Land use change impacts on floods at the catchment scale: Challenges and opportunities for future research

Research gaps in understanding flood changes at the catchment scale caused by changes in forest management, agricultural practices, artificial drainage and terracing are identified. Potential strategies in addressing these gaps are proposed, such as complex systems approaches to link processes across time scales, long-term experiments on physical-chemical-biological process interactions, and a focus on connectivity and patterns across spatial scales. It is suggested that these strategies will stimulate new research that coherently addresses the issues across hydrology, soil and agricultural sciences, forest engineering, forest ecology and geomorphology

Effects of crop residues and reduced tillage on macrofauna abundance

Abstract Conservation agriculture is promoted to safeguard resilient properties of soils and to reclaim degraded arable lands. This is achieved through creating necessary conditions for fauna recolonisation. A study was carried out at Kadoma and Southeast Lowveld of Zimbabwe to assess the effects of conservation agriculture practices on soil macrofauna diversity in the 2008-2009 agricultural season. A randomized complete block design experiment, where four crop residue levels (0t/ha, 2t/ha, 4t/ha and 6t/ha) were replicated four times on un-tilled plots at five sites, was used. Soil fauna found in collected monoliths were identified and quantified. Analysis of variance showed significance (P<0.001) in site and treatment effects on both macrofauna abundance and diversity. Reduced tillage with residue cover yielded significantly (P<0.05) higher species richness and macrofauna abundance than conventional systems. There was a significant correlation (r 2 =0.767) between residue amount and species richness. Although there was no apparent consistent relationship between treatment and species richness, diversity and evenness; abundance was in the order 6t/ha>4t/ha>2t/ha>0t/ha>Conventional systems. The major macrofauna groups observed were termites, ants and beetle-larvae. It was concluded that short-term conservation agriculture systems has significantly positive effects on macrofauna species richness and abundance, which are crucial for initiating soil regeneration. The results are discussed in the context of sustainable crop production using conservation agriculture by resource poor farmers

Grassland degradation significantly enhances soil CO2 emission

Grassland degradation reduces net primary production and, subsequently, soil fertility and soil organic carbon stocks (SOCs); however, little is known about its impact on soil CO2 emissions, particularly the emissions relative to SOCs and biomass produced. The main objective of this study, performed in KwaZulu-Natal province of South Africa, was to quantify the impact of grass basal cover, as main indicator of grassland degradation, on soil CO2 emissions. The soil CO2 emissions were measured from three grass cover levels (non-degraded, with 100% grass cover, moderately degraded: 25 < grass cover < 50%; and highly degraded: 0 < grass cover < 5%) using a LI-COR 6400XT. The measurements were done at three randomly selected positions in each grass cover level, from January 2013 to April 2015. At each position, measurements were done once during winter months and twice during summer months, resulting in a total of 1053 measurements for the entire study period. The measured average gross soil CO2 emission was significantly higher (1.78 +/- 0.013 g CO2-C m(-2) day(-1)) in non-degraded than moderately (1.60 +/- 0.12 g CO2-C m(-2) day(-1)) and highly degraded grasslands (0.68 +/- 0.10 g CO2-C m(-2) day(-1)). However, when expressed relative to SOCs and aboveground biomass produced, the trends were opposite. Average soil CO2 emission relative to SOCs was lowest in the non-degraded grassland (0.034 +/- 0.01 g CO2-C g(-1)C day(-1)) and highest in the moderately degraded grassland (0.058 +/- 0.02 g CO2-C g(-1)C day(-1)) with the highly degraded grassland being intermediate (0.04 +/- 0.00 g CO2 g(-1)C day(-1)). Similarly, soil CO2 emission relative to aboveground biomass produced was lowest in the non-degraded grassland at 0.15 +/- 0.02 kg CO2-C kg(-1) biomass year(-1), which was almost 5 fold lower than 0.73 +/- 0.01 kg CO2-C kg(-1) biomass year(-1) in the highly degraded grassland. Gross soil CO2 emission correlated significantly and positively with SOC (r = 0.83 and 0.82 for SOC content and stocks, respectively), SON (0.67 and 0.53 for content and stocks, respectively), C:N ration (0.62), and soil water content (0.75) but negatively with clay content (-0.89). Soil CO2 emission relative to SOCs correlated significantly and negatively with both SOC (-0.50 and -0.51 for content and stocks, respectively) and SON (-0.45 and -0.42 for content and stocks, respectively). While gross CO2 emissions decreased with grassland degradation, CO2 emission relative to both SOCs and aboveground biomass increased with grassland degradation. These results point to direct links between grassland degradation and global warming because CO2 is one of the key greenhouse gases. Therefore, strategies for rehabilitating degraded grasslands need to aim at reducing soil CO2 emission in order to mitigate climate change

