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Aim Biochar-based fertilizers (BBF) have gained increasing interest in recent years, yet their effects on crop productivity have not been reviewed. Methods We conducted a meta-analysis of the published literature (2011-2021) using 148 pairwise comparisons between crop productivity after additions of BBF, of conventional fertilizers (fertilized control), and a non-fertilized control. Results On average, BBF applied at very low application rates (mean of 0.9 t ha −1 ) increased crop productivity by 10% compared with fertilized controls and 186% compared with non-fertilized controls. This mean crop productivity increase is comparable to that reported when biochar is used as a soil conditioner (i.e., 15 t-30 t ha −1 to increase crop productivity by 10%). This crop yield increase suggests that biochar acts as a matrix to increase fertilizer use efficiency to a larger extent than conventional fertilizer alone. Cluster analysis revealed that BBFs have the potential to increase crop productivity by 15% when added to soils that are not responsive to conventional fertilizers. BBF produced at a highest heating temperature (HHT) of >400 °C increased crop productivity by 12% as opposed to those produced at a HHT of ≤400 °C that showed no increase. BBF with C contents >30% in the final mixture caused the largest increase in crop productivity by 17%, whereas those with C contents ≤30% had no effect. Conclusion This study has shown that biochar can be an effective constituent of novel fertilizers with enhanced efficiency, which may contribute to lower nutrient losses and lower negative environmental impacts.

Biochars are new, carbon-rich materials that could sequester carbon in soils improve soil properties and agronomic performance, inspired by investigations of Terra Preta in Amazonia. However, recent studies showed contrasting performance of biochar. In most studies, only pure biochar was used in tropical environments. Actually, there is little knowledge on the performance of biochar in combination with fertilizers under temperate climate. Therefore, we conducted an experiment under field conditions on a sandy Cambisol near Gorleben in Northern Germany. Ten different treatments were established in 72-m 2 plots and fivefold field replicates. Treatments included mineral fertilizer, biogas digestate, microbially inoculated biogas digestate and compost either alone or in combination with 1 to 40 Mg ha −1 of biochar. Soil samples were taken after fertilizer application and maize harvest. Our results show that the biochar addition of 1 Mg ha −1 to mineral fertilizer increased maize yield by 20 %, and biochar addition to biogas digestate increased maize yield by 30 % in comparison to the corresponding fertilizers without biochar. The addition of 10 Mg ha −1 biochar to compost increased maize yield by 26 % compared to pure compost. The addition of 40 Mg ha −1 biochar to biogas digestate increased maize yield by 42 % but reduced maize yield by 50 % when biogas digestate was fermented together with biochar. Biochar-fertilizer combinations increased K, Mg and Zn and reduced Na, Cu, Ni and Cd uptake into maize. Overall, our findings demonstrate that biochar-fertilizer combinations have a better performance than pure fertilizers, in terms of yield and plant nutrition. Therefore, an immediate substitution of mineral fertilizers is possible to close regional nutrient cycles.

