Semiarid Farmland Research Articles

Combining Freshwater Irrigation with Vegetable Selection to Mitigate the Occurrence of Per- and Polyfluoroalkyl Substances in Edible Vegetable Parts in a Semiarid Farmland in Northwestern China

Combining Freshwater Irrigation with Vegetable Selection to Mitigate the Occurrence of Per- and Polyfluoroalkyl Substances in Edible Vegetable Parts in a Semiarid Farmland in Northwestern China

Enhancing carbon sequestration and greenhouse gas mitigation in semiarid farmland: The promising role of biochar application with biodegradable film mulching

Long-term mulching has improved crop yields and farmland productivity in semiarid areas but also increased greenhouse gas (GHG) emissions and depleted soil fertility. Biochar application has emerged as a promising solution for addressing this issue. In this study, we investigated the effects of four biochar application rates (no biochar (N)=0 t ha–1, low (L)=3 t ha–1, medium (M)=6 t ha–1, and high (H)=9 t ha–1) under film mulching and no mulching over three growing seasons. We assessed the impact on greenhouse gas emissions, soil organic carbon sequestration (SOCS), and maize yield to evaluate the productivity and sustainability of farmland ecosystems. Our results demonstrated that mulching increased maize yield (18.68–41.80%), total fixed C in straw (23.64%), grain (28.87%), and root (46.31%) biomass, and GHG emissions (CO2, 10.78%; N2O, 3.41%), while decreasing SOCS (6.57%) and greenhouse gas intensity (GHGI; 13.61%). Under mulching, biochar application significantly increased maize yield (10.20%), total fixed C in straw (17.97%), grain (17.69%), root (16.75%) biomass, and SOCS (4.78%). Moreover, it decreased GHG emissions (CO2, 3.09%; N2O, 6.36%) and GHGI (12.28%). These effects correlated with the biochar addition rate, with the optimal rate being 9.0 t ha–1. In conclusion, biochar application reduced CO2 and N2O emissions, enhanced CH4 absorption, and improved maize yield under film mulching. It also improved the soil carbon fixation capacity while mitigating the warming potential, making it a promising sustainable management method for mulched farmland in semiarid areas.

Continuous maize cultivation with high nitrogen fertilizers associated with the formation of dried soil layers in the semiarid farmland on the Loess Plateau

• Different land use types were chosen to determine soil desiccation. • Long-term maize cultivation with high yield caused a DSLs in the deep soil layers. • Crop rotations are recommended for maize production in the semiarid environment. Sustainable agriculture ensures food security and combats climate change by minimizing reliance on water resources. Maize ( Zea mays L.) is commonly grown with plastic mulching practice on the Loess Plateau of China, but its impact on soil desiccation is not well understood. We compared the effects of different land-use, including 17-year continuous wheat cultivation, 19-year pea-wheat rotations, 12-year continuous maize cultivation (high yield), 30-year multi-crop rotations, and 9-year continuous maize cultivation (varying yield) under four nitrogen (N) fertilization rates (i.e., 0, 100, 200, and 300 kg N ha −1 ). Average crop evapotranspiration during 2009–2020 for long-term continuous wheat, pea-wheat rotation, high-yielding maize, and multi-crop rotations was 222, 201, 277, and 393 mm, respectively, while average effective precipitation from March to September was 329 mm for all treatments. Continuous high-yielding maize cultivation formed a dry soil layer (DSL) in the deep soil profile (>400 cm), which was not found in other cultivation modes. After 9-year continuous high-yielding maize cultivation, 300 kg N ha −1 applying (20.9 Mg ha −1 biomass yield) formed the DSLs in the 360–960 cm soil profiles, while under 200 kg N ha −1 (20.1 Mg ha −1 biomass yield), the soil water content was almost close to the threshold of DSL in the 600–740 cm soil depth; while under 0 and 100 kg N ha −1 (<15 Mg ha −1 biomass yield), the DSL was not found along the soil profile, indicating that DSL formation under continuous maize cultivation was is driven by high N rates (or high yield level). These results suggest that long-term high-yielding maize cultivation with plastic mulching causes severe soil water depletion, resulting in the formation of a DSL in the deep soil profile. To maintain productivity, farmers should not be encouraged to carry out long-term continuous cropping of high-yielding maize in the semiarid environment on the Loess Plateau.

