Loess Plateau In Northwest China Research Articles

Seasonal variation of net ecosystem carbon exchange and gross primary production over a Loess Plateau semi-arid grassland of northwest China

Grassland ecosystems store approximately one-third of the global terrestrial carbon stocks, which play a crucial role in regulating the carbon cycle on regional and global scales, but the current scientific understanding of the variation in net carbon dioxide exchange (NEE) on grassland ecosystems is still limited. Based on the eddy covariance technique, this study investigated the seasonal variation of ecosystem respiration (Reco) and gross primary production (GPP) from 2018 to 2020 in a semi-arid grassland on the Loess Plateau in northwest China. The results indicated that the annual cumulative average NEE value was − 0.778 kg C/m2, the growing season cumulative value accounted for approximately 83.81%, which suggested that the semiarid grassland showed a notable soil carbon sink. The correlation analysis revealed that soil temperature (Ts) (RReco = 0.71, RGPP = 0.61) and soil water content (SWC) (RReco = 0.47, RGPP = 0.44) were the two main driving factors in modulating the variation of daily average GPP and Reco (P < 0.01). Therefore, the monthly average of GPP and Reco increased with the increase in Ts (RGPP = 0.716, P < 0.01; RReco = 0.586, P < 0.05), resulting in an increase in the carbon sequestration capacity of the grass ecosystem. This study also showed that soil moisture has a promoting effect on the response of Reco and GPP to Ts, and the correlation among GPP, Reco, and Ts was much stronger under wet conditions. For instance, the coefficient of determination of Reco and GPP with Ts under wet conditions in 2018 increased by 0.248 and 0.286, respectively, compared to those under droughty conditions. Additionally, the temperature sensitivity of Reco (Q10) increased by 46.13% compared to dry conditions. In addition, carbon exchange models should consider the synergistic effect of Ts and SWC as one of the main driving factors for theoretical interpretation or modeling. Under the potential scenario of future global warming and the frequent extreme weather events, our findings have important implications for predicting future CO2 exchange and establishing an optimal ecological model of carbon flux exchange.

Responses of Soil Respiration to the Interactive Effects of Warming and Drought in Alfalfa Grassland on the Loess Plateau

Elevated temperature and frequent drought events under global climate change may seriously affect soil respiration. However, the underlying mechanism of the effects of warming and drought on soil respiration is not fully understood in the context of the Loess Plateau. This study examined the response of soil respiration (Rs) to multiple factors, including warming (W), drought (P), and their interaction (WP), in the semi-arid grassland of the Loess Plateau in Northwest China. The research period was from May to November 2022, with an open-top heating box used for warming and a rain shelter used for drought. The results showed the following: (1) Rs ranged from 1.67 μmol m−2 s−1 to 4.77 μmol m−2 s−1, with an average of 3.36 ± 0.07 μmol m−2 s−1. The cumulative soil carbon flux ranged from 500.97 g C·m−2 to 566.97 g C·m−2, and the average cumulative soil respiration was 535.28 ± 35.44 g C·m−2. (2) Warming increased Rs by 5.04 ± 3.11%, but drought inhibited Rs by 3.40 ± 3.14%, and the interaction between warming and drought significantly reduced soil respiration by 11.27 ± 3.89%. (3) The content of particulate organic carbon (POC), dissolved organic carbon (DOC), soil organic carbon (SOC), and readily oxidized carbon (ROC) decreased with the increased soil depth. ROC after W and WP treatments was significantly higher than that of the control, and POC after P treatment was significantly higher than CK (p &lt; 0.05). (4) The seasonal variation of soil respiration was positively correlated with soil temperature, soil water content, plant height, and leaf area index (p &lt; 0.05), but the response rules differed during different regeneration periods. Soil water content; soil water content and leaf area index; and soil water content, soil temperature, and leaf area index were the factors that regulated the variation in soil respiration in the first, second, and third regeneration periods, respectively. These results clearly showed the limiting effect of drought stress on the coupling between temperature and soil respiration, especially in semi-arid regions. Collectively, the variations in soil respiration under warming, drought, and their interactions were further regulated by different biotic and abiotic factors. Considering future warming, when coupled with increased drought, our findings indicate the importance of considering the interactive effects of climate change on soil respiration and its components in arid and semi-arid regions over the next decade.

