Soil Fertility Management, Mitigating GHG Emissions and Sustainable Agriculture

A special issue of Soil Systems (ISSN 2571-8789).

Deadline for manuscript submissions: closed (31 August 2023) | Viewed by 35433

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Guest Editor
International Fertilizer Development Center, P.O. Box 2040, Muscle Shoals, AL 35662, USA
Interests: nutrient management; fertilizers and environment; GHG emissions; C and N cycling; nitrogen-use efficiency; balanced fertilization; integrated soil fertility management
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Special Issue Information

Dear Colleagues,

Soil fertility management plays a critical role in the sustainable improvement of crop productivity, and reducing environmental pollution including mitigation of greenhouse gas (GHG) emissions. With  increasing cropping intensity coupled with inappropriate application of fertilizers and organic inputs, soil fertility is in a declining trend, particularly in most developing countries in Asia and Africa. Most farmers’ use of fertilizer is imbalanced (excessive use of nitrogen and low or no use of secondary and micronutrients), leading to the mining of nutrients from soils. This results in lower crop productivity, posing a challenge to meeting an increasing global food demand.  Inefficient fertilizer application has not only reduced farm profits but also increased GHG emissions from soils. Therefore, it is important to identify sustainable strategies to improve soil fertility and fertilizer use efficiency by increasing plant nutrient uptake and reducing their losses to the environment.

Authors are invited to submit their work on sustainable strategies to improve soil fertility through efficient management of fertilizers, including the use of enhanced efficiency fertilizers, balanced fertilization, adoption of 4Rs (right source, right rate, right time, and right placement) of nutrient stewardship approaches, management of soil organic matter, mitigation of greenhouse gas emissions, and improved crop productivity.

Dr. Yam Kanta Gaihre
Guest Editor

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Keywords

  • soil fertility
  • fertilizer management
  • balanced fertilization
  • nitrogen use efficiency
  • mitigating GHG emissions
  • improving crop productivity
  • environmental pollution

Published Papers (11 papers)

