Método Otimizado de Controle de Plantas Daninhas para o Aumento do Rendimento da Tangerina Kinnow através da Melhora das Propriedades Físicas do Solo - Trabalho de Conclusão de Curso - TCC (2024)

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Planta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 1151103-PD-2016 (9 páginas) PROVA GRÁFICASAJID, M.1*AHMAD, S.1JASKANI, M.J.1YASIN, M.1ArticlePLANTA DANINHA* Corresponding author: <saeedsandhu@uaf.edu.pk>Received: September 6, 2016Approved: June 12, 2017Planta Daninha 2018; v36:e018168903SOCIEDADE BRASILEIRA DACIÊNCIA DAS PLANTAS DANINHAS1 University of Agriculture, Faisalabad, Pakistan.Doi: 10.1590/S0100-83582018360100084<http://www.sbcpd.org>ISSN 0100-8358 (print) 1806-9681 (online)OPTIMUM WEED CONTROL METHOD INCREASES THE YIELDOF KINNOW BY IMPROVING THE PHYSICAL PROPERTIES OFSOILMétodo Otimizado de Controle de Plantas Daninhas para o Aumento doRendimento da Tangerina ‘Kinnow’ através da Melhora das PropriedadesFísicas do SoloABSTRACT - Going towards sustainable fruit culture, it is very important that soilfertility should maintain by adopting the proper weeds control and adding the organicmatter. This research was carried out to identify the most suitable weed controlmethod for Kinnow orchard. The plants of Kinnow at the age of 6 years grown underdrip irrigation were selected. Weeds of orchard were managed by mulching (woodchip and black polyethylene), mechanical (cultivator and rotavator) and chemical(glyphosate) methods. Mechanical weed control was taken as control treatment.The plants where wood chip mulching was used for weed control showed maximumincrease in shoot length (24.00 cm), chlorophyll contents (84.00 SPAD value) andyield (11.88 ton ha-1) followed by the plants where weeds were controlled with chemicalcontrol while lowest shoot length (12.00 and 12.33 cm), chlorophyll contents (41.00and 42.67 SPAD value) and yield (3.80 and 4.70 ton) was achieved in cultivator androtavator treatment respectively. Wood chip mulch also improved soil physicalproperties by reducing bulk density (1.49 Mg m-3), soil penetration resistance(785.33 kPa) and by enhancing soil organic matter (1.17%), hydraulic conductivity(34.50 mm hr-1) and soil microbial biomass carbon (159.68 g kg-1) followed byglyphosate control while lowest values of soil physical properties were obtained incultivator and rotavator weed control. Wood chip mulch also reduced weed dryweight (45.25 g) and efficiently controlled weeds (95.66%) as compared to otherweed control methods. In this case, wood chip mulch performed better in all studiedparameters than plastic mulch, rotavator, cultivator and glyphosate weed control.So, wood chip mulch should be recommended to citrus grower for improving soilphysical properties and yield.Keywords: citrus, mulches, glyphosate, mechanical control, soil physical properties,yield.RESUMO - Na fruticultura sustentável, é muito importante manter a fertilidade dosolo adotando-se o controle adequado de plantas daninhas e adicionando-sematéria orgânica. Assim, esta pesquisa foi realizada para identificar o modo decontrole de plantas daninhas mais adequado para pomares de tangerina Kinnow.Foram selecionadas plantas de Kinnow com idade de 6 anos, cultivadas sobirrigação por gotejamento. As plantas daninhas do pomar foram submetidas acontrole por meio de cobertura (com cavacos de madeira ou com polietileno preto),controle mecânico (cultivador e enxada rotativa) e métodos químicos (glifosato).O controle mecânico de plantas daninhas foi adotado como tratamento de controle.Copyright: This is an open-accessarticle distributed under the terms of theCreative Commons Attribution License,which permits unrestricted use,distribution, and reproduction in anymedium, provided that the originalauthor and source are credited.Planta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 2As plantas onde foi utilizada a cobertura com cavacos de madeira para controle das plantas daninhasmostraram aumento máximo em comprimento da parte aérea (24,00 cm), teores de clorofila (valor doíndice SPAD de 84,00) e rendimento (11,88 t ha-1), seguidas pelas plantas nas quais o controle deplantas daninhas