Impact of Various Types of Mulch Materials on Plant Growth, Yield and Quality Attributes of Kinnow Mandarin

Kinnow mandarin is a hydrid between ‘King’ (Citrus nobilis Lour.) and ‘Willow Leaf’ (Citrus deliciosa Tan.) of family Rutaceae developed at the University of California Research Centre, Riverside, USA by Dr. H.B. Frost in 1935 and introduced in India in 1959. Among citrus group, it is one of the important fruit crops commercially grown in North-Western parts of India (Arora et al., 2018). Kinnow mandarin has become the most popular among citrus growers of North Western parts of India because of higher yield potential and is adapted under arid and semi-arid climatic conditions of Punjab, Rajasthan, Haryana and Himachal Pradesh (Kumar et al., 2015). Consumers prefer Kinnow mandarin due to its attractive colour, high juice content, distinctive flavour and rich in vitamin C, vitamin B and b-carotene (Mahajan et al., 2018). Canal water is the major source of irrigation in majority of Kinnow mandarin growing areas. In most of these areas, available ground water has poor quality (brackish to saline) which is detrimental to the plant growth.  In present climate change scenario, water scarcity poses greater risk of yield reduction and economic losses to Kinnow growers. Therefore, cost effective techniques are needed to improve water use efficacy in these regions.
      
Mulching is a promising agronomic practice in which covering the soil surface with a thin layer of either organic (crop residues, dried weeds etc.) or inorganic (polyethylene) materials is practiced to conserve soil moisture and soil health thereby, plant growth and yield (Jordán et al., 2011). Several researchers studied the effect of various mulching materials such as dead organic mulch (Hammermeister, 2016), crop residue mulch (Budianta et al., 2018), horticultural fabric and corn straw mulches (Liao et al., 2021), plastic film, biodegradable paper and bio-based film mulches (Zhang et al., 2019), polyethylene, paddy straw and rice husk mulches (Lalruatsangi and Hazarika 2018 polyethylene mulch (Bhandari et al., 2017; Wang et al., 2019) under fruit tree canopy. Mulching plays significant role in suppression of weeds (Hammermeister, 2016; Sharma and Sharma, 2019), enhanced water use efficiency (El-Naggar et al., 2018, Singh et al., 2017; Suo et al., 2019), improved soil health (Budianta et al., 2018), reduce soil erosion and maintain soil temperature (Sarkar et al., 2019). It is an effective practice that enhance fruit yield and improve fruit quality in acid lime (Lalruatsangi and Hazarika 2018) and citrus (Kuniga et al., 2018; Wang et al., 2019; Xuemei et al., 2017). Therefore, this study was conducted with the objective to assess the impact of various mulch materials on plant growth, yield and fruit quality of Kinnow mandarin under drip irrigated condition.

A field trial was conducted at experimental Kinnow orchard of the ICAR-AICRP on Fruits, Department of Horticulture, Agricultural Research Station (SK Rajasthan Agricultural University), Sriganganagar during 2017 to 2019. Kinnow mandarin trees budded on Rough lemon (Citrus jambhiri Lush.) rootstock having uniform vigour and age with spacing of 6 × 6 m were selected. All the experimental trees were maintained under similar agronomical practices and irrigated through drip irrigation on alternate days. The experiment was laid out in randomized block design with three replications and single tree as treatment unit and the data were collected on various parameters. Six different types of mulch materials including inorganic and organic mulches viz.,  polyethylene (bicolour) 100 µ, bio-mulch (dried local weed grasses) (5 cm thickness), mustard straw mulch (5 cm thickness), sugarcane trash mulch (5 cm thickness), control (no mulching + no weeding) and hand weeding were applied (Fig 1). The mulches were applied after fertilization in month of February. Organic mulches were applied every year and polythene mulch was retained for all three years.



The canopy volume was calculated based on the formulae (Westwood, 1978) Where,
H = height of the tree.
W = width (width was minor axis while height was major axis).
 
