Irrigation depth far exceeds water uptake depth in an oasis cropland in the middle reaches of Heihe River Basin

Different Responses in Root Water Uptake of Summer Maize to Planting Density and Nitrogen Fertilization

Modifying farming practices combined with breeding has the potential to improve water and nutrient use efficiency by regulating root growth, but achieving this goal requires phenotyping the roots, including their architecture and ability to take up water and nutrients from different soil layers. This is challenging due to the difficulty of in situ root measurement and opaqueness of the soil. Using stable isotopes and soil coring, we calculated the change in root water uptake of summer maize in response to planting density and nitrogen fertilization in a 2-year field experiment. We periodically measured root-length density, soil moisture content, and stable isotopes δ¹⁸O and δD in the plant stem, soil water, and precipitation concurrently and calculated the root water uptake based on the mass balance of the isotopes and the Bayesian inference method coupled with the Markov Chain Monte Carlo simulation. The results show that the root water uptake increased asymptotically with root-length density and that nitrogen application affected the locations in soil from which the roots acquired water more significantly than planting density. In particular, we find that reducing nitrogen application promoted root penetration to access subsoil nutrients and consequently enhanced their water uptake from the subsoil, while increasing planting density benefited water uptake of the roots in the topsoil. These findings reveal that it is possible to manipulate plant density and fertilization to improve water and nutrient use efficiency of the summer maize and the results thus have imperative implications for agricultural production.

Performance of Satellite-Based Evapotranspiration Models in Temperate Pastures of Southern Chile

Farmers in the temperate zone of southern Chile have started to irrigate historically rainfed pastures during recent years to reduce dairy productivity losses against increasingly severe summer droughts. The lack of information on pasture water requirements (i.e., evapotranspiration), however, hampers the implementation of efficient irrigation programs. Here, we use in-situ observations to evaluate the skill of four remote sensing Surface Energy Balance (SEB) models and two satellite-based global evapotranspiration products (PML_V2 and GLEAM) to estimate actual evapotranspiration (ETa) of pastures in southern Chile during 2014–2017. Daily ETa measured at an evaluation site over the period ranges between 1.2 mm and 6.2 mm day−1 during the growing season (October–March), with an annual maximum of about 4.8 mm day−1 in January and a minimum 0.6 mm day−1 in June. Only the Simplified SEB (SEBS) model and its operational variant (SSEBop) and the PML_V2 global evapotranspiration product perform well, capturing 63–79% of the variance of in-situ evapotranspiration with an error between 0.75 mm day−1 and 1.1 mm day−1. The readily available PML_V2 product can be used as a convenient way to determine average water footprint of pastures and the two SEBs models can be implemented to monitor irrigation requirements in near-real time from field to regional scales. These results demonstrated a high potential of satellite observations for monitoring evapotranspiration and quantify the water footprint of pastures in southern Chile for a sustainable irrigation practice.

Water Use Strategies of Dominant Species (Caragana korshinskii and Reaumuria soongorica) in Natural Shrubs Based on Stable Isotopes in the Loess Hill, China

Water is a key and limiting factor for ecosystem processes (carbon dioxide fixation, vegetation growth, respiration, etc.) and functions (NPP, Net Primary Productivity) in arid and semi-arid areas. As the main regulator, knowledge of plant water use patterns is essential in understanding the SPAC (Soil-Plant-Atmosphere-Continuum) cycle. The tree-planting project in the southern and northern mountains of Lanzhou city aims to improve the ecological environment and promote urban construction. In this study, we analyzed the water use strategies of the dominant plants C. korshinskii and R. soongorica in natural shrubs of southern and northern mountains of Lanzhou city using oxygen stable isotope techniques. The result showed that the flexible water uptake pattern of C. korshinskii and its faster response to precipitation pulse, compared with R. soongorica, might help it to make full use of water and nutrients and adapt to the dry environment. However, R. soongorica progressively switched to suck up deeper soil water and increased the water use proportion from 0.5% to 84.4% as the seasons changed, indicating a greater degree of ecological plasticity. The flexible water use strategies of C. korshinskii and R. soongorica in the same habitat reduced competition for water and nutrients and enhanced adaptability to arid environments. The work presented here provides insights into vegetation restoration and ecological management for the southern and northern mountains of Lanzhou city.

