Measures Adopted in Taiwan to Strengthen Healthy Soil-Plant Interactions for Resilient Agriculture

Measures Adopted in Taiwan to Strengthen Healthy Soil-Plant Interactions for Resilient Agriculture

Published: 2022.10.25
Accepted: 2022.10.19
75
Agricultural Chemistry Division, Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan
Agricultural Chemistry Division, Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan
Agricultural Chemistry Division, Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan
Plant Pathology Division, Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan
Plant Pathology Division, Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan
Applied Zoology Division, Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan
Plant Pathology Division, Taiwan Agricultural Research Institute, Wufeng, Taichung, Taiwan
Taiwan Agricultural Research Institute

ABSTRACT

With the increase in the frequency and intensity of extreme climates caused by global warming, not only the frequency of agricultural disasters in Taiwan has increased, but the patterns have also changed. High temperature and drought frequently happened in recent years, while rarely occurred in the past. In response to the impact of global warming on crop production, Taiwan has taken steps to adapt and reduce greenhouse gas emissions to improve agricultural resilience. The results showed that using the automated equipment combined with the alternate wetting and drying irrigation can effectively save irrigation water, while laser leveling technology can both save irrigation water and increase shallot yield. Through the progress made in the development of organic farming of perennial fruit trees, and many incentives of subsidies on machines, facilities, and fertilizers, the acreage adopting organic farming has already reached 12,578 hectares in 2022. Environmentally friendly management could effectively control soil-borne pathogens and pests and increase strawberry and banana yields. Adopting conservation tillage and crop rotation could improve farmland productivity in the coastal areas compared to the conventional two crops rice system. The conservation tillage and crop rotation system have increased field productivity potential by up to 30%.

Keywords: water use efficiency, organic farming, environmentally-friendly management, conservation tillage, and crop rotation

INTRODUCTION

Recently, accelerating global warming has increased the frequency and intensity of natural disasters influencing human life. Compared to 1970, the frequencies of extreme weather, flood, and drought in 2019 had increased by 254%, 448%, and 650%, respectively, according to the Emergency Events Database (EM-DAT) from The Centre for Research on the Epidemiology of Disasters (CRED). Based on statistics from the Council of Agriculture (COA), the major types of agricultural disasters in the past are typhoons and torrential rain. High temperature and drought also frequently happened in recent years, though rarely occurred in the past (Figure 1). With climate change, Taiwan's agricultural losses due to weather disasters from 2006 to 2021 are estimated at NT$1.8 billion (US$59,147 million)  to NT$17 billion (US$566.241 million).

In light of threats from climate change, the enhancement of soil carbon sequestration is (considered) to serve as the best or most important approach to alleviating global warming and increasing the resilience of agriculture. Suggested management strategies for soil carbon sequestration recommended by FAO include as follows: conservation/reduced tillage, crop rotations, cover cropping, organic farming, balanced combined applications of chemical fertilizer and manure, deep plowing, planting perennials in degraded/marginal land, adding compost/biochar, etc. This  paper introduces some agricultural management strategies for coping with climate change, which involve raising water use efficiency of crops, promoting organic farming, environmentally-friendly management of soil-borne plant diseases and soil pests, and improving farmland productivity in the coastal areas.

RAISING WATER USE EFFICIENCY OF CROPS

Management of paddy field irrigation using intelligent water-level monitoring devices

As water resources are getting seriously short with climate change, raising water use efficiency in paddies is needed urgently. Although alternate wetting and drying irrigation (AWD) in paddy fields is considered an effective water-saving technique for rice production, precise control of water supply is truly essential and recommended to improve water-saving efficiency and crop yield. To this end, TARI cooperated with the National Chung Hsing University, Miaoli District Agricultural Research and Extension Station, and Taichung District Agricultural Research and Extension Station to develop intelligent water level monitoring devices and solar-powered automatic irrigation water valves. According to the experiments conducted on TARI's farm in 2019, using the automated equipment combined with alternate wetting and drying irrigation, the irrigation amount of first- and second-crop rice could be saved by 30.9% and 49.8%, respectively, with little impact on rice yield (Wu et al. 2019; Table 1). From 2020 to early (half) 2021, in the face of the worst drought ever seen in nearly 50 years, the COA has organized several short-term training courses introducing this innovative device/management to farmers, and subsidized farmers to purchase water-saving irrigation facilities to save irrigation water.

Application of land laser leveling on paddy field and furrow irrigation

Currently, in Taiwan, large-scale paddy leveling is carried out with general machinery and equipment. Restricted by mechanical defects and personnel operating experience, it is difficult to improve the leveling accuracy. Hence, laser leveling with laser light measurement was introduced to increase leveling precision far better than the existing manual and machinery operation.

