Effect of using local ducks to control insects in paddy fields in duck-fish-rice systems on economic benefits
 and insecticide residue levels

 

Nguyen Thi Minh,  Le Viet Ly and E R Orskov
 

National Institute of Animal Husbandry, Hanoi
 

 

Abstract

   

In the North of Vietnam the increasing use of insecticides to control insect pests in the rice fields is causing serious problems in terms of residues in rice and surface and ground water, resulting in health concerns for both humans and livestock. Two experiments were carried out therefore to investigate the effects of growing and laying ducks, either alone or together with fish, on net economic benefits for small rice farmers and on insecticide residue levels in paddy rice and water. The treatments in Experiment 1 were: Rice with and without insecticides (R), and ducklings-rice (DR) with no insecticides applied.

 

Rice yield was not affected by treatment and was 4013 and 4015 kg/ha for R and DR, respectively. The maximum residue limit (MRL) for insecticides was 4.2 g/kg paddy for the rice only (R) treatment, which is considered potentially dangerous. Net economic benefit for rice only was 2.72 million VND/ha, and for ducklings-rice was 9.91 million VND/ha.

 

In Experiment 2 the treatments were: Rice only (R) with insecticides applied; Ducks and rice (DR); Fish and rice (FR); Ducklings, fish and rice (DFR); and layer ducks, fish and rice (LDFR). Rice yields were 8.6 and 15.0 % higher for the DFR and LDFR treatments, respectively, compared to rice only. Fish yields were 2222 kg/ha for the FR treatment, and more than double this value when ducks were included in the system (4639 and 4792 kg/ha for the DFR and LDFR treatments, respectively). Net economic benefits were 1.16, 8.51, 44.22 and 55.64 million VND/ha from the rice (R), Fish-rice (FR), Ducklings-fish-rice (DFR) and layer ducks-fish-rice (LDFR) systems, respectively. Maximum residue limits (MRL) of insecticides were 3.9 to 4.3 g / kg paddy and  0.05 g /litre water in the rice only treatment.

 

It is concluded that the duck-fish-rice systems, with both ducklings and layer ducks, gave the highest economic benefits, and in addition eliminated insecticide residues in paddy and water.

 

Key words: Rice, insecticides, ducks, MRL (maximum residue limit of insecticides), duckling-fish-rice system, layer ducks-fish-rice system, fish-rice system, economic benefits

 

 

Introduction

 

In the North of Vietnam there is a serious problem of contamination of food for humans, as well as feeds for animals, because of excessive use of insecticides, especially in the rice crop.  A preliminary technical evaluation of the duck-rice system was carried out using 350 local ducklings in a rice area of 0.504 ha. Replacing conventional fertilizer application and weeding by growing ducklings (1,400 / ha) had no effect on rice yield and resulted in reduced production costs, and complete elimination of insecticide residues in the paddy rice.

 

The main objective of the present study therefore was to evaluate different strategies for reducing or even eliminating the use of insecticides for rice, using local ducks in duck-rice and duck-rice-fish systems. It is expected that this study will help extension staff, researchers, policy makers and farmers to produce food and feeds not contaminated with insecticides, thus improving both human and animal health.

 

Experiment 1. Effect of using local ducks to control insects in paddy fields in duck - fish - rice systems on economic benefits and insecticide residue levels

 

Materials and methods

 

There were in total eight treatments (Table 1), with rice alone (R), with or without insecticide application, and with one or two applications of fertilizer and weeding, or in combination with ducks (DR).

 

 

At harvest, 5 samples of rice (each from an area of 1 m²)  were taken from each of the four corners and the centre of each plot, and then dried  in the sun. The concentrations of insecticides in the rice samples were determined at the Northern Pesticide Control Centre (NPCC). Calculations were made of rice yields, duck production, MRL (maximum residue limit) of insecticides and economic benefits from the different systems.
 

 

Results and discussion

 

The effects of combining ducks with rice on rice yields and MRL are shown in Table 2.

