Study on Rice Paddy Agroecosystem in Different Cultivation Methods and Landscapes

Study on Rice Paddy Agroecosystem in Different Cultivation Methods and Landscapes

Published: 2020.07.07
Accepted: 2020.07.06
47
Hualien District Agricultural Research and Extension Station, Taiwan
Hualien District Agricultural Research and Extension Station, Taiwan
Taiwan Agricultural Research Institute
Director
Counseling Office, Council of Agriculture, Taiwan
Former research assistant
Hualien District Agricultural Research and Extension Station, Taiwan
Former research assistant
Hualien District Agricultural Research and Extension Station, Taiwan
Former research assistant
Hualien District Agricultural Research and Extension Station, Taiwan
Hualien District Agricultural Research and Extension Station, Taiwan

ABSTRACT

The biodiversity in rice paddies is influenced by factors such as the surroundings and farming methods employed but is also related to the rice yield and production costs. In 2013, a survey was conducted in Hualien County to determine the community structure of invertebrates in rice paddies farms using organic farming methods versus conventional farming methods. The results revealed that the paddies farmed using organic farming methods contained 188 animal species, whereas those farmed using conventional farming methods had only 137. The paddies farmed using organic farming methods also produced more animal species in each functional group. Concerning the effect of farming methods on regulating major pests, a 2017 survey demonstrated that for rice paddies farmed using organic methods, the number of Trichomma cnaphalocrocis, which is the natural predator of Cnaphalocrocis medinalis, increased as the number of Cnaphalocrocis medinalis increased. This phenomenon was not observed in the rice paddies farmed using conventional farming methods. Thus, organic rice paddies are more biodiverse and contain more natural predators for all pests, resulting in more favorable pest regulation. Regarding the biodiversity of rice paddies in different landscapes, a study compared the number of arthropods and aquatic organisms in rice paddies in coastal areas with those in rice paddies in shallow mountain areas. The results revealed that the percentages of detritivores and aquatic collectors were higher in the coastal paddies than in the shallow mountain paddies, whereas the shallow mountain paddies had more diverse functional groups, surrounding woodlands, and herbaceous plants on paddy ridges. Similarly, a survey was conducted in Yilan to identify the arthropod composition of rice paddies, and the results demonstrated that the heterogeneity of the landscapes surrounding farmlands is the crucial factor influencing biodiversity. For instance, farmlands surrounded by more mixed forests and other crops have lower number of animal species than large rice paddies with a homogeneous landscape. A comparison between rice paddies in Hualien’s plain regions and those in its shallow mountain regions supported this statement: for the rice paddies in shallow mountain regions, the number of Micraspis discolor, predators of Delphacidae pests, increased as the number of Delphacidae pests increased, effectively achieving biological control and reducing the density of pests. This phenomenon was not observed in the rice paddies in the plain regions. The results of this study show that maintaining landscape diversity has a major effect on biodiversity,it also  facilitates food production, and diminishes ecological loads. Similarly, to improve the ecological services of monotonous landscapes, maintaining or building green belts may increase biodiversity in large rice paddies.

INTRODUCTION

Biodiversity conservation is susceptible to how land is used agriculturally, and environmentally friendly agricultural activities are a crucial method of maintaining the functions of the ecosystem. As the public begins to pay more attention to food safety and the environmental friendliness of agricultural operations, organic farming has become increasingly popular. Most agricultural activities have a certain effect on the environment and biodiversity (Kleijn, 2006), and positive changes to agricultural operations can protect the health of agroecosystems. Hole et al. (2005) collected and reviewed nearly 100 research articles that compared the effects of organic farming methods and conventional farming methods on maintaining biodiversity. More than two-thirds of the studies of organism communities (such as vertebrates, arthropods, annelids, plants, and microorganisms) have demonstrated that organic farming methods lead to higher biodiversity and number of species (including parasites and predators) than do conventional farming methods (Fan et al., 2013; Bianchi et al., 2013). High biodiversity regulates the effects of farmland pests on farmlandsand is thus crucial to farmers; such regulation is known as the regulating services (one type of ecosystem services). Pest regulation is influenced by factors such as farming methods, surrounding environment, and surrounding landscape. Recent studies have demonstrated that heterogeneity in the landscape of large-scale farmlands has a strong effect on farmland biodiversity (Benton et al., 2003; Wilby et al., 2006).

