Rice crops uptake large amounts of potassium (K), which is mainly supplied from inorganic fertilizer. Alternate K sources are essential to preserve natural reserves and to recycle unused K containing stubbles. We have evaluated the performance of rice straw (RS) in farmers' field following integrated plant nutrient system (IPNS) for supplementing K requirement of rice and compared with agro-ecological zone (AEZ )-based chemical fertilizer and farmers' practice in Tista Meander Floodplain soils of Bangladesh during 2013-2015. Application of RS @ 4.5 t ha −1 + IPNSbased fertilizer replaced full dose of chemical K fertilizer without significant reduction in grain yield of Boro rice. The K uptake with RS incorporation was similar to AEZ-based chemical fertilizer use. Considering soil health and environmental issue, RS + IPNS-based fertilizer management was the best option for growing wetland rice. INWASCON

Proper nitrogen (N) management of high yielding rice varieties is crucial for obtaining their potential yield benefit. In this study, we compared the effect of different N rates on rice growth, yield, and N use efficiency of two high yielding rice varieties (BRRI dhan58 and BRRI dhan75) in a Boro (dry season)-fallow-T. Aman (wet season) cropping pattern. The N rates were: 0, 25, 50, 75, 100, 125, 150 and 175 kg ha −1 which were assigned in randomized complete block design with three replications. In Boro season, BRRI dhan58 showed higher response to applied N compared to BRRI dhan75 in T. Aman season. The calculated optimum N dose to maximize yield of BRRI dhan58 and BRRI dhan75 were 142 kg ha −1 and 82 kg ha −1 , respectively. The agronomic N use efficiency and fertilizer N recovery efficiency were comparatively higher in BRRI dhan58 grown in Boro season than BRRI dhan75 grown in T. Aman season, while in both seasons, the N use efficiencies decreased with increased N rates. This study results suggest that variety-specific N fertilization with respect to growing season is the best N management practice to maximize rice yield avoiding the excess use of N fertilizer.

Decomposed organic materials, in combination with plant growth-promoting bacteria (PGPB), are environmentally friendly and reduce synthetic fertilizer use in rice production. A bio-organic fertilizer (BoF) was prepared using kitchen waste (79%), chita-dhan (unfilled rice grain) biochar (15%), rock phosphate (5%), and a consortium of 10 PGPB (1%) to supplement 30% nitrogen and to replace triple superphosphate (TSP) fertilizer in rice production with an improvement of soil health. PGPB were local isolates and identified using 16S ribosomal RNA partial gene sequences as Bacillus mycoides, Proteus sp., Bacillus cereus, Bacillus subtilis, Bacillus pumilus, Paenibacillus polymyxa, and Paenibacillus spp. Isolates could fix N2 by 0.7–1.4 g kg–1, solubilize 0.1–1.2 g kg–1 phosphate, and produce 0.1–40 g kg–1 indoleacetic acid. The performance of BoF was evaluated by 16 field experiments and 18 farmers’ field demonstration trials during the year 2017–2020 in different parts of Bangladesh. Performances of BoF were evaluated based on control (T1), full synthetic fertilizer dose of N, P, and K (T2), BoF (2 t ha–1) + 70% N as urea + 100% K as muriate of potash (T3), 70% N as urea + 100% P as TSP + 100% K as muriate of potash (T4), and 2 t ha–1 BoF (T5) treatments. At the research station, average grain yield improved by 10–13% in T3 compared with T2 treatment. Depending on seasons, higher agronomic N use efficiency (19–30%), physiological N use efficiency (8–18%), partial factor productivity (PFP)N (114–150%), recovery efficiency (RE)N (3–31%), N harvest index (HIN) (14–24%), agronomic P use efficiency (22–25%), partial factor productivity of P (9–12%), AREP (15–23%), and HIP (3–6%) were obtained in T3 compared with T2 treatment. Research results were reflected in farmers’ field, and significant (P < 0.05) higher plant height, tiller, panicle, grain yield, partial factor productivity of N and P were obtained in the same treatment. Application of BoF improved soil organic carbon by 6–13%, along with an increased number of PGPB as compared with full synthetic fertilizer dose. In conclusion, tested BoF can be considered as a green technology to reduce 30% synthetic N and 100% TSP requirements in rice production with improved soil health.

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High soil temperature due to climate change may influence nutrient mineralization and soil biology. An incubation study was conducted at Bangladesh Rice Research Institute to determine the effect of temperature (28°C and 45°C) on nutrient mineralization and soil microbial population of two different soils (terrace and saline soil) having different nutrient management practices (chemical fertilizer and integrated nutrient management). Terrace soil was clay loam and saline (6 ds m-1) soil was sandy loam in texture. Total N and organic C content was significantly high in terrace soil compared to saline soil. High temperature (45°C) enhanced C mineralization by 33% in integrated nutrient management (INM) of terrace soil and 41% in chemical fertilizer treatment in saline soil. The NH 4 +-N mineralization was increased by 3 fold in saline soil at 45°C as compared to the same at normal temperature of 28°C. Temperature and nutrient management options also significantly influenced phosphorus (P) and potassium (K) mineralization. High temperature significantly enhanced P mineralization in INM compared to chemical fertilizer amendment. In terrace soil, at 28°C temperature K mineralization was high in chemical fertilizer amended soil as compared to INM treatment. Temperature and nutrient sources affected soil bacterial population significantly compared to fungi, and actinomycetes. Phosphate solubilizing bacteria (PSB) were more resistant to high temperature compared to free-living N 2 fixing bacteria. In general, high temperature and nutrient management practices affected C, N, P, K mineralization and soil biology; although mode of action varied and depending on soil types and nutrient management practices.