Biochar, compost and biochar-compost: effects on crop performance, soil quality and greenhouse gas emissions in tropical agricultural soils

The declining of soil fertility due to intensive agriculture represents the main constraint to agricultural productivity. Sustainability of agriculture may be threatened by the progressive reduction of soil organic matter without adequate restoration. Appropriate soil management practices can improve soil quality by utilizing organic amendments as an alternative to mineral fertilizers for increasing soil productivity and plant growth and improve biological fertility. The use of indicators, like physical and chemical properties, as quantitative tools could allow to assess soil quality. Emphasis has been also given to biological and biochemical properties, strictly linked to soil fertility, among which soil enzyme activities and microbial biomass may provide an “early warning” of soil quality and health changes, such as the loss or the increase of organic matter. The research started with a preliminary monitoring phase based on soil sampling in the selected farms in the Plane of Sele river. The obtained results indicated a great variability among the farms. The monitoring phase allowed to evince the most affected properties by agricultural management under greenhouse. The electrical conductivity, the content of phosphorus and sodium were higher in soils under greenhouse than those of controls. The control samples, not subjected to intensive farming, generally richer in organic carbon, showed higher enzymatic activity levels as shown for arylsulphatase and -glucosidase. In conclusion a clear evidence is that the control samples always showed better values of chemical properties and higher enzymatic activities to indicate a negative effect of intensive agriculture practices on fertility of studied soils. Among all studied sites in the preliminary monitoring phase of the research two farms, having different physical-chemical soil properties, were selected. The effect of organic amendments in the medium-long term (1 year) was studied by supplying different kinds and amounts of organic matter. In particular, compost from municipal solid waste, as a source of easily degradable organic matter, and wood (scraps of poplars pruning), as a slow degradation source, were used. Organic amendments (30t/ha and 60t/ha) at compost/wood different ratios (2/1 and 10/1) were added to the chosen soils. The analysis of results shows positive effects of organic amendments on all soil properties of the two farms, but no different response by increasing the amount of amendment or changing the kind of mixture supplied to agricultural soils. Instead the nature of soil was able to affect the response to amendment treatments. In order to better understand the role of organic matter on soil quality and to know its interactions with the natural organic matter a study on humic substances of soils of the two farms under different treatments was conducted. The extracted humic fraction was analyzed by high field NMR spectroscopy, FT-IR spectroscopy and elemental analysis (HCNS). After one year from the application of organic amendments the analysis obtained from high field NMR, FT-IR and the elemental analysis indicated that an interaction of organic matter with soil components, with positive effects on soil fertility. In addition, soil samples of the first sampling were analyzed by low field Fast Field Cycling NMR and the results showed the effect of the mineral amendment is modulated by the nature and the amount of the organic carbon added to the soil.

The degradation of soil structure in paddy fields is critical, and the application of organic amendments is an effective way to enhance soil structure and function. However, the mechanisms by which different organic amendments influence soil aggregate-associated humus carbon and nutrients remain unclear. Considering this, four treatments were employed in a randomized complete block design with three replications: (1) chemical fertilizer (CK); (2) chemical fertilizer plus organic amendment (MC); (3) chemical fertilizer plus organic amendment containing Bacillus subtilis (FT); and (4) Chemical fertilizer plus organic amendment containing polyacrylamide (PM). The results showed that all soil improvement measures significantly increased the proportion of macroaggregates (>2 mm and 2–0.25 mm), primarily the 2–0.25 mm fraction (34.53–48.46%), and the mean weight diameter (MWD), compared to CK. Soil organic carbon (SOC), humic acid carbon (HAC), fulvic acid carbon (FAC), humin carbon (HUC), total nitrogen (TN), and total phosphorus (TP) were predominantly concentrated within the macroaggregates. Relative to CK, the PM increased the HUC content in large aggregates (>2 mm) and significantly enhanced HAC by 19.53% within the same fraction, while the FT significantly boosted FAC by 31.78% in the >2 mm fraction. Furthermore, MC, FT, and PM treatments significantly enhanced SOC, TN, and TP contents within large macroaggregates compared to CK, with PM generally showing the highest SOC and TN levels, and FT being the highest in terms of TP in large aggregates (though differences among treatments were non-significant). Correlation analysis revealed that only in large aggregates did SOC show significant positive correlations with humus carbon fractions (except HAC), as well as with TN and TP. The amendments, particularly PM, effectively enhanced nutrient and humus carbon accumulation within large aggregates and improved aggregate stability. Notably, PM strengthened the direct pathways for the formation of SOC and humus carbon. In summary, the combined application of chemical fertilizer and organic amendments, containing polyacrylamide positively influenced aggregate stability and nutrient accumulation in paddy soil.

