MSc

The study entitled Organic and inorganic amendments for surface and
subsoil acidity amelioration in southern laterites of Kerala was conducted in the
Department of Soil Science and Agricultural Chemistry, College of Agriculture,
Vellayani during 2021-2023 with the objectives to evaluate various organic
amendments and liming materials for amelioration of surface and subsoil acidity in the
southern laterite soils (AEU -8) of Kerala and assessment of the effect on crop
production using tomato as test crop. The experiment comprised of two parts viz.
column incubation experiment and field validation of amendments for soil acidity.
A column incubation study was conducted under laboratory conditions for 12
weeks using the southern laterite soils (AEU-8) of College of Agriculture, Vellayani, to
elucidate the acid neutralization capacity of organic and inorganic amendments applied
to the soil and to monitor the amelioration of surface and sub soil acidity. Soil samples
were collected to a depth of 60 cm from the experiment site and filled in polyvinyl
chloride (PVC) tubes of 10 cm diameter and 60 cm length and with facility to collect
the leachate in such a manner as to attain the same bulk density as that of the field.
Treatments were applied to the top 15 cm soil on weight basis and thoroughly mixed.
The soil columns were maintained at field capacity. There were 17 treatments which
included farmyard manure (FYM) @ 20 t ha-1
, humic acid (HA) @ 10 kg ha-1
, poultry
manure (PM) @ 1 t ha-1
and coconut frond biochar (CFB) @ 10 t ha-1
along with lime
or dolomite or calcium silicate (CS) or phosphogypsum (PG) at lime requirement (LR)
and soil alone.
Biochar produced from coconut frond by the process of slow pyrolysis and other
organic amendments, were analysed for various physical and chemical properties using
standard procedures. Humic acid recorded the highest bulk density (0.51 Mg m-3
) while
the lowest was for CFB (0.36 Mg m-3
). The highest pH was for CFB (10.70) followed
by HA (9.84). The TOC (41.11%), P (0.95%), K (0.91%), Ca (0.56%), Mg (0.45%), S
(0.25%) and B (6.28%) were highest for CFB while the highest value of N (2.97%) was
for PM. Fe (813.30 mg kg-1
), Mn (94.50 mg kg-1
), Zn (40.12 mg kg-1
) and Cu (5.13 mg
kg-1
) were highest for FYM. CCE of lime, dolomite, PG and CS were 123.5%, 124 %,
58.1% and 58.06% respectively. The highest concentration of total Ca was observed for
lime (37.10%) and for total Mg, was for dolomite (16.03%).
Three leching events were performed in the prepared soil columns at 4, 8 and
12 weeks of incubation by adding double the pore volume of water. Leachate was acidic
in pH for all the treatments and showed an increase up to 12th week of incubation. The
EC, total OC, P, K, Ca, S, Mg and B contents in the leachate decreased from the 4
th
week to 12th week. Total N content showed a general decrease from the 4
th week to 8th
week and an increase at 12 weeks except for the treatment supplied with CFB along
with either lime, dolomite, PG or CS which showed a gradual increase. The cumulative
contents of total Fe, Mn, Zn and Cu were significantly highest for the control treatment.
pH of leached soils showed significant increase at all depths after the incubation
period compared to control and it decreased as depth increased from 0-15 cm to 30-60.
CFB @ 10 t ha-1 with lime as per LR showed the highest value for pH at 0-15 cm depth
of soil and it was on par with PM @ 1 t ha-1 with lime as per LR and CFB @ 10 t ha-1
with CS as per LR. Significantly highest pH was noticed for FYM @ 20 t ha-1 with CS
as per LR at 15-30 cm depth of soil. At 30-60 cm depth of soil significantly highest
value for soil pH was observed for CFB @ 10 t ha-1 with PG as per LR. Significantly
lower mean values for exchangeable Al3+ and H+
at different depths were observed for
the treatment combination CFB @ 10 t ha-1 with CS as per LR. The exchangeable Ca
content increased significantly at all depths of soil compared to the control. The higher
mean values for exchangeable Ca were recorded by CFB @ 10 t ha-1 with CS as per LR
treatment at 0-15, 15-30 and 30-60 cm depths of soil. Significantly highest value for
exchangeable Mg was recorded by the treatment supplied with CFB @ 10 t ha-1 with
dolomite as per LR at all the depths of soil. Available N was significantly higher for the
treatment receiving PM @ 1 t ha-1 with lime as per LR which was on par with dolomite
or PG or CS as per LR and with FYM @ 20 t ha-1 + PG as per LR. Available P showed
the maximum value for treatment supplied with FYM @ 20 t ha-1 + CS as per LR which
was on par with CFB @ 10 t ha-1 with CS as per LR. The treatments receiving CFB @
10 t ha-1 with lime as per LR gave the maximum value which was on par with CS or PG
or dolomite as per LR. The available S content was highest for CFB @ 10 t ha-1 with
PG as per which was on par with all the treatments receiving PG as per LR with FYM
@ 20 t ha-1
or HA @ 10 kg ha-1
or PM @ 1 t ha-1
. Available Fe, Mn, Zn and Cu were
recorded highest for the control treatment.