Long-term film mulching with manure amendment increases crop yield and water productivity but decreases the soil carbon and nitrogen sequestration potential in semiarid farmland

Plastic film and gravel mulching in combination with fertilization are widely used to increase crop yields and water productivity (WP) in arid and semiarid areas, but soil surface mulching may stimulate soil organic carbon (SOC) mineralization; therefore, film mulching with manure amendment was proposed to improve soil fertility. However, the combined effects of these practices on yield, WP, and the stocks of SOC and total nitrogen (TN) need to be better understood. This study investigated the long-term effects of different practices on crop yields, WP, and SOC and TN stocks in the 0–20, 20–40 and 40–60 cm layers based on a 12-year spring maize (Zea mays L.) field experiment on the Loess Plateau. The treatments included no mulching + NPK (CK), gravel mulching + NPK (GM), film mulching + NPK (FM), and film mulching + NPK + cow manure (FCM). In 2019 and 2020, compared with the control, both FM and FCM significantly increased crop yields, WP, N uptake efficiency (NupE) and N fertilizer productivity (NfP). Compared with CK, the FCM treatment significantly increased the SOC and TN stocks by 44.10% and 39.51%, respectively, on average, and the minimum C input that could maintain the soil C balance on the Loess Plateau was 0.67 Mg ha−1 yr−1. Over the 12 experimental years, compared with the initial value in 2009, the trends of SOC and TN contents in the FM treatment were downward, while those in the FCM treatment increased by 41.61% and 30.27%, respectively, but yearly input of manure led to SOC equilibrium. Compared with CK, the FCM treatment significantly decreased SOC and TN sequestration potential by 33.38% and 19.59%, respectively, on average in topsoil (0–20 cm), but it had less of an effect on SOC and TN sequestration at 20–40 and 40–60 cm soil depths. The reasons for SOC reaching equilibrium in the FCM treatment were analyzed, and periodic subsoiling was proposed to break the equilibrium state to further improve the sequestration amount of SOC and TN at 0–60 cm soil depths. In conclusion, film mulching with manure amendment was recommended as a long-term strategy to improve soil productivity and soil fertility in semiarid farmland.

Environmental and Biophysical Effects of the Bowen Ratio over Typical Farmland Ecosystems in the Loess Plateau

The Bowen ratio (β) comprehensively reflects physical characteristics of the land-surface climate. In this study, eddy covariance systems installed at Dingxi and Qingyang were used to conduct energy distribution measurements and observations characteristic of semi-arid and semi-humid farmland ecosystems on the China Loess Plateau. We studied mechanisms by which eco-environmental factors influence β. Additionally, we investigated responses of physiological and ecological factors to water and heat exchange under seasonally dry and wet conditions within each farmland ecosystem. Our results showed that sensible heat flux in the semi-arid farmland was the main consumer of available energy. In the semi-humid area, latent heat flux in summer had the dominant role in energy distribution (mean β 0.71). The β in the semi-arid region was 1.5 times higher than that in the semi-humid region during the growing season. β increased with an increase in the vapor pressure deficit (VPD) and ground–air temperature difference (Ts − Ta), and decreased significantly with an increase in effective precipitation and soil moisture. The change in β with environmental factors was more clear-cut in semi-arid areas than in semi-humid areas. The Priestley–Taylor coefficient (α) and β satisfied a power function law in the growing season. There was a strong correlation between them, with the coefficients of determination for semi-humid and semi-arid areas being 0.62 and 0.72, respectively. β decreased with an increase in the normalized difference vegetative index (NDVI), with this phenomenon being more obvious in the semi-humid zone (R2 = 0.40). β responded more rapidly to NDVI in the semi-arid area than in the semi-humid area. There was a negative exponential relationship between canopy stomatal conductance (Gs) and β, which displayed a stronger declining trend with the increase in Gs in the semi-arid area than in the semi-humid area. This study provides an important reference for the determination of land-surface characteristics of semi-arid and semi-humid farmland ecosystems on the Loess Plateau and for improving parameterization of land-surface processes.

