The role of soil organic matter (SOM) in agricultural systems has been widely studied in conjunction with the potential for greenhouse gas mitigation. However, the link between SOM accumulation in ...croplands, crop productivity and yield stability has not yet been clearly established. In this paper, we collected data on provincial yearly crop productivity (yields, total cropland area) during 1949–1998 and the average SOM contents in croplands sampled and determined from the National Soil Survey in 1979–1982 of mainland China. The cereal productivity was assessed both with an overall mean of 1949–1998 and with the mean values for different time periods within this overall time, respectively. The yield variability within a single stabilizing stage, and between the fluctuating years, was calculated as a negative measure of yield stability. The correlation between SOM and cereal productivity was very significant for most provinces, but the relationship has become less significant as we approach the present. Moreover, the average yield variability was very significantly and negatively correlated with the cropland SOM level. The findings support our previous hypothesis from case studies, that C sequestration in China's croplands may provide win–win benefits, by enhancing crop productivity and stabilizing yield. This offers a sound basis as a greenhouse gas mitigation strategy by promoting C sequestration in croplands, and enhancing food security in China's agriculture.
Understanding how to manage N inputs to identify the practices that maximize N recovery has been an organizing principle of agronomic research. Because growth in N fertilizer inputs is expected to ...continue in an ongoing effort to boost crop production over coming decades, understanding how to efficiently manage recovery of fertilizer N will be important going forward. Yet synthesis of published data that has traced the fate of 15N‐labeled fertilizer shows that less than half of the N taken up by crops is derived from current‐year N fertilizer. The source of the majority of N in crops is something other than current‐year fertilizer and the sources are not really known. This is true for maize (only 41% of N in crops was from current‐year N fertilizer), rice (32%), and small grains (37%). Recovery of organic fertilizer N (manure, green manure, compost, etc.) in crops is low (27%), though N recovery in subsequent years (10%) was greater than that for mineral fertilizers. Thus, while research on efficiency of N fertilizer use through improved rate, type, location, and timing is important, this research fails to directly address management of the majority of the N supplied to crops. It seems likely that the majority of non‐fertilizer N found in crops comes from turnover of soil and crop residue N. We encourage the research community to revisit the mental model that fertilizer is a replacement for N supply from turnover of soil organic N (SON) and consider a model in which N fertilizer augments ongoing SON turnover and makes an important longer term contribution to SON maintenance and turnover. Research focused on the efficient recovery of N current‐year fertilizer inputs neglects this potential role for building soil N and managing soil N turnover, which seems likely to be the most important source of crop N.
We synthesized 15N fertilizer studies and integrated these with other N budget data to better understand the source of the N found in cereal crops. Most crop N comes from a source other than current year's fertilizer. We believe that research focused on the efficient recovery of N current‐year fertilizer inputs neglects the role for building soil N and managing soil N turnover, which seems likely to be the most important source of crop N.
The use of biochar as a soil amendment had been increasingly advocated for its effects on carbon sequestration and greenhouse gas emission mitigation as well as on improvement of soil fertility. ...However, lack of a general assessment of biochar effects on soil physical properties made it difficult for the recommendations for its practical use for soil quality improvement in global agriculture. In this study, we performed a meta-analysis of literature data published by October 2015 and quantified biochar effects on selected soil physical properties. The literature data covered a range of feedstocks, pyrolysis temperature, soil and experimental conditions. Results showed that biochar amendment significantly improved all the soil physical properties tested. On average, soil bulk density was significantly reduced by 7.6% whereas soil porosity significantly increased by 8.4%, aggregate stability by 8.2%, available water holding capacity (AWC) by 15.1% and saturated hydraulic conductivity by 25.2%. Furthermore, the changes in soil bulk density were negatively correlated to porosity and AWC. In addition, these effects were greater in coarse textured soils than in fine textured soils. While the size of biochar effect on soil physical properties varied with the amount of biochar added, changes in bulk density only was correlated to application rates of crop residue and wood biochar. Overall, biochar amendments could likely improve soil hydrological properties though varying with biochar and soil conditions. Use of biochar thus could offer a viable option to improve moisture storage and water use efficiency for soils poor in organic carbon in arid/semiarid zones. More studies on dynamics of soil hydrological behaviors following biochar amendment should be deserved in field conditions for a sound understanding of biochar's potential in world agriculture.
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•Biochar effect on soil physical properties was quantified using meta-analysis.•Biochar exerted significant improvements on soil physical properties.•Greater effect size was found for Ksat and AWC than on bulk density, porosity and MWD.•Greater effect size was exhibited in coarse-textured soils than in fine-textured soils.•Application rate and bulk density change correlated for crop residue and wood biochar.
