Biochar is increasingly used in crop production as a fertilizer; however, its effects on nutrient cycling and stoichiometry in rice paddy soil–plant systems are unclear. We tested for effects of contrasting rates of biochar on soil and rice plant organ carbon (C), nitrogen (N), and phosphorus (P) concentrations and stoichiometry and soil physicochemical properties in early and late paddies. Overall, biochar reduced soil bulk density by an average of 7.4%, while application at 10, 20, and 40 t ha−1 increased soil C and N concentrations in early paddies by 31.6, 41.3, and 104.2%, respectively, and by 8.0, 5.0, and 21.8%, respectively; in late paddies, there were increases of 23.0, 94.1, and 117.0%, respectively, and 6.7, 15.4, and 18.0%, respectively (P < 0.05). Following biochar application at 10, 20, and 40 t ha−1, soil concentration of P decreased in early paddies by 10.9, 19.0, and 13.9%, respectively, and increased in late paddies by 4.3, 16.4, and 20.1%, respectively. Biochar increased ratios of soil C:N and C:P in early and late paddies (P < 0.05), and there was no effect on concentration and stoichiometry of soil available nutrients. Biochar reduced rice plant organ concentration of N and P in early rice and increased leaf N:P ratios. Despite the biochar application improved nutrient status in plant–soil system, we did not observe a significant increase in yield (P > 0.05). According to the N:P value of leaves between treatments, it was found that biochar alleviated the current situation of N limitation in paddy fields during the mature period and transformed the N limitation of early rice into a joint limitation of N and P. These results show that the addition of biochar to subtropical paddy soils leads to a short-term reduction in soil bulk density and increases in soil C and N concentrations and soil fertility. Thus, biochar applied at optimal rates is likely to improve the sustainability of subtropical paddy rice production.

Poultry manure (PM) has been shown to boost crop productivity. However, little is known about its favorable interactions with wood biochar (B) on sweet potato (Ipomoea batatas L.) growth and yield, and soil qualities. Hence, a 2-year field trial was conducted in the southwest Nigeria at two locations (Owo – site A and Obasooto – site B) to co-apply PM and wood B as soil amendments to boost sweet potato productivity and soil quality. The experiment consisted of a 3 × 4 factorial layout with three replications. PM and B significantly reduced soil bulk density and improved porosity and moisture content with their rate of application when compared to the control. As PM and B applications increased from 0 to 10.0 t ha−1 and 0 to 30.0 t ha−1, respectively, soil chemical properties and sweet potato growth and tuber yield increased. Co-application of 10.0 t ha−1 PM and 30.0 t ha−1 B increased tuber yield by 220% compared to treatments without PM or B. Significant synergistic interactions between PM and B were observed for all parameters. In comparison with other treatments, co-applying PM and B to sweet potato soils is a viable sustainable option for increasing sweet potato productivity and soil sustainability.

Application of biochar to rice has shown to elicit positive environmental and agricultural impacts due to its physicochemical properties. However, the relationship between greenhouse gas (GHG) emissions, rice yield, and soil nutrient status under biochar amendment remains unclear. In this study, rice yield and methane (CH4) and nitrous oxide (N2O) emissions were quantified in response to biochar application rate (0, 10, 20, and 40 t ha−1) to early and late subtropical rice cropping systems. We found that application of 10 t of biochar ha−1 to early rice reduced average CH4 emission fluxes, while all biochar application rates diminished average emissions in late rice paddy. Total global warming potential (GWP) and GHG intensity (GHGI) were inherently greater in late rice than early rice cropping. In early rice, GWP and GHGI were found to be similar between soil control, 10 and 20 t of biochar ha−1 treatments, although the largest occurred in the 40 t of biochar ha−1 treatment, whereas in late rice cropping, they were not affected by biochar application rates. Compared to the nil-biochar application, biochar application at varied rates did not affect rice yield. However, compared to 10 t biochar ha−1, increasing biochar application rate to 40 t ha−1 significantly decreased total rice yield (sum of early and late cropping). Generally, application of biochar increased soil salinity and total Fe and Fe2+ content while reducing soil bulk density. Temporal effects of biochar application were noted on CH4 emission flux, soil temperature, and soil Fe2+ and Fe3+ in early rice; and soil temperature, salinity, NH4+-N, NO3−-N, and soil Fe2+ and Fe3+ in late rice. This study confirms that the application of biochar at the lower rate of 10 t ha−1 is optimal for maintaining rice yield while reducing GHG emissions. Moreover, the study demonstrates the potential benefit of biochar in sustainable subtropical rice production.