Maize is one of the important cereal crops grown in rainfed regions of northwestern Himalayas, however, persistent use of chemical fertilizers coupled with poor soil nutrients and water holding capacity due to coarse textured soils poses serious threat to sustaining maize yield and soil health. To address these bottlenecks, a long-term experiment with application of organic manures and mineral fertilizer provides insights to quantify changes in soil organic carbon (SOC), crop yield and rain water use efficiency (RWUE) in rainfed area having low water use efficiency. A twelve years field experiment was conducted under dry sub-humid Inceptisols in northern India to study the potential impacts of organic and mineral fertilization on maize ( Zea mays L.) productivity, water use efficiency and soil quality. Ten treatments were assessed, involving different nitrogen levels (20, 30, and 40 kg N ha⁻¹) combined with 10 tha⁻¹ year⁻¹ of farmyard manure (FYM), in-situ green manure from sunhemp, and the incorporation of Leucaena leucocephala leaves at 5 tha⁻¹ year⁻¹, including an unfertilized control. Maize yield increased linearly with increasing nitrogen application rates. The combination of FYM @ 10t ha −1 and 40 kg N ha −1 (T4) yielded the highest maize production. Manure addition improved soil organic carbon (SOC) and major soil nutrients (N, P and K) while unfertilized control showed decline in soil nutrients compared to their initial values. Compared with control, incorporation of 10 t ha −1 FYM increased SOC by 1.3, 1.41, 1.44 times at application rate of 20, 30, 40 kg N ha −1, respectively. Application of N@40 kg ha −1 + 10t FYM ha −1 showed highest rain water use efficiency (RWUE) and relative production efficiency index (RPEI) (2.74 kg ha −1 mm −1 and 82, respectively) and the lowest rank sum of 6. Highly significant positive relationship existed between RPEI and RWUE, RPEI and sustainability yield index (SYI), RWUE and SYI indicated the superiority of FYM in combination with mineral fertilizer. Regression models, correlating yield with monthly rainfall and crop growing periods, indicated that the integration of FYM (10 tha⁻¹) with 40 kg N ha⁻¹ was most effective in achieving the highest relative soil quality index (RSQI) of 76 and the greatest sustainability yield index (SYI) of 49.3%. Based on results, we recommend balanced fertilization (N@40 kg ha −1 +10t FYM ha −1 ) which is easily manageable by farmers as the optimal strategy for improving soil quality and achieving sustainable maize productivity in nutrient depleted Inceptisols of northern India.

Soil water-holding capacity decreases due to long-term mineral fertilizer application. The objective of this study was to determine how replacing mineral fertilizer with maize straw affected the soil water retention curve, soil water content, soil water availability, and soil equivalent pore size. Replacement treatments in which 25% (S 25 ), 50% (S 50 ), 75% (S 75 ), and 100% (S 100 ) of 225 kg ha −1 nitrogen from mineral fertilizer (CK) was replaced with equivalent nitrogen from maize straw were conducted for five years in the Loess Plateau of China. The Gardner model was used to fit the soil water retention curve and calculate the soil water constant and equivalent pore size distribution. The results indicated that the Gardner model fitted well. Replacing nitrogen from mineral fertilizer with nitrogen from straw increased soil specific water capacity, soil readily available water, soil delayed available water, soil available water, soil capillary porosity, and soil available water porosity over time. S 25 increased field capacity and wilting point from the fourth fertilization year. S 50 enhanced soil readily available water, soil delayed available water, soil available water, and soil available water porosity from the fifth fertilization year, whereas S 25 and S 75 increased these from the third fertilization year or earlier. Soil specific water capacity, soil readily available water, soil delayed available water, soil available water, soil capillary porosity, and soil available water porosity could better reflect soil water-holding capacity and soil water supply capacity compared with field capacity and wilting point.

Nitrogen (N) supply from organic amendments [such as farmyard manure (FYM), slurries or crop residues] to crops is commonly expressed in the amendment’s Nitrogen Fertiliser Replacement Value ( NFRV ). Values for NFRV can be determined by comparison of crop yield or N uptake in amended plots against mineral fertiliser-only plots. NFRV is then defined as the amount of mineral fertiliser N saved when using organic amendment-N (kg/kg), while attaining the same crop yield. Factors known to affect NFRV are crop type cultivated, soil type, manuring history and method or time of application. We investigated whether long-term NFRV depends on N application rates. Using data from eight long term experiments in Europe, values of NFRV at low total N supply were compared with values of NFRV at high total N supply. Our findings show that FYM has a significant higher NFRV value at high total N supply than at low total N supply (1.12 vs. 0.53, p  = 0.04). For the other amendment types investigated, NFRV was also higher at high total N supply than at low total N supply, but sample sizes were too small or variations too large to detect significant differences. Farmers in Europe usually operate at high rates of total N applied. If fertiliser supplements are based on NFRV of the manure estimated at low total N supply, N fertiliser requirements might be overestimated. This might lead to overuse of N, lower N use efficiency and larger losses of N to the environment.