Ice-covered soil significantly minimizes topsoil water loss in a semi-arid farmland

Flood irrigation is widely used as the most common farmland irrigation measure worldwide. However, the larger water evaporation after flooding seriously affects soil water maintenance, especially in winter and spring in the semi-arid and arid regions of north China. Hence, how to more efficiently maintain soil water content (SWC) after flood irrigation has become an important issue. This study examined whether ice-covered soil after flood irrigation can maintain high soil moisture based on a field investigation. Our results showed that the increase of SWC due to flood irrigation was markedly higher in the topsoil than in the subsoil layer, and the soil water supplement mainly happened on the cultivated horizon. Compared with the fields with no flood irrigation, SWC of the topsoil in the fields with no ice cover and with ice cover after flood irrigation increased by 56.4% and 75.6%, respectively. Farmland with ice cover presented a higher SWC than that with no ice cover after flood irrigation, and SWC increased for the topsoil and subsoil layer by 12.25% and 8.56%, respectively. Our findings proved that ice cover significantly enhanced soil water replenishment efficiency of flood irrigation to the soil layer, and the ice-covered soil after flood irrigation maintain higher SWC for both soil layers. The ice-covered soil after winter flood irrigation contributes to a better soil water habitat for farming production as an effective agricultural water management measure.

Long-Term Film Mulching with Manure Amendment Increase Crop Yield and Water Use Efficiency But Decrease the Soil Carbon and Nitrogen Sequestration Potential in Semiarid Farmland

Long-Term Film Mulching with Manure Amendment Increase Crop Yield and Water Use Efficiency But Decrease the Soil Carbon and Nitrogen Sequestration Potential in Semiarid Farmland

Can organic carbon and water supplementation sustain soil moisture–carbon balance under long-term plastic mulched semiarid farmland?

Plastic mulching (PM) is regarded as a promising way to increase crop production. However, its reported that plastic mulching may decrease soil organic carbon content and been unfavorable for sustainable agricultural production. Confirmation of the effects of plastic mulching on soil water and organic carbon balances in a long term, including finding efficient ways to improve these balances, is crucial for the sustainability of agricultural production in semiarid rain-fed areas. We conducted field experiment (2010–2019), with spring maize and wheat as tested crops, using four treatments of plastic mulching (PM), plastic mulching with supplementary irrigation (PMI), plastic mulching with organic fertilizer application (PMO) and without mulching (CK). The results of this 10-year field experiment showed that PM with supplementary irrigation and organic fertilizer application not only significantly increased yield and Water productivity (WP) of wheat and maize, but also had a positive effect on soil water budget. The soil water budget of PMI, PMO and PM significantly increased by 120.4%, 96.1% and 105.8% in wheat and by 149.7%, 28.2% and 53.6% in maize, compared with CK, respectively. The improved soil water condition resulted in a significant increment of yield, PMI, PMO and PM increased yield by 122.8%, 89.7% and 67.0% for wheat, by 237.8%, 183.0% and 148.4% for maize, respectively, compared with CK. The 10 years of continuous PM significantly decreased soil organic carbon content (SOC) in 0–10, 10–20, 30–50 and 50–70 cm profiles by 22.5%, 19.1%, 15.6% and 15.3% for wheat, but had no significant effect for maize. The PMO significantly increased soil organic carbon content in 0–30 cm profiles for both wheat and maize, but the soil organic carbon budgets were negative for all four treatments, the PMO accelerated soil organic carbon loss for maize but had little effect for wheat compared with PM and CK. However, PMI, PMO and PM significantly increases crop bio-carbon production, resulted in the positive total carbon budget and significantly increased by 25.0, 15.0, 11.5 Mg ha−1 in wheat and 105.1, 74.1, 74.0 Mg ha−1 in maize, respectively, as compared with CK. These results suggested that the soil organic carbon budget differed for the two crops, also affected by water or organic carbon supplementation. A more appropriate crop rotation system with organic fertilizer application should be developed, to increase crop production and soil quality under plastic mulched condition in such semiarid rain-fed areas.

