Response of soil water dynamics to precipitation years under different vegetation types on the northern Loess Plateau, China

Implementation of the Grain-for-Green project has led to rapid land cover changes and resulted in a significantly increased vegetation cover on the Loess Plateau of China during the past few decades. The main objective of this study was to examine the responses of soil water dynamics under four typical vegetation types against precipitation years. Soil water contents (SWCs) were measured in 0–4.0 m profiles on a hillslope under the four vegetation types of shrub, pasture, natural fallow and crop in a re-vegetated catchment area from April to October in normal (2010), dry (2011), wet (2014) and extremely wet (2013) years. The results indicated that precipitation and vegetation types jointly controlled the soil water temporal dynamics and profile characteristics in the study region. SWCs in 0–4.0 m profiles of the four vegetation types were ranked from high to low as crop>fallow>pasture>shrub and this pattern displayed a temporal stability over the four years. In the extremely wet year, SWC changes occurred in the 0–2.0 m layer under shrub and pasture while the changes further extended to the depth of 4.0-m deep layers under fallow and crop. In the other three years, SWCs changes mainly occurred in the 0–1.0 m layer and kept relatively stable in the layers deeper than 1.0 m for all the four vegetation types. The interannual variation in soil depth of SWCs was about 0–2.0 m for shrub and pasture, about 0–3.4 m for fallow and about 0–4.0 m for crop, respectively. The dried soil layers formed at the depths of 1.0, 0.6, 1.6 and 0.7 m under shrub, and 1.0, 1.0, 2.0 and 0.9 m under pasture, respectively in 2010, 2011, 2013 and 2014. The infiltrated rainwater mostly stayed in the 0–1.0 m layer and hardly supplied to soil depth >1.0 m in normal, dry and wet years. Even in the extremely wet year of 2013, rainwater recharge depth did not exceed 2.0 m under shrub and pasture. This implied that soil desiccation was difficult to remove in normal, dry and wet years, and soil desiccation could be removed in 1.0–2.0 m soil layers even in the extremely wet year under shrub and pasture. The results indicated that the natural fallow was the best vegetation type for achieving sustainable utilization of soil water and preventing soil desiccation.

Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation

Water storage pit irrigation is a new method suitable for apple trees.It comes with advantages such as water saving,water retention and drought resistance.A precise study of soil water movement and root water uptake is essential to analyse and show the advantages of the method.In this study,a mathematical model(WSPI-WR model)for 3D soil water movement and root water uptake under water storage pit irrigation was established based on soil water dynamics and soil moisture and root distributions.Moreover,this model also considers the soil evaporation,pit wall evaporation and water level variation in the pit.The finite element method was used to solve the model,and the law of mass conservation was used to analyse the water level variation.The model was validated by experimental data of the sap flow of apple trees and soil moisture in the orchard.Results showed that the WSPI-WR model is highly accurate in simulating the root water uptake and soil water distributions.The WSPI-WR model can be used to simulate root water uptake and soil water movement under water storage pit irrigation.The simulation showed that orchard soil water content and root water uptake rate centers on the storage pit with an ellipsoid distribution.The maximum distribution region of soil water and root water uptake rate was near the bottom of the pit.Distribution can reduce soil evaporation in the orchard and improve the soil water use efficiency in the middle-deep soil.

Effects of rainwater harvesting on herbage diversity and productivity in degraded Aravalli hills in western India

Over-exploitation and rural growth have severely damaged native vegetations of Aravalli hills in Rajasthan, India. This study was conducted to evaluate the effects of different restoration practices （i.e., rainwater harvesting （RWH） and planting of tree seedlings） on improve- ment in soil water and nutrients and growth and biomass of herbaceous vegetation. Contour trench （CT）, Gradonie （G）, Box trench （BT）, V-ditch （VD） and a control were imposed on 75 plots （each of 700 m 2 ） in natural slope gradient defined as 10%, 10% 20% and 20% slopes in 2005. Each plot had three micro-sites of 1-m 2 at up （USP）, middle （MSP） and lower （LSP） part of the plot for observation in 2008. The existed gradient （due to soil texture and topographic features） of soil pH, EC, SOC, NH 4 - N, NO 3 -N and PO 4 -P in June 2005 between 20% to 10% slopes were decreased in 2008 after applying RWH techniques. Such improvement in soil status promoted vegetation growth and biomass in higher slope gra- dients. Soil water, species diversity and herbage biomass increased from USP to LSP, and RWH techniques had positive role in improving SOC, nutrients, vegetation population, evenness and growth at MSP. Despite of lowest SWC, regular rain and greater soil water usage enhanced green and dry herbage biomasses in 10% 20% and 20% slopes, compared with 10% slope. The highest diversity in CT treatment was related to herbage biomass, which was enhanced further by highest concentrations of SOC and PO 4 -P. Further, CT treatment was found to be the best treat- ment in minimizing biomass variance in different slopes. Conclusively, soil texture and topographic features controlled soil water and nutrients availability. Rainwater harvesting techniques increased soil water storage and nutrient retention and also enhanced vegetation status and biomass by minimizing the effects of hillslopes. Thus depending upon the site conditions, suitable RWH technique could be adopted to increase herb- age biomass while rehabilitating the degraded hills.

Response of soil hydrothermal processes within the active layer to variable alpine vegetation conditions on the Qinghai‒Tibet Plateau

Alpine vegetation plays an important role in the thermal stability of the permafrost under a warming climate,as it affects ground hydrothermal dynamics.The response of soil hydrothermal dynamics in the active layer to permafrost degradation under different alpine grassland types is unclear on the Qinghai‒Tibet Plateau.In this study,long-term soil temperature and soil water content in the active layer were monitored in situ from October 2010 to December 2018 at five sites in the Kaixinling permafrost region on the interior Qinghai‒Tibet Plateau along the QinghaieTibet Railway.The sites included an alpine steppe(AS),three alpine meadows(AM)with different degrees of degraded vegetation,and an alpine swamp meadow(ASM).Based on field-monitored data,the variations in soil temperature,soil water content,and freezeethaw processes were examined in the active layer.The response characteristics of the soil hydrothermal processes to climate change were analysed under the different alpine grasslands.The results showed that the duration of the thawing and freezing stages of the active layer of the AMs was shorter than that of the ASM and the AS.The average mean annual soil temperature(MAST)in the active layer of the AM((-1.25±0.50)℃)was lower than those in the AS((-0.71±0.39)℃)and ASM((-0.45±0.57)℃),while the AM had the highest rate of soil temperature increase((0.2±0.06)℃ per year).The annual amplitude of ground temperature in the active layer increased with the transition direction of the alpine vegetation type from ASM to AM to AS.The small surface offset(SO)and thermal offset(TO)(absolute values)indicated that the ground thermal state of the AM was more unstable,as it was more sensitive to the increase in air temperature than the ASM or the AS.Soil properties controlled the distribution of soil water content within the active layer,but vegetation improved the shallow soil structure by producing more belowground phytomass,thus,enhancing soil water content in the 0-30 cm layer.The average soil water content at depths of 0-30 cm was directly proportional(p<0.05)to the phytomass.Soil water contents at depths of 0-30 cm in the ASM((37.7±5.3)%)and the AM((40.8±5.9)%)were significantly higher than those in the AS((22.7±3.2)%).These results provide valuable insight into the hydrothermal interactions between the degradation of permafrost and alpine vegetation under a warming climate.