Taiwan is located in the subtropical zone, where a warm climate, fertile soils and ample rainfall make it possible to grow crops throughout the year. The people living on the island thus enjoy an abundant food supply, as well as the island's natural beauty which has given it the historical name of "Formosa", meaning `beautiful'.
The island now is less beautiful than it was, because of environmental pollution caused by industrial activity, as well as by the excessive use of chemical fertilizers and pesticides in agriculture. As in other developed countries, modern agricultural practices in Taiwan have greatly increased agricultural production, but their impact on the ecological and economic systems has not always been positive. In some cases, it has even led to reduced farm profits. The sustainability of modern agriculture has thus become a subject of great concern to the policy makers, researchers and farmers of Taiwan. There is an urgent need to establish a feasible sustainable agricultural system in Taiwan, which was officially recognized in 1986 when the Council of Agriculture, Executive Yuan, held a meeting to evaluate the possibility of adopting an organic farming system in Taiwan. In 1988, all aspects of the problems involved were discussed thoroughly at a Symposium on Organic Farming held in Changhua, and several research programs dealing with organic farming were then begun at a number of agricultural institutes, including a three-hectare organic farm in Taichung District Agricultural Improvement Station.
According to Lockeretz (1988), sustainable agriculture is a loosely defined term that encompasses a range of strategies for addressing a number of problems, including loss of soil productivity from erosion and related nutrient losses, the pollution of surface water and groundwater from pesticides and fertilizers, and low farm incomes as a result of reduced commodity prices and high production costs.
The present paper describes the strategies for establishing a sustainable agricultural system in Taiwan based on the results of current research on organic fertilizer applications, crop rotation, integrated pest management, weed management etc. The extension of sustainable agriculture to farmers in Taiwan is also discussed.
Use of Chemicals in Taiwan's Agriculture
Prior to 1950, chemical fertilizers and pesticides were not widely used by farmers in Taiwan. Crop production at that time depended mainly on green manures and compost made of rice straw, sugarcane leaves, and cattle and hog wastes. Farmers sometimes mixed bonemeal, or soybean cake and other plant products, into compost to increase its nutrient value ( Fig. 1). The natural ecology was fairly well balanced at that time.
After 1960, chemical fertilizers such as ammonium sulfate, urea, calcium ammonium nitrate, calcium superphosphate, potassium chloride etc. were increasingly used, reaching a peak of 140,000 mt in 1974 ( Fig. 2). Insecticide use also increased, to reach a peak of 23,000 mt in 1984. The use of herbicides and fungicides showed a corresponding increase: on average, 1,500-1,700 mt of herbicides and 200-500 mt of fungicides have been used each year from 1978 up to the present ( Fig. 3). The heavy use of chemical products in agricultural production over the past 30 years in Taiwan has resulted in an increased level of environmental pollution.
Application of Organic Matter
Source of Organic Materials
The organic matter (OM) content of the soil is often used as an index of soil fertility. Generally, organic matter influences the soils in three ways, by altering the physical, the chemical, and the biological properties. The term "soil organic matter" covers all kinds of plant tissues and animal residues in the soil. Soil organic matter may turn into humus after decomposition and become an active component of the soil. Organic matter used for agriculture in Taiwan may be classified into the following categories: crop residues, green manure, common compost, mushroom compost, cattle manure, hog manure, poultry manure, municipal refuse, wastes from the extraction of vegetable oil, and residues from processing animal products (Hsieh and Hsieh 1989). Organic materials should be composted before they are applied to the soil. A suitable method of composting has been described by Hsieh and Hsieh (1990).
Application Rate of Organic Matter
The application rate of organic matter is determined mainly by soil fertility, the nutrient content of the organic material concerned, and the nutrient requirements of the crop. However, less than 2% organic matter in the soil is generally considered to be "insufficient", 2.5% is "fair", and more than 5% is "plenty".