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Research

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14 pages, 3709 KiB  
Article
Effects of Water Management and Rice Varieties on Greenhouse Gas Emissions in Central Japan
by Sunchai Phungern, Siti Noor Fitriah Azizan, Nurtasbiyah Binti Yusof and Kosuke Noborio
Soil Syst. 2023, 7(4), 89; https://doi.org/10.3390/soilsystems7040089 - 18 Oct 2023
Cited by 1 | Viewed by 1651
Abstract
Greenhouse gas (GHG) emissions from paddy fields depend on water management practices and rice varieties. Lysimeter experiments were conducted to determine the effect of rice varieties (lowland; Koshihikari (KH) and upland; Dourado Precoce (DP)) on GHG emissions under two water management practices: alternate [...] Read more.
Greenhouse gas (GHG) emissions from paddy fields depend on water management practices and rice varieties. Lysimeter experiments were conducted to determine the effect of rice varieties (lowland; Koshihikari (KH) and upland; Dourado Precoce (DP)) on GHG emissions under two water management practices: alternate wetting and drying (AWD) and continuous flooding (CF). A repeated cycle of drying and wetting in AWD irrigation was performed by drying the soil to −40 kPa soil matric potential and then rewetting. Consequently, the closed chamber method was used to measure direct emissions of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). The result revealed that water management significantly affected CH4 and N2O emissions (p < 0.05), while no significant effect was observed between different rice varieties. Although, AWD irrigation reduced CH4 emissions, it increased N2O emissions compared to CF irrigation, likely due to increased oxygen supply. AWD irrigation decreased GWP by 55.6% and 59.6% in KH and DP, respectively, compared to CF irrigation. Furthermore, CH4 and N2O emissions significantly correlated with soil redox potential and volumetric water content. These results suggest that AWD irrigation might be an effective water management method for mitigating GHG emissions from rice fields in central Japan. Full article
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14 pages, 17090 KiB  
Article
Effects of Irrigation Regimes and Rice Varieties on Methane Emissions and Yield of Dry Season Rice in Bangladesh
by Muhammad Ashraful Habib, S. M. Mofijul Islam, Md. Ashraful Haque, Lutful Hassan, Md. Zulfiker Ali, Swati Nayak, Manzoor Hussain Dar and Yam Kanta Gaihre
Soil Syst. 2023, 7(2), 41; https://doi.org/10.3390/soilsystems7020041 - 20 Apr 2023
Cited by 7 | Viewed by 2637
Abstract
Adoption of the right rice variety and water-saving irrigation method could reduce greenhouse gas (GHG) emissions in lowland rice cultivation. A study was conducted at the research farm of Bangladesh Agricultural University, Mymensingh, Bangladesh, in 2019 during the Boro (dry) season to determine [...] Read more.
Adoption of the right rice variety and water-saving irrigation method could reduce greenhouse gas (GHG) emissions in lowland rice cultivation. A study was conducted at the research farm of Bangladesh Agricultural University, Mymensingh, Bangladesh, in 2019 during the Boro (dry) season to determine the impacts of different rice varieties (BRRI dhan29, BRRI dhan47, BRRI dhan69, Binadhan-8, Binadhan-10, and Binadhan-17) on methane (CH4) emissions under two irrigation methods, i.e., alternate wetting and drying (AWD) and continuous flooding (CF). The treatments were laid out in a split-plot design, considering water regime as the main plots and rice variety as the sub-plots. The emission rates of CH4 were determined by collecting air samples using the closed chamber technique and measuring the concentrations using a gas chromatograph. CH4 emission rates varied with the growth and development of the rice varieties. The lowest cumulative CH4 emission rate was observed in Binadhan-17, particularly under AWD irrigation. Across the rice varieties, AWD irrigation significantly reduced the cumulative CH4 emissions by about 35% compared with CF. No significant variation in rice yield was observed between AWD (5.38 t ha−1) and CF (5.16 t ha−1). This study suggests that the cultivation of Binadhan-17 under AWD irrigation could be effective at reducing the carbon footprint of lowland rice fields. Full article
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12 pages, 3804 KiB  
Communication
Wetting Pattern of Cow Urine Patch in an Andisol Assessed through Bromide Concentration Distribution: A Pilot Study
by Magdalena A. Ramírez-Sandoval, Dante E. Pinochet and M. Jordana Rivero
Soil Syst. 2022, 6(4), 80; https://doi.org/10.3390/soilsystems6040080 - 20 Oct 2022
Cited by 1 | Viewed by 1645
Abstract
Cow urine is a rich source of mobile nutrients such as nitrate (NO3) and potassium (K+). The aim of this experiment was to evaluate the wetting pattern distribution through soil profile of cow urine patch in an andisol. [...] Read more.
