Improved Soil Organic Carbon Content Research Articles

Soil bacterial community is influenced by long‐term integrated soil fertility management practices in a Ferralsol in Western Kenya

AbstractIntroductionSoil bacterial community structure, abundance and diversity, important in biogeochemical cycling, are influenced by several anthropogenic and edaphic factors. Numerous agronomic practices have been promoted to improve soil fertility and crop production in western Kenya, but little is known on their impacts on soil microbial diversity in the region.Materials and MethodsIn this study, conducted in 2019, we assessed the influence of various long‐term (17 years) agronomic management practices, involving application of farmyard manure (FYM) either sole or under different combinations with inorganic nitrogen (N), phosphorus (P) and potassium (K), using 12 treatments, on bacterial community composition, relative abundance and diversity. The bacterial community composition was assessed through amplicon sequencing on an Illumina Miseq platform conducted in MR DNA Laboratory, USA.ResultsThe soil bacterial community composition and diversity were predominantly higher under management practices with application of FYM, either sole or in combination with inorganic fertilisers compared to treatments with either sole NPK fertiliser or no input application. Certain bacterial taxa, involving Proteobacteria, Bacteroidetes, Nitrospirae, Fusobacteria, Nitrospinae and Actinobacteria predominated in management practices where FYM was added either solely or in combination with chemical fertilisers. In addition, several soil chemical parameters showed significant influences on bacterial composition, relative abundance and diversity indices. Soil pH, soil organic carbon (SOC), N, K, Ca, Mg, Cu, Zn, Fe and cation exchange capacity consistently showed strong positive correlation with numerous bacterial phyla. Bacterial phyla were significantly affected by treatments. Some bacterial phyla, like Chloroflexi and Acidobacteria, were mostly dominant in treatments applied with organic inputs but were depressed under carbon‐deficient treatments (no‐input control and sole NPK application treatments).ConclusionThis study revealed that long‐term agricultural management practices that seek to improve SOC content and nutrient availability also stimulated bacterial diversity and shifted bacterial composition.

Assessing residue and tillage management options for carbon sequestration in future climate change scenarios

Soil carbon depletion is a major concern for food security in drylands. The objective of this study is to test tillage with residue management under sequential and intercropping systems for carbon sequestration in semi-arid tropical drylands of India. We report the findings from a long-term field experiment (9 years) used to simulate the effect of residue and tillage management in Maize-chickpea sequential and Maize-Pigeonpea intercropping systems for the four possible future climate projections using APSIM model. These findings demonstrate a sustainable route with inclusive growth, as pledged at the UN climate change summit. A comparison of results under SSP 2.6 and 4.5 Wm−2 with SSP 8.5 shows that demand pressure from competitive marketplaces inhibits the establishment of soil carbon sinks and significantly reduces crop yields, likely due to indiscriminate chemical fertilizer use. We observed that a better decision in selecting cropping system might improve soil organic carbon content (SOC). SOC content ranging from 0.9 to 1.2% in Maize-pigeonpea intercropping and 0.85–1.1% in maize-chickpea sequential cropping systems, demonstrate good potential in the climate change mitigation exertions. Early SOC saturation (20 years) led to a decreased carbon stock in topsoil without residue addition practises. The addition of crop residues significantly increased SOC levels under both conventional and minimum tillage and created additional income for farmers. Simulation analysis showed impact of SOC changes on crop yield which remained nearly stable for 85 years. Therefore, hardy straw biomass of crops covering a large tract in dryland tropics, can be a scalable and sustainable solution to yield losses, while mitigating climate change through carbon sequestration.

