CHAPTER 3 - AMMONIATION OF CROP RESIDUES

Zhang Zhishan
Ministry of Agriculture
Yan Qiaojuan
China Agricultural University

Introduction

As early as 1933, a German scientist started research on straw treatment with ammonia. In 1938, scientists in the former Soviet Union treated wheat straw with anhydrous ammonia to increase digestibility. In the 1950s, a Danish patent was issued on ammonia treatment technology. From the 1970s, Bangladesh, Canada, Denmark, Egypt, India, Japan, Niger, Norway, Tunisia, United Kingdom and USA started research on straw ammoniation. Some countries have popularized ammoniation at national level. Straw ammoniation technologies were introduced to Norway in 1975 with government financial support, and in 1988 total straw treatment had reached 130 thousand tonne, 17.3 percent of total straw output. For environmental protection, Denmark recently prohibited straw burning.

Chinese farmers have known that human urine can be used to treat straw for cattle feed. It is pity that no research has been done on this. From the 1980s, China started to adjust its animal production structure with a new policy of a grain saving strategy. Fundamental research and experiments were started. MOA began to popularize straw ammoniation in 1987. In 1989, straw ammoniation became one of ten key extension techniques of MOA, and by 1993 it had been popularized throughout the country, with 11.7 million tonne of straw treated, the largest in the world. FAO and UNDP had several successful projects on straw utilization for feeding animals. At FAO's suggestion, international conferences on Increasing Animal Production with Local Resources were organized in China on three occasions. These conferences provided the opportunity to exchange experiences among different countries.

The principle and effects of straw ammoniation

The main component of straw is fibre, including cellulose and hemicellulose that can be digested by ruminants. Some cellulose and hemicellulose are bound to lignin and resistant to microbial attack. The role of ammoniation is to destroy this link, so these fractions are available to the animal. Ammoniation usually increases digestibility by 20 percent and CP content up to 1-2 times. It can also improve palatability and consumption rate. The total nutritional value can be doubled, reaching 0.4-0.5 feed units for each kilogram of ammoniated straw. In addition, ammoniation reduces mould development, destroys weed seeds (e.g. wild oat, false sorghum, etc.), parasite eggs and bacteria.

Ammonia sources for straw ammoniation

The sources of ammonia to treat straw include anhydrous ammonia, urea, ammonium bicarbonate and aqueous ammonia.

Anhydrous ammonia

Anhydrous ammonia means "ammonia without water." Its formula is NH₃, and its N content is 28.3 percent. The normal dosage is 3 percent by weight of the straw DM. It is the most economical source of ammonia.

The boiling point of anhydrous ammonia is -33.3°C, its vapour density is 0.59 (that of air is 1) and its liquid density 0.62 (that of water is 1). Gas pressure is 1.1 kg/cm² at -17.8°C and 13.9 kg/cm² 38°C. At normal temperature and pressure, anhydrous ammonia is a gas. Expensive pressure containers are required not only to keep it as a liquid, but also to transport and store it. Anhydrous ammonia is a potentially dangerous and toxic material, and stringent safety precautions need to be observed when using it. Its natural ignition temperature is 651°C. If the ammonia content in the air reaches 20 percent, an explosion from self-ignition could occur. Attention should be paid to possible ammonia explosions, even though it seldom happens.

Urea

The N content of urea is 46.7 percent. Its formula is CO(NH₂)₂. It is decomposed into ammonia and CO₂ by ureases at ambient temperature. The chemical reaction is:

Urea dosage needed to treat straw may vary a lot. The recommended dosage is 4-5 percent urea on DM basis, taking into consideration the effect of ammoniation and costs. Urea can be transported conveniently at normal temperature and pressure. It is harmless to humans. Treating straw with urea does not need complex equipment and the sealing conditions are not as strict as with anhydrous ammonia. It is known that farmers in Bangladesh ammoniate straw in bamboo baskets lined and covered with leaves of a kind of banana. From the Yellow Cattle Magazine, it is known that, in Anhui province, technicians use urea as a source of ammonia to treat straw without cover and get good results, which is beneficial for extension of straw ammoniation to rural areas. At present, urea is a widely used source of ammonia in China. Urea is not as effective as anhydrous ammonia for straw treatment, but it is better than ammonium bicarbonate.