BACKGROUND AND AIMS: For the last decade, there has been an increasing global interest in using biochar to mitigate climate change by storing carbon in soil. However, there is a lack of detailed ...knowledge on the impact of biochar on the crop productivity in different agricultural systems. The objective of this study was to quantify the effect of biochar soil amendment (BSA) on crop productivity and to analyze the dependence of responses on experimental conditions. METHODS: A weighted meta-analysis was conducted based on data from 103 studies published up to April, 2013. The effect of BSA on crop productivity was quantified by characterizing experimental conditions. RESULTS: In the published experiments, with biochar amendment rates generally <30 t ha⁻¹, BSA increased crop productivity by 11.0 % on average, while the responses varied with experimental conditions. Greater responses were found in pot experiments than in field, in acid than in neutral soils, in sandy textured than in loam and silt soils. Crop response in field experiments was greater for dry land crops (10.6 % on average) than for paddy rice (5.6 % on average). This result, associated with the higher response in acid and sandy textured soils, suggests both a liming and an aggregating/moistening effect of BSA. CONCLUSIONS: The analysis suggests a promising role for BSA in improving crop productivity especially for dry land crops, and in acid, poor-structured soils though there was wide variation with soil, crop and biochar properties. Long-term field studies are needed to elucidate the persistence of BSA’s effect and the mechanisms for improving crop production in a wide range of agricultural conditions. At current prices and C-trading schemes, however, BSA would not be cost-effective unless persistent soil improvement and crop response can be demonstrated.
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•N from the urea was bound strongly by the functionalised surfaces of the biochar.•Biochar-mineral urea composite reduced the N leaching in soil.•Biochar-mineral urea composite was ...more effective on the retention of NH4+-N.•Biochar-mineral urea composite increased maize root growth and N use efficiency.
Over use of N fertilizers, most commonly as urea, had been seriously concerned as a major source of radiative N (Nr) for severe environment impacts through leaching, volatilization, and N2O emission from fertilized croplands. It had been well known that biochar could enhance N retention and use efficiency by crops in amended croplands. In this study, a granular biochar-mineral urea composite (Bio-MUC) was obtained by blending urea with green waste biochar supplemented with clay minerals of bentonite and sepiolite. This Bio-MUC material was firstly characterized by microscopic analyses with FTIR, SEM-EDS and STEM, subsequently tested for N leaching in water in column experiment and for N supply for maize in pot culture, compared to conventional urea fertilizer (UF). Microscopic analyses indicated binding of urea N to particle surfaces of biochar and clay minerals in the Bio-MUC composite. In the leaching experiment over 30 days, cumulative N release as NH4+-N and of dissolved organic carbon (DOC) was significantly smaller by >70% and by 8% from the Bio-MUC than from UF. In pot culture with maize growing for 50 days, total fresh shoot was enhanced by 14% but fresh root by 25% under Bio-MUC compared to UF. This study suggested that N in the Bio-MUC was shown slow releasing in water but maize growth promoting in soil, relative to conventional urea. Such effect could be related mainly to N retention by binding to biochar/mineral surfaces and partly by carbon bonds of urea to biochar in the Bio-MUC. Therefore, biochar from agro-wastes could be used for blending urea as combined organo/mineral urea to replace mineral urea so as to reduce N use and impacts on global Nr. Of course, how such biochar combined urea would impact N process in soil-plant systems deserve further field studies.
Aims A field experiment was conducted to investigate the effect of biochar on maize yield and greenhouse gases (GHGs) in a calcareous loamy soil poor in organic carbon from Henan, central great ...plain, China. Methods Biochar was applied at rates of 0, 20 and 40 tha−1 with or without N fertilization. With N fertilization, urea was applied at 300 kg N ha−1, of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Soil emissions of CO2, CH4 and N2O were monitored using closed chambers at 7 days intervals throughout the whole maize growing season (WMGS). Results Biochar amendments significantly increased maize production but decreased GHGs. Maize yield was increased by 15.8% and 7.3% without N fertilization, and by 8.8% and 12.1% with N fertilization under biochar amendment at 20 tha−1 and 40 tha−1, respectively. Total N2O emission was decreased by 10.7% and by 41.8% under biochar amendment at 20 tha−1 and 40 tha−1 compared to no biochar amendment with N fertilization. The high rate of biochar (40 tha−1) increased the total CO2 emission by 12% without N fertilization. Overall, biochar amendments of 20 tha−1 and 40 tha−1 decreased the total global warming potential (GWP) of CH4 and N2O by 9.8% and by 41.5% without N fertilization, and by 23.8% and 47.6% with N fertilization, respectively. Biochar amendments also decreased soil bulk density and increased soil total N contents but had no effect on soil mineral N. Conclusions These results suggest that application of biochar to calcareous and infertile dry croplands poor in soil organic carbon will enhance crop productivity and reduce GHGs emissions.
•Biochar significantly increased soil pH, organic matter and immobilized soil Cd and Pb.•Biochar treatment consistently reduced rice Cd and Pb content in three years.•Contaminated biochar from the ...study field contained much higher heavy metals than fresh biochar.•Biochar caused metal immobilization primarily due to the precipitation and surface adsorption.
