Study on Site Specific Nutrient Management (SSNM) for sugarcane (Saccharum officinarum L.) in the Mekong Delta (tóm tắt + toàn văn)

CHAPTER 1
INTRODUCTION
1.1 Rationale
Sugarcane (Saccharum officinarum L.) is an annual crop
producing the most biomass then it requires a large amount of
nutrient inputs for its life cycle. There are some methods to assess
nutrient status of sugarcane in order to determine correct rate of
fertilizer, such as: (i) the Critical Nutrient Concentration (CNC)
method has developed table of critical nutrient value and optimum
range of sugarcane leaf that is considered as standard for diagnosis;
however, this way will be not precise when other nutrient
concentrations vary in tissue (Walworth and Sumner, 1986; Bailey,
1989, 1991 and 1993); (ii) the Diagnosis and Recommendation
Integrated System (DRIS) is suggested by using at least 3 ratios
(normally 6 to 7) of nutrient concentration for diagnosis (Walworth
and Sumner, 1987). The DRIS has been applied successfully to
explain result of leaf analysis in many kinds of crops, including
sugarcane (Beaufils and Sumner, 1976; Elwali and Gascho, 1984;
Beverly, 1991; Reis, 1999 and Hundal et al., 2005). Nevertheless, it
seems to be as a “qualitative method” by showing “lack or excess of
nutrients” situation but not providing fertilizer application rates to
crop; (iii) the Site-Specific Nutrient Management (SSNM) is based
on crop yield at a particular plot gained from two main sources: soil
nutrient-supplying capacity and fertilizer application. Determining
amount of fertilizer input will reduce nutrient loss on one hand and
improve fertilizer use efficiency on the other hand. The SSNM
approach has been applied successfully for rice crop (Dobermann et
al., 2002) and hybrid corn over the world (Pasuquin et al., 2014), but
the application for sugarcane is limited.
Besides the need to determine fertilizer rate, timing of
fertilization for increasing nutrient use efficiency by crops need to be

considered as well. Using leaf colour chart (LCC) to diagnose
nitrogen content in crop was considered a simple, easy method and
have been popularly applied to rice. However, the study of LCC in
sugarcane is still limited.
1
1.2 Research objectives
(i) To assess current sugarcane farming and use of NPK
fertilizer in alluvial (Soc Trang province) and acid sulfate soils (Hau
Giang province).
(ii) To determine effect of NPK fertilizer inputs to the
nutrient uptake, growth and yield of sugarcanes under the two soil
types.
(iii) To determine recovery efficiency (RE) and agronomic
efficiency (AE) in order to suggest NPK application for sugarcane
cultivation.
(iv) To evaluate LCC application for nitrogen timing on
sugarcanes in two soils.
1.3 Object and scope of research
• Object of research: NPK application for sugarcane
(Saccharum officinarum L.)
• Scopes of research:
 Field experiments were carried out on sugarcane farmers
in Cu Lao Dung district of Soc Trang province and Long
My district of Hau Giang province.
 Research period: January 2011 to January 2013.
 Omission plot experiments were implemented to evaluate
the omission of N, P, K nutrients
 Study on growth and N, P, K uptake of sugarcane
aims at improving scientific knowledge having a
database for calculating “soil nutrient-supplying

capacity” and fertilizers rate to achieve “target yield”
based on SSNM principle.
1.4 Limitations of research
• About fertilizer: only study N, P, K nutrients by inorganic
fertilizer for sugarcane; the sugarcane pressmud was
introduced as “improved treatment” according to the SSNM
recommendation.
2
• About location and experimental design: to minimize
variation in statistical analysis, the experiments were
designed as randomized completely block with 4 replications
at two soil conditions. The research did not apply “on-farm
research” in several locations as recommended by SSNM.
• About soils: limited in two soil types in the Mekong delta
such as: (i) alluvial soil (Dystric Fluvisols) in Cu Lao Dung-
Soc Trang and acid sulfate soil (Thionic Gleysols) in Long
My-Hau Giang.
1.5 Scientific and practical significances
+ Scientific significance
This study is based on the principle of SSNM. Fertilizer
recommendation for small scale where soil, crop, climate, weather,
cultural practice should be the same. Therefore, recommendation
based on crop need at specific field will get higher fertilizer use
efficiency.
Principally, calculation of fertilizer rates based on the SSNM
method comes from nutrient balance which is manifested by crop
yield. According to this approach, there are two sources of nutrient,
such as soils and fertilizers to create optimum yield of crop. In this
research, NPK fertilizer rates have been extrapolated based on the
difference between sugarcane nutrient requirements and the soils

nutrient supplying capacity. In addition, the database on growth and
nutrient uptake of sugarcane in Mekong delta soils has been
constructed in this study, which would be useful to assess crop
growth and nutrient balance on the sugarcane soils.
+ Practical significance
The results can be applied for sugarcane farming in the
Mekong delta. By simple and easy practice, the study results help to
reduce production costs then increase price competition in the
region.
In the coming crops, determination of NPK fertilizers rates can
be updated by extension workers or farmers through “omission plot
technique” at some representative sugarcane fields in the Mekong
delta.
3
The result from LCC application for sugarcane is important
reference to help farmers estimate when to test leaf color and apply
nitrogen exactly as crop need in the two soil types.
1.6 Innovativeness
- SSNM and LCC have been applied first time in the Mekong
delta, the results showed that the method is helpful for determining
NPK fertilizers rates and nitrogen application timing for sugarcane
in the Mekong delta.
- Soil-supplying capacity of N, P, K for sugarcane have been
determined. Percent ratio of N, P, K from soils to total crop
requirement in order to achieve target yield were recorded as
32.6%N, 46.2%P
2
O
5
, 56.1%K