Since the nutrient content of organic fertilizers varies greatly according to the type of organic material, while the nutrient requirements of different crops also vary, the type of organic fertilizer should be selected to meet the requirements of the particular crop. Generally, leafy vegetables require more nitrogen for better vegetative growth, while fruit trees and fruiting vegetables require less nitrogen and more phosphorus and potassium for better flowering. Therefore, for a crop like spinach, the farmer should apply poultry manure or some other manure with a high nitrogen content, or mix a substantial amount of high-nitrogen manure into the composting material to get better results. For fruiting vegetables such as tomato, common compost or other low-nitrogen materials such as rice bran can be used, or a low proportion of high-nitrogen manure in the composting material. The application rates generally used for common organic fertilizer in Taiwan is shown in Table 1.
Effect of Green Manure on Crop Yield
An experiment was carried out to study the effect of Berseem clover, milk vetch, and rape, used as a green manure, on the grain yield of sorghum (Tsai, Huang and Lay 1989). After only one crop of green manure had been plowed under, the soil organic matter content increased slightly ( Fig. 4) while the grain yield of sorghum increased proportionally with the amount of green manure (Berseem clover) applied. Fig. 5 shows that the grain yield of sorghum increased about 20% when 20 mt of Berseem clover was applied, and by 45% when 30 mt/ha of clover was applied.
Effect of Different Livestock Manures
Several experiments have been carried out to compare the effects of organic and chemical fertilizers on the yield and quality of sweet corn and vegetable soybean. In the corn experiments, chemical fertilizers (N-P 2O 5-K 2O at a rate of 200-60-60 kg/ha) were applied to the conventional farming plot. Five treatments were applied to the organic plots. On three of these (treatments 2,3,4) the composted manure of hogs, cattle and chickens, respectively, was applied at a rate of 25 mt/ha. A mixture of one half chicken manure and one half cattle manure was applied to the plot with treatment 5, and a mixture of one half chicken manure and one half hog manure to the plot with treatment 6. Bacillus thuringiensis, and extracts of hot pepper and tobacco leaves, were used to control pests (Hsieh et al. 1992).
The results, shown in Table 2, indicated that the fresh ear yield of sweet corn harvested from the organic plots was equivalent to that of corn given chemical fertilizer, except for the plot with cattle manure which gave a lower corn yield. This was in spite of the fact that the incidence of corn borer was significantly lower in the plot fertilized with cattle manure than in the plot with chemical fertilizer. The nitrogen and magnesium content of the corn grain were significantly higher in corn from the plot with chemical fertilizer, while the phosphorus and potassium content was slightly higher in the organic plots than in the chemical one.
A similar study of vegetable soybean showed a marked difference in pod yield, according to whether the plot was fertilized with organic compost or chemical fertilizer. All types of organic fertilizer except hog manure gave a higher pod yield than chemical fertilizer ( Table 3) possibly because the improved soil conditions after organic fertilization offered a better soil environment in which the roots of the leguminous soybean could grow.
Crop Performance in an Organic Farming System
In order to evaluate the feasibility of organic farming in Taiwan, experiments were carried out to compare rice yields from conventional (chemical) farming with those from organic farming, as well as an intermediate system (a mixture of chemical and organic fertilizers). A high-quality rice variety, Taichung 189, was planted at a spacing of 25 cm x 21 cm under the following fertilizer treatments: 1. Conventional farming: Chemical fertilizer at a rate of N-P 2O 5-K 2O: 160-60-60 kg/ha was applied. 2. Intermediate type of farming: Half the fertilizer applied was chemical, (80 kg N, 30 kg P 2O 5, 30 kg K 2O) and half was organic compost (6.6 mt/ha). The latter was applied as a basal fertilizer. 3. Organic farming (A): Composted hog manure (13.3 mt/ha) was applied as a basal fertilizer. 4. Organic farming (B): Composted chicken manure (6.6 mt/ha) was applied as a basal fertilizer.
