonchemical treatments (hoeing, whiteand black plastic mulches) and bioorganic fertilizers on weed control efficacy % in mandarin’s grove. (Average of two seasons)
white plastic mulch
Black plastic mulch
Farmyard manure + biofertilizer
Chicken manure + biofertilizer
Rice straw compost
Rice straw compost + biofertilizer
Weeds compost + biofertilizer
Maize stalks compost
Maize stalks + biofertilizer
LSD at 5% for compost: 7.5; for weed control: 5.6 and for interaction: 8.7
Figure 1. Effect of weed control treatments without or with bio-fertilizers on weed density % after 5 months from mulch application in mandarin grove.
The data revealed that covering the soil with black plastic mulch attained the highest weed control efficacy followed by white plastic mulch and the lowest efficacy was recorded at using hoeing treatment (Figure 1). Our findings agree with Bredell (1973) who mentioned that hand cultivation was not effective in controlling weeds and the weeds re-growth occurred rapidly. Also, Mohanty et al. (2002); Abou Sayed-Ahmed et al. (2005) and Abouziena et al. (2008) reported that black polyethylene mulch completely eliminated all weed species through non-penetration of sunlight. It could be concluded that black plastic mulch was more effective than white plastic mulch and hoeing for controlling weeds.
Figure 2. Effect of organic fertilizers without or with bio-fertilizers on weed density (%) after 5 months from mulch application in mandarin grove.
Figure 3.Effect of non-chemical weed control treatments on fruit yield of mandarin trees (kg tree-1).
a) Effect of fertilization treatments on weeds
Concerning the weed density under fertilization treatments, data in Figure 2 revealed that the lowest weed density was observed under rice straw compost + biofertilizer, while the highest weed density was recorded at using the inorganic treatment. These results agree with the findings by Coleman (2012) who found that the plant residues can release allelopathic compounds that may suppress the weed growth. Also, he stated that the plants produce and store a great number of organic compounds, which can be released into the environment by volatilization, root exudation, leaching from live or dead plant parts, or by decomposing plant residues and may suppress the weed growth (Rice, 1987; Coleman, 2012). Abu Irmaileh et al. (2011) reported that most annual weeds did not appear in composted manure under peach, pear and olive trees. Christoffoleti et al. (2007) reported that covering the soil surface with different plant residues was effective on the weed population dynamics through chemical factors (carbon/nitrogen ratio), biological (parasitism and predation by microorganisms, insects and small mammals) and physical factors (less direct sunlight reaching the soil surface, reduce soil temperature variation and physical obstruction of weed emergence). However insignificant (p ≤ 0.05) differences were recorded among the organic treatments on weed density as well as between fertilization with and without biofertilizer addition (Figure 2). Addition of the biofertilizer to the compost had insignificant effect on the weed density.
Figure 4. Effect of organic fertilizers on fruit yield of mandarin trees (kg tree-1).
Figure 5. Effect of the interaction between organic fertilizers and non-chemical weed control treatments on fruit yield of mandarin trees (kg tree-1). Abbreviations: RSC; rice straw compost, biof; biofertilizer, WC; weed compost, MS; maize stalks compost, FYM;farmyard manure compost, CM; chicken manure, NPK; chemical fertilizer.
c) Interaction between nonchemical treatments (hoeing, white and black plastic mulches) and fertilization treatments on the weeds:
Data in Table 2 showed that the interaction between the used treatments on weeds had significant (p ≤ 0.05) effect on the control efficacy of weeds. Using of black plastic mulch treatment exhibited the highest control as compared with the used treatments and completely controlled the weeds (100% control) at using farmyard manure, chicken manure + biofertilizer and weeds compost treatments. In general, using of black plastic mulch achieved, in average, 95% weed control, while using of white plastic mulch exhibited 85% control with insignificant (p ≤ 0.05) difference with mechanical weeding (84%) as shown in Table 2. Similar findings were mentioned by Pelizza et al. (2009); Ustuner and Ustuner (2011) who reported that the percentage of effectiveness of black plastic for weed control was 99.9%.