2
O in Cu Lao Dung and 32.9%N,
59.6% P
2
O
5
và 63.4% K
2
O in Long My.
- At the same NPK fertilizer application rates, response to
sugarcane yield in Long My was about 89% compared to Cu Lao
Dung. Using “improved treatment” by using sugarcane pressmud at
10 tons/ha made sugarcane yield increased at both study sites.
- Farmers in the research areas almost have not applied K for
sugarcane. The application of potassium made Brix degree of
sugarcane increased in both Cu Lao Dung and Long My.
CHAPTER 2
LITERATURE REVIEW
2.1 Sugarcane farming in Soc Trang and Hau Giang
Soc Trang and Hau Giang are located in the lower Mekong
delta. According to Hua Thanh Xuan (2008), Soc Trang is one of the
largest sugarcane producers in the Mekong delta in term of planted
areas. Most sugarcanes are planted in the island of Cu Lao Dung and
Long Phu formed by alluvial deposition. Currently sugarcane yield
in Cu Lao Dung is higher than average of the world. Hau Giang has
the highest ranks of sugarcane planted area as well as production in
the Mekong delta, annual planted area of sugarcane in Hau Giang is
situated after rice with 13,063 ha and yield of 82,60 tons per ha
(Statistical Year Book, 2010).
4

2.2 Botanical characteristics, growth and nutrient
requirement
2.2.1 Botanical characteristics of sugarcane
2.2.2 Periods of growth
2.2.3 Nutrient requirement
Sugarcane is a long crop that belongs to C
4
pathway creating
big amount of production and needs high humidity, nutrients,
sunshine to optimize its productivity. It is estimated that one ton of
sugarcane production requires 0.56-1.20 kgN, 0.38-0.82 kgP
2
O
5
,
1.00-2.50 kgK
2
O, 0.25-0.60 kgCa, 0.20-0.35 kgMg, 0.02-0.20 kgNa
and 2.0-2.7 kgS together with micronutrients (Zender, 1990). On
average, one sugarcane crop takes away 208, 53, 280, 30, 3.4, 1.2
and 0.2 kg N, P, K, S, Fe, Mn and Cu respectively from soils to
achieve yield of 100 tons per ha (Singh and Yadav, 1996). Nutrient
requirements are different by soil conditions from place to place
(Natesan et al., 2007).
2.2.4 Quality parameters of sugarcane
2.3 Characteristics of K88-92 sugarcane variety
2.4 Fertilizer
2.4.1 Fertilizer recommendation for sugarcane
Fertilizer is the most important factor of nutrient supply for
sugarcane, accounting for about 50% of yield increase. Fertilizer

recommendation is higher in the tropical than sub-tropical regions.
Saini et al. (2006) recommended fertilizer for sugarcane production
as 400 kgN, 170 kgP and 180-190 kgK depending on time and soil
conditions.
2.4.2 Role of N, P and K
2.4.2.1 Nitrogen (N)
Nitrogen is a key nutrient affecting yield and quality of
sugarcane. Nitrogen increases sugarcane yield through increases of
shoots, stalk height, diameter of internode (Abayomi, 1987).
Seasonal nitrogen use efficiency is estimated at 0.841 tons sugarcane
kg
-1
N (Chattopadhyay et al., 2004). Quantity of nitrogen fertilizer in
the world ranges from 50 to 300 kgN ha
-1
and 1 kg of nitrogen can
create 0,5-1,2 tons ha
-1
(Hunsigi, 1993).
5
2.4.2.2 Phosphorous (P
2
O
5
)
Phosphorus is an essential element to promote creation of roots
and increase of branches but its availability depends on local soils
and fertilizer application. Increase of sugarcane yield after
phosphorus use is results of sucker development, biomass, and
density. At optimum phosphorous level, sugar concentration and

juice purity are also better (Elamin et al., 2007).
2.4.2.3 Potassium (K
2
O)
Potassium nutrient plays important roles in plant growth and
metabolism. Potassium fertilizer application often increases sugar
concentration and juice return, especially the case of late harvest
(Hunsigi, 2011).
2.5 Site-specific Nutrient Management approach
2.5.1 Definition
Site-specific nutrient management (SSNM) is an approach to
feeding crop with nutrients as and when needed. The application and
management of nutrients are dynamically adjusted to crop needs of the
location and season. This method helps farmers adjust fertilizers to
address lack of nutrients between required nutrients to maximize crop
yield and nutrient reserve of the soils, organic materials, and irrigation
water. The SSNM approach aims to increase farmers profit through
higher yield, application of nutrients (mainly N, P and K) locally and
seasonally, and optimal use of existing indigenous nutrient source such
as crop residues and organic fertilizers.
2.5.2 Principles of SSNM
2.5.2.1 Principles of SSNM
According to Witt et al. (2006) the SSNM provides maize
farmers knowledge to maximize fertilizer use and profit by balance
of required nutrients for high yield and indigenous nutrient supply
from soils, organic matters, crop residues, fertilizers and water. This
new method is based on model of QUEFTS (Quantitative Evaluation
of the Fertility of Tropical Soils) developed in Africa for maize crop
(Janssen et al., 1990; Smaling và Janssen, 1993) and later for rice
crop (Witt et al., 1999; Wang et al., 2001; Dobermann et al., 2002).