A sugar_vinegar microbic solution, together with other natural pesticides, were used for pest control during the experiment.
The results, shown in Table 4, indicate that the application of composted chicken manure gave as good a grain yield (7.43 mt/ha) as that from conventional farming which depended solely on chemical fertilizer.
Crop rotations and biological diversity have long been utilized very successfully in traditional agricultural production systems. It is important to explore the potential of the effect of crop rotation when it is used in a sustainable agricultural production system. Since an appropriate rotation of different crops may help control pests, rotation is an important component in integrated pest management systems.
Effect of Rotation on Crops
Legumes contribute nitrogen to the succeeding crop, and proper utilization of legumes as a green manure may help improve soil fertility for better crop production. Annual legumes are useful as rotation crops with common annual crops, vegetables, and flowers. Annual legumes can also improve the production of perennial forage crops, if they are properly utilized. Francis and Clegg (1989, 1990) concluded that rotation effects were primarily due to the increased nitrogen made available to crops grown after soybean, peanut and other legume crops. Other effects of rotation include increased soil moisture. It is generally agreed, however, that the most important benefit of rotation is control of insects and diseases, while another benefit common to all types of rotation is the improved control of weeds (Stinner and Blair 1990).
An experiment was carried out at Taichung, central Taiwan, to evaluate the economic returns from a rotation of sorghum, corn, peanut, Job's tears, soybean, green manure and rice. The yield of each crop varied in different types of cropping system, but the net profit per year was 3.7-60% higher than the traditional rice-rice cropping pattern ( Table 5).
Minimum or conservation tillage is a crop planting system that may leave 30% or more of the residues of the preceding crop lying untouched on the soil surface. This system can reduce production costs as well as runoff and soil erosion, and can also conserve soil organic matter and increase soil moisture retention. This is partly because the higher moisture content under no-tillage offers better conditions for phosphorus diffusion. Minimum tillage systems also tend to have a more abundant microbial soil community, as a result of the reduced frequency and intensity of soil disturbance, and a more stable soil biomass (Heuse and Stinner e t al. 1984). Corn planted in the field without tillage thus often gives a higher yield than when it is grown with tillage ( Table 6) (Lian and Wong 1988). No-tillage is worth recommending for sustainable farming systems, in view of its lower production costs.
Pest control should be based on a thorough understanding of the habitat, food preferences and other behavior of the pest, so that the most effective biological, cultural, as well as chemical controls can be combined in an ecologically and economically sound integrated pest management (IPM) strategy. The aim of IPM is to maximize natural and cultural controls, and use pesticides only as a last resort.
Cultural control reduces pest damage through manipulation of the environment. Cultural control is often associated with mechanical operations such as tillage, interplanting, crop rotation, and adjusting the time of planting and harvesting. Although cultural practices alone may not give satisfactory pest control, they are important in minimizing pest injury.
Crop Rotation and Inter-Planting
Crop rotation systems offer many advantages in terms of improved soil structure and fertility, and control of erosion as well as various pest species. The value of crop rotation is limited where the control of highly mobile insects, pathogen spores, or airborne weed seeds is concerned, all of which move readily from field to field (Francis and Cregg 1990). However, some soilborne diseases such as Fusarium may be reduced by proper rotation or intercropping with leek and green onion, and nematodes can be partially controlled through crop rotation or by intercropping with marigold or Cassia tora*. The results of experiments conducted in Taichung indicated that the rotation of rice with corn, or of rice with peanut, reduced the incidence of rice diseases (leaf blast, bacterial leaf blight, Helminthosporium leaf spot and sheath blight) to 1.6-3.4%, and insect pests (rice borer, brown plant hopper) to only 0.1-3%. Crop rotation is useful for the control of many other insect pests, including beet armyworm ( Spodoptera exigua (HÃ¼bner)) the western corn rootworm, ( Diabrotica virgifera Leconte), the white-fringed beetle ( Graphognathus leugoloma Boh), and the rice stem borer ( Scirpophaga incertulas (Walker)).