In most cases, the highest weed control efficacy was obtained under compost fertilization compared to chemical fertilization (Table 2). Abu Irmaileh et al. (2011) reported that weeds were significantly reduced and fruit trees were significantly larger in the treatments with manures in the black polyethylene-covered treatments as compared to the non-covered treatment. Moreover, Putnam et al. (1983) reported that adding some of the plant residues of rye, wheat, sorghum, or barley residues on the soil surface exhibited numerous physical and chemical attributes that contribute to weed suppression. In our study, insignificant (p ≤ 0.05) differences were noticed among the efficacy of weed control measures under bio-fertilization and without fertilizer addition (Table 2).
Effect of some bio-organic fertilizers, hoeing and polyethylene soil cover on T. semipenetrans
Data presented in Table 3 (Appendix 1) illustrated the nematode population densities and efficacy percentage of the tested treatments on reduction of T. semipenetranslarval numbers either in soil or roots throughout the experimental period compared to untreated check. All the used agents have significantly (p ≤0.05 or 0.01) reduced the T. semipenetranseither in soil or roots as compared to the control. Statistical differences were observed between and within the treatments. Under application of hoeing treatment, the means of results revealed that at using the maize stalks compost, chicken manure compost and rice straw compost + biofertilizer achieved the high efficacy in reducing T. semipenetrans larvae in both soil and roots (Table 3). However, weeds compost + biofertilizer, farmyard manure compost, and maize stalks compost surpassed other treatments in decreasing the nematode numbers at covering the soil of with white plastic treatment (Table 3). On the other hand, the treatments of chicken manure compost + biofertilizer, rice straw compost and weeds compost at covering the soil of mandarin grove with black plastic treatment attained the high efficacy in reducing the nematode numbers in both soil and roots (Table 3). This is in agreement with the findings of Siti et al. (1982); Heald and Robinson (1987); Farahat et al.(1994); Ismail et al. (1997) where soil solarization showed an increase in plant growth through increased soil moisture accumulation, soil temperature management, increase in available soil nutrients and control of phytoparasitic nematodes. Besides, reductions in total soil and root nematode populations due to polyethylene soil mulching were associated with the increase in soil heat energy (Ismail et al., 1997).
Table 3. Efficacy of some bio-organic fertilizers, hoeing and whiteand black plastic mulches treatments on controlling the citrus nematode, T. semipenetrans in Balady mandarin orchard (average of two seasons).
Number of citrus nematode larvae after application 200 g-1soil
Number of citrus nematode larvae/5g roots after
RSC + bio
white plastic mulch
Black plastic mulch
Data are means of four replicates. *Figures in parenthesis indicate percentage nematode reductions according to Handerson and Tilton formula (Werner, 1981). Abbreviations: A; initial populations before application (0 days), RSC; rice straw compost, MSC; maize stalks compost, WC; weeds compost, FYMC; farm yard manure compost, CM; chicken manure, Mo; month
Collective comparisons amongst efficacies percentage of the treatments in management T. semipenetransin both soil and roots (Table 4, Appendix 2)revealedthat the treatments of weeds compost + biofertilizer at covering the soil with white plastic as well as the treatment of chicken manure compost + biofertilizer at covering with black plastic were the best in two sampling periods in reducing the citrus nematode numbers, while using of rice straw compost either under hoeing or at covering the soil with black plastic mulch surpassed the other treatments in one period (Table 4).
Table 4. Percentages reductions and frequency of successful of some bio-organic fertilizers, hand hoeing and polyethylene soil cover treatment in Tylenchulus semipenetrans control.
*Percentage of reduction (efficacy %), were calculated on the basis of soil + root nematode population by Handerson and Tilton formula.
**Most successful treatments in connection with some bio-organic fertilizers, hand hoeing and polyethylene soil cover treatments =two cases in weeds compost + biofertilizer + white plastic mulch; two cases in chicken manure compost+ biofertilizer + black plastic mulch; one case of each rice straw compost + hand hoeing, maize stalks compost + hand hoeing, weeds compost + hand hoeing, farm yard manure compost + white plastic mulch and rice straw compost + black plastic mulch.