Recent studies have focused on how the number of flowering plants around farmlands can be increased to provide parasites with alternative food sources, ensuring stability of the natural predators and strengthening biological control. This method is referred to as ecological engineering, habitat manipulation, or farms aping. Rice paddies are generally farmed in large scale. Thus, diversifying the vegetation surrounding rice paddies is critical to the health of the agroecosystem. According to studies conducted worldwide, an increase in the number of honey plants around rice paddies can increase the rice paddy biodiversity, especially the number of predators, parasitoids, and neutral species. Biodiversity is crucial to ecosystem pest control (Lin, 2017; Gurr. et al., 2016). Zhu et al. (2015) discovered that by growing sesame flowers around rice paddies, the nectar of the sesame flowers increased the lifespan and reproductive rate of three types of parasitic wasps, indirectly affecting the effectiveness of pest control. This shows that the degree of landscape vegetation diversity around farmlands affects the farmlands’ biodiversity and pest control. Because pollen and nectar are sources of nutrients for most beneficial predatory insects to attain maturity, an appropriate number of flowering plants will attract these insects, subsequently improving the ecosystem services (Kopta et al., 2012) and reducing the cost and labor required to implement other pest control measures. Accordingly, the cultivation of flowering plants has become a method with which organic farms can sustainably manage pests.

The agricultural industry is transitioning from being oriented toward yield to being oriented toward a diverse value model (Enoki et al., 2014). The types of value that the industry can provide include production, regulation, support, and culture-based ecosystem services (Daily, 1997). Farmlands offer ecosystem services such as reducing the urban heat island effect, preventing floods, maintaining groundwater levels, and decreasing soil salinity (Chen, 2013), and protecting farmland biodiversity can maintain such ecosystem services. Farmers previously used pesticides to kill pests. However, pests have become resistant to pesticides, and the public have become concerned with environmental protection and food safety. Reducing pesticide use, engaging in environmentally friendly and greening endeavors, and avoiding cement use to increase the numbers of pest predators may thus be a favorable alternative. Additionally, these methods reduce the amount of money that farmers must spend on pesticides and produce safer food. For local residents, maintaining biodiversity enables them to experience the rich ecology of the past, and experience camps and other activities can be held to increase the revenue of farmers or local residents. Ecological and organic farming have thus become a recent trend.

Rice paddies account for one-third of Taiwan’s total farming land, and rice is the staple food of the Taiwanese people. Thus, when pursuing sustainable agricultural development, balancing biodiversity conservation with greater agricultural production is necessary (Butler et al., 2007). New agricultural policies should be developed, new farming methods evaluated, and the effects of different farming methods on local agroecosystems determined. When attempting to inhibit pests and diseases, the use of conventional methods such as chemical pesticides may cause the death of non-pest invertebrates sensitive to pesticides and cause species recolonization to take longer because of pest residue, the latter of which alters the community of invertebrates on rice (Geiger et al., 2010). Accordingly, the present study investigated farmlands cultivated using different farming methods and the landscapes surrounding this farmland, analyzing differences in the structure of invertebrate communities and biodiversity in rice paddies.

FARMING METHODS AND BIODIVERSITY

Biodiversity of organic and conventional rice paddies

A survey investigated the number of arthropods in rice paddies farmed using organic and conventional farming methods (hereafter referred to as organic and conventional rice paddies, respectively) in Hualien (2013; Table 1). Pests accounted for high percentages of the arthropods in both types of rice paddy. However, the percentages of pests were higher for the organic rice paddies. Regarding natural enemies (parasitoid and predator), the organic rice paddies had more and a greater variety. Organic rice paddies had significantly higher percentages of predators than conventional rice paddies and almost significantly higher percentages of parasitoid hymenoptera. Neutral species were specified to include Sarcophaga and Ephydridae (Saprophagous diptera insects), Chironomidae (which feed on organic debris and are resistant to environments with low dissolved oxygen), and omnivorous Formicidae. The percentages of these neutral species were higher in conventional rice paddies than in organic rice paddies.

Conventional rice paddies, in which pests were controlled using chemicals, contained fewer animal species for each ecological functional group than organic rice paddies did. Although the number of pests in the conventional rice paddies was controlled, these paddies housed more Diptera species such as Chironomidae and Sepedon, which are highly resistant to pollution. Although these animal species do not directly feed on rice or crops, they feed on organic debris and algae and inhabit semiaqueous environments such as farmland and irrigation canals when they are still in the larval stage; they likely change the rice paddy environment. Conventional rice paddies had fewer pest predators (both in number and variety) than organic rice paddies did. Thus, if the dominant pest species change, such as being replaced by those highly resistant to chemicals, the number of pest predators might not increase quickly enough, resulting in economic and agricultural losses (Fan et al., 2013).

able 1.  The numbers of species and relative abundance of each ecological function groups in organic and conventional fields.

