Effect of Cover Crops Associated With Lettuce Production Under No-Tillage System

The use of cover crops has benefits for the chemical, physical and biological properties of the soil. However, together with the need for good vegetable productivity, considerable challenges arise in several regions of Brazil. The preparation of conventional soil for initiating no-tillage systems is necessary to create a management history and assimilate the benefits of the no-tillage system in vegetables, ensuring sustainable production. The objective of this research was to evaluate lettuce yield as a function of different cover crops as a function of resistance to soil penetration. The experiment was conducted in the horticulture sector of the University of Rio Verde, Rio Verde, Goiás, Brazil. The cover crops used were sunflower (Helianthus annuus), sunn hemp (Crotalaria juncea), and fallow, and the vegetable used was lettuce (Lactuca sativa). The variables analyzed were plant height and lettuce yield, straw decomposition, and soil resistance to penetration. The collected data were submitted to analysis of variance, and if significant, was compared by Tukey test (p < 0.05) and regression analysis. The lettuce height in the different management systems showed no statistical differences. The decomposition of the straw presented accentuated degradation for the evaluated cover crops and the productivity was bigger in the straw of crotalaria and fallow. Soil resistance for cover crops was not greater than 2 MPa.

Organic matter of sod-podzolic soil after transition to a fallow state

Soil plays a crucial role in carbon sequestration in terrestrial ecosystems. It is known that the strengthening of carbon sequestration processes occurs with a decrease in the intensity of soil treatments. The study of changes in organic matter and physical properties of sod-podzolic soil 16 years after the transition from arable soils to a fallow state against the background of weak water erosion was carried out. A significant increase in the content and reserves of total carbon in fallow soil compared to arable soil was found, mainly due to carbon of the light fraction. On arable soil, the content of the light fraction in the lower part of the field was significantly higher than in the upper part, due to the washing away of light particles as a result of erosion, these differences were smoothed out on fallow soil. There are no significant changes in the density, density of the solid phase and total porosity in fallow soil at this stage of succession, compared with arable soil. In fallow soil, the content of macro-aggregates (including water-bearing ones) was noticeably higher, and the share of micro-aggregates was lower than in arable soil.

Long-Term Bare Fallow Soil Reveals The Temperature Sensitivity of Priming Effect of The Relatively Stabilized Soil Organic Matter

Priming plays an important role in modifying the decomposition of soil organic matter (SOM), but there are large uncertainties in the temperature effect on priming mainly due to the variation in SOM stability. Long-term bare fallow offers a unique opportunity to isolate the relatively stabilized SOM pool and study its properties. We tested the temperature effect on priming of the relatively stabilized SOM pool by incubating soil samples collected from a bare fallow (representing the relatively stabilized SOM) and its adjacent old field (containing both stabilized SOM and labile SOM) at 10 and 20°C for 815 days. We amended the soil samples with C4 maize leaves to distinguish the CO2 source released from the soils (formed under C3 vegetation) and the substrate added (i.e. maize leaves) based on the natural abundance of δ13C. In all cases, there was a positive priming effect on native SOM decomposition when fresh organic matter (maize leaves) was added. The temperature sensitivity of priming effect (calculated as the difference in SOM decomposition due to the addition of maize leaves) in the bare fallow soil and the old field soil was quite different: increasing temperature significantly enhanced the magnitude of priming effect in the bare fallow soil, whereas had no effect on the magnitude of priming effect in the old field soil. The increase of the amount of microbial biomass C by maize leaves application was higher in the bare fallow soil than in the old field soil. Furthermore, for maize leaves-treated soil, temperature increase significantly increased the rate of microbial N mining throughout the incubation in the bare fallow soil, but had minor effect on microbial N mining in the old field soil at the end of incubation. We conclude that the priming effect of the relatively stabilized SOM was sensitive to temperature increase, which may be mainly driven by greater microbial growth and microbial demand for N. This work highlights the vulnerability of stabilized SOM to priming effect under global warming and reveals the potential role of microbes in regulating soil C dynamics under future climate change.