foi realizado quimicamente, em comparação com as plantas com controle por meio docultivador e da enxada rotativa, nas quais houve menor comprimento da parte aérea (12,00 e 12,33 cm),menores teores de clorofila (valores de SPAD de 41,00 e 42,67) e menor rendimento (3,80 e 4,70 t),respectivamente. A cobertura com cavacos de madeira também melhorou as propriedades físicas dosolo, reduzindo a densidade do solo (1,49 Mg m-3) e a sua resistência à penetração (785,33 kPa); emcontrapartida, houve aumento do teor de matéria orgânica do solo (1,17%), da condutividade hidráulica(34,50 mm h-1) e do carbono da biomassa microbiana do solo (159,68 g kg-1). O segundo melhorresultado foi obtido pelo controle com glifosato, enquanto os menores valores das propriedades físicasdo solo foram observados no controle de plantas daninhas com o uso do cultivador e da enxadarotativa. A cobertura com cavacos de madeira também reduziu a massa seca das plantas daninhas(45,25 g) e exerceu controle eficiente delas (95,66%), em comparação com outros métodos de controle.Nesse caso, a cobertura com cavacos de madeira obteve melhor desempenho no controle de plantasdaninhas, em todos os parâmetros estudados, do que a cobertura plástica, a enxada rotativa, o cultivadore o glifosato. Assim, recomenda-se a cobertura com cavacos de madeira para que os citricultoresconsigam melhorar as propriedades físicas do solo e o rendimento.Palavras-chave: citrinos, cobertura do solo, glifosato, controle mecânico, propriedades físicas do solo,rendimento.INTRODUCTIONWeed management operations include conventional practices such as cultivation andapplication of residual herbicides among the rows of citrus orchards in Pakistan. Herbicides areknown as the best option in weed management strategy; however, mishandling this technologycan create many problems, e.g., residual contents of herbicides, cropping limitations,contamination of underground water and development of genetically resistant weeds (Verdu andMas, 2007). Important environmental concerns include repeated tillage on orchard ground, whichresults in soil erosion, and long-term herbicide application. Questions have been raised concerningthe long-term environmental impact of repeated tillage on soil erosion and pesticide applicationon soil and underground water quality (Duran et al., 2004; Verdu and Mas, 2007).Alternatively, best management practices, which have been effectively implemented in someof the main citrus growing areas in the world (Sansavini, 1997), combine conventional andmodern farming systems in order to optimize both environmental quality and economic profit.Manual weeding is adopted in most developing countries because herbicidal weed control isunaffordable and it also has environmental concerns. Mulching is one of the most profitablemethods which can be adopted in citriculture. Mulch is a protective layer of organic or inorganicmaterial which is spread on soil surface. Along with a number of benefits, mulch restricts weedgrowth.Living mulches, black polyethylene mulches and dead organic mulches (such as straw, barksand wood shavings) can be used for good weed control. Many researchers have accounted thereturns and restrictions of each of them (Liedgens et al., 2004).Black polyethylene mulches are spread for weed management of many crops in organicgrowing systems (Bond and Grundy, 2001). Black polythene reduces weed growth and improvesfruit yield as a result of improved soil moisture. However, in this type of mulch, organic matterand nutrients are not added to the soil (Bredell, 1973).Adequate thick layer of organic mulches such as straw and bark can suppress weeds effectivelyalong with enrichment of soil with organic matter and nutrients(Merwin et al., 1995). Microbesdecompose organic mulches and produce phytotoxic compounds which kill weed species. Weedsare also suppressed by the physical presence of organic mulches which create hindrance inlight and reduce the photosynthetic activity of weed populations (Ozores-Hampton et al., 2001).Decomposition of organic material is a continuous process. Because of this periodic re-application,complete suppression has to be attained. However, decomposition