FOR ETTER FARMER LIVELIHOODS, FOOD SECURITY AND ENVIRONMENTAL SUSTAINABILITY

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Paper Number 12

Nutrient recycling for sustainable agriculture in Viet Nam*


* This country report has not been formally edited and the designations and terminology used are those of the author.

Pham Quang Ha1, Mike McLaughlin2, Ingrid Oborn3

Summary

Viet Nam with a population 83.0 million, has reached its security in food on a national scale. Food production in Viet Nam, which has reached 36 million tonnes annually, was obtained from the full cultivation of about 11 million ha of agricultural lands. The great achievement in food security is largely obtained from liberal increases in fertilizers across the country. Viet Nam farmers used an average of 234 fertilizer unit per ha in 2004 a significant increase compared with 134 unit in 1998 and only 18 unit in 1976. However, it is fully recognized that supporting a large population on a small base of cultivable land has tremendous consequence on the environment. Researchers indicated and warned very strongly that under the current fertilization regime, potassium is being depleted from improper nutrient balance in applied fertilizers and which is exacerbated by recent increases in rice yield. This situation is especially true since only about 30 percent of soil resources in Viet Nam are of good quality and the rest have several soil fertility constraints and measure to mitigate their limitations vary and perhaps expensive. The widening prevalence of soil erosion, land degradation and decline of soil fertility in Viet Nam are generally attributed to land overuse. Aside from judicious use of chemical fertilizers, nutrient recycling is one important key in agricultural management to keep the balance in plant nutrient and soil fertility. In this paper, the authors described the integrated approached for fertilizer uses and nutrient recycling as support for some representative sustainable cropping systems in Viet Nam.

1. Introduction of Viet Nam agriculture soils

The total territory of Viet Nam is 32 924 000 ha but only 35 percent of it is used for agriculture. Total cultivated soil is 11 569 591 ha, of which more than 50 percent are problem soils such as arenosol, thionic fluvisol and acrisols.

1.1 Soil fertility status

Beside two alluvial soils of Viet Nam (Red river fluvial soil and Mekong river fluvial soil), soil fertility in Viet Nam is not very high. The widespread soil in Viet Nam has low pH, low C, low N and very low CEC. It is especially true for soil with light texture as sandy soil or acrisol. The dominant feature of a degraded soil (Acrisol) is shown in Table 2. Results of routine soil testing conducted recently reveal that almost all of Vietnamese soil are low in N content, 80 percent of soil

Table 1. Main cultivated soils of Viet Nam

No.

Soil group name

FAO-Unesco

Area (ha)

Percent

1

Sandy soil

Arenosol

533 434

4.61

2 Saline soil Salic fluvisol

971 356

8.39

3

Acid sulfate soil

Thionic Fluvisols

1 863 128

16.10

4 Alluvial soil Fluvisols

3 400 058

29.38

5 Red soil Ferralsols

3 010 594

26.02

6

Grey Degraded soil

Haplic Acrisol

1 791 021

15.48

Total of cultivated soil

 

11 569 591

100

Total of cultivated soil

 

11 569 591

35

Total of Viet Nam soil

 

32 924 000

100

Source: Viet Nam soil Assoc. 1996.

Table 2. Selected physico-chemistry of Haplic-acrisols in Viet Nam

No.

Item

Unit

Mean

Std.

N

1

pHH2O

  4.69 0.49 52
2 pH KCl   4.05 0.43 52
3 Bulk density

g/cm3

1.47 0.23 16
4 Density

g/cm3

2.60 0.11 16
5 Porosity % 43.29 9.08 16
6 Texture        
 

2-0.2 mm

% 24.72 9.96 16
 

0.2-0.02 mm

% 32.44 14.65 16
 

0.02-0.002 mm

% 14.05 8.15 16
 

<0.002 mm

% 28.79 10.83 16
7 OC % 1.19 0.74 50
8 CEC

cmolc/kg

6.93 3.88 53
9

Ca++

cmolc/kg

1.75 1.62 53
10

Mg++

cmolc/kg

0.42 0.36 50
11

K+

cmolc/kg

0.15 0.08 49
12

Na+

cmolc/kg

0.11 0.11 53
13

Al3+

cmolc/kg

0.76 0.63 44
14

H+

cmolc/kg

0.06 0.03 53
15 N % 0.106 0.06 53
16

P2O5

% 0.062 0.05 53
17

K2O

% 0.19 0.22 52
18 P (bray II) mgP/kg 29.22 29.13 52

samples are deficient in K, 87 percent in P, 72 percent in Ca and 48 percent in Mg (Nguyen van Bo et al., 2003).

