Semi-arid Northwestern Research Articles

Physiological responses of a black locust plantation to drought stress based on a throughfall exclusion experiment in semi-arid northwestern China

Abstract Drought poses a significant threat on the ecosystem stability of extensive areas of black locust (Robinia pseudoacacia L.) plantations in northwestern China. However, limited understanding of the physiological responses of black locust to drought has impeded the development of proactive measures to alleviate potential adverse effects of drought. This study investigated the physiological impacts of varying drought intensities, manipulated by a throughfall exclusion experiment, on a 20-year-old black locust plantation in northwestern China. The experiment involved 40% throughfall exclusion for moderate drought, 80% exclusion for extreme drought, and no exclusion for control. One year after the implementation of the experiment, both predawn (Ψpd) and midday (Ψmd) leaf water potentials were significantly lower under drought treatments compared to those in control (P < .01). Stomatal conductance (gs) exhibited a strong reduction, leading to decreased leaf transpiration and photosynthesis under drought. However, the reduction in gs did not effectively prevent the decrease in Ψmd. Instead, both Ψpd and Ψmd became more negative with increasing drought stress, but their difference remaining relatively constant (being ~1.1 MPa) across treatments. These results suggest that black locust adopts a balanced water regulatory strategy between isohydry and anisohydry to cope with drought stress. These results contribute to an enhanced understanding of the crucial physiological responses of black locust under drought stress, offering valuable insights for future management strategies aimed at sustaining the ecosystem stability of black locust plantations in an increasingly arid climate.

Vulnerabilities of Smallholder Farmers' Livelihoods and Adaptations to Climate Change and Variability in Semi-Arid Northwestern Ghana: Observations and Perspectives

Vulnerabilities of Smallholder Farmers' Livelihoods and Adaptations to Climate Change and Variability in Semi-Arid Northwestern Ghana: Observations and Perspectives

Nitrogen and carbon cycling and relationships to radium behavior in porewater and surface water: Insight from a dry year sampling in a hypersaline estuary

Biogeochemical transformations within highly saline subterranean estuaries (STE) dramatically affect solute cycling, resulting in submarine groundwater discharge (SGD) with distinct chemical signatures. The study hypothesizes that biogeochemical processes within hypersaline bay porewaters (PW) simultaneously affect nitrogen, carbon, and radium cycling. We measured radium isotopes (226Ra, 224Ra, and 223Ra), nutrients (dissolved inorganic nitrogen [DIN: NH4+ + NO2− + NO3−], HPO42− [DIP], HSiO3− [DSi], dissolved organic carbon [DOC]), total alkalinity (TA), dissolved inorganic carbon (DIC), stable isotopes, and major cations in PW and surface water (SW) of Baffin Bay, a well-mixed, semi-enclosed estuary along the semiarid northwestern Gulf of Mexico coast, over three seasons in a characteristically dry year. This study's findings show a concurrent increase in NH4+, DIP, DSi, and TA/DIC with reduced metal species (e.g., Mn and Fe) and Ra during the hot and dry seasons, particularly in PW, under increasingly reducing conditions. Principal component analyses (PCA) suggest these increases are primarily driven by dissimilatory nitrate/nitrite reduction to ammonium (DNRA) and dissolution of lithogenic particles and biogenic CaCO3, modulated by organic matter degradation or remineralization. While more significant terrestrial groundwater inputs may contribute to solutes and Ra supply in the STE, the biogeochemically induced variability in solute concentrations in PW primarily drives larger SGD-derived fluxes, particularly notable in hot months. During a typically dry year, these fluxes, estimated as the average of 226Ra and 223Ra mass balance models (e.g., July/November fluxes in Mmol∙d−1: 0.093/0.092 of NO3−; 0.2/0.02 of NO2−; 72/16 of NH4+; 72.2/18 of DIN; 1.5/0.2 of HPO42−; 20/9 of HSiO3−; 42/37 of DOC; 503/399 of TA; 582/431 of DIC) are orders of magnitude (∼4 for DIN and DIC, ∼3 for DIP, DSi, and DOC, and ∼2 for TA) greater than surface runoff inputs. These substantial SGD inputs likely sustain phytoplankton growth and potentially fuel harmful algal blooms while countering estuarine acidification.

