Large quantities of agricultural by-products and animal waste are produced each year in Taiwan. These include about 730 thousand mt of swine manure, 1,860 thousand mt of chicken manure, 300 thousand mt of cattle manure, 310 thousand mt of sugarcane bagasse, 310 thousand mt of straw, 17 thousand mt of rice husk, 50 thousand mt of bark, 70 thousand mt of fruit and vegetable wastes from markets, 50 thousand mt of mushroom wastes and 5 thousand mt of coconut wastes. In order to reduce the pressure on land-fill sites and conserve natural resources, we should compost these organic wastes and recycle them onto arable land. Organic materials contain plant nutrients, and their use will reduce the amount of chemical fertilizer which Taiwan needs to import or manufacture.
The island of Taiwan has a subtropical climate, with relatively high temperatures and humidity all year around. The level of microbial activity in compost is high, and the organic carbon conversion rate is also high. According to Wang (1989), the organic carbon consumption per hectare is around 20 mt/year. A suitable amount of organic manure is urgently needed to maintain the organic matter content of the soil at an appropriate level. In recent years, the treatment and recycling of organic wastes has become an important topic in Taiwan.
Effect of Animal Waste Compost on Crop Yields and Soil Quality
Nitrogen Value of Composted Cattle Manure
Continuous field trials were carried out over three years (1995 - 1999) in Lu-Chiao, Central Taiwan, to check the nitrogen fertilizer value of composted cattle manure. The soil where the trials were carried out was a silt loam with a pH of 7.4 and an organic matter content of 28 g/kg. Three crops were grown each year in rotation: cabbage, and spring and summer crops of rice.
Each crop received treatments either of NPK, or of composted cattle manure at various rates (see Table 1). The nitrogen content of the composted cattle was equivalent to 1.0, 2.0 and 3.0 times the nitrogen in the applied chemical fertilizer. The yield response of the three crops to the various treatments is shown in Table 2.
It can be seen that the yield response of crops to nitrogen in compost was lower than the response to chemical fertilizer. The relative nitrogen efficiency of compost for cabbage was 0.276, while that for rice was 0.232 - 0.297 ( Table 3). The data indicate that the value of nitrogen in composted cattle manure was only about 25% that of chemical fertilizer. However, after repeated applications, the N-value of compost increased gradually year by year.
N-fertilizer value of compost made from various kinds of livestock manure (cattle, hog and chicken) was further tested in two soil series, using rice, cabbage and peanut as indicator crops. The properties of the compost are shown in Table 4. Of the soil series tested, both were recent alluvial soils, one with a pH of 5.1 (Tou-Nan), and one a calcareous soil with a pH of 7.9 (Yi-Chu).
The effect of compost on the yields and yield index of rice, cabbage and peanut are shown in Table 5. It is clear that the effect of the compost varied, according to the kind of soil and crop ( Table 6). For rice yields, the relative N-value of chicken manure was the highest, but was only 37% of the N-value of chemical fertilizer. Cattle manure was the second, (34%) and hog manure lowest (32%). For cabbage, the hog manure was the highest (37%) followed by chicken manure (29%) and cattle manure (25%). For peanut, cattle manure was the highest (21%), followed by hog manure (19%), and chicken manure (11%).
Sorenson and Jensen (1995) have indicated that the mineralization rate and the amount of nitrogen released from compost varies according to the soil texture. Our experiments gave the same results. In the short term, it seems that the nitrogen present in compost is less efficient that the nitrogen in N fertilizer. However, in the long term, at the end of two years of tests, the soil zinc content in all plots with applied compost was higher than the plot given chemical fertilizer. The plot treated with composted hog manure had a higher accumulation of copper, from the copper sulfate often included in the diet of pigs for growth promotion. The levels of phosphorus and potassium were also high, especially in plots treated with hog and chicken compost.
Long-Term Effects of Composted Animal Wastes on Soil Fertility and Crop Yield
Experiments were carried out in order to evaluate the feasibility of organic farming in Southern Taiwan. Three farming methods and two cropping systems were tested, at a site with sandstone and slate mixed alluvial soils. The three farming methods were:
- Conventional with recommended chemical fertilizer and pesticides;
- Intermediate (half chemical fertilizers were used, and half organic);
- Organic (no chemical pesticides and only organic fertilizers were used).