Ammonium bicarbonate

The nitrogen content of ammonium bicarbonate is 15-17 percent; its formula is NH₄HCO₃. It can be decomposed into NH₃, CO₂ and H₂O at a suitable temperature (above 60°C). The chemical reaction is:

The dosage of ammonium bicarbonate, estimated by its N content, is 14-19 percent of straw DM. But, according to the experiments carried out in Zhejiang and Shanxi Agricultural Universities, using 8-12 percent of ammonium bicarbonate can give the same result as with 14-19 percent.

Ammonium bicarbonate is a major product of the fertilizer industry and it is readily available at low price. It has a retail price of ¥ 300/ton (compared to more than ¥ 1000 for urea) and it is easy to use. Since ammonium bicarbonate is an intermediate product of urea breakdown, theoretically, in the right concentration, its effect should be similar to urea. Reports from Zhejiang Agricultural University indicate that in the humid south, straw ammoniated with urea showed more mould spots than with ammonium bicarbonate. It does not decompose completely at low temperature, thus in cold climates the effectiveness of treatment with ammonium bicarbonate is not good. When treating with ammonium bicarbonate in an oven, one day is enough, since the temperature reaches 90 °C and it decomposes completely.

Aqueous ammonia

Aqueous ammonia is a solution of ammonia in water. The concentration is quite variable, but the usual value is 20 percent. At this concentration, the normal dosage is 12 percent by weight of straw DM. It is only adapted to areas near to fertilizer factories because its low N content makes transport expensive.

Other sources

Besides the above sources of ammonia, human and animal urine also can be used to treat straw. However, collection difficulties limit practical applications.

Methods for ammonia treatment of straw

At present, the methods for popular ammonia treatment of straw in China include stack, silo or bunker, and oven methods. Each uses a different ammonia source.

Stack method

The procedure for the stack method is as follows. First, an area is selected with an elevated, dry and even surface. This area is covered with non-toxic polyethylene sheet and the baled or loose straw (chopped or whole) is stacked on it. It is better to bale straw or to chop it into pieces. Especially for hard and thick maize stover, chopping before treatment facilitates feeding, saves plastic and reduces the danger of puncturing the plastic. The moisture content of straw should be adjusted to 20 percent or more during stacking (anhydrous ammonia requires a low-moisture straw compared with urea and ammonium bicarbonate). The high moisture has a positive effect on straw treatment. However, after treatment, it is difficult to ventilate the straw and it can be easily attacked by mould. A wooden bar, which will be pulled out when ammonia injection starts, is placed before stacking so that ammonia can be injected easily and conveniently. The stack is sealed with non-toxic polyethylene sheet and injected with 3 percent anhydrous ammonia by weight of straw DM. At the end, the hole left when the pipe is removed is sealed with good quality tape.

Operators working with ammonia must be trained and should strictly follow relevant regulations to ensure personal safety. Treatment time varies inversely with temperature. For example, more than four weeks are needed at a temperature of 5-15°C, but only one week at >30°C.

Straw treatment with anhydrous ammonia is simple and efficient, but particularly suited for large-scale use. The method also had been widely applied in developed countries. It requires some expensive equipment. For instance, the cost of an EQ144 ammonia truck tank carrying 5.1 tonne is ¥ 16 000; a 200-kg ammonia bottle costs ¥ 2 500; a 400-kg bottle costs ¥ 4 500; and an 8.82 kW four-wheel tractor costs ¥ 8 000. Furthermore, anhydrous ammonia is not well suited for private farmers because of its dangers.

In order to explore the best supply system of ammonia for farmers, ammoniation stations have been built in Hebei Xingtai region, Boxiang county; Baoding region, Dingxing county; and Henan Zhoukou region, Fugou county. These stations have accumulated experiences during the past few years to share with other regions.

Selection of plastic film

The basic requirements for plastic film are that it is non-toxic, durable and suitable for sealing. The plastic often used is polyethylene. Thickness, width and colour are determined by practical situations. Thick film (about 0.12 mm) is used for maize stover; thin film (less than 0.12 mm) for wheat straw. Width of film is determined by the size of stack and market availability. If used in the open air, black colour should be preferred, because it is durable and absorbs solar energy, which heats the stack and shortens treatment time. If used indoors, film colour has no obvious influence on treatment. The amount of film required can be calculated by the size of stack.

The ammoniation station in Fugou County made a covering sheet that was especially suitable for a 500-kg wheat straw stack. Covering the stack greatly improves treatment efficiency.