Strong links between aggregate stability, soil carbon stocks and microbial community composition across management practices in a Chinese dryland cropping system

Increasing soil carbon (C) stocks and improving soil structure are critical challenges in semi-arid agroecosystems. Conservation tillage has been widely applied to promote aggregate stability, enhance soil organic C (SOC) storage, and conjointly influence microbial community composition. However, the relation among soil microbial groups, aggregate stability and SOC stocks under management practices remains unclear. We conducted a 17-year field experiment in a spring maize cropping system on the Loess Plateau of northwest China, comparing three types of management: conventional tillage with residue removal (CT-RR), reduced tillage with residue incorporation (RT-RI) and no-tillage with residue mulching (NT-RM). We evaluated aggregate stability index (ASI), SOC stocks and microbial community composition at 0–10 and 10–25 cm. The results showed that RT-RI and NT-RM significantly increased ASI by 11% and 16% relative to CT-RR in the 0–10 cm layer; RT-RI significantly increased ASI by 13% relative to CT-RR in the 10–25 cm layer (p < 0.05). The RT-RI increased the SOC concentrations and SOC stocks of macroaggregates (>250 μm), which harbor most of the total SOC stocks in bulk soil. Both RT-RI and NT-RM increased total microbial biomass and biomass of six microbial groups (i.e., gram-negative bacteria (GN), gram-positive bacteria (GP), total bacteria (B), total fungi (F), arbuscular mycorrhizal fungi (AMF) and saprophytic fungi (SF)) at 0–10 cm, and RT-RI increased the above groups at 10–25 cm. Across a range of microbial community indicators, we found strong positive relationships between SOC and GN, ASI and AMF in bulk soil. A random forest analysis indicated that GN and F were the best microbial predictors of SOC concentrations and overall aggregate stability, whereas AMF/SF was the best predictor of SOC concentrations within aggregates and the stability of individual aggregate size classes. These results demonstrated a strong link between aggregate stability, SOC dynamics and microbial community composition, and suggest that conservation tillage increases both soil aggregation and SOC storage, thus providing sustainability and technical feasibility for the development of dryland agroecosystems.

Soil enzyme activities, physiological indicators, agronomic traits and yield of common buckwheat under herbicide combined with safeners

In the pursuit of green agricultural development, alleviating the harmful effects of herbicides is critical. Herbicide safeners have been identified as an effective solution to safeguard crops without compromising the herbicidal efficacy. However, the impact of combined applications of herbicide and safeners on the physiological characteristics, growth, yield of common buckwheat, and soil enzyme activities remains unclear. Therefore, a two-year (2021 and 2022) field experiment was conducted in the Loess Plateau region of Northwest China under seven treatments: herbicide metolachlor application alone (H1); herbicide metolachlor combined with gibberellin (H1S1); herbicide metolachlor combined with brassinolide (H1S2); herbicide metolachlor combined with naian (H1S3); herbicide metolachlor combined with jiecaotong (H1S4); manual weeding (CK1) and spraying the same volume of water (CK2). The results indicated that H1S3 minimized herbicide toxicity while sustaining the herbicide control efficacy. H1S2 treatment significantly increased the chlorophyll content (SPAD value), superoxide dismutase (SOD), peroxidase (POD) activities, and decreased the malondialdehyde (MDA) content of the leaves compared to H1 treatment. Additionally, the safeners helped restore the biochemical homeostasis of the soil by preventing the inhibition of invertase and urease activities and increasing soil catalase activity. Furthermore, H1S2 promotion of dry matter accumulation, alleviation of herbicide inhibition on plant height, stem diameter, grainnumber per plant and thousand-grain weight resulted in a significant increase in grain yield (14.36 % in 2021 and 27.78 % in 2022) compared to other safener treatments. Overall, this study demonstrates that brassinolide as a safener can effectively mitigate the negative effects of herbicide on the growth and development of common buckwheat while also improving grain yield. These findings provide valuable technical guidance for sustainable and intensive production of common buckwheat in the Loess Plateau of Northwest China.