The rate of chemical fertilizer applied to each crop is listed in Table 7. The results showed that the soil pH, the level of phosphorus in the soil, and the soil organic matter content all increased over time in the organic plot ( Fig. 1, Fig. 2, Fig. 3). In the chemical plot, they all decreased. The level of soil exchangeable potassium also rose slightly in both the organic and mixed plots and fell in the chemical plot ( Fig. 4). The plot which combined chemicals and organic inputs had the best ability to build up soil nitrogen, and produced the highest crop yield. However, the nitrate content of the harvested crop was also high.
For cabbage, conventional farming methods gave the highest yields, probably because of crop losses from pests in the organic plots. The same was true of lettuce. Corn yields were generally higher in the organic and mixed plots than in the conventionally farmed plot. Yields in all plots were relatively high, showing that suitable crops or varieties, grown using modern cultivation techniques by experienced growers, gave a good harvest ( Fig. 5).
Thus, it seems that organic farming can be practiced successfully in southern Taiwan. Soil fertility will improve if organic methods are used. However, Chao studied the soil from the organic farming plot, and found that the levels of 0.1 extractable zinc increased from 11.5 mg/kg at the beginning of the treatment to 27.8 mg/kg at the end. Similarly, copper increased from 10.0 to 29.1 mg/kg. With long-term compost applications, it is necessary to monitor the accumulation of toxic substances such as heavy metals.
Effects of Composted Livestock Manure on Wax-Apple
Studies were made of the effect of composted animal waste on the yield and quality of wax apple ( Syzygium samarangense Merr. Perry). Experiments over four years showed that the compost plot had a higher soil pH and a higher content of calcium and magnesium than the chemical plot. However, plant biomass, fruit yield, and the sweetness and size of fruit, were the same in organic and chemical treatments ( Table 8).
Half organic plus half chemical fertilization gave a better average weight per single fruit. However, the cost of organic fertilizer was 20 times higher than that of chemical fertilizer. While very light applications of compost lowered fruit yield, large ones tended to accumulate excess nutrients in the soil. Chen et al. (2001) suggested that half organic and half chemical fertilizer is best for wax apple orchards.
Use of Organic Wastes As Substitutes for Growing Media
Taiwan imports a large quantity of growing media each year for the cultivation of pot plants. The most common imported media are peat moss, perlite, vermiculite and tree-fern. Recently, EC countries have begun to prohibit the mining and selling of peat moss and similar materials. Now that the supply is limited, we need to find local substitutes. Ideal growing media should have good physical, chemical and biological properties which produce healthy plants.
Pot Culture Media for Cucumber Seedling
Organic wastes from agriculture and aquaculture production were composted and used as a substitute growing medium for cucumber seedings. The chemical properties and nutrient content of the compost and media were analyzed, as shown in Table 9. Composts based on various raw materials were evaluated, according to the growth of the seedlings. All the composts could supply the nutrients needed by the seedlings without any additional chemical fertilizer.
Compost for sale in Taiwan contains a high level of soluble salts (EC), which makes them less suitable as growing media for pot plants. Tsai (2001) selected 20 brands of commercial compost, and mixed them with peat moss at a ratio of 1:1 as media for cucumber seedlings grown in pots. He found that only three brands of compost were suitable for this purpose. All three had a particle size of 0.6 - 2.0 mm diameter, a pH of 6.35 - 8.87, an EC of 1.69 - 2.31 dS/m, an organic matter content of 620 - 870 mg/kg, and a total nitrogen content of 13.0 - 19.3 g/kg, with 4.7 - 12.3 g/kg phosphorus, 7.5 - 12.5 g/kg potassium, 12.4 - 17.2 mg/kg calcium, and 2.8 - 7.3 mg/kg manganese. Tsai ( ibid) also found that several commercial compost products were good for the growth of cucumber seedlings when mixed with peat moss, coconut fiber, vermiculite or wood chips at a ratio of 1:1 ( Table 10). However, rice hull and bagasse were not suitable. From the point of view of production costs, wood chips and coconut fiber were promising substitutes for growing media.