Combining slow-release fertilizer and plastic film mulching reduced the carbon footprint and enhanced maize yield on the Loess Plateau

Agricultural practices significantly contribute to greenhouse gas (GHG) emissions, necessitating cleaner production technologies to reduce environmental pressure and achieve sustainable maize production. Plastic film mulching is commonly used in the Loess Plateau region. Incorporating slow-release fertilizers as a replacement for urea within this practice can reduce nitrogen losses and enhance crop productivity. Combining these techniques represents a novel agricultural approach in semi-arid areas. However, the impact of this integration on soil carbon storage (SOCS), carbon footprint (CF), and economic benefits has received limited research attention. Therefore, we conducted an eight-year study (2015–2022) in the semi-arid northwestern region to quantify the effects of four treatments [urea supplied without plastic film mulching (CK-U), slow-release fertilizer supplied without plastic film mulching (CK-S), urea supplied with plastic film mulching (PM-U), and slow-release fertilizer supplied with plastic film mulching (PM-S)] on soil fertility, economic and environmental benefits. The results revealed that nitrogen fertilizer was the primary contributor to total GHG emissions (≥71.97%). Compared to other treatments, PM-S increased average grain yield by 12.01%–37.89%, water use efficiency by 9.19%–23.33%, nitrogen accumulation by 27.07%–66.19%, and net return by 6.21%–29.57%. Furthermore, PM-S decreased CF by 12.87%–44.31% and CF per net return by 14.25%–41.16%. After eight years, PM-S increased SOCS (0–40 cm) by 2.46%, while PM-U decreased it by 7.09%. These findings highlight the positive effects of PM-S on surface soil fertility, economic gains, and environmental benefits in spring maize production on the Loess Plateau, underscoring its potential for widespread adoption and application.

Nature of climate change-induced risks in semi-arid northwestern Ghana: Gauged observations, perceptions of smallholder farmers, and perspectives for livelihood adaptation

Climate variability and impact have been an endemic challenge to smallholder farmers who largely depend on rainy weather for livelihoods in semi-arid north-western Ghana. Many households in semi-arid regions exhibit low levels of adaptive capacity due to ineffective adaptation strategies and poor coping strategies. This study examined (1) trends in gauged rainfall and temperature data spanning the period from 1984 to 2014 and (2) smallholder farmers’ perceptions about yearly cyclical weather, and difficulties associated with climate change adaptations. The study adopted the participatory rural appraisal design using questionnaire, interviews and focus group discussions for collection of data for analysis. Estimated parameters partially supported that yearly temperatures are increasing, whereas annual rainfall is declining, although the latter is not significantly related to the former. Smallholder farmers’ perceptions about changing weather conditions did not corroborate the observed declining annual rainfall trend. These farmers are faced with livelihood-affecting risks during either ‘prolonged dry periods from October to May’ or ‘short annual rainy season from mid-May to September. Therefore, access to climate information and available climate adaptation strategies could improve farming activities and livelihoods of farmers in response to climate change.

Spatial patterns of climate change and associated climate hazards in Northwest China

Northwest China (NWC) is experiencing noticeable climate change accompanied with increasing impacts of climate hazards induced by changes in climate extremes. Towards developing climate adaptation strategies to mitigate the negative climatic impacts on both the ecosystem and socioeconomic system of the region, this study investigates systematically the spatial patterns of climate change and the associated climate hazards across NWC based on high resolution reanalysis climate dataset for the period 1979 to 2018. We find that NWC overall is under a warming and wetting transition in climate with change rate of temperature and precipitation around 0.49 °C/10a and 22.8 mm/10a respectively. Characteristics of climate change over the NWC however vary considerably in space. According to significance of long-term trends in both temperature and aridity index for each 0.1° × 0.1° grids, five types of climate change are identified across NWC, including warm-wetting, warm-drying, warm without wetting, wetting without warming and unchanging. The warm-wetting zone accounts for the largest proportion of the region (41%) and mainly locates in the arid or semi-arid northwestern NWC. Our findings show most region of NWC is under impacts of intensifying heatwave and rainstorm due to significant increases in high temperature extremes and precipitation extremes. The warming but without wetting zone is found under a more severe impact of heatwave, particularly for areas near northern Mount. Qinling and northern Loess Plateau. Areas with stronger wetting trend is suffering more from rainstorm.