Intensive agricultural practices with excessive use of chemical fertiliser have led to the deterioration of soil fertility where soil losses its ability to sustain a consistent crop system with high yield. Compost is a potential substitution to chemical fertiliser. As a biological additive, compost can improve soil quality and crop productivity, controlling plant diseases and reduce nutrient loss and water pollution. However, the effect of compost application to enhance the quality of the soil may be inconsistent due to the slow release nature of the nutrients, compost quality, types of feedstocks and other factors. To evaluate the effects of compost application, it may involve a large number of parameter analyses, which can be costly and time ineffective. There is no indicator to reduce the number of analyses concerning the effect of compost application on soil fertility. In this study, a ranking method is proposed to identify the minimum number of parameters able to track the effect of compost application on soil fertility and the environmental impact. A total of 23 soil parameters were selected through literature review and ranked for their importance to show the effect of compost use. The ranking method was developed based on (1) the reporting frequency of environmental and soil fertility parameters and (2) impact of the selective parameter to the environment. Soil C and N contents were found to be the most frequently reported parameters (85 and 90 %) to affect soil fertility upon compost application. Both contents in the soil also change significantly before and after compost application. Heavy metals and N2O emissions were found to impact the environment most due to the toxicity of heavy metal to the environment and human health and high global warming potential of N2O. Based on the ranking method, nine parameters (N, NO3--N, P, K, micro-nutrients, heavy metals, C, pH and N2O emissions) were selected. 60 % of soil analyses were reduced following this ranking method. For the future study, a weightage system could be implemented on each criterion to decide the more essential parameters to be evaluated based on different soil or crop type and under different agricultural practices.

Purpose The deterioration of agricultural soil can be alleviated by maintaining an appropriate level of soil organic matter by using organic amendments such as compost and biochar. The aim of this study was to investigate the effects of olive waste-based compost, wood-based biochar and their combination on the chemical and microbial properties of loamy clay soil and the agrophysiological traits of maize. Method Zea mays was grown under greenhouse conditions for 3 months in pots filled with alkaline soil collected from 0-30 cm depth. The experiment was arranged in a completely randomized design with 5 replicates and 3 treatments: compost-soil [1:10 (v/v)], biochar-soil [1:20 (v/v)] and (1:2)-ratio biochar-compost combination (BCC). ResultsBiochar addition singly or in BCC increased soil TOC, EC, and pH. Furthermore, adding biochar to compost increased the levels of macro- and micronutrients compared to those under single application of biochar. The soil fertility improved significantly with regard to available phosphorus and potassium, nitrogen, and micronutrients. Single application of biochar had a negative impact on mycorrhizal symbiosis and was statistically insignificant for soil viable cultivable microorganisms. Conclusion Overall, single application of compost gave the best results in terms of plant growth and soil fertility improvement; thus, a synergistic effect of both amendments was not observed, which could be due to the quantity of the applied biochar and the duration of the experiment.