Technology of omission plots is useful to determine fertilizers
required to meet target yield (Witt and Doberman, 2002). In this
method N, P and K fertilizers are applied in sufficient amounts to
6
overcome deficiencies and ensure high yield. The target yield can be
determined from plots without limitation of NPK. In other words, the
SSNM is an approach based on the plant that utilizes the omission
plot technique to determine the yield obtained with only the soil
reserves (omission plots) compared to the attainable yield obtained
when nutrients are not limiting.
2.5.2.2 Steps of SSNM
Step 1: Determine target yield
Step 2: Estimate soil nutrient-supplying capacity
Step 3: Calculate N, P and K nutrient inputs to meet
deficiencies between crop need and soil supply
2.5.2.3 Parameters in the SSNM
2.5.3 Agronomic efficiency of N, P and K
Agronomic efficiency of N, P or K (AE
N
, AE
P
or AE
K
) is the
increase in yield per unit of fertilizer N, P
2
O
5
or K
2

O applied.
Fertilizer recommendation based on yield response and agronomic
efficiency is an alternative approach where soil testing is not used
regularly. This sounds good approach compared to other supportive
decision making tools.
2.5.4 Use of “improved treatment” in SSNM for sugarcane
2.5.5 Managemnet of nitrogen in sugarcane farming
2.5.5.1 Determine timing to apply nitrogen fertilizer
2.5.5.2 Manage nitrogen nutrient to balance supply and
demand
2.5.5.3 Diagnose nitrogen by LCC technique
Leaf color is considered as an indicator to diagnose
requirement of nitrogen fertilizer for crop. Previous studies show
that rice genotype and nitrogen management based on LCC affected
yield and yield components (Nagappa et al., 2002). Farmers believe
that when the leaves shift from dark to light green or yellow, crop
needs more nitrogen. Similarly, LCC is applied for sugarcane too
(Gaddanakeri et al., 2007). Chandrashekara (2009) reported that
application of nitrogen at 50 and 60 kgN/ha with LCC=6, sugarcane
yields were high (150.5 and 151.7 tons/ha in the first crop and 123.8
and 125.0 tons/ha in the second crop respectively), CCS, juice, Brix,
Pol and fructose, total uptake of N, P, K less than traditional
practice.
7
2.6 Method of soil nutrient assessment in sugarcane
2.7 Nutrient interaction in sugarcane farming
CHAPTER 3
RESEARCH METHODOLOGY
This study consists of four main activities:
3.1 Activity 1: Survey on current sugarcane farming and

fertilizer application in the research areas
Household survey was conducted in sugarcane areas of Cu Lao
Dung (Soc Trang) and Long My (Hau Giang) districts to understand
farming techniques such as veriety, quantity of fertilizer use, yield.
3.2 Activity 2. Study effects of fertilizers on sugarcane
growth, NPK uptake, and yield
This is a factorial experiment in a randomized complete block
design with 2 factors, 4 replications, and 8 treatments as NPK, NP,
NK, PK and NPK, NP, NK, PK in combination with sugarcane
pressmud in Cu Lao Dung (Soc Trang) and Long My (Hau Giang) to
assess effects of nutrient omission application (N, P, K) and
sugarcane pressmud to growth, nutrient uptake, and yield of
sugarcane. The experiment was carried out from January 2011 to
January 2012.
3.3 Activity 3. Determine return efficiency (REX) and
agronomic efficiency (AEX) to recommend fertilizer (N, P, K)
application for sugarcane
There were two field experiments including sugarcane
cultivated by planting (January 2011 to January 2012) and by
ratooning (January 2012 to December 2012) which is a practice of
growing a crop from the stubbles of previous crop at the same field
in Activity 2 to determine AE and RE for NPK fertilizer
recommendation of sugarcane at two research sites.
3.4 Activity 4. Diagnose for nitrogen application timing by
LCC technique
8
The experiment was randomized complete block design with 4
replications and four treatments as PPB-1, PPB-2, PPB-3 and PPB-4
in Cu Lao Dung-Soc Trang and Long My-Hau Giang (Table 3.5).
The experiment was carried out from January 2012 to January 2013

to diagnose timing for nitrogen application by LCC technique.
Table 3.5: Treatment of nitrogen application timing
Treatment
Nitrogen application timing (Day after cultivation)
10-20 60 90 120 150
PPB-1 1/5 1/5 1/5 1/5 1/5
PPB-2 1/5 1/5 2/5 LCC LCC
PPB-3 1/5 1/5 LCC
PPB-4 Weekly measurement, applied N when LCC<2
Note: Treatments with LCC application, applied N when LCC<2 with amount of 1/5N
CHAPTER 4
RESULTS AND DISCUSSIONS
4.1 Activity 1: Survey on current sugarcane farming and
fertilizer application in the research areas
In Cu Lao Dung, most farmers applied nitrogen fertilizer at
level of 250-300 kgN/ha (36.1%) and 300-350 kgN/ha (31.1%).
Similarly, farmers in Long My used nitrogen fertilizer at level of
300-350 kgN/ha (34.5%). For phosphorus fertilizer, common dosage
were 100-150 kgP
2
O
5
(37.7%) in Cu Lao Dung whereas in Long My
most cases were below 100 kgP
2
O
5
. Farmers payed less attention on
potassium application in both of study sites. According to Nguyen
Huy Uoc (2001) it is necessary to apply potassium fertilizer at 140-

200 kgK
2
O/ha to reach 70-80 tons/ha sugarcane and sugar
concentration above 10 CCS.
On average, at household level sugarcane yield were 158
tons/ha in Cu Lao Dung and 135 tons/ha in Long My if farmers
applied NPK sufficiently.
4.2 Activity 2. Study effects of fertilizers on sugarcane
growth, NPK uptake, and yield
9
4.2.1 Effects of nutrient omission application in
combination with sugarcane pressmud use on growth and
development of sugarcane
Nitrogen omission application (Treatment PK) resulted in
plant height, diameter, and density lower than nitrogen application
treatments (NPK, NK, NP) at 40, 120, 150, 210 and 330 days after
cultivation. However, phosphorus omission application (Treatment
NK) and potassium omission (Treatment NP) such above yield
parameters were neglibigle decrease. The efficiency of sugarcane
pressmud application increased the stalk height in Cu Lao Dung but
not in Long My. The stalk height is an important parameter of
growth and yield.
4.2.2 Effects of nutrient omission application in
combination with sugarcane pressmud use on N, P, K uptake
* Nitrogen uptake (N)
On Cu Lao Dung and Long My, treatments of without N
application showed that total nitrogen uptake was lower than that of
nitrogen application.
Table 4.20: Effects of N, P, K omission application in combination with
sugarcane pressmud on total nitrogen uptake (kgN/ha) in sugarcane.