Forecasting Monthly Water Deficit Based on Multi-Variable Linear Regression and Random Forest Models

Forecasting water deficit is challenging because it is modulated by uncertain climate, different environmental and anthropic factors, especially in arid and semi-arid northwestern China. The monthly water deficit index D at 44 sites in northwestern China over 1961−2020 were calculated. The key large-scale circulation indices related to D were screened using Pearson’s correlation (r). Subsequently, we predicted monthly D with the multi-variable linear regression (MLR) and random forest (RF) models at certain lagged times after being strictly calibrated and validated. The results showed the following: (1) The r between the monthly D and the screened key circulation indices varied from 0.71 to 0.85 and the lagged time ranged from 1 to 12 months. (2) The calibrated and validated performance of the established MLR and RF models were all good at the 44 sites. Overall, the RF model outperformed the MLR model with a higher coefficient of determination (R2 > 0.8 at 38 sites) and mean absolute percentage error (MAPE < 50% at 30 sites). (3) The Pacific Polar Vortex Intensity (PPVI) had the greatest impact on D in northwestern China, followed by SSRP, WPWPA, NANRP, and PPVA. (4) The forecasted monthly D values based on RF models indicated that the water deficit in northwestern China would be most severe (−239.7 to −62.3 mm) in August 2022. In conclusion, using multiple large-scale climate signals to drive a machine learning model is a promising method for predicting water deficit conditions in northwestern China.

Assessing levels of selected heavy metals with other pollutantsin soil and water resources in Nandom District in the semi-arid northwestern Ghana.

This study assessed heavy metal contaminations of soils in cultivated fields (or farms) and water samples from rivers, boreholes, and dug-out wells in Nandom District in semi-arid northwestern Ghana. Other parameters of water from the three sources were also measured and then compared to the permissible limits in the literature. The results showed that soils in farms across the study communities significantly (P ≤ 0.05) had higher levels of chromium (Cr = 0.456 ± 0.132mgkg-1), iron (Fe = 214.8 ± 1.52mgkg-1), lead (Pb = 0.854 ± 0.03mgkg-1), nickel (Ni = 2.813 ± 0.4mgkg-1), and arsenic (As = 1.753 ± 0.42mgkg-1) when compared to permissible limits set by World Health Organization (WHO) and Food and Agricultural Organization (FAO) for food crops. Water from the study sites significantly (P ≤ 0.0001) had lower levels of heavy metals than the permissible limits set by FAO for irrigation of growing crops. Thus, the water sources appear to be safe for irrigation in the study area. Nonetheless, these sources of water in Nandom District had significantly higher levels of total suspended solids, turbidity, and coliforms that were above the maximum limits indicated in the guidelines of WHO and the Government of Ghana for drinking water. Therefore, treatments of water for drinking are required to minimize any potential threats to public health.

Response of dual‐purpose winter wheat yield and its components to sowing date and cutting timing in a semiarid region of China

AbstractDual‐purpose winter wheat (Triticum aestivum L.) has been advocated on the Loess Plateau of China to fill feed gap and integrate crop–livestock systems; however, the effects of sowing date on the recovery after cutting and interactions between various management practices are largely unclear. Field experiment was conducted in 2015–2017 in semiarid northwestern China to investigate the effects of sowing date and cutting timing on forage yield, grain yield, and its components of dual‐purpose winter wheat cultivars. The experiment combined four cutting treatments, that is, winter cutting, spring cutting, winter–spring cutting, and control, two sowing dates (22 Sept., 2 Oct.), and two cultivars (early to mid‐maturing Zhongmai and late‐maturing Longyu4). Results showed delayed sowing decreased forage yield by 33.4%, but still had the potential to produce an average of 1.6 t ha−1 of forage, with average protein content of 290 g kg−1. Response of winter wheat grain yield to cutting ranged from −38.9 to 1%, with a delay of 1–7 d in maturity. Delayed sowing induced insignificant yield penalties. More forage and higher kernel protein content were produced if crops were cut in winter–spring, but this came with large reductions (30.1% in Longyu4 and 38.9% in Zhongmai) in grain yield, mainly due to reductions in kernels per spike and kernel weight. This study suggests that Longyu4 and Zhongmai are suitable varieties for dual‐purpose winter wheat in the Loess Plateau. For higher forage and grain yield, Longyu4 is suitable for sowing in middle or late September, whereas Zhongmai is suitable for delaying sowing. Winter cutting or spring cutting is acceptable to maintain the forage and grain yield, whereas winter–spring cutting is disadvantageous to grain yield in our study area.