2. Food production in Viet Nam

Rice dominates Vietnamese agriculture (Table 3). Viet Nam’s agriculture sub-sector, particularly rice, has seen a dramatic production increase since 1986. Rice production was 11.6 millions tonnes in 1980, more than 31 million tonnes in 2000 and 38 millions tonnes in 2004. Viet Nam is now in safe situation in terms of food and each year exports about 3 millions tonnes of rice.

Table 3. Area and production figures for the major crops in Viet Nam (Statistical Data of Viet Nam agriculture, forestry and fishery 2003, statistical publishing house)
 

Crop

Sown area
(thousand ha)

Average yield
(tonne/ha)

Rice 7 499.3

4.63

Maize 909.8

3.22

Sweet potato 219.9

7.24

Vegetables 200.0

20-100

Sugarcane 306.4

53.91

Cassava 371.9

14.7

Soybean 166.5

1.35

Groundnut 242.8

1.67

Fruit crops 719.8

6.38

Coffee 513.7

1.50

Tea 116.2

0.22

Rubber 436.5

0.18

Increased production, particularly in rice, has been achieved through greater cropping intensity including fertilizer use rather than any other factor in cropping area.

3. Fertilizer use

Contributing to the increased yield were the widespread adoption and use of improved, high yielding varieties, better irrigation, plant protection, together with inputs of fertilizer. According to research from NISF (1998-2000), one unit of N-P-K gives in average of 7.5-8.5 kg of paddy. Each year, Viet Nam spends almost $600 millions US for importing almost 100 percent, 80 percent and 10 percent of the country’ requirement in K, N, and P respectively, for food production. Details of fertilizer sources and uses are shown in Tables 4 and 5. Viet Nam farmers used an average of 234 fertilizer unit per ha in 2004 comparison with 134 unit in 1998 and only 18 unit in 1976.

Table 4. Chemical fertilizer sources (1 000 tonnes) in Viet Nam

Items

Source

1996

1997

1998

1999

2000

2001

2002

2003

2004

Urea Total 1 597 1 610 2 011 1 940 2 279 1 699 1 907 2 149

1 941.5

Imported 1 467 1 480 1 944 1 890 2 159 1 600 1 800 1 889

1 708

NPK Total 530 678 913 913 1 200 1 385 1 035 2 000

1 871.2

Imported 350 318 411 133 200 155 0 0

306

DAP Imported 298 268 364 545 591 510 616 923

593

Ssp + FMP Produced 950 890 934 1 061 1 220 974 1 058 1 276

1 282.1

MOP Imported 108 296 344 711 350 835 900 1 050

807

SA Imported 311 128 343 501 436   524 125

665

SUM Total 3 794 3 870 4 909 5 671 6 076 5 400 6 040 6 900

7 159.8

Imported 3 484 3 380 4 340 4 841 4 956 3 100 3 840 3 987

4 079

Source: Gen. Statistic. Dept. 2004.