enhances soil aggregationand water-holding capacity (Haynes, 1980).Planta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 3Mulches are not only used for inhibition of weeds but their main goal is to achieve a betterenvironment with maximum profit. According to the “Guidelines International Organization forBiological and Integrated Control of Noxious Animals and Plants”, trials involving mulches,especially loose materials from adjacent crops and furniture industry, are entirely appropriatein view of the modern approach to integrated plant protection in sustainable production systems.Therefore, this work evaluated the performance of mulches, herbicides and mechanical controlon soil physical properties and yield of citrus reticulate cv. Blanco.MATERIAL AND METHODSThe study was conducted on Kinnow mandarin (Citrus reticulate cv. Blanko) plants at thePostgraduate Research Station (PARS), University of Agriculture, Faisalabad, Pakistan (Latitude31o-26oN and longitude 73o-06oE). The long-term average yearly precipitation and the averagemonthly air temperatures are shown in Table 1 (Water Management Metrological Observatory,PARS). During the study, from February 2013 to January 2015, accumulated rainfall was 22.87mm, and average monthly temperature was 24.35 oC. The drip-irrigation system in use consistedof one drip line for each plant. Irrigation scheduling was designed based on tensiometer readingsin the top 30 cm soil layer. The amounts of fertilizers applied were 700g per tree per year N,300 g per tree per year P and 300g per tree per year K. The trees in PARS were spaced at 3.35 mwhile rows were 6.70 m apart.There were five treatments which were repeated four times and ten trees per treatmentwere selected. Weed control methods (treatments) included wood chip mulch, plastic mulch,cultivator, rotavator and glyphosate, which were applied in February 2013. The cultivator, therotavator and glyphosate were applied four times a year. The wood chip mulch and the polyethylenemulch were applied 3 times a year. Thickness of the wood chip mulch and the polyethylenemulch was 3 cm and 0.05 mm, respectively. The depth of the cultivator and the rotavator was6 inches.Physio-chemical characteristics of the soil were determined before conducting the experiment(Table 2). During August, 2013, at moisture contents close to field capacity, undisturbed soilcores were taken from the field using a core soil sampler. For core sampling, three equally-spaced points around the plant were marked for sampling. These samples were taken from anarea of approximately 65-70 cm radius from the tree trunks within each plot. The total area ofeach plot where treatments were applied was 0.45 ha. Each value reported in the text is themean of 10 values (4 replicates x 3 samples). Thus, the samples were taken from an area awayfrom the tracks of tractors (from edges of tree canopy) where machinery had not affected the soilduring field operations. Separate sets of core sampling were prepared from each treatment atsoil depths of 0-15, 15-30, 30-50 and 50-100 cm for soil bulk density determinations (Klute,Table 1 - Temporal variations in temperature and rainfallduring the two-year study (2013-2014)Month Temperature (oC) Rainfall (mm) January 10.20 1.21 February 13.80 55.0 March 20.00 1.30 April 26.60 21.6 May 32.00 4.61 June 33.70 67.5 July 33.00 4.71 August 31.31 114.8 September 31.00 3.31 October 27.11 0.00 November 19.00 0.51 December 14.51 0.00 Table 2 - Physico-chemical characteristics of the experimentalsite before the beginning of the experiment1986). Field saturated hydraulic conductivity(kfs) was measured following the proceduresgiven in Klute (1986). Soil penetrationresistance (SPR) was measured using a coneCharacteristic Value Sand (% 55.5 Silt (%) 16.5 Clay (%) 22.01 Textural class (%) Sandy clay loam Total Nitrogen (%) 0.105 Available Phosphorus (mg kg-1) 7.4 Extractable Potassium ((mg kg-1) 145.7 Planta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 4penetrometer. The cone was pressed into the soil until soil surface was leveled with the base ofthe cone. The measurements of SPR, bulk density (BD) and kfs were carried out in January,after