In the last years, sustainable horticulture has been increasing; however, to be successful this practice needs an efficient soil fertility management to maintain a high productivity and fruit quality standards. For this purpose composted organic materials from agri-food industry and municipal solid waste has been used as a source to replace chemical fertilizers and increase soil organic matter. To better understand the influence of compost application on soil fertility and plant growth, we carried out a study comparing organic and mineral nitrogen (N) fertilization in micro propagated plants, potted trees and commercial peach orchard with these aims: 1. evaluation of tree development, CO2 fixation and carbon partition to the different organs of two-years-old potted peach trees. 2. Determination of soil N concentration and nitrate-N effect on plant growth and root oxidative stress of micro propagated plant after increasing rates of N applications. 3. Assessment of soil chemical and biological fertility, tree growth and yield and fruit quality in a commercial orchard. The addition of compost at high rate was effective in increasing CO2 fixation, promoting root growth, shoot and fruit biomass. Furthermore, organic fertilizers influenced C partitioning, favoring C accumulation in roots, wood and fruits. The higher CO2 fixation was the result of a larger tree leaf area, rather than an increase in leaf photosynthetic efficiency, showing a stimulation of plant growth by application of compost. High concentrations of compost increased total soil N concentration, but were not effective in increasing nitrate-N soil concentration; in contrast mineral-N applications increased linearly soil nitrate-N, even at the lowest rate tested. Soil nitrate-N concentration influenced positively plant growth at low rate (60- 80 mg kg-1), whereas at high concentrations showed negative effects. In this trial, the decrease of root growth, as a response to excessive nitrate-N soil concentration, was not anticipated by root oxidative stress. Continuous annual applications of compost for 10 years enhanced soil organic matter content and total soil N concentration. Additionally, high rate of compost application (10 t ha-1 year-1) enhanced microbial biomass. On the other hand, different fertilizers management did not modify tree yield, but influenced fruit size and precocity index. The present data support the idea that organic fertilizers can be used successfully as a substitute of mineral fertilizers in fruit tree nutrient management, since they promote an increase of soil chemical and biological fertility, prevent excessive nitrate-N soil concentration, promote plant growth and potentially C sequestration into the soil.

The primary function of agricultural soils is for food, feed, fibre and fuel production. Management measures in agricultural soils should therefore focus on improving and/or sustaining this function, in both the short and long term in a sustainable manner. Both agricultural crop production and crop quality are closely linked to soil quality (i.e. soil fertility). This is largely determined by factors including nutrient and water supply, but the soil’s suitability as a growth medium for roots and as a habitat for soil organisms is also important. These factors are all dependant on a multitude of bio-physical, chemical and environmental factors. Nutrient supply is dependent on fertilisation (e.g. synthetic supplies of essential plant nutrients) and decomposition (via mineralisation by soil microbes) of soil organic matter and organic amendments (e.g. animal manure, compost and crop residues) and the buffering capacity of nutrients (Box 4.2). Water supply is determined by weather conditions, irrigation and soil physical properties including soil texture and soil structure (see Box 4.1). Soil organic matter is crucial to both nutrient and water supply in many soils, while a good soil structure can enhance both root growth and the ability of the plants to utilise available nutrients and water in the soil. Soils containing low amounts of soil organic matter require higher inputs of chemicals and irrigation, and the long-term sustainability of high-input farming is now under scrutiny. It is widely hypothesised that the high-input farming typical of much of agriculture (largely reliant on plentiful water supplies and chemical fertilisers whose manufacture uses a lot of energy) will not be sustainable in the long term and that new approaches to farming are now required.

Abstract: In Burkina Faso, information about composts’ role in greenhouse gas reducing is scarce. This study assessed six urban composts application effects on soil carbon storage in sorghum three-year experiment. Composts were applied at 3 t DM ha-1 year1 rate, single or combined with 50 t ha-1 year-1 urea rate. Soil properties were analyzed with soil sampled in the early 20 cm of soil. The treatments were compared to a control without any fertilization and a 50 t ha-1 year-1 urea treatment. Comparisons were also done between single composts treatments and composts combined with 50 t ha-1 urea ones. In comparison to the control, single or combined with urea composts application improved soil bulk density, fine soil rate and organic carbon contents. Single composts treatments carbon storage ranging from 8.76 to 11.58 t ha-1 were not significantly different from the control. However, when composts were combined with urea, carbon storage ranged from 8.42 to 13.07 t ha-1 and was significantly increased by comparison to the control. Best composts seemed to be those produced with various and balanced composting materials. Eco-friendly urban waste composts adoption could improve soil fertility and mitigate greenhouse gas emission. Keywords: urban wastes composts, soil fertility, greenhouse effect, Burkina Faso