Heavy metal contamination in croplands has been a serious concern because of its high health risk through soil-food chain transfer. A field experiment was conducted in 2010–2012 in a contaminated rice paddy in southern China to determine if bioavailability of soil Cd and Pb could be reduced while grain yield was sustained over 3 years after a single soil amendment of wheat straw biochar. Contaminated biochar particles were separated from the biochar amended soil and microscopically analyzed to help determine where, and how, metals were immobilized with biochar. Biochar soil amendment (BSA) consistently and significantly increased soil pH, total organic carbon and decreased soil extractable Cd and Pb over the 3 year period. While rice plant tissues’ Cd content was significantly reduced, depending on biochar application rate, reduction in plant Pb concentration was found only in root tissue. Analysis of the fresh and contaminated biochar particles indicated that Cd and Pb had probably been bonded with the mineral phases of Al, Fe and P on and around and inside the contaminated biochar particle. Immobilization of the Pb and Cd also occurred to cation exchange on the porous carbon structure.
Elevated CO₂ and temperature strongly affect crop production, but understanding of the crop response to combined CO₂ and temperature increases under field conditions is still limited while data are ...scarce. We grew wheat (Triticum aestivum L.) and rice (Oryza sativa L.) under two levels of CO₂ (ambient and enriched up to 500 μmol mol⁻¹) and two levels of canopy temperature (ambient and increased by 1.5–2.0 °C) in free‐air CO₂ enrichment (FACE) systems and carried out a detailed growth and yield component analysis during two growing seasons for both crops. An increase in CO₂ resulted in higher grain yield, whereas an increase in temperature reduced grain yield, in both crops. An increase in CO₂ was unable to compensate for the negative impact of an increase in temperature on biomass and yield of wheat and rice. Yields of wheat and rice were decreased by 10–12% and 17–35%, respectively, under the combination of elevated CO₂ and temperature. The number of filled grains per unit area was the most important yield component accounting for the effects of elevated CO₂ and temperature in wheat and rice. Our data showed complex treatment effects on the interplay between preheading duration, nitrogen uptake, tillering, leaf area index, and radiation‐use efficiency, and thus on yield components and yield. Nitrogen uptake before heading was crucial in minimizing yield loss due to climate change in both crops. For rice, however, a breeding strategy to increase grain number per m² and % filled grains (or to reduce spikelet sterility) at high temperature is also required to prevent yield reduction under conditions of global change.
Elevated atmospheric CO
concentration (CO
) can stimulate plant growth through enhanced photosynthetic rate. However, plant C, N and P ratios in response to elevated CO
combined with canopy warming ...in rice-winter wheat rotation system remain largely unknown. Here we investigated the impacts of elevated CO
and warming on plant nutrient ratios under open-air conditions. Four treatments including the ambient condition (CK), elevated CO
(500 ppm, CE), canopy warming (+2 °C, WA), and the combination of elevated CO
and warming (CW) were used to investigate the responses of plant C, N and P ratios in a rice-winter wheat rotation system in southeast China. Results showed that elevated CO
increased C:N ratio in whole plant by 8.4-14.3% for both crops, and increased C:P ratio by 11.3% for rice. The changes in ratio were due to an increase in C concentration by 0.8-1.2% and a reduction in N concentration by 7.4-10.7% for both crops, and a reduction in P concentration by 10.0% for rice. Warming increased N allocation in rice leaf and N concentration by 12.4% for rice, resulting in increases in the ratios of N to C and P by 11.9% and 9.7% in rice, but not in wheat. However, CW had no effect on plant C:N ratio in rice, indicating the positive effect of elevated CO
could offset the negative impact of warming on C:N ratio. By contrast, CW significantly decreased plant C:P and N:P ratios by 16% due to the increase in P allocation in stem for wheat. These results suggest that impacts of climate change on plant nutrient balance occur through interactions between the effects of climate change on nutrient uptake and allocation, which is important for food quality and productivity under global climate change.
Soils are subject to varying degrees of direct or indirect human disturbance, constituting a major global change driver. Factoring out natural from direct and indirect human influence is not always ...straightforward, but some human activities have clear impacts. These include land‐use change, land management and land degradation (erosion, compaction, sealing and salinization). The intensity of land use also exerts a great impact on soils, and soils are also subject to indirect impacts arising from human activity, such as acid deposition (sulphur and nitrogen) and heavy metal pollution. In this critical review, we report the state‐of‐the‐art understanding of these global change pressures on soils, identify knowledge gaps and research challenges and highlight actions and policies to minimize adverse environmental impacts arising from these global change drivers. Soils are central to considerations of what constitutes sustainable intensification. Therefore, ensuring that vulnerable and high environmental value soils are considered when protecting important habitats and ecosystems, will help to reduce the pressure on land from global change drivers. To ensure that soils are protected as part of wider environmental efforts, a global soil resilience programme should be considered, to monitor, recover or sustain soil fertility and function, and to enhance the ecosystem services provided by soils. Soils cannot, and should not, be considered in isolation of the ecosystems that they underpin and vice versa. The role of soils in supporting ecosystems and natural capital needs greater recognition. The lasting legacy of the International Year of Soils in 2015 should be to put soils at the centre of policy supporting environmental protection and sustainable development.
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