Table 5. Mineral fertilizer use kg/ha/year

Items

1996

1997

1998

1999

2000

2001

2002

2003

2004

N

77.0

87.2

86.3

95.5

108.2

133.2

122.0

136.0

120.2

P2O5

28.6

32.7

29.8

31.3

40.4

50.8

60.4

89.7

63.3

K2O

5.3

13.7

17.9

22.0

33.4

41.7

60.9

73.4

50.3

Total

110.9

133.6

134.0

148.8

182.0

225.7

243.3

299.1

233.8

Efficient fertilize use in Viet Nam is still very low. According to research results (NISF, 1998-2000) efficient fertilizer use depends not only on the crop variety, cropping systems, soil and seasons but also on the use in combination with other fertilizrs. On average, efficient use of fertilizer for rice is 34-50 percent, 13-20 percent and 31-40 percent respectively for N, P and K in the Red River Delta soil (fluvisol). Results showed that the efficiency of N fertilizer use for rice is closely relative with that of P fertilizer. For rice, the recommendation for fertilization is often in relation (ratio) with other element/s, N:P or N:P:K, such as (1:0.5:0.4).

4. Farmyard manure resources and use

Data collected from on-farm trials conducted between 1991 and 2000 (Nguyen van Bo et al., 2003) showed the response of plants to fertilizer and farmyard manure (FYM). In North Viet Nam, farmers generally use about 7-12 tonnes of FYM for each rice crop. These rates vary according to season and to the availability of farm organic sources. If the manure from all Viet Nam’s domestic animal production were collected and used, it is estimated that more than 200 unit of fertilizer were supplied from organic sources (Table 6). In principle, it is understood that organic fertilizer support soil fertility maintenance by supplying nutrient and enhancing soil physical condition. Crop yield generally increased when organic nutrients are applied in addition to mineral fertilizers (Table 7). Response to organic fertilizer in selected cropping system is very much higher in low fertility soil such as degraded soil (Acrisol).

Table 6. Potential nutrient from organic sources kg/ha/year

Items

1996

1997

1998

1999

2000

2001

2002

2003

2004

N 43.2 43.4 42.9 40.8 39.2 39.7 41.4 43.7

39.7

P2O5

48.9 49.5 49.2 47.1 46.1 48.1 50.6 53.8

49.3

K2O

105.3 105.4 104.2 98.7 94.0 93.4 96.9 102.5

94.9

Total

197.4

198.3

196.2

186.6

179.3

181.2

188.9

200.0

183.9

* Organic source (pig, cattle, cow, goat, sheep, chicken)

Table 7. Crop yield on Acrisol and in Fluvisol as affected by FYM

Treat

Crops

Soil

Yield (tonne/ha)

Difference (%)

NPK Rice Acrisol 3.32

100

NPK + FYM Rice Acrisol 4.02

121

NPK Tea Acrisol 0.68

100

NPK + FYM Tea Acrisol 0.83

122

NPK Maize Fluvisol 3.45

100

NPK + FYM Maize Fluvisol 4.33

126

5. Balance fertilization in relation to organic fertilizer

Integrated nutrient management is the efficient use of all types and forms of nutrients, both those originating from the field or farm and those from outside the field or farm. Balanced fertilization is achieved when the cropping system is supplied with the correct proportions of N, P, K, Mg and other nutrients.

There are three main approaches to soil fertility and plan nutrition management:

  1. Plant crops adapted to indigenous soil nutrient supply;
  2. Improve the soil fertility to meet the crop’s requirement; and,
  3. Fertilization with organic and inorganic materials.

Crop residue management is a subject to study and to practice in Viet Nam especially for the sloping area and degraded soil (Acrisols). Normally the soil in the area is very low in CEC (cation exchange capacity), low in organic matter, N, P and K (as reported above in the Table 3). Returning crop residue to soil significantly improves soil physico-chemical properties. However, inappropriate agricultural practices and continuous cropping without adequate nutrient are occurring in many places in Viet Nam fields. Recent research results emphasize that there is a large potassium imbalance. For example, each ton paddy exploits from soil about 20 kg K2O, which means a 200 kg K2O per ha for a rice annual yield of 10 tonnes. Nutrient depletion is indicated not only for major elements (N, P, K, S, Mg...) but also for micro-elements (Mo, Bo) as well. Further, imbalance (depletion or eutro-phication) in fertilization alters the chemical and physico-chemical characteristics of soil and destroys microorganisms’ lives. Management of the soils requires integrated practices that can increase fertility, nutrient and water holding capacity. Biological management of the soils can be an effective way to increase soil quality through management of biomass, i.e. farmyard manures, crop residues, green manures and alley cropping. In addition, theeffective management of the soils needs careful consideration of appropriate techniques not only to address the issue of low productivity but also to protect the environment.

