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Calculate K Fertilizer Requirement |
The requirement of K fertilizer of cassava is estimated by taking into account
the indigenous nutrient supply, target yield and agronomic efficiency of K
fertilizer use by cassava.
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K fertilizer (kg/ha) = |
Target yield (t/ha) – Yield in K omission plot (t/ha) |
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Agronomic efficiency of K (AEK) |
ie. tuberous root yield increase (ton) per kg K fertilizer applied
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Indigenous Potassium Supply
The average value of indigenous potassium supply (IKS) was found to be similar
in all crops sampled, but more than two fold ranges were measured among the
cassava fields in each year (table 1). The IKS ranged from about 98 to 207 kg K/
ha and coefficient of variation (CV) of IKS ranged from 18 to 29 per cent in
each year. Among the four crops sampled in the same cassava field, average
standard deviation of potassium supply was 15 kg/ha. This average estimation
error (or crop to crop variability) of a field-specific measurement is due to
the spatial variability arising because of rotation of nutrient omission plots
and changes in climatic and crop management factors, different varieties grown
in the same field in different years, and errors associated with plant sampling
and chemical analysis. Over the short term, the present average levels of
indigenous supply would be sufficient to get a tuberous root yield of 25 t/ ha
assuming potassium requirement of 5.33 kg/ ton tuberous root yield.
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Table 1: Variation of the indigenous potassium supply (kg/ha)
among cassava farms in India |
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Year
|
Mean
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Min
|
Max
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CV
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2003
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164.25 |
115.65 |
206.93 |
19.32 |
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2004 |
169.41 |
104.63 |
186.91 |
24.31 |
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2005 |
174.37 |
98.67 |
188.43 |
18.41 |
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2006 |
157.61 |
111.41 |
198.43 |
28.65 |
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Tuberous root yield and K uptake
Tuberous root yield and K uptake There was a significant increase in tuberous
root yield and potassium uptake in SSNM in all the four crops grown during
2003-2006 compared to FFP (Table 2). The average yield difference between SSNM
and FFP for the four crops grown was 8.72 t ha-1 (23%, P=0.005) and the differences in tuberous
root yield over the years were not statistically significant (P=0.247). In nine
farms, the average yield exceeded 40 t ha with a maximum of 47.69 t/ha and in
five farms, yields in the SSNM exceeded 10 t/ha compared to FFP, clearly
indicating the superiority of SSNM approach.
Significant differences were noticed in plant K uptake in SSNM compared with FFP
treatments. On an average, plant K uptake decreased by 7.87 kg/ha (3.91%,
P=0.011). Similar trends in potassium uptake were observed over the years
(P>0.05).
Table 2: Effect of site specific nutrient management (SSNM) on root yield, plant
potassium accumulation and K fertilizer use in cassava farms in India. |
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Treatment |
D |
P > ITI |
|
SSNM |
FFP |
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Tuberous root yield, t/ha |
37.35 |
28.63 |
8.72 |
0.005 |
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Plant K uptake, kg/ha |
201.01 |
208.89 |
-7.88 |
0.011 |
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K Fertilizer, kg/ha |
105 |
123 |
-18 |
0.006 |
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D-SSNM – FFP
P > ITI - probability of a significant mean difference between SSNM and
FFP
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Fertilizer Use
The average rate of K in FFP plots was 123 kg K2O/ha. Detailed survey indicated
that most of the farmers applied fertilizers without taking into account the
actual soil fertility status. The K rates were not found to be significantly
correlated with IKS (r = 0.34). On an average, 18 kg ha-1 less fertilizer K was used in SSNM treatments
than in FFP (-15%, P=0.006). Lower fertilizer K rate in the SSNM treatment
resulted from model based predictions that accurately accounted for the high
native soil K status measured as plant K uptake in K omission plots.
Potassium Use Efficiency
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The potassium use efficiency in the SSNM treatment was increased significantly
in SSNM treatment where the field- and season- specific P management was
practiced (Table 3). Less fertilizer K was applied in SSNM plots compared with
the FFP and there was significant increase in agronomic efficiency (AEP),
recovery efficiency (REP) and physiological efficiency (PEP) of potassium.
Across the four crops grown, the AEK increased by 41 kg kg-1 (64%, P=0.000), REK by 0.13 kg kg-1 (65%, P=0.002) and PEK by 22 kg kg-1 (68%, P=0.040). The results of the study provide
on-farm evidence that the present potassium management practice in India for
cassava is inconsistent with the physiological nutrient requirements of the crop
and that is one of the major reasons that prevents further increase in
productivity of cassava (Byju et al., 2006, 2008, 2009, 2010a, b). In addition
to this, it also results in nutrient imbalance and losses. The importance of
application of 50 per cent of K fertilizer before 10 days after planting and the
rest 45-60 days later is highlighted in many studies (Mohankumar 2000., Nayar et
al. 1985) as against what is observed in FFP.
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Table 3: Effect on site specific nutrient management (SSNM) on
fertilizer K use efficiency of cassava farms in India. |
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Treatment |
D |
P>ITI |
P>IFI |
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SSNM |
FFP |
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AEP, kg tuber/kgK |
115 |
74 |
41 |
0.000 |
0.030 |
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REP, kg K/kg K |
0.37 |
0.24 |
0.13 |
0.002 |
0.040 |
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PEP, kg tuber/kg K |
69 |
47 |
22 |
0.040 |
0.025 |
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References
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