Measurement of the stack density

Weighing the stack is a basic task for straw treatment. It is well known that it is important to inject the correct amount of ammonia: too little ammonia is ineffective; too much ammonia increases the cost and has no further effect on treatment. The exact weight of straw must be known so that the correct amount of ammonia can be applied. But weighing is difficult under field conditions. A simple method is to first measure the average density of stack for various straws, then to multiply it by its volume. Stack density depends upon plant species, moisture content and particle size. Of course, density also varies with time. In order to get reliable data, it is necessary to measure many stacks (at least 8 for each straw type). Density is expressed in kg/m³. In old stacks, volume is measured first, then it is weighed. New stacks are weighed before stacking and volume measured after. It is very easy to calculate the volume of rectangular and cylinder stacks. The volume of stack with irregular shape may only be estimated. In 1989, 9 stacks of air-dried straw were measured in Boxiang county during the FAO project. The average density was 55 and 79 kg/m³ for new and old wheat straw, and 79 and 99 kg/m³ for new and old maize stover, both whole, respectively.

Ammonia dosage measurement

The precision of ammonia injection depends on not only the correct weight of straw but also the correct amount of ammonia. Currently there are two main methods for ammonia injection used in China. One is to inject ammonia into the stack directly from an ammonia truck tank filled in the factory (Figure 3-1), the other is to inject it from a bottle (Figure 3-2).

Figure 3-1. Transfer of anhydrous ammonia from tank truck to stack of crop residues

At present, domestically produced ammonia flow meters are not available in China, and the price of imported ammonia flow meters is very high.. The Non-conventional Feeds Institute of China Agricultural University has developed an ammonia flow meter. With a flow of 3-5 kg/min, the error is less than 3 percent. The price of the meter and its accessories is ¥ 500 and it is ready to go to the market.

In most situations, the amount of ammonia to be injected is estimated by the injecting time. This method is not very precise because both the pressure and the flow rate of the ammonia vary with temperature. Sometimes ammonia dosage is estimated by the weight of the ammonia bottle. This method is more precise for ammonia injection. In brief, there are still many problems to be solved in terms of measuring ammonia dosage.

Figure 3-2. Transfer of anhydrous ammonia from ammonia bottle to stack of crop residue

Proposal for "one stack - one bottle"

In order to solve the measurement problems of ammonia dosage, F. Sundstol, FAO expert, proposed "one stack, one bottle." This approach could overcome the measurement difficulties, since a whole bottle would be used for a standard stack. At the same time, small bottles should be easily transported by small tractors with trailer, or by bicycle, an obvious advantage for rural areas with bad roads. In addition, farmers can buy ammonia bottles and store them for later use. For the small ammonia bottle system it is very important to select the appropriate size. If the ammonia dosage is 3 percent of the straw, the net weight of ammonia should be 15, 30 and 60 kg for 500, 1 000 and 2 000 kg stacks, respectively. A large stack should have a weight multiple of the small stack, so that entire bottles can be used.

The "one stack, one bottle" system has been tried in Henan, Hebei and other regions. It has been found that there are still some problems to resolve before it is generalized. Firstly, the small ammonia bottle is thin and long, inconvenient for transport by bicycle. Secondly, the popularization of the "small ammonia bottle" implies more people involved in their transport, with increased accident risk. It is also imperative to strengthen training for safety operation.

Plate 3-1. Ammoniating operation with anhydrous ammonia, stack method

Plate 3-2. Ammoniating pit in farm yard

Plate 3-3. FAO expert checks the operation of transferring anhydrous ammonia from tank truck to bottle

Plate 3-4. Trainees in ammoniation workshop watch the operation of ammonia transfer

Silo or bunker method

Ammoniating straw with urea in silos or bunkers has been widely used in China. This method has many advantages: silos or bunkers may be used for either ammoniating or ensiling year round; bunkers are easy to manage and avoid rodent damage to plastic films. Silos or bunkers constructed with cement are the best, since they save on plastic (only one sheet is needed, to cover) and minimize repairs. Once a silo or bunker is constructed, it can be used for several years. In addition, the bunker facilitates the estimation of straw weight.