Cow urine is a rich source of mobile nutrients such as nitrate (NO3) and potassium (K+). The aim of this experiment was to evaluate the wetting pattern distribution through soil profile of cow urine patch in an andisol. Two field experiments across two consecutive years were carried out to compare cow urine patches in relation to initial wetting pattern and volume of soil affected. Bromide (Br) has successfully been used as an inert hydrologic tracer to indicate the movement of NO3 and K+ in soil–water systems. The distribution of Br (used as a urine tracer) on the soil surface and down the profile was irregular in all the patches. Cow urine patches covered a surface area of 0.27 and 0.35 m2, respectively, and penetrated to a depth of 70 cm. The rapid downward movement of urine occurred through macropore flow but even so, between 27% and 40% of the applied Br was detected in the 0–5 cm soil layer. Br showed concentrations greater than 1500 mg kg−1 and up to 3000 mg kg−1, and as the concentration of Br decreases, the frequency and depth of affected layers increases. Despite the differences in moisture and in the distribution of the Br concentration in both years, the concentration frequency of 500 to 1500 mg kg−1 represented around 37% of the affected volume of soil (bulb of urine) in both years. Up to 40% of the bulb represented N equivalent rates between 187 and 975 kg N ha−1. These values can potentially be emitted in gases such as NH3, N2O, and N2. It is suggested that the presence of N in the volume of affected soil could vary due to the moisture content of the soil, and that in andisols of southern Chile under permanent grasslands there are a large number of macropores that would induce preferential flows. Full article
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11 pages, 1367 KiB  
Article
Will Biochar Suppress or Stimulate Greenhouse Gas Emissions in Agricultural Fields? Unveiling the Dice Game through Data Syntheses
by Simeng Li and Celeste Y. Chan
Soil Syst. 2022, 6(4), 73; https://doi.org/10.3390/soilsystems6040073 - 20 Sep 2022
Cited by 8 | Viewed by 1527
Abstract
With the increasing popularity of biochar as a soil amendment worldwide in recent years, a question of concern arises as to whether the application of biochar would suppress or stimulate greenhouse gas (GHG) emissions. In this study, published data extracted from independent individual [...] Read more.
With the increasing popularity of biochar as a soil amendment worldwide in recent years, a question of concern arises as to whether the application of biochar would suppress or stimulate greenhouse gas (GHG) emissions. In this study, published data extracted from independent individual studies were systematically selected, statistically processed, graphically presented and critically analyzed to understand biochar’s influences on the emissions of CO2, CH4 and N2O—the three major GHGs emitted in agricultural fields. The results revealed not only the significant importance of biochar’s pyrolysis temperature for its impacts on GHG emissions, but also the dissimilar influences on the generations of different GHGs. The application of biochar, in general, stimulated the emissions of CO2 and CH4 to various extents. With biochar pyrolyzed under relatively lower temperatures (e.g., <500 °C), higher application rates generally resulted in more stimulated CO2 and CH4 emissions; whereas those pyrolyzed under relatively higher temperatures (e.g., >550 °C) became less stimulative (and sometimes even suppressive) for CO2 and CH4 emissions, especially when applied at higher rates. Nevertheless, the response of N2O emission to biochar application contrasted with those of CO2 and CH4. The results may contribute to better regulations for biochar application in combating GHG emissions in agriculture. Full article
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13 pages, 2072 KiB  
Article
Optimum Rate and Deep Placement of Nitrogen Fertilizer Improves Nitrogen Use Efficiency and Tomato Yield in Nepal
by Naba Raj Pandit, Dyutiman Choudhary, Shashish Maharjan, Krishna Dhakal, Shree Prasad Vista and Yam Kanta Gaihre
Soil Syst. 2022, 6(3), 72; https://doi.org/10.3390/soilsystems6030072 - 17 Sep 2022
Cited by 7 | Viewed by 2913
Abstract
In Nepal, blanket fertilizer recommendations without considering diverse soil types, nutrient status, climate and crop management practices along with imbalanced fertilization practices by farmers, mainly “urea fertilizer,” have resulted in reduced nitrogen use efficiency (NUE) and productivity in tomato production. Optimizing the rate [...] Read more.
In Nepal, blanket fertilizer recommendations without considering diverse soil types, nutrient status, climate and crop management practices along with imbalanced fertilization practices by farmers, mainly “urea fertilizer,” have resulted in reduced nitrogen use efficiency (NUE) and productivity in tomato production. Optimizing the rate of nitrogen (N) fertilizer, application time and improved application methods could increase crop yields and NUE and reduce environmental costs. This study was conducted to identify the optimum N rate and application method for increased tomato yield and NUE. Multilocation trials (n = 28) conducted in a randomized complete block design with nine treatments across five districts included the omission of N, P and K (N0, P0, K0), variable N rates of 100, 150, 200 and 250 kg ha−1 (N-100, N-150, N-200 and