08 Oct 2014

Effect of Controlled-Release Urea on Banana yields in Guangxi



Abstract: Applying controlled-release urea (CRU) to crops with long growing seasons is considered to be an idea practice to reduce times of fertilizer applications and enhance nitrogen use efficiency. For this purpose, a CRU field trial was conducted on banana, one of the major tropical fruits in Guangxi. The field trial consisted of nine treatments with different rates (100, 80 or 70 % of the full N rate) and splitting application times (2 or 3 times) of CRU. Comparison of paired CUR and regular urea (RU) with the same N rates was also tested. The results indicated that the CRU 100% treatments produced significantly higher fruit number/bunch and banana yield than the RU 100% treatment. Though the two treatments of CRU 100% achieved higher plant height, early flower bunch emergence, thicker stem girth, higher fruit weight, higher nitrogen uptake and economic returns than the treatment of RU100%, there were no significant differences among these N treatments. Further field trials are needed to determine CRU performance on banana under different soil fertility, yearly-variable climate, N rates and timing of applications.

1. Materials and methods
The field experiment was conducted on the pilot farm of Guangxi Academics of Agricultural Sciences located in Xixiangtang District, Nanning City in 2013. The soil in study is classified as a red soil with pH 6.2, organic matter (OM) 21.15 g/kg, available N, P, K as 115, 35 and 142 mg/kg, respectively. The soil was adequate in phosphorus (P), potassium (K) and calcium (Ca), medium in OM, nitrogen (N) and magnesium (Mg), and deficient in boron (B).
Two N sources were used. The controlled release urea (CRU, N 44%) was from Agrium Inc. and the regular urea (RU, N 46%) was purchased from local fertilizer market. Calcium magnesium phosphate (P2O5 18%) was used for P and potassium chloride (K2O 60%) for K. All P and 40% of K were used as basal fertilizers and 60% of K was as topdressings.
The local bred banana cultivar, Guijiao No. 6 was selected as the testing crop with a plant population of 1950 seedlings/ha. The trial was conducted as a completely randomized design with nine treatments (Table 1) with three replications and plot size of 41.4 m2 (10 plants).
Table 1 Treatments description of the CRU study in 2013 in Guangxi
TreatmentTreatment description
CK (PK) No N fertilizer used
RU 100% regular urea-N in 6 splits, one basal + 5 topdressings
CRU 100%CRU 100% used as 2 splits, one basal + one topdressing
CRU 80 %CRU 80% used as 2 splits, one basal + one topdressing
CRU 70% CRU 70% used as 2 splits, one basal + one topdressing
CRU 80%+RU 20%2 splits, one basal + one topdressing
CRU 100% 3 splits, one basal + two topdressings
CRU 80%+RU 20%3 splits, one basal + two topdressings
80% N rate with CRU 60%+RU 40% blends 2 splits, one basal + one topdressing
Timing of fertilization for each treatment: (1) RU 100%: basal application was on March 18, 2013. Topdressings were conducted in 5 times at seedling stage on May 5 and June 4, at vigorous growth stage on July 5, at budding stage on August 22 and at fruit swelling stage on September 7, respectively. (2) CRU 100% and CRU80%+RU 20%: basal application was on March 18. Topdressings were conducted twice at vigorous growth stage on July 5 and at fruit swelling stage on September 17. (3) the RU 100% and the rest treatments: basal application was on March 18 and topdressing at vigorous growth stage on July 5. The full fertilizer rates were 672.8-175.5-877.5 kg N-P2O5-K2O/ha.

2. Results and discussion
2.1 Banana yields as affected by different treatments
Table 2 Banana yield as affected by different treatments
Treatment
Yield
Increase vs CK0
Increase vs CK1
(kg/ha)
kg/ha
%
kg/ha
%
CK0
16187 c
-
-
-
-
RU 100% (CK1)
31018 b
14831
91.62
-
-
CRU 100%
33185 a
16998
105.01
2167
6.99
CRU 80 %
31308 a
15121
93.41
290
0.94
CRU 70%
30751 b
14563
89.97
-267
-0.86
CRU 80%+RU 20%
30596 b
14408
89.01
-423
-1.36
CRU 100%
34049 a
17862
110.35
3031
9.77
CRU 80%+RU 20%
30800 b
14613
90.27
-218
-0.7
80% N rate with CRU 60%+RU 40% blends
30295 b
14108
87.15
-723
-2.33
Note: F=27.36 **, LSD0.05=2544.0.
Data from Table 2 showed that CRU 100% significantly increased banana yield no matter CRU was split into two or three applications compared to RU 100%. Reducing CRU-N rate to 80% produced higher banana yield than RU 100%. The rest treatments produced lower banana yield than CRU 100%, indicating the N rate recommended in this experiment was optimal.

