Comparison of Organic and Inorganic Mulching for Weed Suppression in Wheat under Rain-Fed Conditions of Haripur, Pakistan

: Weeds pose a great threat to crop production subsequently distressing the equilibrium of agro-ecological systems globally. Instead of relying on chemical weed control, there is a dire need to explore alternative eco-friendly agricultural practices for weed suppression and sustainable wheat production. Mulching being eco-friendly could potentially serve the purpose towards weed suppression organically. To check the usefulness of mulching, two-year studies were conducted under ﬁeld conditions in Haripur, Pakistan, during 2014 and 2015 to elucidate the response of various mulching materials for weed control in wheat. Six mulch material treatments were used along with Buctril super (used as check) at the rate of 1.235 L ha − 1 to control the most problematic weed species of wheat in Pakistan. Experiments were designed under randomized complete block design with four repeats. The analysis of data revealed a signiﬁcant decrease in weed density, relative weed density, fresh and dry plant biomass at 25, 50 and 75 days after sowing (DAS) where Buctril super at 1.235 L ha − 1 and mulch of black plastic were used followed by sugarcane bagasse and dry leaves of mulberry, as compared with control (untreated). Higher density of weed, relative weed density, fresh and dry plant biomass were observed in test weed species of wheat where lentil was applied with wheat and dry leaves of mulberry were incorporated. Net economic beneﬁts in the form of beneﬁt cost ratio (2.55) were higher where grass clippings were applied followed by sugarcane bagasse (2.43), mulberry leaves (2.49), while the lowest net economic beneﬁts (1.72) were obtained when lentil (grown as live mulch crop) with wheat was intercropped. It was concluded from the study that sugarcane bagasse and grass clippings could be a source to control weeds in the wheat with a minimum cost of production at Haripur, Pakistan, and similar agro-climatic environment.


Introduction
Wheat (Triticum aestivum L.) is considered as a staple food for almost 33% of the world's population [1]. Wheat is produced in irrigated and unirrigated areas in Pakistan. Its cultivation area in rain-fed areas of Pakistan is 1.24 million hectares with average yield of 0.5-1.3 t ha −1 but in irrigated areas, average yield is about 2.7 t ha −1 in spite of genetic yield potential of 6-8 t ha −1 . There are several factors which reduce wheat yield including weed invasion as significant problem in yield reduction up to 40% [2]. Prominent weed species troublesome for wheat production in Pakistan are Avena fatua, Carthamus oxyacantha, Chenopodium album, Convolvulus arvensis, Euphorbia helioscopia, Fumaria indica, Phalaris minor method [15]. Phosphorus and potassium (AB-DTPA extractable) were estimated by the procedure described by Soltanpour and Schwab [16] using spectrophotometer and flame photometer. The Kjeldhal method of Bremner [17] was used for calculation of total nitrogen in the soil. Soil organic matter was estimated by the procedure as described by BALL [18]. The DTPA (diethylenetriaminepentaacetic acid) micronutrient extraction procedure of Lindsay and Norvell [19] was used for estimation of soil zinc, copper, iron and manganese. Analysis of soil for physiochemical properties revealed texture silt loam alkaline with pH 7.1, electrical conductivity 0.29 dSm −1 , organic matter 1.02%, nitrogen 0.051%, phosphorous 0.085 mg 100 g −1 soil, potassium 0.31 mg 100 g −1 soil, zinc 0.232 mg 100 g −1 soil, copper 0.027 mg 100 g −1 , iron 0.024 mg 100 g −1 and manganese 0.97 mg 100 g −1 soil respectively. The weather data of the experimental site (2013-2014 and 2014-2015) is shown in Figures 1 and 2, respectively. Seeds of wheat cultivar Pirsabak-2005 were obtained from the Cereal Crop Research Institute, Pirsabak, Nowshera, and sown in lines by a hand drill using seed rate of 125 kg ha −1 during first week of November, 2013 and 2014. Treatments were designed as T1: Control (No mulching), T2: Maize stalk mulch @ 4 t ha −1 , T3: Dry leaves of mulberry @ 4 t ha −1 , T4: Sugarcane bagasse @ 4 t ha −1 , T5: Grass clippings @ 4 t ha −1 , T6: Living mulch (lentil crop), T7: Mulch of black plastic and T8: Herbicide (Buctril Super @ 1.235 L ha −1 ). Maize stalk, dry leaves of mulberry, sugarcane bagasse, mulch of black plastic and grass clippings were applied after sowing of crops while living mulch (lentil crop) was applied in between rows of the main crop (wheat) after sowing while herbicide was applied after sowing of wheat. Seeds of wheat cultivar Pirsabak-2005 were obtained from the Cereal Crop Research Institute, Pirsabak, Nowshera, and sown in lines by a hand drill using seed rate of 125 kg ha −1 during first week of November, 2013 and 2014. Treatments were designed as T1: Control (No mulching), T2: Maize stalk mulch @ 4 t ha −1 , T3: Dry leaves of mulberry @ 4 t ha −1 , T4: Sugarcane bagasse @ 4 t ha −1 , T5: Grass clippings @ 4 t ha −1 , T6: Living mulch (lentil crop), T7: Mulch of black plastic and T8: Herbicide (Buctril Super @ 1.235 L ha −1 ). Maize stalk, dry leaves of mulberry, sugarcane bagasse, mulch of black plastic and grass clippings were applied after sowing of crops while living mulch (lentil crop) was applied in between rows of the main crop (wheat) after sowing while herbicide was applied after sowing of wheat. Phosphorus (100 kg ha −1 ) form di-ammonium phosphate, potash (100 kg ha −1 ) form sulfate of potash and nitrogen (150 kg ha −1 ) form ammonium sulphate was applied in two splits: half at the time of sowing while the remaining nitrogen was applied at tillering stage. Crop was harvested manually on April 20, 2014 and 2015. Leaf area of wheat plants were measured using portable leaf area meter (CI-202, CID Bio-Science Inc., USA). Plants were sun dried after harvesting, weighed and biological yield was recorded using spring balance. The plots were separately threshed and grain yield was determined by electrical balance.