 

Table 2. Effect of including ducks in rice fields on insecticide concentrations and duck performance (MRL is Maximum residue limit)
System	Rice only (R)					Ducklings -  Rice (DR)
Plot	1	2	3	4	X	5	6	7	8	X
Rice  yield (kg/ ha)	4039	4081	3969	3964	4013	4056	4084	3989	3931	4015
Duck production
Mortality (%)	-	-	-	-	-	2.8	2.5	2.6	2.1	2.5
Mean  live weight, g	-	-	-	-	-	1070	1080	1035	1020	1051
MRL (g / kg paddy)	4.3	4.1	-	-	4.2	-	-	-	-	-

 

The rice yield was the same in the DR and R systems, and the  ducklings had normal growth rates with similar daily weight gains as in conventional intensive rearing systems. The NPCC had previously reported MRL levels of insecticides in maize fodder of 5 mg/kg,  on wheat straw and fodder (dry) of 5 mg/kg and in wheat of 0.2 mg/kg. The MRL in paddy from our trial samples varied from 4.1 to 4.3, which is rather high and may be dangerous for consumers (humans and animals). An economic analysis of the treatment effects is shown in Table 3.

 

Table 3. Inputs and outputs for rice and for ducklings (Experiment 1; million VND / ha)
System	Rice only (R)					Ducklings -  Rice (DR)
Plot	1	2	3	4	X	5	6	7	8	X
Inputs
For rice	5.03	5.86	4.75	5.58	5.31	3.92	3.92	3.92	3.92	3.92
For ducklings	-	-	-	-		6	7.8	9.6	11.4	8.7
Total					5.31					12.6
Outputs
From rice	8.08	8.16	7.94	7.93	8.03	8.11	8.17	7.98	7.86	8.03
From ducklings	-	-	-	-		10	13	16	19	14.5
Total					8.03					22.5
Net economic benefit					2.72					9.91

 

It is concluded that ducks combined with rice eliminates insecticide residues from paddy rice and gives substantially higher economic benefits to producers compared to rice only. The system is particularly suitable for rice cultivation on a small scale in the North of Vietnam, which is quite different from the South. Because of the narrow fields between the villages, and the poor fertility of the soil, ducks cannot be raised on a large scale,  and they are  scavenging in the fields only during the  daytime. At night, they are kept in shelters and given supplementary feed. The densities of ducks in this trial varied from 0.10 to 0.19 ducks / m² (1 duck / 5 to 10 m²), which may not be suitable in the South of Vietnam,  as in the Mekong delta a density of 1 duck / 18 mm² has been reported.

  

Experiment 2. Effect of using local ducklings and layer ducks to control insects in a duck-fish-rice system with or without the use of insecticides

 

Materials and methods

 

Based on farmers’ aquaculture experience and practices in North and Central Vietnam, the following experimental design for fish raising was applied (Table 4). The experiment was designed as shown in Table 5, with an area of 0.072 ha per plot, and the number of fish (6700) was equivalent to 167.5 kg of fingerlings per hectare.

 

Table 4. Species and densities of fingerlings
Fish species (position in pond)	Fingerlings		Fingerling size (cm)
	Numbers/ha	Mean weight (g)	Harvest once/year	Harvest twice/year
Silver Carp, Tench (top)	1100	25	3	6
Black / White Carp (top)	3100	-	6	20
Tilapia, Major (middle)	1400	25	3	6
Common carp (bottom)	1100	25	3	6
Total	6700

 

Table 5. Experimental design
System	Rice (R)	Fish-Rice (FR)	Duckling-Fish-Rice  (DFR)				Layer duck-Fish-Rice (LDFR)
Plot	1	2	3	4	5	6	7	8	9	10
Ducklings / ha	-	-	1000	1300	1600	1900	-	-	-	-
Layer ducks / ha	-	-	-	-	-	-	400	600	800	1000
Use insecticides	yes	-	-	-	-	-	-	-	-	-

 

Results and discussion

 

The effect of eliminating insecticides and using local growing ducklings or laying ducks on the yields of fish and rice, and on insecticide levels in rice and water are shown in Table 6.

