The Influence of Moss Colonization and Biochar Application on Evaporation Losses and Surface Crack in Shallow Carbonate–Derived Laterite During Dry–Wet Cycles

AimsSoil water deficit in karst mountain lands is becoming an issue of concern owing to porous, fissured, and soluble nature of underlying karst bedrock. It is important to identify feasible methods to facilitate soil water preservation in karst mountainous lands. This study aims to seek the possibility of combined utilization of moss colonization and biochar application to reduce evaporation losses in carbonate-derived laterite.MethodsThe treatments of the experiments at micro-lysimeter included four moss spore amounts (0, 30, 60, and 90 g·m−2) and four biochar application levels (0, 100, 400, and 700 g·m−3). The dynamics of moss coverage, characteristics of soil surface cracks and surface temperature field were identified. An empirical evaporation model considering the interactive effects of moss colonization and biochar application was proposed and assessed.ResultsMoss colonization reduced significantly the ratio of soil desiccation cracks. Relative cumulative evaporation decreased linearly with increasing moss coverage under four biochar application levels. Biochar application reduced critical moss coverage associated with inhibition of evaporation by 33.26%-44.34%. The empirical evaporation model enabled the calculation of soil evaporation losses under moss colonization and biochar application, with the R2 values ranging from 0.94 to 0.99.Conclusions Our result showed that the artificially cultivated moss, which was induced by moss spores and biochar, decreased soil evaporation by reducing soil surface cracks, increasing soil moisture and soil surface temperature.Moss colonization and biochar application has the potential to facilitate soil moisture conservation in karst mountain lands.

Numerical Study of Desiccation Cracking In Clayey Soil: A New FEM-MPM Coupling Method.

Desiccation cracking is a critical phenomenon soliciting the soil hydro-mechanical behavior, and significantly affects the performance of soil in geotechnical engineering. For this reason, an increasing interest toward studying and simulating the soil crack propagation, after a severe exposure to dry conditions (induced by desiccation), has been noticed during the recent years. However, major gaps remain in the previously developed models to properly provide a realistic prediction of the cracks pattern scheme especially when using the classical Finite Element Method (FEM), widely used in the geotechnical application. In this study, owing to the limitation of this method in re-meshing and dealing with large deformation, the authors were prompted to couple FEM with a mesh-free method: The Material Point Method (MPM) to overcome the individual drawbacks of each method. The dominant influencing factors on soil desiccation cracking have been assessed through a desiccation test performed in climatic chamber and using a digital image processing technique (image analysis) for a quantitative description of the studied sample. A model that relates porosity with suction and tensile strength was used to study the effect of the shrinkage phenomena in desiccation term, and to simulate the crack propagation in a thin clayey soil layer using the Code_Bright software. Consequently, a clear and connected crack pattern was observed, the problem of mesh dependency was clearly overcome proving the validity of the approach and providing a further insight into the behavior of clayey soil exposed to desiccation factors.

Conservation Agriculture Could Improve the Soil Dry Layer Caused by the Farmland Abandonment to Forest and Grassland in the Chinese Loess Plateau Based on EPIC Model

Converting farmland to forest and grassland alleviated water loss and soil erosion. However, water-intensive grasslands and woodlands could form dry soil layers in the arid or semi-arid zones. Therefore, it is necessary to explore a management method to solve this pedological problem. In this study, based on the Environment Policy Integrated Climate (EPIC) model, the crop productivity and soil dry layer was predicted from 2018 to 2038 in alfalfa and apple land. Then, conservation agriculture and conventional tillage systems were used to repair the soil dry layer in apple and alfalfa systems from 2039–2050 in order to explore their potential. Model verification showed that EPIC simulations of yield, ET, and SWC were generally reliable. The predicted results showed that soil drought was more intense in alfalfa systems. Alfalfa’s annual decrease rate and total amount in the soil available water (SAW) were 27.31 mm year−1 and 652.76 mm, higher than 13.62 mm year−1 and 476 mm of the apple system, and the DSLT of apple’s system was thicker, but DSL-SWC was higher than alfalfa. In the recovery process, the restoration degree of soil desiccation in conservation agriculture was significantly higher than in conventional tillage systems (p < 0.05). In addition, the recovery effect increased with the increase of planting times of shallow root crops, such as potato and soybean. The recovery rate was 27.1 ± 1.72 mm year−1, DSLT was 750 ± 51.2 cm in conventional tillage systems, and the recovery rate was 44.7 ± 1.99 mm year−1, DSLT was 258.3 ± 74.9 cm in conservation agriculture systems. This study provides an effective farmland management method to alleviate soil desiccation and further reveals the new role of the Epic Model in future drought assessment.

Effects of water-saving pruning on the growth and water consumption of jujube (Ziziphus jujuba Mill.) in a loess hilly region with deep soil desiccation

In order to study whether jujube trees can grow normally under rain-fed conditions in loess hilly areas, we planted jujube trees (Ziziphus jujuba Mill.) 4 years after felling a 23-year-old apple orchard. The growth process of the jujube trees and the variation in soil water content (SWC) were monitored for three consecutive years following planting in order to study the effects of the water-saving pruning (WSP) technique. Results showed that: (1) The soil at a depth of 0–1,000 cm had been desiccated when the area was an apple orchard. (2) Under rain-fed condition, the jujube trees with WSP technique were always able to maintain normal growth while the jujube trees with conventional pruning method had a normal growth stage of only 4 years. And the water use efficiency of the jujube trees with WSP technique was much higher than that of the jujube trees with conventional pruning. We recommend WSP in jujube orchard management, because the jujube trees with WSP could maintain normal growth in deep dried soils of the loess hilly region, as WSP can reduce the water consumption of the jujube trees and may has positive effect on soil moisture restoration.