N-250), use of urea briquettes (UB) with deep placement (UBN-150) and a control (CK). N input in UB was reduced by 25% from the recommended N rate of 200 kg ha−1 considering its expected higher NUE. Yield responses from an NPK omission plot revealed N as the most limiting plant nutrient. Applications of fertilizer at N-100, N-150, N-200 and N-250 increased tomato yield by 27%, 35%, 43% and 27%, respectively, over N0. Tomato yields responded quadratically to the added N fertilizers with optimum rates ranging from 150 to 200 kg ha−1 across districts. UBN-150 significantly increased tomato yield by 12% over N-150 and produced a similar yield to N-200 (the recommended rate). The highest partial factor productivity of nitrogen (PFPN) was observed at N-100 and the highest agronomic efficiency of N (AEN) was at N-200. Deep placement of UB at-150 increased PFPN by 8% and 21% and AEN by 27% and 21% compared with N-150 and N-200, respectively. These results have positive implications for developing efficient N fertilization strategies to increase tomato yields and reduce environmental impacts in Nepal. Full article
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12 pages, 2251 KiB  
Article
Improvement of Salinity Tolerance in Rice Seedlings by Exogenous Magnesium Sulfate Application
by Tran Dang Xuan, Can Thu Huong, Nguyen Van Quan, La Hoang Anh, Tran Dang Khanh and Ramin Rayee
Soil Syst. 2022, 6(3), 69; https://doi.org/10.3390/soilsystems6030069 - 31 Aug 2022
Cited by 8 | Viewed by 2735
Abstract
This study was conducted to develop the salt tolerance of rice by exogenous application of magnesium sulfate supplement (MgSO4). The salinization was carried out on 7-day-old rice seedlings including BC15 (salinity tolerant) and DT84DB (salinity susceptible) varieties with 0.5 mM MgSO [...] Read more.
This study was conducted to develop the salt tolerance of rice by exogenous application of magnesium sulfate supplement (MgSO4). The salinization was carried out on 7-day-old rice seedlings including BC15 (salinity tolerant) and DT84DB (salinity susceptible) varieties with 0.5 mM MgSO4. The exogenous application of MgSO4 significantly improves the growth of seedlings of both varieties. In addition, antioxidant activities increase in line with the raise of total phenolic and total flavonoid contents. Remarkably, the contents of momilactone B (MB) and phenolic compounds including tricin, ρ-coumaric, salicylic, cinnamic, benzoic, and ferulic acids simultaneously rise in both varieties treated by salinity and 0.5 mM MgSO4. Interestingly, MB was not found in the salt-treated samples but presents with considerable contents in the salt and MgSO4-treated cultivars. The findings imply that MgSO4 may significantly improve the salt tolerance of rice seedlings through the enhancement of secondary metabolic synthesis pathways, of which phenolic acids and momilactone B may play a crucial role in the response of rice to salt stress. In contrast, momilactone A (MA) did not show any contribution in salinity tolerance of examined rice cultivars at the early seedling stage. Further investigations on the effect of MgSO4 exogenous application in improving salinity tolerance of various rice varieties at other growing stages should be carried out. Full article
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15 pages, 5338 KiB  
Article
Comparison of Surface Water or Treated Municipal Wastewater Irrigation on Alfalfa Establishment, Soil Fertility, and Soil Microbial Conditions
by Leonard M. Lauriault, Nicole Pietrasiak, Murali K. Darapuneni, Andrew J. Dominguez and Gasper K. Martinez
Soil Syst. 2022, 6(3), 67; https://doi.org/10.3390/soilsystems6030067 - 10 Aug 2022
Viewed by 1786
Abstract
Water scarcity for agricultural irrigation is increasing globally while generation of treated municipal wastewater (TWW) is increasing due to urban expansion. Municipalities seek uses for their TWW, which is safe to apply to forage crops. Alfalfa (Medicago sativa) is the most [...] Read more.
Water scarcity for agricultural irrigation is increasing globally while generation of treated municipal wastewater (TWW) is increasing due to urban expansion. Municipalities seek uses for their TWW, which is safe to apply to forage crops. Alfalfa (Medicago sativa) is the most important forage crop worldwide being adapted to a wide range of environmental factors, including irrigation with low quality water. A strip plot study with four replications at New Mexico State University’s Rex E. Kirksey Agricultural Science Center at Tucumcari, NM USA, compared the effects of surface water (SW) and TWW on alfalfa establishment and soil fertility and microbial growth. Alfalfa established equally well when irrigated with equal amounts of TWW or SW. After one year, the application of TWW increased soil P and plant N and P more so than SW. Most microbial soil health indicators were positively increased by alfalfa establishment in virgin soil; however, the effect was greater with TWW compared with SW (1147, 1184, 1961, and 4991 nmol g−1 for total microbial biomass of soil irrigated with SW and TWW at seeding and after one year, respectively, LSD0.05 = 710). Thus, TWW irrigation could reduce applied fertilizer P to meet alfalfa’s requirement and increase soil health compared with SW. Full article
