IJERD – International Journal of Environmental and Rural Development (2010) 1–1

Research article
erd

Soil Fertility Management in Rainfed Lowland Rice
Eco-systems
MAK SOEUN
Graduate School of Agricultural Sciences, Royal University of Agriculture, Cambodia
Agricultural Extension Department, Ministry of Agriculture, Forestry and Fisheries
E-mail: mak_soeun@camnet.com.kh
Received 28 December 2009

Accepted 5 March 2010

Abstract Rice (Oryza Sativa L.) is a staple food of the Cambodian population andaccounts for 68-70 percent of daily calorie intake. Rainfed lowland rice ecosystems areoften hampered by drought, submergence and soil problems (Acid Sulphate) that areassociated with low productivity and with a high incidence of poverty. A study was
conducted to identify the best practices in soil fertility management and conservation on
sandy soil for improving rice yield and cost effectiveness of rainfed lowland riceproduction systems in order to contribute to the improvement of food security and income
generation of rural farmers. Three experiments were conducted in rainfed lowland riceagro-ecosystems in Champei commune, Bati district of Takeo province from the middle of2006 to the middle of 2009: (i) assessment of agro-ecosystem analysis and rice agroecosystems, (ii) study on interaction and cost-effectiveness of NPK fertilizers and compost
on rice yield in sandy soil in rainfed lowland production systems and (iii) on-farm adaptive
research on interaction of NPK fertilizers and compost in sandy soil of rainfed lowland
rice ecosystems. The results clearly indicated that the factors and parameters impacting on
rice productivity and yield are poor soil fertility (sandy loam soil) and poor soil fertility
management. Two options of best practices were identified for improving soil fertility
management and rice yield. Firstly, for farmers raising a limited number of cattle (1-2
cattle) and limited access to compost fertilizers should use N25P13K15 or Urea at 44 kg,
DAP 25 kg and KCl 25 kg plus 5 tones of compost per hectare. Secondly, for farmers
raising more cattle and producing large amounts of compost fertilizer recommendations
are the same with 10 tones of compost per hectare.
Keywords soil fertility, sandy soil, rainfed lowland, rice productivity, Cambodia

INTRODUCTION
Rice, Oryza sativa L., is a staple food for the Cambodian population and accounts for 68-70
percent of daily calorie intake. The rice Agro-Ecosystem in Cambodia is categorized according togeographical location, ranging from mountainous to deepwater areas including upland, rainfed
lowland, floating rice and dry season rice (Men Sarom, 2007). Rainfed lowland rice ecosystems areoften hampered by drought, submergence and soil problems (Acid Sulphate) that are associatedwith low productivity and with a high incidence of poverty. These ecosystems have many factors
and constraints to rice production such as poor soil quality, flood and drought, water problems, pest
and diseases and crop management practices of farmers.
Recently increasing fuel and fertilizer prices have also raised concerns for farmers, especiallyfor rice farming, to maintain the delicate balance between sufficient profitability for farmers andsufficient rice supply at affordable prices for the urban and non-farming rural poor. As fertilizer
prices increase, research and extension workers often advise farmers to reduce fertilizer use to savemoney. However, crop yield is directly related to the amount of nutrient taken up by the crop. Useof less of fertilizer means lower crop yield and less profit for farmers. Important questions are: howmuch fertilizer is needed to maximize profit and how could we improve rice production under these
conditions?
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To address these constraints, we conducted the research study: “Strategy for Soil Fertility
Management in Rainfed Lowland Rice Eco-system in Cambodia”. This research aimed to identify
the best practices in soil fertility management and conservation on sandy soil for improving rice
yield and cost effectiveness of rainfed lowland rice production systems in order to contribute toimproved food security and income generation for rural farmers. Objectives of the research were:
1. To identify the problems and constraints in rice production systems and to identify options toaddress these in rainfed lowland rice eco-system in Cambodia
2. To develop best practices for effective application of NPK fertilizers and compost on rice
yield and cost-effectiveness in sandy soil under rainfed lowland production systems in
Cambodia
3. To identify the best practices of appropriate fertilizer application, that could be adopted by
farmers for improving rice yield and soil fertility management in sandy soil under rainfed
lowland rice ecosystems and4. To develop extension packages or technical implementing procedures (TIP) for extension
workers and farmers to use in rice production of rainfed lowland rice ecosystems in Cambodia.
MATERIALS AND METHODS
Three research studies were conducted: (i) agro-ecosystem analysis and rice agro-ecosystems
assessment in Champei commune, Bati district of Takeo province; (ii) study of interaction of NPK
fertilizers and compost on rice yield and cost effectiveness for production in sandy soil in rainfed
lowland rice agro-ecosystems in Cambodia and (iii) adaptive research on farmer fields (on-farmtrials) on rice yield and cost effectiveness of production on sandy soil in rainfed lowland rice agroecosystems in Cambodia.
Agro-ecosystem and rice eco-systems analysis in Champei commune
Agro-ecosystems analysis (AEA) is a participatory analysis tool used by multi-disciplinary teams
in participation with farmers to identify the problems, constraints and impacts on rice production
systems and to identify options and measures to overcome these. The assessment used the agroecosystems analysis (AEA) tools and methods including secondary data collection (e.g. commune
profile), soil sampling and analysis, meteorology data (rainfall and temperatures), rapid rural
appraisal (RRA-time line/trend lines, transect walks, seasonal calendars, venn diagrams andproblem trees or causes and effect analysis). Check list questionnaires of fertilizer use, soil fertility
management, and farming systems were also used with farmer cooperators.
Interaction of NPK fertilizers and compost on rice yield and cost effective rice production
Fertilizer recommendations for the Prateah Lang Soil type in rainfed lowland rice ecosystems inChampei commune are N50P25K30, which means 50 kg N, 25 kg P and 30 kg K, with 5 to 10 tonesof compost. The improved aromatic rice variety of Phkar Rumduol was selected for theexperiments during the wet seasons of 2007 and 2008. Nine different treatment combinations of
NPK and compost rates were tested: N0P0K0 (T1), 5 t of compost (T2), 10 t of compost (T3),
N25P13K15 (T4), N25P13K15 + 5 t of compost (T5), N25P13K15 + 10 t of compost (T6), N50P25K30 (T7),
N50P25K30 + 5 t of compost (T8) and N50P25K30 + 10 t of compost (T9).
On-farm adaptive research (on-farm trials) on rice yield and cost effectiveness of production
These experiments were conducted in nine selected farmer fields on sandy loam soils (Prateah
Lang soil type) with four selected combinations of NPK and compost: N50P25K30, 10 tones ofcompost, N50P25K30 + 10 t of compost and N25P13K15 + 10 t of compost. Phkar Rumduol rice variety
was also selected for these experiments during the wet seasons of 2007 and 2008.