Interannual Variations of Evapotranspiration and Water Use Efficiency over an Oasis Cropland in Arid Regions of North-Western China

The efficient use of limited water resources and improving the water use efficiency (WUE) of arid agricultural systems is becoming one of the greatest challenges in agriculture production and global food security because of the shortage of water resources and increasing demand for food in the world. In this study, we attempted to investigate the interannual trends of evapotranspiration and WUE and the responses of biophysical factors and water utilization strategies over a main cropland ecosystem (i.e., seeded maize, Zea mays L.) in arid regions of North-Western China based on continuous eddy-covariance measurements. This paper showed that ecosystem WUE and canopy WUE of the maize ecosystem were 1.90 ± 0.17 g C kg−1 H2O and 2.44 ± 0.21 g C kg−1 H2O over the observation period, respectively, with a clear variation due to a change of irrigation practice. Traditional flood irrigation generally results in over-irrigation, providing more water than actual crop requirements. Unlike flood irrigation, which can infiltrate into deep soil layers, drip irrigation can only influence the shallow soil moisture, which can lead to decreases of soil moisture of approximately 27–32% and 36–42% compared with flood irrigation for shallow and deep layers, respectively. Additionally, drip irrigation decreases evapotranspiration by 13% and transpiration by 11–14%, leading to increases in ecosystem and canopy WUE of 9–14% and 11%, respectively, compared to the traditional irrigation practice. Therefore, the drip irrigation strategy is an effective method to reduce irrigation water use and increase crop WUE in arid regions. Our study provides guidance to water-saving cultivation systems and has implications for sustainable water resources management and agriculture development in water-limited regions.

Using a modified soil quality index to evaluate densely tilled soils with different yields in Northeast China

Northeastern China has long-term densely tilled soils that supply approximately 20% of the annual total national grains. There are very few reports on the agricultural soil quality subjecting to the predatory tillage. Here, the soil quality index (SQI) of a brunisolic soil was calculated using the minimum data set (MDS) and integrated quality index (IQI). The topsoil layer was divided into plow layer (11.9 ± 1.9 cm) and plow pan (11.4 ± 2.6 cm) in fields of high yields (HYB), medium yields (MYB), and low yields (LYB). Our results showed that the MDS of the topsoil layer only contained chemical indicators. The bulk density (BD), as one of the most important soil quality indicators, was found of no significant differences in the topsoil layers. In different layers (i.e., the topsoil layer, plow layer, and plow pan), the value of SQI presented a consistent tendency of HYB > MYB > LYB (p < 0.05). The correlation between SQI and yield was higher in the plow layer (0.60) and plow pan (0.63) than the topsoil layer (0.47). This further verified the reasonability of using soil stratification for SQI calculation. Our findings indicate the potential of using soil quality assessments to examine soil productivity (e.g., fertilizer deficiency) in crop lands with soil stratification.

Water Stable Isotopes in an Alpine Setting of the Northeastern Tibetan Plateau

Hydrological processes produce effects on water resources in inland mountainous regions. To perform a comprehensive investigation of the important segments of the water cycle, using the Qilian Mountains as a case study, precipitation, soil, plant, river, and groundwater were collected during the plant growing season of 2016. All samples were collected on a monthly basis, except precipitation, which was collected on a per event basis. The results showed that: the “temperature effect” was apparent, which suggested a drier climate background; there were differences in the slope and intercept of the local meteoric water line, using different regression methods; and the δ18O of soil water varied greatly in the topsoil, tended to be similar in the deep soil, and became increasingly depleted as the soil depth increased. The responses of the soil water isotopes to precipitation pulses had different boundaries. The major water source for Caragana Fabr. in no-precipitation month was located in the 0–30 cm soil layer, but was different in months when precipitation occurred. Overall, the findings from the stable isotopes provide insights into hydrological processes and offer a platform to understand mountainous water cycle in arid areas.

Estimating the Root Water Uptake of Surface-Irrigated Apples Using Water Stable Isotopes and the Hydrus-1D Model

The future production of irrigated fruit orchards in the Loess Plateau of China is threatened by a shortage of freshwater. To improve water use efficiency under conditions where irrigation is limited, it is necessary to quantify the root water uptake (RWU) of apple trees. The RWU of apple trees was estimated under surface irrigation using water stable isotope technology and the Hydrus-1D model. Using the Romero-Saltos and IsoSource models, the stable isotopes of water in stems, different soil depths, and different precipitation were analyzed in a 5-year-old dwarfing apple orchard during two seasons 2016 and 2017. Hydrus-1D model was able to simulate the RWU of apple using the maximum coefficient of determination (0.9), providing a root mean square error of 0.019 cm3 cm−3 and a relative error of 2.25%. The results showed that the main depth of RWU ranged from 0–60 cm during the growth season, with the main contribution occurring in the 0–40 cm depth. These findings indicated that reducing the traditional surface irrigation depth will be important for improving the irrigation water use efficiency.

