Effect of Mulching on Growth and Yield of Peanut (Arachis hypogaea L.) on the Coastal Sandy Land in Nghe An Province, Vietnam

Peanut (Arachis hypogaea L.) is one of the most valuable legumes of tropical and subtropical regions (Jadon et al., 2018). It is also an important oil and cash crop in Vietnam and worldwide (Le et al., 2019). Peanut in Dien Chau district, Vietnam is mainly grown on nutrient-poor soil. Therefore, to achieve high productivity and high efficiency of investment, should have the effect of technical measures accordingly.

The practice of mulching has been widely used as a management tool in many parts of the world. It makes more favourable conditions for plant growth and development as well as efficient crop production (Sathiya et al., 2020). Mulching can be used on the soil surface mainly to prevent loss of water by evaporation (Ji and Unger, 2001; Pawar et al., 2004), to cut down the weed growth (Lalitha et al., 2010), to reduce temperature fluctuations and to promote soil productivity (Khan, 2002; Sun et al., 2015). Different mulching methods i.e., application of paddy straw and plastic mulching provide a better environment to the plant (Kader et al., 2017). When compared to other mulches plastic mulch plays a positive role in water conservation by forming a completely impermeable to water mainly due to prevention of direct evaporation of moisture from the soil limiting the water losses and soil erosion over the surface (Trivedi and Gupta, 2016). Straw mulch adds nutrients to the soil when decomposed by microbes and help in carbon sequestration (Raju, 2013; Marwein et al., 2019).

Peanut can be grown under different land configuration methods like flatbed method, broad bed furrow, ridges and furrows and raised bed and furrow and mulched with organic or plastic mulching as a better management practice to enhance the growth and yield of peanut over the conventional method of cultivation (Li et al., 2010). In this study, an experiment was designed and conducted in a farmer’s field with the following objectives: (1) Assess the impact of different mulch treatments on peanut productivity. (2) Understand the yield contributing factors and identify economically viable and environment-friendly mulching options.

Experimental design

Field experiments were carried out during the 2019 spring crop at the research area of the Institute of Agriculture and Natural Resources, Vinh University in Dien Chau district, Nghe An province, Vietnam (105.30-105.45°N, 18.20-19.50°E). This research was conducted on the peanut variety L14, which was recognized as a technically advanced variety according to Decision No. 5310 QD/BNN-KHCN, November 29, 2002.

The experiment consisted of three mulch treatments, viz., plastic mulch, straw mulch and no-mulch control. All the treatments were replicated thrice in a complete randomized block design. Before sowing, 1 ton ha^-1 of microbial organic fertilizers + 30 kg ha^-1 N + 90 kg ha^-1 P₂O₅ + 60 kg ha^-1 K₂O + 500 kg ha^-1 lime powder was applied. Mineral fertilizer rates were determined based on the nutritional requirements of peanut and soil nutrient availability.

Each experimental plot consisted of 40 plants m-2 (spacing 25 cm × 20 cm). In the broad bed furrow system, beds were formed at 1 m width followed by 50 cm furrows. Polyethene sheets of 7-micron thickness with holes at the required spacing were spread over the soil in the mulched plots and seeds were sown. Organic mulching with paddy straw was spread at 5 cm thickness two weeks after sowing. Cultural practices, such as land preparation and pest management practices, which were by the recommendations from the Industry-standard 10-TCN 340:2006 on peanut varieties-procedure to conduct tests for value of cultivation and use.
 
Data collection
 
The soil moisture (%) was measured on 15^th Jan, 25^th Jan, 04^th Feb, 14^th Feb, 24^th Feb, 05^th Mar, 15^th Mar, 25^th Mar, 04^th Apr and 14^th Apr by gravimetric method. Plant height (cm) was measured from the ground level (at the plant’s base) to the top of the highest point, including the terminal leaflet using a graduated meter stick. It was recorded from 10 randomly selected plants within the net plot. The number of branches per plant was obtained by direct counting of branches from 10 randomly selected plants in each plot. LAI was estimated as (LAI = surface area of sampled leaf/ground area occupied by the sampled plants). Dry biomass (g plant^-1) was obtained after oven drying plants at 105°C until the mass is constant. The number of pods per plant was counted directly from ten sample plants of each plot (with three replications) and an average was calculated after harvesting. One hundred pods weight (g) and one hundred seeds weight (g) are obtained from a random sample of 100 pods and 100 seeds, respectively and weighed. 
  
In each experimental plot, data on pod yield were recorded on ten randomly selected plants harvested.

Soil moisture

Mulch prevents soil water evaporation and thus helps retain soil moisture. The monthly rainfall figures for the experimental period are given in Fig 2, the average rainfall during the experiment was 48.98 mm. The effects of mulching on soil moisture depend on precipitation and climatic factors. The soil moisture variation is not the same under different mulching materials (Fig 1). In general, the mulching treatments store higher soil moisture compared to the bare soil (no mulch). Mulch retards soil erosion and rapid infiltration of rainwater into the soil. Optimum soil moisture ensures good emergence and seedling growth. Contrasting results were also reported in regard to soil moisture storage under different mulching materials. Ramakrishna et al., (2006) reported that plastic mulch treatment stored the highest amount of soil moisture compared to the organic mulch treatments, which stored greater moisture than the bare soil. Similar results under mulch were reported by Pawar et al., (2004); Ghosh et al., (2006); Raju (2013) and (Jain et al.  2018).