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IJERD – International Journal of Environmental and Rural Development (2010) 1–1

RESULTS AND DISCUSSION
Agro-ecosystem and rice ecosystem analysis in Champei Commune
Agriculture and soil condition: Based on agro-ecosystem analysis (AEA), rice-based farming is amajor occupation in Champei commune and most families also raise cattle and pigs as well as
poultry (chicken and ducks). The AEA identified Prateah Lang soil type (red yellow podzol) with
642 ha as the major soil type in the rainfed lowland rice eco-systems in Champei Commune. Thiswas followed by the Bakan soil types (Grey Hydromorphs or Luvisols) covering 585 ha. Kbal Po(Alluvial soil or gleysol) was also found to be a major soil type covering 354 ha in recession rice
and irrigated dry season rice areas. The Prateah Lang soil is of low fertility and needs to be
improved for better yield and profits. NPK is the major fertilizer used with combinations of Urea,
DAP and NPK (16-16-20) at a rate of about 1-2 bags or 50 to 100 kg/ha for wet season rice. Riceyields are in the range of 1.5 to 2.5 tonnes per hectare.
Table 1 Soil properties in main rice soils in Champeir commune, Bati district, Takeo
Soil property
Organic matter (OM) %C%
N%P (ppm)K meq/100g soil
pH

Prateah Lang soil
(Red yellow podzol)
0.67
0.29
0.04
21
0.03
4.5-5.1

Bakan soil
(Grey Hydromorph)
1.12
0.68
0.043
37
0.07
5.7

Kbal Po soil
(Alluvial soil)
1.8
0.91
0.10
46
0.19
5.9

Source: Soil result analysis, September 2007, Soil Lab analysis, General Directorate of Agriculture.