Waterleaf (Talinum triangulare), like many other leafy vegetable is cultivated in home gardens to improve nutritional quality for the family and may provide additional income for female farmers. However, the role of Talinum cultivation is often counteracted by declining soil fertility. In recent years, biochar (pyrolysed biomass) has gained importance as a soil amendment tool. However, not much attention has been focused on the influence of biochar on soil quality and plant growth in the humid tropics. This study was conducted to assess different locally available crop waste residues as possible sources of biochar for home garden or small-scale production units of leafy vegetable using Talinum as proxy on highly weathered acid soils in the humid tropics. The experimental set-up was a pot experiment in a complete randomized design in five replicates using biochar sources from cassava stems, rice husk, corncob and sawdust. The results obtained showed that biochar samples had a high cation exchange capacity (CEC), total nitrogen, total carbon and pH (7.8 to 10.8), as compared to the no-input soil (pH 5.7). It is evident that adding biochar to poor and acidic soils could possibly increase the pH and reduce lime requirements. Positive and significant response of biochar (P<0.05) application were also observed with the growth, nutrient uptake, and yield of waterleaf. Biochar produced from rice husks obtained the best response followed by sawdust, cassava and corncob. Similarly, the C and N uptake of waterleaf was generally higher with rice husk biochar use as compared to the other treatments. This study has demonstrated that biochar production could be useful in valorizing crop waste residues and biochar use is likely to enhance the productivity of leafy vegetables. More research on possible combination of biochar and other farming strategies such as the application of animal manure and mineral fertilizer to maximize Talinum production should be encouraged. Key words: Biochar, cassava stems, crop waste, residues, nitrogen, soil pH, Talinum.

To understand the influence of organic manures composted with the wheat straws, oilcakes and cottonseed cakes, and chemical fertilizers on soil organic carbon and soil productivity, a long-term plot experiment was established in a calcareous fluvo-aquic soil (aquic inceptisol) in Fengqiu county, Henan province, China in September 1989 and was used to monitor soil respiration during the maize and wheat growth seasons from June 2002 to June 2003. The study involved 7 treatments: organic manure (OM), half organic manure plus half fertilizer N ((1/2OM),) fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK) and control (CK). The input of NPK as either organic manures or chemical fertilizers not only greatly improved soil productivity but also was of benefit to the soil as a carbon sink. However, the organic carbon in soils amended with organic manure was greatly higher than in the soil fertilized with chemical fertilizers and increased with the rate of organic manure applied. CO_(2) flux resulted from soil respiration mainly occurred during the maize growth period, accounting for 56%~59% of annual CO_(2) emission, whereas 32%~37% during the wheat growth period. The study suggests that the combination application of organic manures and chemical fertilizers should be the optimal measure from the viewpoint of environment and economy. A further study is necessary to elucidate the reasonable and feasible ratio of organic manure to chemical fertilizers, which will benefit the soil fertility, productivity and global environment.

Crop yield, plant nutrient uptake and soil physicochemical properties under organic soil amendments and nitrogen fertilization on Nitisols

Benefits of biochar, compost and biochar–compost for soil quality, maize yield and greenhouse gas emissions in a tropical agricultural soil

Field experiment was carried out to study the effect of peanut-shell-biochar amount on quality of flue-cured tobacco leaves and carbon pool in tobacco growing soil in 2013 in Hanzhong municipality of Shaanxi province. The variety tested was Yunyan97. Results showed that:(1)Adding biochar could increase soil total carbon, readily oxidizable active organic carbon, dissolved organic carbon, organic carbon mineralization rate, soil carbon activity, soil carbon activity index and soil carbon pool management index.(2)Adding biochar could increase Nic, K+ and Cl- content of cured leaves and their contents increased with the increase of biochar amount. Adding appropriate amount of biochar could improve sensory quality of cured-leaves.(3) Conventional fertilization with biochar amount of 600kg/hm2 rendered the best effect.(4)Excess amount of biochar could cause negative influence on flue-cured tobacco leaves and further research about increasing application of biochar with reduced nitrogen fertilizer technology need to be carried out.