Cu Lao Dung – Soc Trang, December 2011.
Factor
Days after planting (DAP)
40 120 150 210 330
Inorganic
fertilizer
(A)
NPK 2.69
a
197.91
a
240.9
a
287.8
a
287.0
a
NP 2.95
a
171.27
b
216.2
b
196.1
b
231.4
b
NK 2.77
a
168.71

b
193.86
c
208.3
b
216.4
b
PK 2.33
b
107.16
c
117.64
d
101.4
c
93.7
c
Organic
(B)
KBB 2.73 152.07
y
175.91
y
169.9
y
192.7
y
BBM 2.64 170.45
x
208.39

x
226.9
x
221.6
x
F
A
* ** ** ** **
F
B
ns * ** ** *
F
AxB
* ns * ** ns
CV (%) 9.8 8.6 8.4 9.2 13.6
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
It confirmed that soil nutrient-suppying capacity could not
meet nitrogen requirement of sugarcane (Table 4.20 and 4.21).
Interaction of nutrient omission application and sugarcane pressmud
10
in Cu Lao Dung showed that nitrogen was high when NPK applied
in combination with sugarcane pressmud at 150 and 210 days after
cultivation, the NPK+BBM treatment had the highest nitrogen
uptake (as 262.8 and 362.7 kgN/ha respectively).
Table 4.21: Effects of N, P, K omission application in combination with
pressmud on total nitrogen uptake (kgN/ha) of sugarcane in acid sulfate
soils in Long My – Hau Giang, December 2011.
Factor
Days after planting (DAP)

40 120 150 210 330
Inorganic
fertilizer
(A)
NPK 45.25
a
304.55
a
317.01
a
566.88
a
282.7
a
NP 41.70
ab
258.49
b
267.03
b
442.75
b
203.7
b
NK 38.29
bc
236.68
b
236.89
c

443.46
b
180.0
b
PK 32.47
c
137.85
c
118.11
d
272.29
c
93.1
c
Organic
(B)
KBB 37.05
y
225.96 236.26 405.84
y
183.8
BBM 41.81
x
242.82 233.26 456.85
x
195.4
F
A
* ** ** ** **
F

B
* ns ns * ns
F
AxB
ns ns ns ns *
CV (%) 15.6 12.2 10.6 13.6 12.9
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
* Phosphorus uptake (P
2
O
5
)
With phosphorus omission treatment, total phosphorus uptake
was lower the others in alluvial soils in Cu Lao Dung but it was not
clear in acid sulfate soils in Long My (Table 4.22 and 4.23). There
was an interaction between nutrient omission application and
combination with pressmud on total phosphorus uptake of sugarcane
in Cu Lao Dung at 120 and 150 days after cultivation (Table 4.22).
11
Table 4.22: Effects of N, P, K omission application in combination with
pressmud on total phosphorus uptake (kgP
2
O
5
/ha) of sugarcane in alluvial
soils in Cu Lao Dung – Soc Trang, December 2011.
Factor
Days after planting (DAP)
40 120 150 210 330

Inorganic
fertilizer (A)
NPK 0.75 59.67
a
66.10
a
63.5
a
129.1
a
NP 0.76 48.20
bc
58.75
b
51.3
b
98.9
b
NK 0.77 51.22
b
41.43
c
44.8
c
79.8
c
PK 0.85 41.95
c
41.24
c

45.0
c
59.7
d
Organic (B) KBB 0.78 39.48
y
51.86 45.9
y
83.5
y
BBM 0.77 61.05
x
53.40 56.4
x
100.2
x
F
A
ns * ** ** **
F
B
ns ** ns ** *
F
AxB
ns * ** ns ns
CV (%) 11.5 4.3 8.5 11.1 14.9
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
Table 4.23: Effects of N, P, K omission application in combination with
pressmud on total phosphorus uptake (kgP

2
O
5
/ha) of sugarcane in acid
sulfate soils in Long My – Hau Giang, December 2011.
Factor
Days after planting (DAP)
40 120 150 210 330
Inorganic
fertilizer
(A)
NPK 14.99
a
95.97
a
130.58
a
168.66
a
157.7
a
NP 14.09
ab
83.66
b
118.08
b
123.71
b
101.9

b
NK 13.59
ab
73.65
b
91.79
c
107.96
bc
93.2
b
PK 11.24
b
52.83
c
70.86
d
96.87
c
94.0
b
Organic
(B)
KBB 12.74 71.60
y
103.43 116.38
y
92.6
y
BBM 14.22 81.45

x
102.22 132.23
x
129.8
x
F
A
ns ** ** ** **
F
B
ns * ns * **
F
AxB
ns ns ns ns ns
CV (%) 20.8 12.8 11.5 13.6 14.2
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
* Potassium uptake (K
2
O)
Potassium obmission application did not reduce total
potassium uptake of sugarcane in Cu Lao Dung site. With potassium
treatment but nitrogen omission application, absorbability of
potassium was affected at both study sites (Table 4.24 and 4.25). Use
12
of pressmud showed that sugarcane uptake potassium at high level in
Cu Lao Dung but not in Long My district.
Table 4.24: Effects of N, P, K omission application in combination with
pressmud on total potassium uptake (kgK
2

