Biochar addition coupled with nitrogen fertilization impacts on soil quality, crop productivity, and nitrogen uptake under double-cropping system

Biochar and inorganic fertilizer when co-applied have been reported to increase crop yield and enhance soil fertility. However, studies on this complementary effect on soil properties and noodle rice performance in China are still scanty. To investigate the effects of biochar application coupled with inorganic fertilizers on soil sustainability and yield and yield attributes of noodle rice, outdoor pot experiments were conducted in the early and late growing seasons in 2018. The treatment combinations were T-1 (B0 t/ha + N270 kg/ha), T-2 (B20 t/ha + N270 kg/ha), T-3 (B40 t/ha + N270 kg/ha), T-4 (B60 t/ha + N270 kg/ha), T-5 (B0 t/ha + N360 kg/ha), T-6 (B20 t/ha + N360 kg/ha), T-7 (B40 t/ha + N360 kg/ha), and T-8 (B60 t/ha + N360 kg/ha). The results compiled across the seasons showed an increase in Pn (net photosynthetic rate), grain yield, N uptake, gel consistency, amylose content (AC), and protein content in biochar-treated pots as compared to T-1. Average increases of 63.24, 63.66, 14.85, 58.0, 59.0, 22.39, and 2.9% were observed in soil porosity, moisture content, pH, organic carbon, total nitrogen, available phosphorus, and available potassium in T-4 over T-1 across the seasons, respectively. Root morphological characteristics such as total root length, surface area, volume, and average root diameter were significantly improved in T-3, T-4, T-7, and T-8. Starch-related enzymes such as starch branching enzyme (SBE), starch debranching enzyme (DBE), and soluble starch synthase (SSS) were not affected significantly; however, granule-bound starch synthase (GBSS), ADP-glucose pyrophosphorylase (ADPG), and starch synthesis (SS) enzyme showed higher activity in 40 and 60 t B/ha across N rates. Conclusively, biochar application of 60 t/ha along with 270 kg N/ha is a promising option for improving soil quality and increasing photosynthesis, yield, and yield attributes of noodle rice.