During 2015 and 2016, studies were conducted at Absaraka and Dickinson, North Dakota to evaluate the impacts of hemp (applied at 1156 m3 ha−1) and commercial paper mulch, as well as soil-applied biochar (applied at 11.25 m3 ha−1), on weed suppression and strawberry growth during the establishment year, and on weed suppression and strawberry yield during the production year, in a matted row production (MRP) system. During 2015, biochar influenced dry weed biomass only within the hemp mulch, with slightly more weed biomass associated with biochar application compared to zero biochar (3.1 vs 0.4 g m−2), suggesting that biochar may have increased weed germination and/or emergence from beneath hemp mulch. Biochar application also slightly increased soil pH, from 6.9 in non-amended soil to 7.0 in amended soil. Strawberry runner number during 2015 was greater in association with hemp or paper mulch compared to zero mulch (4.5 and 4.9 vs 2.4 runners plant −1, respectively). This result mirrored a similar differential in per berry mass across sites (7.6 and 7.4 vs 6.2 g berry −1 for hemp mulch, paper mulch and zero mulch, respectively). These results may be related to hemp and paper mulch reducing maximum soil temperatures during summer 2015. During the establishment year, both hemp and paper mulch suppressed weeds well compared to zero mulch, although at Absaraka hemp mulch provided slightly better weed suppression than paper mulch. During the production year, both mulches continued to suppress weeds compared to zero mulch at Dickinson. However, at Absaraka, only hemp mulch provided weed suppression compared to zero mulch, possibly because of faster paper degradation caused by greater numbers of large precipitation events and greater relative humidity at Absaraka compared to Dickinson. Weeds were removed from plots during 2015 to allow separation of weed suppression from other possible mulch impacts; therefore, yield data do not reveal striking differences among mulch treatments. Because previous research has demonstrated the impact of weed management during the establishment of strawberries in a matted row system, we concluded that hemp mulch may provide more durable weed suppression compared to paper mulch, which would increase strawberry yield protection in an MRP system. Material cost may be an issue for implementing hemp mulch, as hemp hurd cost was 25 times paper mulch at the application rates used in this study. However, hemp mulch could still be a beneficial option, especially for organic strawberry growers desiring a renewable and environmentally sound replacement for plastic mulch who are able to find affordable local sources of this material.

Use of biochar (B) and poultry manure (PM) as soil amendments can improve the productivity and sustainability of tropical agriculture. Our fieldwork is the first research on the agronomic use of B and PM for the growth of cocoyam in sandy soil of the humid tropics. In this study, the effects of B, PM and their mixture were investigated on soil properties, mineral and nutrient concentrations, growth, and corm and cormel yields of cocoyam during the 2017 and 2018 cropping seasons. The experiment consisted of 4 × 2 factorial combinations of B (0, 10, 20, and 30 Mg ha−1) and PM (0 and 7.5 Mg ha−1). In both years, the application of B and PM either alone or in combination improved soil physical and chemical properties, plant nutritional status, growth, and corm and cormel yields of cocoyam. The combination of 30 Mg ha−1 B and 7.5 Mg ha−1 PM (B30 + PM7.5) gave the highest corm and cormel yields of cocoyam. Pooled over the 2 years, application of B at 30 Mg ha−1 and PM at 7.5 Mg ha−1 (B30 + PM7.5) significantly increased corm yield of cocoyam by 47 and 66%, respectively, when compared with sole PM at 7.5 Mg ha−1 and B at 30 Mg ha−1. Lowest corm and cormel yields were obtained for the unmanure control. The combination of 30 Mg ha−1 B and 7.5 Mg ha−1 PM is recommended for soil fertility management and cocoyam production in the rainforest agroecology of SW Nigeria.

Biogas digesters convert waste matter into a natural gas-like fuel and a nutrient-rich digestate by-product. This digestate has the potential to be used as a soil amendment to benefit crop production with or without biochar, a purported nutrient sponge. In a greenhouse study of several crop species, the effects of digestate fertilization on crop growth, photosynthetic efficiency, vegetable production and chemical nutrient levels were tested. Results indicate that increasing potency of the applied digestate fosters higher growth and fruit production rates of several studied plants but to a lesser degree than a conventional fertilizer. More potent digestate application increases antioxidant capacity, total phenolics content and ascorbic acid levels in kale compared to the control chemical fertilizer test groups but has confounding results on legume nutrient levels. Additionally, the combined application of biochar and biogas digestate added to compost and used as potting media positively impacts crop germination. This work has relevance to agrarian communities that could benefit from recycling livestock and food waste into fuel and a renewable fertilizer.

