MSc

The present study entitled "Effect of phosphorus solubilizers on the
availability of native P in phosphorus rich soil" ‖ was carried out in the Department of
Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani during
2017-’18. The study was envisaged to evaluate the effect of phosphate solubilizers on
the solubility and availability of native phosphorus and its impact on crop growth and
yield of test crop tomato var. Vellayani Vijai.
The experiment was laid out in a randomized block design with fourteen
treatments and three replications viz. KAU POP (T1), 75% P + PSB (T2), 75% P
+AMF (T3), 75% P + Psuedomonas fluorscences (T4), 50% P + PSB (T5), 50% P +
AMF (T6), 50% P + P. fluorscences (T7), 25% P + PSB (T8), 25% P + AMF (T9),
25% P + P. fluorscences (T10), PSB (T11), AMF (T12), P. fluorscences (T13), Absolute
control (T14).
From the study, it was observed that a significant increase in soil pH from the
initial value of 4.5 was noticed in all the treatments except the control plot. The
highest pH value of 5.2 was recorded by the treatment T9 (25% P +AMF). The
treatments imposed no significant difference with respect to the electrical
conductivity, organic carbon, organic matter and available nitrogen content.
However, the treatment T4 (75% P + P. fluorscences) registered the highest value for
organic carbon (1.11%) and organic matter content (1.91%) and T6 for available N
content (282 kg ha -1). The analysis of the data indicated that available K content in
soil was significantly influenced by the application of P solubilisers with the highest
value recorded for the treatment T4 (162.33 kg ha-1) .
Application of 75% P +AMF (T3) recorded the highest value for available
phosphorus (111.52 kg ha -1). It was also, observed from the study that the available P
increased to the maximum at 3 months after planting (MAP) and decreased at 4
MAP. The analysis of data on available micro nutrients revealed that the treatments
had significant influence on available Zn content with the highest value recorded by
T9 (4.67 mg kg-1) whereas the effect was non-significant with respect to available Fe,
Mn and Cu content. Exchangeable aluminium and hydrogen content of soil tends to
decrease at harvest stage. The treatment T10 registered the lowest values of 0.073
cmol (H+) kg-1 and 0.266 cmol (Al+3) kg-1 for H+ and Al+3 respectively.
The analysis of different P fractions revealed that Al-P, Fe-P, occluded P and
reductant soluble P decreased over a period of 4 months while Ca-P and saloid P
fractions increased. The highest values were recorded by the treatments T13 (182.6 kg
ha-1), T6 (123.52 kg ha-1), T9 (41.43 kg ha-1), T14 (45.2 kg ha-1), T14 (32.33 kg ha-1),
T3 (8.22 kg ha-1) for Al-P, Fe-P, Ca-P, occluded P, reductant soluble P and saloid P
respectively.
Studies on enzyme activities and microbial population revealed a positive
influence of P solubilisers. Activities of major soil enzymes viz dehydrogenase,
urease, acid phosphatase and alkaline phosphatase showed an increased trend and
reached the maximum at the final stage of crop growth (harvest stage).The treatments
T11 (58.89 μg of p-nitrophenol released g-1 ) and T9 (9.95 μg of p-nitrophenol released
g-1) registered highest value for acid phosphatase and alkaline phosphatase activity
respectively. The highest value for dehydrogenase and urease were observed in T3
and T6 treatments with mean values of 336.7 μg of TPF released g-1 soil 24 h-1 and
69.45 ppm of urea hydrolysed g-1 of soil 24 h-1 respectively. The highest values for
microbial biomass carbon (380 μg g-1 soil) and microbial biomass phosphorus (71.83
μg g-1 soil) were observed in treatments T9 and T5 respectively. With respect to the
population P solubilisers (microbial load), the highest value was noticed in treatment
T6.
Application P fertilizer along with P solubilisers has improved the plant
characters like no of primary branches, days to 1st flowering and no of fruits. The
treatment T2 registered the highest no of fruits (36 / plant). The treatments did not
impose any significant effect on fruit characters like TSS (%) and Vitamin C content.
While the highest values for lycopene (12.33 μg g-1) and beta carotene (382.60 IU)
were observed in treatments T5 and T2.
The highest fruit yield (1.52 kg/plant) and dry matter yield (84.80 g/plant) of
test crop, tomato was noticed with the application of treatment T3. This was found to
be on par with treatment T4 with an average fruit yield of 1.49 kg/plant yield and dry
matter yield of 81.80g/plant. The treatment T3 recorded highest values for P content
in fruits (0.67%), shoots and roots (0.45%) and total uptake of P (38.89 kg ha-1).
Similarly the highest B: C ratio was recorded in the treatment T3 indicating the
superiority of T3 (1.72) over the other treatments.
Correlation studies revealed a significant positive correlation between
available phosphorus and yield (r= 0.89**), available P and saloid P fraction
(r=0.918**), alkaline phosphatase activity and pH (r=0.936**), dehydrogenase and
organic carbon (r=0.672**), urease activity and organic carbon (r=0.701**). From the
study it was observed that microbial load is positively correlated with acid
phosphatase activity (r=0.793**), alkaline phosphatase activity (r=0.545*) and urease
activity (r=0.604*).
It is evident from the study that treatments T3 (75%+AMF), T4 (75% P +
Psuedomonas fluorscences), and T6 (50%+AMF) were superior among the
treatments. But considering the available P content, P fractions, plant yield, P uptake
and B : C ratio, the treatment T3 (75%+AMF) was considered as the best treatment.