The Effectiveness of Plastic Mulch for Conserving Dieng Agricultural Land Using Soil-Quality Index Based on Microarthropods

DIAN AGUSTINA, UDI TARWOTJO, RULLY RAHADIAN

Master of Biology, Faculty of Science and Mathematics, Universitas Diponegoro
Jl. Prof. H. Soedarto, SH Tembalang Semarang, 50275
E-mail: dianagustinaa28@gmail.com

Abstract
Dieng farmers apply plastic mulch to reduce erosion and to prevent the loss of nutrients. This study aims to determine the effectiveness of plastic mulch in maintaining the quality of potato farmland using the biological soil quality index (QBS-ar) based on microarthropods. Soil sampling was conducted in six different locations, i.e., flat area with mulch, sloped area with mulch, the flat area without mulch, sloped area without mulch, flat forest area, and sloped forest area. Microarthropods was extracted from soil samples using a Berlese Funnel method. Soil quality was analyzed using QBS-ar index which calculated based on Eco-morphological Index (EMI). The results showed that the value of QBS-ar index in potato farmland using plastic mulch was much higher than in farmland without plastic mulch, regardless in flat or sloped area. Compare to the soil in the forest area, the value of QBS-ar index in farmland which using plastic mulch, especially in the flat area, was relatively similar. Hence, the use of plastic mulch for potato cultivation in the hilly area is effective in maintaining soil quality. This finding would be beneficial for developing a soil conservation strategy to achieve sustainable agriculture in Dieng agricultural area.
Keywords: Soil conservation, soil degradation, QBS-ar