Plant-soil interactions can enhance earth barrier systems in urban spaces

<p>Climate change is expected to introduce increasing threats to human health and the urban built environment, due to extreme events such as heavy precipitation. In the urban environment, impermeable hard-engineered surfaces may exacerbate climate change effects and increase the risk of floods. Adaptation solutions are essential to limit the climate change impacts on the urban environment. Research is needed to design new environmentally friendly multi-layer earthen barrier systems that can mimic the natural hydrological processes (e.g., plant-soil interaction) removed by urbanization.</p><p>In this study, potential barrier materials were selected from both natural soils and recycled waste materials (e.g., recycled concrete aggregates). Contrasting herbaceous species (legumes, grasses and forbs) were selected and grown for five months in compacted soil columns and saturated hydraulic conductivity (<em>K</em><sub>sat</sub>) was tested for each soil column. Following <em>K</em><sub>sat</sub> tests, all soil columns were saturated and left for evapo-transpiration. Plant water uptake, matric suction and soil strength (penetration resistance) were measured.</p><p>Among the materials tested in this study, recycled concrete aggregate (RCA) was the most suitable material for the barrier drainage layer, having a <em>K</em><sub>sat</sub> equal to natural gravel, but with 14% lower dry density (2.3 Mg/m<sup>3</sup>) and seven-fold greater water holding capacity (0.08 g/g). However, a portion of the water stored in the RCA was strongly bound to micropores and not available for plants. Plant growth in soil columns increased <em>K</em><sub>sat</sub>. On average <em>K</em><sub>sat</sub> of four-month old vegetated soil (3.2e<sup>-5</sup> ± 2.0e<sup>-6</sup> m/s) was four times larger than that of control fallow soil (6.9e<sup>-6</sup> ± 1.4e<sup>-6</sup> m/s). However, tested species differed in their effect on <em>K</em><sub>sat</sub>, ranging from 9.9e<sup>-6</sup> ± 1.3e<sup>-6</sup> m/s of <em>Festuca ovina</em> (Grass) to 4.1e<sup>-5</sup> ± 3.7e<sup>-6</sup> of <em>Lotus pedunculatus</em> (Legume). In the fallow soil, daily evaporation led to an average water loss of 0.49 ± 0.04 g per 100 g of soil, evapo-transpiration led to a daily water loss up to 2.58 ± 0.10 g per 100 g of soil in<em> Lotus corniculatus</em> columns. Thus, soil drying and induced matric suction strengthened the vegetated soil and further increased its ability to store water. For instance, soil vegetated with <em>L. corniculatus</em> had seven times faster water absorption and twenty-five times greater strength compared with control fallow soil. Plants affected the hydraulic conductivity and water relation of the barrier system. Root systems can increase soil hydraulic conductivity through root-induced channels. This may enable faster drainage during floods, but we found large differences between species. Transpiration restored the water holding capacity of barrier systems after heavy rain events and induced strengthening of soil.</p><p>We suggest that vegetation should not be simply selected for aesthetically “greening” the barrier system, but specifically selected for its role in improving soil engineering function. There is a substantial scope to choose species to manipulate hydrological properties of the barrier system and improve its performance during extreme climate events.</p>

The Effect of Willow (Salix sp.) on Soil Moisture and Matric Suction at a Slope Scale

The aim of this study is to provide new knowledge on the effect of willow on hillslope hydrology at a slope scale. Soil moisture and matric suction were monitored in situ under willow-vegetated and fallow ground covers on a small-scale hillslope in Northeast Scotland for 21 months. The retrieved time series were analysed statistically to evaluate whether the dynamics of soil moisture and matric suction changed with the hillslope zone (i.e., toe, middle, and crest) under the two ground covers. The effect of air temperature and rainfall on the dynamics of soil moisture and matric suction, as well as the relationship between the two soil-water variables, under both ground covers, were also investigated by analysing the cross-correlation between time series. The results of 21 months of monitoring showed that willow contributed substantially to reduce soil moisture and to increase matric suction with respect to fallow soil. Additionally, willow-vegetated soil exhibited higher water retention and moisture buffering capacity than fallow soil. The effect of willow was highest at the hillslope toe due to a denser vegetation cover present within this zone. Both air temperature and rainfall had a strong effect on soil moisture and matric suction. However, the effect of air temperature was more consistent and easier to interpret than that of rainfall. Soil moisture and matric suction were shown to have a complex relationship and the soil water characteristic curve for vegetated soil requires further research. This study provides novel, field-based information supporting the positive effect of willow on hillslope hydrology. The results gathered herein will undoubtedly enhance the confidence of using woody vegetation in Nature-based Solutions (NBS) against geo-climatic hazards.