O/ha) of sugarcane in alluvial
soils in Cu Lao Dung – Soc Trang, December 2011.
Factor
Days after planting (DAP)
40 120 150 210 330
Inorganic
fertilizer
(A)
NPK 4.44 417.48
a
337.23
a
350.2
a
811,4
a
NP 4.48 362.61
b
270.35
b
281.7
b
609,6
b
NK 4.46 400.93
ab
250.82
b
296.1
b

622,9
b
PK 4.73 296.77
c
183.50
c
229.4
c
455,6
c
Organic
(B)
KBB 4.45 328.92
y
244.79
y
285.1 591,3
y
BBM 4.09 409.98
x
276.16
x
193.5 658,5
x
F
A
ns ** ** ** *
F
B
ns ** * ns **

F
AxB
ns ** ** * ns
CV (%) 17.2 10.4 8.9 11.3 11.5
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
Table 4.25: Effects of N, P, K omission application in combination with
pressmud on total potassium uptake (kgK
2
O/ha) of sugarcane in acid
sulfate soils in Long My – Hau Giang, December 2011.
Factor
Days after planting (DAP)
40 120 150 210 330
Inorganic
fertilizer
(A)
NPK 68.20 414.69
a
501.02
a
771.05
a
552.9
a
NP 60.49 341.48
b
409.22
b
447.01

c
330.1
c
NK 59.18 393.97
a
323.78
c
580.17
b
409.8
b
PK 56.27 249.14
c
221.96
d
388.78
c
350.9
c
Organic
(B)
KBB 56.07 325.14
y
367.21 521.93 407.3
BBM 62.99 374.51
x
360.78 571.57 414.4
F
A
ns ** ** ** **

F
B
ns * ns ns ns
F
AxB
ns * ns ns *
CV (%) 15.8 12.7 18.9 21.3 11.3
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
Sugar and starch crops require large amount of potassium than
others. Their requirements can exceed 800 kg/ha including luxury
consumption. According to Humbert (1968) one sugarcane crop with
100 tons takes away 500 kgK
2
O/ha.
13
4.2.3 Effects of nutrient omission application in
combination with sugarcane pressmud use on sugarcane yield at
alluvial and acid sulfate soils
Table 4.26 and 4.27 indicated that NPK application increased
sugarcane yield at both alluvial soils in Cu Lao Dung and acid sulfate
soils in Long My. The yield could reach 176 tons/ha in alluvial soils in
Cu Lao Dung (Table 4.26) and 156.9 tons/ha in acid sulfate soils in
Long My (Table 4.27) when NPK applied sufficiently. N, P, and K
omission applications caused lower yield than NPK use, the yield
differences were recorded 14-66 tons/ha in Cu Lao Dung and 9-55
tons/ha in Long My.
Treatments in combination with 10 tons/ha of sugarcane
pressmud increased the stalk height, plant diameter then increased
sugarcane yield.

Table 4.26: Effects of N, P, K omission application in combination with
pressmud on sugarcane yield in alluvial soils in Cu Lao Dung – Soc Trang,
December 2011.
Factor
Yield components
Yield at
harvest
(tons/ha)
Stalk
height (m)
Plant
diameter
(cm)
Plant
density
(plant/m
2
)
Inorganic
fertilizer
(A)
NPK 2.72
a
2.96
a
8.53 176.0
a
NP 2.50
c
2.87

b
8.47 162.3
b
NK 2.63
ab
2.80
b
8.32 154.2
c
PK 2.38
c
2.60
c
8.31 110.2
d
Organic (B) KBB 2.50
y
2.76
y
8.43 148.6
y
BBM 2.62
x
2.85
x
8.38 152.8
x
F
A
* ** ns **

F
B
* * ns **
F
AxB
ns ns ns ns
CV (%) 6.0 2.7 4.4 1.8
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
14
Table 4.27: Effects of N, P, K omission application in combination with
pressmud on sugarcane yield in acid sulfate soils in Long My – Hau Giang,
December 2011.
Factor
Yield components
Yield at
harvest
(tons/ha)
Stalk height
(m)
Plant
diameter
(cm)
Plant
density
(plant/m
2
)
Inorganic
fertilizer

(A)
NPK 2.91
a
2.58
a
9.07 156.9
a
NP 2.72
b
2.36
b
8.47 147.9
b
NK 2.83
ab
2.33
b
9.27 143.3
c
PK 2.61
c
2.16
c
8.52 109.1
d
Organic
(B)
KBB 2.70
y
2.29

y
8.80 137.1
y
BBM 2.83
x
2.43
x
8.87 141.6
x
F
A
* ** ns **
F
B
* * ns **
F
AxB
ns ns ns ns
CV (%) 6.1 4.2 10.2 2.2
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
4.2.4 Effects of nutrient omission application in
combination with sugarcane pressmud use on Brix (%), CCS
(%) of sugarcane at alluvial and acid sulfate soils
The Brix degree increased at different age of sampling (Table
4.28).
Table 4.29: Effects of N, P, K omission application in combination with
pressmud on Brix and CCS at alluvial soils in Cu Lao Dung and acid
sulfate soils in Long My at 330 days after planting, December 2011.
Factor