Stimulation of soil organic matter fractions by maize straw return and nitrogen fertilization in the Loess Plateau of Northwest China

Soil organic matter (SOM) fractions play a key role in sustaining soil productivity; however, these fractions are relatively low in agricultural soils due to crop residue removal and tillage practices. Straw return has been reported to improve SOM fractions; however, its effects on soils with different nitrogen status is lacking. Therefore, a two-year experiment was conducted on an existing five-year different nitrogen rates (0, 75, 150 and 375 kg Nha−1 yr−1) trial field to assess the effects of nitrogen fertilizer rate and straw return on SOM fractions at different soil depths. The experiment had four nitrogen rates: 0 (CK, control), 75 (low N, LN), 150 (medium N, MN), and 375 (high N, HN) kg Nha−1 yr−1 with and without straw return (S, 9 t ha−1). The results showed that straw return significantly stimulated the SOM fractions at both 0–20 and 20–40 cm soil depths. Compared with the control, treatment MN with straw increased carbon pool management index (28.52 %), dissolved organic carbon (45.89 %), microbial biomass carbon (66.11 %), readily organic carbon (27.07 %), humic acid carbon (21.69 %), and humin carbon (10.34 %) at 0–20 cm soil depth; however, these fractions were comparable to those of HN with straw. Total organic carbon and carbon pool management index showed a positive and significant correlation with labile SOM fractions in the soil. The application of 150 kg N ha−1 after straw return stimulates SOM fractions, which in turn maintains the fertility and productivity of loess soil.

Application of Organic Fertilizers Optimizes Water Consumption Characteristics and Improves Seed Yield of Oilseed Flax in Semi-Arid Areas of the Loess Plateau

Organic fertilizers are an important source of nutrients for improving farmland fertility. To explore high-yield, efficient and green production technology for oilseed flax in dryland agricultural areas, a field split plot experiment was conducted in the semi-arid area of the Loess Plateau in northwest China from April to August in 2020 and 2021. The study compared and analyzed the effects of different nutrient sources and their application rates on water consumption characteristics, grain yield and water use efficiency of oilseed flax. The main plots were fertilizer types (sheep manure, chicken manure and chemical fertilizer), while the subplots were fertilizer application rates (sheep manure: S1-12,500 kg·hm−2 and S2-25,000 kg·hm−2; chicken manure: C1-5800 kg·hm−2 and C2-11,600 kg·hm−2; chemical fertilizer: F1-N 112.5 kg·hm−2, P 75 kg·hm−2, K 67.5 kg·hm−2 and F2-N 225 kg·hm−2, P2O5 150 kg·hm−2, K2O 135 kg·hm−2). The results showed that compared with chemical fertilizers, organic fertilizers significantly increased the soil water storage capacity of the 0–160 cm soil layer during the whole growth period of oilseed flax and significantly reduced water consumption. During two growing seasons, the application of 25,000 kg·hm−2 sheep manure significantly reduced water consumption during the seedling-bud period and green fruit period-maturity period of oilseed flax by 16.13% and 23.19% compared with CK, respectively. Thousand-grain weight, yield and water use efficiency were significantly increased by 14.70%, 48.32% and 61.29%, respectively. These results indicate that the application of 25,000 kg·hm−2 sheep manure can significantly increase soil water storage capacity of the 0–160 cm soil layer, reduce water consumption during the whole growth period of oilseed flax and thus improve grain yield and water use efficiency of oilseed flax. It is a suitable fertilization technology for the high-yield, efficient and green production of oilseed flax in the semi-arid areas of northwest Loess Plateau.

Numerical simulation and experiment of the emergence of young potato sprouts through soil‐covered plastic mulching

AbstractIn this paper, the effect of covering the plastic film mulch with soil of different thicknesses, on the resistance of potato young stems to break through the plastic film was simulated using the explicit dynamic analysis software LS‐DYNA. The constitutive models of young potato stems, plastic film, and covering soil, specific to potato cultivation on the Loess Plateau of Northwest China, were established. The influence of the covering soil thickness on the resistance to breaking by the potato sprout was analyzed and the film breaking time and sprout resistance to growth were then compared. The simulation results reveal that, to minimize both film breaking time and resistance to sprout growth, a thickness of about 40 mm of the film‐covering soil can be considered a good choice in potato cultivation using plastic‐film mulching technology. The results were confirmed experimentally by the authors and matched previous experimental research reported in the literature.