The mode of action of organic amendments may be due to that these materials undergo decomposition processes with liberal water and release of many compounds including ammonia, phenols aldehydes and water toxic products which were found to have nematicidal effects (Ismail and Mohamed, 2012; Usman and Siddiqui, 2013). These toxic products are drained into soil spaces and kill nematodes (Alam, 1991). The organic materials affect nematode population by enhancing the development of nematode natural enemies (D,Errico and Maio, 1980) and by improving crop performance to increase tolerance to nematodes (Novaretti et al., 1989). It is clear from the present study that adding all the treatments to the soil could reduce the effects of the nematode on the plant growth.
Effect of the used treatments on the mandarin yield
a) Effect of hoeing, white and black plastic mulches:
In comparison to hoeing treatment, the effect of covering soil by plastic mulch treatments had insignificant (p ≤ 0.05) effect on diameter, height, weight and total soluble solids (TSS) of fruits. On the other hand, fruit shape index, fruits number and fruit yield per tree were significantly (p ≤ 0.05) affected by the previous applied treatments (Figure 3 and Table 5 (Appendix 3)). At using hoeing, it’s achieved the highest average of fruit shape index (1.44) followed by black plastic mulch (1.36) and the lowest value obtained at applied white plastic mulch (1.24). The values of fruit shape index which attained by using the previous treatments were always more than one. This means that these treatments make fruits of cylindrical shape, whereas the other treatments make it more spherical (El-Seginy, 2000). Also, data presented in Table (5) revealed insignificant (p ≤ 0.05) differences were determined in total soluble solids percent of mandarin fruits between the used treatments. These results agreement with those by Abouziena et al. (2008) who reported that total soluble solids of mandarin fruits was unaffected by any of the mulch treatments. Also, Saied et al. (1993) found that TSS and total acidity percentages in pear fruits were not significantly affected by using of black or white polyethylene and hoeing treatments.
The increases in yield number of fruits per tree and fruit weight are also associated with general reductions in soil and citrus root nematode. These results are in agreement with Nakhla and Ghali (1996); Protopapadakis (1998) who found that polyethylene sheets lead to earlier fruit maturity and increased fruit yield. Besides control of T. semipenetrans resulted in increasing yield and fruit size in the two studied seasons following polyethylene mulching treatment. It is also associated with other factors as soil heat energy parameters, vigorous root and vegetation growth as also reported by Timmer and Davis (1982).
Covering the soil of mandarin orchard with black plastic mulch was recorded the highest fruit yield per tree, followed by white plastic then hoeing treatments (Figure 3). Similar findings were reported by Shirgure et al. (2003); Abouziena et al. (2008). In addition, the applied of white mulch also repels aphids which spread some virus diseases in vine trees (Kumar and Lal, 2012). Moreover, black plastic mulch increased the fruit yield per tree by 38.0 and 7.9% than that of hoeing and white plastic mulch, respectively. These increases may be attributed to the increment of fruits number per tree under black plastic mulch by 36.9 and 10.2% compared to hoeing and white plastic mulch treatments, respectively (Table 5). Bdr El-Deen (2004) reported that controlling weeds with winter tillage + hoeing four times / year reduced yield per tree by 9.5%, compared with the weed control treatment by polyethylene mulch.
Effect of fertilization treatments:
The data in Table (5) indicated that the compost type had a significant (p ≤ 0.05) effect on fruit parameters. This increment may be attributed to, that the application of composts to the sandy soils can improve the soil structure, cation exchange capacity, organic matter content as well as decreasing the soil content of calcium carbonate (Abd Elhamid et al., 2004; El-Khayat and Abdel Rehiem, 2013).
The highest fruit yield/tree was obtained by the application of weeds compost + biofertilizers followed by chicken manure+ biofertilizers.El- Khawaga (2012) reported that reducing the percentage of mineral N fertilizer from 100 to 50 % and at the same using compost enriched with actinomyces at 25 to 50 % and Bacillus polymyxa inEwaise mango orchardshad an announced promotion on leaf area, total chlorophylls, leaf contents of N, P and K, yield as well as quality of the fruits comparing with the mineral N alone. He attributed the promotion effect of using organic and biofertilization on the yield to their essential role on enhancing growth and nutritional status of the trees.
