Journal of Agrometeorology 23 (4) : 243-248 (December 2021)

Potential benefits of altering the cassava farming practices in the water shortage
regions of Vietnam
VAN HONG, NGUYEN1 and TRUONG AN, DANG2

1
Sub-Institute of Hydrometeorology and climate change, Ho Chi Minh 70000, Vietnam
19 Nguyen Thi Minh Khai, Dist 1, HCM City, Vietnam
2
University of Science, Vietnam National University, Ho Chi Minh 70000, Vietnam
227 Nguyen Van Cu Str., 5 Dist., Ho Chi Minh City, Vietnam
*Corresponding author email : dtan@hcmus.edu.vn

ABSTRACT

The work was proceeded to define the suitable period for planting cassava crops in Han Thuan Bac district of
Binh Thuan province, Vietnam to reduce the negative impacts of weather factors. The work was deployed applying the
FAO-Aqua Crop model to calculate the tuber yield of cassava plants under the cassava farming practices (CFP) to seek
the suitable planting period (SPP). The applied model was appraised through the calibration and validation procedures
with the index of agreement (IA), correlation coefficient (CC) and the Root Mean Square Error (RMSE) varying from
0.82 to 0.88, 0.81 to 0.89 and 0.21 to 0.29, respectively. Based on the calibrated and validated procedures it can state
that the proposed model is suitable for simulating the tuber yield of cassava across the study area. The simulated
results indicated that the application of the CFP on Julian days from 110 to 150 for Vu Xuan crop and from 100 to 140
for Vu He crop the tuber yield of cassava can improve up to 8.9 per cent and 6.0 per cent, respectively compared to
the current farming practices.

Key words: Farming practice, potential risks, cassava, off-seasonal rainfall, tuber yield

