1.     Vietnam chemical fertilizer demand for agriculture production.

2. Farm-yard manure used in Vietnam for food production.

3.  Fertilizer  production in Vietnam

4.     Fertiliser import requirement

Items	1997	1998	1999
Urea	1,448,061	1,949,793	1,650,000
SA	127,926	343,408	310,000
NPK	318,654	461,145	0
DAP	267,654	346,256	400,000
KCl	295,881	335,640	360,000
Total	2,458,373	3,354,213	2,720,000

   Each year Vietnam spends in average of  400 to 500 millions US $ to import fertiliser for agriculture production.
 
 
 
 
 
 

                                                              prof. Dr. Do Anh
                                             Vietnam Soil Science Society

         Before 1954, Vietnam’s agriculture used to be an organic one. After the liberation of Northern Vietnam, the Government started importing chemical fertilizer, in the early 1960s the Bac giang  Factory were constructed. The chemical fertilizer produce domestically could meet only 8% of nitrogen fertilizer requirement has to be imported. However, FYM occupies 70-80% of annual amount of fertilizers used in agriculture. Thai binh province, a good example of intensive cultivation of rice in 1966 used 8-10 tons of FYM/ha/cop to obtain 5 tons of paddy/ha/crops.

         Our survey data conducted in 1997 showed that in Nguyen Xa village, Dong Hung district, Thai binh provnince and Xuan Kien village, Xuan truong district, Nam Dinh province, to obtain 15 tons of paddy/ha/2 crops the farmers have used 400-500 kg FYM/360m2/crop (equivalent to 11.1 – 13.9 tons FYM/ha/crop). Up to now, farm yard manures still have the effect of crop yield increase. According to Bui Huy Dap (1978), the Red River Delta of Vietnam  used the highest rate of FYM compared with the other South East Asian countries. In places with good intensive cultivation of rice, in order to obtain 5 tons of paddy/ha/2 crops the farmers have applied 50-60% N from FYM, 15-20% N from green manures, 20% N from chemical fertilizer; to obtain  tons of paddy/ha/year 48% N from chemical fertilizers has been used. The recommended organic fertilize share was 55% (Bui Huy dap, 1980). In many places 70-75% N from chemical fertilizer and 25-30% N from organic fertilizers have been used (Bui Dinh Dinh, 1985, Nguyen Huu Te, 1986). in the 1990s, in good examples of intensive cultivation of rice, 1/6 N from FYM has been used to obtain 10-11 tons of paddy/ha/years (Nguyen Nhu Ha, 1995).

         FYMis an organic fertilizer containing 3 NPK nutrients necessary for crops. The NPK contents in FYM depending on animal feeds and processing methods vary from 0.35% N, 0.15% P2O5, 0.6% K2O (Le Van Can, 1978) to 0.25-0.4-0.5% respectively (Nguyen Vy, 1982), 0.3-0.15-0.4% respectively (Bui Dinh Dinh, 1995).

          According to Vishinski (1948-1949), the first value of FYM is nitrogen. However, according to Onadera (1996), the nitrogen use coefficient of FYM was very low being only 13% (compared with 50% of that of chemical fertilizer  N). According to Vishinski (1971) for the first year N use coefficient of FYM was only 20%. Dinh Dinh (China, 1970) reported that N coefficient of pig manure and cattle manure were 17% and 16%, respectively. The data recently published (Tran Thuc Son, 1995) were 34,6% and 50% of N use coefficient of FYM for Cr 203 rice variety in spring rice crop and summer rice crop, respectively. Nguyen Nhu Ha (1999) proposed to consider FYM a source of potassium supply. According to Vu Huu Yem (1995) 1 ton of FYM contained 30-50 g MnO, 4 g B, 2 g Cu, 82-96 g Zn.

           FYMcan also improve soil: Application of 1 tons of FYM is to supplement 150-200 kg of organic matter to the soil which causes increase in soil humus. After 3 crops of continuous FYM application, the soil pH changed from 5.3 to 5.9 (Viet Chi, 1963). Application of FYM improved the soil CEC (Hoang Thi Minh, 1995) and increased soil moisture retention capacity thus decreasing the irrigated water norm for rice (Ha Hoc Ngo, 1993).