harvesting citrus in each year. Soil microbial biomass carbon (SMBC) was determinedusing the fumigation–extraction method (Bhatt and Binmeru, 2014). Soil organic matter wasdetermined using the methods described by Moodie et al. (1959). Weed dry weight and weedcontrol percentage were determined by following the procedures of Abouziena et al. (2008).Shoot growth data were recorded for three flushes (spring, summer and late summer fallflush) each year. Flush length was measured for the tagged branches from four sides of theplant. Shoot growth data were taken at maturity/cease of growth, while canopy diameter andstem diameter were measured in (m) and (cm), respectively. Citrus yield in each treatment wasrecorded by weighing harvested fruit from each treatment using a WUE-SEP digital electricbalance. Yield was recoded in ton ha-1. The data were analyzed statistically using five weedcontrol methods and four replications in a randomized complete block design, using the CO-STATSsoftware. There were ten plants in each treatment. The means were compared with the leastsignificant difference (LSD) test at the probability level of 0.05% (Steel and Torrie, 1997).RESULTS AND DISCUSSIONShoot growth indices (cm)Wood chip mulch resulted in the greatest increase of shoot length, as compared to all otherweed control methods, followed by plastic mulch (Figure 1), while there was minimum shootlength with the rotavator and the cultivator. Among the mulches, the wood chip mulch increasedshoot length (24.00 cm) more than the plastic mulch (19.66 cm) during SpF. Lowest SpF wasfound in plants where weeds were irradiated with the cultivator (12.00 cm) and the rotavator(12.33 cm). During the SF stage, the wood chip mulch enhanced shoot length to 17.50 cm, followedby plastic mulch (13.33 cm). The lowest length of SF was found in plants where weed was irradiatedwith the cultivator (8.66 cm) and the rotavator (10.66 cm). Wood chip mulch also enhanced LSFto 20.16 cm, followed by plastic mulch, which was 16.66 cm. The lowest LSF was found in plantswhere weeds were irradiated with the cultivator (10.66 cm) and the rotavator (10.66 cm). Increasedshoot growth in plants where weeds were irradiated with wood chip mulch was due to highchlorophyll contents (Nguyen et al., 2013), high organic matter and hydraulic conductivity (Rehmanet al., 2012), low soil bulk density (Walsh et al., 1996), low soil penetration resistance (Hoaglandet al., 2008), high soil microbial biomass carbon (Ingels et al., 2005) and reduced competition ofcitrus plants with weeds (Abouziena et al., 2008). Lower shoot length in the cultivator and theFigure 1 - Effect of weed control methods on shoot growth of Citrus reticulata.Shoot growth (cm)Weed control methodsPlanta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 5rotavator was due to degradation of soil structure (Rehman et al., 2012), nutrient loss resultingfrom high volatilization,reduced organic matter (Merwin and Stiles, 1994), higher bulk density(Mari and Chang, 2008), lower hydraulic conductivity (Rehman et al., 2012), lower soil organicbiomass carbon (Smith et al., 2008) and higher weed competition with young citrus plants(Abouziena et al., 2008).Chlorophyll contents (SPAD Value)Data on chlorophyll contents as affected by weed control methods showed that the wood chipmulch led to the highest increase in chlorophyll contents, followed by the plastic mulch, whilethe lowest amount of chlorophyll contents was achieved in the rotavator and he cultivator(Figure 2). Among the mulches, the wood chip mulch caused the highest increased in chlorophyllcontents (84.00 SPAD value) as compared to the plastic mulch (77.50 SPAD value). The lowestamounts of chlorophyll contents were found in the plants where weeds were irradiated with thecultivator (42.16) and the rotavator (43.66). The increased amount of chlorophyll contents in thewood chip mulch was due to improved soil conditions, e.g., improved soil structure (Bredell et al.,1976), bulk density (Laurent et al., 2008), organic matter (Ingels et al., 2005), higher nutrientavailability (Patrick et al., 2004), optimum soil moisture (Hembree et al., 2006), low soilpenetration resistance (Rehman et al., 2012) and soil microbial biomass carbon (Kabir and Koide,2002) which, in turn, produced improved root growth to facilitate absorption of nutrients andmoisture in order to produce higher chlorophyll contents. Lower chlorophyll contents in plantswhere weeds were irradiated with cultivator and rotavator were due to destruction of soilstructure, loss of nutrient and moisture (Salton and Mielniczuk, 1995) higher compaction andbulk density (Bertol et al., 2004) which, in turn, produced underdeveloped roots, and disturbancein taking moisture and nutrients. Our findings are in agreement with the findings of Yao et al.(2005).Chlorophyll contentsWeed control methodsYield (ton ha-1)The results showed that wood chip mulch gave more yield, followed by the plastic mulch,while lowest yield was recorded in the rotavator and the cultivator treatments. Among themulches, the wood chip mulch gave higher yield (11.88 ton ha-1) as compared to the plasticmulch (10.58 ton) (Figure 3). The lowest yield was found in plants where weeds were irradiatedwith the cultivator (3.81 ton ha-1) and the rotavator (4.71 ton ha-1). The higher yield in the woodFigure 2 - Effect of weed control methods on chlorophyll contents of Citrus reticulata.Planta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 6Yield (ton)Weed control methodsFigure 3 - Effect of weed control methods on yield of Citrus reticulata.chip mulch was due to improved physical soil properties (Kirandeep et al., 2010) and availabilityof optimum moisture and temperature (Shirgure et al., 2003) which, in turn, produced highergrowth with high fruit yield (Shirgure, 2012). The reason for the lowest yield in the cultivatorand the rotavator is soil degradation, erosion and nutrient loss, because the nitrogen present inthe soil is in organic form. Tillage increases the rate of mineralization and causes nitrogen toescape as a result of leaching or volatilization (Varennes, 2003). On the other hand, root injuriescaused by tillage are also another yield limiting factor by which plant growth was adverselyaffected and resulted in poor yield (Hogue and Neilsen, 1987). Our results are in line with thoseof Sanchez et al. (2006).Soil bulk density (Mg m-3)Bulk density showed little reduction by increasing soil depth in the cultivator and the rotavatorwhile, by contrast, the mulches showed a slight increase in bulk density with increasing soildepth; however, these differences were non-significant (Figure 4). Data on bulk density at 0-15 cmdepth showed that the wood chip much produced the lowest bulk density, followed by the plasticmulch, while the highest bulk density was found in the weed control by the rotavator and thecultivator. Among the mulches, the wood chip mulch showed lower bulk density (1.49 Mg m-3) ascompared with the plastic mulch (1.57 Mg m-3) through the soil profile 0-15 cm (Figure 4). Thehighest bulk density was found in plants where weeds were irradiated with the cultivator(1.72 Mg m-3) and the rotavator (1.73 Mg m 3). Bulk density is defined as weight per unit volume.Lower pore space among soil particle leads to higher compaction, which ultimatly reducedavailability of nutrients and reduced root growth (Viera and Klein, 2007). Lower bulk density inplots where weeds were controlled with mulches was due to higher microorganism activitiesand hydrothermal regulations (Fidalski et al., 2010). On the other hand, higher bulk density wasdue to the movement of heavy vehicles mounted for tillage implements on wet soils (Mari andChang, 2008).Organic matter (%)The results showed that organic matter was reduced through the soil profile. The maximumamount of organic matter was found in the top 0-15 cm layer of soil. Then, it started to declinewith increasing soil depth. The minimum amount of organic matter was found in the 50-100 cmdepth of soil. Among the weed control methods, the wood chip mulch and plastic mulch showedthe highest amount of organic matter, followed by the glyphosate weed control. Among the mulches,Planta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 7the wood chip mulch showed the highest amount of organic matter (1.17%) as compared to theplastic mulch (1.09%) through