Animal type and quantity determine bunker size. It should be known how much straw (air dried) can be placed per m³ of bunker; how much ammoniated straw an animal requires per year; whether the bunker may also be used for ensiling; and how many treatments are required per year. Average weight of air-dried and chopped crop residue (wheat, rice and maize), measured in different regions, is about 150 kg per m³. Straw intake varies with animal type, size and concentrate level. Generally speaking, daily straw intake is 2 to 3 percent of liveweight. For example, daily net straw intake is 4-6 kg for a 200 kg steer, equivalent to 1.5-2 tonne per year. If the silo is used for straw, 1 m³ will hold about 650 kg (25 percent DM). With these data, the size of a silo or bunker can be designed according to practical needs (number of ammoniations per year, numbers of animals).

There are many types of bunkers. They can be built on the surface, underground, or half-and-half. It is recommended to build rectangular bunkers that, by adding internal walls, can be divided into double or twin bunkers for sequential treatment (Figure 3-3). If a double bunker is used for silage, a second fermentation can be started in the second compartment while straw is being used from the other half. Double bunkers are very common in Henan Zhoukou region. For instance, a bunker with a volume of 2 m³ requires 500 bricks, a bag of cement and a wagon of sand. Its total cost is ¥ 100. The cost of a double-bunker holding 4 m³ is ¥ 200, affordable to farmers. One bunker of 2 m³ can hold 300 kg of wheat straw. The two bunkers can be used in turns. One bunker of ammoniated straw is enough for two cattle for a month. If a bunker is used for silage, one bunker can hold more than 1 000 kg. The silo or bunker method has been well received by farmers.

Figure 3-3. A twin bunker

Operation

First, straw is chopped to about 2 cm long. The general principle is that thick and hard residues, such as maize stover, should be cut shorter, while soft materials may be a little bit longer. Then urea (or ammonium bicarbonate) is added to water and stirred to completely dissolve it. Normally, 100 kg of dried straw needs 5 kg urea and 40-60 kg water. Next, the urea solution is sprayed repeatedly over the straw. Before loading the silo, straw can be spread in an open area to facilitate uniformity in spray application. While straw is added to the silo, each layer should be compacted till the bunker is full, and then it is covered with plastic film, held firmly in place by a layer of fine soil (Figure 3-4). Treatment time with urea is a little longer than with anhydrous ammonia.

Figure 3-4. Flow chart of the ammoniation of crop residues with urea

When treating straw with urea, the speed of urea decomposition into ammonia should be taken into consideration. It depends on ambient temperature and amount of ureases present in the straw. Decomposition rate increases with temperature, so this method is well adapted to warm regions (or warm seasons). In general, it is suggested to add some substance rich in ureases, such as soybean cake powder, to accelerate urea breakdown. Maize stover contains much more ureases than other cereal straws, so ureases are not required. In China, maize stover is one of the three main crop residues, along with rice and wheat straw. The nutritive value of maize stover is higher than other straws, either before or after ammoniation. However, it was seldom used as feed because it is thick and hard, and not easy to be store and transport. Nowadays it should be preferentially used as feed because processing and treatment methods (chopping, kneading, heat-extrusion, baling and ammonia treatment) are available to overcome these problems.

Oven method

Straw can be quickly treated quickly with ammonia in an oven. The Non-conventional Feed Institute of China Agricultural University has developed a metal, self-assembly oven for ammonia treatment. The oven is composed of a chamber, a heating system, an air circulating system and a straw trailer. The chamber must be insulated, sealed and resistant to corrosion by acid or alkali. The heating device may be an electric heater or a coal-fired steam heater, depending on local conditions. Shanxi Wanrong County used steam to heat the oven, with good results. The straw trailer should be convenient for loading, unloading, transport and heating. A metal mesh trailer with steel wheels is the preferred option.

Operation

Ammonium bicarbonate (8-12 percent of straw DM) is first dissolved in water. Straw (baled or loose; chopped or whole) is placed on the trailer. The solution is uniformly sprayed over the straw, adjusting moisture content to about 45 percent. Once the trailer is full, it is moved into the chamber, the door is closed and heating started. If heating is by electricity, the heating tube needs to be set to control the chamber's temperature at about 95 °C. After heating for 14-15 hours, it is turned off. The chamber should remain sealed for 5-6 hours more, and then the straw trailer is moved outside for ventilation. Once ammonia residues are gone, the straw can be fed.

The oven can shorten treatment time considerably since it only takes 24 hours to treat straw. In addition, oven treatment is not weather dependent, so ammoniation can be done all year round. However, the cost is relatively high, limiting its application. In recent years in Jilin Province, straw has been treated in a coal-heated chamber usually used for flue-curing tobacco. The investment for the oven was avoided and fuel expenses reduced, so treatment cost was greatly decreased.