INTRODUCTION

Dieng plateau has a problem regarding land degradation. Most of Dieng residents are a farmer who grows various crops including potato. The farmers were cleared-cutting perennial plants and changed to crops which resulted in soil erosion and making them use chemical fertilizers uncontrollably. Without proper management, the cultivation of potato in Dieng might increase erosion and land degradation that far from the efforts to achieve sustainable agriculture (Pradana et al., 2015). 
 	One of the farmers efforts to maintain land qualities is by using plastic mulch. The use of plastic mulch can protect the soil from direct raindrops so that it can prevent the loss of nutrients. Besides, plastic mulch is physically able to keep the soil temperature more stable and maintain the moisture around the plant roots (Annisa et al., 2014). The use of plastic mulch for agricultural cultivation requires a monitoring program. The organisms that can be used as monitoring agents are soil microarthropods because they are very sensitive to changes in soil environmental conditions. There had not been enough research regarding the effect of using plastic mulch towards the presence of microarthropods. The research that has been done only focus on the plant. The use of plastic mulch in Permana et al. (2017) studies may significantly increase the growth and results of soybean crops. Meanwhile, the research conducted by Haque et al. (2018) shows that plastic mulch has the effect of increasing the growth and results for saline soils where plant growth is generally poor. Therefore, this study is important to examine the condition of soil quality under the plastic mulch using a microarthropod soil as its model. 
Few parameters can be used to monitor the land quality such as by viewing it from physical or chemical aspects of the soil. However, it is also important to consider it from the parameter of the biotic environment as well because of the presence of microarthropods inside the soil. This organism has an important role in producing nutrients for the soil. Soil microarthropods are the main structure of food webs as a decomposer. It also contributes to soil aggregation by producing organic matter. The numbers of soil microarthropods are quite large, and their role in land formation and transformation is very beneficial. Their life cycle and its natural history in the field can help assess the ecological condition of the soil (Gardi et al., 2002).
Microarthropods is a useful model due to its highly diversified taxonomically and ecologically, especially in eudaphic forms which unable to survive with various disturbances, for example from farming. (Parisi, 2005). Recently, an integrated approach has been proposed in the form of Biological Soil Quality Index (QBS-ar). This index is based on the concept of higher quality soils means a higher number of microarthropods groups that can adapt to the habitat of the soil. (Paolo et al., 2010).
Microarthropods can be used as an indicator to measure the soil quality because they are very sensitive to the change of soil environmental condition. According to Parisi et al. (2005), the biological indices of soil quality can be discovered by observing the microarthropods found in the soil. Microarthropods have a significant role in the soil food chain. Their purpose is to distribute the energy from microfauna to microfauna on a higher trophic level (Culliney, 2013). Microarthropods are one of the most important inhabitants even in strongly disturbed soils (Dunger & Voigtlander, 2005).
	The reason why QBS-ar is easy to use to assess the soil quality is that it does not require a complex identification of taxonomy. The assessment is only based on the biological morphology according to the adaptation level of soil habitat. Then, each group of microarthropods is given scores based on Ecomorphological Index (EMI). The calculation results are only seen from the adaptation of microarthropods to their new habitat without classification to species level. Thus the costs and labor are reduced (Paolo et al., 2010). This research is really necessary to determine the effectiveness of using plastic mulch towards the cultivation of potato farms using the QBS-ar index so that in the future it can be used as a reference for better farmland management.
MATERIALS AND METHODS
Study area
	The study area was located in the Dieng PlateauKejajaran District, Wonosobo Regency, Central Java. The sampling locations were chosen based on the usage of plastic mulch as an alternative agricultural technique and based on contour variation that had been carried out in the Dieng Plateau. Forest land in Dieng Plateau was chosen as reference stations for comparison purpose. The sampling location was divided into six research locations: 
1.	MF: potato agricultural land using plastic mulch which was located on flat land.
2.	MS: potato agricultural land using plastic mulch which was located on the land with 28° of the slope. 
3.	NF: potato agricultural land without using plastic mulch which was located on flat land.
4.	NS: potato agricultural land without using plastic mulch was located on the land with 28° of the slope.
5.	FF: a flatted forest with a high amount of vegetation.
6.	FS: a forest with 35° of the slope with a high amount of vegetation.
Soil sampling
	The boundary of the sampling area was decided according to the width of the land, representative area, and potato's homogenous. There were five sampling points each taken from the middle of the station. There are two soil samples taken from its sampling point for microarthropod identification and soil physical-chemical analysis. Soil samples were taken using a small shovel measuring 10 cm depth and 10 cm in diameter. The sample can only be taken at ≥ 40% of soil humidity. 
Extraction of microarthropods and identification
	The microarthropod samples were extracted using the Berlese-Tullgren funnel (Parisi et al., 2005). For the extraction process, it used 40W of light on the top of the funnel to increase the soil temperature up to 35ºC. A 500mL plastic bottle filled with 75% alcohol was placed under the funnel to trap the microarthropod that comes down. This process took around seven days to complete. The process of identifying and grouping the taxa was performed by observing the micro-morphology using a microscope and identification book. 
Data analysis
	QBS-ar (Biological Soil Quality) index was used to analyze the soil microarthropods data. The QBS-ar index is based on a direct relationship between soil quality and the number of microarthropods adapted to soil habitats. The identification process uses a biological form approach towards morphological class according to their level of adaptation to the soil environment (Gagnarli et al., 2015). 
	The EMI values range from 1 (zero adaptation to the soil) to 20 (maximum adaptation to the soil) (Menta et al., 2017). As reported in Parisi et al. (2005), some group only show one EMI value because all species inside the taxa shows the same level of adaptation to the soil (e.g., being maximum in Proptura, while being moderate in Blattaria). As for the other group, it shows that they are in the range of 1 and 5, or 1 to 20, or 10 to 20 with the level of adaptation of different species to the soil. In general, the edaphic form scores the EMI value of 20, the hemiedaphic are given an EMI rating equivalent to its soil adaptation level, and for the epigeous, it scored 1 EMI value.
The soil physicochemical data was analyzed using Person correlation. It includes the analysis of pH value of the soil, soil temperature, soil moisture, N-total, soil organic matter, and C/N ratio.

