Soil carbon, multiple benefits

Forests, 2018

Forests provide valuable ecosystem and societal services, including the sequestration of carbon (C) from the atmosphere. Management practices can impact both soil C and nitrogen (N) cycling. This study examines soil organic C (SOC) and N responses to thinning and fertilization treatments. Soil was sampled at an intensively managed Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation in northwestern Oregon, USA. Management regimes-thinning, fertilization plus thinning, and no (control) treatment-were randomly assigned to nine 0.2-ha plots established in 1989 in a juvenile stand. Prior to harvest, forest floor and soil bulk density and chemical analysis samples were collected by depth to 150 cm. During a single rotation of ~40 years, thinning treatments significantly reduced SOC and N stocks by 25% and 27%, respectively, compared to no treatment. Most of this loss occurred in deeper soil layers (below ~20 cm). Fertilization plus thinning treatments also reduced SOC and N stocks, but not significantly. Across all management regimes, deeper soil layers comprised the majority of SOC and N stocks. This study shows that: (1) accurately quantifying and comparing SOC and N stocks requires sampling deep soil; and (2) forest management can substantially impact both surface and deep SOC and N stocks on decadal timescales.

Basic and Applied Ecology, 2021

Fire and overgrazing reduce aboveground biomass, leading to land degradation and potential impacts on soil organic carbon (SOC) and total nitrogen (TN) dynamics. However, empirical data are lacking on how prescribed burning and livestock exclusion impact SOC in the long-term. Here we analyse the effects of 19 years of prescribed annual burning and livestock exclusion on tree density, SOC and TN concentrations in the Sudanian savanna ecoregion at two sites (Tiogo and Laba) in Burkina Faso. Results revealed that neither livestock exclusion nor prescribed burning had significant impact on SOC and TN concentrations. The results at both sites indicate that 19 years of livestock and fire exclusion did not result in a significant increase in tree density compared to grazing and annual prescribed burning. The overall mean (± SEM) of SOC stocks in the 0–50 cm depth increment in the unburnt (53.5 ± 4.7 Mg C ha−1) and annually burnt (56.4 ± 4.3 Mg C ha−1) plots at Tiogo were not statistically ...

Biochar

Biochar amendment improves the physical, chemical and biological characteristics of different soil types under different climatic and environmental conditions. In this study, effects of biochar or live pasture plants existing alone or co-existing on selected soil properties of sandy loam soil under humid lowland tropical climatic conditions were investigated. The changes measured in the amended soil, with or without plants, were compared to the unamended and unplanted soils. Biochar amendment with or without pasture improved moisture retention, lowered bulk density, increased pH and kept the electrical conductivity within ranges conducive for pasture growth. Generally, contents of all the nutrients increased following biochar amendment, however pasture establishment without amendment resulted in depletion of available potassium and magnesium. Under all treatment conditions, soil organic carbon and soil organic matter were significantly depleted. Cogon grass is invasive under all land use systems and contributes to greenhouse gas emissions through slash-and-burn. Using biomass from the grass instead of burning would mitigate CO 2 emissions from the tropics.

Plants, 2022

Plant roots are primary factors to contribute to surface and deep soil carbon sequestration (SCS). Perennial grasses like vetiver produce large and deep root system and are likely to contribute significantly to soil carbon. However, we have limited knowledge on how root and shoot decomposition differ and their contribution to SCS. This study examined biomass production and relative decomposition of vetiver which was grown under glasshouse conditions. Subsequently the biomass incubated for 206 days, and the gas analysed using ANCA-GSL. The results confirmed large shoot and root production potential of 161 and 107 Mg ha−1 (fresh) and 67.7 and 52.5 Mg ha−1 (dry) biomass, respectively with 1:1.43 (fresh) and 1:1.25 (dry) production ratio. Vetiver roots decomposed more rapidly in the clay soil (p < 0.001) compared with the shoots, which could be attributed to the lower C:N ratio of roots than the shoots. The large root biomass produced does indeed contribute more to the soil carbon ac...

Agronomy for Sustainable Development, 2022

Soils are the basis of life on land and the ways in which we manage them for crop production, impact their role, functions and quality. Conventional farming uses industrial inputs to a level that is economically justified, whilst organic farming systems avoid mineral fertilizers and synthetic chemical pesticides. This study investigates the long-term effect of organic and conventional farming systems on soil quality. The DOK trial (bioDynamic, bioOrganic, Konventionell (German for conventional)) running since 1978 in Therwil (CH), compares bioorganic (BIOORG), biodynamic (BIODYN), and conventional (CONFYM) farming systems at two farmyard manure intensities corresponding to 0.7 and 1.4 livestock units per hectare with a purely mineral fertilized system (CONMIN) and an unfertilized control (NOFERT). The treatments in the DOK trial vary in plant protection and receive system-specific organic matter inputs differing in rate and quality. With this work, we revisit the soil organic carbon (SOC) dynamics across 42 years and redefine the previous perception of mainly declining SOC contents after 21 years of organic and conventional management ). After 42 years, we found SOC contents to be increased in BIODYN 1.4 and to a lesser extent also in BIOORG 1.4. CONFYM 1.4 showed stable SOC contents, while systems fertilized with manure of 0.7 livestock units and CONMIN lost SOC. SOC loss was highest in NOFERT. Enhanced biological soil quality under organic and particularly biodynamic management highlights the close link between soil biology and SOC changes. The impact of farming systems on SOC was detectable after 2 decades of continuous management. We conclude that recycling manure at a level of 1.4 livestock units per hectare permits maintenance of SOC levels and that composting manure, as performed in BIODYN 1.4, helps to further increase SOC levels and improve biological soil quality.