MSc

Investigation entitled" Soil Test crop response studies on coleus in laterite
soil of Kerala" consisting of two experiments namely fertility gradient experiment
and STCR experiment was conducted during 2002 in the farm attached to the
College of Horticulture, Vellan ikkara.
Objective of the study was to develop soil test based balanced fertilizer
recommendation for specific yield targets of coleus in laterite soils of kerala and
provide a basis for fertilizer recommendation for maximum and economic tuber
yield at varying soil test values.
The fertility gradient experiment was conducted to create desired gradient
in soil fertility in one and the same field by applying graded doses ofN, P, and K
fertilizers and raising fodder maize var.Co.l. After development of fertility
gradient, the STCR experiment was conducted in the same field with the test crop,
coleus variety Nidhi.The treatment structure consisted of four levels of N
(0,20,40, and 80 kg ha'), three levels of P20S (0,45 and 90 kg ha-I) and five levels
of K (0, 25, 50, 100, 200 kg ha-I) along with three levels of FYM (0, 7.5 and 15 t
ha-I)
The nutrient requirement of coleus, variety Nidhi were estimated to be
9.15,1.38 and16.38 kg ha-I N, P20S and K20 respectively to produce one tonne of
tuber. The soil efficiencies worked out as 21,46.85 and 40.85 per cent for N,
. ,
P205 and K20 respectively for coleus in laterite soil. The contribution of
nutrients from the fertilizers for coleus was calculated as 61.6,9.57 and 56.60 per
cent for N, P205 and K20 respectively.
From the above basic data, fertilizer prescription equation for specific yield
targets of coleus variety Nidhi in the laterite soil were derived as follows,





Without rVM
FN =14.85T-0.34SN
FP205 =14.42T-l J.21SP
FK20 =28.98T-0.87SK
FN, F P20S, F K20 - Fertilizer N, P20S and K20 respectively
T - Target yield of tuber in t ha-I
SN, SP, SK - Soil available N, P and K in' kg ha-I respectively
.
WithFYM



FN




14.85 T - 0.34 SN - 0.34 ON
14.42 T - 11.21 SP - 3.25 OP



F K20 = 28.93 T - 0.87 SK - 1.22 OK
Where,
ON, OP and OK are quantities ofN, P and K supplied through organic
manure in kg ha"
Multiple regression models calibrated with yield as dependent variable and
STVs for available N, P and K and applied nutrients as independent variables had
67.4 per cent predictability. Among the three fertilizer nutrients, FN only showed
the normal type (+, -, -) of response.
The fertilizer adjustment equation fur v,!rying levels of soil available N for
maximum tuber yield (t ha") of coleus in laterite soil was derived as FN= 168 SN,
where FN is fertilizer N (kg ha"): SN is available N (kg ha-I) is soil. The behavior
of applied p and K was found to produce responses other than normal and hence
optimization coula not be done for fertilizer P and K at varying soil test values.
Simple correlations coefficient was worked out for Nutrient uptake, soil
available nutrients, applied nutrients with yield of coleus. Available nutrients

-!


showed higher positive correlation" than that of allied nutrients. The uptake of
nutrients (N, P and K) also significantly correlated with yield of coleus.
This study is useful to adjust fertilizer doses based on the specific objective
and available resources of coleus farmers of the state.