Substituting Inorganic Fertilizers with Organic Amendment Reduced Nitrous Oxide Emissions by Affecting Nitrifiers’ Microbial Community

Excessive inorganic fertilizers are one of the main causes of nitrous oxide (N2O) emissions. Organic fertilizers can not only reduce the use of nitrogen (N) fertilizers by increasing soil organic matter but are also safe for the environment. The partial replacement of nitrogen (N) fertilizers with organic fertilizers can potentially reduce N2O emissions. To illuminate the best ratio for the nitrogen replacement of inorganic fertilizer, the present experiment was conducted in dryland areas of central Gansu Province and different portions of inorganic N fertilizers (200 kg ha−1); i.e., 0, 50, 37.5, 25, and 12.5% were replaced with commercial organic fertilizers to test their effects on soil physicochemical properties, the grain yield of maize, N2O emissions, and the diversity of ammonia-oxidizing archaea (AOA) and bacterial (AOB) communities. Results showed that the maximum N2O emission was obtained by 100% inorganic fertilizers and the lowest was obtained at the control (no fertilizer). Substituting inorganic fertilizers with organic manure not only reduced N2O emissions but also improved soil organic carbon content and soil moisture and typically improves grain yield and biomass. The highest reduction in N2O emissions was recorded by 50% substitution. Furthermore, 37.5% and 12.5% substitutions did not reduce the grain yield and biomass compared to 100% inorganic fertilizer, and a 37.5% substitution performed better in improving soil fertility. Organic fertilizer increased the amoA copy number of AOA but decreased that of AOB. Nitrososphaera (AOA) and Nitrosospira (AOB) were the most dominant ammonia-oxidizing communities. Structural equation modeling indicated that AOB contributes more N2O emissions than AOA and is more sensitive to changes in pH, moisture, and NO3−−N, and the input of organic fertilizers may affect AOB by influencing soil physicochemical traits. In summary, replacing a reasonable proportion (37.5%) of inorganic fertilizers with organic manure improves soil fertility, reduces N2O emissions, and stabilizes production.

Soil properties resulting in superior maize yields upon climate warming

The impacts of global climate warming on maize yield vary regionally. However, less is known about how soil modulates regionally specific impacts and soil properties that are able to alleviate adverse impacts of climate warming on maize productivity. In this study, we investigated the impacts of multiple soil inherent properties on the sensitivity of maize yield (SY,T) to growing season temperature across China. Our results show that a 1°C warming resulted in the largest yield decline (11.2 ± 6.1%) in the mid-eastern region, but the moderate yield increase (1.5 ± 2.9%) in the north-eastern region. Spatial variability in soil properties explained around 72% of the variation in SY,T. Soil organic carbon (SOC) content positively contributed the greatest extent (28.9%) to spatial variation of SY,T, followed by field capacity (9.7%). Beneficial impacts of increasing SOC content were pronounced in the north-eastern region where SOC content (11.9 ± 4.3 g kg−1) was much higher than other regions. Other soil properties (e.g., plant wilting point, sand content, bulk density, and saturated water content) were generally negatively correlated with SY,T. This study is the first one to answer how soil inherent properties can modulate the negative impacts of climate warming on maize yield in China. Our findings highlight the importance of SOC in alleviating adverse global warming impacts on maize productivity. To ensure food security for a rapidly increasing population under a changing climate, appropriate farming management practices that improve SOC content could reduce risk of adverse effects of global climate warming through a gain in yield stability and more resilient production in China’s maize belt.

Untangling microbial diversity and functional properties of Jeevamrutha

Jeevamrutha (JA) is a complex microbial bioformulation derived from local resources (cow dung, cow urine, jaggery, pulse flour, soil, and water) used in traditional Indian organic agriculture. Farmers using JA frequently describe it as inexpensive, sustainable, and environmentally friendly, and it improves plant and soil health. Additionally, limited research studies conducted on JA support the farmers' claim. To increase JA's credibility and acceptability among users, it must be scientifically validated in-depth. It was hypothesised that the structural and functional diversity of microbes, metabolites and proteins is key to JA's success. In order to comprehend the dynamics of JA during the incubation period, physico-chemical parameters and microbial diversity were analysed until the 12-day of incubation. Dynamics of JA's pH, EC, DO, aerobic and anaerobic, and cultivable and uncultivable microbial load determined JA as a fermentative process. Phylum Firmicutes, Bacteriodetes, and Proteobacteria, and genus, Lactobacillus, Streptococcus and Clostridium, dominated the microbial composition of JA. In addition, the presence of bacteria, bacteriophages, fungi, and unclassified microorganisms in JA demonstrated the complexity of microbial diversity. The variety of JA's metabolites (lactic acid, ascorbic acid, caproic acid, succinic acid, betaine, choline, stachydrine, trehalose, etc.), proteins (chaperone proteins, heat shock proteins, elongation factor-Tu, etc.) and exopolysaccharides, that have the potential to promote microbial survival and proliferation in JA and soil. Field trials were conducted for four years under two distinct agroclimatic conditions to assess the impact of JA on soil health. At the end of the experimental period, JA along with farmyard manure/vermicompost, improved soil organic carbon content, water holding capacity, microbial load, and activity to varying degrees in both trials. This study provides in-depth information regarding the structural diversity and functional properties of JA, as well as their significance in enhancing soil health and encouraging farmers to use JA.