Biochar has received attention due to its potential for mitigating climate change through carbon sequestration in soil and improving soil quality and crop productivity. This study evaluated the effects of rice straw biochar (RSB) and rice husk ash (RHA) each applied at 5 Mg ha−1 and four N levels (0, 40, 80, and 120 kg ha−1) on soil fertility, growth, and yield of rice and wheat for three consecutive rice–wheat rotations. RSB significantly increased electrical conductivity, dehydrogenase activity, and P and K contents when compared to control (no amendment) up to 7.5 cm soil depth. Both RSB and RHA did not influence shoot N concentration in wheat plant but significantly increased P and K concentrations at 60 days after sowing. Grain yields of both rice and wheat were significantly higher in RSB as compared to control (no amendment) and RHA treatments. While the highest grain yields of rice and wheat were observed at 120 kg N ha−1 in RHA and no biochar-treated plots, a significant increase in grain yields was observed at 80 kg N ha−1 in RSB treatment, thereby saving 40 kg N ha−1 in each crop. Both agronomic and recovery N efficiencies in rice and wheat were significantly higher in RSB-amended soil compared to control. Significant positive correlations were observed between soil N, P, and K concentrations and total N, P, and K concentrations in aboveground biomass of wheat at 60 days after sowing. This study showed the potential benefits of applying RSB for improving soil fertility and yields of rice and wheat in a rice–wheat system.

Amendment of recalcitrant organic materials with high carbon/nitrogen (C/N)-ratio may improve and maintain soil labile C for a longer period, thus enhancing the productivity of soils with low fertility; however, immobilization of N may affect the plant growth negatively. To reduce the negative impacts, recalcitrant organic materials can be pre-incubated with N-rich sources or applied in combination with fertilizers. The current study evaluated sawdust biochar (BC) and pre-incubated cattle manure–sawdust mixture (CS) amendments with synthetic fertilizers in improving soil carbon pool, soil fertility and maize (Zea mays L.) yield on a tropical Alfisol. Four treatments: control, site-specific fertilizer (SSF), site-specific fertilizer with sawdust biochar (BC + SSF) or pre-incubated cattle manure-sawdust mixture (CS + SSF), were evaluated for two seasons with maize. The residual effect was evaluated in the third season. During the year of active C application, lability index, C management index and potentially mineralizable N were significantly greater in CS + SSF than BC + SSF treatment. However, the same indices measured in the third season with no further application of amendments were significantly greater in BC + SSF than in CS + SSF treatment, indicating an increase in more recalcitrant C pool with BC amendment. Application of organic amendments improved soil fertility parameters compared with the application of fertilizer alone. Maize yield was significantly increased by fertilizer, with or without organic amendments; with significantly greater yield in BC + SSF than other treatments. Results suggest that soil amendment with BC had greater potential to improve the soil carbon pool and maintain labile carbon for a longer period than a pre-incubated CS.

Pyrolized carbon in biochar can sequester atmospheric CO2 into soil to reduce impacts of anthropogenic CO2 emissions. When estimating the stability of biochar, degradation of biochar carbon, mobility of degradation products, and ingress of carbon from other sources must all be considered. In a previous study we tracked degradation in biochars produced from radiocarbon-free wood and subjected to different physico-chemical treatments over three years in a rainforest soil. Following completion of the field trial, we report here a series of in-vitro incubations of the degraded biochars to determine CO2 efflux rates, 14C concentration and δ13C values in CO2 to quantify the contributions of biochar carbon and other sources of carbon to the CO2 efflux. The 14C concentration in CO2 showed that microbial degradation led to respiration of CO2 sourced from indigenous biochar carbon (≈0.5–1.4 μmoles CO2/g biochar C/day) along with a component of carbon closely associated with the biochars but derived from the local environment. Correlations between 14C concentration, δ13C values and Ca abundance indicated that Ca2+ availability was an important determinant of the loss of biochar carbon.