The first factor affecting dryland winter wheat grain yield under various mulching measures: Spike number

Water is the key factor limiting dryland wheat grain yield. Mulching affects crop yield and yield components by affecting soil moisture. Further research is needed to determine the relationships between yield components and soil moisture with yield, and to identify the most important factor affecting grain yield under various mulching measures. A long-term 9-year field experiment in the Loess Plateau of Northwest China was carried out with three treatments: no mulch (CK), plastic mulch (MP) and straw mulch (MS). Yield factors and soil moisture were measured, and the relationships between them were explored by correlation analysis, structural equation modeling and significance analysis. The results showed that compared with CK, the average grain yields of MP and MS increased by 13.0 and 10.6%, respectively. The average annual grain yield of the MP treatment was 134 kg ha−1 higher than the MS treatment. There were no significant differences in yield components among the three treatments (P<0.05). Soil water storage of the MS treatment was greater than the MP treatment, although the differences were not statistically significant. Soil water storage during the summer fallow period (SWSSF) and soil water storage before sowing (SWSS) of MS were significantly higher than in CK, which increased by 38.5 and 13.6%, respectively. The relationship between MP and CK was not statistically significant for SWSSF, but the SWSS in MP was significantly higher than in CK. In terms of soil water storage after harvest (SWSH) and water consumption in the growth period (ET), there were no significant differences among the three treatments. Based on the three analysis methods, we found that spike number and ET were positively correlated with grain yield. However, the relative importance of spike number to yield was the greatest in the MP and MS treatments, while that of ET was the greatest in CK. Sufficient SWSSF could indirectly increase spike number and ET in the three treatments. Based on these results, mulch can improve yield and soil water storage. The most important factor affecting the grain yield of dryland wheat was spike number under mulching, and ET with CK. These findings may help us to understand the main factors influencing dryland wheat grain yield under mulching conditions compared to CK.

Response of soil respiration to hydrothermal effects of gravel–sand mulch in arid regions of the Loess Plateau, China

Gravel–sand mulching is a traditional no–tillage technique used for more than 300 years on the Loess Plateau. Applying gravel–sand mulch (mixture of gravel and sand) has an impact on the soil environment, soil microorganisms, and crop yield. However, we know surprisingly little of how respiration dynamics at the soil surface is affected by gravel–sand mulching. To study the response of soil respiration (Rs) dynamics to different in gravel–sand mulch thickness and its driving factors, we recorded Rs under a gradient of gravel–sand mulch thickness consisting of six layers (0 cm [CK], 3 cm, 5 cm, 7 cm, 9 cm, 11 cm), in situ, during the growing season by using the LI–6400–09 soil respiration measurement system on the Loess Plateau in northwest China. The trends of all six treatments in diurnal and monthly variation of soil respiration followed a single–peaked curve; the diurnal dynamics trends were consistent with soil temperature changes. With gravel–sand mulch applied, the daily peak of soil respiration decreased, and the peak in Rs under the gravel–sand mulch treatments lagged that of bare land by 2 h. Monthly changes in soil respiration were consistent with soil temperature and precipitation changes, with peaks concentrated in July and August. Compared with bare land (CK), the monthly average soil respiration is lowest at 0.67 µmol∙m–2∙s–1 under a 11–cm thick mulch layer, and reduced by 26.63–61.03% by all mulch applications. Gravel–sand mulch reduced the temperature sensitivity of soil respiration, while soil temperature and soil water content were the main factors determining soil respiration. The thickness of gravel–sand has a significant, negative exponential function relationship with the changes in monthly soil respiration. Further, compared with bare land, the presence of gravel–sand mulch reduced the positive impact of precipitation on Rs. Soil temperature (T), gravel–sand mulch thickness (M), and soil pH were all significant predictors of soil respiration (Rs) (multiple regression model: Rs = 8.561 + 0.077 T – 0.056 M – 0.989 pH), together accounting for 73% of its variation. Hence, by considering all these three factors simultaneously we can better explain the changes to soil respiration in response to gravel–sand mulch. Overall, our results show that as the thickness of the gravel–sand layer increases, soil respiration decreases.