 

Ecological function groups

No. of both appeared species

Organic fields

Conventional fields

No. of sp.z

RAy ,%

No. of sp.

RA ,%

Pests *x

41

67

63.50%

48

49.10%

Pollinators

8

13

2.60%

12

2.30%

Graminivores

8

13

1.50%

9

1.90%

Neutral species *

16

20

17.10%

17

36.30%

Predators *

30

54

11.00%

35

7.60%

Parasitoids

13

21

3.80%

16

2.30%

Total No. of sp.

116

188

 

137

 

 

z numbers of species of each ecological function in treatments

y relative abundance of each ecological function groups in treatments

x Two population proportions test, p<0.05

Pest control ability of organic and conventional rice paddies

A phase II rice survey was conducted in Yuli Township, Hualien in 2018 to determine the major pests and pest predators in organic rice paddies. The results revealed that the number of Trichomma cnaphalocrocis, which parasitizes Cnaphalocrocis medinalis (C. medinalis), increased as the number of C. medinalis increased. Similarly, the number of Micraspis discolor (M. discolor), which are predators of Delphacidae pests, increased as the Delphacidae pest population grew. These findings showed the correlation between the number of major pests and that of their predators in rice paddies. By contrast, in two conventional rice paddies located in the vicinity of the aforementioned organic rice paddies, an increase in the number of C. medinalis was not followed by increases in the numbers of their predators. Thus, organic rice paddies have superior pest regulation. Grass variety surveys of rice paddy ridges demonstrated that organic rice paddy ridges boasted more dicotyledon varieties and higher dicotyledon coverage than conventional rice paddies, suggesting that the heterogeneity of rice paddy habitats is associated with the number of predators M. discolor and parasitoids, resulting in organic rice paddies demonstrating superior pest regulation. In addition to Trichomma cnaphalocrocis, there were 40 families of predators to C. medinalis during the highest tillering stage to the booting stage. These predators were not included in the aforementioned survey.

Biodiversity in shallow mountain areas and coastal areas

In 2017, a survey was conducted in the composition of arthropod species in its shallow mountain and coastal areas in Hualien (Figure. 2); a total of 177 species of arthropods were identified in the land regions, with 130 identified in Dewu, and 127 in Sinshe. The arthropods were categorized according to their functional feeding groups. The results revealed that except for predators, Sinshe possessed more animal species in all functional groups (Figure. 2a) and a greater number of detritivores than did Dewu (Figure. 2b).

A total of 54 species of arthropods were identified in the coastal areas, with 48 and 32 species identified in Dewu and Sinshe, respectively. The arthropods were also categorized according to their functional feeding groups, and the variety and number of arthropod species are illustrated in Fig. 4. The Sinshe rice paddies had higher percentages of collector species (Figure. 4), and more than 90% of the species were constituted by filtering collectors or shredders. In Sinshe conventional rice paddies, filtering collectors accounted for 67.4% of all collector individuals, substantially higher than in other rice paddies farmed using other methods. Rice paddies of all types in Sinshe exhibited high varieties of filtering collectors and shredders. Compared with Sinshe, Dewu had more species in all functional groups except for shredders.

Pest regulation in shallow mountain areas and plain areas

In 2017, a survey investigated the pests and their predators in rice paddies located in Hualien’s shallow mountain and plain areas (Figure 5) to determine the relationships between major rice paddy pests and their predators in different landscapes. The results revealed that in the rice paddies located in shallow mountain areas, the number of M. discolor, which are predators of Delphacidae pests, increased with the number of Delphacidae pests and thus inhibited the density of Delphacidae pests (Figure 6). The findings also revealed the stability of the M. discolor population and their ability to prey on Delphacidae pests within a short period of time. By contrast, in the rice paddies located in plain areas, increases in Delphacidae pest density were not followed by M. discolor density increases. The positive relationships of the number of organisms with insect diversity and plant diversity have already been confirmed (Lawton, 1994; Siemann et al., 1998). Thus, high vegetation diversity in the shallow mountain areas may have been why the pest regulation of M. discolor was maintained. Recent studies have demonstrated that even for conventional rice paddies onto which pesticides are sprayed regularly, more predators can be maintained if the diversity of the landscape surrounding the rice paddies is maintained (Gurr et al., 2016). From a landscape perspective, rice paddies in shallow mountain areas generally have a more favorable ecological composition and balance. Therefore, farmers in such an environment will have lower pest control costs.