Growing Media for Arum Lilies
Various species of arum lilies (Araceae) are common pot plants in Taiwan. Over a million of them are sold in the market each year. Arum lilies are grown in media which have a neutral reaction and a water-holding capacity of 30 - 60%.
Bark compost, bagasse, coconut fiber and carbonized rice hull were tested, mixed with each other or with peat moss. The tested plants grew normally in all mixed media and were comparable to those grown in peat moss only. Some species grew better in coconut fiber mixed with peat moss, others preferred media mixed with bark compost. A similar treatment used to test Spathiphyllum Petite, a vegetatively propagated pot plant, showed that media mixed with carbonized rice hull produced plants with more tillers.
Compost from Animal Manure As a Substitute for Growing Media for Pot Plants
Sludge sediments from livestock manure were composted and used as a substitute for pot plant growing media. About 10% to 20% was used (by volume). Several species of ornamental plant, including Philodendron and Spathiphyllum, were tested. Results showed that media containing 20% composted sludge had the same results as pure media, or even better. The same was seen when 20% composted chicken manure was substituted for growing media.
In general, there was no effect on the length and width of leaves, if composted chicken manure was added. However, plants growing in media with a high percentage of coconut fiber had more leaves. Chicken manure compost has a high pH, and adding it to growing media raised the pH. This change in pH does not always benefit in correcting the acidity of the media.
The high EC of chicken manure compost may be another limitation to its usage. Our experimental results showed no harmful effect from substitution, even when the coconut fiber had a high EC. It seems that the addition of up to 20% composted livestock manure is safe for pot culture.
Table 10 shows the price of organic materials for sale in Taiwan. Rice hull and bagasse compost are relatively cheap. However, before growers decide to use them as media substitutes, they should consider the growth and quality of pot plants, and their sale price, as well as the production cost.
Organic wastes from agricultural production are an important resource for farms in Taiwan. Recycling organic wastes onto arable land can provide some of the plant nutrients needed by crops, and maintain soil fertility. However, most organic wastes have a low plant nutrient content, and their rates of nutrient release are also low. It is important to compost organic wastes before they are applied to crops.
The relative nitrogen efficiency of compost made from animal wastes was low in comparison to chemical fertilizer. The N-efficiency of composted cattle manure and chicken manure was 0.345 and 0.374, respectively, in paddy rice. It was only 0.207 and 0.108 in peanut fields.
Some organic wastes were found to contain a high level of heavy metals, which limited their use. If compost is applied regularly, the nutrient levels of soils and plants, and their heavy metal content, must be checked periodically to prevent nutrient imbalances and soil pollution.
The rational application of compost can increase crop production and product quality. A combination of organic and chemical fertilizer gave better results than either type of fertilizer used alone. Coconut fiber and bark compost can be used as growing media for pot plants and seedlings. Composted animal wastes can be used to substitute for growing media for pot plants. However, their proportion (in volume) to peat moss should not be more than 20 - 25%.
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Index of Images
Figure 1 Effects of Different Types of Farming on PH of Soil
Figure 3 Effects of Different Types of Farming on Available P in Soil
Figure 4 Effects of Different Types of Farming on Exchangeable K in Soil
Figure 5 Comparison of Crop Yield under Different Types of Farming and Cropping Systems
Table 1 Crops and Compost Used in the Field Experiment
Table 2 Yield of Three Crops Given Chemical Fertilizer and Compost Treatments, 1995-99. Figures in Parentheses Are the Yield Index (%).
Table 3 Relative Nitrogen Efficiency of Cattle Manure for Various Crops
Table 5 Yield and Yield Index of Rice, Cabbage and Peanut
Table 6 Relative Nitrogen Efficiencies of Animal Waste Compost for Various Crops
Figure 2 Effects of Different Types of Farming on Organic Matter Content of Soil
Table 4 Properties of Animal Waste Compost Used
Table 7 Rate of Chemical Fertilizer Applied to Crops
Table 8 Effect of Fertilization on Soil Properties of Wax Apple Orchard at 1ST and 5TH Year a)
Table 9 Chemical Properties of Compost Media a)
Table 10 Growth Response of Cucumber Seedlings on Composted Media Mixed with Various Components (50:50), (28 Days after Sowing)
Table 11 Cost Estimation of Media Components
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