The Use of Sex Pheromones to Control Insect Pests
There has been rapid progress in the use of sex pheromones as an attractant to control insect pests in the field. Sex pheromones of many different insects are now being chemically synthesized and are available on the market. Since sex pheromones are not sprayed directly onto the crop, there is no pollution problem. Sex pheromones are basically used to attract and trap insect pests so as to reduce the insect population.
The results of experiments in Taichung by Cheng (1989) indicated that sex pheromone traps at a rate of three traps per 0.1 ha (30 traps/ha) were able to control more than 90% of beet armyworm in a field of green onion ( Table 7). The efficiency of sex pheromone traps for rice borer was 7.3 times higher (3635.2 vs. 496) than that of ordinary illumination traps. (T.S. Liu, personal communication).
Use of Yellow Sticky Plates to Control Insects
Different species of insect are attracted by different colors. Experiments were carried out in Taichung to explore the possibility of catching and killing insects in the field with colored sticky plates coated with insecticide (Omethoate). The results indicated that yellow plastic plates coated with insecticide were effective in controlling leaf miner ( Table 8). This method avoids environmental pollution since the insecticide is not sprayed directly onto the crop. Different insects may be attracted by different colors, so that similar experiments using other colors may indicate what other insect species can be controlled by this method.
Bagging Fruit to Control Melon FLY
The melon fly, Dacus cucurbitae Coquillett, is an important insect pest of sponge gourd and bitter gourd in tropical countries. According to Fang (1989), wrapping the young fruit in paper bags immediately after the petal wilting stage is a good way of protecting the fruit from melon fly damage ( Table 9). Bagging the fruits of other crops also reduces damage by melon fly (Kawasaki et al. 1991).
Use of Plastic Bottle Traps to Control Flat Snail
The flat snail ( Bradybaena similaris (FÃ©russac)) is widely distributed in Taiwan, Mainland China, Japan, India and the islands of the Pacific. It is the most important pest of grape, and is also found on many commercial and ornamental plants and trees in Taiwan. The snail hatches in the soil and moves up into the grape vine, and grape growers generally scatter metaldehyde granules over the ground to control it. However, this method has several disadvantages. It is effective for only a short period, it is costly, and it leaves toxic residues. Recently, a method has been developed of controlling the snail by the use of disposable plastic soda bottles made into traps. These prevent the snails from climbing up into the grapevine. The traps are made by cutting off both ends of the bottle and splitting one side of the body longitudinally to allow it to be sleeved around the stem of the grapevine (Plates 1, 2). The bottles are then stapled firmly around the stem at a height of 1 m above the ground.
Since the bottles are tightly fixed around the grape stem, the snails cannot pas through the neck to infest the vines. Unable to descend, all the snails trapped in the bottle soon die of starvation. These traps give a control rate of more than 94.8% (Chang 1988). This is a very cheap and effective method of controlling flat snail, and is no threat to the environment. It can thus be widely recommended to grape farmers.
Use of Soil Amendment to Control Soilborne Diseases
The low organic matter content and high soil acidity of subtropical soils promote outbreaks of serious soilborne diseases such as crucifer club root; Fusarium wilt of watermelon, cantaloupe, and peas; Fusarium yellows of radish and mustard; and phytophthora blight of cucumber. These diseases cannot be controlled by fungicides.
Sun (1989) and Huang (1992) indicated that amending the soil with S-H mixture ( Table 10), at a rate of 1-1.5 mt/ha, effectively controls all these diseases, plus bacterial wilt of tomato ( Table 11). Soil texture and soil vitality are greatly improved by organic amendments (Sun 1989, Huang 1992).