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11 pages, 1957 KiB  
Article
The Effect of Manure from Cattle Fed Barley- vs. Corn-Based Diets on Greenhouse Gas Emissions Depends on Soil Type
by Tien L. Weber, Xiying Hao, Cole D. Gross, Karen A. Beauchemin and Scott X. Chang
Soil Syst. 2022, 6(2), 47; https://doi.org/10.3390/soilsystems6020047 - 21 May 2022
Viewed by 2340
Abstract
Efforts to reduce greenhouse gas (GHG) emissions from cattle production have led to modifications of livestock diet composition aimed at reducing CH4 emissions from enteric fermentation. These diet modifications can result in varied manure types that may differentially affect GHG emissions when [...] Read more.
Efforts to reduce greenhouse gas (GHG) emissions from cattle production have led to modifications of livestock diet composition aimed at reducing CH4 emissions from enteric fermentation. These diet modifications can result in varied manure types that may differentially affect GHG emissions when applied to soil. The purpose of this experiment was to examine the effect of different manure types on GHG emissions. We conducted an incubation experiment, comparing the manure from livestock fed a corn-based diet (CM) to that from livestock fed a traditional barley-based diet (BM). The manures were applied to three soil types (with varied soil fertility and pH) and compared to a control (without manure application). Carbon dioxide (CO2) emissions were greater from CM than from BM across all soil types (29.1 and 14.7 mg CO2-C kg−1, respectively). However, CM resulted in lower N2O emissions relative to BM in the low fertility soil (4.21 and 72.67 μg N2O-N kg−1, respectively) and in lower CH4 emissions relative to BM in the two acidic soils (0.5 and 2.5 μg CH4-C kg−1, respectively). Total GHG emissions (sum of CO2, N2O, and CH4) were similar between CM and BM across all soil types, but CM (unlike BM) had 52–66% lower emissions in the low fertility soil relative to both CM and BM in the high fertility soil. Our study shows that manure and soil type interact to affect GHG emissions and that CM may mitigate N2O emissions relative to BM when applied to low fertility soils. Full article
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17 pages, 1213 KiB  
Article
Effects of Plastic versus Straw Mulching Systems on Soil Microbial Community Structure and Enzymes in Strawberry Cultivation
by Katherine Muñoz, Sören Thiele-Bruhn, Kilian G. J. Kenngott, Maximilian Meyer, Dörte Diehl, Zacharias Steinmetz and Gabriele E. Schaumann
Soil Syst. 2022, 6(1), 21; https://doi.org/10.3390/soilsystems6010021 - 17 Feb 2022
Cited by 10 | Viewed by 3319
Abstract
This study aimed to evaluate changes in abundance, structure, and enzyme activity of the soil microbiome in response to 4 years of mulching using either black polyethylene plastic film (PM) or wheat straw (SM). Soil samples (depth 0–5 and 5–10 cm) were collected [...] Read more.
This study aimed to evaluate changes in abundance, structure, and enzyme activity of the soil microbiome in response to 4 years of mulching using either black polyethylene plastic film (PM) or wheat straw (SM). Soil samples (depth 0–5 and 5–10 cm) were collected from conventional strawberry plots, in two samplings: 1 week prior (S1) and 7 weeks after straw application (S2). Selected soil properties were monitored in each system and the abundance and structure of microbial communities were characterized via phospholipid fatty acid (PLFA) analysis. The investigation of soil microbial functions included activities of the enzymes chitinase, leucine aminopeptidase, and acid phosphatase, as well as function genes involved in nitrogen transformation. Each mulch system resulted in distinct physicochemical properties. In particular, a pH value higher by one-unit under PM (7.6 ± 0.3) compared to SM (6.5 ± 0.3) was observed. Values for SOC, DOC, and total-N were 15%, 22%, and 16% higher in PM than in SM. The microbial biomass (total PLFAs) was 1.5-fold higher in SM compared to PM. The abundance of soil fungi (F) and bacteria (B) increased by 37% and 44% after straw incorporation compared to PM (S2). In particular, Gram-negative bacteria (gr–) increased by twofold in SM. Consequently, wider F:B and gr+:gr– ratios were observed in PM. According to the shifts in microbial abundance, the activity of the enzyme chitinase was lower by 27% in PM, while the activity of the acid phosphatase increased by 32%. Denitrification genes were not affected by the mulching systems. In conclusion, the abundance and structure of the investigated microbial groups and the enzyme activities were strongly influenced by the mulching system. In detail, effects on microbiota were primarily attributed to the altered soil pH and probably the input of degradable organic matter with straw mulching in SM. This resulted in higher abundance of soil microorganisms in SM, although measures within this cultivation system such as fungicide application may have exerted adverse effects on the microbiota. Full article
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Review