Growth parameters

Table 1 showed that, under the conditions of plastic mulch and straw mulch, the germination rate (97.5% and 96.7% respectively) was much higher than that of no-mulch control (77.8%). However, the results of LSD index analysis showed that the germination rate between plastic mulch and straw mulch had no significant difference.



In the condition of plastic mulch, the soil temperature increased by 2.5-3.9°C during the day at the early growth stage and 0.6-1.1°C at the late growth stage. The total cumulative temperature for the whole growth process is higher than that of no-mulch control at 195.3-379.8°C. Therefore, the growing time was shortened from 134 days to 128 days. Better seedling emergence in less time may be due to more ambient soil temperature, a more uniform supply of soil moisture and reduction in soil compaction around the seeds under mulch, which helps to promote faster germination and emergence. Similar results under mulch were reported by Shaikh et al., (2004), Ramakrishnan et al., (2006), Ghosh et al., (2006).

The mulching measure also affects the tree height and the number of branches per plant. Observations on plant growth showed that the peanut plants in plastic and straw mulched plots were generally tall, more vigorous than in the no-mulch control. The more favourable soil environment under the plastic and straw mulch, especially during the early part of the growing season, resulted in an increased number of branches per plant. Similar results have been reported by other studies (Kumar and Ngachan, 2001; Shaikh et al., 2004). Plastic mulching created a suitable condition for plant growth by influencing soil temperature, moisture retention, improved soil texture and microbial activities (Ghosh et al., 2006).
 
Leaf area index (LAI)
 
The data in Table 2 showed that the LAI of mulched treatments were larger than that of the control treatment and had a significant difference. It was a cumulative effect of a better growth environment, higher nutrient mobilization and better partitioning to shoot system that resulted in broader leaves (Jain et al., 2017). LAI increased and was maximum during the pod formation period and decreased during harvest. Magagula et al., (2019) observed that the highest LAI value was 4.63-4.93, which declined to 1.93-2.47 as maturity. Our results are also consistent with previous studies (Zhang et al., 2012; Jain et al., 2018; Mondal et al., 2020).

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Nodule and dry matter weight
 
The number of nodules per plant had a significant difference in mulched treatments over no-mulch control at the flowering, pod setting and harvesting stages. Jain et al., (2017, 2018) reported that the number of nodules per plant was also recorded higher in polythene mulched peanut over no-mulch peanut.

The dry matter accumulation capacity of the peanut increases with the growing stages and obtained the highest value at harvest (Table 3). At this period, dry matter accumulation was highest in plastic mulch and lowest in no-mulch control. There was a significant difference in the dry matter weight between the mulched treatments and no-mulch control. The change in dry matter accumulation could be due to the leaf area and leaf area index (Olanyika and Etejere, 2015). Zayton et al., (2014) also reported that applying rice straw mulch lead to an increase in the biomass yield of about 28.90% as compared to no-mulching. Subrahmaniyan et al., (2008) and Jain et al., (2017) also reported that dry matter accumulation between polythene film mulches and no-mulch peanut differed markedly at all the crop growth stages. These results agreed with Mondal et al., (2018) and Sathiya et al., (2020).

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Yield components and yield
 
Mulch treatments have consistently yielded more than that of no-mulch control. Among the mulches, plastic mulch had significantly greater yields than straw mulch but there was no significant difference. Some authors report a significant increase in pod yields with the use of plastic mulch, which has been attributed to warmer soil temperatures. The warmer temperature may increase the absorption of nutrients and water as well as the production and translocation of carbohydrates. Our result conforms to the findings of Khistaria et al., (1994); Khan (2002); Pawar et al., (2004) (Table 4).

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The number of pods per plant, the 100-pods weight and 100-seeds weight under plastic mulch were significantly higher as compared to straw mulch and no-mulch control. The shelling percentage under all the treatments is non-significant. Ghosh et al., (2006) also reported that the yield attribute significantly contributing to higher pod yield under mulch is the number of pods per plant, the 100-pods weight and 100-seeds weight. A similar increase in yield due to mulching was reported in Peanut (Ramakrishnan et al., 2006; Jain et al., 2017).

Crop performance results demonstrate that pod yield was higher in mulched plots. There were variations in pod yield between three mulch treatments, which can be partly explained by the rainfall amount and soil moisture. An improved soil physical environment and retention of a greater amount of water under mulched conditions (give the 3.92% age increase in soil moisture) for a longer period might be the possible reason for better yield (Khan, 2002; Taufiq et al., 2017). Ramakrishna et al., (2006) reported that the polythene mulched plots produced the highest yields - 94.5% higher than the unmulched plots and 25.5% higher than the straw mulched plots. The more favourable soil environment under the polythene and straw mulch, especially during the early part of the growing season, resulted in the increased number of pods per plant, pod mass and pod yield. Similar results under mulch were reported by Mondal et al., (2020); (Jain et al., 2018).

In the conditions of mulch, the plant growth factors, leaf area index, the number of nodules per plant, dry matter accumulation, yield components and yield of peanut was much higher than that of no-mulch control. Among the mulches, plastic mulch was found superior to vegetative mulches in the pod yields and water-use efficiency and moisture conservation. However, every type of mulch has some strengths and weaknesses, making it suitable for some situations and not for others. Availability, durability and cost of the materials are the important issues to be taken into considerations for the selection of mulching materials. The straw mulch saves the labour cost and after decomposition, adds plant nutrients to soils; this is an extra advantage of the straw mulch over the plastic mulch.