Cu Lao Dung Long My
Brix (%) CCS (%)
(*)
Brix (%) CCS (%)
(*)
Inorganic
fertilizer (A)
NPK 17.9 8.3 21.4 10.6
NP 17.1 7.8 19.6 9.4
NK 18.2 8.5 21.3 10.6
PK 18.8 8.9 21.6 10.8
Organic (B) KBB 17.8 8.2 20.8 10.2
BBM 18.3 8.6 21.2 10.5
Note:
(*)
CCS (%) = (Brix * 0.66) – 3.5 (Nguyen Bao Ve, 2011); increase
1 unit of CCS the price of sugarcane will increase 100 VND per kg
Potassium omission application decreased Brix but the
nitrogen omission application was not. Qasim et al. (2003) and
Shirazi et al. (2005) reported that there was a relationship between
15
sugar concentration and potassium which can increase air exchange
during photosysnthesis process resulting higher yield and sugar
content. The CCS was estimated according to Nguyen Bao Ve
(2011) which is presented in Table 4.29.
In general, both sites at 330 days after planting, fertilizer
treatments increased CCS. Combination with pressmud also
increased CCS at the same period.
4.3 Activitiy 3. Determine return efficiency (RE
X

) and
agronomic efficiency (AE
X
) to recommend fertilizer (N, P, K)
application for sugarcane
4.3.1 Determine parameters used to estimate fertilizer in
the SSNM approach
4.3.1.1 Soil NPK supplying capacity in Cu Lao Dung – Soc
Trang and Long My – Hau Giang
Figure 4.13 showed that the sugarcane yield increase of N, P,
K nutrients was recorded in the following order of 45, 17 and 11
tons/ha in Cu Lao Dung and 38, 13 and 9 tons/ha in Long My. In
combination with pressmud, the sugarcane yield increase of N, P,
K nutrients was recorded in the following order of 51, 21 and 11
tons/ha in Cu Lao Dung and 46, 14 and 12 tons/ha in Long My.
Therefore, it is conluded that the increase of sugarcane yield was
ranked as of N>P>K.
(a) (b)
Figure 4.13: Increase of sugarcane yield (tons/ha) when NPK application at
level of 300-125-200 kg/ha in combination with sugarcane pressmud at 10
tons/ha: (a) Cu Lao Dung and (b) Long My, plant cane crop 2011-2012 and
ratoon 2012
16
4.3.1.2 Determine agronomic efficiency (AE
X
) and return
efficiency (RE
X
) to recommend fertilizer (N, P, K) application for
sugarcane at alluvial and acid sulfate soils

a) Agronomic efficiency (AE
X
) of N, P, K fertilizers
In Cu Lao Dung alluvial soils, agronomic efficiency of
nitrogen (AE
N
) was 0.15; it means that increase 1 kg of nitrogen will
increase 150 kg of sugarcane. Similarly, agronomic efficiency of
phosphorus (AE
P
) was 0.14 and agronomic efficiency of potassium
(AE
K
) was only 0.05. In Long My acid sulfate soils, the agronomic
efficiency was lower with AE
N
, AE
P
,

AE
K
was recorded as 130 kg
sugarcane/kgN, 100 kg sugarcane/kgP
2
O
5
and 50 kg
sugarcane/kgK
2

O respectively. Pressmud application did not
increase AE
x
at both study sites.
b) Recovery efficiency (RE
X
) of N, P and K
In Cu Lao Dung, over the two crops the recovery efficiency of
nitrogen (RE
N
) was 49%, phosphorous (RE
P
) 33% and potassium
(RE
K
) 93%. In combination with pressmud, the recovery efficiencies
of N, P, K were recorded as 37, 17 and 53% respectively.
In Long My, the recovery efficiency of nitrogen (RE
N
) was
48%, phosphorous (RE
P
) 45% and potassium (RE
K
) 77%. In
combination with pressmud, the recovery efficiencies of N, P, K
were recorded as 43, 13 and 82% respectively.
4.3.2 Estimate fertilizers for sugarcane in Cu Lao Dung
alluvial soils and Long My acid sulfate soils
Based on the household survey in Cu Lao Dung (Soc Trang)

and Long My (Hau Giang) presented in Table 4.10, sugarcane yield
in Cu Lao Dung (158 tons/ha) and Long My (135 tons/ha) were
considered as target yield to estimate nutrient inputs for the two
sites. NPK fertilizer application were estimated according to
Pasuquin et al. (2014) with AE
N
, AE
P
, and AE
K
have been calculated
above (section 4.3.1.2, part a). Thus, NPK application was
recommended as 328N-156P
2
O
5
-279K
2
O (kg/ha) in Cu Lao Dung
and 334N-168P
2
O
5
-296K
2
O (kg/ha) in Long My.
17
4.4 Activity 4. Diagnose nitrogen application timing for
sugarcane by LCC application
4.4.1 Effect of nitrogen application timing on Brix degree

Table 4.46 showed that nitrogen application methods affected
Brix degree of sugarcane cultivated in Cu Lao Dung at 330 days
after cultivation. The highest Brix degree (21.5%) was recorded at
PPB-4, used nitrogen when LCC<2, (p<0.05). However, the Brix
degree was not significantly different by nitrogen application timing
in Long My site.
Table 4.46: Effects of nitrogen application timing on Brix degree of
sugarcane at 8 and 11 months in Cu Lao Dung and Long My, December
2012.
Methods Brix degree (%Brix)
Cu Lao Dung Long My
8 months 11 months 8 months 11 months
PPB-1 13.2 19.1
b
16.3 20.4
PPB-2 14.1 20.6
b
16.4 20.7
PPB-3 13.0 18.4
b
16.8 21.1
PPB-4 13.2 21.5
a
16.5 20.7
F ns * ns ns
CV (%) 12.4 5.0 7.0 6.4
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant

4.4.2 Effects of nitrogen application timing on sugarcane

yield and yield components
Sugarcane yields at harvest in Cu Lao Dung and Long My
were presented in Table 4.47 and 4.48. They showed that sugarcane
yiled with PPB-4 was higher than the others (PPB-1, PPB-2 and
PPB-3). It confirmed that using LCC technique (LCC<2) to apply
nitrogen resulting in higher sugarcane yield.
18
Table 4.47: Effects of nitrogen application timing on sugarcane yield and
yield components at 330 days after cultivation in Cu Lao Dung, December
2012.
Methods Yield components
Yield at
harvest
(tons/ha)
Stalk height
(m)
Plant
diameter
(cm)
Plant
density
(plant/m
2
)
PPB-1 2.8
b
3.1 7.8
b
164.9
c

PPB-2 2.8
b
3.0 8.2
a
174.4
b
PPB-3 3.1
a
2.8 8.2
a
171.6
b
PPB-4 3.0
ab
3.2 8.3
a
183.1
a
F * ns * **
CV (%) 4.3 6.3 2.7 1.7
Note: In a column means followed by the same letter were not significantly different via
Duncan test, *: significant at 5%; **: significant at 1%; ns: non significant
Table 4.48: Effects of nitrogen nitrogen application timing on sugarcane
yield and yield components at 330 days after cultivation in Long My,
December 2012.
Methods Yield components
Yield at
harvest
(tons/ha)
Stalk height

(m)
Plant
diameter
(cm)
Plant
density
(plant/m
2
)
PPB-1 3.1
b
2.4
b
7.6 153.2
b
PPB-2 3.0
b
2.8
a
7.6 156.3
b
PPB-3 3.3
a
2.7
ab
7.9 159.3
b
PPB-4 3.3
a
2.7

ab
8.1 166.5
a
F ** ns ns **
CV (%) 1.8 7.3 3.9 2.5
Note: In a column means followed by the same letter were not significantly
different via Duncan test, *: significant at 5%; **: significant at 1%; ns: non
significant
Sugarcane yield was high with method of 300 kgN/ha in
combination with LCC measurement weekly (LCC<2 applied 1/5N).
4.4.3 Leaf nitrogen content at different nitrogen
application timing when LCC<2 or before fertilizer use
In Cu Lao Dung, Table 4.49 showed that when LCC<2 leaf
nitrogen content ranged 1.30 to 1.68%, lower than critical value
significantly (p<0.05). In Long My, Table 4.50 showed that regular
nitrogen application or LCC<2, the leaf nitrogen content was also
lower than critical value (1.80%) (p<0.05). Therefore, we can
19
conclude that indigenous nitrogen from soils could not meet nutrient
needs of sugarcane.
Table 4.49: Mean comparison of leaf nitrogen content (%N leaf) at
different nitrogen application timing in Cu Lao Dung, December 2012.
Methods Leaf nitrogen content (%N)
Time 1 Time 2 Time 3 Time 4 Time 5
PPB-1 1.42
**
1.47
**
1.78
ns

1.57
**
1.30
**
PPB-2 1.31
**
1.57
**
1.83
ns
1.48
**
1.36
**
PPB-3 1.34
**
1.52
*
1.66
*
1.46
**
1.35
**
PPB-4 1.39
**
1.63
*
1.68
**

1.52
**
1.45
**
Critical value
(*)
1.80
Note: In a column: *: significant at 5%; **: significant at 1%; ns: non significant via
T-test with critical value
(*)
( McCray and Mylavarapu, 2010)
Table 4.50: Mean comparison of leaf nitrogen content (%N leaf) at
different nitrogen application timing in Long My, December 2012.
Methods Leaf nitrogen content (%N)
Time 1 Time 2 Time 3 Time 4 Time 5
PPB-1 1.40
**
1.46
**
1.61
*
1.28
**
1.21
**
PPB-2 1.45
**
1.55
**
1.68

*
1.43
**
1.31
**
PPB-3 1.45
**
1.57
**
1.58
**
1.45
**
1.24
**
PPB-4 1.49
**
1.61
**
1.57
**
1.39
**
1.31
**
Critical value
(*)
1.80
Note: In a column: *: significant at 5%; **: significant at 1%; ns: non
significant via T-test with critical value

(*)
( McCray and Mylavarapu, 2010)
When LCC<2, leaf nitrogen content varied from 1.31 to
1.61%, significantly lower than the critical value (p<0.05).
4.5 Economic efficiency of SSMN method
Results from Table 4.51 showed that SSNM method created
higher net profit than traditional method, it was 17.1 million VND in
Cu Lao Dung and 27.4 million VND in Long My. This economic
efficiency results from yield increase by SSNM application (17.3%
in Cu Lao Dung and 24.8% in Long My) and decrease of cost for
fertilizer (18.5% in Cu Lao Dung and 13.9% in Long My).
20
Table 4.51: Comparison of economic efficiency between SSNM method
and traditional fertilizer application of farmers at two study sites
Items
Cu Lao Dung Long My
SSNM Farmers SSNM Farmers
Yield (t/ha) 183 156 166 133
Yield difference (t/ha) 27 33
Yield difference (%) 17.3 24.8
Gross return (VND/ha)
(price x production)
109,800,000 93,600,000 99,600,000 79,800,000
Gross return difference
(VND/ha) 16,200,000 19,800,000
Gross return difference
(%)
17.3 24.8
Fertilizer N (kg/ha) 300 334 300 350
Fertilizer P