Mineral fertilizers and organic manure are used as soil amender to enhance the mineral status of the soil. These fertilizers contain trace metals besides providing macro and micronutrients. The present study was performed to observe the effect of mineral fertilizers, poultry manure and cow manure on trace metal content of soil and various parts (root, shoot, and grains) of maize plant (Zea mays L.). The analysis of metals was performed by atomic absorption spectrophotometer (AA-6300 Shimadzu Japan). The highest level of Pb, Fe, Ni and Cu was observed in the root as 0.36–0.55, 70.41–83.03, 4.98–7.44 and 2.94–4.43 mg kg− 1, respectively. The highest level of Cd, Zn and Mn was determined in grains as 0.44–1.59, 28.05–46.39 and 26.24–46.57 mg kg− 1, respectively. The values of all metals were found within their permissible limit given by FAO/WHO except for the Cd. The interactive use of mineral and organic fertilizers enhanced the level of trace metals in maize as compared to their sole application. In the present findings, the health risk index for all metals was less than 1 in all treatments. So, it was concluded that the level of metals in poultry manure, cow manure and mineral fertilizer treated maize did not pose any potential threat to the consumers.

Crop uptake and neglecting to apply phosphate (P) fertilizer are important reasons for P deficit in the agro-ecosystem. Recycled manure from within the system was adopted to evaluate the effects of mineral fertilizer combined with or without manure on crop yield, P budget, and P use efficiency in a continuous 20-year field trial. The experiment contained eight treatments: no fertilizer, manure (M), N fertilizer (N), N fertilizer with manure (N + M), N and P fertilizers (NP), NP fertilizers with manure (NP + M), N, P, and K fertilizers (NPK), and NPK fertilizers with manure (NPK + M). The yield and P uptake of soybean and maize increased with the sequential supplement of N, P, and K fertilizers. Application of recycled manure not only increased the yield and P uptake of crops but also reduced the inter-annual fluctuations in soybean yield. Although application of mineral P fertilizer was the main method to preserve P budget surplus and increase soil available P, recycled manure could be a positive supplement. The proportion of residual fertilizer P converted to soil available P under NP, NP + M, NPK, and NPK + M treatments was 9%, 7%, 3%, and 8%, respectively over a 20-year period. Moreover, P use efficiency in NP and NPK treatments gradually increased first and then stabilized at around 20%, but the value was obviously lower than that from manure. The results clearly demonstrated that integrated application of mineral NPK fertilizers and recycled manure was a useful method to improve crop yield and soil P fertility.

Microbial inoculants, including those formed from multiple species, may have dual functions as biostimulants and/or biocontrol agents, and claimed agricultural benefits are instrumental for regulatory categorisation. Biostimulants include commercial products containing substances or microorganisms that stimulate plant growth. Biostimulant microbes can be involved in a range of processes that affect N and P transformations in soil and thus influence nutrient availability, and N and P fertilizers can influence soil microbial diversity and function. A glasshouse experiment was conducted to investigate the effect of a multiple species microbial inoculant relative to a rock-based mineral fertilizer and a chemical fertilizer on wheat growth and yield, and on microbial diversity in the rhizosphere. The microbial inoculant was compared to the mineral fertilizer (equivalent to 5.6 kg N ha and 5.6 kg P ha ), and to the chemical fertilizer applied at three rates equivalent to: (i) 7.3 kg N ha and 8.4 kg P ha as recommended for on-farm use, (ii) 5.6 kg N ha and 6.5 kg P ha which matched the N in the mineral fertilizer, and (iii) 4.9 kg N ha and 5.6 kg P ha which matched P content in the mineral fertilizer. Despite an early reduction in plant growth, the microbial inoculant treatment increased shoot growth at maturity compared to the control. Similarly, grain yield was higher after application of the microbial inoculant when compared to control, and it was similar to that of plants receiving the fertilizer treatments. Using 16S rRNA sequencing, the microbial inoculant and fertilizer treatments were shown to influence the diversity of rhizosphere bacteria. The microbial inoculant increased the relative abundance of the phylum . At tillering, the proportion of roots colonized by arbuscular mycorrhizal (AM) fungi increased with the microbial inoculant and mineral fertilizer treatments, but decreased with the chemical fertilizer treatments. At maturity, there were no treatment effects on the proportion of wheat roots colonized by AM fungi. Overall, the multiple species microbial inoculant had beneficial effects in terms of wheat yield relative to the commercial mineral and chemical fertilizers applied at the level recommended for on-farm use in south-western Australia.