Growth Response of Tartary Buckwheat to Plastic Mulching and Fertilization on Semiarid Land

Integrated hole-sowing, fertilization, and plastic mulching techniques are common agronomic practices applied to collect rainwater and to improve rainwater utilization in semiarid rain-fed regions. However, little is known about the growth responses of tartary buckwheat (Fagopyrum tataricum L.) to the practices adopted in semiarid areas of Loess Plateau in Northwest China. To address the concerns, a long-term field experiment was conducted in 2015–2017. Four fertilization levels, namely, high fertilization level (N–P2O5–K2O: 120–90–60 kg ha−1, HF), moderate fertilization level (80–60–40 kg ha−1, MF), low fertilization level (40–30–20 kg ha−1, LF), and zero fertilization level (ZF), were applied to hole-sown tartary buckwheat with whole plastic mulching, in comparison to the control with no-mulching and zero fertilization (CK). Several key growth-influencing indicators were measured in the consecutive experimental years, including soil temperature (Ts), soil water storage (SWS), leaf area index (LAI), dry matter (DM), and grain yield. The results showed that in different precipitation years, 2015 (193 ± 23 mm), 2016 (149 ± 19 mm), and 2017 (243 ± 28 mm), the ZF, LF, MF, and HF treatments had the potential to optimize Ts in 0~25 cm soil layers (at 5 cm interval). The four treatments improved SWS in 0~300 cm soil layers by 3.5% and increased soil water consumption in the pre-anthesis period by 22.4%, compared with CK. Moreover, the four treatments shortened the pre-anthesis growth period by 0.4~5.4 d, while extended the post-anthesis growth period by 5.7~10.0 d, giving rise to an overall extension of 0.6~5.0 d for a whole growth period of tartary buckwheat. Furthermore, the ZF, LF, MF, and HF treatments increased LAI by 4.4~225.3% and DM weight by 41.5~238.0%. The rain yield of the four treatments was increased by 14.0~130.4%, and water use efficiency (WUE) was improved by 11.3~102.7%, especially for the LF treatment, compared with CK. The study indicated that the technique of hole-sowing and plastic mulching combined with a low fertilization rate was an effective measure for tartary buckwheat to optimize crop growth and to boost grain yield and WUE on semiarid lands.

[Effects of canopy density on understory plant diversity in Robinia pseudoacacia plantations on the Loess Plateau of China].

To solve the problems of understory plant shortage and biodiversity reduction caused by high tree density of Robinia pseudoacacia plantations on the Loess Plateau in northwest China, we analyzed the data collected by field survey and from literatures. We used the upper boundary line method to examine the impacts of canopy density on understory plant diversity. Based on field survey at the Guanshan Forest Farm of Jingchuan County of Gansu Pro-vince, the species number of understory plants in R. pseudoacacia plantations was higher than that in natural grassland (91 vs. 78). The dominant species varied with canopy density, which was completely different from that of natural grassland. A comprehensive analysis of both literature data and field survey data showed that, when mean annual precipitation (MAP) <550 mm or >550 mm, the increases in canopy density first led to a stable understory plant coverage and then a sharp or slight decrease, and understory plant biomass showed a sharp and continuous decrease or a slight increase and then decrease. Understory plant species richness and other diversity indices (Shannon, Simpson, and Pielou indices) first increase and then decrease, with bigger variation range under lower MAP. In all, the characteristics (coverage, biomass and species diversity, etc.) of understory plant community in R. pseudoacacia plantations were strongly affected by canopy density, with higher sensitivity under lower MAP. There was a general threshold range of canopy density of 0.45-0.6. When canopy density was above or below this thre-shold range, it would lead to a rapid decrease of the most characteristics of understory plant community. Therefore, keeping canopy density within the rational range of 0.45-0.6 in the management of R. pseudoacacia plantations is the key to make all the above-mentioned understory plant characteristics at relatively high level.

Distribution characteristics of microplastics in soil of Loess Plateau in northwest China and their relationship with land use type

The widespread distribution of microplastics (MPs) in soil has aroused great concern. The land use type can affect the distribution characteristics of MPs, whereas the abundance of MPs in the Loess Plateau region and the influence of different land use types on it are unclear. This study checked into the distribution of MPs in the Loess Plateau region, studied the abundance of MPs in woodland, construction land, grassland and cultivated land, and analyzed the distribution characteristics of their shape, size, and color. The abundance of MPs in the Loess Plateau region reached 2982.34 items/kg, dominated by black, small size and fragment MPs. The order of average abundance of MPs was: cultivated land (3535 items/kg) > construction land (2809 items/kg) > woodland (2781 items/kg) > grassland (2658 items/kg). Fragment MPs were predominant in woodland, construction land and cultivated land, but film and fiber MPs were predominant in grassland. MPs in cultivated land and construction land mainly sourced from human activities, MPs in woodland and grassland were more likely to come from atmospheric deposition. Human activities and sunlight exposure can cause MPs to break down, while trees in woodland block rays of light, slowing MPs breakage to some extent. And the polymer type of MPs was mostly PE and the main ones were black. This study may provide important data for follow-up research on MPs in terrestrial ecosystems.