Yield, Economic Benefit, Soil Water Balance, and Water Use Efficiency of Intercropped Maize/Potato in Responses to Mulching Practices on the Semiarid Loess Plateau

Increasing agricultural productivity without undermining further the integrity of the Earth’s environmental systems such as soil water balance are important tasks to ensure food security for an increasing global population in rainfed agriculture. The impact of intercropping maize (Zea mays L.) with potato (Solanum tuberosum L.) on yield, land equivalent ratios (LER), water equivalent ratio (WER), water use, energy output, and net economic return were examined under seven planting systems: potato grown solely or intercropped on the flat field without mulching, maize grown solely or intercropped with potato on ridges or flat field with or without plastic film mulched. The three intercropping systems had 3–13% less water use than the monocropping. Among the intercropped systems, flat field caused more depletion of soil water than ridged field for both years. Compared to monocultures, intercropping with plastic film mulching and ridging significantly increased LER and WER. Meanwhile, intercropping with mulching and ridging significantly increased net economic return and energy output by 8% and 24%, respectively, when compared to monocropping. These results suggest that maize under plastic film mulched ridge-furrow plot intercropped with potato under flat plot without mulching increased energy output, net economic return, and water use efficiency without increasing soil water depletion, which could be an optimal intercropping system for the semiarid farmland on the western Loess Plateau.

Interrelation between harvester ant activity, soil fertility, and land management in the arid lands of the Negev Desert, Israel

Much of the open lands in arid areas are highly degraded reaching a state grazing or crop yields become low and non-profitable a state grazing or crop yields become low and non-profitable. Implementation of deep tilling and fertilization to enhance yields may cause destructive outcomes for the environment. An alternative approach may be conservation agriculture practices also involving the triangular interrelation among the harvester ant activity, soil fertility, and land management practices to maximize and increase the sustainable agricultural utilization of semi-arid farm land. In order to define this interrelation, a study was carried out at three sites in the northern Negev, Israel between 2014 and 2017. In each site, three different land management practices were carried out (cereal breeding, grazing, and conservation). The findings indicate that in the first three years, the harvester ants' foraging activity increased soil organic matter content by 0.25% per year, followed by an increase of 0.5 % year−1, caused by ants' nesting and foraging. In this state, partial grazing or rainfed crop breeding using a conservative tillage scheme can be carried out until sustainability. Cultivations such as fertilizing with organic matter and land management practices such as savanna trees or local perennials plantations may strengthen the interrelation among the harvester ant activity, soil fertility and biological productivity leading to an increased sustainable agriculture utilization.

Soil microbial community and network changes after long-term use of plastic mulch and nitrogen fertilization on semiarid farmland

Soil microbes are crucial for improving soil quality and productivity. Plastic film mulch (FM), in conjunction with fertilization, has significantly improved crop yields over vast areas of dryland production. However, how these practices affect soil microbial communities, especially as regards co-occurrence patterns within microbial taxa, is unclear. The objective of this study was to determine the effects of 10 years of FM and four nitrogen (N) fertilization rates [0 (N0), 100 (N100), 250 (N250), and 400 (N400) kg N ha−1] on soil bacterial and fungal diversity, community structure, composition, and the co-occurrence network in a rainfed maize (Zea mays L.) field on the Loess Plateau of China. Results showed that N fertilization and FM did not affect soil microbial biomass carbon, but these practices changed the soil bacterial and fungal community structures. The bacterial community structure was dominantly affected by N fertilization, owing to the increased soil N content and decreased soil pH, which reduced bacterial community diversity and altered the relative abundance of some copiotrophic/oligotrophic taxa (e.g., Gemmatimonadetes, Acidobacteria, Rokubacteria, and Planctomycetes). Plastic mulch played a greater role in regulating the fungal community structure, primarily because FM increased soil moisture and promoted soil organic matter decomposition, thereby reducing fungal richness and altered the relative abundance of Chytridiomycota, Mortierellomycota, Glomeromycota, and Mucoromycota. Moreover, FM mediated the effects of N fertilization by reducing soil N content, and then increased the N threshold that caused changes in microbial structure. Network analysis indicated that FM caused an unstable co-occurrence network with fewer positive and negative links, while N fertilization increased both positive and negative (except N400) links, indicating enhanced cooperation and competition among microbes. These results indicate that long-term plastic mulch and high N fertilization could result in risk for soil quality in terms of soil microbial community structure and stability, suggesting that developing new management strategies is necessary to sustain dryland productivity.