Other options

Besides the above three widely used methods, there are still some other methods for straw treatment. For instance, ammoniation within plastic bags was readily accepted by farmers due to low initial cost. However, repeated purchases of plastic bags increased costs and restricted wider application. In some places, straw is treated in locally available containers (such as vats). This latter method may be worth advocating.

Factors influencing effectiveness of ammoniation

There are a number of factors that influence the effectiveness of straw ammoniation, including dosage, moisture content, temperature and treatment time.

Ammonia dosage

Experiments relating ammonia dosage to digestibility were conducted by Sundstol et al. (1978). Results showed a significant improvement in in vitro digestibility by increasing ammonia dosage from 1 to 2.5 percent of straw DM, and a slight improvement from 2.5 to 4 percent. There were no further effects beyond 4 percent. In recent years, many similar experiments have been carried out with similar results. The economic optimum ammonia dosage probably lies between 2.5 and 3.5 percent of DM.

When treating straw with anhydrous ammonia, urea, ammonia bicarbonate or aqueous ammonia, the dosage should be estimated by their nitrogen content: 82.3, 46.7, 15 and 20 percent, respectively. As the conversion ratio of nitrogen to ammonia is 1.21, the dosage of other sources can be calculated by the following equation:

Optimum dosages (per 100 kg of straw) are: 2.5-3.5 kg for anhydrous ammonia; 4.5-6.2 kg for urea; 13.8-19.3 kg (8-12 kg in practice) for ammonium bicarbonate; and 10.3-14.5 kg for aqueous ammonia (20% N).

Normally, treating 100 kg air-dry straw requires either 3 kg of anhydrous ammonia, 4-5 kg of urea, 8-12 kg of ammonium bicarbonate or 11-12 kg of aqueous ammonia (20% N).

Moisture content of straw

Moisture content of straw is another important factor determining the effectiveness of treatment. Ammonia combines with water to form ammonium hydroxide (NH₄)OH.

Regarding the optimum moisture content of straw, experts from China and abroad have different opinions. Sundstol et al. (1979) found that increasing moisture content of straw from 12 to 50 percent had a positive effect on in vitro organic matter digestibility (IVOMD) (Figure 3-5), regardless of temperature. With extremely low moisture (3.3 percent), ammonia treatment had no positive effect on enzyme solubility and straw IVOMD. Sundstol and Ekeern (1982) found that a 6-week treatment with 2 percent anhydrous ammonia of straw with 2.5, 5.0, 7.5 and 10.0 percent moisture, produced corresponding IVOMDs of 52.1, 58.5, 59.1 and 66.0 percent, respectively. Treating straw with 15-20 percent moisture with aqueous ammonia (25 percent) was better than with anhydrous ammonia. Aqueous ammonia improved the moisture content of straw. For example, using 2 percent aqueous ammonia to treat straw is equivalent to adding 6 percent water to straw. Experiments proved that the straw IVOMD could be gradually improved by increasing moisture from 2.5 to 50 percent.

Experiments conducted by Professor Ji Yilun of Shanxi Agricultural University indicated that the optimal moisture content of straw was about 45 percent when treated with urea or ammonia bicarbonate. High moisture contents would result in handling problems and greater risk of damage during storage (e.g. mould development).

The positive effect of higher moisture has also been found in practice. Straw from both the top and the bottom of the stack has high digestibility and good intake due to its moisture content. Straw treated by the Animal Bureau of Zhoukou Region in Henan Province during the FAO project in 1989, with the proportions 100 kg straw: 100 kg water: 5 kg urea, gave good results despite the high moisture content.

On the whole, higher moisture content of straw may improve digestibility. Moisture content can reach 50 percent or more, if straw can be transported and stored without becoming mouldy.