Sampling and Observations
Weeds density (m −2 ) at 25, 50 and 75 days after sowing (DAS) was noted through quadrates of 50 × 50 cm (0.25 m −2 ) from every plot at 25, 50 and 75 DAS (BBCH) at principal growth stages 2, 4 and 7 [20]. The weeds species found in the quadrat were identified and their number was noted by uprooting from the ground. The numbers of weeds were counted by randomly throwing quadrat at two different locations in each plot and then the average was taken.
The relative weed density (m 2 ) at 25, 50 and 75 DAS was determined using the following formula: Relative weed density RD = Density of a given weed species Density of total weeds × 100 Weed dry biomass was noted in quadrats of 50 × 50 cm (0.25 m −2 ) at 25, 50 and 75 DAS. Weeds were clipped off, put in paper bags and oven dried at 70 °C for 72 h. After drying, weed dry weight was measured using a digital balance (T × 323 L, Shimadzu, Japan). Phosphorus (100 kg ha −1 ) form di-ammonium phosphate, potash (100 kg ha −1 ) form sulfate of potash and nitrogen (150 kg ha −1 ) form ammonium sulphate was applied in two splits: half at the time of sowing while the remaining nitrogen was applied at tillering stage. Crop was harvested manually on 20 April 2014 and 2015. Leaf area of wheat plants were measured using portable leaf area meter (CI-202, CID Bio-Science Inc., Portland, OR, USA). Plants were sun dried after harvesting, weighed and biological yield was recorded using spring balance. The plots were separately threshed and grain yield was determined by electrical balance.

Sampling and Observations
Weeds density (m −2 ) at 25, 50 and 75 days after sowing (DAS) was noted through quadrates of 50 × 50 cm (0.25 m −2 ) from every plot at 25, 50 and 75 DAS (BBCH) at principal growth stages 2, 4 and 7 [20]. The weeds species found in the quadrat were identified and their number was noted by uprooting from the ground. The numbers of weeds were counted by randomly throwing quadrat at two different locations in each plot and then the average was taken.
The relative weed density (m 2 ) at 25, 50 and 75 DAS was determined using the following formula: Relative weed density (RD) = Density of a given weed species Density of total weeds × 100 Weed dry biomass was noted in quadrats of 50 × 50 cm (0.25 m −2 ) at 25, 50 and 75 DAS. Weeds were clipped off, put in paper bags and oven dried at 70 • C for 72 h. After drying, weed dry weight was measured using a digital balance (T × 323 L, Shimadzu, Japan).

Economic Analysis
Economic analysis of different treatments, cost of wheat production (seedbed preparation, tillage, sowing, land rent, watch and ward, cost of fertilizers, harvesting and threshing was calculated etc.) in the years 2014 and 2015 was calculated [21]. The variable cost incurring from various mulching materials and herbicide use during the two growing seasons was calculated. The gross income was determined on the basis of wheat yield per hectare according to prevailing market value (Source: Agriculture Policy Institute, Islamabad, Pakistan). Benefits cost ratio (BCR) was calculated for all individual treatments using the following formula and best treatment contributing towards wheat income was identified.

BCR =
Gross income Total cos t After BCR calculation, net income (USD ha −1 ) was worked out for each treatment by the following formula: Net income USD ha −1 = Gross income − Total variable cos t

Statistical Analysis
The collected data were analysed by analysis of variance (ANOVA) and means were compared by employing Tukey's honestly significant difference (HSD) test at 5% probability using Statistix 8.1.

