| Abstract |
A study entitled “Effect of thermochemical organic fertilizer on soil carbon<br/>pools, nutrient dynamics and crop productivity in Ultisols” was conducted from 2018<br/>to 2020 at the Department of Soil Science and Agricultural Chemistry, College of<br/>Agriculture, Vellayani with the objective to study the effect of thermochemical<br/>organic fertilizer on soil carbon pools, nutrient dynamics, their retention and leaching,<br/>and crop productivity in comparison with conventional organic fertilizers in Ultisols<br/>using tomato - amaranthus cropping sequence.<br/>The study includes production and characterization of organic fertilizers,<br/>leaching study using soil columns, an incubation experiment and field experiments<br/>using tomato - amaranthus cropping sequence. For the leaching study and incubation,<br/>the treatments were addition of FYM, ordinary compost (OC), vermicompost (VC),<br/>microbial compost (MC), unfortified (TOF) and fortified thermochemical organic<br/>fertilizer (F-TOF) @ 50 g per soil column/ pot and an absolute control. For the field<br/>experiment on tomato-amaranthus cropping sequence, the treatments were T 1 – FYM<br/>+ POP recommendation of NPK, T 2 - FYM + soil test based recommendation of NPK<br/>(STBR), T 3 - OC + STBR, T 4 - VC + STBR, T 5 - MC + STBR, T 6 - TOF + STBR, T 7 -<br/>F-TOF + STBR, T 8 - F-TOF alone and T 9 - absolute control.<br/>The organic fertilizers required for the study viz., OC, VC, MC, TOF and F-<br/>TOF were produced from bio-waste from vegetable markets and food waste from<br/>college hostels and FYM was purchased. The physical and chemical properties of<br/>organic fertilizers were in accordance with the standards of FCO. VC, OC, MC and<br/>FYM were neutral to slightly alkaline in reaction while TOF and F-TOF were slightly<br/>acidic. The lignin content (27.9 %) and the carbon pools viz., TOC (43.90 %),<br/>WSOC (1642 mg kg -1 ), labile carbon (1776 mg kg -1 ) and recalcitrant organic carbon<br/>(32.45 mg kg -1 ) were highest for TOF followed by<br/>F-TOF. The N content was<br/>391highest for MC (2.61 %), P for VC (1.36 %) and K (2.56 %), Ca (1.12 %), Mg (0.78<br/>%), Zn (254 mg kg -1 ) and B (4.64 mg kg -1 ) for F-TOF while S (550 mg kg -1 ), Fe<br/>(9580 mg kg -1 ) and Pb (4.16 mg kg -1 ) for FYM. All the organic fertilizers contained<br/>Pb, but within permissible limit, while, Cd was not detected in any of them.<br/>The soil column study was conducted to assess the extent of leaching loss of<br/>nutrients from F-TOF amended soil in comparison with other organic fertilizers and<br/>their nutrient retention ability in soil. Soil columns amended with organic fertilizers<br/>in the surface layer were subjected to leaching on 1 st , 4 th , 8 th , 12 th , 16 th , 20 th and 24 th<br/>weeks with double the pore volume of water. During the leaching, the mineralized<br/>nutrients moved downwards and deposited at different depths in the soil column in<br/>accordance with their mobility and the rest was lost in leaching water. Leachates from<br/>organic fertilizer amended soils showed slightly acidic pH, which decreased up to 8 th<br/>week followed by an increase towards 12 th week. EC was highest at first week<br/>followed by a decrease towards 24 th week. The highest cumulative loss of N (172.34<br/>mg L -1 ), Ca (273.86 mg L -1 ) and Mn (3.97 mg L -1 ) was from VC while that of P (7.22<br/>mg L -1 ), K (333.36 mg L -1 ), Mg (144.41 mg L -1 ), Cu (0.080 mg L -1 ) and B (0.166 mg<br/>L -1 ) was from F-TOF. For S the loss (4.19 mg L -1 ) was highest from FYM, and Fe<br/>(4.71 mg L -1 ) and Zn (4.58 mg L -1 ) from OC. The leachate did not contain Pb and Cd.<br/>The leached soil in the soil columns maintained a higher level of nutrients<br/>compared to the level prior to the addition of organic fertilzers even after leaching for<br/>24 weeks. In the surface soil, highest quantity of total N was retained by MC; P, Mn<br/>and Cu by VC and K, Ca, Mg, Zn and B by F-TOF while FYM retained highest<br/>quantity of S and Fe. Evaluating the available nutrient status of the leached soil, it<br/>was found that F-TOF had highest availability for K, Mg, S, Fe, Zn, Cu and B.<br/>Availability of P and Mn was highest in VC amended soil and Ca from MC.<br/>Availability of Pb and Cd were not detected in the leached soil.