Biochar and vinasse are by-products of biofuel production that can be used as soil amendments. However, their addition to the soil might affect PRE herbicide activity. Although studies have shown that biochar has a high herbicide adsorption capacity, there is little information available about biochar effect on weed control especially under field conditions. Therefore, the objective of this study was to determine the influence of biochar and vinasse application on atrazine and pendimethalin availability and herbicide activity under in vitro and field conditions. In vitro atrazine and pendimethalin herbicidal activities were not influenced by vinasse addition, but biochar application reduced atrazine and pendimethalin injury for all evaluated species. A sorption experiment confirmed high affinity of biochar for atrazine and pendimethalin. Linear regression analysis showed that the slope for atrazine and pendimethalin adsorption was 16 and 4 times higher in soil with biochar than in soil alone. Under field conditions, biochar at 0.5 kg m−2 reduced atrazine and pendimethalin weed control 75% and 60%, respectively. These results suggested that the use of biochar as a soil amendment in cropping system could decrease PRE herbicide efficacy. Therefore, mitigating practices such as the use of higher rates or reliance on POST herbicides and cultivation might be necessary to ensure proper weed control.

Vinasse and biochar are by-products of biofuel production that can be used as sources of nutrients to crops or soil amendments to improve soil quality. Despite the recent interest in biochar and vinasse effects on soil properties, little is known about their effect on weed communities. We hypothesized that the addition of biochar and vinasse to the soil could affect weed seed germination and growth, and that different weed species would show different responses to these soil amendments. Therefore, the objectives of this study were to determine the effects of vinasse and biochar on the germination and growth of Palmer amaranth, sicklepod, and southern crabgrass. The study was conducted under laboratory and growth chamber conditions. Treatments consisted of four levels of vinasse (0, 10, 20, and 40 L m−2) and biochar (0, 0.5, 2.5, and 12.5 kg m−2) applied to a sandy loam soil. Biochar at 0.5 and 2.5 kg m−2 increased germination of Palmer amaranth but had no effect on sicklepod and southern crabgrass. Vinasse reduced germination of all species. However, sicklepod germination was less affected by vinasse at 10 and 20 L m−2 than the other two species. Vinasse at 40 L m−2 decreased Palmer amaranth, southern crabgrass and sicklepod germination 57, 26 and 87%, respectively. Biochar had no consistent effect on the vegetative growth of the species studied. Vinasse at 10 L m−2 stimulated growth of sicklepod and southern crabgrass compared to the nontreated control. Our results suggested that vinasse used as a soil amendment could affect weed community structure by decreasing germination of susceptible species, but plants and weed species that can get established in vinasse amended soils might show higher growth rates.

Yellow rattle is a hemiparasitic weed that is becoming increasingly problematic in hay fields in the northeastern United States. The biomass of yellow rattle was assessed in two experiments in which commercially available soil amendments were applied to an infested hay field under no-till management. The amendments were applied in the fall of 2010 and 2011 and included wood ash, biochar, hardwood sawdust, lime, and K. Wood ash applied at a rate of 8,967 kg ha−1 (4 tons per acre) had the greatest suppressive effect and reduced yellow rattle biomass the following summer by 86 and 92% relative to the untreated control in Experiments 1 and 2, respectively. Two additional treatments included in Experiment 2, a doubled rate of wood ash and sawdust applied at a rate of 13,450 kg ha−1, also reduced yellow rattle biomass. No other treatments affected yellow rattle biomass. A partial least-squares regression (PLSR) analysis that included aboveground plant community and soil biochemical data explained only 42.4% of the variation in yellow rattle biomass, suggesting that the mechanisms responsible for the suppression of yellow rattle by wood ash and sawdust are complex. Amending hay fields with wood ash or sawdust may be an effective nonherbicide strategy for managing yellow rattle infestations. Additional research will be required to determine the mechanisms and generality of yellow rattle suppression by wood ash and sawdust amendments to the soil.

Converting biomass to charcoal produces physical and chemical changes greatly increasing environmental recalcitrance, leading to great interest in the potential of this carbon form as a long-term sequestration strategy for climate change mitigation. Uncertainty remains, however, over the timescale of charcoal’s environmental stability, with estimates varying from decadal to millennial scales. Uncertainty also remains over charcoal’s effect on other aspects of carbon biogeochemical cycling and allied nutrient cycles such as nitrogen. Radiocarbon is a powerful tool to investigate charcoal mineralization due to its sensitivity; here we report the results of a study using 14C-dead charcoal (pMC=0.137±0.002) in organic-rich soil (pMC=99.76±0.46), assessing charcoal degradation over 55 days of incubation. Using this method, we discriminated between decomposition of indigenous soil organic matter (SOM) and charcoal by microorganisms. SOM was the major source of carbon respired from the soil, but there was also a contribution from charcoal carbon mineralization. This contribution was 2.1 and 1.1% on days 27 and 55, respectively. We also observed a negative priming effect due to charcoal additions to soil, where SOM mineralization was repressed by up to 14.1%, presumably arising from physico-chemical interactions between soil and charcoal.