Aims This study aimed to disentangle tree-crop-fertilizer interactions in agroforestry systems, which has been suggested as an entry point for sustainable intensification of smallholder farming systems in sub-Saharan Africa (SSA). Although tree-crop systems generate multiple economic and ecological benefits, tree-crop competition commonly occurs. We hypothesized that mineral fertilizers affect facilitative and competitive interactions differently in tree-crop systems. Methods Tree-crop-fertilizer interactions were explored for wheat growing under Faidherbia albida, and maize growing under Acacia tortilis and Grevillea robusta through omission trials of nitrogen (N) and phosphorus (P) in open fields and fields under tree canopy, using a split plot design. The experiments were conducted in Ethiopia and Rwanda, replicated four times, and over two seasons. Results Our results demonstrated that the presence of F. albida significantly improved N and P use efficiencies, leading to significantly higher ( P < 0.001 ) grain yields in wheat. This tree species contributed around 64 kg ha −1  yr. −1 of mineral N. The P use efficiency of wheat under F. albida was double that of open field wheat. By contrast, G. robusta and A. tortilis trees lowered nutrient use efficiencies in maize, leading to significantly less maize grain yields compared with open fields receiving the same fertilization. Probabilities of critically low crop yields and crop failure were significantly greater for maize growing under the canopy of these species. Conclusions Our results showed that recommended fertilizer rates led to facilitative interaction only with F. albida, highlighting that fertilizer recommendations need to be adapted to agroforestry systems.

The application of organic fertilizer can improve soil fertility and maintain soil biodiversity. Soil enzyme activity can reflect the relationship between microbial nutrient demand and environmental nutrient availability. The experiment was established with a split-plot design, which included two main plots and two subplots. The main plots were 3 nitrogen levels (0, 150, 300 kg N ha −1 ). The two subplots were chemical fertilizer alone and combination of manure and inorganic application; the soil enzyme activity and chemical properties of each treatment were measured and analyzed. In the study, ecological enzyme stoichiometry was used to study the limitation of microbial resources in dryland wheat system. The results showed that the combined application of manure and chemical fertilizers did not significantly increase the activities of soil C, N and P cycling-related enzymes but decreased the activities of soil L-leucine aminopeptidase (LAP). Long-term application of organic fertilizer and mineral fertilizer significantly increased the accumulation of soil organic carbon (SOC) and nitrogen (TN) and increased soil microbial biomass (MBC, MBN). Organic fertilizer treatment significantly increased soil available phosphorus (AP) and soil NO 3 − -N contents, and decreased SOC/AP and TN/AP, but had no significant changes under different nitrogen application levels (N0, N1, N2). GHG emissions were increaseed with the amount of nitrogen applied, the addition of manure did not significantly increase the CO 2 and N 2 O emissions, and soil organic matter mineralization and gas emission fluxes decreased at ripen stage. The C-acquiring enzyme was negatively correlated with N-acquiring enzyme but positively correlated with P-acquiring enzyme. The microbial limiting effect of C and P on microbial metabolism becomes increasingly intense as the reproductive period progresses. Redundancy analysis of soil enzyme activities and chemical properties showed that soil TN and MBN could better explain the variation characteristics of soil enzyme activities. Therefore, the study of soil extracellular enzyme stoichiometry and microbial nutrient restriction can give us a more comprehensive understanding of the soil environment. There are more implications can be given under different nitrogen management modes and different growth stages. The results also provided an effective theoretical basis for regulating the changes of soil microbial environment.