RESULTS AND DISCUSSION
When the research was conducted in the flat condition, the quality of the soil in potato farmland using plastic mulch was better than in that one without plastic mulch. It is shown in Table 1 which the value of QBS-ar index in potato farmland using plastic mulch was much higher (70) than in farmland without plastic mulch (45). It seems that the plastic mulch protects the soil effectively from the harsh of an abiotic environment. Mahmudi et al. (2017) stated that plastic mulch could preserve soil temperature which benefited soil microorganisms to decompose organic matter. The increase in the number of microorganisms is strongly related to the existence of microarthropods. According to Coleman et al. (2004), microarthropods have an important role in plant litter fragmentation. The result of this fragmentation causes the surface area to expand, thus increasing the activities of microbes.
In sloped potato agricultural land, the QBS-ar index value when using plastic mulch is also higher (56) than that of without using plastic mulch (43) (Table 1). This is indicated that the plastic mulch can retard the nutrients from eroding in the sloped land. Thus the condition of the soil quality can be maintained. It is supported by Fahrurrozi (2009) who suggested that the soil could be protected from rainfall by using the plastic mulch, so it keeps the nutrients from washing away. Unlike in the farmland with plastic mulch, the existence of microarthropods in the farmland that of without plastic mulch is relatively easily extinct because of washing away due to soil erosion. The abundance of soil microarthropods is related to soil quality. Larasati et al. (2016) suggested that microarthropods will continuously maintain the nutrient cycle process.
The index value of biological soil quality in the forest are higher (76- 77) than those in potato agricultural land (43 -70), regardless with or without the plastic mulch and any variation of slope (Table 1). This might be because of the soil in Dieng potato agricultural land exposed to chemical fertilizers and pesticides intensively. According to Isnaini (2006), the use of chemical fertilizers in the long term causes the levels of soil organic matter to decrease, soil structure to be damaged and environmental pollution. If it continues, this could reduce soil quality and environmental health. Moreover, the high value of the QBS-ar index in the forest is related to the vegetation condition. The vegetation in the study site is relatively better than in potato cultivation area, regarding diversity and density. Wang et al. (2013) stated that vegetation affects the ability of the soil to hold water to prevent erosion and landslides. Vegetation root systems can significantly improve the stability of the soil and act as anti-erosion agent (Zheng et al., 2007). The activity of soil organisms is strongly dependent on the condition of vegetation. Plants play a role in supplying organic matter to the soil either through the production of litter or root exudates while soil organisms are responsible for most biological processes related to nutrient cycles and decomposition of organic matter (Widyati, 2013).

Table 1. The comparison of QBS-ar Index in flat area with plastic mulch (MF), sloped area with plastic mulch (MS), flat area without plastic mulch (NF), sloped area without plastic mulch (NS),  flat area in the forest (FF), and sloped area in the forest (FS). 
Microarthropods group	Potato Agricultural Land		Forest Land	
	MF	MS	NF	NS		FF	FS	
Collembola	20	10	10	8		20	20	
Hemiptera	-	-	-	-		1	-	
Coleoptera adults	10	-	-	-		15	20	
Coleoptera larvae	-	10	10	10		-	-	
Holometabolous larvae	-	-	-	-		-	10	
Hymenoptera	5	5	5	5		5	5	
Diptera adults	-	-	-	-		1	1	
Diptera larvae	-	-	-	-		10	-	
Araneae	5	-	-	-		5	-	
Acari	20	20	20	20		20	20	
Psocoptera	-	1	-	-		-	-	
Symphyla	10	10	-	-		-	-	
QBS-ar	70	56	45	43		77	76	

Collembola	
 Acari	
  Coleoptera adults	
 Araneae	

Hymenoptera	
 Hemiptera	
 Diptera adults	
 Psocoptera	

Diptera larvae	
 Symphyla	
 Coleoptera larvae	
Holometabolous larvae	
Figure 1.  Microarthropods found in potato agricultural land and forest land.

