MSc

Biomineral enriched composts (Bokashi) – A tool for enhancing nutrient availability and enzyme activity in rhizosphere
The study entitled “Biomineral enriched composts (Bokashi) – A tool for enhancing nutrient availability and enzyme activity in rhizosphere” was carried out during 2020-22 in the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani. The objective of the study was the production and evaluation of biomineral enriched composts for enhanced nutrient availability, yield of test crop (Bhindi) and enzyme activity in the rhizosphere. The study comprised of three parts viz., production and characterization of biomineral (Bokashi) composts from different organic sources, soil incubation study for evaluating the nutrient release pattern and field experiment for evaluating the performance of the biomineral enriched (Bokashi) compost.
Bokashi composts were prepared from two substrates S1 (Aquatic weed Limnocharis flava) and S2 (Aquatic weed Limnocharis flava and banana pseudostem in 1:1 ratio). The substrates were allowed to ferment anaerobically using EM solution and the matured composts were enriched with three minerals like M1 (Calcium apatite), M2 (Epsom salt) and M3 (Sylvinite) at 2% rate in different combinations. The design followed was Completely Randomized Design with 14 treatments replicated thrice. The treatment combinations were T1 – Bokashi compost prepared from L.flava enriched with calcium apatite, T2 - Bokashi compost prepared from L.flava enriched with epsom salt, T3- Bokashi compost prepared from L.flava enriched with sylvinite, T4 –Bokashi compost prepared from 1:1 mixture of L.flava and banana pseudostem enriched with calcium apatite, T5 - Bokashi compost prepared from 1:1 mixture of L.flava and banana pseudostem enriched with epsom salt, T6 - Bokashi compost prepared from 1:1 mixture of L.flava and banana pseudostem enriched with sylvinite, T7- Bokashi compost prepared from L.flava enriched with calcium apatite and epsom salt, T8 - Bokashi compost prepared from L.flava enriched with epsom salt and sylvinite, T9 - Bokashi compost prepared from L.flava enriched with calcium apatite and sylvinite, T10 - Bokashi compost prepared from 1:1 mixture of L.flava and banana pseudostem enriched with calcium apatite and epsom salt, T11 - Bokashi compost prepared from 1:1 mixture of L.flava and banana pseudostem enriched with epsom salt and sylvinite, T12 - Bokashi compost prepared from 1:1 mixture of L.flava and banana pseudostem enriched with calcium apatite and sylvinite , T13 – Bokashi compost prepared from L.flava enriched with calcium apatite, epsom salt and sylvinite and T14 - Bokashi compost prepared from 1:1 mixture of L.flava and banana pseudostem enriched with calcium apatite, epsom salt and sylvinite. To all the treatments (T1 – T4) zeolite was added at a rate of 0.5%.
The physico-chemical and biological properties of the produced composts were subjected to analysis. Based on the analysed parameters like major and minor nutrient, enzyme activity, C:N ratio, fertilizing index the best seven composts selected for incubation study and field experiment were T2, T7 , T10, T11, T12, T13 and T14. Among these T13 (Bokashi compost prepared from L.flava enriched with calcium apatite, epsom salt and sylvinite) was selected as the best compost with the highest values of nitrogen, phosphorous, micro nutrients and enzyme activity while the lowest value of C:N ratio was also reported by T13.
In part 2 of the study a soil incubation was carried out to investigate the nutrient release pattern of selected composts. The design followed is CRD with 8 treatments which was replicated thrice. One kg soil was incubated at field capacity for four months. The treatments were T1 - Absolute control, T2 to T8 - selected best seven composts. The treatments were imposed at surface of the soil at 20 g kg-1 and thoroughly mixed. Soil sample was drawn at 1st, 4th, 8th, 12th and 16th week of incubation and analysed for organic carbon, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, dehydrogenase and cellulase activity. From the study, it was observed that nitrogen, phosphorous, potassium, calcium, sulphur, iron, copper, organic carbon and enzyme activity were found to be maximum at the 4th week of incubation. Zinc content was observed to be maximum during 12th week of incubation while magnesium content was highest during 16th week of incubation. Manganese availability was maximum during 8th week of incubation.
In part 3 of the study a field experiment was conducted from February – May 2022 with Bhindi (var. Anjitha) as the main crop and Amaranthus (var. Arun) as the residual crop. In the field experiment 9 treatments were imposed viz. T1 - Absolute control, T2 to T8 – selected best seven composts and T9¬ - KAU POP recommendation.
Analysis of postharvest soil for chemical properties revealed that the highest value of organic carbon (1.14 %) and nitrogen (319.86 kg ha-1) was recorded for T7. The highest value for available phosphorous (91.65 kg ha-1) was recorded for T8 which was on par with T6 (89.67 kg ha-1) and T7 (88.59 kg ha-1). The potassium content was found to be the highest for T6 (273.91 kg ha-1) which was on par with T8 (270.60 kg ha-1). T7 recorded the highest values of iron (48.54 mg kg-1), zinc (4.79 mg kg-1), copper (1.88 mg kg-1) and boron (0.832 mg kg-1). While manganese (25.62 mg kg-1) was reported to be the highest with regard to T8. The highest value of cellulase activity was recorded by T7 (45.53 µg glucose hydrolysed g-1 soil h-1) while T8 recorded the highest value of dehydrogenase activity (302.68 µg of TPF hydrolysed g-1 of soil 24 h-1).
Analysis of rhizosphere soil showed the highest value of microbial biomass carbon (91.14 mg kg-1 soil), glomalin (14.27 mg g-1), humic acid (9.21 %), fulvic acid (9.98), fungi (5.52 log cfu g-1), actinomycetes (5.16 log cfu g-1) and soil respiration (4.17 mg CO2 g-1) for T7 while T8 recorded highest value for bacteria (7.90 log cfu g-1).
T7 recorded the highest value for number of fruits per plant (30.67) which was on par with T5, T6, and T8. Fruit girth was found to be the highest for T7 (5.06 cm) which was on par with T6, T8 and T9. T7 also recorded the highest value for fruit length (23.81 cm), yield per plant (570.42 g) and total yield (21.05 t ha-1). The highest B: C ratio (2.26) was reported by T7. The highest yield of amaranthus (130.23 kg ha-1) was recorded for T7.
From the study, T13 (Bokashi compost prepared from L.flava enriched with calcium apatite, epsom salt and sylvinite) was concluded as the best compost. T7 (Bokashi compost prepared from L. flava enriched with calcium apatite, epsom salt and sylvinite) and T8 (Bokashi compost prepared from the 1:1 mixture of L.flava and banana pseudostem enriched with calcium apatite, epsom salt and sylvinite) recorded the highest values for the available nutrient status during incubation period like nitrogen, phosphorous, magnesium, sulphur, iron, manganese, zinc, copper, organic carbon and enzyme activity. Considering both the soil parameters and yield parameters T7 (Bokashi compost prepared from L. flava enriched with calcium apatite, epsom salt and sylvinite) was recorded as the best treatment.