The Use of Natural Pesticides in Sustainable Agriculture
As natural pesticides are prepared from natural products, application of these materials has a less unfavorable impact on the environment than chemicals. They are now used widely in sustainable agriculture for the control of diseases and insects in Japan, the United States, and many other countries. According to our preliminary studies, tobacco leaf extract solution is effective in controlling aphids, snails and leaf rollers, and has the same effect on some other insect pests. Extract of hot pepper can be used to control aphids, leaf mites, ants, and some virus diseases transmitted by aphids. Garlic oil can be used to control aphids, leaf mites, powdery mildew, rust, and many other insects and diseases. Spraying vinegar can control powdery mildew disease, while combining vinegar with fermented sugar and effective microorganisms gives more effective control of both insects and diseases.
As Tables 12 and 13 show, natural pesticides cannot give complete control of peanut thrips and sweetcorn borer, but they do lower the rate of infestation. However, in our preliminary studies the control effect of natural pesticides is far from satisfactory. Further studies should be made, using a wider range of natural pesticides. Even if more effective natural pesticides are identified, they will probably be best used as one measure in an IPM system.
Integrated Weed Management
Integrated weed management relies heavily on cultural practices such as mulching or mechanical tillage during the first four to eight weeks of crop growth. This allows the crop to become well-grown before the emergence of weeds, and allows crops to compete effectively with weeds by shading them. Mechanical control of weeds by tillage operations includes primary tillage, secondary tillage, hand weeding and tillage during the fallow period. Cover crops and mulches are also a good way of managing weeds. Small hand-operated weeding machines can easily control weeds in paddy fields.
Extension of Sustainable Agriculture in Taiwan
In 1986, various small demonstration organic plots were set up around the island to demonstrate the usefulness of organic fertilizers to farmers. At the same time, green manure demonstration plots were also set up in farmers' fields, with the support of a government subsidy. Altogether 211 townships in 18 counties and cities took part in this demonstration program. As a result of these field demonstrations, farmers began to apply more organic matter to their farms, particularly to orchard crops such as grape, pear, apple, peach, mango, citrus, starfruit, pineapple, and guava. Application of organic matter to upland crops and rice is still rather limited, because of the lower value of these crops.
In 1989, an integrated organic demonstration farm was set up to grow sponge gourd and pea in central Taiwan, in which 11 farms participated. Another three-hectare organic demonstration farm in which 11 farms participated was established nearby to produce green onion, cucumber, phaseolus bean and cabbage.
Neither of these two organic farms was very successful, because those operating them lacked experience in non-chemical methods of pest control. However in 1990 a government-sponsored organic farm was established to produce sponge gourd. Green manure crops were grown on two-thirds of the land to increase the N source, while the remaining land received 2 mt/ha of cattle compost and soybean meal, plus slag as a basal fertilizer. No chemical pesticides were applied, and pests were controlled by available non-chemical IPM methods. The result was a 25% increase in the yield of high-quality sponge gourd. This farm can therefore be considered to represent a successful organic farming system. In the same year, a 10-ha citrus farm based on organic methods was established, and it too has been very successful, with regard not only to production but also to marketing.
Modern agriculture, based on the monoculture of cash crop varieties that require high inputs, needs heavy applications of inorganic fertilizers, and of synthetic chemicals for pest control. Intensive production has tended to accelerate wind and water erosion of soils, and to contaminate surface water and groundwater (Lockeretz 1988).
There is a growing awareness of the need to adopt more sustainable and integrated systems of agricultural production, that depend less on chemicals and other energy-based inputs (Sun 1992). Such systems can often maintain good yields, and at the same time lower the cost of inputs, increase farm profits and solve ecological problems. Some countries which have adopted intensive farming have found that, although yields are high, they are now experiencing greater problems of pests, diseases, and weeds, and increased environmental stress. Hence, there is an urgent need to develop and extend to farmers sustainable farming systems that can maintain productivity and farm profits without endangering resources and polluting the environment.