Weather change has negatively influenced the care, suitable for nutrient-poor and arid soils (Mai, 2017;
aspects of socio-economic fields (Lee and Dang, 2019; Fermont et al., 2009). Cassava plants is also considered
Miyan, 2015). Agricultural sector is assessed as vulnerable a low-risk cropand uses as anideal raw material for other
compared to other sectors (Dhatt and Jhanji, 2021). An manufacturing fields.
investigation on the impacts of climate change (ICC) on
In the cassava cultivation regions of BinhThuan
tuber yield of cassava plant in the Togo region showed
province such as Tanh Linh, Bac Binh and Ham Thuan
that cassava crops are meeting the potential challenges.
Bac,cassava growers usually sow the cuttings based
Emaziye (2015) conducted a study on the weather factors
on rainfed (Mai, 2017). According to Howeler (2010)
on tuber yield of cassava in the rural households of Delta
cassava is maintaining an increasing important in human
State, Nigeria and reported that precipitation is the major
life and humanity is increasingly looking for clean fuel
factor which has been significantly affected by altering
sources to replace fossil fuels (Dhatt and Jhanji, 2021).
in climate factors. In Nigeria, Ropo and Ibraheem (2017)
As an acknowledgment of the importance of cassava for
investigated the ICC on the tuber yield of cassava plant human life, the research projects on cassava have been
in Port Harcourt and stated that the precipitation is one widely deployed across continents such as in the Delta
of the weather factors has dominated on the tuber yield. State of Nigeria by Emaziye, (2015), in East Africa by
In Ham Thuan Bac district, cassava is commonly grown Fermont et al. (2009), in Asia by Howeler (2010) and in
in most rural areas and is evaluated as a key crop to Vietnam by Bien (2007) and Mai, (2017).
contribute increase the income of local cassava growers
(Bien et al., 2007; Mai, 2017). According to Emaziye Studies on the ICC on irrigation use water for cassava
(2015), cassava cuttings are easy to sow, no require much crops reported that the CFP plays an important role in
Vol. 23, No. 4 HONG et al. 297
mitigating the lack of irrigation water and reducing the crop (Fig.1). For crop and management module, the detailed
yield (Mai, 2017). According to Howeler (2010), climate data information about cassava variety, sowing density as
change has impacted on the growth and harvest stages well as fertilizer rates has also been presented in Table 1.
of cassava cultivation regions, and they recommended A high yielding cassava variety called KM98-5 is widely
that it is necessary to build a CFP for cassava crops in grown with the cycle varying from 9 to 14 months based
the context of climate change. Thus, the detection of the on local weather conditions (Bien, 2007; Mai, 2017).
suitable growing periods to sow the cassava cuttings is The information of crop management has been provided
stated an effective adapt solution to limit the adverse in Table 1. In the entire study area, KM98-5cassava
weather factors. The primary aim of this work, therefore, cuttings were sownwith spacing of 0.8 m x 0.8 m around
was to detect the suitable periods for CFP across the study the first week of May for Vu Xuan crop while Vu He
area to maintain as well as improving the tuber yields of crop cassavas was sown with spacing of 0.85 x 0.85 m in
cassava crops. the fourth week of March (Table 1). In addition, the rate
of fertilizer used to fertilize cassava cuttings was up to
MATERIALS AND METHODS
10 t ha-1 manure, 0.2 t ha-1nitrogen fertilizer, 0.15 t ha-1
Study area P2O5, and 0.15 t ha-1 K2O, respectively for Vu Xuan crop
while the respective ratios to 10 t ha-1 manure, 0.25 t ha-1
Binh Thuan is located at latitude 10o33’42”- nitrogen fertilizer, 0.20 t ha-1 P2O5, and 0.20 t ha-1 K2O,
11o33’18” N and longitude 107o23’41”-108o52’18”E and respectively for Vu He crop. For the simulation of the
Ham Thuan Bac is one of the districts in Binh Thuan soil module, the soil samples across the study area were
province. The study area has a large cassava cultivation analyzed and has shown that the soil was sandy loam with
area compared to other provinces in Vietnam (Bien, pH of 5.5 - 5.7 and its physicochemical properties has
2007; Mai 2017). The weather is governed by two main been described in Table 2.
monsoon circulations namely northeast and southwest,
which alternately blow throughout the year. The wet Evaluating the performance of the AquaCrop model
season is also known as the southwest monsoon, lasting
The AquaCrop model was evaluated analyzing
from May to October while the dry season is also called
the correlation between the observed tuber yield of
north east monsoon from November to April. Annual
cassava and simulated AquaCrop model for both Vu Xuan
mean temperature about 27.0oC and precipitation around
and Vu He crops during the study period 2011-2020. The
1000 mm with approximately 80 per cent of annual
statistical methods as such correlation coefficient (CC),
precipitation falls the wet season (Mai, 2017).
Root Mean Square Error (RMSE) and index of agreement
Model description (IA) are adapted (Kumar et al., 2021).

The AquaCrop model is designed by FAO-Food The CC is defined as follows:

and Agriculture Organization for simulating irrigation
use water, calculating components yield as well as crop
yield (Abedinpour et al., 2012). The model is designed (1)
based on combination of four sub-models namely climate,
where Oi and Si are observed tuber yield of
crop, soil, and management module (Abedinpour et al.,
cassava and simulated AquaCrop model, respectively; is
2012; FAO, 2017). Detailed introduction of the model can
the mean value of Oi, and n is the number of data points
be found in Abedinpour et al. (2012).
and the RMSE is calculated by:
Data description

To deploy this work, the climate parameters viz.,

(2)
temperature, radiation, wind speed, rainfall, relative
humidity for simulating the climate module are provided And the IA is given by the Eq.(3):
298 Potential benefits of altering the cassava farming in Vietnam December 2021
Table 1: Crop characteristics of cassava plants in the study area

Crop calendar Sowing density Fertilizer rate (tha-1)

Crop
Plant Harvest (plantha-1) NPK Urea Kali Manure
Vu Xuan 10-May 05-July 16000 0.20 0.15 0.15 10
Vu He 30-Mar 20-Feb 14000 0.25 0.20 0.20 10