Results of AEA also indicated that the sandy soil in Champei commune is generally low inorganic matter content (0.64%), low pH (4.5-5.1), low CEC and low N, P, K, S, and Mg. Somelocations have Fe, S and Mn toxicity and poor drainage. Low productivity and low yield of rice inrainfed lowland rice is primarily due to poor soil fertility. Production is often reduced by drought
and flood. Production is also limited by poor crop management practices including poor land
preparation, poor on-farm water management, poor fertilizer management, poor weed management,
use of unpure seed and poor post-harvest practices. Pests, especially an outbreak of brown plant
hoppers (BPH), appeared in the 2007 wet season.
Climatic conditions
Rainfall: During the past ten years the average rainfall in Champei commune was 1,249 mm andduring 2000 and 2001 the rainfall was higher than previous years. The Commune received 1,555
mm in 2000 and 1,597 mm in 2001. In 2007, rainfall commenced in March and annual total amountwas 1,213 mm. However in 2008, rainfall was only 1,040 mm which was lower than the ten year
average. Rainfall variability is a constraint for rice production in the rainfed lowland (Fig. 1).
Temperature: The average temperature during the past ten years has not changed much. The peakof the hot season is during April and May (30 oC). From June to December the average temperaturedeclines from 29 oC to 26 oC. Maximum temperatures are high during April-May with 35-36 oC
and declines to 31-33 oC from June to December. Minimum temperature is less variable (20 oC to
26 oC). These temperatures provide good conditions for rice plant growth, especially in the rainfed
lowland rice ecosystem (Fig. 2).
These results clearly indicated that the factors and parameters impacting on rice productivity
and yield were poor soil fertility (sandy soil) and poor soil fertility management. The study also
identified options for improving fertility management on sandy loam soils in rainfed lowland rice
ecosystems and identified best practices and cost-effective soil fertility management for improving
rice production and quality. Adoption of these practices would contribute to improved household
food security and income generation for rural poor farmers.
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A v e r a g e temperature,T e m p e r a tu r e s℃,
Average

Average Temperatures,oC. 1998-2008

600
500
400
2008
Average 98-08
200
100
0

D
ec

O
ct

N
ov

Se
pt

Ju
l
Au
g

Ju
n

Ap
r

M
ay

M
ar
c

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Ja
n

32
30
2007

28

oC.

2007
300

Fe
b

Average Average
rainfall,mm/monthrainfall, mm

Average rainfall in Takeo province (Donkao station) during
1998-2008

2008

26

Aveg.Temp.1998-2008

24
22
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Months
Month

Month

Month

Fig. 2 Monthly average temperatureduring 1998-2008 in Bati district

Fig. 1 Average rainfall during 1998-2008
in Bati district

Interaction of NPK fertilizers and compost on rice yield and cost effective rice production
The results of fertilizer experiments during the wet season 2007 and 2008 indicated that on sandy
soil, the optimum rate of fertilizer application for increasing rice yield is N25P13K15 (Urea 44 kg,
DAP 25 kg and KCl 25kg) plus 5 to 10 tonnes of compost per hectare. The fertilizer treatments
differed significantly for their effect on rice yield (P<0.01). N25P13K15 plus 10 tones of compost on
sandy soils (Prateah Lang Soil) gave a rice yield of 3.50 t/ha in the 2007 wet season and 4.17t/ha in
the 2008wet season. N25P13K15 plus 5 t of compost gave a yield of 2.81 t/ha in the 2007 wet season
and 3.42/ha in the 2008 wet season (Fig. 3).
4

WS 2007
WS 20082

G ra in y ie ld , T /h a

6
4

T1

T2

1.18

1.66 2.07 1.51 2.82 3.48

T3

T4

T5

T6

WS 2008

2.02 2.78 3.09 2.74 3.42

4.17

T7

T8

Series1

2

Linear (Series1)

1.5
1

0.5

T9

0

1.92 3.18 3.03
3.01 4.04

3

2.5

0

WS 2007y = 0.3532x - 7.8601
R2 = 0.6937

3.5

Grain yield, t/haGrain yield, t/ha

G r ai n yi el d b y d i f f er ent t r eat ment s i n w et seaso n
2 0 0 7 and 2 0 0 8

0

3.8

5

10

15

20

25

30

35

Paniclelength,Panicle lenght,
CM cm

Tr e a t me nt

Treatment

Grain yield, t/ha
G ra in y ie ld , T /h ay = 0.2598x - 3.5877
R2 = 0.7925

Series1
Linear (Series1)

3000000

Cost and net benefit, Riels

5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0

Fig. 4 The correlation between panicle
length and yield of experiment 2007
Cost and net benefit, Riels

Fig .3 Grain yield for NPK and Compost trials
in wet season 2007 and 2008

2500000
2000000
Cost of vary, r/ha

1500000

Net benefits, r/ha

1000000
500000
0
T1

T2

T3

T4

T5

T6

T7

T8

T9

Treatm ent
Treatment
Treatment

0

5

10
15
20
25
Panicle length, cm
Panicle lenght, CM

30

35

Fig. 5 The correlation between panicle lengthand yield of experiment 2008.