Insignificant (p ≤ 0.05) difference was noticed with respect to fruit yield per tree between rice straw compost and chemical fertilizer, while addition of biofertilizer attained significantly (p ≤ 0.05) surpassed the two previous treatments (Fig. 4). Rashad et al. (2011) found that all the used types of rice straw compost showed a high fertilizer value when applied at the rate of 5% (w/w) as indicated by ameliorating the soil microbial population, chemical properties, plant growth response and subsequently the productivity of sandy soil comparing to the mineral fertilizer.
Using the chicken manure compost without biofertilizers significant (p ≤ 0.05) surpassed the other composts in fruit yield per tree, while the lowest yield was recorded at using maize stalks compost treatment. The variation in fruit yield between the different of composts may be attributed to, that the mineralization is higher at tighten C/N ratios of the material concerned. For example, straw from legumes (C/N = 15 – 25) mineralizes fast, cereal straw (C/N = 50 – 100) slowly (Amlinger et al., 2007). The treatments of chicken manure and composted rice straw without biofertilizer surpassed the chemical treatment in fruit yield by 34.9 and 14.0%, respectively (Figure 4). On the other hand, application of maize stalks compost caused a reduction in the fruit yield by 8.1%.
Table 5. Effect ofweedcontroltreatments and bio-organic fertilizers and their interactions on mandarin yield (average of two seasons).
b) Interaction between hoeing, whiteand black plastic mulches and fertilization treatments:
Generally, the association action between composted plant wastes and biofertilizer caused to increase the number and fruit yield under different pest control treatments (Table 5 and Figure 5). The treatment of composted weeds was recorded the greatest fruits yield under black plastic mulch. Similar finding was reported by Abu Irmaileh et al. (2011) who mentioned that weeds were significantly reduced and fruit trees were significantly larger in the treatments with manures in the black polyethylene -covered treatments as compared to the non-covered treatment. Ustuner and Ustuner (2011) reported that covering the soil with black plastic mulch prevented seeds of weeds to germinate, increased the growth of roots and fertility of soil by keeping soil moisture. Also, they reported that plastic mulches caused increase the temperature of soil in a value of 3 to 5°C, and for this reason, it would ensure better blossoming of roots and stimulate powerful growth. Additionally, plastic mulches keep the soil moisture (Smith et al., 2000).Moreover, the diversity of microorganisms in mature composts exhibit suppressive effects on several pathogens and diseases which could harm plant life or human health (Amlinger et al., 2007).
The highest TSS in fruits was observed with rice straw compost + biofertilizer under white plastic mulch treatment followed by that of maize stalks + biofertilizer under black plastic mulch (Table 5 (Appendix 3)). Helail et al. (2012) reported that the increments of mandarin yield in composted manure treatments may be attribute to the compost act as slow release N fertilizers and regulating the release of their own nitrogen at the proper time as the plant need. Also, they gave the highest values of residual N due to their low acidity index, while soluble ones gave the lowest values of available N left in the soil. In addition, the role of N as a constituent of amino acids and protein as well as its importance in cell division and development of meristematic tissues (Mengel and Kirby, 1987). Also, Verdú and Mas (2007) reported that mulching is one weed control strategy in mandarin orchards that also provides other benefits, such as soil protection or avoiding herbicide pollution. Moreover, Shirgure et al. (2003) reported that the highest fruit yield/tree, fruit weight and total soluble solids of Nagpur mandarin (C. reticulata)were recorded at using black and white polyethylene mulch.
Finally, the dual effect of the additive organic and inorganic fertilizers as well as polyethylene sheets in increasing the growth and yield of Balady mandarin and controlling the associated weeds and T. semipentrans is verified. This approach of nematode and weeds control has an advantage over the use of herbicides or nematicidal chemicals, since it is less expensive, safer and easy to apply with no pollution risks and can improve soil structure and nutritional status.
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