the soil profile of 0-15 cm (Figure 5). By comparison, the lowestamount of organic matter was found in the cultivator (0.51%) and the rotavator (0.54%). Thehigher organic matter content in the plots where the sweed were controlled with the wood chipmulch was due to biological activity, which decomposed wood chips and added organic matter inthe soils (Ingels et al., 2005). The lower organic matter in the plots where weeds were removedwith the cultivator and the rotavator were due to soil degradation, erosion and nutrient loss.Tillage increases the rates of mineralization and decomposition because of an increase in soiltemperature, and it causes the escape of nitrogen because of volatilization (Varennes, 2003).Our results are in line with findings of Merwin and Stiles (1994). They found a significant increasein soil organic matter content after application of organic mulches.Bulk density Mg-3Weed control methodsFigure 4 - Effect of weed control methods on soil bulk density.Figure 5 - Effect of weed control methods on soil organic matter.Organic matter (%)Weed control methodsPlanta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 8Hydraulic conductivity (mm hr-1)Hydraulic conductivity showed reduction trends as soil depth increased. Hydraulic conductivitywas maximum at 0-15 cm soil depth and minimum at 50-100 cm soil depth. The wood chipmulch and the plastic mulch showed the highest hydraulic conductivity, followed by glyphosate,while the lowest hydraulic conductivity was found in the weed control by the rotavator and thecultivator. Among the mulches, the wood chip mulch increased hydraulic conductivity(34.50 mm hr-1) as compared to the plastic mulch (32.50 mm hr-1) (Figure 6). By contrast, thelowest hydraulic conductivity was found in the cultivator (25.50 mm hr-1) and the rotavator(26.50 mm hr-1) through the soil profile of 0-15 cm. Hydraulic conductivity is the ability of thesoil to conduct water through the soil profile. This property affects the flow of water through thesoil. Hydraulic conductivity depends upon macrospores and microspores (Wahl et al., 2004).Micropores are often produced as a result of continuous tillage (Holden, 2005). However,macrospores are produced by biological activities in mulched fields (Zhou et al., 2008). It isunderstood that microspores are responsible for surface ponding, lower infiltration rate and soilcompaction (Daraghmeh et al., 2008). Higher hydraulic conductivity in plots where weeds werecontrolled with mulches was due to macrospores, improved water holding capacity of soil anddrainage of extra water to deeper layers (Alvarez and Steinbach, 2009). However, Lower hydraulicconductivity in plots where weeds were removed with the cultivator and the rotavator was due tomicrospores, reduced transport of water, reduced infiltration rate, surface ponding and compactionof soil (Pagliai et al., 2004). Our findings are in accordance with the findings of Ahmad andMahmood (2005).Hydrolic conductivity (mm hr-1)Weed control methodsFigure 6 - Effect of weed control methods on soil hydraulic conductivity.Soil penetration resistance (kPa)Lower values of soil penetration resistance (SPR) were found in plants where weeds wereirradiated with the wood chip mulch and the plastic mulch, followed by glyphosate, the rotavatorand the cultivator. Among the mulches, the wood chip mulch showed lower values of SPR(785.33 kPa) as compared to the plastic mulch (759.81 kPa) (Figure 7). However, the highestvalues of SPR were found in the rotavator (945.50 kPa) and the cultivator (917.50 kPa). LowerSPR rates in the wood chip mulch might have been due to higher soil organic matter lower bulkdensity (Henderson et al., 1988), higher hydraulic conductivity (Rayhani et al., 2007), Our resultsare line with the findings of Pervaiz et al. (2009).Planta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 9Penetration resistanceWeed control methodsFigure 7 - Effect of weed control methods on soil penetration resistence.Soil Microbial Biomass Carbon (SMBC) (g kg-1)The wood chip mulch and the plastic mulch showed a higher amount of soil microbial biomasscarbon (SMBC), followed by glyphosate, while the minimum amount