Wheat cultivars with small root length density in the topsoil increased post-anthesis water use and grain yield in the semi-arid region on the Loess Plateau

Large distribution of roots in topsoil layers allow more uptake of soil water and nutrients during the vegetative growth, but it may be disadvantageous if soil water deficit develops during the reproductive stage. The relationship between the distribution of roots in topsoil (0–0.4 m) and soil water use, dry matter and nitrogen (N) accumulations, and grain yield was examined in winter wheat (Triticum aestivum L.) with contrasting root size in the topsoil. Two old landraces (CW134 and JM47, larger root length and biomass in the topsoil) and two modern wheat cultivars (CH58 and LH7, smaller root system size in the topsoil), were grown in the field during two seasons (2016–2017 and 2017–2018) under rainfed and irrigation conditions in the semi-arid farmland on the Loess Plateau. Root biomass and root length density (RLD) in topsoil (0–0.4 m) was significantly higher in the old landraces than in the modern cultivars (P < 0.05) under rainfed and irrigation in both seasons (no such difference in subsoil, 0.4–1.0 m). The modern cultivars had significantly higher grain yield, grain N concentration, water-use efficiency (WUE), and 1000-grain weight (P < 0.05). Seasonal water use was similar among all cultivars, but post-anthesis water use was higher in the modern cultivars, particularly under rainfed conditions in both seasons. Root biomass and RLD in the topsoil was positively correlated with pre-anthesis water use, but negatively correlated with after anthesis water use. Post-anthesis water use was closely related to post-anthesis dry matter, N accumulation, yield and WUE under rainfed conditions. To conclude, large distribution of roots in the topsoil had non-advantage for wheat grown under rainfed conditions. The small distribution of roots in the topsoil (characteristics of modern wheat cultivars) enhanced post-anthesis water use, increased post-anthesis dry matter and N accumulation, and hence attained higher grain yield and grain N when grown in the semi-arid environment.

Height and diameter affect survival rate of jujube suckers transplanted in a semi-arid farmland of New Mexico

Height and diameter affect survival rate of jujube suckers transplanted in a semi-arid farmland of New Mexico

Optimal Wheat Seeding Rate is Influenced by Cultivar‐Specific Topsoil and Subsoil Root Traits

Competition among plants for limited soil resources is influenced, in part, by seeding rate. This study aimed to investigate how cultivars that differ in root traits affect water acquisition and the optimal seeding rate. Three cultivars of winter wheat (Triticum aestivum L.) with contrasting root systems (CW134, more roots in topsoil and less roots in subsoil; CH58, small root biomass; CH1, less roots in topsoil and more roots in subsoil) were sown at 180, 225, and 280 seeds m−2 in 2014–2015 and 2015–2016 in a semiarid farmland on the Loess Plateau of China. As the seeding rate increased, grain yield declined in CW134, with topsoil roots increasing and subsoil roots decreasing in both seasons. In contrast, both grain yield and subsoil roots increased in CH1, and the highest grain yield was produced by CH1 at 280 seeds m−2 in both seasons. Subsoil root traits had a positive effect on soil water consumption after anthesis, which was strongly affected by yield components in the dryer season (2015–2016). However, the reverse was true for topsoil root traits. In 2014–2015, the topsoil roots had a positive effect on soil water consumption before anthesis, and aboveground traits at anthesis had a greater positive effect on yield components. To maintain higher yields in semiarid environments, genotypes with more topsoil roots should have lower seeding rates to alleviate the negative effect of excessive topsoil roots on postanthesis water absorption, while the reverse may be true for genotypes with more roots in subsoil layers.Core Ideas Excessive topsoil roots negatively affected postanthesis water absorption under drought stress. Increased root length in subsoil layers helped exploitation of deep soil water after anthesis. In semiarid areas, genotypes with large topsoil root traits should use lower seeding rates. Increased seeding rates may help yields of genotypes with more roots in subsoil layers.

Response of Maize Productivity and Resource Use Efficiency to Combined Application of Controlled‐Release Urea and Normal Urea under Plastic Film Mulching in Semiarid Farmland