Soil tillage impact on the relative contribution of dissolved, particulate and gaseous (CO2) carbon losses during rainstorms

Although the impact of water erosion on soil carbon losses has been widely investigated, little is known about the relative contributions of dissolved, particulate and gaseous losses, a prerequisite for understanding the mechanisms of carbon (C) export from soils and designing mitigation procedures. The main objective of this study was to quantify the losses of dissolved organic and inorganic C (DOC, DIC), particulate organic C (POC) and soil CO2 from runoff microplots on tilled (T) and no-tilled (NT) soils. The study was performed in the Beauce region in central France under Luvisols using 45 and 80 mmh(-1) artificial rains. At 45 mm h(-1), T plots produced C erosion at an average of 1189.7 +/- 114.8 mg C m(-2) h(-1) with 76.9% of it being POC (915.0 +/- 100.0 mg C m(-2) h(-1)), 21.7% DOC (258.3.0 +/- 7.6 mg C m(-2)h(-1)), 1.4% (16.3 +/- 7.2 mg C m(-2)h(-1)), DIC and 0.01% CO2. NT decreased total soil C losses by 95% (from 0.8 to 0.038 g C m(-2)h(-1)) and soil C losses were as CO2 only. At 80 mm h(-1) NT surprisingly increased C erosion by 40% compared to T (from 39.4 to 55.3 g C m(2) h(-1)), with 95.5% of the C losses being POC vs 88.7% for T. These results on rainstorm-induced C fluxes from soils controlled by tillage are expected to be of future value: (1) for selecting appropriate land management that will mitigate against C losses from soils and improve soil carbon sequestration and; (2) to better understand the Global Carbon Cycle and further develop the existing models

On the impact of grassland management on soil carbon stocks: a worldwide meta-analysis

International audienceGrasslands occupy 70% of whole agricultural land and hold significant amounts of carbon, a key element in the regulation of Earth's soils fertility, biomass production and climate. Previous work has shown that carbon stocks of grassland soils have been largely depleted worldwide due to missuse or mismanagement but that shifts in management could also potentially increase soil carbon stocks and mitigate against the degradation of natural ecosystems. However, the existing literature points to large discrepancies in the impact of grassland management practices on soil carbon, which the present study investigated. Here we considered 235 experimental sites in 18 countries across the world where shifts in grassland management involved different grazing strategies (free, F vs controlled, C; high, H vs low, L density grazers), grazers exclusion (E), mowing (M) and burning (B). The best performing practice was controlled grazing with high density of grazers (CHG) with an average soil organic carbon content (SOCC) increase of 21% and with 100% of the studies pointing to a SOCC increase. This was followed by E (14.9%; 60%) and FLG (13.3%; 80%). On average, burning grasslands, decreases SOCC by 9.3% but 31% of the studies pointed to an increase, thus indicating discrepancies in the impact of grassland management. CLG and mowing did not significantly impact SOCC. These results also indicated that B decreased SOCC the most under moist to humid climates (−10.9% vs −1.7% under arid to semi-arid), while that E was only beneficial in arid to semi-arid grasslands. Adoption of rotational high-intensity grazing in place of free grazing grasslands, should be seriously considered by policy and decision makers to mitigate against climate change while fostering economic and social development

