This work showed for the first time that organic nutrient transformation techniques based on locally available materials (manure, green waste and advanced biochar) can increase fertilizing efficiency of the resulting substrate by a factor of three compared with other organic amendments without biochar. We used three different composting methods to investigate the techniques of organic nutrient transformations; i) conventional composting (composting process completed without turning the piles) ii) aerobic composting (composting process with manual turning of piles) and iii) bokashi composting (anaerobic lacto-fermentation). Composting was carried out in the absence (compost alone) and the presence of biochar (co-composted). Biochar was produced locally from an invasive forest shrub ‘Eupatorium adenophorum’. A pot trial with maize grown in silty loam soil was carried out to investigate the agronomic effect produced using three above-mentioned composting methods that were compared with conventional mineral fertilizers (NPK). Significant effects of co-composted bokashi-biochar (60 t ha⁻¹) were observed on maize growth, which increased biomass by 243% compared to mineral NPK, also showing better growth effects than conventional and aerobic composting amendments. Improved soil available nutrients (available P and other exchangeable base cations (K⁺, Ca²⁺ and Mg²⁺)) were probably the cause of the superior growth effect of co-composted bokashi-biochar.

Reducing chemical fertilizers is critical for maintaining soil health and minimizing environmental damage. Biochar-based organic fertilizers reduce fertilizer inputs, improve soil fertility, increase crop productivity, and reduce environmental risks. In this study, a pot experiment was conducted in a greenhouse to assess the potential of biochar-based organic and inorganic fertilizers to improve soil fertility and Okra yield. Seven treatments with three replicates were arranged in a completely randomized design (CRD). Three treatments included biochar-blended formulations (i) biochar mixed with mineral NPK fertilizer (BF), (ii) biochar mixed with vermicompost (BV), and (iii) biochar mixed with goat manure (BM); two treatments included biochar enrichment formulations (iv) biochar enriched with cow urine (BCU) and (v) biochar enriched with mineral NPK fertilizer in aqueous solution (BFW), and the remaining two included control treatments; (vi) control (CK: no biochar and no fertilizers) and (vii) fertilized control (F: only recommended NPK fertilizer and no biochar). Mineral NPK fertilizers in BF, BFW, and F were applied at the recommended rate as urea, di-ammonium phosphate (DAP), and muriate of potash (MOP). Organic fertilizers in BV, BM, and BCU treatments were applied in equal quantities. All biochar-amended treatments showed improved soil chemical properties with higher pH, organic carbon, total N, and available P and K compared to the two non-biochar control plots (CK and F). Biochar blended with goat manure (BM) showed the highest effect on soil fertility and fruit yield. BM (51.8 t ha⁻¹) increased fruit yield by 89% over CK (27.4 t ha⁻¹) and by 88% over F (27 t ha⁻¹). Similarly, cow urine-enriched biochar (BCU) (35 t ha⁻¹) increased fruit yield by 29% and 28% compared to CK and F, respectively. Soil pH, OC, and nutrient availability (total N, available P, and available K) showed a significantly positive relationship with fruit yield. The study suggests that using biochar-based organic fertilizers, such as BCU and BM, could outperform recommended mineral fertilizers (F) and produce higher yields and healthy soils, thereby contributing to mitigating the current food security and environmental concerns of the country.

The optimum dose of fertilizers for crops varies with soil, agro-ecology, and crop management practices. Optimizing application dose is critical to reduce nutrient loss to the environment and increase nitrogen use efficiency (NUE), crop yields, and economic return to farmers. An experiment was conducted to determine the optimum N dose for increasing maize (Zea mays L. cv, Manakamana-3) yield, NUE, and farm profits under rainfed conditions. Five levels of N (0, 60, 120, 180, and 240 kg ha⁻¹), and a non-fertilized treatment were tested in a randomized complete block design with three replications. Effects of each treatment on yield and yield attributing traits, plant lodging and Sterility (plants with no cob or grain formation), NUE, and stay green trait of maize were recorded. Application of N above 120 kg ha⁻¹ (N120) did not have any significant effects on yield and yield components. Nitrogen, at N120 and above, produced highly fertile plants (though sterility slightly increased at N180 and N240), higher N uptake, and lower dead leaf area (18–27%). N120 produced the highest agronomic; yield increase per unit of N application (AEN—26.89 kg grain kg⁻¹ N) and physiological efficiency of N (PEN—42.67 kg grain kg⁻¹ N uptake), and net benefit (USD 500.43). Considering agronomic, economic, and NUE factors, an N dose of 120 kg ha⁻¹ was found optimum for the cultivation of rainfed maize (Manakamana-3) under sandy loam soil.