of SMBC was found in themechanical control. Among the mulches, the wood chip mulch showed higher SMBC(159.68 g kg-1) contents as compared to the plastic mulch (147.45 g kg-1) (Figure 8). By contrast,the lowest amount of SMBC was found in the cultivator (128.01 g kg-1) and the rotavator(128.20 g kg-1). A higher amount of SMBC in the wood chip mulch might be due to addition oforganic material to soil, e.g., mulch which enhanced decomposition of that material (Gassenand Gassen, 1996). Similar results were found by Lal et al. (2003).Weed control (%)The results showed that the wood chip mulch and the plastic mulch performed best ascompared to glyphosate while the rotavator and the cultivator showed poor weed control. Amongthe mulches, the wood chip mulch performed more in controlling weeds (95.00%) as compared tothe plastic mulch (89.50%) (Figure 9). The lowest weed control was achieved in the cultivator(60.00%) and the rotavator (66.50%). This may have been due to physical barriers provided by themulches. These barriers caused reduction in weed seed germination and seedling growth byreducing light which, in turn, caused reduction in photosynthesis. Mulches do not allow watercontents to escape to the air; in turn, there is an increase in soil moisture, and higher soilmoisture does not allow weed seeds to germinate. In some cases, if seedlings emerge, theybecome chlorotic and die. On the other hand, weed seeds remain in deep layers of soil as a resultof no tillage. Our findings are in line with the findings of Mohanty et al. (2002) and Shirgure etal. (2003) in citrus orchards. Lower weed control in the cultivator and the rotavator may havebeen due to breaking, thus exposing deeper soil layers to surface. Soil deep layers are seedbanks of weeds. If tillage is applied, weed seeds come out of deeper layers and starts to germinate.Our findings are in line with the findings of Clements et al. (1996).Weed dry weight (g)The data showed that the wood chip mulch and the plastic mulch produced lower weed dryweight, followed by weed control with glyphosate. The highest weed dry weight was found in therotavator and the cultivator (Figure 10). Among the mulches, the wood chip mulch showed lowerPlanta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 10Figure 8 - Effect of weed control methods on soil microbial biomass carbon.Figure 9 - Effect of weed control methods on weed control (%).Figure 10 - Effect of weed control methods on weed dry weight (g).Soil microbial biomasss carbon (g kg-1)Weed control methodsWeed control (%)Weed control methodsWeed dry weiht (g)Weed control methodsPlanta Daninha 2018; v36:e018168903SAJID, M. et al. Optimum weed control method increases the yield of kinnow by improving the physical properties of soil 11weed dry weight (22.33 g) as compared to the plastic mulch (39.00 g) (Figure 10). Weed dry weightin glyphosate was found to be higher (44.58 g) than in the mulches but lower than in the rotavatorand the cultivator. Maximum weed dry weight was found in the rotavator (103.00 g) and thecultivator (108.33 g). Lower weed dry weight in the wood chip mulch may have been due tohigher weed control. Our findings are in line with the findings of Radwan and Hussein (2001),who reported that mulches did not allow weeds to flourish which, in turn, produced lower weeddry weights. Higher weed dry weights were also found by Clements et al. (1996), who reportedthat higher weed dry weight in the rotavator and the cultivator was due to breaking and exposingdeeper soil layers to soil surface, which contains a huge amount of weed seeds, which lead tohigher weed population and higher weed dry weight.It is concluded that mulching is the most suitable weed control method in citrus. It improvesplant health and yield by improving soil physical properties and microbial biomass carbon. Thiswill also help to reduce the use of weedicides, which le1ave their residual effects in the air aswell as in crops.AKNOWLEDGEMENTSThe authors are highly thankful to the Endowment Fund Sectreate, University of AgricultureFaisalabad, for providing financial support to conduct these projects. 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