Spatial distribution and the influencing factors of organic carbon of biological crusts on regional scale in Mu Us sandy land, China

As an important soil cover in deserts, biological crusts play a central role in ecosystem function such as nutrient cycling, nitrogen fixation, and carbon sequestration. Many biological crust organisms could fix CO2 through photosynthesis to improve soil organic carbon content. There is a knowledge gap in the origin of soil organic carbon (SOC) from biological crusts on a regional level, which restricts the prediction of soil carbon pool. Based on 45 plots in the Mu Us sandy land (42200 km2), we measured the SOC content and soil organic carbon density (SOCD) of two types of typical biological crusts (moss crusts, algal crusts) and their underlying soils, and analyzed together with the climate data, soil and vegetation factors to investigate the spatial distribution characteristics and controlling factors of organic carbon of biological crusts at the regional scale. The results showed that: 1) biological crusts significantly increased SOC and SOCD compared with bare ground. Moss crusts and the underlying SOC (4.93 g·kg-1) and SOCD (0.41 kg·m-2) were higher than those of algal crusts (1.89 g·kg-1, 0.18 kg·m-2). 2) On the regional scale, the SOC and SOCD of biological crusts had clear spatial distribution characteristics, demonstrating a banded distribution and block mosaic from northeast to central and west to southeast. 3) The SOC and SOCD of biological crusts and their underlying soils were mainly affected by climate, soil and vegetation conditions, while the main controlling factors depended on the types of biological crusts. The SOC and SOCD of moss crust were controlled by annual maximum temperature and potential evapotranspiration, whereas those of algal crusts were controlled by water vapor pressure.

Afforestation influences soil organic carbon and its fractions associated with aggregates in a karst region of Southwest China

Variations in soil organic carbon (SOC) and its fractions within soil aggregates in response to land-use change are important to understand the carbon cycles in terrestrial ecosystem. However, responses of total SOC, SOC fractions, and SOC stability in different soil aggregates to land-use change are less addressed, especially in karst regions with serious land degradation. Therefore, bulk soil samples were collected under four land uses with similar geographical characteristics and previous framing practices including farmland (FL), Bamboo forest (BA), landscape tree planting (LAT), and orange orchards (ORO) in a karst region of Southwest China. Contents of total SOC and three carbon fractions based on their degree of oxidizability (F1, very labile; F2, inert; F3, oxidizable resistant) in bulk soil and different soil aggregates (macro-aggregate, micro-aggregate, and silt+clay fraction) were measured. Afforestation significantly increased contents of total SOC and three carbon fractions in bulk soil and soil aggregates, and the influence was more obvious in macro-aggregate than the other aggregates. Contents of total SOC, F1, F2, and F3 under afforestation land increased by 41.73%, 58.19%, 33.91%, and 40.55%, respectively, in bulk soil, by 55.60%, 79.24%, 121.77%, and 43.30%, respectively, in macro-aggregate, by 52.80%, 33.57%, 20.14%, and 75.02%, respectively, in micro-aggregate, and by 26.21%, 35.60%, 29.26%, and 23.75%, respectively, in silt+clay fraction than those under FL. In bulk soil and soil aggregates, proportions of F1, F2, and F3 in total SOC ranged from 0.11 to 0.18, from 0.13 to 0.22, and from 0.60 to 0.73, respectively, suggesting that the stable carbon was the predominant carbon fraction in the study area. Afforestation decreased the values of stability of SOC in macro-aggregate and silt+clay fraction, while it increased the value in micro-aggregate. Although both BA and ORO had higher SOC content in bulk soil than the LAT, but the SOC stability in bulk soil under BA was significantly lower than that under ORO. In conclude, afforestation form FL improved SOC content and altered SOC stability in bulk soil and soil aggregates, and conversion of FL to ORO might be the best choice to increase SOC sequestration in the four land-use types compared in karst regions of Southwest China.