How do land tenure arrangements influence adaptive responses of farmers? A study of crop farmers from semi-arid Ghana

This study investigated land tenure potential to influence farmers’ adaptive responses to climate change. A quantitative approach was employed to determine how crop farmers’ farmland tenure arrangements influence their adaptive responses to climate change impacts in the Lawra District of semi-arid north western Ghana. Field data were gathered from 248 farming households between January and May, 2017 through a multi-stage sampling procedure. About 55.2%, 45.6%, 44.4%, 80.6% and 64.5% of the farmers adopted early maturing crop varieties, zai farming techniques, agroforestry, crop rotation and adjustment in planting dates respectively as adaptive choices to the impacts of climate change. Binary logistic regression models showed that farmland size, years of land occupancy or usage, method of land acquisition and perceived level of farmland tenure security significantly (p ≤ 0.05) influenced farmers adaptive responses. We recommend that, government and non-governmental organizations should always consider farmers land tenure arrangements particularly regarding how they access or acquire their farmlands, the size of their farmlands and how they perceive the tenure security of those lands in the design and implementation of adaptation policies and programmes targeted at farmers so as to enhance sustainable adaptation.

A new method for quantifying threshold water tables in a phreatic aquifer feeding an irrigation district in northwestern China

In semi-arid northwestern China, the groundwater level continues to decline with the development of the irrigated agriculture, resulting in grassland ecosystem degradation. Threshold water tables play an important role in sustaining both grassland ecology and irrigated agriculture. This paper proposes a new method to calculate the threshold water tables based on the quantification of the transport rate of wetting front, by which the optimal layout of well groups in an irrigation district will be discussed; furthermore, this paper will discuss the advantages of using the threshold water tables as the management target to regulate groundwater pumping and ensure an appropriate water table for the ecological system in the irrigation district. The proposed method is applied to an irrigation district in the West Liaohe River Plain, which is a typical area with mixed agricultural and rural lands in northwestern China. The threshold water table in the case study irrigation district is estimated as 10 m; the interference radii of the pumping wells are 340 m, 270 m and 150 m in three different sub-districts, where the well depth is greater than 100 m, 60–80 m and less than 60 m, and the interference radius values are 225–310 m, 165–225 m and 150 m, respectively.

Long-term effectiveness of indigenous and introduced soil and water conservation measures in soil loss and slope gradient reductions in the semi-arid Ethiopian lowlands

Across the world, on-site and off-site effects of soil erosion accelerated by anthropogenic land-use/cover changes have been partly offset by the implementation of soil and water conservation (SWC) measures. However, studies evaluating the effectiveness of SWC over longer periods are currently rare. The dimensions of the terraced fields and SWC were measured at 242 sample fields that had slope gradients between 2.0 and 6.5% in three villages in the semi-arid Ethiopian Rift Valley (Ethiopian lowlands). In the study area, both indigenous contour weed hedgerows (denber) and introduced bund techniques, such as soil and stone bunds, are observed as major SWC measures. The establishment of the oldest SWC dated back to 65 years ago. Long-term effectiveness of the SWC was assessed in terms of the reduction in soil loss rates and slope gradient change of the terraced fields. Long-term quantitative assessment of SWC across the world has been conducted only in highlands; however, no case studies were conducted in lowlands. It is partly because the model that assessed the long-term effectiveness of SWC measures for the highlands appears to be inapplicable to lowlands. In the lowland model used in this study, the mid-point of the field was connected with that of the upper and lower fields by straight lines, which were assumed to represent the original slopes before the SWC establishment. The difference in slope gradient between the present slope and the original slope of the field without SWC was used for the estimates of slope reduction. The measured mass of the soil loss zone of the field was used to determine the long-term mean intra-field soil loss rate, while that of the sediment deposition zone was used to determine the long-term mean intra-field sediment accumulation rate behind the lower SWC. The mean net soil loss from the terraced fields was 19.6 Mg ha−1 yr−1, which was higher than that in the semi-arid northwestern highlands (Tigray); however, that from the stone bund fields was 13.7 Mg ha−1 yr−1, which was lower than that in Tigray. The soil and stone bunds retained 52–72% of the intra-field soil loss, compared to 34% retained by the denber. Slope gradients were reduced annually by 0.03% grade for the denber fields and 0.17–0.28% grades for the soil and stone bunds fields. Uncertainty analysis proved these estimates had relative uncertainty of <10% in general. All the SWC measures investigated in this study were effective in reducing soil loss from cropland and in reducing slope gradients of cropland in Ethiopian lowlands. Farmers’ efforts to place eliminated weeds on the lower hedgerows and bunds and a subsequent regeneration mechanism of weed hedgerows sustain the long-term effectiveness of not only denbers but also other bunds even without any extra maintenance efforts by farmers in the Rift Valley.