In Nepal, blanket fertilizer recommendations without considering diverse soil types, nutrient status, climate and crop management practices along with imbalanced fertilization practices by farmers, mainly “urea fertilizer,” have resulted in reduced nitrogen use efficiency (NUE) and productivity in tomato production. Optimizing the rate of nitrogen (N) fertilizer, application time and improved application methods could increase crop yields and NUE and reduce environmental costs. This study was conducted to identify the optimum N rate and application method for increased tomato yield and NUE. Multilocation trials (n = 28) conducted in a randomized complete block design with nine treatments across five districts included the omission of N, P and K (N0, P0, K0), variable N rates of 100, 150, 200 and 250 kg ha⁻¹ (N-100, N-150, N-200 and N-250), use of urea briquettes (UB) with deep placement (UBN-150) and a control (CK). N input in UB was reduced by 25% from the recommended N rate of 200 kg ha⁻¹ considering its expected higher NUE. Yield responses from an NPK omission plot revealed N as the most limiting plant nutrient. Applications of fertilizer at N-100, N-150, N-200 and N-250 increased tomato yield by 27%, 35%, 43% and 27%, respectively, over N0. Tomato yields responded quadratically to the added N fertilizers with optimum rates ranging from 150 to 200 kg ha⁻¹ across districts. UBN-150 significantly increased tomato yield by 12% over N-150 and produced a similar yield to N-200 (the recommended rate). The highest partial factor productivity of nitrogen (PFPN) was observed at N-100 and the highest agronomic efficiency of N (AEN) was at N-200. Deep placement of UB at-150 increased PFPN by 8% and 21% and AEN by 27% and 21% compared with N-150 and N-200, respectively. These results have positive implications for developing efficient N fertilization strategies to increase tomato yields and reduce environmental impacts in Nepal.

Rice is a major crop for half of the world’s population, and nitrogen (N) fertilizers play a crucial role in its production. However, imbalanced N fertilizer uses and traditional fertilization practices have led to low nitrogen use efficiency (NUE), increased N footprints, and reduced rice yields and farmers’ income. There are limited studies where the integration of both agronomic and molecular advancements to enhance NUE is discussed, particularly in developing countries. This review highlights novel agronomic and molecular strategies to enhance NUE, rice yields, and profitability, while minimizing environmental impact. The agronomic strategies include the 4R Nutrient Stewardship framework, enhanced efficiency nitrogen fertilizers (EENFs), nano-fertilizers, biochar-based fertilizers, biological N fixation, and sensor-based fertilizer management in major rice-growing countries. The molecular mechanisms focus on N uptake, assimilation, and utilization, highlighting the role of hormones, key genes, transcription factors (TFs), and regulatory pathways. Moreover, we examine promising rice genotypes and cultivars with improved NUE and grain yield. Additionally, this paper offers deep insights into recent advancements in molecular genetics, such as multi-omics approaches (transcriptomics, metabolomics, and metagenomics), the Genome-Wide Association Study (GWAS), Quantitative Traits Loci mapping (QTLs), Single Nucleotide Polymorphisms (SNPs) analysis, and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR-Cas9)-mediated genome editing, which serve as valuable tools for developing rice cultivars with enhanced NUE and grain yield.

Reduction of nitrogen (N) input in cropping systems is critical to reduce environmental pollution and achieve sustainable development goals. Multi-location field trials for maize (n = 120) and rice (n = 84) were conducted across nine districts in Nepal during 2018 and 2019 to assess the potential of polymer coated urea (PCU) and urea briquette (UB) to increase agronomic N use efficiency (AE_N), crop productivity and farm profits over conventional urea (CU). Nitrogen rates applied in PCU and UB treatments were 22% to 50% lower than CU (120 and 100 kg N ha⁻¹ for maize and rice respectively). In maize, both PCU (8.4 t ha⁻¹) and UB (8.5 t ha⁻¹) applied at 50% and 25% lower N rates respectively produced similar grain yields compared with CU (7.9 t ha⁻¹). Similar results were observed in rice where PCU and UB applied at 22% less N led to a productivity of 5.4 and 5.5 t ha⁻¹ respectively over CU (5.1 t ha⁻¹). Moreover, both PCU and UB increased maize and rice yields significantly compared with current farmer’s practices (FP). In both maize and rice, PCU and UB significantly increased partial factor productivity of N (PFP_N) and agronomic NUE (AE_N) compared with CU. Furthermore, PCU and UB increased farmer’s net income by US$88 and US$148 in maize and by US$10 and US$87 in rice respectively. These results suggest that PCU and UB could save N input by 22-50% while maintaining similar or even higher yield and higher benefit to farmers compared with CU.