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32 pages, 3291 KiB  
Review
Biochar Improves Soil Fertility and Crop Performance: A Case Study of Nigeria
by Abdulrahman Maina Zubairu, Erika Michéli, Caleb Melenya Ocansey, Norbert Boros, Gabriella Rétháti, Éva Lehoczky and Miklós Gulyás
Soil Syst. 2023, 7(4), 105; https://doi.org/10.3390/soilsystems7040105 - 22 Nov 2023
Cited by 1 | Viewed by 3061
Abstract
Africa, specifically Nigeria, has witnessed a dramatic increase in population over the last century, prompting efforts to ensure sustainable food production and quality. Concerns for soil sustainability and food security have led to the exploration of cost-effective methods, such as biochar, to enhance [...] Read more.
Africa, specifically Nigeria, has witnessed a dramatic increase in population over the last century, prompting efforts to ensure sustainable food production and quality. Concerns for soil sustainability and food security have led to the exploration of cost-effective methods, such as biochar, to enhance soil quality. Researchers in Nigeria and Africa as a whole have investigated biochar’s potential to improve soil fertility and crop performance across various agroecological zones. This paper aims to review recent biochar research priorities on soil fertility and crop performance with an emphasis on various sole biochar applications and combinations with fertilizers to determine the research gaps that need to be developed more in biochar research in Nigeria. From the papers reviewed, sole biochar applications and biochar + macronutrients and biochar + manure combinations were studied more dominantly, while biochar + micronutrients research projects were scanty despite their low content in the semi-arid soils of Nigeria. The studies were spread across the country with the majority taking place in derived savanna and humid forest, while Sudan savanna and Sahel savanna received less research attention despite being characterized by a low-fertile soil and vast area of land. Research involving BC in the context of Sahel savanna (SLS) and Sudan savanna (SS) soils is strongly encouraged in Nigeria. This research should encompass a wide range of investigations, including sole BC applications and combinations of BC with macronutrients, micronutrients, and manure, as well as exploring its potential as a slow-release fertilizer. Incorporating exclusive biochar in substantial amounts appears economically unfeasible within the context of local biochar production. However, it can be utilized in the synthesis of slow-release fertilizers, requiring smaller quantities and potentially offering cost-effectiveness. This approach enhances soil condition and crop productivity. Challenges are faced due to less commercial production as a result of inadequate power and structural facilities. Exploring the modification of local biochar for slow-release fertilizers through future research offers potential profitability. Full article
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14 pages, 276 KiB  
Review
The Central Role of Soil Organic Matter in Soil Fertility and Carbon Storage
by Jörg Gerke
Soil Syst. 2022, 6(2), 33; https://doi.org/10.3390/soilsystems6020033 - 31 Mar 2022
Cited by 50 | Viewed by 9888
Abstract
The aim of the paper is to give an overview on the chemistry of soil organic carbon (SOC) affecting nutrient availability, the emission of greenhouse gases and detoxifying harmful substances in soil. Humic substances represent the stable part of SOC, accounting for between [...] Read more.
The aim of the paper is to give an overview on the chemistry of soil organic carbon (SOC) affecting nutrient availability, the emission of greenhouse gases and detoxifying harmful substances in soil. Humic substances represent the stable part of SOC, accounting for between 50 and more than 80% of organically bound carbon in soil. Humic substances strongly affect the soil solution concentration of several plant nutrients and may increase P-, Fe-, and Cu- solubility, thereby increasing their plant availability. Soil organic carbon, mainly humic substances, can detoxify monomeric Al in acid soils, can strongly bind toxic heavy metals, making them unavailable to the plant roots, and may strongly bind a vast variety of harmful organic pollutants. Increasing SOC is an important goal in agriculture. The inclusion of mixtures of semi-perennial plant species and cultivars may strongly increase SOC and humic substance content in soils. To increase SOC, farmyard manure and its rotted or composted forms are superior compared to the separate application of straw and slurry to soil. The storage of carbon, mainly in organic form, in soils is very important in the context of the emission of greenhouse gases. Worldwide, soils release about 10 times more greenhouse gases compared to fossil fuel combustion. Small increments in SOC worldwide will strongly affect the concentration of atmospheric CO2. The public discussion on soil fertility and greenhouse gas emissionshas been politically controlled in a way that leaves the important and positive contribution of soil organic carbon and mainly humic substances partly misinterpreted and partly underestimated. Full article
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