Figure 3-5. Effects of varying moisture contents and treatment temperatures on straw IVOMD when treated with 3.4% ammonia in DM for 8 weeks

Temperature and treatment time

High temperature reduces treatment time, since, in general, chemical reactions occur faster. High temperature had a positive effect on both N content and IVOMD of ammonia-treated straw. At a temperature around 45°C, treatment for 3-7 days greatly improved digestibility, whereas the reaction was extremely slow near -20°C. The season effect on ammonia treatment of oat straw in stacks had been studied by Alibes et al. (1983) in Spain, who divided 6 tonne into two parts for treatment in summer (38°C) and in winter (7°C). The results indicated that the CP content, DM digestibility, OM digestibility as well as straw intake were higher for summer treatment by 83, 12, 12.3 and 19.3 percent, respectively. Sundstol et al. (1978) treated oat straw containing 12.5 percent moisture and 3.4 percent CP with 3.4 percent NH₃ in DM at temperatures of -20°C, 4°C, 17°C and 24°C for 8 weeks. The CP contents after treatment were 6.5, 7.3, 8.3 and 8.5 percent, respectively. Sundstol et al. (1978) believed that ammonia treatment may significantly increased N content at temperatures over 25°C, but in longer treatment times (e.g. 3 weeks) increasing temperature from 40°C to 120°C had no positive effect on IVOMD. The length of treatment time for different temperatures had been given by Sundstol et al. (1978):

A closed stack may be stored for a long time without becoming mouldy, and stacks should not be opened before it is necessary to use the treated feed. After opening a stack of ammonia-treated straw, it should be aerated for a time before feeding. In cold climates, increasing treatment time has positive effects on ammoniation, but CP content decreases slowly after opening. Beijing Dairy Institute treated rice straw with 3 percent hydrous ammonia and the CP content of treated straw reached 7.8 percent, but 3 months later was below 7 percent.

Quality of material being treated

In general, straw quality after ammoniation depends a lot on pre-treatment quality. Greater improvement is obtained from low quality materials.

Pressure

High pressure is beneficial for ammonia treatment. Experiments conducted by Lie (1975) indicated that increasing the pressure from 1 to 5 kg/cm² had a positive effect on IVOMD. Sundstol and Owen (1984) had carried out experiments with similar results. It is known that if ammoniated straw is wafered or pressed into pellets, N-content and IVOMD can be further improved.

Quality evaluation of ammoniated straw

There are three methods to evaluate quality of ammoniated straw: sensory evaluation, chemical analysis and biological tests. The physical changes in straw can be visually observed as an easy, but imprecise, way to evaluate treated straw quality. By chemical analysis, the components of straw such as CF and CP can be measured, but by itself it can not give an estimate of overall nutritive value and animal intake. The scientific method of evaluation of straw quality is through biological tests. For example, digestibility in sacco (in the rumen), cellulase digestibility test, and especially digestibility in vivo, can estimate not only the digestibility but also the speed of digestion.

Sensory evaluation

Properly ammoniated straw is soft, brownish yellow or light brown, and with a light fragrance after excess ammonia has evaporated. If straw appears white or grey and is sticky or clumps, it means that it has been attacked by mould. This damaged straw should not be used as feed. Of course, this situation seldom occurs if treatment is correct. Mould normally results from high moisture content, defective sealing or delayed ventilation after opening. If, after ammoniation, straw colour is nearly the same as before treatment, it means that ammoniation did not go very well, but it can still be used as feed.

Chemical analysis

Chemical analysis is being widely used in China at present. This method evaluates the extent of straw quality improvement by analysing the main parameters (as digestibility of DM and CP) before and after ammoniation. Lu Xilei (1991), from the Beijing Dairy Institute, ammoniated straw by ensiling with anhydrous ammonia at 3 percent DM on the farm. Comparisons of the main parameters between ammoniated straw and Chinese wild-rye hay are shown in Table 3-1. After treatment CP content improved by 5.44, 3.98 and 5.02 percent for wheat straw, rice straw and maize stover, respectively. The corresponding figures for digestibility were 10.3, 24.0 and 20.0 percent, respectively. Digestibilities of ammoniated wheat straw and maize stover were nearly the same or higher than Chinese wild-rye hay.

Table 3-1. Nutritional comparison between ammoniated straw and Chinese wild-rye hay

SOURCE: Lu Xilei, 1991.

Biological tests

Biological tests, especially the nylon bag in sacco method for digestion rate, has been widely applied not only in science and research institutes but also in some production units. For example, in Henan Zhoukou region, the straw degradation rate was measured by the nylon bag technique in sheep during the FAO project (1989-1990). The results, presented in Table 3-2 and Figure 3-6, showed that the maximum rate of degradation (P-value) for ammoniated barley reached 77.1 from 52.1 percent in untreated straw. In the last five years, the Institute of Animal Production and Health in Hebei Province has measured digestibility rates for 9 feedstuffs (89 samples) by the nylon bag technique in sheep. These feeds include beans, cakes, pomace, dregs, animal by-products, leaf and straw. The nylon bag technique provides a foundation for systematic development of the feed resource.