Identifying Barriers and Enablers for Climate Change Adaptation of Farmers in Semi-Arid North-Western China

The changing climate represents a large challenge for farmers, and adaptation responses are necessary to minimize impacts. Mixed approaches, which involve the analysis of meteorological data, web-based surveys, and face-to-face interviews, explore producers’ barriers and pressing needs to enhance climate resilience based on the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) approach in semi-arid north-western China. According to the main categories of farming activity, 85 crop farmers, 68 animal farmers, and 81 agro-tourism operators were interviewed. We found that most of the producers perceived climate impacts, and they encountered multiple adaptation obstacles, of which institutional and normative obstacles were more serious, such as farmers unable to obtain resources or government incentives, lacked scientific, and efficient coping measures. The survey also observed that crop farmers had a pressing need for agricultural subsidies, while animal farmers and agro-tourism operators had a strong enabler for animal housing infrastructure and credit facilities, respectively. Given the heterogeneity of the context and climate change experience of different categories of farmers, it is necessary to formulate flexible adaptation strategies and adjust them according to specific climate stress and farming conditions. To achieve the Sustainable Development Goals and implement the 2015 Paris Agreement, policymakers should plan and introduce appropriate adaptation strategies to minimize the adverse effects of climate change such as improving irrigation and weather forecasting system through technological advancement, cost reduction of farm inputs, ensuring availability of information, providing agricultural subsidies to the farmers, and increasing the access to agricultural markets.

Maize Straw Strip Mulching as a Replacement for Plastic Film Mulching in Maize Production in a Semiarid Region

Straw strip mulching in maize (Zea mays L.) production is showing a positive effect with the increasing negative effects coming from crop straw and plastic film residues. Therefore, it is imperative to develop comprehensive utilization of straw, and promote the green development of agriculture in rainfed regions. A dryland field experiment was conducted in semiarid northwestern China in 2017 and 2018 and included three treatments: maize straw strip mulching with alternating strips of mulched and non-mulched soil (MSSM), and double ridge-furrow fully mulched soil with white or black plastic film (DRWP or DRBP, respectively). The results show that the interaction between mulching treatment and year significantly influenced maize silage yield, grain yield, biomass yield, aboveground plant water content at silage maize harvest stage, ears ha−1, kernels ear−1, and thousand kernel weight (p &lt; 0.001, p = 0.002, p &lt; 0.001, p &lt; 0.001, p &lt; 0.001, p &lt; 0.001, p &lt; 0.001, and p &lt; 0.001, respectively). For silage, maize growth under straw strip mulching was greater than that of the double ridge mulching system. Silage yield of MSSM was significantly higher than that of DRWP and DRBP, but maize grain and biomass yields under MSSM were significantly lower those under DRWP and DRBP in 2017 and 2018. Compared with the double ridge mulching system, net economic return from silage with MSSM was significantly increased by 28.31% and 20.85% in 2017 and 2018, respectively, and net economic return from grain was 6.67% lower in 2017 and 2.34% higher in 2018. The MSSM treatment exhibited water-temperature coupling; the MSSM treatment significantly reduced soil temperature in the 0–25 cm soil layer by 1.23–2.14 °C and increased soil water storage in the 0–200 cm soil layer by 9.75 and 24.10 mm in 2017 and 2018, respectively, thereby delaying growth development of maize by about 13 days. Therefore, straw mulch can replace plastic film mulch and serve as an environmentally friendly cultivation method for maize in semiarid rainfed regions.