       
Fully ripen fruits at golden orange colour stage were harvested during mid-January. Total number of fruits tree-1 were counted and yield was recorded by weighing the fruits. 10 fruits tree-1 were randomly collected and sent to fruit laboratory for further physico-chemical analysis. In laboratory, the fruits were washed with tap water to remove dirt followed by air drying. Average fruit weight was calculated by weighing ten fruits on digital weighing balance. The transverse diameter (length) and longitudinal diameter (width) and peel thickness of fruits from each experimental tree were measured with the help of vernier caliper. Juice content of fruit was extracted separately for each replication and weighed. The average juice percentage was calculated based on the formulae.
 
TSS (°Brix) of juice was measured by using hand refractometer. Total titratable acidity and ascorbic acid content were estimated through standard techniques (AOAC, 2000). All the common cost concepts of agricultural economics were used to interpret the results. To analysis of common cost of cultivation the variable and fixed inputs used in cultivation of Kinnow mandarin were included. The additional cost of each treatment was calculated based on the price of mulch material for each tree separately. Then total cost of cultivation was calculated by addition of common cost of cultivation and additional cost of treatment. Gross return was obtained by multiplying the yield per hectare with the prevailing wholesale price of Kinnow mandarin in local market. The field experiment was laid out in randomized block design with three replications and data were analyzed statistically by analysis of variances as one-way ANOVA. Significance was tested using F-test at a 5% level of probability (P<0.05). The standard error of the mean (SEm±), the critical difference (CD) at 5% level of probability (P< 0.05) were worked out for the study of each parameter by Gomez and Gomez (1984).

Growth and yield
 
Data presented in Table 1 showed that various mulch materials enhanced the plant growth and yield of Kinnow mandarin as compared to control. A maximum canopy volume (5.62 m³) was recorded with sugarcane trash mulch followed by bicolour polyethylene mulch (5.48 m3). Maximum number of fruits (485.30 tree^-1) and yield (95.44 kg tree^-1) was recorded with bicolour polyethylene mulch followed by sugarcane trash mulch (480.31 tree^-1 and 91.80 kg tree^-1, respectively). These two treatments were at par for all growth and yield parameters but significantly superior over control. The lowest canopy volume (3.91 m³) and yield (60.90 kg tree^-1) was recorded in control. Canopy structure of tree can directly affect light interception and the potency of light energy utilization. Optimum canopy structure is base of perfecting photosynthetic efficiency and achieving higher fruits yield. The increase in canopy volume of the plant was due to increased availability of soil moisture, nutrients and moderate evaporation from soil surface (Lalruatsangi and Hazarika 2018), enhanced the soil organic carbon contents and its active fractions in the soil (Gu et al., 2017) or might be due to better hydrothermal conditions provided by mulch as confirmed by Kaur and Mahal (2017). Improvement in canopy volume and yield of Kinnow mandarin might be due to fact that the bicolour polyethylene mulch and sugarcane trash mulch maximized nutrient uptake, enhanced water use efficiency and improved soil health. Reduced evaporation losses and modified infiltration capacity and optimized soil temperature were responsible for enhanced water availability in mulching treatments. In control, more weed infestation resulted in higher moisture loss from the soil surface and competition for nutrients may be accountable to minimized these parameters. These findings were in agreement with the results of Liao et al., (2021) in apple, Bhandari et al., (2017) in litchi and Jamir and Dutta (2020), Kumar et al., (2015), Kuniga et al., (2018), Lalruatsangi and Hazarika (2018), Liu et al., (2012), Wang et al., (2019), Xuemei et al., (2017) in citrus fruits. Further, strong and significant correlation between canopy volume and yield in Kinnow has been reported by Rattan et al., (2020) which confirmed the greater canopy volume and yield due to mulching in present findings.