Mulching Materials Effect on Weed Density
Higher reduction (up to 96%) in weed density of all the tested weeds was observed under Herbicide spray at 25, 50 and 75 DAS respectively. Maximum weed density reduction (93%) of Convolvulus arvensis on 25 DAS was observed where mulch of black plastic and herbicide spray were applied separately (Table 1). Dry leaves of mulberry and living mulch affect were minimum on weed density of all weeds at all the three stages of application ( Table 1). The overall trend of weed density reduction by various mulching treatments was in the following order: herbicide spray > black plastic mulch > sugarcane bagasse > maize stalk mulch > grass clipping > living mulch > dry leaves of mulberry. The magnitude of reduction (up to 90%) in weed density by black plastic mulch was noted comparable to herbicide spray at all the three growth stages.

Mulching Materials Effect on Relative Weed Density
Lowest relative weed density of Carthamus oxyacantha and Convolvulus arvensis was observed where herbicide was sprayed and it was statistically similar to mulch of black plastic, sugarcane bagasse and maize stalk ( Table 2). Maximum relative weed density was also noticed in dry leaves of mulberry treatment and found statistically (p ≤ 0.05) similar to mulching of lentil intercropped with wheat and control. The overall maize stalk mulch was found best to reduce the relative weed densities of the tested weeds at 25, 50 and 75 DAS. However, the effect of grass clippings was highest in reducing relative weed densities of Euphorbia helioscopia, Fumaria indica, Phalaris minor and Sonchus oleraceus at all the three growth stages (Table 2). The values represent the averages (±standard error (SE)) of three independent replicates followed by different letters within columns are significantly different at p ≤ 0.05, according to Tukey's honestly significant difference (HSD) test. The values represent the averages (±SE) of three independent replicates followed by different letters within columns are significantly different at p ≤ 0.05, according to Tukey's HSD test.

Mulching Materials Effect on Fresh Biomass
Highest reduction in fresh biomass of all the weed species was observed under Herbicide spray at 25, 50 and 75 DAS respectively ( Table 3). The other mulching treatments found effective in reducing fresh biomass were black plastic mulch followed by sugarcane bagasse, grass clipping, maize stalk mulch and living mulch respectively. Overall black plastic mulch and sugarcane bagasse were found as best mulching treatments to reduce the fresh biomass of all the investigated weed species at 25, 50 and 75 DAS (Table 3).

Mulching Materials Effect on Dry Biomass
Highest decrease in dry biomass of all the weed species was recorded under herbicide application (Table 4). Black plastic mulch and grass clipping followed by sugarcane bagasse were found as best treatments to reduce the dry biomass of all the tested weeds at 25, 50 and 75 DAS. The effect of black plastic mulch and sugarcane bagasse in reducing dry biomass of Avena fatua and Carthamus oxyacantha was similar and statistically alike to herbicide treatment. Similarly, grass clippings and maize stalk mulch produced statistically similar effects in dry biomass reduction of Carthamus oxyacantha (Table 4).

Mulching Materials Effect on Plant Height, Number of Leaves, Leaf Area, 1000-Grain Weight and Grain Yield of Wheat
The effect of mulching treatments on wheat plant height was significant (Table 5). Maximum plant height of wheat was obtained where herbicide was sprayed followed by black plastic mulch. Minimum plant height was recorded where lentil was intercropped with wheat, however, it was statistically similar to dry leaves of mulberry and control where no mulch was applied. The numbers of leaves in wheat crops at 25, 50 and 75 DAS were significantly affected by mulching treatments. Wheat produced more number of leaves where herbicide was sprayed and it was statistically similar to black plastic mulch followed by sugarcane bagasse and maize stalk mulch. Similarly more leaf area of wheat was recorded where herbicide was sprayed and it was statistically similar to black plastic mulch followed by sugarcane bagasse. Minimum leaf area of wheat plants was noted where lentil was intercropped with wheat, however, it was statistically similar to dry leaves of mulberry and control ( Table 5). The effects of mulching treatments on 1000 grain weight and grain yield of wheat were significant (Table 5, Figure 3). Maximum 1000 grain weight was obtained where sugarcane bagasse was applied followed by grass clipping mulch and dry leaves of mulberry. Minimum 1000 grain weight of wheat was recorded under control. Maximum wheat yield (5.87 t ha −1 ) was recorded where plastic mulch was used followed by herbicide spray (5.81 t ha −1 ) and dry leaves of mulberry (5.72 t ha −1 ).

Economic Analysis of Treatments
The economic analysis indicated highest BCR (2.55) and net earnings (678 USD ha −1 ) where grass clippings were used as mulch followed by dry leaves of mulberry, sugarcane bagasse, control, mulch of black plastic and herbicide spray to combat weeds in wheat ( Table 6).