           Though the agricultural production in the period of industrialization and modernization uses high rates of chemical fertilizer, the organic fertilizer in general and FYM in particular will always play an important role in serving the intensive cultivation to ensure high and stable crop yield and enhance soil fertility.

 Nguyen Van Bo

1.Introduction

In the mid - 1960s of this century, fertilizes was one of important factors of the Green Revolution (together with crop variety and irrigation), helping many populated countries towards self-sufficiency of food and release from starvation like China, India during 20-25 years. However, in the early 1990s, due to subjective and objective reasons, fertilizes stared to be criticized as the a source of nitrate pollution and eutrophication of water bodies, cause of greenhouse effect, accumulation of heavy metals in soils and agricultural products. And thus, fertilizer which used to save the world is now criticized as an enemy of the environment. This paper considers the role of fertilizer (at present as the well as the in future) in Vietnam's agriculture on its way to wards industrialization and modernization.

2.Fertilizer and national food security.

The world's population in creased from 3 billion people in 1960 to 5.3 billion people in 1990 and is estimated to reach 8.5 billion people in 2025. This population growth is a great pressure on natural resources and first of all on the soil and water sources because man needs food, foodstuff, fuel, raw material for industry as the well as other necessities of life.

In the past, the cereal output was based mainly on 2 factors: area and crop yield. However, recently when cultivated area is gradually coming closer to the maximum limit, the role of crop yield has the become more and more important.

Let us look at the tendency of chance in cultivated area of the world and of Vietnam during some decades. On the world's average, during 25 years (1965-1990)cultivated area increased by 9.4% and population during the same time increased by 68.5% leading to the decrease in cultivated area per capita by 35.15 or an annual decrease of 1.4%. In Vietnam, this tendency occured with higher rate. During 65 years (1930-1995), the cultivated area per capita decreased from 2548m² to 732m² or the decrease rate was 1.1%/years. Therefore, in the modern agriculture, the crop output will mainly be solved by crop yield. According to calculation by IF PRI (1996), at present yield in crease contributes to more than 80% of cereal output increase and in the future, the increase in output will be based only on yield increase.

Thus, to ensure national food security, each country can used one or more solutions with different priority order such as: area increase, crop increase, intensive cultivation and population growth limitation. For Vietnam, intensive cultivation is almost the only solution, and in intensive cultivation, the role of fertilizer is more and more important.

Fertilizer can contribute to increasing crop yield through many different mechanisms of effect. But the most important thing is that fertilizer provides the plants with essential nutrients that the soil is not able to supply, contributing to maintaining the soil fertility in farming process. Moreover, along with economic yield, fertilizer contributes to increasing the biomass and thus increasing the organic matter to return to the soil -the most important factor for the tropical soils. The simultaneous increase of used fertilizer amount and cereal output or paddy yield with the same rate in developing countries as well as in Vietnam proves that be above remark is completely well-based.

3.Fertilizer and stability of soil fertility.

We known that to grow, develop and yield, every plant has to mobilize nutrients, mostly from the soil. Let us look back to the Vietnam's agriculture 30-40 years ago. At that time, the Vietnamese farmers mainly cultivated traditional, old and low-yielding rice varieties, therefore their nutrient requirement was very low, too. Moreover, at that time most farmers cultivated one rice crop or one dry-farming crop, so the annual nutrient uptake was the not yes large. Thanks to the above-mentioned reason, with only 5-8 ton FYM /ha together with continuous irrigation of alluvial water, the nutrient requirement of crops could be ensured.

However, in recent years, especially in the 1980s and 1990s, Vietnam's agriculture has had progresses in crop variety. The foreign high-yielding and intensive cultivation-suitable varieties of rice and maize have been introduced in to Vietnam and gradually replaced the old ones. With progresses of heterosis, many hybrid rice varieties have also been broadly cultivated. Of course, high yielding new crop varieties also require high nutrient amount and thus the demand for supplying nutrients must increase.