Table 3-2. Nylon bag (in sacco) dry matter degradation of wheat straw (%)

Note: (1) RSD = residual standard deviation

Figure 3-6. Digestibility curve

Straw degradation rate can be calculated by the equation:

p = a + b (1-e^-ct)

where:

p = the amount degraded at time (t)
a = soluble material which is immediately digestible,
b = the fraction which will be digested in the given time,
c = the rate constant for digestion of b,
a + b = the asymptote or the potential extent of digestion,
e = natural log
t = degradation time

The above parameters give an indication of feed quality. Considering the popularity of ammoniation, it is imperative to establish a standard suitable for estimating treated straw quality.

Animal experiments with ammoniated straw

Feeding experiments with beef cattle

A UNDP-funded project, Beef cattle production system based on ammoniated straw, was effected between 1991-1992 in Huaiyang and Shangshiu counties of Henan Province; Boxiang county in Hebei Province, and some other regions. At the same time, beef cattle feeding experiments were conducted.

Experiments in Huaiyang county

Experiments were conducted in more than 100 counties with 259 animals. Cattle had ad libitum access to ammoniated straw and received a concentrate supplement according to body weight. Each animal needed 0.5 to 2.25 kg of concentrate feed (3/4 cotton seed cake + 1/4 maize grain). Results of feeding experiments are presented in Table 3-3, and the economic benefits in Table 3-4.

Results showed that average daily gain between 150 and 450 kg was 0.5 kg. The ratio of concentrate to weight gain was in the range of 0.83 to 3.5. This ratio was less than 2 for cattle under 350 kg. It took 498 days to go from 150 to 450 kg. Experiments with calves were also conducted. The results demonstrated that it took less than 2.5 years from birth to market weight (450 kg) under the current management regime. It took less than 2 years to bring cattle to 400 kg.

Table 3-3. Feeding experiments with ammoniated straw in Huaiyang county

Table 3-4. Economic analysis from studies in Huaiyang county

NOTES: Feed prices: cotton seed cake, ¥ 0.4/kg; maize, ¥ 0.5/kg; urea, ¥ 1.0/kg; wheat straw, ¥ 0.04/kg. De preciation of feeding equipment and health care were ¥ 0.1/head/day. Cattle price was ¥ 3.8/kg. Worker labour costs were covered by manure sales.

Experiments in Shangshui County

The experiments were carried out on 85 private farmers, with 344 cattle, during 1992. Cattle had free access to ammoniated straw mixed with concentrate according to body weight. Each beast consumed 1.5 to 2 kg concentrate (3/4 cotton seed cake + 1/4 ground maize) per day. The results of feeding experiments are shown in Table 3-5, and the economic benefits in Table 3-6.

Average daily gain was between 608 and 629 g from 150 to 450 kg when cattle consumed ammoniated straw supplemented with 1.5-2 kg concentrate per day. The ratio of concentrate to weight gain was 2.39-3.29. It took 482 days from 150 to 450 kg, with a daily average input of ¥ 1.31, an output of ¥ 2.36 and net profit of ¥ 506.1 per animal.

Table 3-5. Feeding experiments with ammoniated straw in Shangshui county

Table 3-6. Economic analysis of studies in Shangshui country

NOTES: Feed prices: cottonseed cake, ¥ 0.4/kg; maize grain, ¥ 0.5/kg; urea, ¥ 1.0/kg; wheat straw, ¥ 0.04/kg. Depreciation of feeding e quipment and health care were ¥ 0.1/head/day. The price of live cattle was ¥ 3.8/kg.

Studies by Institute of Animal Production and Health in Hebei Province

Twelve 18-month-old cattle were divided into 4 groups receiving ad libitum four straw sources: wheat straw, maize stover, ammoniated wheat straw and ammoniated maize stover. In addition, each animal received 1.5 kg of cotton seed cake per day. The study lasted 80 days, starting 21 February 1992. The results are presented in Table 3-7.