5.1 A case study of nutrient recycling in 4 crops of season-based cropping systems

Crop rotation of four annual crops, spring rice, summer soybean, late summer rice and winter potato, respectively, was conducted on degraded soil in Bacgiang province (North Viet Nam). Results in Table 8 and in Figure 1 showed that crop residues returned to soil had immediate positive effect on yield. In case of no fertilizer input, the yield of all studied crops increased up to 70-100 percent and saving up to 20 percent fertilizers with completed fertilization (fertilizer with farmyard manure).

Use of crop residue or crop residue with suitable rate of chemical fertilizers seems to be more efficient compared to that of not using crop residues. Actually, a rotation of 4 crops in a year leave in the field at least 140 kg N ha-1 and 241 kg P2O5 ha-1 based on farmers’ practice. A saving of 20-30 percent for N and P fertilization was derived and crop yields were at an acceptable level not only for rice but also for soybean and potato.

Table 8. Crop yields (mean and std) as affected by crop residues returning to soil

 

Spring rice (quintal/ha)

Soybean (quintal/ha)

Summer rice (quintal/ha)

Winter potato (quintal/ha)

Control (T1) 22.25 (0.49) 5.40 (2.82) 16.70 (1.69)

26.90 (2.26)

T1 + Residue (T2)

29.90 (2.54) 10.75 (0.49) 27.30 (1.41)

42.45 (7.14)

Fertilizer + FYM (T3)

59.20 (2.12) 16.75 (0.49) 39.90 (0.42)

122.90 (16.22)

80% T3 + Residue (T4)

59.90 (2.44) 17.75 (1.62) 43.25 (1.19)

129.60 (20.08)

IMPROVING PLANT NUTRIENT MANAGEMENT
FOR
ETTER FARMER LIVELIHOODS, FOOD SECURITY
AND ENVIRONMENTAL SUSTAINABILITY

Figure 1. Crop yields as affected by different treatments on Acrisols

Table 9. Nitrogen fertilizer use efficiency for rice as affected by crop residues to soils

 

Spring rice 2003

Summer rice 2003

 

Mean (%)

Std

Mean (%)

Std

Low input (T1) 10.46 0.40 15.54 1.53

T1 + Residue (T2)

19.96 1.39 25.16 0.48

High input (T3)

44.09 14.08 39.72 2.95

T3 + Residue (T4)

43.88 20.61 39.72 1.26

By N-15 technique (FAO/IAEA, 2001), the study showed that, at low mineral fertilizer input, crop residue positively affected the nitrogen fertilizer uptake. Crop residues had no effect on N uptake efficiency at high input level. It is supposed that most of N uptake comes from other sources such as soils, bio-fixation, irrigation or rain rather than from direct fertilization. If fertilization is low, the relative N-lost is higher.

5.2 Warning of overloading nutrient to soils

Nutrients sources can be of mineral or organic in origin. The principle of balance fertilization is to make full use of both of these sources in an integrated way that is economically and environmentally sound. Recently, organic farming has been promoted as an alternative to common agriculture in Viet Nam. The adverse effect is that some fertilizers and organic materials contain not only nutrients but also heavy metals (Table 10). This may be toxic in some level with high accumulation through time. In some areas of very intensive cropping systems with cash crop such as vegetable and flower, fertilizer use were especially high, both for inorganic and organic materials, soil was probably overloading of fertilization (Table 11).

Table 10. Mineral fertilizers and farmyard manure using in different cropping in North Viet Nam (2003-2004)

Cropping system

Location, Code

NPK (kg/ha)

FYM (tonne/ha)

Rice-Rice-Soybean

HaTay, PT01

729

22

Rice-Rice ThaiBinh, KX04

621

19

Rice-Rice-Maize

NamDinh,VB02

448

17

Rice-Rice-Maize

NinhBinh, NB02

1 356

28

Maize-Soybean-Maize

VinhPhuc, VT02

780

8

Mulberry VinhPhuc, YL03

279

8

Vegetables VinhPhuc, ML1

1 700

110

Flower VinhPhuc, ML1

1 530

160

Source: Pham Quang Ha et al., 2002. Study on Fluvisol of Viet Nam.