Based on the acidity amelioration ability, best five treatments from the column
incubation experiment viz. CFB @ 10 t ha-1 with dolomite as per LR, FYM @ 20 t
ha-1 with PG as per LR, FYM @ 20 t ha-1 with CS as per LR, HA @ 10 kg ha-1 with CS
as per LR and CFB @ 10 t ha-1 with CS per LR each along with NPK as per POP were
selected for field validation using tomato as the test crop including KAU POP, KAU
organic POP and absolute control. The physical properties of soil such as bulk density,
porosity, water holding capacity and aggregate stability were significantly improved by
the application of CFB @ 10 t ha-1
along with CS or dolomite as per LR, compared to
other treatments. The surface and subsoil acidity were significantly reduced by the
application of treatments compared to the control. Treatments receiving CFB @ 10 t
ha-1 with dolomite or CS as per LR showed significant improvement for pH,
exchangeable Al3+ and H+
, and exchangeable Ca and Mg compared to other treatment
combinations. CFB@ 10 t ha-1 with CS as per LR recorded the highest value for
available OC, N, K and B and it was on par with CFB @ 10 t ha -1 with dolomite as per
LR. FYM @ 20 t ha-1 with PG as per LR showed highest value for available P and S
which was on par with the treatment receiving CFB @ 10 t ha-1 with dolomite or CS as
per LR.
Plant height, number of branches per plant, root length and volume, fresh weight
of shoot and root, dry matter production, number of fruits per plant and yield were
highest for the treatment receiving CFB @ 10 t ha-1 with CS as per LR which was on
par with CFB@ 10 t ha-1 with dolomite as per LR. The higher mean values for uptake
of N, P, K, Ca, S and B by tomato was for CFB @ 10 t ha-1 with CS as per LR.
Significantly higher mean values for uptake of Mg, Mn and Zn by tomato was
significantly higher for CFB@ 10 t ha-1 with dolomite as per LR, while FYM @ 20 t
ha-1 with CS as per LR showed the highest improvement for total uptake of Fe and Cu
by tomato. The quality parameters of tomato fruit such as vitamin C and lycopene
content were significantly improved by the application of treatments and the higher
mean values was observed for FYM @ 20 t ha-1 with PG as per LR and CFB @ 10 t ha1 with CS as per LR, respectively.
It may be inferred that there was significant movement of exchangeable calcium
and magnesium through the depth in all treatments. Exchangeable H+
and Al3+ were
significantly reduced by the combined application of organic and inorganic
amendments. The highest acidity amelioration capacity in both incubation and field
study was recorded by CFB @ 10 t ha-1 with CS as per LR. The treatment combinations
CFB @ 10 t ha-1 with dolomite or CS as per LR, FYM @ 20 t ha-1 with CS or PG as per
LR, and HA @ 10 kg ha-1 with CS as per LR were superior to other treatment
combinations in reducing pH, exchangeable Al3+, and H+
and improving exchangeable
Ca and Mg of the soil during the incubation study. Application of CFB @ 10 t ha-1 with
dolomite or CS as per LR showed the highest reduction in acidity parameters and
improved the content and uptake of nutrients during the field study. Application of CFB
@ 10 t ha-1 with dolomite or CS as per LR and NPK as per POP increased the fruit yield
by 26 % and 37 % compared to KAU POP. From the study, it can be concluded that
CFB @ 10 t ha-1
along with dolomite as per LR is the economically viable and best
treatment for amelioration of surface and subsoil acidity.