Landslide susceptibility mapping in the Loess Plateau of northwest China using three data-driven techniques-a case study from middle Yellow River catchment

Accurate landslide susceptibility maps are relevant for stakeholders to take effective measures and perform land use planning. The present research aims at using three data-driven approaches to generate landslide susceptibility map for the middle Yellow River catchment (northwest China) and comparing their performances, including the weighted information value (WIV), where the IV model was integrated with analytic hierarchy process (AHP), the support vector machine (SVM) and the random forest (RF) models. A landslide inventory map including 684 historical landslides was generated first by visual interpretation of remote sensing images combined with a field survey. A total of 14 thematic layers were applied to serve as the landslides influencing factors. The Pearson correlation coefficient analyzed the correlation among these factors, and the C5.0 decision tree algorithm determined the factor importance. The results demonstrated the correlation between every two factors were all less than 0.5. Three factors (including distance to road, distance to river, and slope) were the most important contributions to the landslide occurrences in the region, whereas five factors (including NDWI, plan curvature, profile curvature, surface roughness, and aspect) had minor importance. All the models predict that most of the historical landslides are identified in moderate and high susceptibility areas. For the prediction percentage of landslides in high susceptibility areas, both SVM and RF models exceed 70%. The RF model represented the best performance, with high susceptibility zones accounting for 21.9% and landslide numbers accounting for 90.5%. The comparison among the receiver operating characteristic curves indicated that the accuracy was higher in the RF model than in the other two models: the area under the curve (AUC) for the RF was 0.904, whereas that for the WIV and the SVM were 0.845 and 0.847, respectively. Hence, the RF was proven suitable for assessing the landslide susceptibility in the region. Current results can provide valuable references for future studies and landslide risk mitigation strategies.

Long-Term Baseflow Responses to Projected Climate Change in the Weihe River Basin, Loess Plateau, China

Climate change is a significant force influencing catchment hydrological processes, such as baseflow, i.e., the contribution of delayed pathways to streamflow in drought periods and is associated with catchment drought propagation. The Weihe River Basin is a typical arid and semi-arid catchment on the Loess Plateau in northwest China. Baseflow plays a fundamental role in the provision of water and environmental functions at the catchment scale. However, the baseflow variability in the projected climate change is not well understood. In this study, forcing meteorological data were derived from two climate scenarios (RCP4.5 and RCP8.5) of three representative general circulation models (CSIRO-Mk3-6-0, MIROC5, and FGOALSg2) in CMIP5 and then were used as inputs in the Soil and Water Assessment Tool (SWAT) hydrological model to simulate future streamflow. Finally, a well-revised baseflow separation method was implemented to estimate the baseflow to investigate long-term (historical (1960–2012) and future (2010–2054) periods) baseflow variability patterns. We found (1) that baseflow showed a decreasing trend in some simulations of future climatic conditions but not in all scenarios (p &lt; 0.05), (2) that the contribution of baseflow to streamflow (i.e., baseflow index) amounted to approximately 45%, with a slightly increasing trend (p ≤ 0.001), and (3) an increased frequency of severe hydrological drought events in the future (2041–2053) due to baseflows much lower than current annual averages. This study benefits the scientific management of water resources in regional development and provides references for the semi-arid or water-limited catchments.

Pepino (Solanum muricatum) Metabolic Profiles and Soil Nutrient Association Analysis in Three Growing Sites on the Loess Plateau of Northwestern China