 
Physico-chemical characterization of Kinnow mandarin
 
The data presented in Table 1 and 2 revealed that various mulches significantly increased the fruit quality parameters viz., fruit length, fruit width, fruit weight, total soluble solids (TSS), ascorbic acid and juice content while reduced the peel thickness and acidity of Kinnow mandarin fruits. An average maximum fruit length, fruit width, fruit weight, TSS, ascorbic acid and juice content (6.51 cm, 8.07 cm, 196.74 g, 12.47°Brix, 46.89 mg/100 ml and 51.37%, respectively) and minimum peel thickness and acidity (2.10 mm and 1.03%, respectively) were recorded in the bicolour polyethylene mulch followed by sugarcane trash mulch. In sugarcane trash mulch applied trees, fruit length (6.42 cm), fruit width (7.61 cm), fruit weight (191.36 g), TSS (11.98 °Brix), ascorbic acid (46.52 mg/100 ml) and juice content (49.90%) were recorded with peel thickness and acidity (2.15 mm and  1.05% respectively). Both the above mentioned treatments were at par to each other in all parameters except fruit width. The minimum fruit length, fruit width, fruit weight, TSS, ascorbic acid and juice content (5.28 cm, 6.38 cm, 166.09 g, 8.33 °Brix, 33.45 mg/100 ml and 40.96% respectively) with maximum peel thickness and acidity (3.67 mm and 1.31% respectively) were recorded in control treatment. The changes in physico-chemical quality attributes of Kinnow mandarin fruits might be due to the appropriate availability of nutrients and soil moisture content continuously during the growth and development period of fruits. While in control, severe weed infestation competed for nutrients and soil moisture. The fluctuation in soil moisture and temperature were also the major cause of poor fruit quality.


       
The superiority of plastic mulch and sugarcane trash over other mulches could be due to these mulches are completely or more efficiently impermeable to water. Thus, these mulches consequently regulate direct evaporation of soil moisture and reduce the water losses soil erosion more significantly over the surface. These findings were in close conformity with the results of Bhandari et al., (2017) in litchi, Bhattacharjee et al., (2020), Das and Dutta (2018) in mango, Shen et al., (2019) in apple, Bhanukar et al., (2015) in Kinnow mandarin, Lalruatsangi and Hazarika (2018) in acid lime and Liu et al., (2012), Shimazaki and Nesumi (2016), Wang et al., (2019) in citrus fruits.
 
Economics of technology
 
The economics of various mulching treatments was worked out and presented in Table 3. The cost of each treatment was calculated based on the price of mulch material for each tree separately. The income was calculated according to the saleable market mean price of the fruits. The highest B:C ratio 2.49 with net profit (Rs. 1,58,370.00 ha^-1) was obtained from the bicolour polyethylene mulch followed by sugarcane trash mulch (B:C ratio 2.45) as compared to control (BC ratio 1.96). The bicolour polythene mulch gave an additional income of Rs. 75,620.00 as compared to control. More or less similar findings have been reported by Bons et al., (2018), Kumar et al., (2014) in Kinnow mandarin, Bhattacharjee et al., (2020) in guava and Lalruatsangi and Hazarikaand (2018) in acid lime. Although the initial effect of polythene mulching on plant growth and yield is positive, its residual impact needs to be worked for plant growth yield and economics.

Based on the findings of this study, either bicolour polyethylene mulch or organic mulch (sugarcane trash) have significant impact on plant growth, yield and physico-chemical attributes of Kinnow mandarin with the higher returns as compared to control treatment. Organic and inorganic mulches showed positive effects on growth and quality attributes due to enhanced water use efficiency and improved soil moisture conservation resulted into improved physico-chemical properties of soil providing congenial environment to the root zone of the tree. While in control, lower soil moisture regimes, more weed infestation resulted in higher moisture loss from the soil surface and competition for nutrients minimized these parameters. The technology (organic sugarcane trash mulch) will also be helpful for crop residue management and organic Kinnow mandarin production.

Authors are grateful to ICAR-AICRP on Fruits and Zonal Director Research, Agricultural Research Station, SKRAU, Sriganganagar for providing necessary facilities during the course of investigation.

None.