The Effects of Wind Erosion Depending on Cropping System and Tillage Method in a Semi-Arid Region

Wind erosion is a major environmental problem in arid and semi-arid regions, where it has significant impacts on desertification and soil degradation. To understand the effects of cropping systems and tillage methods on the reduction of soil wind erosion, wind tunnel investigations were performed on soil samples from an irrigated field in an experiment conducted in semi-arid northwestern China in 2016–2018. Three cropping systems for annual spring wheat (Triticum aestivum L.)/maize (Zea mays L.) strip intercropping (W/M), a two-year wheat-winter rape-maize rotation (WRM), and a two-year wheat-maize rotation (WM)) were each evaluated with two tillage methods (conventional tillage without wheat straw retention (CT) and no-tillage with 25–30 cm tall wheat straw (NT)). The mean rate of soil erosion by wind with NT was 18.9% to 36.2% less than that with CT. With increasing wind velocity, the rate of soil erosion by wind increased for both CT and NT but was faster with CT than NT. Soil wind erosion occurred with a wind velocity ≥14 m s−1, and NT greatly decreased the rate of soil erosion when wind velocity exceeded 14 m s−1. W/M, WRM, and WM with NT increased non-erodible aggregates by 53.7%, 53.7%, and 54.9% in 2017, and 51.3%, 49.6% and 44.6% in 2018, respectively, than conventional tillage. At a height of 0–20 cm, the rate of soil transport with CT decreased with increasing height. The volume of soil transport at a height of 0–4 cm and soil transport percentage at a height of 0–4 and 0–20 cm (Q0–4/Q0–20) with NT were less than with CT. These findings show that NT with cropping system intensification can be an effective strategy for resisting wind erosion in irrigated semi-arid regions, thereby reducing the negative environmental impacts of crop production.

The Middle to Upper Paleolithic transition in the southern Levant: New insights from the late Middle Paleolithic site of Far’ah II, Israel

Far’ah II is an open-air site in the north western Negev desert (Israel). Previous excavations in the 1970’s revealed a rich, in situ Middle Paleolithic (MP) assemblage composed of flint and limestone artifacts, animal bones and charcoal. Renewed excavation at the site were undertaken in 2017, to re-date it and provide a more accurate constrain to the sites’ age, as well as collect samples for paleoclimatic proxies. Our new Optically Stimulated Luminescence and 14C ages together with the stable oxygen isotope signature of the loess sediments, constrain the age of the upper archaeological horizon to <49 ka. This age agrees with the younger limit of 60–50 ka, obtained by Electron Spin Resonance ages, measured in the 1990’s. The heavy δ18O values in carbonates point to cooler climatic conditions than those that prevailed during the preceding short, warm episode between 58 and 49 ka. The fauna, pollen and charcoal collected during the excavation portray a savanna-like environment with a mix of Irano-Turanian and Saharo-Arabian elements and a minor Mediterranean component. The lithic assemblage exhibits large technological variability typical of the Late MP (LMP), amongst which are technological traits that are clearly present in the Initial Upper Paleolithic (IUP) assemblages at the nearby, and roughly contemporaneous, site of Boker Tachtit. If population replacement was the trigger to the MP-UP transition, we would have expected to see a clear break in the cultural material at the onset of the Upper Paleolithic. The semi-arid north western Negev, as an interim region between the Mediterranean and Saharo-Arabian ecozones could have facilitated interaction between populations moving north or south due to fluctuating climatic conditions and changes in population pressures, possibly leading to the emergence of new technological traditions that are observed in the later UP.

Dense subsoils limit winter wheat rooting depth and soil water depletion

AbstractDense subsoils pose a challenge to dryland winter wheat (Triticum aestivum L.) production in the Palouse region of the semiarid northwestern United States. Subsoils, commonly fragipans and argillic horizons, may restrict root growth and limit crop access to critical stored soil water, but this phenomenon is not well characterized in the Palouse. During the 2017–2018 growing season, an on‐farm study of soil profiles in two commercial winter wheat fields in eastern Washington and northern Idaho was established to observe the effects of soil bulk density on winter wheat root system depth and subsoil water depletion. At harvest, grain yield, root density, soil bulk density, and postharvest soil water and nitrogen content were measured to 120 cm at 15‐cm segments in the profile. Root‐restrictive depth (RRD) was defined as the depth where root density was less than or equal to 0.25 intersections cm−2 cross‐sectional area. Soil bulk density negatively affected root density and consequently increased the probability of shallow RRD. Shallow RRD was common, with 38% of profiles having RRD less than or equal to 105 cm. Postharvest soil‐water content at the bottom of the measured profile (105–120 cm) was 41% higher in profiles with RRD of 90 cm than nonrestricted profiles. Yield declined with increase in postharvest soil water content at 105–120 cm depth. Findings indicate that dense subsoils can reduce stored soil water depletion by limiting root density and root system depth that, in turn, limits yield.