Landscape heterogeneity

In 2018, the present study conducted an ecological survey in highly and lowly fragmented rice paddies located in Yilan County (Figure 7). The results demonstrated that the lowly fragmented rice paddies contained significantly greater varieties and numbers of arthropods than the highly fragmented rice paddies. The lowly fragmented organic rice paddies had 66.7 arthropod species, whereas the highly fragmented organic rice paddies had 54.3. The lowly fragmented conventional rice paddies possessed 58.3 arthropod species, whereas the highly fragmented conventional rice paddies had 51. The differences in number of arthropod species between paddies farmed using the two methods were nonsignificant. Concerning ecological functional group classification, the lowly fragmented rice paddies possessed significantly more predator species than the highly fragmented rice paddies did; the organic rice paddies had significantly greater variety and number of predator species than the conventional rice paddies did; and the lowly fragmented rice paddies possessed significantly more numbers of parasitoids than the highly fragmented rice paddies did (Table 4).

The fragmentation of rice paddies had a significant effect on the arthropods discovered in these rice paddies. Rice paddies in Sanxing Township, Yilan County, are mostly surrounded by mixed forests and other crops; a 2017 experiment selected complete and large-scale rice paddies as their lowly fragmented rice paddies sample. The result showed that the number of species identified in these paddies was lower than that identified in highly fragmented rice paddies. Thus, in the 2018 experiment, only rice paddies surrounded by mixed forest and other crops were selected as the sample paddies, and greater biodiversity in lowly fragmented rice paddies was discovered than in the 2017 experiment, indicating the considerable effect of habitat heterogeneity on arthropod diversity. Studies have also demonstrated that plant diversity affects insect diversity; the number of herbaceous plants affects insect population compositions and the number of insects, and woody plants attract greater diversity of phytophagous insects than do herbaceous plants because of their complex structure (Lawton, 1983; Lewinsohn et al., 2005; Knops et al., 1999). This explains why lowly fragmented rice paddies surrounded by mixed forest and other crops have greater numbers of arthropods than do highly fragmented rice paddies and why relatively complete, large, and lowly fragmented rice paddies contain lower numbers of arthropod species than highly fragmented paddies. Additionally, it reveals that plant diversity has a crucial effect on insect populations in farm ecosystems, which are constantly disturbed by human activity.

Table 2.  Effects of organic and landscape fragmentation factors on arthropods community in paddies in 2018.

 

Patternz

Pest

Graminivore

Predator

Parasitoid

Scavenger

Pollinator

Total

Species

H-O

13.7±0.6

8.0±1.0

14.3±0.6

5.0±1.0

12.3±3.1

1.0±1.0

54.3±2.1

 

H-C

8.0±2.7

6.3±0.6

13.7±2.1

10.3±2.1

12.7±0.6

0

51.0±6.0

 

L-O

14.7±1.2

10.0±1.0

17.7±0.6

11.7±0.6

12.0±1.7

0.7±0.6

66.7±0.6

 

L-C

12.7±1.2

9.7±2.5

15.0±1.0

9.7±2.1

10.7±2.1

0.7±0.6

58.3±6.0

 

 

 

 

 

 

 

 

 

 

P valuey

 

 

 

 

 

 

 

 

F-factor

0.015*z

0.014*

0.011*

0.110

0.356

0.667

0.005**

 

O-factor

0.003**

0.273

0.046*

0.105

0.685

0.217

0.050

 

I-factor

0.079

0.455

0.195

0.004**

0.504

0.217

0.353

 

 

CONCLUSION

Rice paddies play a crucial role in Taiwan’s wetland ecology. Different farming methods and the landscapes surrounding rice paddies affect the ecosystem composition of these paddies. Recent surveys have discovered that compared with organic rice paddies, conventional rice paddies, which are subjected to long-term chemical pesticide spraying, contain fewer numbers of animal species for every ecological function group, resulting in a less balanced ecological composition. When the climate conditions are suitable for pest growth, the farmers are forced to rely on pesticides because the number of pest predators does not necessarily grow with pests. Additionally, herbicides, a commonly used type of agricultural chemicals, exterminate ridge grass and flowers, which pest predators live and feed on. The more heterogeneous are the large environments that surround rice paddies, the more biodiverse are the rice paddies, and the more stable is the rice paddy growth. Such rice paddies are less prone to losses caused by pests because the various surrounding habitats provider for predators from a wide variety of functional groups. Therefore, agricultural producers should consider the environment surrounding farmlands, and various types of artificial vegetation and water habitats should be created whenever necessary to maintain favorable environments for rice paddies and improve the ability of the paddies to recover from pests.

 

 

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