According to an experiment conducted at TARI, the average soil level difference in the control field and that of laser leveling implemented field is 11.2 cm and less than 4 cm, respectively (Figure 2). Estimated with irrigation fully flooded paddy surface, the irrigated water required for each irrigation per ha can be reduced by 755 tons, shortening irrigation depth and economically saving water use of up to 20-25% compared to the control field without laser leveling. Trials on shallots also showed similar results. By comparing the production of shallots in the laser leveling demonstration area and the uneven control area, the average yield increased from 960 kg to 1440-1800 kg, an increase of about 50-87.5%. Due to the good quality of shallots, the wholesale price is higher than the market price, so farmers in the demonstration area increased their income by 74-117% compared with those in the control area (Table 2).

Extension of Organic farming

Organic agriculture is widely recognized as an effective way to enhance soil carbon sequestration, which is beneficial for climate change mitigation and adaptation. Organic farming was introduced to Taiwan in 1987 and began to be promoted in 1995. In addition, since 1999, many regulations and guidelines for organic farming and certification standards for organic products have been developed. Due to the small area of arable land and the large population, each farmer in Taiwan has less than 1 hectare of arable land, and farmers usually invest heavily on fertilizers and pesticides to ensure high yields. In addition, with a rapid decomposition of soil organic matter and a high incidence of pests and diseases due to the hot/ humid climate, the initial extension stage is not ideal and limited to only 5,850 hectares in 2012, and even present stagnating in 2013 and 2014. Recently, through the progress made in the development of organic farming of perennial fruit trees, and many incentives of subsidies on machines, facilities, and fertilizers, also reinforced with the promulgation of Organic Agriculture Promotion Ac in 2018, the acreage adopting organic farming has already reached 12,578 hectares till July 2022 (Figure 3).

Establishment of large and labor-saving organic vegetable cultivation technology

Currently, the acreage of organic farming in Taiwan covers around 1.5 % of arable lands with produce supporting a very limited population. Due to a lack of cultivation expertise and high production costs in the initial cultivation stage, the production yield of organic farming is lower than conventional farming and rendered much higher selling price which is less acceptable to the general consumers. Also, the smaller the organic framing land, the more risk of contamination it is to neighboring fields. In the vegetable diet of elementary and junior high school, students commonly favored cruciferous vegetables suitable for being produced in the cool seasons of autumn and winter. In summer, cruciferous vegetable grown in the open field is usually damaged by torrential rain and typhoon, while in facility cultivation, low production yield is also observed due to pest damages. In 2017, the Taiwan Agricultural Research Institute cooperated with Taiwan Sugar Company and introduced improvement measures including replacing seed sowing by transplanting nursery seedlings, reducing soil bulk density, and manipulating soil nutrients to speed up the growth of vegetables thus enhancing competitiveness against weeds and increasing efficiency of facility use. It resulted in vegetables being harvested 8 days earlier, yields 35%-60% higher than conventional seed sowing practice, and saves labor by eliminating the need for manual weeding from transplanting to harvesting (Figure 4).

Establishment of orange organic farming

Many factors such as long growth period, and difficulty in the management of fertilizers/water/pests, make organic citrus farmers frustrated and would not like to devote themselves to citrus organic farming. An organic citrus technological team has been organized at the Taiwan Agricultural Research Institute (TARI) to establish a demonstrative citrus orchard in Guken, Yun-lin County, where researchers can teach farmers about pruning, soil fertility improvement, nutrients adjustment, and pest control to improve organic citrus yield and fruit quality. After the technical introduction through the TARI team, soil pH in the demonstrative field was lowered by 0.3 units than CK (pH 8.1), organic matter content raised than CK (18 g kg-1) by 12 g-1 kg, while soil available K raised higher than that of CK (111 mg-1 kg) by 52 mg-1 kg. In addition, leaf N, Ca, and Mg contents of demonstrative citrus were higher than CK by 0.4%, 0.8%, and 0.17%, respectively. Furthermore, compared with CK, the yield, soluble solids content, and citric acid content of citrus fruit in the demonstrative field were increased by 43%, 1.5 °Brix, and 0.07%, respectively. Thus, the produce from the demonstrative field is more acceptable to the consumer than that in the past.

ENVIRONMENTALLY-FRIENDLY MANAGEMENT OF SOIL-BORNE PLANT DISEASES AND SOIL PESTS

Soil-borne plant pathogens and pests are considered a major limitation to crop production. These causal agents, such as pathogenic fungi, nematodes, and cutworms…, cause severe yield loss for many crops. After harvest, they often survive for long periods in the soil and will be the damage source for the next crop season. For sustainable agriculture, several non-pesticide strategies are recommended in Taiwan, including crop rotation, irrigation, tillage, field sanitation, soil amendments, soil sterilization, resistant stocks (grafting), antagonistic microorganisms (biological control), and eco-friendly plant protectants, and so on.

