Planting methods and nitrogen effects on crop yield and soil quality under direct seeded rice in the Indo-Gangetic plains of eastern India

A field trial was conducted during the kharif (rainy) seasons of 2002 and 2003 at the Research Farm, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, India. The trial was carried out to study the effect of planting methods, sources and levels of nitrogen on soil properties, yield and NPK uptake by rice (Oryza sativa L.) under direct seeded condition. Planting methods significantly influenced the physical, chemical and biological properties of soil. Bulk density (1.385gcm⁻³), organic carbon (0.43%) and soil moisture content (15.46%) were higher in zero till seeding plots than rotavator and conventional seeding. However, infiltration rate, soil temperature, pH and electrical conductivity showed a declining trend under this treatment and were found maximum (11.54mmh⁻¹, 36.21°C at 55 DAS, 30.65°C at harvest, 7.59 and 0.47dsm⁻¹) with conventional seeding. The maximum population of bacteria (25.60×10⁵), fungi (14.26×10⁴) and azotobactor (10.19×10³) were found in the plot with zero till seeding while in case of actinomycetes the highest population (25.61×10⁵) was found in conventional seeding. Nitrogen sources as well as levels failed to bring about any significant change in the soil properties. The highest grain (3825kgha⁻¹) and straw yields (5446kgha⁻¹) and N, P, K uptake were recorded in conventional seeding and were found significantly superior to zero till seeding (3144kgha⁻¹) but it remained at par with rotavator seeding (3585kgha⁻¹). Among the nitrogen sources, neem (Azadirachta indica) coated urea produced significantly higher grain (3761kgha⁻¹) and straw yields (5396kgha⁻¹) with greater NPK uptake than prilled urea and prilled urea+spent mentha. (The distillation waste of mint (Mentha arvensis) herbage is known as spent mentha.) Application of 150kgNha⁻¹ produced maximum grain (3828kgha⁻¹) and straw yields (5460kgha⁻¹) although it remained at par with 100kgNha⁻¹ (3738 and 5393kgha⁻¹).