Different soil nutrients affect the accumulation characteristics of plant metabolites. To investigate the differences among the metabolites of pepino grown in greenhouses on the Loess Plateau in northwest China, we investigated the main soil nutrients and their correlation with metabolites. A total of 269 pepino metabolites were identified using UPLC-QTOF-MS to detect metabolites in fruits from three major pepino growing regions and analyze their differential distribution characteristics. A total of 99 of these substances differed among pepino fruits from the three areas, and the main classes of the differential metabolites were, in order of number: amino acids and derivatives, nucleotides and derivatives, organic acids, alkaloids, vitamins, saccharides and alcohols, phenolic acids, lipids and others. An environmental factor analysis identified soil nutrients as the most significant differentiator. Five soil nutrient indicators: TN (total nitrogen), TP (total phosphorus), AP (available phosphorus), AK (available potassium), and OM (organic matter), exhibited significant differences in three growing sites. Metabolite and soil nutrient association analysis using redundancy analysis (RDA) and the Mantel test indicated that TN and OM contributed to the accumulation of amino acids and derivatives, nucleotides and derivatives, and alkaloids while inhibiting organic acids, vitamins coagulation biosynthesis. Moreover, AP and TP were associated with the highest accumulation of saccharides and, alcohols, phenolic acids. Consequently, differences in soil nutrients were reflected in pepino metabolite variability. This study clarified the metabolite variability and the relationship between pepino and soil nutrients in the main planting areas of northwest China. It provides a theoretical basis for the subsequent development of Pepino’s nutritional value and cultivation management.

Anti-Erosion Influences of Surface Roughness on Sloping Agricultural Land in the Loess Plateau, Northwest China

The roughness of surface soil and the benefits produced by tillage for slope runoff and sediment reduction have attracted considerable interest; however, there are inconsistencies in existing research results. In this study, we have studied the anti-erosion influences of several typical tillage practices on both runoff and sediment generation in areas of sloping farmland in the Loess Plateau of northwest China. Rough surfaces were prepared manually, according to the surface microtopography of the plateau’s sloping farmland, using four tillage practices; a smooth surface was used as a control. Rainfall simulation experiments were performed using three rainfall intensities and five slope gradients. A path analysis was used to analyze the interactive effects of the slope gradient, rainfall intensity, and the surface roughness on the sediment yield and runoff volume. According to our findings, the gradient of a slope and the intensity of the rainfall both had a positive effect, while the surface roughness had a negative effect; the rate of 40.8% and 21.0% was lower than the values under CK on sediment yield and runoff volume. The interaction between the rainfall intensity and surface roughness always had a runoff reduction effect. Conversely, there was a critical slope gradient between 5° and 10° for sediment yield. The interaction between the slope gradient and surface roughness also had a runoff reduction effect, which was diminished by increasing the rainfall intensity. However, their interactive influence on sediment yield was inconsistent, with a critical slope gradient between 10° and 15°. Based on the comprehensive interactive effects among all three factors, we concluded that rainfall intensity, slope gradient, and surface roughness collectively played a crucial role in promoting runoff and sediment generation under tillage. The results support soil and water conservation by tillage on the sloping farmlands of the Loess Plateau.

Impacts of Site Conditions and Stand Structure on the Biomass Allocation of Single Trees in Larch Plantations of Liupan Mountains of Northwest China

Understanding the determinants of tree biomass allocation patterns among organs is crucial for both predicting the rate and potential of forest carbon sinks and guiding future multifunctional forest management. However, it is still not clear how the site conditions (e.g., elevation) and stand structure (e.g., tree dominance, stand density) affect the biomass allocation of single trees in forests. This study was implemented in the Liupan Mountains of the Loess Plateau of Northwest China by collecting the related information of biomass data of 110 sample trees with different dominance and influencing factors within 23 sample plots of larch plantations set up along the elevation gradient. Based on these data, the response tendency and functions of biomass allocation of single trees to individual influencing factors of site conditions and forest structure were analyzed. Moreover, the results illustrated that the ratio between root biomass and aboveground biomass decreased significantly with rising stand age and tree density, but increased significantly with rising elevation, and there was no significant relationship with the dominance of individual trees. The results of this study revealed the importance of considering the influencing factors of site conditions and stand structure when developing dynamic models of tree biomass allocation. The results and research methods used in this study provide useful tools for quantifying the biomass allocation and carbon storage partitioning in the study area and other similar regions.