Partial substitution of chemical fertilizer by organic fertilizer benefits grain yield, water use efficiency, and economic return of summer maize

Partial substitution of chemical fertilizer with organic fertilizer (PSCFOF) is being increasingly recognized as a promising approach for achieving sustainable agriculture. However, comprehensive evaluation of the effect of PSCFOF on the grain yield, water use efficiency (WUE), and its economic return of summer maize is lacking. In this study, field experiments examining the following five treatments were conducted over the 2019 and 2020 growing season: T1, application of chemical NPK fertilizer alone; and T2–T5, substitution of 15%, 30%, 45%, and 60%, respectively, of the chemical N rate of T1 with organic fertilizer. Compared with T1, the other treatments reduced the soil bulk density, and improved soil organic carbon content and the percentage of macro-aggregates (≥0.25 mm) in the 0–20 cm soil layer. The grain yield and WUE of T2 and T3 were significantly higher than that of T1, where as T1, T4 and T5 had similar effect. The higher grain yield and WUE under T2 and T3 treatments may related to its strong root system, higher soil water content, and elevated plant N uptake, which further improved the post-silking photosynthetic capacity, biomass production, and harvest index. The results of the economic benefit analysis indicated that, T2 and T3 increased the net benefit by 2257 and 1404 CNY ha-1, respectively, compared to T1. However, the net benefit was reduced under T4 and T5 treatments. In conclusion, by comparison with T1, T2 and T3 improved the grain yield, WUE, and economic benefit of summer maize. Although T2 can achieve the optimal economic benefits in a short-term, T3 may be a better choice from the perspective of long-term ecological and economic benefits, because of its greater potential to reduce chemical N fertilizer application rate.

Optimal agricultural spreading scheduling through surrogate-based optimization and MINLP models

The most commonly used definition of climate smart agriculture (CSA) is provided by the Food and Agricultural Organisation of the United Nations, which defines CSA as “agriculture that sustainably increases productivity, enhances resilience, reduces/removes greenhouse gas where possible, and enhances achievement of national food security and development goals”. In this definition, the principal goal of CSA is identified as food security and development, while productivity, adaptation, and mitigation are identified as the three interlinked pillars necessary for achieving this goal. In the context provided by the CSA, soils are seen as a lever to improve the carbon footprint of agriculture, namely through their role as carbon sinks. Improving soils and in particular agricultural soils’ content in soil organic carbon (SOC) in one of the measures enabling to improve the environmental impact of agricultural practices. In this context, composts can be seen as an important feedstock for sustainable farming. To support the development of organic amendment strategies enabling to increase soils’ SOC content, this work proposes a novel methodology to optimize the monthly scheduling of composts and mineral fertilizers amendments. The schedule proposed maximizes soil health - via improved SOC content - while ensuring optimal gross operating surplus from agriculture. This problem is subjected to certain operational, regulatory and soil-dynamics constraints which leads to a complex optimization problem and has to be solved in a relatively short time period for decision-making purposes. This is a nonlinear optimization problem (NLP) which is based on a soil-simulation model from which the analytic functions are not explicitly available for the optimization model. Operational and regulatory constraints are explicitly defined and integer and continuous variables are needed in the modeling. In order to effectively solve it in a deterministic way, a novel surrogate-modeling approach for the objective functions and constraints is proposed. Another novelty comes from the implementation of a continuous-variable-reduction procedure in order to build effective surrogates. The optimisation model results obtained from a real case study show that local optimal solutions can be identified with short computation times. The evaluated scenario shows that the optimized strategy could increase by 8% the carbon in soil after 13 years while increasing by 7% the estimated agricultural profit when compared to expert based application schedules.