Environmentally-friendly management of soil-borne plant pathogens

There are various plant diseases caused by soil-borne pathogens, including fungi, bacteria, and nematodes. It is a challenge to detect and diagnose several soil-borne pathogens responsible for serious plant diseases. However, there are several strategies that could be applied for general disease suppression.

1. Crop rotation. Rotating different crops could break the life cycles of certain insects and pathogens and prevent them from multiplying. In Taiwan, crop rotation with rice planting (paddy fields) is widely recommended in the cultivation of vegetables, ornamental crops, and so on. For example, two seasons of rice planting were needed after 3-4 continuous seasons of Welsh onion cultivation.

2. Farm sanitation. Field sanitation involves the removal of sources of diseases, pest infestation, and weeds from the field; therefore, the primary pest sources will be reduced.

3. Soil amendments. There are several soil amendments recommended for crop protection in Taiwan, including S-H mixture, AR3-2 mixture, LT-M mixture, and so on. These soil amendments were mixed with the soil to protect crops from Fusarium wilt, bacterial wilt, Sclerotinia rot, Pythium root rot, root-knot nematodes, etc.

4. Soil sterilization. It includes steam treatment, soil solarization or flooding of the soil with heat. However, the disadvantages of these approaches are their high cost and high fuel consumption.

5. Resistant rootstocks. There are several popular cultivations of grafted crops used to obtain resistance to soil-borne diseases in Taiwan, such as citrus with resistant citrus rootstock against nematodes and collar rot, watermelon with squash rootstock against Fusarium wilt, bitter guard with loofa rootstock against Fusarium wilt, tomato with eggplant rootstock against bacterial wilt, and so on.

6. Natural crop protectants. Several kinds of plant extracts were tested as potential agents for the management of soil-borne plant diseases in Taiwan. However, most of them were still tested under laboratory conditions, except for the emulsified cinnamon oil, which has been patented to be used to control tomato nematodes by regularly drenching into the greenhouse soil.

Management of soil-borne plant diseases by biological control

Soil-borne plant diseases usually result from the reduction of biodiversity of soil microorganisms. Beneficial microorganisms that compete, repel, or antagonize disease-causing pathogens will render soil disease-suppressive. Crops grow in disease-suppressive soils much better than in soils low in biological diversity. Beneficial organisms can be introduced into the soil for the purpose of reducing disease incidence. Or, the soil environment makes more favorable for them through the use of compost and other organic amendments. High biodiversity of microbial populations usually creates soil conditions unfavorable for plant diseases to develop.

1. Biological soil disinfestation (BSD). It has been proven to be effective against a wide range of soil-borne pathogens. The treatment steps include (1) introduction of easily decomposable organic materials e.g., molasses, rice bran, rice straw, wheat bran, etc., at a rate of 100-200kg/acre of soil, (2) flooding the soil by irrigation, and (3) covering the soil surface with plastic film to maintain the reduced soil conditions.

2. Biological control of soil-borne diseases. The biocontrol agents which have been used in Taiwan include Trichoderma koningii, T. harzianum, T. atroviride, T. virens, Bacillus subtilis, B. amyloliquefaciens, Streptomyces saraceticus, and S. padanus. All of them were tested to be useful for crop protection and some of them were patented.

3. Application of biocontrol agent with other practices for controlling strawberry anthracnose- the most important strawberry disease in Taiwan. Healthy strawberry seedlings were produced in a greenhouse by spraying with a biocontrol agent, B. amyloliquefaciens P-2-2 fermentation broth. The seedlings were then transplanted to the field where the soil was treated with BSD, and the biocontrol agent was sprayed on the plants in the field regularly during the growing period. The strategy could reduce the loss of about US$8,450 per hectare and give farmers good market opportunities (Figure 5).

4. Improving soil fertility and inoculating arbuscular mycorrhizal fungi to reduce banana Fusarium wilt. Banana growth was impeded due to soil compaction, poor drainage, and nutrient unbalance under inappropriate farming management. In this circumstance, a banana was easily infested by Fusarium wilt and resulting in poor crop yield and quality. Through improving soil physical-chemical properties by incorporating coffee ground compost, adjusting soil fertility, and inoculating the banana seedlings with arbuscular mycorrhizal fungus, could strengthen banana growth, lower the incidence rate of Fusarium wilt, and enhance banana production and fruit quality. 539 days after the banana was transplanted, the incidence rate of Fusarium wilt in the CK treatment was 21%, while in the ICM treatment was 11% (Table 3). As to crop yield, banana production in the ICM treatment (2,113 kg/0.1ha) was 17% higher than that in the CK treatment (1,806 kg/0.1ha), and farmers gain more profit by NTD16,270 (US$542) per 0.1ha.