Soil sickness represents a condition in which the long-term use of non-sustainable agricultural practices causes changes in the physical, chemical and biological properties of soils that, in turn, negatively affects plant vegetative and reproductive performances. By an extensive analysis of literature, we found that soil sickness is pervasive in agro-ecosystems, occurring in 111 cultivated plants belonging to 41 taxonomic families. To explain the phenomenon of soil sickness, three main hypotheses have been proposed, including soil nutrient depletion or imbalance, build-up of soilborne pathogens coupled with shift in the composition of soil microbial community composition, and presence of phytotoxic and autotoxic compounds. Starting from a detailed analysis of mechanisms it was previously suggested that all proposed hypotheses have as common origin, i.e. the alteration of organic matter cycle caused by intensive agricultural practices. Based on this consideration, in the present thesis different organic management strategies, in terms of organic matter type and application frequency, were used in order to recover a soil affected by soil sickness. Soil was subjected for two years to 11 different treatments including two ordinary soil managements, eight organic amendment treatments and one untreated soil as the control. At the end of each year, cumulated crop production of Eruca sativa, soil properties and soil microbiota were evaluated. Compared to the use of ordinary managements, the beneficial effects on soil properties and microbial community derived by the use of organic amendments were evident already after one year of conditioning. In detail, pH values near the neutrality, high soil organic carbon content and good level of soil aggregation, as well as an improvement in soil microbial functionality, richness and diversity were observed in soil treated with organic amendments, especially when easily decomposable materials rich in labile carbon and organic nitrogen (i.e., alfalfa plus glucose) were applied at high rate once a year. In contrast, cumulated crop production at the end of the first year was higher in soil with ordinary managements than in soil with application of organic materials. However, during the second year of soil conditioning, an increase in productivity and quality of the crop was observed in soil treated with organic materials as compared to the soil subjected to conventional management. Finally, soil conditioned for two years was used to evaluate the effects that ordinary and organic management strategies had in the disease suppression of soilborne phytopathogenic fungi and viruses. Application of organic amendments, by positively affecting soil properties and soil microbiota, showed a restoration of natural soil suppressivines against soilborne pathogens (i.e., Sclerotinia sclerotiorum and Fusarium oxysporum f. sp. raphani). Surprisingly, this study reports for the first time that the use of organic matter reduces the incidence of Tomato spotted wilt virus infection, as well as the mortality of infected plants, probably by the induction of systematic resistance. In conclusion, this study revealed that applications of organic materials have an immediate positive effect on soil fertility as well as on soil microbiota, while the increase of crop productivity are of longer-term nature. In addition, the positive effect that organic amendments have on microbial communities, including their abundance, diversity and richness of the several taxa, results in a recovery of the natural soil suppression against soilborne pathogens and the induction of plant resistance against airborne pathogens like viruses. However, the effects on crop production, soil fertility and disease suppression varied depending on quality, amount and frequency of application of organic matter. Therefore, future studies that include different combinations of organic amendment types and application frequencies, as well as different soil types, crop species and pathosystems, are needed to better understand the role of organic matter as a means to recover of soils affected by soil sickness.

To improve paddy soil fertility，the effects of fertilization on the distribution of total organic carbon along with fractionation and hot water-solubility in paddy field soil profiles were studied. This work included accumulation of soil organic carbon and its soil profile evolution from a 10-year fertilization experiment with pig manure amendments in Pinghu County，Zhejiang Province. Results showed that in the 0－45 cm horizon soil organic carbon content differed greatly between pig manure treatments and no pig manure amendments. With organic fertilizer amendments，soil organic carbon increased with the increase of soil profile. Total organic carbon differed greatly from sandy carbon and amylaceous carbon （P＜0.05）. Soil organic carbon in the 0－45 cm horizon consisted mainly of sandy carbon；whereas in the 45－85 cm horizon it was comprised mainly of amylaceous carbon and sticky carbon. Also，with the pig manure amendments，hot water-soluble organic carbon content of the soil increased.［Ch，2 fig. 4 tab. 28 ref.］

This study was conducted to evaluate the effects of different organic fertilizers, i.e. powdery animal compost 10, 20 and 30 kilogram, powdery miscellaneous compost 10, 20 and 30 kilogram, granular miscellaneous compost 10 and 20 kg/plant/year, respectively on the soil properties, plant nutrition and quality of jujube cultivated on the weakly acid soil. The results showed that the soil properties and leaf nutritions of jujube were influenced by the types and the amount of composts. Soil pH, organic matter and fertility were increased for the application of organic fertilizer than the treatments of non-organic fertilizer. On the other hand, the concentration of nitrogen, potassium and microelements in the leaves were all reduced at the anthesis stage, however, the phophorus was increased for the application of organic fertilizers. The application of organic fertilizers will supply the efficient phosphorus and microelements for the anthesis and increasing of fruit quality. The quality test of jujube showed that the application of three types of organic fertilizer will increase the quality of jujube than the treatment of no organic fertilizer. The application of powdery miscellaneous compost for 20-30 kilogram per plant will increase the fruit weight and sugar degree of jujube than the applications of different amount of powdery animal compost and granular miscellaneous compost.