Table 11. Annual nutrient budget (mean, std) at the field levels

Cropping systems

Input levels

N (kg/ha)

P(kg/ha)

K (kg/ha)

Cu (g/ha)

Zn (kg/ha)

Dry vegetable

Fertilizer +
chicken
manure +
rice straws +
compost

390 (350) 420 (161) 291 (203) 401 (326) 3.96 (1.23)

Water vegetable

Waste water
from city +
horn +
borne + ash +
compost

489 (375) 155 (32) 137 (366) -72 (103) 2.43 (3.88)
Source: NISF-Rurbifarm project report, 2004.

Table 12. Heavy metals in some manure recycling for agriculture in North Viet Nam

 

Cu (mg/kg dry)

Pb (mg/kg dry)

Zn (mg/kg dry)

Cd (mg/kg dry)

Sludge 45 27 154

0.39

std

5.1

0.35

5.43

0.01

Pig manure 250 14 556

0.65

std

413

6.8

835

0.22

Goat manure 19 7.5 75

0.21

std

2.0

2.6

12

0.05

Chicken manure 64 16 222

1.49

std

54

8

106

1.78

Cow manure 67 20 153

0.48

std

71

8

70

0.07

TCVN7209-2002 Viet Nam standard for agri. soil

50 70 200

2

Source: LWR/119/1198 (NISF-Viet Nam ACIAR project, 2002).

6. Conclusion

At low level farming system input, nutrient recycling in Viet Nam was widely applied years ago. The main activity consists of using farmyard manure and crop residues. Today, nutrient recycling should involve a balance approach of environment-friendly fertilization. Results and experiences showed that recycled nutrient may save chemical input but it can not replace all chemical inputs. Biological and environmental farming should integrate harmoniously with intensive agriculture. This is probably a sustainable way that different stake-holders will accept and it will save not only agricultural productivity but also save the environment that we all need such as soil, water and other life forms.

Acknowledgment

The authors gratefully acknowledge the International Atomic Energy Agency (IAEA) for N-15 technique, the Rurbifarm/EU project ICA4-CT-CT-2003-10021 for nutrient and water recycling, the ACIAR/LWR/119/1998 projects for bio-solid recycling study both in technical and material support. Thanks are also due to FAO (Regional Office for Asia and the Pacific) for the invitation to the Regional Workshop on Improving Plant Nutrient Management for Better Farmer Livelihood, Food Security and Environment. Beijing, People’s Republic of China, 12-16 December 2005.

References

FAO/IAEA 2001. Use of isotope and radiation methods in soil and water management and crop nutrition. Training course series 14. FAO/IAEA, Vienna, 2001.

LWR/119/1998. NISF-Viet Nam ACIAR project report, 2002.

NISF (1998-2000). Annual Research Results. Proceeding of NISF, Hanoi, 1999.

Nguyen Van Bo, Ernst Mutert, Cong Doan Sat (2003). BALCROP: Balance Fertilization for Better crop in Viet Nam. Potash & Phosphate Institute.

Pham Quang Ha et al., 2002, 2003, 2004. Study on Fluvisol, Acrisols of Viet Nam.

Rurbifarm project. 2004. Second annual report. Sustainable farming at the rural-urban interface. NISF-Hanoi-Viet Nam

STAT, 2004. Gen. Statistic. Statistical yearbook 2003. Statistical publishing house. Hanoi, 2004.


1 Dept. of Soil Environment Research, National Institute for Soil and Fertilizers, Chem, Tu Liem, Hanoi, Viet Nam.

2 School of Earth and Environmental Sciences, The University of Adelaide, PMB1, Glen Osmond, SA 5064, Australia.

3 Dept. of Soil Science, Swedish University of Agricultural Sciences (SLU, Uppsala, Sweden).

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