Random Forests with Bagging and Genetic Algorithms Coupled with Least Trimmed Squares Regression for Soil Moisture Deficit Using SMOS Satellite Soil Moisture

Soil Moisture Deficit (SMD) is a key indicator of soil water content changes and is valuable to a variety of applications, such as weather and climate, natural disasters, agricultural water management, etc. Soil Moisture and Ocean Salinity (SMOS) is a dedicated mission focused on soil moisture retrieval and can be utilized for SMD estimation. In this study, the use of soil moisture derived from SMOS has been provided for the estimation of SMD at a catchment scale. Several approaches for the estimation of SMD are implemented herein, using algorithms such as Random Forests (RF) and Genetic Algorithms coupled with Least Trimmed Squares (GALTS) regression. The results show that for SMD estimation, the RF algorithm performed best as compared to the GALTS, with Root Mean Square Errors (RMSEs) of 0.021 and 0.024, respectively. All in all, our study findings can provide important assistance towards developing the accuracy and applicability of remote sensing-based products for operational use.

Different facets of dryness/wetness pattern in southwestern China over the past 27,000 years

Frequently happened meta-droughts have arisen broad social attention under current global climate change. A paleoclimatic perspective is expected to gain our understanding on the causes and manifestation more comprehensively. Southwestern China has been threatened by severe seasonal droughts. Our current knowledge of millennial-scale drying/wetting processes in this region is primarily based on the variability of the Indian Summer Monsoon. However, water availability over land does not always follow the monsoonal precipitation but also depends on water loss from evaporation and transpiration. Here, we reconstructed precipitation intensity, lake hydrological balance and soil water stress index (SWSI) covering the last 27,000 yr, based on grain size, geochemical and pollen records from Yilong Lake, to discuss the long-term nexus and discrepancies of dryness/wetness patterns in meteorological, hydrological and soil systems in central Yunnan region, SW China. Our results show that the long-term change trajectories among precipitation, hydrological balance and soil moisture were not completely consistent. During periods of low precipitation, hydrological balance and soil moisture were primarily controlled by temperature-induced evaporation change. This caused opposite status of precipitation with hydrological balance and soil moisture during the Last Glacial Maximum and Younger Dryas. During periods of high precipitation – the early to late Holocene, intensified evaporation from the lake surface offset the effects of increased precipitation on hydrological balance. But meanwhile, abundant rainfall and dense vegetation canopy avoided soil moisture deficit that might result from rising temperature. To sum up, hydrological balance in central Yunnan region was more vulnerable to temperature change while soil moisture could be further regulated by vegetation changes on millennial scale. As such, under future climate warming, surface water shortage in central Yunnan region can be even more serious. But for soil systems, efforts to reforestation may bring some relief to soil moisture deficit in this region.

Potential soil moisture deficit: A useful approach to save water with enhanced growth and productivity of wheat crop

Wheat is the main crop in the world ranks after rice and the largest grain source of Pakistan. Among several reasons for diminishing wheat yield in Pakistan, water stress throughout the growing season decreases crop production because of the short life span. Two years (2015–16 and 2016–17) field experiments were conducted to assess the impact of various water regimes (full irrigation, irrigation at 45, 60, and 75 mm potential soil moisture deficit (PSMD)) on the growth and yield of wheat. Maximum crop growth rate was recorded by application of irrigation at 45 mm PSMD. Application of irrigation at 45 mm PSMD ensured maximum radiation use efficiency regarding total dry matter production and grain yield. The maximum number of productive tillers, spike length, and grain yield were recorded under 45 mm PSDM treatment. The present results show that the effect of water is more pronounced regarding the growth and productivity of wheat. Application of irrigation at 45 mm PSMD ensures higher economical yield.

Changes of Streamflow Caused by Early Start of Growing Season in Nevada, United States