Tabel.2 The soil physico-chemical parameter of potato crop soil and forest soil of Dieng
Parameter	Potato Agricultural Land		Forest Land	
	MF	MS	NF	NS		FF	FS	
N total	0.15	0.29	0.23	0.41		0.38	0.35	
Organic matters	2.07	2.60	1.74	1.80		3.34	3.25	
The ratio of C/N	13.56	9.12	7.69	4.41		8.74	9.2	
Soil pH 	6.1	6.5	6.1	6.5		6.7	6.9	
Soil Temperature	17.6	16.6	17.2	16.8		10.8	10.2	
Soil Humidity	88	89	100	91		50.6	50.6	

Table 3. The correlation (Rs) of biological soil quality index (QBS-AR-ar) with soil physico-chemical parameter 
Parameters	Correlation (Rs) 	
N total	0.243	
Organic matters	0.968*	
C/N	0.359	
Soil pH	0.492	
Soil Temperature	-0.543	
Soil Humidity	-0.928*	
*Correlation is significant at 5% level.

The correlation analysis indicates that organic matters have a significant correlation to QBS-ar index (Rs = 0.968)(Table 3). The correlation coefficient shows a positive value, meaning that the higher the organic matters, the higher the QBS-ar index value. This is possible because the usage of plastic mulch can prevent the soil nutrients, some of which are organic matters, from washing away. The result of the research conducted by Gagnarli et al. (2015) shows that the QBS-ar index is higher in a grape farm using organic management than that of using integrated pest management (IPM). The research conducted by Husna et al. (2016) also stated that the richest microarthropods taxa were found in the farms that contain high organic matters.
Suin (2003) showed that soil organic matters determine soil organism density, including soil microarthropods. Soil organic matters are including litter and soil organisms, whether decomposed or not. The distribution of organic matters in soil affects the existence of soil microarthropods since it is associated with the source of nutrition. 
The only soil physico-chemical factors which has a significant correlation, except soil organic matter, is soil humidity (Table 3). The correlation between soil humidity and QBS-ar index value indicates a negative correlation (-0.928). Both extremely high or extremely low humidity environment condition can cause a negative impact on microarthropods. A desiccated condition also decreases the population of microarthropods since majority animal has a small tolerance limit of environmental humidity. Abiotic factors such as soil humidity could affect the presence of soil microarthropods taxa (Larasati et al., 2016).
	According to Hamdani (2009),  using plastic mulch can maintain more stable soil temperature and preserve humidity around the roots of plants. Giving mulch and legume inoculant can affect the number of bacteria in root nodules and can affect the growth of soy plants of Grobogan variety (Ni’am & Bintari, 2016). Furthermore, plastic mulch is also able to keep water (in soil) from excessive evaporating  (Noorhadi & Supriyadi, 2003). Research by Samiyarsih et al. (2018) states that relatively high humidity causes the pathogen Sphaceloma babatas to penetrate, infect, and damage tissue in sweet potato plants.
	This study proves that the usage of plastic mulch on potato farming system can improve the soil quality. It is indicated from the higher QBS-ar index value in the farmland, either in flat or sloped land condition, which using plastic mulch than those of without using plastic mulch. According to Fahrurrozi (2009), the usage of plastic mulch is more effective. An example of the effectiveness of plastic mulch to protect soil physically from direct raindrops, protrude the soil below it, prevent nutrients from washing away, prevent the splashing of soil granules on plants, prevent soil water from evaporating, and decelerate the release of carbon dioxide in the soil which results from respiratory activities by microorganisms.
	The usage of plastic mulch is useful for soil quality through modification of soil temperature, weed competition, reduction of evaporation, soil compaction and erosion. Under plastic mulch, soil properties such as temperature, moisture content, rainfall density, aggregate stability and availability of nutrients can be improved. Growth and yield of plants are also positively affected by plastic mulch due to modification of soil microclimate (Lalitha et al., 2010). 
This research would be beneficial for developing a sustainable agriculture through a strategy of soil conservation in Dieng area in order to prevent soil degradation and soil erosion. Hence, the farmers could be benefited in economy, ecology and in terms of socio-cultural aspects. 

CONCLUSION
According to biological soil quality index based on microarthropods, application of plastic mulch on potato cultivation is effective to maintain the soil quality in order to conserve soil in Dieng agricultural land. 
ACKNOWLEDGMENTS

We are thankful to the farmers in the upland of Dieng who have allowed us to conduct research on their agricultural farm and to those who are contributing to the success of this research.  
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