Soil affected by sodicity was 434 million hectare

Soil
degradation caused by salinity and sodicity is of universal concern. The area
of land affected by sodicity was 434 million hectare and by salinity 376
million hectare in world. In India 3.79 million hectare and in Tamil Nadu 0.35
million hectare have been affected by sodicity respectively. It was caused by inadequate drainage, especially under
dense soil conditions. Soil sodicity is characterized by high pH, high
water soluble and exchangeable sodium, low biological activity, poor physical
properties and deficiency of many essential plant nutrients in crops. Plant under sodic soil condition cannot able to grow due to
the higher concentration of Na+ ions
concentration which favors reverse osmosis and finally plant wilt then die Despite available advanced technologies of management
today, millions of hectares of land under sodicity, severely reduce crop
production worldwide. Hence, it is necessary to develop cheap and
effective technologies for problem soils utilizing the locally available
resources without disturbing the ecological balance.

However, gypsum is one of the potential
soil amendments to reclaim sodic soil and to improve plant growth and
development. Other than this several amendments have been shown to protect
various plant species against sodicity stress by reducing exchangeable sodium
ion concentration, but they are not cost effective compared to gypsum. Even
though the gypsum is effective, because of its low solubility (0.2%) in soil
condition, this process will take more time to reclaim the sodic soil. Further,
gypsum also application at regular
intervals needed again and again needs to be applied to keep the sodium content
below the favorable level. But, insoluble portion of the gypsum will be settled
at sub-soil layer and resulted in formation of calcareous sodic soil. Once
calcareous sodic soil condition is developed we cannot apply gypsum, in that situation we need to look for
alternate amendments. In addition to above, mined gypsum sources also keep on
declining. Based on the above, identification of suitable alternate for gypsum
or development of suitable process to increase gypsum solubility under sodic
soil condition is need of the hour.

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Keeping
this view in mind, experiments were carried out to increase the solubility of sparingly
soluble gypsum by using pressmud and aluminum sulphate. The main objective of
this study was to evolve an economically feasible and practically
viable management strategy through conjoint use of gypsum with amendments like pressmud
and aluminum sulphate, So as to hasten the solubilization of gypsum and enhance
cropgrowth under gardenland condition in a sodic soil. The experiment was
carried out in the farm at Anbil Dharmalingam Agricultural College and Research
Institute, Trichy using Vamban 2 (VBN 2) variety of greengram.

The
study included an incubation experiment, soil column leaching and a field
experiment with eight treatments. The treatments comprised of a gypsum @ 10 t
ha-1 (T1), pressmud @ 20 t ha-1 (T2), aluminium sulphate @ 2 t ha-1 (T3),
gypsum @ 5 t ha-1 + pressmud @ 10 t ha-1 (T4),
gypsum @ 5 t ha-1 + aluminium sulphate @ 1 t ha-1 (T5),
aluminium sulphate @ 1 t ha-1 + pressmud @ 10 t ha-1 (T6),
gypsum @ 2.5 t ha-1 + pressmud @ 5 t ha-1 + aluminium
sulphate @ 0.5 t ha-1 (T7) and control (T8)
for incubation and leaching experiments, which were conducted in CRD design with
three replication. The soil was sandy clay loam (Typic Ustropepts) in
texture, low in organic carbon and nitrogen and medium in phosphorus and
potassium.

For field experiment gypsum @ 6 t ha-1 (T1),
pressmud @ 20 t ha-1 (T2), aluminium sulphate @ 2 t ha-1
(T3), gypsum @ 3 t ha-1 + pressmud @ 10 t ha-1
(T4), gypsum @ 3 t ha-1 + aluminium sulphate @ 1 t ha-1
(T5), aluminium sulphate @ 1 t ha-1 + pressmud @ 10 t ha-1
(T6), gypsum @ 1.5 t ha-1 + pressmud @ 5 t ha-1
+ aluminium sulphate @ 0.5 t ha-1 (T7) and control (T8)
with recommended dose of fertilizers and also two factors were maintained
throughout the experiment viz., without seed treatment and foliar spray (F1)
and seed treatment and foliar spray at crop growth staged with 80 µM sodium
nitroprusside (F2) respectively were used. Field experiment was laid
out in FRBD (Factorial Randomized Block Design) design and replicated thrice.
The soil was sandy clay loam (Typic Ustropepts) in texture, low in
organic carbon and nitrogen and medium in phosphorus and potassium. Dose of
gypsum was given on the basis of gypsum requirement (GR), 50 % GR was followed
in T1 and remaining were half of that dose.

In
the incubation and soil column leaching study the amendments were added solely or in combination. As gypsum added with
pressmud resulted in a progressive decrease in soil pH with advancement in
period of incubation. A significant increase in the organic carbon, cation
exchange capacity and available nutrients were also observed.

In
the field experiment, combined application of gypsum and pressmud along with
recommended dose of fertilizer had a profound influence in enhancing the
availability of nutrients and reducing the soil pH at post-harvest stage. The
electrical conductivity, organic carbon and cation exchange capacity of soil
were also increased at post-harvest stage. Sodium nitropruside application as
seed treatment and foliar spray (80um) at different growth period
increased the crop growth and grain yield due to development of salt tolerance
in the plant

Application
of   gypsum along with pressmud led to
significant reduction in soil pH (9.02 to 7.85), exchangeable sodium percentage
(22.15 per cent to 14.36 percent) and also increased the nutrient availability.
This treatment (T4) also registered significantly the highest grain
yield of 695 kg ha-1, followed by T2
(660 kg ha-1) when the plant
treated with 80 µM sodium nitroprusside (F2) which differed
significantly with each other as well as the rest of the treatments. The lowest
grain yield (320 kg ha-1) was
recorded in the control (T8) which did not receive any amendments
and foliar spray of seed treatment (F1).