The concept of sustainable agriculture has become important in Taiwan in recent years, and emphasizes the integration of agricultural systems and ecological processes to maintain profitable production with reduced environment pollution. A sustainable system must be both economically profitable and environmentally sound (Hsieh 1992). However the most difficult problem in sustainable agriculture in Taiwan is how to control by non-chemical methods the insects and diseases which are particularly serious in the hot, humid climate of Taiwan. Much more research is needed on this problem.
To feed more than 20 million people from a total of only 900,000 ha of arable land is a great challenge to Taiwan's agriculturalists. A new Regional Agricultural Development Program, launched by the government in July 1991, has as its main objectives the development of new production systems which focus on efficient use and regeneration of resources. Particular attention will be given to recycling resources such as livestock manure, making efficient use of water and fertilizers, and the biological control of pests (Sun 1992). In addition, large quantities of various kinds of green manure are now being grown between cropping seasons and on fallow land. Education and extension programs are being conducted for consumers as well as for farmers. It is only when consumers can accept the concept of sustainable agriculture, that there will be an incentive for farmers to practice it. More research is needed, not only on new technology for sustainable agriculture, but on marketing strategies to ensure a profitable return for the farmer.
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In the discussion, Dr. Sri Adiningsih was interested in the income from organic farming, and whether this was sustainable. She was also concerned at the very high level of organic matter applied in the experiments discussed by Dr. Hsieh, and questioned whether farmers would be able to apply such large amounts, particularly in view of the labor cost. Dr. Hsieh replied that modern organic farming has only been practiced recently in Taiwan (traditional farming is of course entirely organic). For this reason, there is not yet a marketing structure to handle organic products, although this will be developed in the future. He felt that Taiwan had an abundance of organic materials, especially since its warm climate makes possible the production of crops all year round. In the past many farmers used to burn their rice straw, but they are now prohibited from doing this, and must use the straw as a raw material. Taiwan also produces more than 10 million head of hogs a year, with a consequent huge volume of livestock manure which is now being used to make organic fertilizer, as is cattle and poultry manure. He said that there are two types of organic fertilizer used in Taiwan: one is the farmer's own compost made from farm by-products, and the other is the commercial compost made by Taiwan's 120 compost companies, most of which is sold to farmers. It is bulky and costly to transport to the farm, but machinery is now available to broadcast organic materials which helps reduce application costs.
Flat snails eating grape
Use of plastic bottle trap to
control flat snail on grape vines
Index of Images
Figure 2 Consumption of Chemical Fertilizers in Taiwan
Figure 3 The Consumption of Pesticides in Taiwan
Figure 4 Effect of Green Manure on Soil Organic Matter Content after Harvest
Figure 5 Relationship between the Fresh Weight of Berseem Clover and the Grain Yield Indices of Spring Sorghum
Table 1 Application Rates for Organic Fertilizers in General Use in Taiwan
Table 2 Effect of Chemical Fertilizer and Composted Livestock Manure on the Yield of Sweetcorn
Table 4 Performance of Taichung 189 Rice under Different Cultural Systems
Table 5 Yield of, and Net Profits from, Crops Grown in Different Cropping Systems in Central Taiwan
Table 6 Yields of Corn Grown under Tillage Compared to No-Tillage, Southern
Table 7 Control of Beet Armyworm by Sex Pheromone Traps, Taiwan
Figure 1 Consumption of (Non-Commercial) Organic Fertilizers in Taiwan, 1940-1990
Table 3 The Effects of Chemical Fertilizers and Composted Livestock Manure on the Yield of Vegetable Soybean
Table 8 Control of Chrysanthemum Leaf Miners by Yellow Sticky Plates
Table 9 Effect of Bagging Gourds on Infestation by Melon FLY
Table 10 Components of the S-H Soil Amendment
Table 11 Control of Soilborne Vegetable Crop Diseases by S-H Mixture in Taiwan 1983-1988
Table 12 Effect of Natural Pesticide on Corn Borer
Table 13 Effectiveness of Natural Pesticides in Controlling Peanut Thrips and
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