2
O
5
(kg/ha) 125 154 125 168
Fertilizer K
2
O (kg/ha) 200 17 200 5
Total fertilizer cost
(VND/ha)
17,384,511 14,676,630 17,384,511 15,266,304
Fertilizer cost difference
(VND/ha)
2,707,880 2,118,207
Fertilizer cost difference
(%)
18.5 13.9
Net profit (VND/ha) 92,415,489 78,923,370 82,215,489 64,533,696
Net profit difference
(VND/ha)
13,492,120 17,681,793
Net profit difference
(%)
17.1 27.4
Note: price of sugarcane 600 VND/kg; fertilizer application as 300N-125P
2
O
5
-200K
2
O

(kg/ha) (Figure 4.13) and yield (t/ha) (Table 4.46 and 4.47) from 2 study sites
21
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
5.1 CONCLUSIONS
5.1.1 Current sugarcane farming and fertilizer application
in research areas
In Cu Lao Dung, most farmers applied nitrogen rates of 250-
300 kgN/ha (36.1%) and 300-350 kgN/ha (31.1%). Similarly,
farmers in Long My used nitrogen rates of 300-350 kgN/ha
(34.5%). For phosphorus fertilizer, common rates were 100-150
kgP
2
O
5
(37.7%) in Cu Lao Dung whereas in Long My most cases
were below 100 kgP
2
O
5
. Farmers payed less attention on potassium
application in both of study sites. Most farmers (93.4% in Cu Lao
Dung and 95% in Long My) used potassium below 50 kgK
2
O/ha.
On average, at household level sugarcane yield were 156
tons/ha in Cu Lao Dung and 133 tons/ha in Long My; however,
when farmers applied NPK sufficiently, sugarcane yield reached
158 tons/ha in Cu Lao Dung and 135 tons/ha in Long My.
5.1.2 Effects of NPK application on sugarcane growth,

nutrient uptake and yield
+ Effect on sugarcane yield components: Nitrogen omission
application (PK treatment) caused plant height, diameter, and density
lower than nitrogen application treatments (NPK, NK, NP) at
sampling time of 40, 120, 150, 210, and 330 days after planting.
However, phosphorus omission application (NK treatment) and
potassium omission application (NP treatment) did not affect yield
components. Using sugarcane pressmud increased plant height in Cu
Lao Dung but not in Long My.
+ Effect on NPK uptake: Both Cu Lao Dung and Long My
soils, nitrogen omission application showed that total nitrogen
uptake was lower than treatments with nitrogen use. It confirmed
that soil nitrogen-supplying capacity could not meet nitrogen
requirement of sugarcane. Supply nitrogen from pressmud increased
nitrogen uptake of sugarcane in Cu Lao Dung alluvial soils.
With phosphorus omission treatment, total phosphorus uptake
was lower the others in alluvial soils in Cu Lao Dung but it was not
22
clear in acid sulfate soils in Long My. Pressmud application
increased phosphorus uptake of sugarcane at both experimental sites.
Potassium obmission application did not reduce total
potassium uptake of sugarcane in Cu Lao Dung site but nitrogen
obmission application decreased total potassium uptake at two study
sites. Pressmud application increased potassium uptake of sugarcane
in Cu Lao Dung alluvium soils but not clear in Long My acid sulfate
soils.
Percent ratios of soil N, P, K supplying capacity to total crop
requirement in order to achieve target yield were recorded as
32.6%N, 46.2%P
2

O
5
, 56.1%K
2
O in Cu Lao Dung and 32.9%N,
59.6% P
2
O
5
và 63.4% K
2
O in Long My.
+ Effect on sugarcane yield and quality: Potassium application
increased Brix in Cu Lao Dung and Long My. Applying pressmud
did not increased Brix of sugarcane. Nitrogen, phosphorus and
potassium omission application caused lower sugarcane yieldIn
combination with pressmud at 10 tons/ha increased plant height,
diameter and yield of sugarcane.
+ Assessment of NPK supply from soils through yield
increase:
At the same fertilizer rate of 300N-125P
2
O
5
-200K
2
O (kg/ha),
response to sugarcane yield in Long My was about 89% compared to
Cu Lao Dung. Using “improved treatment” by using sugarcane
pressmud at 10 tons/ha increased sugarcane yield at both study sites.

5.1.3 Determine agronomic efficiency (AE
X
) and recovery
efficiency (RE
X
) to recommend fertilizer (N, P, K) application for
sugarcane
+ Based on AE
X
RE
X
, NPK fertilizer recommendations for Cu
Lao Dung was 328N-156P
2
O
5
-279K
2
O (kg/ha) and Long My was
334N-168P
2
O
5
-296K
2
O (kg/ha)
5.1.4 Diagnose timing to apply nitrogen for sugarcane by
LCC application
LCC technique was evaluated as the most effective way to
determine nitrogen application timing in sugarcane production in this

study. Higher sugarcane yield were received with the LCC
application It was recorded that when leaf color LCC<2, leaf
23
nitrogen content was 1.30-1.68% in Cu Lao Dung and 1.31-1.61% in
Long My which were lower than critical value of 1.80%N.
5.1.5 Economic efficiency of SSNM
The SSNM increased net profit from 17.1 million VND/ha in
Cu Lao Dung to 27.4 million VND/ha in Long My compared to
traditional practice of farmers. This increase thanks to yield increase
(17.3% in Cu Lao Dung and 24.8% in Long My) and fertilizer cost
reduction (18.5% in Cu Lao Dung and 13.9% in Long My).
5.2 RECOMMENDATIONS
Study on soil and water environments causing different yield of
sugarcane between Cu Lao Dung and Long My;
Study effects of sugarcane pressmud application on leaf color
and extension of time for each nitrogen application;
Futher study factors affecting nitrogen application timing on
sugarcane based on results of this research.
24