Using a mixture of microalgae, biochar, and organic manure to increase the capacity of soil to act as carbon sink

Microalgae, biochar, or organic manure (OM) can be used as soil amendments to enhance soil organic carbon (OC) content. In the present study, a mixture of all three was used to test whether they could further improve soil OC content and the soil’s ability to retain and fix carbon. A laboratory incubation study was carried out to evaluate the efficacy of using microalgae, biochar, OM, or their mixture, as a soil amendment to improve OC in soil extract. Metabolic processes and soil microbial community structuring were analyzed to explore the mechanism by which the mixture increased the capacity of soil to act as a carbon sink. OC increased markedly (2.9 times its initial level) following the amendment of the soil with a treatment comprising microalgae, biochar, and the highest dose of OM. Microalgal metabolites were utilized by soil microorganisms as a carbon source. Biochar reduced the concentration of extracellular polysaccharides, whereas OM increased extracellular protein concentration. These metabolites affected the relative proportions of different groups of soil microorganisms, thereby increasing the proportion of Rhodobacter and Runella, which exerted a positive synergistic effect on soil OC and increased the soil’s capacity to fix carbon. A mixture including microalga, biochar, and OM as a soil amendment improved the OC of soil extract, and its effect was greater than that of any of its components alone. The findings of this study can help in devising ways to increase the OC content and the CO2-fixing capacity of the soil.

Soft Clay Soil and Organic Soil Amendment Effects on Soil Organic Carbon in Paddy Cultivation Area

Soft clay soil has become a major problem in paddy cultivation area. Nearly half of the total paddy field in Kedah State, Malaysia cannot be utilized for paddy cultivation because of soft clay soil. The problem is related to the presence of weak hardpan structure that permits the soil to experience continuous wet condition. The soil also causes in the alteration of many processes soil organic carbon sequestration and turnover, but the main effect on the land is decrease in soil fertility. To investigate the effects of soft clay soil on soil organic carbon content, stock and change rate, the trial has been conducted in Alor Senibong paddy field area in Kedah, Malaysia examining the problematic paddy field that associated with soft clay soil problem. Hasil Tani Organic Compound (HTOC) was an organic soil amendment that used to enhance soil organic carbon in this study. Paddy field with the presence of soft clay soil showed a low soil organic carbon content and stock around 0.67% and 1.01 t·ha-1, respectively (depth 0-15 cm). The reduction of soil organic carbon content in soft clay soil was likely because of the waterlogged soil environment, the stability of soil aggregates and decline in humification process which then reduced soil organic carbon input. After being treated with HTOC, soil organic carbon content and carbon stock in soft clay soil have significantly increased by 0.67-3.14% and 1.01-4.76 t·ha-1 (depth 0-15 cm), respectively, yielding a mean monthly carbon change rate of 4.36 g C kg−1·mth.−1 (depth 0-15 cm). As whole, the succession of HTOC application to improve soil organic carbon content in this study could be employed in other paddy field areas that associated with soft clay soil problem.

Long-term application of manure over plant residues mitigates acidification, builds soil organic carbon and shifts prokaryotic diversity in acidic Ultisols

Addition of organic materials is believed to be a feasible practice for mitigating Ultisols acidification and loss of soil organic carbon (SOC). However, how organic materials mitigate acidification, affect SOC content and aggregation and shift microbial community structure requires further investigation. In this study, we used high-throughput sequencing of microbial DNA to evaluate the relationships between soil properties, aggregation and prokaryotic communities in soil subjected to 27 years of inorganic and organic fertilization. The field experiment included seven treatments: no fertilization (control), inorganic NPK fertilizer (I), inorganic NPK fertilizer plus liming (CaCO3) (IL), and inorganic NPK fertilizer plus peanut straw (IPS), rice straw (IRS), radish (IR), or pig manure (IPM). Amendment with NPK fertilizer plus pig manure more effectively increased soil pH, SOC, total nitrogen (TN), available phosphorus (AP) and dissolved organic carbon (DOC) compared with NPK fertilizer plus crop residues. IPM also increased the mass proportion of large macroaggregates (>2000 μm) from 7.8% in the control to 30.6% while it reduced effective diffusion coefficient of oxygen (DCo) from 12.58 × 10−6 m2 s−1 in the control to 2.81 × 10−6 m2 s−1. Application of pig manure increased prokaryotic diversity and altered prokaryotic community structure, while crop residues did not. Soil pH was the predominant factor influencing prokaryotic community structure. Bacillales and Clostridiales accounted for 47.5% and 21.4%, respectively of the indicator species in the IPM and the relative abundances of them were increased, compared with the other treatments. Furthermore, the relative abundances of Bacillales and Clostridiales were correlated with SOC, TN, AP and DOC, and negatively with DCo in the soil. Overall, our results suggest that application of NPK fertilizer plus pig manure rather than crop residues enhanced soil pH, improved SOC content and aggregation, increased prokaryotic diversity and altered community structure of prokaryote after 27-year fertilization.