2.2 Plant height, stem girth and fruits per bunch as affected by different treatments
Table 3 Plant height, stem girth and fruits per bunch as affected by different treatments
TreatmentPlant height
Increase vs CK1
Stem girth
Increase vs CK1
Fruit/bunch
Increase vs CK1
cm
cm
%
 cm
cm
%
 
cm
%
CK0
181.3
-21.2
-10.4
39.82
-
-
93.4
-
-
RU 100% (CK1)
204.5
-
-
46.01
-
-
120
-
-
CRU 100%
205.4
0.9
0.4
46.46
0.5
1
127.3
7.3
6
CRU 80 %
204.7
0.2
0.1
46.26
0.2
0.5
123.4
3.4
2.8
CRU 70%
205.2
0.8
0.4
46.23
0.2
0.5
121.8
1.8
1.5
CRU 80%+RU 20%
204.4
-0.1
0
45.55
-0.5
-1
120.5
0.5
0.4
CRU 100%
204.7
0.3
0.1
46.3
0.3
0.6
127.9
7.9
6.6
CRU 80%+RU 20%
204.9
0.4
0.2
45.17
-0.8
-1.8
121.5
1.5
1.2
80% N rate with CRU
60%+RU 40% blends
204.7
0.3
0.1
45.27
-0.7
-1.6
119.8
-0.2
-0.2
Note: for plant height: F=3.36, LSD0.05=10.83; for stem girth: F=4.45, LSD0.05=2.51; for fruit number per bunch: F=9.39, LSD0.05=8.46.

Table 3 showed that there was virtually no significant differences in plant height among the treatments, implying no matter how high or low the N rates are is sufficient to support banana to grow to its full height.
Similar to plant height, the plant girth was not significantly affected by different N treatments.
Among all the N treatments, only the two CRU 100% treatments significantly enhanced fruit number per bunch compared to the RU 100% treatment. There was no statistical differences among the other treatments.

2.3 Nitrogen uptake by banana plants as affected by different treatments
Table 4 N absorption by plants as affected by different treatments
TreatmentN rateBanana yieldN uptakeAg efficiencyN required to produce 1 t fruitN use efficiency
kg/ha
kg/ha
kg/ha
kg/kg
kg
%
CK0
-
16187 c
92.6
-
5.72
-
RU 100% (CK1)
672.8
31018 b
151.1
22.0
4.87
33.3
CRU 100%
672.8
33185 a
163.2
25.3
4.92
40.2
CRU 80 %
538.2
31308 a
149.6
28.1
4.78
32.5
CRU 70%
470.9
30751 b
146.4
30.9
4.76
30.6
CRU 80%+RU 20%
672.8
30596 b
150.6
21.4
4.92
33.0
CRU 100%
672.8
34049 a
165
26.6
4.85
41.3
CRU 80%+RU 20%
672.8
30800 b
152
21.7
4.93
33.8
80% N rate with CRU 60%
+RU 40% blends
538.2
30295 b
148.9
26.2
4.92
32.1
Nitrogen contents were higher in the sheath and lower in the fruit and pseudostem. There were no significant differences in total N uptake or N use efficiency by plants as affected by different treatments, though the two CRU treatments achieved higher N uptake and N use efficiency compared to the RU100% treatment.

2.4 Economic profit as affected by different treatments
Table 5 Economic profit as affected by different treatments
Treatment
Banana yield
Income
Income increase
kg/ha
USD/ha
USD/ha
%
CK0
16187
8491.80
-7780.00
-51.22
RU 100% (CK1)
31018
16271.80
-
-
CRU 100%
33185
17408.69
1136.89
6.99
CRU 80 %
31308
16423.93
152.13
0.93
CRU 70%
30751
16131.64
-140.16
-0.86
CRU 80%+RU 20%
30596
16050.16
-221.64
-1.36
CRU 100%
34049
17862.13
1590.33
9.77
CRU 80%+RU 20%
30800
16157.54
-114.26
-0.70
80% N rate with CRU 60%+RU 40% blends
30295
15892.62
-379.18
-2.33
Note: Banana price: 0.52 USD/kg; urea: 0.32 USD/kg; CRU price is unknown and treated the same as urea here (This needs recalculation once CRU price is clear).
Table 5 showed that the two CRU 100% produced the highest profit and followed by the treatment of CRU 80%, though there were no significant differences among the N treatments.

The work was done by the IPNI collaborator in Guangxi, China. The project leader was Prof. Hongwei Tan from the Guangxi Academy of Agricultural Sciences.

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