Along with cultivation of new crop in varieties, the increase in land use coefficient through crop increase is also the reason for increasing the complementary nutrient requirement. The comparative nutrient uptake for the period 1975-1993 in our country is an example.

Thus, apart from the reason causing soil degradation like erosion, leaching... the imbalance of nutrients taken up by plants and nutrient, applied to the soil is also a factor causing soil degradation and this type of soil degradation tends to increase. IRRI has warned that declining productivity of soils has become a widespread trend.

According to Oldeman et al. (1990), from 1945 to 1990 the nutrient depletion due to imbalance between fertilizer application amount and nutrient uptake by plants caused slight degradation to 20.4 million ha, moderate degradation to 18.8 million ha and severe degradation to 6.6 million ha. According to Stoorvogel and Smaling (1990), in Asia the above-mentioned process has caused soil degradation to 4.6, 9.0 and 1.0 million ha, respectively, and in South America to 24.5, 31.1 and 12.6 million ha, respectively.

In the mountainous regions, where shifting cultivation is still used by farmers, in the past the fallow period is only 5 years, even 3 years, a time period not enough for natural recovery of soil fertility. Of course, in this circumstance the farmers have to cut down forests and consequently the forest area of Vietnam decreased from 14 million ha in 1945 to only 9.3 million ha in 1995. This is really a vicious circle, making the farmers from poor to poorer and the soil more and more degraded. the elimination of shifting cultivation basis, in which the nutrient balance through fertilizer application plays a decisive role.

Theoretically and practically, for a long time we know that fertilizer together with some other measure can lessen the pressure on soil resource and protect the environment. Firstly, fertilizer sufficiently provides the plans with essential nutrients stably and in a long term to get high yield and ensure national food security. At the same time, with high yield the amount of by-product returned to the soil is also high thus increasing the soil organic matter, improving soil properties, increasing the effective water amount and decreasing soil erosion. Moreover, the use of fertilizer will increase land use coefficient, the food output will increase and the requirement of deforestation for food production will decrease and the environment is protected. For some problem soils such as acid sulphate soils, coastal sandy soils, degraded soils... fertilizer application not only supplies nutrients but also improves soil through limitation or elimination of crop yield limiting factors in the soil. Moreover, in some cases, fertilizers (especially phosphorus, potassium and some other microelements) accelerate the process of nitrogen fixation of leguminous plants, strengthening the nutrients to the soil. Therefore, fertilizer if used reasonably will not cause soil degradation, but will stabilize soil fertility. Of course, the harmonious combination of various nutrient sources such as organic fertilizers, mineral fertilizers, biofertilizers... will ensure a stable ground of intensive cultivation. 

At present, in the world the use of fertilizer is quite different. In some places, such as Africa, only about 10-15 kg N +P₂O₅ + K₂O/ha is applied, but in Western Europe 200 kg N + P₂O₅ +K₂O/ha is applied. The neighbouring countries of Vietnam such as South Korea - 466 kg, China - 303 kg, Malaysia - 198 N+P₂O₅+K₂O/ha are applied. Thus, the fertilizer application rate of Vietnam is not high compared with that of many other Asian countries (about 130 kg N+P₂O₅+K₂O/ha/year).

4.Measures to increase the fertilizer use efficiency

Fertilizer use efficiency is changing greatly depending on soil type, crop type, even crop variety, fertilizer kind, irrigation and level of intensive cultivation. According to FAO (1987), on the average in developing countries application of 1 ton of nutrient gives a yield increase, much lower than that obtained in Western Europe and Nothern America (15-20 ton). In Vietnam, despite many progresses in fertilizer use, the coefficient of nitrogen fertilizer use is only 35-45%, that of phosphorus and potassium fertilizer is about 50-60%. In Asian developing countries, for rice the nitrogen fertilizer use coefficient is only 30-35% and in general, for all types of fertilizer it is not higher than 40% (Balu Bumb, 1996). This shows that a large amount of chemical fertilizer is lost due to leaching, erosion, volatilization, fixation... This does not only cause fertilizer waste but also leads to the danger of environmental pollution. Thus, for Vietnam the annual loss of nitrogen fertilizer accounts for about 1-1.2 million tons of urea-equivalent fertilizer or hundreds of million USD. This is not to mention the environmental impacts caused by this loss.

