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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) |
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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/ha
of K 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
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Mean
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Min
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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
There was a significant increase in tuberous root yield and potassium uptake in
SSNM plots in all the four crops grown during 2003-2006 compared to FFP plots
(Table 2). The average yield difference between SSNM and FFP plots for the four
crops grown was 8.72 t/ha (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 plot 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 |
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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 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 (AEK), recovery
efficiency (REK) and physiological efficiency (PEK) of potassium. Across the
four crops grown, the AEK increased by 41 kg/kg (64%, P=0.000), REK by 0.13
kg/kg (65%, P=0.002) and PEK by 22 kg/kg (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 of 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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