Variance components and heritability of traits related to root : shoot biomass allocation and drought tolerance in wheat

Enhanced root growth in plants is fundamental to improve soil water exploration and drought tolerance. Understanding of the variance components and heritability of root biomass allocation is key to design suitable breeding strategies and to enhance the response to selection. This study aimed to determine variance components and heritability of biomass allocation and related traits in 99 genotypes of wheat (Triticum aestivum L.) and one triticale (X. Triticosecale Wittmack) under drought-stressed and non-stressed conditions in the field and greenhouse using a 10x10 alpha lattice design. Days to heading (DTH), days to maturity (DTM), number of tillers (NPT), plant height (PH), spike length (SL),shoot and root biomass (SB, RB), root to shoot ratio (RS), thousand kernel weight (TKW) and yield (GY) were recorded. Analyses of variance, variance components, heritability and genetic correlations were computed. Significant (p70%) for RS observed in this population constitute several bottlenecks for improving yield and root mass simultaneously. However, indirect selection for DTH, PH, RB, and TKW, could help optimize RS and simultaneously improve drought tolerance and yield under drought-stressed conditions

Reduced form modeling of limit order markets

The impact of agricultural practices on CO2 emissions from soils needs to be understood and quantified to enhance ecosystem functions, especially the ability of soils to sequester atmospheric carbon (C), while enhancing food and biomass production. The objective of this study was to assess CO2 emissions in the soil surface following tillage abandonment and to investigate some of the underlying soil physical, chemical and biological controls. Maize (Zea mays) was planted under conventional tillage (T) and no-tillage (NT), both without crop residues under smallholder farming conditions in Potshini, South Africa. Intact top-soil (0?0.05 m) core samples (N = 54) from three 5 ? 15 m2 plots per treatment were collected two years after conversion of T to NT to evaluate the short-term CO2 emissions. Depending on the treatment, cores were left intact, compacted by 5 and 10%, or had surface crusts removed. They were incubated for 20 days with measurements of CO2 fluxes twice a day during the first three days and once a day thereafter. Soil organic C (SOC) content, soil bulk density (?b), aggregate stability, soil organic matter quality, and microbial biomass and its activity were evaluated at the onset of the incubation. CO2 emissions were 22% lower under NT compared with T with CO2 emissions of 0.9 ? 0.10 vs 1.1 ? 0.10 mg C?CO2 gC?1 day?1 under NT and T, respectively, suggesting greater SOC protection under NT. However, there were greater total CO2 emissions per unit of surface by 9% under NT compared to T (1.15 ? 0.03 vs 1.05 ? 0.04 g C?CO2 m?2 day?1). SOC protection significantly increased with the increase in soil bulk density (r = 0.89) and aggregate stability (from 1.7 ? 0.25 mm to 2.3 ? 0.31, r = 0.50), and to the decrease in microbial biomass and its activity (r = ?0.59 and ?0.57, respectively). In contrast, the greater NT CO2 emissions per m2 were explained by top-soil enrichment in SOC by 48% (from 12.4 ? 0.2 to 19.1 ? 0.4 g kg?1, r = 0.59). These results on the soil controls of tillage impact on CO2 emissions are expected to inform on the required shifts in agricultural practices for enhancing C sequestration in soils. In the context of the study, any mechanism favoring aggregate stability and promoting SOC allocation deep in the soil profile rather than in the top-soil would greatly diminish soil CO2 outputs and thus stimulate C sequestration

Thigh-length compression stockings and DVT after stroke

Controversy exists as to whether neoadjuvant chemotherapy improves survival in patients with invasive bladder cancer, despite randomised controlled trials of more than 3000 patients. We undertook a systematic review and meta-analysis to assess the effect of such treatment on survival in patients with this disease