Table 2: Chemical attributes of the soil in the study area

Depth Sand Silt Clay Al Fe Mg Mn Ca K Na Si

pH
(cm) (%) (g)
0-20 6.7 60 20 20 13.5 1.7 0.4 0.2 1.6 3.9 0.6 71.5
20-40 6.5 50 20 30 12.8 2.1 0.6 0.6 1.2 4.2 1.7 63.3
40-60 5.9 58 15 27 11.7 2.4 0.3 0.3 1.1 3.6 0.8 58.9

Fig. 1: Input weather parameters for simulating the climate module of the Aquacrop model

Fig. 2: Compared results between the observed tuber yield of cassava and simulated model of Vu Xuan and Vu He crops

yield of cassava and simulated AquaCrop model and n

(3) is the number of data points while is average value of
observed tuber yield data.
O and S in the Eq. (3) are the observed tuber
Vol. 23, No. 4 HONG et al. 299
Table 3: Tuber yield corresponds to optimal Julian days for cassava sowing crops in the study area

Vu Xuan crop Vu He crop

Tuber Rate of Tuber Rate of
yield increase SD CV(%) yield increase SD CV(%)
(t ha-1) (%) (t ha-1) (%)
Current 42.5 - - - Current 38.4 - - -
110 46.3 8.9 2.9 4.8 100 39.9 3.9 3.3 5.2
120 45.7 7.5 2.5 4.3 110 40.7 6.0 3.0 4.8
130 45.1 6.1 3.4 5.4 120 39.9 3.9 2.8 4.3
140 44.2 4.2 2.1 3.9 130 39.8 3.6 3.9 6.5
150 43.3 1.9 2.3 4.1 140 39.0 1.6 3.6 4.9
SD: Standard deviation; CV: Coefficient of variation; Current: current tuber yield; 110-150 and

RESULTS AND DISCUSSION the study area.

Results showed that the simulated AquaCrop Relationship between the farming practices and weather
model is in a good agreement with the observed tuber factors
yield of cassava plant with IA = 0.81-0.89, RMSE = 0.24-
The analysis of historical precipitation data series
0.32 and CC =0.84-0.93, respectively for both Vu Xuan
across the study area pointed out that the alteration of the
and Vu He crops. Based on the findings, it can be stated
that the AquaCrop model is good agreement to apply for CFP for both Vu Xuan and Vu He crops compared to the
simulating tuber yield of cassava plants across study area current farming practices will enhance the furnishing
(Fig.2). of abundant precipitation on the growth stage but poor
precipitation in the harvest stage of cassava tubers.
Evaluating the tuber yield under the farming practices Specifically, the CFP of Vu Xuan crop on 120 Julian
days the growth stages of cassava will be provided with
In the cassava cultivation regions of Ham Thuan
abundant amount of water from precipitation while the
Bac district, cuttings are commonly grown depend on local
harvest stage of cassava tubers will be receiving low
precipitation situation (Bien, 2007; Mai, 2017). Climate
precipitation amount, resulting in a good growth and
variability has a significant impact to the meteorological
parameters, especially the precipitation factor, resulting harvest of cassava tubers (Fig.3). These findings were
in the lack of irrigation service water and thus the CFP in agreement with the reports of Ropo and Ibraheem
is poorly adapted to current weather conditions, leading (2017). They confirmed that for the water shortage
to the decline in crop yield. The results indicated that regions, precipitation plays a key role in the growth and
the application of the CFP for Vu Xuan crop on Julian development stages of crop.
days from 110 to 150 the tuber yield of Vu Xuan crop CONCLUSION
will increase varying from 1.9 per cent to 8.9 per cent
compared to the current sowing calendar (Table 3). The research was proceed applying the FAO-
For Vu He crop, the tuber yield can increase from 1.6 AquaCrop model to simulating the tuber yield of
to 6.0 per cent if the CFP has deployed on Julian days cassava crops across the study area to seek the suitable
from 100 to 140 compared to the current sowing calendar planting period. The applied model was appraised and
(Table 3). Specifically, the maximum tuber yield of Vu proven its good performance through the calibration
Xuan crop cassava can be obtained up to 45.7 tha-1 if the and validation procedures with high correlation of the
CFP is conducted on 120 Julian days while the optimal index of agreement, correlation coefficient and the root
tuber yield of Vu He crop cassava can be enhanced upto mean square error between the observed tuber yield and
40.7 t ha-1 (Table 3). Generally, the alteration of the CFP simulated model. Based on the findings, tuber yield can
for both Vu Xuan and Vu He crops can contribute to a be improved positively compared with the current crop
significant improved tuber yield of cassava crops across yield if the cassava farming practice has to be deployed
300 Potential benefits of altering the cassava farming in Vietnam December 2021