In order to increase the fertilizer use efficiency, it is the necessary to apply fertilizer to right soil, right crops, with right timing, right fertilizer kind, at right fertilizer rate and ratio. To do this, the analysis of soils and plants at suitable stages to identify right requirement of each nutrient is very important. In some developed countries, the farmers have applied technology of exact fertilizer application according to guidelines of calculated formulae based on models and computers. In Vietnam, the application of QUEFTS formula or Chlorophyll-meter has decreased the nitrogen application rate by 15-20% while crop yield is kept unchanged, the fertilizer use efficiency has the thus been increased considerably. Of course, in Vietnam's conditions, the use of advanced mathematical models, exact fertilizer application, sophisticated equipment is the not yet popular, but some parts of this content such as the identification of crop yield limiting factors of soils and nutrient requirement of each type of crops have to be regularly and properly implemented.

At present, balanced fertilization is considered the most important measure to increase fertilizer use efficiency. Unbalanced fertilization can decrease fertilizer use efficiency by 20-25% (FAO,1992). In developing countries as well as in Vietnam, unbalanced fertilization with rather high application rate of nitrogen fertilizer has decreased fertilizer use efficiency. It is unbalanced fertilization that leads to the alternative appearance of new crop yield limiting factors: Before the 1970s it was nitrogen, in 1970s-1980s phosphorus and in 1990s many soil regions-potassium. According to research results, the following up limiting factors many be sulphur and magnesium. However, it is necessary to emphasize the concrete but ever-changing nature of the concept of balance: Balance of requirement and uptake of crops, balance of nutrients at different growth stages, balance in relation to fertilizer efficiency-related natural conditions as well as balance with each type of crops in a cropping system.

One of the measures to increase fertilizer use efficiency is to increase the nutrient content of fertilizer. In this way, plant nutrients can be increased through the elimination of mixed substances or elements unnecessary for crops, such as production of urea (46%N) to replace ammonium bicarbonate or ammonium sulphate, ammonium chloride: or in production of DAP, TSP with high phosphorus content (46%P₂o₅) to gradually replace single superphosphate or fused magnesium phosphate. The increase of nutrient content can also be done through the production of compound, mixed fertilizer containing 2-3 elements or more such as MAP, DAP, NPK fertilizers of all kinds. The increase of nutrient content of fertilizers considerably the costs of bagging, transportation and application, especially for a country with difficulties in communication and with fertilizer-producing factories or importing ports situated far from places of fertilizer utilization like Vietnam.

Diversification of methods of supplying nutrients to crops is also very efficient. The application of foliar fertilizers containing macro-, meso- and micronutrients increases fertilizer use considerably. Some nutrients being applied to the foliage can also solve the lack of nutrients or physiological diseases of crop that cannot be solved if they are applied to the soil due to the low efficiency.

The production of fertilizer specific for crop type (crop-specific fertilizers)is a priority direction in measures to increase fertilizer use efficiency. These fertilizer help meet the nutrient requirements of crops which are sufficient in rate, correct in nutrient kind and suitable in ratio. The production of crop-specific fertilizers in Vietnam is successful and prospective.

The increase of fertilizer use efficiency is also related to ensuring the fertilizer quality. At present, apart from some tens of macro fertilizers produced industrially by the process of chemical synthesis/reaction, there are hundreds, even thousands of mixed fertilizers, foliar fertilizers, plant growth stimulants which are not controlled by the government. They are circulated with of fertilizer arbitration organizations, therefore the farmers are always suffering from losses once having bought the false fertilizer or low-quality fertilizers, and the legitimate fertilizer producers and traders suffer from losses and risks.

5.Fertilizers and the environment.

Like many other developing countries, Vietnam does not apply high rate of fertilizer, therefore the danger of environmental pollution is not yet high. However, with a development rate as that at present, Vietnam will soon become the country using high fertilizer application rate per area unit in the world.

