Rhizophere dynamics of thermochemical organic fertilizer fortified with nitrogen biosources in amaranthus

Abstract

A study entitled “Rhizosphere dynamics of thermochemical organic fertiliser fortified with nitrogen biosources in amaranthus” was conducted from December 2020 to August 2021 at the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani with the objectives of studying the dynamics of physicochemical and biological soil health parameters of the rhizosphere against root free soil consequent to the application of thermochemical organic fertiliser fortified with various organic nitrogen sources with and without arbuscular mycorrhizal fungi (AMF) and evaluation of its influence on the growth and yield of amaranthus. Characterization of farm yard manure (FYM), poultry manure (PM), neem cake (NC), vermicompost (VC), coir pith compost (CPC), organic nano NPK (nano NPK), and thermochemical organic fertiliser (TOF) were carried out. The pH of manures was slightly acidic to neutral, and the EC was within safe ranges. TOF had the highest TOC. PM recorded the highest N and nano NPK recorded significantly higher P and K. Zn, Cu and B were also the highest in nano NPK. TOF had higher Ca, Mg, S, Fe, Mn. Heavy metals (Pb, Cd) were below detectable limits. A pot culture trial of Amaranthus (var. Arun) was done to study the dynamics of the physicochemical and biological soil health parameters of the rhizosphere as against root free soil. Potting mixture was prepared with soil, coir pith (CP) and TOF fortified with nitrogen bio sources so as to provide 1 per cent nitrogen and also fortified with organic nano NPK at 0.1 per cent N in the ratio 1:1:1 on volume basis. TOF was fortified with different organic nitrogen sources for a pot culture study for 30 days in a CRD experiment. The pH of the growing media decreased slightly at harvest, whereas EC increased. Carbon fractions and nitrogen fractions were highest in TOF+PM +AMF while there was a general decrease in both the parameters in all the treatments at the harvest stage compared to the initial. P, K, Ca, S, Zn, B content were higher in TOF+NPK +AMF whereas Mg and Cu were higher in TOF+PM +AMF. Fe and Mn remained significantly different at rhizosphere zone only. In all the treatments rhizosphere soil observed lower soil nutrient content than the bulk soil. Biological properties such as dehydrogenase activity, microbial biomass carbon, 175 indole acetic acid, total organic acids were higher in TOF+PM +AMF. The shoot and root nutrient contents of TOF+NPK+AMF were higher than other treatments. TOF+NPK+AMF was also superior in number of primary branches, shoot weight and shoot dry matter content. Plant height was higher in TOF+FYM+AMF whereas stem girth was higher in TOF+NC. TOF+VC+AMF recorded highest root weight (104.07g plant-1 ), root dry weight (13.01plant-1 ) whereas root volume (63.33cm3 ), total root length (31.66 cm) was highest with TOF+CPC+AMF. Three best treatments from the pot culture study were subjected to field testing in micro plots to evaluate the influence of the fortified TOF on the soil health and growth and yield of amaranthus (var. Arun) for two seasons (C1, C2) in RBD. Field soil had strongly acidic pH, safe EC, medium OC, low N, K, high P, inadequate Ca, Mg, S and B. After the harvest of each crop, the soil pH progressively decreased whereas EC and OC increased. Soil available nitrogen was higher in TOF+NPK+AMF@OPOP100 %. P, K, S, Fe, Cu and B contents were highest in TOF+NPK+AMF@OPOP100 %. Soil available Ca and Mg was on par with TOF+VC@OPOP100 % in C2. Mn and Zn in C2 was higher in TOF+NPK+AMF@OPOP100 %. Plant shoot N, P, K, Ca, Mg, S and micronutrients were the highest in TOF+NPK+AMF@OPOP100 %. At C2 shoot Ca was on par with TOF+VC@OPOP100 %. Root N, P, K, Ca, Mg, S and micronutrients were highest in TOF+NPK+AMF@OPOP100 %. TOF+NC+AMF@OPOP100 % recorded highest root N in C2. TOF+VC@OPOP100 % recorded the highest earthworm number in C1 and C2. Micro arthropod counts were the highest in TOF+NPK+AMF@OPOP100 %. Dehydrogenase activity and microbial biomass carbon (MBC) of TOF+NPK+AMF@OPOP100 % in C1and C2 were significantly higher than other treatments. B:C ratio was highest for TOF+NPK+AMF@OPOP100 % (1.57). TOF fortified with various nitrogen bio-sources enhanced soil organic carbon and possessed comparable fertility value as conventional organic manures and is environmentally safe since heavy metal content is below detectable levels. Fortification of thermochemical organic fertilizer facilitated efficient root dynamic characters coupled with proliferation of rhizospheric microorganisms, which favoured enhanced mineralisation of soil available nutrients and root nutrient acquisition. TOF fortified with nano NPK is an effective and efficient substitute for conventional organic manures and help in realising higher productivity and profitability in amaranthus.