Soil Organic Carbon of Purple Soil as Affected by Different Application of Biochar

Soil organic carbon (SOC) is the most important part of the soil carbon pool and soil labile organic carbon is a key indicator of changes in the soil carbon pool. In order to study changes in SOC and its labile components with different biochar additions to soil, a field experiment was conducted at Chongqing National Purple Soil Fertility and Fertilizer Efficiency of Long-Term Monitoring Station. Different amounts of biochar (0 kg·hm-2, CK; 4000 kg·hm-2, 0.5 BC; 8000 kg·hm-2, BC; 16000 kg·hm-2, 2BC) combined with fertilizer were applied to purple soil in this hilly area. SOC and soil labile carbon content were determined for purple soil rape-maize rotation systems. Results showed that:① Application of biochar can significantly improve SOC content; within a certain range, the amount of added biochar is correlated with SOC content. The content of soil microbial biomass carbon (SMBC) increased with application of 8000 kg·hm-2 biochar, but decreased with application of 4000 and 16000 kg·hm-2. The content of dissolved organic carbon (DOC) and readily oxidized carbon (ROC) in soil increased with different amounts of biochar; the highest DOC (198.83 g·kg-1) and ROC (4.86 g·kg-1) were obtained under low biochar addition treatments. ② The application of biochar significantly decreases the ratio of soil ROC to SOC and microbial entropy. The ratio of soil ROC to SOC and microbial entropy of 0.5 BC treatment are 20.45% and 4.11%, respectively, lower than for CK. Moreover, 0.5 BC and BC treatments can significantly improve the ratio of soil DOC to SOC. In summary, biochar addition in soil leads to low soil microbial activity but higher soil stability. An appropriate biochar treatment can stimulate accumulation of SOC, and 0.5BC treatment can improve soil DOC and ROC.

Including a one-year grass ley increases soil organic carbon and decreases greenhouse gas emissions from cereal-dominated rotations – A Swedish farm case study

Increased soil organic carbon (SOC) content has been shown to increase soil fertility and carbon sequestration, but SOC changes are frequently neglected in life cycle assessment (LCA) studies of crop production. This study used a novel LCA application using simulated SOC changes to examine the greenhouse gas (GHG) impact of a combined food and energy crop production from a crop rotation perspective. On a case pig farm, introduction of one year of grass ley into a cereal-dominated crop rotation was simulated. The grass and pig manure were used for biogas production and the digestion residues were used as fertiliser on the farm. This crop rotation shift increased the SOC stocks by an estimated 27 and 49% after 50 years and at steady state, respectively. The estimated corresponding net wheat yield increase due to higher SOC was 8-16% and 16-32%, respectively, indicating that initial loss of low-yield oat production can be partly counterbalanced. Net SOC increase (corresponding to 2 t CO2-eq ha(-1) a(-1)) was the single most important variable affecting the GHG balance. When biogas replaced fossil fuels, GHG emissions of the combined energy food crop rotation were approx. 3 t CO2-eq ha(-1) a(-1) lower than for the current food crop rotation. Sensitivity analyses led to variation of only 2-9% in the GHG balance. This study indicates that integrated food and energy crop production can improve SOC content and decrease GHG emissions from cropping systems. It also demonstrates the importance of including SOC changes in crop production-related LCA studies. (C) 2017 The Authors.