Economic Analysis of Treatments
The economic analysis indicated highest BCR (2.55) and net earnings (678 USD ha −1 ) where grass clippings were used as mulch followed by dry leaves of mulberry, sugarcane bagasse, control, mulch of black plastic and herbicide spray to combat weeds in wheat (Table 6). The values represent the averages (±SE) of three independent replicates followed by different letters within columns are significantly different at p ≤ 0.05, according to Tukey's HSD test. The values represent the averages (±SE) of three independent replicates followed by different letters within columns are significantly different at p ≤ 0.05, according to Tukey's HSD test.

Discussion
The effect of various mulch materials on relative weed density, weed density, biomass of weed species in wheat was significant in the current research study. Notable reduction in relative weed density, weed density, and fresh and dry biomass of weed species was noticed where herbicide and black plastic mulch were used followed by sugarcane bagasse in comparison to control (no mulch was used). Maximum relative weed density, weed density, and weed biomass was observed where lentil was intercropped with wheat and dry leaves of mulberry applications which may be due to the phytotoxic effects of herbicide. Application of herbicides provides quick outcomes by blocking energy production units of weed plants. Herbicides also affect cellular respiration of weed plants. Reduction in relative weed density, weed density, fresh and dry biomass of wheat weeds using mulch of black plastic are in line with Ashrafuzzaman et al. [22] who reported that black plastic mulch could result in 100% control of all weeds in maize. Kareem et al. [23] reported that mulch of black plastic progressively reduced weeds density in okra plants. Mulches reduce evaporation and erosion of soil as well as cause reduction in weed growth and increase crop yield in different crops [24,25]. Mulching helps in reducing soil evaporation, conserving moisture, controlling soil temperature, reducing weed growth, and improving microbial activities [26]. Grass clippings, dry leaves of mulberry and sugarcane bagasse decreased relative weed density, weed density, and biomass of weeds in wheat crops. Reduction in weeds density and their fresh and dry biomass by these mulching treatments might be due to the presence of allelochemicals which have phytotoxic effects on weeds. Earlier, Sampietro et al. [27] reported that sugarcane straw had trans-ferulic, cis-ferulic, vanillic and syringic acids. The allelochemicals of phenolic nature increase leakage of root cell constituents, inhibited dehydrogenase activity and reduced chlorophyll content in lettuce. In an another research study, biomass production in soyabean plants biomass reduced because of low chlorophyll content when they were treated with phenolic acids (vanillic acids, ferulic, p-coumaric) [28]. The increase in relative weed density, biomass of weed species were recorded in the current study, where lentil (living mulch) was intercropped with wheat. High weed density and relative weed density might be due to competition for essential resources (nutrients, moisture and light). Majority of weeds belong to C 4 category of plants which are efficient to CO 2 and absorb nutrients. Moreover, weeds have deep root systems and uptake moisture and nutrients more deeply than other C 3 plants such as wheat and lentil. Weeds have high photosynthetic rates due to high carboxylation rate. Higher leaf area in wheat due to herbicide, plastic mulch and sugarcane bagasse applications might have led to higher dry matter accumulation in the crop on account of higher radiation interception over a prolonged period of time. Better resource acquisition and utilization might have favored wheat growth, higher tillers, spikes, more dry matter accumulation and higher 1000-grain weight by wheat plants. Our results conform with those of Chhokar et al., [29] and Santos [30] who reported that herbicides offer a sizeable increase in crop productivity corresponding to their weed control spectrum. Sugarcane bagasse had allelochemicals which are toxic to weeds, reduce weeds growth, their density, and hence increased 1000 grain yield in wheat. Other possible reasons behind increasing the wheat grain yield may be due to increase in soil water availability by sugarcane bagasse applications. Sugarcane bagasse on its decomposition produces organic acids, which mobilize the insoluble phosphorus from soil to soil solution in the available form. In an earlier research, sugarcane bagasse not only improved the physical condition of the soil but also enhanced macro-spore for a better root growth, and ultimately improved the cane yield [31]. These results also confirmed the findings of Lamont [32] who found that sugarcane bagasse is good option for better crop yield. Kader et al. [33] and Wang et al. [34,35] found that mulching is beneficial for yield enhancement with reduced input resources. Nwosisi et al. [36] revealed similar results with organic mulching in sweet potato cultivars.

Conclusions
Based on reduction in weed density, relative weed density, fresh biomass, dry biomass of different weed species of wheat and corresponding positive influence on plant height, number of leaves, leaf area and 1000-grain weight of wheat it was concluded that grass clippings and sugarcane bagasse each used at 4 t ha −1 as a mulch and easily available provided effective weed control in wheat. Therefore, this can be used for decreasing weed dynamics in wheat under rain-fed conditions with reduced cost of production in Haripur, Pakistan.