The fluctuation of streamflow in snowmelt-dominated watersheds may be an indicator of climate change. However, the relationship between the start of growing season (SOS) and the streamflow in snowmelt-dominated watersheds is not clear. In this study, we update the Coupled Hydro-Ecological Simulation System (CHESS) model by incorporating the Growing Season Index (GSI) module to estimate the start of the growing season. The updated CHESS model is then used to calculate the streamflow in the Cleve Creek, Incline Creek and Twin River watersheds located in Nevada in the United States from 1981 to 2017. This updated CHESS can be applied in any regions that are suitable for deciduous vegetation. The streamflow in the static and dynamic scheme in the three watersheds have been simulated between 1981 and 2017 with the NS of 0.52 and 0.80 in the Cleve Creek, 0.46 and 0.75 in the Incline Creek, and 0.42 and 0.70 in the Twin River watersheds, respectively. The results illustrate that the SOS have come around 3–5 weeks earlier during the last 37 years. The results illustrate a high correlation between the temperature and the timing of the SOS. Early SOS leads to a substantial increase in total annual transpiration. An increase in annual transpiration can reduce aquifer recharge and increase cumulative growing season soil moisture deficit. Comparing to the streamflow without vegetation, the streamflow with vegetation is smaller due to transpiration. As the SOS comes earlier, the peaks of the streamflow with vegetation also come earlier. If the shifts in SOS continue, the effects on annual rates of transpiration can be significant, which may reduce the risk of flooding during snowmelt. On the other hand, earlier SOS may cause soil moisture to decline during summer, which would increase the drought stress in trees and the risk of wildfires and insect infestation.

Arbuscular Mycorrhizal Fungi Regulate Polyamine Homeostasis in Roots of Trifoliate Orange for Improved Adaptation to Soil Moisture Deficit Stress

Soil arbuscular mycorrhizal fungi (AMF) enhance the tolerance of plants against soil moisture deficit stress (SMDS), but the underlying mechanisms are still not fully understood. Polyamines (PAs) as low-molecular-weight, aliphatic polycations have strong roles in abiotic stress tolerance of plants. We aimed to investigate the effect of AMF (Funneliformis mosseae) inoculation on PAs, PA precursors, activities of PA synthases and degrading enzymes, and concentration of reactive oxygen species in the roots of trifoliate orange (Poncirus trifoliata) subjected to 15 days of SMDS. Leaf water potential and total chlorophyll levels were comparatively higher in AMF-inoculated than in non-AMF-treated plants exposed to SMDS. Mycorrhizal plants recorded a significantly higher concentration of precursors of PA synthesis such as L-ornithine, agmatine, and S-adenosyl methionine, besides higher putrescine and cadaverine and lower spermidine during the 15 days of SMDS. AMF colonization raised the PA synthase (arginine decarboxylase, ornithine decarboxylase, spermidine synthase, and spermine synthase) activities and PA-degrading enzymes (copper-containing diamine oxidase and FAD-containing polyamine oxidase) in response to SMDS. However, mycorrhizal plants showed a relatively lower degree of membrane lipid peroxidation, superoxide anion free radical, and hydrogen peroxide than non-mycorrhizal plants, whereas the difference between them increased linearly up to 15 days of SMDS. Our study concluded that AMF regulated PA homeostasis in roots of trifoliate orange to tolerate SMDS.

EVALUATION OF THE GROWING CONDITIONS OF SEA-BUCKTHORN PLANTATIONS UNDER INUNDATIVE IRRIGATION

Sea-buckthorn grows well on slope lands that are high-ly drained and lack stagnant water. The optimum soil mois-ture content for sea-buckthorn corresponds to 70% of the lowest moisture capacity. Under continuous soil moisture deficit, the leaf surface area decreased, the fruits were poorly set as a result of ovary drop during the first half of the growing season, and berry size decreased. In this re-gard, the study of the water regime of the soil under sea-buckthorn plantations the possibility of its regulation re-mained quite topical. The available moisture in the humus horizons of chernozem in May 2004 corresponded to a satisfactory level. At the end of summer, the moisture con-tent of the chernozem decreased to unsatisfactory state. As a result, the plants experienced water deprivation throughout the growing season. Naturally, the need arose for irrigation, especially in June and August with irrigation rates of 490 and 280 t per m3, respectively. In the underly-ing horizons, the soil moisture deficit was weaker. In the humus horizons, the available moisture in the chernozem in the middle of the slope did not differ much from the mois-ture content at its top. At the same time, in the transitional BC layer in the second half of summer, the available mois-ture content was significantly higher. This difference was also found in the parent rock. In the lower part of theslope, the one-meter soil layer contained a greater amount of moisture which contributed to the decrease of its deficit during the entire growing season. This was especially no-ticeable in the illuvial horizon and parent rock. In the sec-ond half of summer,the available moisture content here remained higher than in the upper slope sites. In conclu-sion, it should be noted that only humus-accumulative hori-zons A (arable) + AB needed irrigation with different irriga-tion rates depending on the location of the sea-buckthorn plantations on the slope and their growth features.