 

Table 6. Effect of local ducks on fish and rice yields and insecticide levels
System	Rice (R)	Fish-Rice (FR)	Duckling-Fish-Rice  (DFR)				Layer Duck-Fish-Rice (LDFR)
Plot	1	2	3	4	5	X	6	7	8	9	10	X
Rice yield (kg/ ha)	4125	4195	4667	4500	4361	4387	4479	4722	4944	4750	4556	4743
Fish yield (kg/ha)	-	2222	3889	4278	4833	5556	4639	3889	4583	5000	5694	4792
MRL
g / kg paddy	4.2	-	-	-	-	-		-	-	-	-	-
g / litre water	0.05	-	-	-	-	-		-	-	-	-	-

 

It can be seen from Table 6 that rice yields were not changed when fish were raised in the rice plots, but were increased by 8.6% and 15.0%, respectively, when ducklings and layer ducks scavenged in the fields. Fish yields were more than doubled when ducklings and laying ducks were raised in the plots. The economic analysis of the treatment effects is shown in Table 7, and a comparison between the systems investigated in the two experiments is shown in Table 8.

Table 7. Inputs and outputs for rice, ducks and fish, Experiment 2  (million VND / ha)
System	(R)	(FR)		(DFR)				(LDFR)
Plot	1		2	3	4	5	X	6	7	8	9	10	X
Inputs
Rice	7.92		7.36	3.92	3.92	3.92	3.92	3.92	3.92	3.92	3.92	3.92	3.92
Fish	-		15.58	13.9	13.9	13.9	13.9	13.9	13.9	13.9	13.9	13.9	13.9
Ducklings	-		-	6	7.8	9.6	11.4	8.7	-	-	-	-	-
Layers	-		-	-	-	-	-		30.24	45.36	60.48	75.6	52.92
Total	7.92		22.94				26.52						70.74
Outputs
Rice	9.08		9.23	10.27	9.9	9.59	9.65	9.85	10.39	10.88	10.45	10.02	10.44
Fish	-		22.22	38.89	42.78	48.33	55.56	46.39	38.39	45.83	50	56.94	47.92
Ducklings	-		-	10	13	16	19	14.5	-	-	-	-	-
Layers	-		-	-	-	-	-		38.8	58.32	77.76	97.2	68.02
Total	9.08		31.45				70.74						126.38
Net economic benefit	1.16		8.51				44.22						55.64

 

Table 8. Comparison of inputs, outputs and  benefits between systems, Experiment 1 and 2 (million VND/ha) (Rice sale: 2 200 VND/kg; Fish sale: 10 000 VND/kg; Layer benefit: 200 VND / egg.
System	(R)	(FR)	(DFR)	(LDFR)
				DFR	LDFR
Inputs
For Rice	6.62	3.92	7.36	3.92	3.92
For Fish	-	8.7	-	8.7	52.92
For Duck	-	-	15.58	13.9	13.9
Total	6.62	12.62	22.94	26.52	70.74
Outputs
From Rice	8.56	8.03	9.23	9.85	10.44
From Fish	-	14.5	-	14.5	68.02
From Duck	-	-	22.22	46.39	47.92
Total	8.56	22.53	31.45	70.74	126.38
Net economic benefit	+1.94	+9.91	+8.51	+44.22	+55.64

 

 

Conclusions 

• The duck-fish-rice system can give very high economic benefits, over 20 times higher than for rice only, and more than four times higher than for ducks-rice and fish-rice.

• The environment  and food safety are improved, as insecticide residues are eliminated.

• It is proposed to extend the results to more farmer households to increase their income, to provide training for farmers, and to provide information for policy makers on the beneficial aspects of environmental protection through expanding the duck-fish-rice system.

 

 

Acknowledgements

This research was partially financed by the bilateral SAREC project 2000-2002.