Stable isotope measurements show increases in corn water use efficiency under deficit irrigation

Deficit irrigation has usually improved crop water use efficiency (WUE), but there are still gaps in our understanding of the mechanisms. Four irrigation treatments were a conventional furrow irrigation (CFI), border irrigation (BI), alternate furrow irrigation (AFI), and an AFI(M/2) (the amount of irrigation was 50% of the AFI). The volume of irrigation water applied were nearly the same for CFI, BI, and AFI. The isotope (δ18O and δD) method was used to quantify corn root water uptake (RWU) during 2013-2014. Compared to CFI and BI, corn yield and WUE were 17.0-30.2% and 13.3-33.8% higher in AFI, respectively. No significant yield reduction were observed between AFI and AFI(M/2). Corn RWU was more from deeper soil with increasing growth stage for AFI(M/2), AFI, and CFI, but from shallower depth for BI. The depth for RWU varied in the order of AFI(M/2)  > AFI > CFI > BI. The maximum root density was in the depth of 40-80 cm at the growing stage in AFI, and 4-26% more water was extracted from the wetter and deeper root zones. The WUE increased under deficit irrigation, and stimulated the root growth with attendant decreases in water loss to deep percolation.

Agricultural water policy reforms in China: a representative look at Zhangye City, Gansu Province, China

Water resources are essential for agricultural production in the grain-producing region of China, and water shortage could significantly affect the production and international trade of agricultural products. China is placing effort in new policies to effectively respond to changes in water resources due to changes in land use/land cover as well as climatic variations. This research investigates the changes in land, water, and the awareness of farmer vis-à-vis the implementation of water-saving policies in Zhangye City, an experimental site for pilot programs of water resources management in China. This research indicates that the water saved through water-saving programs and changes in cropping structure (2.2 × 10⁸ m³ a^-1) is perhaps lower than the newly increased water withdrawal through corporate-led land reclamation (3.7 × 10⁸ m³ a^-1). Most critically, the groundwater withdrawal has increased. In addition, our survey suggests that local government is facing a dilemma of water conservation and agricultural development. Therefore, the enforcement of the ban on farmland reclamation and irrigation water quotas in our study area is revealed to be relatively loose. In this vein, the engagement of local stakeholders in water governance is essential for the future sustainable management of water resources.

The full annual carbon balance of a subtropical coniferous plantation is highly sensitive to autumn precipitation

Deep understanding of the effects of precipitation on carbon budgets is essential to assess the carbon balance accurately and can help predict potential variation within the global change context. Therefore, we addressed this issue by analyzing twelve years (2003-2014) of observations of carbon fluxes and their corresponding temperature and precipitation data in a subtropical coniferous plantation at the Qianyanzhou (QYZ) site, southern China. During the observation years, this coniferous ecosystem experienced four cold springs whose effects on the carbon budgets were relatively clear based on previous studies. To unravel the effects of temperature and precipitation, the effects of autumn precipitation were examined by grouping the data into two pools based on whether the years experienced cold springs. The results indicated that precipitation in autumn can accelerate the gross primary productivity (GPP) of the following year. Meanwhile, divergent effects of precipitation on ecosystem respiration (Re) were found. Autumn precipitation was found to enhance Re in normal years but the same regulation was not found in the cold-spring years. These results suggested that for long-term predictions of carbon balance in global climate change projections, the effects of precipitation must be considered to better constrain the uncertainties associated with the estimation.

Biomimetic water-collecting materials inspired by nature

Nowadays, water shortage is a severe issue all over the world, especially in some arid and undeveloped areas. Interestingly, a variety of natural creatures can collect water from fog, which can provide a source of inspiration to develop novel and functional water-collecting materials. Recently, as an increasingly hot research topic, bioinspired materials with the water collection ability have captured vast scientific attention in both practical applications and fundamental research studies. In this review, we summarize the mechanisms of water collection in various natural creatures and present the fabrications, functions, applications, and new developments of bioinspired materials in recent years. The theoretical basis related to the phenomenon of water collection containing wetting behaviors and water droplet transportations is described in the beginning, i.e., the Young's equation, Wenzel model, Cassie model, surface energy gradient model and Laplace pressure equation. Then, the water collection mechanisms of three typical and widely researched natural animals and plants are discussed and their corresponding bioinspired materials are simultaneously detailed, which are cactus, spider, and desert beetles, respectively. This is followed by introducing another eight animals and plants (butterfly, shore birds, wheat awns, green bristlegrass, the Cotula fallax plant, Namib grass, green tree frogs and Australian desert lizards) that are rarely reported, exhibiting water collection properties or similar water droplet transportation. Finally, conclusions and outlook concerning the future development of bioinspired fog-collecting materials are presented.