Assessing the effects of ecological engineering on carbon storage by linking the CA-Markov and InVEST models

Ecological engineering has become an essential tool in efforts to address environmental crises, improve human well-being, and achieve sustainability. However, efficient assessment of changes resulting from ecological engineering remains a challenge. In this study, we evaluated the effects of ecological engineering on carbon storage in the upper reaches of the Heihe River Basin in semi-arid northwestern China by linking the CA-Markov and InVEST models. Firstly, the CA-Markov model was used to simulate land use/cover change (LUCC) following the implementation of ecological engineering programs. Then, the InVEST model was adopted to assess changes in carbon storage due to LUCC. The results showed that ecological engineering could increase carbon storage by 10.27 Tg from 2015 to 2029 by increasing the proportion of land cover types with higher carbon storage capacity. The relative error of the linked model was 0.22%, indicating that the linked model was highly applicable in assessments of the effects of ecological engineering on carbon storage in the study area. This study will provide a reference for guiding ecological engineering efforts.

The Nativity and Distribution of the Cryptic Invader Phalaris arundinacea (Reed Canarygrass) in Riparian Areas of the Columbia and Missouri River Basins

Cryptic invaders are inherently difficult to study due to morphological similarity with native lineages of the same species or genus. Wetland and riparian systems are particularly prone to plant invasions, and have been impacted by a number of widespread cryptic invaders such as Phalaris arundinacea (reed canarygrass). Here we combine molecular genetic analyses with species distribution modeling to assess the nativity of Phalaris and determine potential drivers of non-native Phalaris invasion in riparian areas across a large region of the semiarid northwestern USA. Based on our genetic analyses, we found that throughout our study region Phalaris is largely non-native, and no modern-day samples from our study region were of native North American origin. At least half of the four species distribution models suggested that non-native Phalaris invasion across the region was associated with warmer temperatures, more growing days, wetter summers, drier winters, higher nitrogen levels, shallower stream slopes, and at sites closer to roads and without a history of grazing. These findings can be used to determine the best locations for targeted monitoring. Furthermore, there is the potential for increased Phalaris invasion with climate change-induced temperature increases.

Drivers of farmer satisfaction with small-scale irrigation systems

Climate change impacts the quantity and seasonality of rainfall, threatening Africans' ability to maintain satisfactory yields on rain-fed farms. On the semi-arid northwestern slopes of Mount Kenya, irrigation systems structured around Community Water Projects (CWPs) provide households with piped water, which helps mitigate drought impacts and enhances resilience to increasingly variable rainfall patterns. The vision of these irrigation systems is to equitably distribute water resources among CWP members both for household consumption and to maintain or improve agricultural yields. However, not all households receive equal quantities of water from their CWPs, and little is known about the impact of water provisioning on farmers' opinions or perceptions of CWP performance.In this study, we relate respondents' satisfaction with their CWPs to the quantity of water delivered. Not surprisingly, farmers who received low quantities of water from their CWPs expressed above-average rates of concern regarding drought. In contrast, satisfaction with one's CWP was unrelated to the absolute quantity of water received (log liters/minute), but it was strongly associated with relative measures of water delivery: respondents who received less water than other members of the same water project experienced high rates of dissatisfaction, as did respondents who received less water than in the past. These results suggest that Kenyan farmers may feel particularly dissatisfied—and, perhaps, particularly driven to demand improved water governance—when they perceive inadequate water delivery relative to some reference group.Because relative water quantity dictates satisfaction even after controlling for factors that can be resolved internally at the CWP level (by, for example, striving for uniformity of water flows across and within households), water project managers are limited to some degree in their ability to improve satisfaction through better governance. That said, governance actions that prevent declines in flows over time (e.g. maintaining infrastructure to reduce leaks) could ostensibly lead to meaningful improvements in member satisfaction.