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An experiment entitled ‘Potassium-magnesium interaction in coleus
[Solenostemon rotundifolius (Poir.) J.K.Morton] productivity’ was conducted during
the period from July to November 2020 at Agronomy Farm, College of Agriculture,
Vellanikkara, Thrissur, with the objective to assess the effect of potassium and
magnesium sulphate application on tuber yield of coleus. Potassium (K2O) was
applied @ 60 kg/ha (soil test based), 100 kg/ha (PoP recommendation) and a check
(no potassium). Magnesium sulphate doses tried were 0 kg/ha, 10 kg/ha, 20 kg/ha, 40
kg/ha. The treatments consisted of twelve different combinations of K2O and
magnesium sulphate which was replicated thrice in RBD design. The soil of the
experimental field was medium in potassium and low in magnesium status.
Magnesium sulphate was soil applied at 30 days of planting and in the case of lower
dose of 10 kg/ha, it was foliar applied (2 per cent spray). N and P2O5 were applied as
per PoP recommendation of 60:60 kg/ha. Coleus variety Nidhi was used for the study.
Growth parameters such as plant height, dry matter production of aerial portion,
dry matter production of tubers as well as total dry matter production were significantly
influenced by potassium application. However, LAI and root to shoot ratio at
vegetative stage did not vary significantly with potassium dose. Taller plants were
observed with potassium application @ 60 and 100 kg/ha at 60 DAP.But at 90 DAP
lower value of plant height was registered at higher level of 100 kg/ha K2O.
Magnesium sulphate application also influenced plant height at 90 DAP taller plants
were observed in plants which received 40 kg/ha of MgSO4.
Varied levels of potassium as well as magnesium sulphate did not bring about
variation in chlorophyll content of coleus leaves. However, interaction of potassium
and magnesium sulphate on leaf chlorophyll content was significant and higher values
were observed when K2O was applied @ 60 kg/ha along with MgSO4 @ 20 or 40
kg/ha.
Dry matter production (DMP) of aerial portion increased with increasing
levels of K2O. At 60 DAP and at harvest plants which received 60 or 100 kg/ha
potassium registered higher and comparable aerial DMP. Magnesium sulphate
application did not show any significant influence on DMP at 90 DAP. However at
harvest, aerial DMP with the application of 40 kg magnesium sulphate was superior to
other levels which were at par statistically.
Tuber yield showed significant increase with increase in rate of potassium
applied and showed an increase of 19 per cent when 100 kg of K2O was applied
compared to control (13.80, 14.94 and 16.46 t/ha, at 0, 60 & 100 kg/ha K2O,
respectively). Various levels of magnesium sulphate applied did not show any
influence on tuber yield. However interaction effect of K and Mg was significant and
best combination was 60 K2O with 40 kg MgSO4, 100 kg K2O with 10 or 40 kg
magnesium sulphate, which registered statistically comparable yields. Magnesium and
potassium levels had no influence on yield of unmarketable tuber.
Application of K2O @ 100 kg/ha recorded higher DMP of tuber and total DMP
over 0 and 60 kg potassium. Effect of magnesium sulphate application on dry matter
production of tuber and total dry matter production was non significant. However
interaction effect of potassium and magnesium sulphate was significant with respect
to tuber DMP. Higher and superior values were registered under 100 kg of K2O with
10 kg MgSO4 and 40 kg MgSO4.
Higher K uptake was noticed when K2O was applied @ 60 kg/ha with 40
kg/ha MgSO4 which was on par with K2O at 100 kg/ha with MgSO4 at 10 kg/ha or 40
kg/ha. Potassium and magnesium sulphate application did not cause significant
variation in N, P and secondary nutrient uptake by coleus.
Net returns as well as B-C ratio were higher for K2O application @ 100 kg/ha
along with MgSO4 @ 40 kg/ha or 10 kg/ha. The results of the study indicate that for
better productivity in coleus, potassium may be applied at the rate of @ 100 kg/ha,
even in soils with medium status of available K. Also, K- Mg balance is important
and hence in soils deficient in magnesium and medium in potassium, soil application
of magnesium sulphate @ 40 kg/ha or foliar spray @ 10 kg/ha at 30 DAP, together
with K2O dose of 100 kg/ha can enhance the productivity of coleus.