Optimizing irrigation amount and potassium rate to simultaneously improve tuber yield, water productivity and plant potassium accumulation of drip-fertigated potato in northwest China

High crop water productivity (WPc) and fertilizer use efficiency are the key to ensuring the sustainable development of agriculture in water-deficient areas, such as the northwest China. In order to determine the irrigation amount and potassium rate for optimizing potato yield, plant potassium accumulation and WPc of drip-irrigated potato, a two-year field experiment was conducted on the Loess Plateau of northwest China, with three irrigation levels (W1: 60% ETc, W2: 80% ETc and W3: 100% ETc, where ETc is the crop evapotranspiration) and four potassium levels (K0: kg ha−1, K1: 135 kg ha−1, K2: 270 kg ha−1 and K3: 405 kg ha−1). The results showed that leaf area index, chlorophyll content, aboveground dry matter, tuber yield, starch, vitamin C content and WPc generally increased with the increase of irrigation amount, while they first increased and then decreased with the increasing potassium rate. The trends of reducing sugar and potassium use efficiency were contrary to the above trends. The residue of available potassium in the soil increased with the increase of potassium rate, but decreased with the increase of irrigation amount. Irrigation amount and potassium rate had interaction effects on chlorophyll content, dry matter, tuber yield, reducing sugar, plant potassium accumulation and potassium use efficiency. To ensure high-yield, high-quality, water-saving and fertilizer-saving potato production, a water input (irrigation plus effective rainfall) range of 498–520 mm combined with a potassium rate range of 201–393 kg ha−1 was recommended. These results can provide a theoretical basis for the rational application of irrigation water and potassium fertilizer to improve tuber yield, quality and soil environment of drip-irrigated potato in northwest China.

Optimum plastic mulching application to reduce greenhouse gas emissions without compromising on crop yield and farmers' income

With the rapid socio-economic development in China, poverty alleviation and the reduction of the environmental footprint in the plastic film mulching (PM) planting system have become key to sustainable agricultural production. Although many studies have evaluated the maize yield, agricultural economic benefits, and greenhouse gas (GHG) emissions associated with PM through small-scale field experiments, identifying suitable PM regions in combination with their demographic characteristics and the future development of such systems has received little attention. This study combines a Denitrification-Decomposition (DNDC) model and demographic characteristics to determine the optimum PM region in rainfed areas of the Loess Plateau in northwest China. The results demonstrated that PM produced a higher maize yield, agricultural net profit (ANP), and cost-benefit ratio compared to a control treatment (CK) without PM. An agricultural income far above the poverty level would assist in meeting the goals of alleviating poverty and building a prosperous society. In addition, the PM system produced more GHG emissions, but had a lower greenhouse gas intensity (GHGI) than CK under both low (200 kg N ha−1) and high (300 kg N ha−1) nitrogen (N) fertilizer rates. This study developed a framework to evaluate maize yield alongside economic and environmental indicators. We concluded that PM should be adopted in areas with precipitation less than 500 mm, and concentrated in the region with rainfall of 200–400 mm. The results provide a theoretical basis for the sustainable development of the PM maize planting system, and will contribute to the desired goal of environmentally sustainable agricultural production.

Tracer elements revealed the soil organic carbon sources in a dam-controlled watershed

The dynamics of the soil organic carbon (SOC) pool and the mechanisms that underpin those dynamics are at the frontier of terrestrial carbon (C) cycling research. Soil erosion seriously affects the migration and redistribution of SOC, driving a critical part of the C cycle. In this study, soil samples were collected from a 14.69 m sediment profile formed between 1960 and 2017, which was located in a small agricultural catchment on the Loess Plateau in northwest China. Nuclear tracer elements (137Cs, 210Pb) and stable C isotopes (δ13C) from organic matter were used to quantitatively identify the SOC sources in different siltation stages. The method used assumes that the contribution of a source is proportional to the elemental concentration in that source. SOC in soil samples from different erosion source areas (farmland, forest land, grassland, shrub land and ditch wall) were compared against the deposit in the check dam. The concentration of SOC in the sediments of the check dam was between 1.21 g kg−1 and 4.03 g kg−1. Nearly half of the SOC in the check dam sediments was traced back to the ditch wall. Farmland contributed 24.8 %, while shrub land contributed the least SOC at 0.4 %. SOC erosion attributed to farmland decreased gradually, while the relative contribution from the ditch wall increased. Within the agricultural catchment area, there was a net migration of SOC from the various land cover types (the source) to the sedimentary area behind the dam (the sink). These results indicate that a dynamic balance exists between redistribution and heterotopic storage of SOC during sedimentation. This study provides an opinion for sediment source identification and the soil C cycle in watersheds on the Loess Plateau.