Fig. 3: The cassava farming practices in the study area adjustedto conform with changes in temperature and precipitation
(Source: https://www.vectorstock.com)

on the cassava cultivation fields. The implementation of for an Ancient Crop. Proc. Seventh Regional
the cassava farming practice can enhance to utilize the Workshop, held in Bangkok, Thailand. 25-32.
favorable weather conditions contributing to maintain as
Dhatt, K. K. and Jhanji. S. (2021). Evaluating gladiolus
well as improving crop productivity.
varieties for off-season planting using agro-
Conflict of Interest Statement: The author(s) declare(s) meteorological indices. J. Agrometeorol., 23 (1),
that there is no conflict of interest. 46-53.

Disclaimer: The contents, opinions, and views expressed Emaziye, P.O. (2015). The influences of temperature and
in the research article published in the Journal of rainfall on the yields of Maize, Yam and Cassava
Agrometeorology are the views of the authors and do not among rural households in Delta State, Nigeria.
necessarily reflect the views of the organizations they J. Biol. Agric. Healthcare, 5(1): 63-69.
belong to.
FAO-Food and Agriculture Organization of the United
Publisher’s Note: The periodical remains neutral with Nations. (2017). AquaCrop update and new
regard to jurisdictional claims in published maps and features (Version 6.0), ISBN 978-92-5-109742-
institutional affiliations. 7, p.75.

REFERENCES Fermont, A.M., van Asten, P.J.A., Tittonell, P., van Wijk,
M.T. and Giller, K.E. (2009). Closing the cassava
Abedinpour, M., Sarangi, A., Rajput, T.B.S., Singh, M.,
yield gap: an analysis from small holder farms in
Pathak, H and Ahmad, T. (2012). Performance
East Africa. Field Crops Res., 112: 24–36.
evaluation of AquaCrop model for maize crop in
a semi-arid environment. Agric. Water Manage., Howeler, R.H. (2010). Cassava in Asia: A potential new
110: 55–66. green revolution in themaking. A new future
for Cassava in Asia: Its use as food, feed, and
Bien, P.V., Kim, H., Ngoan, T.N., Howeler, R. and
Fuel to benefit the Poor. Proc. Eighth Regional
Wang, J.J. (2007). New developments in the
Workshop, held in Vientiane, Lao PDR. Oct 20-
cassava sector of Vietnam, Cassava research and
24, 2008, pp.34-64.
development in Asia, exploring new opportunities
Vol. 23, No. 4 HONG et al. 301
https://www.vectorstock.com/faq/members/standard- Agriculture and Forestry.
license
Miyan, M.A. (2015). Droughts in Asian least developed
Lee, S.K. and Dang, T.A. (2019). Irrigation water countries; vulnerability and sustainability.
requirement of rice in Long Xuyen Quadrangle Weather Clim. Extremes, 7:8–23.
area, Vietnam in the context of climate change.
Ropo, O.I. and Ibraheem, A.A. (2017). Response of
J. Agrometeorol., 21(1), 18-23.
cassava and maize yield to varying spatial scales
Mai, N.T.T. (2017). Study on selection of high-yield of rainfall and temperature scenarios in Port
starch and intensive cultivation techniques in Phu Harcourt. Res. J. Environ. Sci., 11(4):137-142.
Yen province. Doctoral thesis, Hue University of

Received : June 2020 : Accepted : August 2021