Combining hill-placed manure and mineral fertilizer enhances maize productivity and profitability in northern Benin

Throughout much of Sub-Saharan Africa (SSA), maize production is characterized by low productivity due to the scarce availability and use of external inputs and recurrent droughts exacerbated by climate variability. Within the integrated soil fertility management (ISFM) framework, there is thus a need for optimizing the application of fertilizers and manure to better use the limited nutrient resources and increase crop yield and farmer income. An on-station experiment was conducted in Northern Benin over a 4-year period to evaluate the effect of hill placement of mineral fertilizer and manure on maize yields and soil chemical properties. The treatments consisted in the combination of three rates of manure (0 (NM), 3 (3M) and 6 (6M) Mg ha−1) and three levels of fertilizer (0% (NF), 50% (50F) and 100% (100F) of the rate recommended by extension (76 kg N + 13.1 kg P + 24.9 K ha−1)). On average across the fertilizer rates, hill-placement of manure significantly improved soil organic carbon content, available P and exchangeable K after 4 years by up to 124, 166 and 77%, respectively, compared to the initial values. As a result of the nutrient inputs and improved soil properties, yields increased steadily over time for all manure and fertilizer combinations. Value-cost ratios and benefit–cost ratios were >2 and generally as good or even better for treatments involving 50F compared to NF or 100F. Although applying half the recommended rate of fertilizer without manure as currently done by many farmers appears to make economic sense, this practice is unlikely to be sustainable in the long term. Substituting 50F for 3M or complementing 50F with 3M are two possible strategies that are compatible with the precepts of ISFM and provide returns on investment at least as good as the current practice. However, this will require greater manure production, made possible in part by the increased stover yields, and access to means of transportation to deliver the manure to the fields.

Beneficial Nutrient Management Practice for Improving Maize (<em>Zea mays</em>) Yield in a Tropical Entisol

Beneficial nutrient management practices could increase maize yield via improving soil fertility. A study was conducted in the mid country wet zone of Sri Lanka (WM2b) on Typic Troporthents aiming to formulate a site specific fertilizer (SF) recommendation and to identify beneficial organic soil amendments (OA) to improve the fertility and productivity of soils for maize cultivation. The SF recommendation was developed using modified missing element technique. Incubated mixture of cattle manure and sawdust at 2:1 wet weight basis (CS-i) and biochar (BC) derived from sawdust were selected as OAs. Four treatments, (i) un-amended control (S), (ii) soil amended with SF (SSF), (iii) cattle manure-sawdust CS-i (2.2 Mg ha-1) with SF (CSi+SF) and (iv) biochar (1.1 Mg ha - 1) with SF (BC+SF) were tested in the field for two consecutive growing seasons (Yala 2013 and Maha 2013/14) for maize. According to missing element technique, soil was deficient in K, Mg, P and Zn nutrients and resulted in 38%, 35%, 27% and 24% relative dry-matter reductions, respectively. Addition of OA+SF significantly improved soil organic carbon content compared to SSF. Green cob yield ranged from 7.9 to 16.5 Mg ha-1 in Yala and 5.4 to 12.4 Mg ha -1 in Maha increasing yield significantly in CS-i+SF, BC+SF and SSF over the un-amended control in both seasons. Soil fertility and maize yield were sustained or improved under combined application of site specific fertilizer and organic amendments. Moreover, cut down of K fertilizer is possible with application of BC and CS-i OAs. Hence, SF recommendation along with biochar or cattle manure-sawdust mixture OAs is a beneficial nutrient management practice for cultivating maize.

Long term effect of crop residue management on yield, economics and soil fertility status in soybean based cropping system

A field experiment was carried out at Agricultural Research Station, Buldana, Maharashtra, India for 10 years (2003–04 to 2013–14) to study effect of soybean crop residue on the yield of succeeding rabi crops and soil health with special reference to organic carbon at fixed site in split plot design with three replications. The main plot treatments comprised four crop residue management viz., wheat with residue incorporation, wheat with no residue incorporation, chickpea with residue incorporation, chickpea with no residue incorporation and sub-plot treatments were fertilizers i. e. 50, 75 and 100% recommended doses of fertilizers for rabi crops. The results revealed that soybean crop residue incorporation significantly influenced grain yield of both the wheat and chickpea crops. The application of 100% recommended dose of fertilizer i. e. 120: 60: 60 kg NPK/ha for wheat and 25: 50: 00 kg NPK/ha for chickpea gave significantly highest grain yield, gross monetary and net monetary returns as well as improved soil organic carbon content.