Environmentally-friendly management of soil borne pests

Traditionally, soil pests (crickets, mole crickets, grub, cutworm, wireworm, mealybugs, etc.) are managed by applying pesticides to the soil, which is harmful to the environment and human health. Several eco-friendly measures could be adopted to control soil pests like irrigation, tillage, natural enemies, and eco-friendly plant protection products. Integrated and applied the above measures to achieve the best effect of controlling soil pests. The measures used are summarized below.

1. Irrigation. After the crops are harvested or fallowed, the fields can be irrigated for 3–7 days to suffocate the pests in the soil.

2. Tillage. Changing the ecological conditions of the soil environment can inhibit the development and reproduction of soil pests. In addition, ploughing the farmland also turns the pests hidden in the ground to the soil surface, due to light, temperature, physical factors such as humidity and predation by birds, frogs and natural enemy insects which can cause a large number of deaths.

3. Natural enemies. Insect-parasitic nematodes are a group of organisms that shows promise as biological control agents for soil pests. It is best to apply entomopathogenic nematodes to moisten the soil in the early morning or late evening. Another useful natural enemy is entomopathogenic fungi. Entomopathogenic fungi use the soil as a habitat for long-term persistency when crops do not exist in the field, but the soil conditions such as the temperature, moisture, pH, and microbes influence the entomopathogenic fungi’s persistence and survival.

4. Eco-friendly plant protection products. Neem oil and plant oils mixture are eco-friendly plant protection products, and are effective against soil pests (root mealybugs, grub, crickets, etc.) when used as a soil drench. Root mealybugs are a serious pest of strawberries, it caused plant tissue to wither, reduced plant growth, and serious death. When strawberry seedlings were infected with root mealybugs, the soil immediately drenched with neem oil or plant oils mixture once a week, could usefully control root mealybugs' damage and recover strawberry seedlings' health (Table 4).

IMPROVING FARMLAND PRODUCTIVITY IN THE COASTAL AREAS BY CONSERVATION TILLAGE AND CROP ROTATION

Farmland productivity is generally low in the coastal areas of Taiwan due to monsoons and salinity. Improving farmland productivity can increase farmers' incomes, enhance soil carbon sequestration, and reduce carbon dioxide emissions. From 2018 to 2020, a three-year crop rotation system (non-tillage corn – direct seeded rice – non-tillage soybean in 2018, non-tillage corn – direct seeded rice – non-tillage corn in 2019, and non-tillage green soybean – direct seeded rice – non-tillage wheat in 2020) was introduced to the low productivity farmlands of Changhua and Yunlin counties.  The benefits observed from rotation among mutual complementary (paddy-upland) crops are co-sharing resources that greatly enhance water/nutrient use and avoid water/nutrient deficiency of subsequent next crops. The cropping order arranged for a high N requirement crop can be after previous N-fixing legumes (e.g. soybean-corn rotation), and that of tillage requiring crop can be after previous non-tillage upland crop (e.g. corn-paddy rotation), which would strengthen water retention capacity of deep layer soil, reducing irrigation demand of current crop and hence, increasing soil available water. After a rotation cycle, when soil fertility at least level, low fertility requiring crop should be selected to plant for inheriting uptake of remaining residual soil moisture of last crops (e.g. rice-soybean rotation). Compared to the conventional two crops rice system, the conservation tillage and crop rotation system have not only increased field productivity potential of up to 30% but also upgraded gross income  by 51~121% (Table 5).

CONCLUSION and Prospect

In response to the impact of global warming on crop production, Taiwan has taken steps to adapt and reduce greenhouse gas emissions to improve agricultural resilience. The results of these measures were as follows. Application of field sensors and automatic control devices can improve the water use efficiency of rice. Use of laser leveling technology can improve the water use efficiency of crops and increase the yield. Introduction of beneficial microorganisms can control soil-borne diseases and insect pests. Adoption of conservation tillage and crop rotation could improve low-productivity of farmlands.

The COA of Taiwan has announced to reach the net-zero emissions target for agriculture by 2040. In the future, in addition to developing cultivation techniques to adapt and mitigate climate change (e.g., improving nitrogen use efficiency), the agricultural machinery required for these cultivations will also be developed to reduce agricultural labor and provide incentives for farmers to participate.

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