Microbiome and nutrient dynamics of organic manures for precision <scp>NPK</scp> management in sunflower (<i>Helianthus annuus</i> L.)

Abstract Organic manure plays an important role in soil fertility, microbial communities and sustainable agricultural strategies. In organic cultivation of crops, manures are mostly used without any calculation of the nutrients added to soil through their application. The quantities of nutrients supplied by the organic manures to the crop have to equalize the quantity of nutrients supplied by inorganic chemical fertilizers, in order to replace chemical fertilizers in organic farming. Since the organic manures release nutrients slowly into the soil over a period of time, the availability of nutrients to the standing crop requires precise estimation. In the present study, the amount of nutrients available in the soil as well as in all the manures was calculated. Moreover, the study included metagenomic analysis of different organic manures used by farmers and gives an insight to the role the microbiome plays in plant growth. Using a formula of STCR‐IPNS (soil test crop response integrated plant nutrition system), the quantities of different combinations of organic manures required to supply nitrogen, phosphorus and potassium (NPK) to sunflower plants were calculated. Organic manure combinations using animal bone meal, neem cake, farmyard manure and vermicompost recorded better growth and yield responses in sunflower plants compared to inorganic chemical fertilizers. Based on the estimation of NPK in the individual manures and in the soil, pot experiments were carried out to understand the effect of organic manures as well as inorganic fertilizers in the vegetative and reproductive growth of sunflower.