Perhaps among the 3 main macro fertilizers being used at present, only potassium fertilizer is not yet considered a source of environmental pollution, but nitrogen and phosphorus fertilizers, if used unreasonably, can cause environmental pollution and mainly through accumulation of nitrate in agricultural products, drinking water and eutrophication of water sources and accumulation of cadmium.

First of all it is nitrate problem. High nitrate rates can increase the nitrate content of drinking water, vegetables, fruit juices... and it is the direct cause of blue baby disease. The reason is that when digested, nitrates (NO₃) may be reduced to nitrites (NO­­₂) changing Oxyhaemoglobine (oxygen-carying substance in blood) to Methaemoblobine, a non-active substance, which at high rates will influence activities of endocrine and form tumours. Nitrite when entered in to human body may react with amine to form Nitrosoamine, a cancer-forming substance. However, at present many people misunderstand that only chemical nitrogen fertilizers are sources of nitrate pollution. In fact, nitrate can be formed from soil organic matter, farmyard manure, agricultural by-products... In some places, such as Runnels Texas State (USA) 3000 mg NO₃/litre) have been found in groundwater (WHO's standard is 50 mg NO₃/litre) though not much chemical fertilizers have been used. The main reason is due to decomposition of organic matter after incorporation of crop residues.Researches with N¹⁵ conducted by PPI (1996) have also found that most of leached NO₃ were not originated directly from applied nitrogen fertilizer, but from organic matter. Research results conducted at Rothamsted Station (United Kingdom) have come to the similar conclusion: The leached NO₃ source came mostly from organic matter and crop residues. Nitrogen coming from these sources in decomposing cycle is easily leached and longer accumulated compared with thatcoming from mineral fertilizer. Thus, the application of organic fertilizers, crop residues or agricultural by-products, crop increase in condition of high temperature, high rainfall will be a big source supplying NO₃.

However in Vietnam, the application rate of nitrogen fertilizer as well as organic fertilizer is not high (except vegetable-growing areas). crop residues and agricultural by-products are not much used because they are used by farmers as fuels, animal feeds, roofing materials in some places... Moreover, a large amount of mineral nitrogen fertilizer (more than 705) is used for flooded rice thus forming inconsiderable amount of nitrate. Therefore, the problem of nitrate pollution can be put forth but it is of partial meaning.

The second fertilizer-related problem of pollution is eutrophication of water sources. This kind of pollution is mainly related to the process of accumulation of phosphorus and nitrogen in water in ponds, lakes, reservoirs... The eutrophication of water sources accelerates growth of algae causing competition for oxygen with fish and other useful aquatic organisms. Limitation of eutrophication of water sources must concentrate mainly on preventing soil erosion and leaching.

The third frequently - mentioned problem of pollution is the danger of cadmium accumulation in agricultural products and this element is contained in phosphorus fertilizers. However, according to different sources, the cadmium content in phosphate deposits is only about 35 - 55 ppm. Vietnamese phosphates, fortunately, hardly contain any cadmium (Nguyen Huy Phieu, 1999). At Rothamsted Experimental Station (United Kingdom), with high rates of phosphorus fertilizer being applied for hundreds of years, inconsiderable accumulation of cadmium in agricultural products has been found.

6.Conclusion

At present, due to shortcomings in research as well as in fertilizer use, sometime and somewhere the evaluation of the role of fertilizer is not yet correct. Moreover, insufficient knowledge of the role of fertilizer leading to the overuse of chemical fertilizer in some places in the world has caused soil degradation, environmental pollution and damage of ecological balance and this is just the reason for an extreme tendency to emerge in the last several decades: Disapprovingof chemical fertilizers to return to traditional organic agriculture. Let us try to imagine When the world or Vietnam stop producing chemical fertilizer. Certainly, in this case with existing area of arable land Vietnam will be able to feed only about half of its current population. Therefore, only scientific approaches based integrated plant nutrition management can allow examining objectively the role of fertilizers in a developing agriculture like that in Vietnam.