MSc

The study entitled “Latex sludge waste biocompost for the management of soil
fertility and productivity” was carried out during 2021-23 at the Department of Soil
Science and Agricultural Chemistry, College of Agriculture, Vellayani. The objective of
the study was production and characterization of latex sludge waste compost; evaluation
on soil physical, chemical and biological properties and crop productivity using bush
cowpea (Vigna unguiculata L.) as test crop. The study comprised of three parts viz.,
production and characterization of latex sludge waste compost, soil incubation study for
evaluating the nutrient release pattern and field experiment for evaluating the
performance of latex sludge waste compost.
The latex sludge waste for conducting the experiment was procured from HLL,
Trivandrum. The latex sludge compost was prepared by aerobic heap method, wherein
it was mixed with bulking agents such as sawdust, cattle manure and zeolite in different
combinations as per ten treatments. To this, 5 per cent of composting inoculum was
added uniformly to all treatments. The design followed was completely randomized
design (CRD) with 10 treatments replicated thrice. The treatment combinations were
T1- Latex sludge waste + Sawdust (1:1), T2-Latex sludge waste + Sawdust + Cattle
manure (1:1:1), T3-Latex sludge waste + Zeolite (1:1), T4- Latex sludge waste + Zeolite
+ Cattle manure (1:1:1), T5-Latex sludge waste + Sawdust (2:1), T6-Latex sludge waste
+ Sawdust + Cattle manure (2:1:1), T7- Latex sludge waste + Zeolite (2:1), T8- Latex
sludge waste + Zeolite + Cattle manure (2:1:1), T9- Latex sludge waste + Zeolite +
Sawdust + Cattle manure (2:1:1:1) and T10- Latex sludge waste alone.
The physico-chemical and biological properties of the produced latex sludge
composts were analysed. Based on the analysed parameters viz., maturity of composts,
clean index, fertilizing index, available major and minor nutrients, enzyme status and
C:N ratio, four best treatments were identified. These treatments were subjected to an
incubation study and a field experiment. The selected treatments were T2, T4, T6 and T9.
Among these T9 (Latex sludge compost prepared from the mixture of latex sludge waste,
zeolite, sawdust and cattle manure in 2:1:1:1 ratio) showed highest values of nitrogen
(1.66%), phosphorus (0.96%), potassium (0.42%), calcium (3.91%), sulphur (0.61%),
iron (1876 mg kg-1), manganese (189 mg kg-1), zinc (290 mg kg-1), copper (35.36 mg
kg-1), dehydrogenase (554.86 µg TPF hydrolysed g -1 compost 24 h -1) and the lowest
value for C:N ratio (12.39). The nutrient content of T6 (Compost prepared from latex
sludge waste, sawdust and cattle manure in 2:1:1 ratio) is comparable with T9.
In part 2 of the study, a soil incubation experiment was carried out to investigate
the nutrient release pattern of selected composts. One kg of 2 mm sieved soil was taken
from the site of field experiment and incubated at field capacity for 3 months. The best
treatments selected after characterization were imposed at the surface of the soil @ 10
g kg-1 and thoroughly mixed. Soil samples were drawn at initial, 1st, 4th, 8th and 12th
weeks of incubation and analysed for evaluating the nutrient release pattern. The
treatments include four composts selected from part 1 and absolute control. From the
incubation study, it was observed that pH and EC was increased during incubation over
a period of three month. Phosphorus, potassium, calcium, sulphur, copper, organic
carbon and dehydrogenase activity were found to be maximum at 4th week of
incubation. Zinc, iron and magnesium content were observed to be maximum at 12th
week of incubation while manganese availability was maximum during 8th week of
incubation. Latex sludge waste, zeolite, sawdust and cattle manure in 2:1:1:1 ratio and
latex sludge waste, sawdust and cattle manure in 2:1:1 ratio recorded the highest values
for the available nutrient status during incubation period.
A field experiment was carried out using bush cowpea var. Bhagyalakshmi as
test crop from March to May 2023, in RBD with 7 treatments replicated thrice. In the
field experiment 7 treatments were imposed viz., T1- Latex sludge waste + Sawdust +
Cattle manure (1:1:1), T2- Latex sludge waste + Zeolite + Cattle manure (1:1:1), T3-
Latex sludge waste + Sawdust + Cattle manure (2:1:1), T4- Latex sludge waste + Zeolite
+ Sawdust + Cattle manure (2:1:1:1) and T5- FYM as per KAU POP, T6- KAU organic
POP and T7- Absolute control.
Analysis of the postharvest soil for chemical properties revealed that the highest
values for organic carbon (1.17%), available nitrogen (322.31 kg ha-1), calcium (314.39
mg kg-1), sulphur (22.72 mg kg-1), iron (39.97 mg kg-1), copper (1.82 mg kg-1), zinc
(5.26 mg kg-1) and dehydrogenase (195.23 µg of TPF hydrolysed g -1 of soil 24 h -1)
were recorded for T4. The highest value for phosphorus (96.56 kg ha-1), potassium
(268.25 kg ha-1), magnesium (57.78 mg kg-1) and manganese (25.54 mg kg-1) were
observed for T2.
Analysis of the rhizospheric soil showed the highest values of soil respiration
(30.14 mg CO2 100g -1 soil) and microbial biomass carbon (78.30 mg kg -1 soil) for T3.
T4 recorded the highest value for microbial respiratory quotient (40.15) which was on
par with T3 (38.06). Bacterial population in the rhizosphere soil was found highest for
T3 (7.79 log cfu g-1 soil), fungi in T4 (4.81 log cfu g-1 soil) followed by T3 (4.79 log cfu
g-1 soil) and actinomycetes in T2 (4.69 log cfu g-1 soil).
Application of latex sludge waste compost had significantly influenced the
biometric and yield parameters of bush cowpea. The root weight (13.5 g) and root
volume (18.67 cm3) were found to be highest in T3 which was on par with T4. The
highest number of effective nodules were noticed in treatment T4 (29.13) which was on
par with T3 and T6. T4 recorded the highest yield (7526 kg ha-1) followed by T3 and
drymatter production (4641 kg ha-1) was found highest in T4. Highest B:C ratio was
recorded in T3 (2.15).
It may be inferred that the compost produced from latex sludge waste, zeolite,
sawdust and cattle manure in 2:1:1:1 ratio had the highest values of N, P, K,
micronutrients and enzyme activity. The nutrient content of latex sludge waste with
sawdust and cattle manure in 2:1:1 ratio is comparable with latex sludge waste with
zeolite, sawdust and cattle manure in 2:1:1:1 ratio. Latex sludge waste compost
application had a positive effect on soil properties during incubation and field study.
From the study, it can be concluded that latex sludge waste, sawdust and cattle manure
in 2:1:1 ratio is economically viable and best treatment.