<br/>392The incubation study for a period of 24 weeks revealed the nutrient release<br/>pattern of organic fertilizers. The peak release of most of the nutrients from organic<br/>fertilizers was from 8 th to 16 th week and for S it extended up to 20 th week. The<br/>availability of K, Ca, Mg, Fe, Zn and B was highest from F-TOF amended soil while<br/>VC maintained the highest values for P, Mn and Cu and FYM for S. The different<br/>fractions of B were highest for F-TOF amended soil and the peak was during 12 th<br/>week of incubation. Available Pb and Cd were not detected in the incubated soil.<br/>Organic fertilizers amended soil maintained a higher microbial count and exhibited a<br/>higher dehydrogenase activity compared to the control and the highest value was<br/>observed with F-TOF amended soil.<br/>During the field experiments, in the first cropping sequence, VC amended<br/>treatment T 4 (VC + STBR) recorded significantly highest fruit yield (40.97 t ha -1 ) for<br/>tomato followed by T 7 (F-TOF + STBR) while in the second cropping sequence F-<br/>TOF gave the highest yield which was statistically on par with VC. While for<br/>amaranthus, F-TOF recorded the highest yield during both the cropping sequences<br/>(24.62 t ha -1 and 26.89 t ha -1 , respectively) followed by VC and both the treatments<br/>were statistically on par in the second cropping sequence.<br/>The quality parameters of tomato and amaranthus were highest for the<br/>treatment T 7 (F-TOF + STBR) but was statistically on par with other treatments<br/>which received organic fertilizers along with POP or soil test based NPK fertilizers.<br/>Evaluating the economic benefits, the performance of VC was the best for the first<br/>tomato followed by F-TOF while for second tomato F-TOF was the best. For<br/>amaranthus, F-TOF performed best during both the sequences. When the overall B:C<br/>ratio for the whole cropping sequence was taken F-TOF was the best followed by<br/>VC.<br/>Uptake of N, P, K, Ca, Mg, S, Zn and B in tomato was highest for F-TOF<br/>while that of Fe, Mn, and Cu was for VC. For amaranthus, the uptake of N, P, K, Mg,<br/>Fe, Zn, Cu and B was highest for F-TOF for both the cropping sequences. Among the<br/>393heavy metals tested only Pb was detected in plant parts and that too in roots only. For<br/>tomato, it was detected only in FYM treated plants while in amaranthus, all the<br/>treatments receiving organic fertilizers showed the presence of Pb. But the Pb content<br/>in the root was within the safe limit. The availability of Pb in the post-harvest soil<br/>was trace and there was no significant difference between the treatments. Cd was not<br/>detected in soil as well as plant samples.<br/>The continuous application of organic fertilizers had improved the physical,<br/>chemical and biological properties of the soil. At the end of the second cropping<br/>sequence, the lowest bulk density and highest water holding capacity was recorded by<br/>the treatment receiving F-TOF + STBR. The highest value for TOC, labile carbon,<br/>microbial biomass carbon and recalcitrant organic carbon in the post-harvest soil<br/>during the cropping sequence was maintained by F-TOF. The N pools, NH 4 -N, NO 3 -<br/>N, organic N and total N at the end of second cropping sequence was also highest for<br/>F-TOF. In the case of availability of P, S, Fe, Mn and Cu in the post-harvest soil,<br/>better performance was showed by VC while F-TOF showed higher availability for<br/>K, Ca, Mg, Zn and B. Biological properties are a better indication of soil health and<br/>application of VC, MC and F-TOF maintained a higher microbial load in soil. The<br/>highest dehydrogenase activity was maintained by F-TOF. Continuous application of<br/>F-TOF and TOF increased the carbon stock of surface and sub-surface soil than other<br/>organic fertilizers.<br/>F-TOF is superior to VC, OC, MC and FYM in terms of increasing carbon<br/>pools and carbon stock of the soil. The nutrient release was highest from F-TOF for<br/>most of the nutrients compared to other organic fertilizers, which might have resulted<br/>more leaching losses. However, the nutrient retention was also highest for F-TOF,<br/>even after the leaching for 24 weeks, suggesting a revisit on the rate and mode of<br/>fortification for F-TOF, popularly marketed in the trade name “Suchitha”. For crop<br/>production, the performance of F-TOF found equally good as that of vermicompost<br/>and was superior to FYM, OC and MC. |