The results confirmed that gains were better with ammoniated straw. Treatment of wheat straw improved growth 85.1 percent (from 348 to 644 g/day) and treatment of maize stover by 45 percent (from 513 to 744 g/day). It also reduced the concentrate needed per kg of gain (from 4.32 to 2.33 kg). In other words, 1.99 kg concentrate was saved and straw conversion rate increased by 46.1 percent. Corresponding figures for maize stover were 2.93 to 2.02 kg of concentrate needed per kg gain; 0.91 kg of concentrate saved; and conversion improvement of 31.1 percent. Intake of crop residue DM varied from 2.14 to 2.83 kg per 100 kg of weight. Intake order was: ammoniated maize stover > maize stover > ammoniated wheat straw > wheat straw.

Table 3-7. Results of feeding experiments in Hebei Province

Experiments in Dingxing County

Experiments were carried out on demonstration farms. Thirty local yellow cattle of 200 to 300 kg BW and 1.5 to 2 years old were selected and divided into 3 groups. Cattle were mainly fed ad libitum with ammoniated wheat straw (treated with 5 percent urea). The groups were supplied with 2, 3 and 4 kg cottonseed cake, respectively, to study the effect of supplement level. The experiments started on 26 May 1992 and lasted 42 days. Results are presented in Table 3-8.

Results showed that daily gains increased with concentrate level, but in a diminishing response. From 2 to 3 kg, gains increased by 217 g/day, or 22.5 percent, but from 3 to 4 kg, only by 105 g/day, or 14.1 percent. The efficiency of concentrate use for growth also decreased with the level.

The results from the above studies show that on the basis of ammoniated straw diets, the concentrate required per kg of weight gain varied from 0.83 to 3.5 kg, starting at 150 kg. The concentrate used per kg of liveweight gain was less in cattle than in swine. Cattle market age can be reduced to 2.5 years. This low-level concentrate feeding system is well suited for Chinese conditions.

Table 3-8. Effects of cottonseed cake ration on daily gain

Feeding dairy cows

The Rowett Research Institute of UK reported the use of ammoniated straw for dairy cows instead of dry hay, without effects on milk yield or quality. Most researchers have tried ammoniated straw feeding for beef cattle and growing cattle, but there have been very few studies on high yielding dairy cows (> 7 000 kg/lactation). In 1999, Lu Xilei from the Beijing Dairy Institute conducted systematic experiments feeding high production cows with ammoniated straw, with great success. Some results are presented here.

Feeding dairy cows with ammoniated rice straw (1990)

Ammoniated rice straw replaced 30 percent of Chinese wild-rye hay in the ration, without negative effects on yield and composition (Tables 3-9 & 3-10).

Table 3-9. Groups of dairy cattle for ammoniated rice straw study

NOTE: (1) Number of dairy cows in each group

Table 3-10. Average milk production and composition when feeding rice straw

NOTE: (1) Number of dairy cows in each group

Feeding dairy cows with ammoniated maize straw (1991)

Feeding experiments were carried out supplying half of the ration as either ammoniated maize stover (group A) or untreated maize stover (group B). The other half was Chinese wild-rye hay. A third group (C) received only Chinese wild-rye hay. The comparisons of milk yield and composition among the three groups are shown in Table 3-11. No negative effects on milk production and composition were found when ammoniated maize stover or untreated maize stover substituted half of the Chinese wild-rye hay, but obvious economic profits were obtained. In other words, ammoniated straw could replace part of Chinese wild-rye hay for high yielding cows (with 7 500 kg of milk per lactation), but whether it could be replaced completely still needs further experimentation. A Shuangqiao farmer obtained good results with total replacement of Chinese wild-rye hay by ammoniated straw.

Table 3-11. Comparison of milk production and composition among three groups

NOTE: (1) Number of dairy cows in each group

Feeding sheep

In Norway, Nedkvitne and Maurtvedt (1980) conducted an experiment with pregnant ewes, feeding them with straw and concentrates. One group was fed with 0.6-0.8 kg forage and another with 0.8-1.0 kg ammoniated straw. Mean values of the 3-year experiment are shown in Table 3-12.

Results showed that there was no obvious difference in the number of lambs born between the two groups. Weight increases during pregnancy for the ammoniated straw group were more rapid than in the untreated group, but weight losses were also greater, so weight balance was better with forage. There were no differences in lamb weight in autumn.

In recent years, some institutes in China have also used ammoniated straw in feeding experiments. For example, Zhen Erying from Hebei Agricultural University used urea-treated rice straw to feed sheep, with satisfactory results.

Table 3-12. Results of feeding ammoniated straw to pregnant ewes

SOURCE: Unpublished report (1991) on dairy cows fed on ammonia-treated residues. Shuangqiao State Farm, Beijing.