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Fig. 6 Net benefit of experiment inwet season 2007

IJERD – International Journal of Environmental and Rural Development (2010) 1–1

Rice yield on-farm trials in wet season 207 and 2008

3000000
52500000

Grain yield, t/ha

2000000

Grain yield, t/ha

C os t a nd ne t be ne fit, R ie ls

Cost and net benefit, Riels

The result of experiment in wet season 2007 and 2008, the correlation between yieldcomponent and yield are also indicated that the increasing of yield components is correlation
between yield in difference treatment of NPK and compost (Figs. 4 and 5).
The gross margin of both wet season experiments in 2007 and 2008 indicated that N25P13K15 or
Urea 44 kg, DAP 25 kg and KCl 25 kg plus 10 t of compost gave net profits from US$ 436 to US$
640 per hectare, respectively. The treatment of N25P13K15 or Urea 44 kg, DAP 25 kg and KCl 25 kg
plus 5 t of Compost gave net profits from 1.49-2.22 Million KHRiels per hectare in 2007 and 2008
(Figs. 6 and 7).
The purpose of these experiments was to identify economic and environmentally soundpractices that could be adopted by farmers with sandy soil in rainfed lowland rice agro-ecosystems.
From the results, we concluded that the two best options for improving soil fertility management
and rice yield were: (a) farmers with few cattle (1-2 cattle) and limited access to compost fertilizers
should use N25P13K15 or Urea 44 kg, DAP 25 kg and KCl 25 kg plus 5 t of compost per hectare, (b)farmers with more cattle and compost fertilizers should use N25P13K15 or Urea 44 kg, DAP 25 kg
and KCl 25 kg plus 10 t of compost per hectare.

Cost of vary, r/ha

1500000

Net benefits, r/ha

1000000
500000

4
3

T1

T2

T3

T4

T5

T6

T7

T8

T9

WS 2008

1
0

0

WS 2007

2

T1

T2

T3

T4

WS 2007

3.21

3.55

4.34

3.98

WS 2008

2.896

2.764

3.823

3.258

Treatment
Treatment

Treatment
TrTreatment
eatment

Fig. 7 Net benefit of experiment inwet season 2008

Fig. 8 Grain yield for On-farm adaptive trials
of NPK and Compost in wet season
2007 and 2008

On-farm adaptive research (on-farm trials) on rice yield and cost effectiveness of production
The results of on-farm adaptive trials with NPK fertilizers and compost during the wet seasons of2007 and 2008 showed that the optimal rate of fertilizer application for better rice yield and profit
was N25P13K15 (Urea 44 kg, DAP 25 kg and KCl 25 kg) plus 10 t of compost per hectare (Fig. 8).
The recommended rate (N50P15K30) and 10 t of compost per hectare gave low rice yield andbenefit. In fact, half the recommendation rate (N25P13K15) plus 10 t of compost on sandy soil gave ahigher rice yield (Phkar Rumduol variety) of 4.34 t/ha and net profit per hectare at US$ 690 in2007 and 3.82 t/ha and net profit at US$538 in 2008 (Figs. 9 and 10). N25P13K15 or Urea 44 kg,
DAP 25 kg and KCl 25 kg plus 10 t of compost gave a net profit per hectare at US$ 692 in 2007
and US$ 540 in 2008, respectively.
3000000

2500000
2000000
Cost of vary, Riels/ha

1500000

Net benefits, Riels/ha

1000000
500000Cost
and net benefit,
Cost of vary and net
Riels/habenefits,riels/ha

benefits,riels/ha

Cost and net benefit,Co stof vary an d net
Riels/ha

300000002500000
2000000
Cost of vary, Riels/ha

1500000

Net benefits, Riels/ha

1000000
500000
0

T1

T2

T3

T4

T1

Treatment
Treatment

T2

T3

T4

Treatment
Treatment

Fig. 9 Net benefit of on-farmexperiment in wet season 2007

Fig. 10 Net benefit of on-farm experiment inwet season 2008

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CONCLUSION
The results showed that use of chemical fertilizer (NPK) alone on sandy soil did not improve soil
and crop productivity. Chemical fertilizer alone has potential negative impacts on soil structure andtexture, micro-organisms in the soil and mineral toxicity to underground water. However use oforganic fertilizer alone on sandy soil also has low effects on soil fertility and crop yield. These
effects have become clear after only several years of continuous applications of organic fertilizers(compost). Two options for best farming practice in rainfed lowland rice are: (1) farmers with few
cattle (1-2 cattle) and limited access to compost fertilizers should use N25P13K15 or Urea 44 kg,
DAP 25 kg and KCl 25 kg plus 5 tonnes of compost per hectare (2) farmers with available cattle
and compost fertilizers should use N25P13K15 or Urea 44 kg, DAP 25 kg and KCl 25 kg plus 5 t ofcompost per hectare. The results of these experiments were also used to develop best practiceextension packages or technical implementing procedures (TIPs). These are used by researchers,
extension workers and farmers for improving soil fertility management and conservation, and riceproduction in the sandy soils of rainfed lowland rice ecosystems in Cambodia. The collection oforganic manure also results in cleaner households, farms and villages and therefore improved
hygiene and sanitation.
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