Accumulation of organic C components in soil and aggregates.

To explore soil organic carbon (SOC) accumulation mechanisms, the dynamics of C functional groups and macroaggregation were studied synchronously through aggregate fractionation and 13C NMR spectroscopy in sandy loam soil following an 18-year application of compost and fertilizer in China. Compared with no fertilizer control, both compost and fertilizer improved SOC content, while the application of compost increased macroaggregation. Fertilizer application mainly increased the levels of recalcitrant organic C components characterized by methoxyl/N-alkyl C and alkyl C, whereas compost application mainly promoted the accumulation of methoxyl/N-alkyl C, phenolic C, carboxyl C, O-alkyl C and di-O-alkyl C in bulk soil. The preferential accumulation of organic C functional groups in aggregates depended on aggregate size rather than nutrient amendments. These groups were characterized by phenolic C and di-O-alkyl C in the silt + clay fraction, carboxyl C in microaggregates and phenolic C, carboxyl C and methoxyl/N-alkyl C in macroaggregates. Thus, the differences in accumulated organic C components in compost- and fertilizer-amended soils were primarily attributable to macroaggregation. The accumulation of methoxyl/N-alkyl C in microaggregates effectively promoted macroaggregation. Our results suggest that organic amendment rich in methoxyl/N-alkyl C effectively improved SOC content and accelerated macroaggregation in the test soil.

A Lixisol Microbial Activity Under Urban Wastes Composts Effect in Donsin, Burkina Faso

Mineralization causes soil carbon loss. This study focuses soil microbial activity measurement in relation with the application of six types of composts in sorghum three-year experiment. Composts were applied single or combined with urea. Organic carbon content, microbial biomass, respirometry and carbon global mineralization rate were evaluated. In comparison to the control, single composts treatments parameters variation rates ranged from -1 to +71%. When composts were combined with urea, parameters variations rates ranged from -8 to +107%. Under single urea, these parameters variation rates ranged from -14% to +31%. Best composts seemed to be those produced with various and balanced composting materials. Eco-friendly composts adoption could improve soil organic carbon content for sustainable microbial process. Keywords : Agro systems; carbon; respirometry; Burkina Faso.

Prediction of soil organic carbon for different levels of soil moisture using Vis-NIR spectroscopy

Visible and near infrared diffuse reflectance spectroscopy has produced promising results to infer soil organic carbon (SOC) content in the laboratory. However, using soil spectra measured directly in the field or with airborne imaging spectrometers remains challenging due to uncontrolled variations in surface soil conditions, like vegetation cover, soil moisture and roughness. In particular, soil moisture may dramatically degrade predictions of SOC content when using an empirical approach. This study aims to quantify the effect of soil moisture on the accuracy of SOC predictions, and propose a method to determine SOC content for moist samples with unknown moisture content. More than 100 soil samples were collected along a transect, in the Grand-Duchy of Luxembourg. The soil samples were air-dried, moistened in steps of 0.05g water g soil−1 until saturation, and scanned in the laboratory with a visible and near infrared diffuse reflectance spectrometer. We computed the normalized soil moisture index (NSMI) to estimate the soil moisture content of the samples (R2=0.74), and used it to spectrally classify the samples according to their moisture content. SOC content was predicted using separate partial least square regressions developed on groups of samples with similar NSMI values. The root mean square error of prediction (RMSE) after validation was always below 5g C kg−1, with a ratio of prediction to deviation (RPD) greater than 2. The SOC content prediction models with a-priori knowledge of soil moisture gave similar RMSE as the ones after the NSMI classification. Hence, the NSMI might be used as a proxy of moisture content to improve SOC content prediction for spectral data acquired outside the laboratory since the method is simple and does not need other data than a simple band ratio of the spectra.