Controlled‐release urea is considered to enhance crop yields while reducing labor costs from fertilizer dressing, but the impacts can range widely depending on water availability in soil. Therefore, we conducted a 3‐yr field study to evaluate the potential role of controlled‐release urea in improving productivity and resource use efficiency of maize in semiarid areas in China. Treatments were established as two mulching modes (plastic film mulching [FM] and no mulching [NM]) and three nitrogen application modes (no nitrogen fertilizer [CK], a 1:2 ratio of controlled‐release urea to common urea [CRU], and common urea only [U]). Higher temperature and soil water content under FM treatments significantly accelerated maize growth and development, as indicated in terms of a larger leaf area index before silking, greater biomass accumulation, and greater grain yield. More robust plants with controlled‐release urea under mulching can better absorb and utilize deep soil water to increase water use efficiency (WUE). Mean shoot biomass, grain yield, and WUE during the three experimental years were 35.3, 19.0, and 12.4% higher in mulching with CRU treatments than in NM with controlled‐release urea treatments, respectively. Significant interactions existed for yield and WUE among surface mulching (SM), nitrogen fertilizer (NF), and sampling year (Y) in the three experimental years, except for SM × NF for WUE. These results demonstrate that a mixture of controlled‐release urea and U at an appropriate ratio under SM can provide a better water/temperature/nitrogen conditions for maize growth to realize relatively high yield with labor and time savings in semiarid farmland.Core Ideas Film mulching benefits topsoil temperature, soil moisture, and utilization of deeper soil water. Combining controlled‐release urea (CRU) and urea increased yield and resource use. Combing CRU and urea under plastic film increased yield and WUE. One‐time application of CRU + urea at an appropriate ratio will satisfy spring maize in dryland farming systems.

Soil microbial communities under film mulching and N fertilization in semiarid farmland

Film mulching and N fertilization can affect soil physicochemical properties, thereby improving plant growth, and may in turn affect soil microbial communities. Therefore, a 2-year field experiment was conducted to research the effects of film mulching and N fertilization on soil microbial communities. The four main treatments were N0F0, N0F1, N1F0, and N1F1, combining two N fertilizer rates (N0, 0 kg N ha−1; N1, 225 kg N ha−1) and two mulching methods (F0, no mulching; F1, film mulching) in the absence and presence of plants. The film mulching treatments significantly increased the mean temperature by 0.2 °C and decreased the soil organic carbon (SOC), mineral N and water soluble organic C by 5.6%, 35.5% and 24.0%, respectively. The N fertilization treatments significantly increased the mineral N, water soluble organic N and KMnO4-oxidizable C by 117.9%, 256.4% and 55.3%, respectively. Additionally, the phospholipid fatty acid (PLFA) analysis of the soil microbial community revealed that the film mulching treatments significantly decreased the total PLFAs by 21.5% and the absolute abundance of fungi (F), bacteria (B), and actinomycetes by 26.7%, 23.1% and 24.6%, respectively. N fertilization significantly decreased the Gram-positive B/Gram-negative B ratio by 9.8%. Film mulching combining N fertilization significantly decreased the F/B ratio by 10.0%. Temperature (P < 0.001) and SOC/total P (P < 0.001) were confirmed to play significant roles in shaping the soil microbial community. Accordingly, short-term film mulching increases soil organic matter decomposition in the top soil and decreases the total soil microbial biomass and most microbial communities.

Residual effects of fertilizer N response to split N applications in semiarid farmland

A better understanding of residual N fate is important for N management in agricultural production. The N application rate and time may dramatically influence N recovery in the plant–soil system, in turn affecting residual N uptake by subsequent crops. A 3-year field experiment was conducted in plastic-mulched maize in semiarid farmland. 15N-labeled urea was applied to microplots with a single application (100% before sowing, N1), two splits (4:6 at sowing and eight-leaf stages, N2), and three splits (4:3:3 at sowing, eight-leaf, and silking stages, N3), and the fate of residual fertilizer N in soils over the following two cropping seasons was examined. Approximately 14.6–18.7% and 5.4–5.8% of labelled fertilizer N were recovered by maize in the second and the third seasons, respectively, with the cumulative recovery efficiency reaching 47.6–60.8% over 3 years. Applying N with three splits significantly increased residual fertilizer N recovery by 24.6% in the second cropping season compared to N1 and N2. About 22.7–32.4% and 15–21% of total labelled N applied was residual in the 0–2 m soil layer after the second- and the third-season harvest, respectively, with the higher residual amount from split N applications. In conclusion, split N applications significantly increased the cumulative fertilizer N recovery in the plant–soil system while decrease the potential losses over 3 years, due to the higher recovery efficiency and the lower N losses from topdressed N.

Biophysical regulation of evapotranspiration in semiarid croplands

Water vapor exchange is a key component in terrestrial surface water balance. However, the biophysical regulation processes that control evapotranspiration (ET) in semiarid farmland areas have not been fully resolved. In this study, seasonal and interannual variances in ET and their environmental controls from 2009 to 2011 were investigated in a semiarid, rain-fed farmland using eddy covariance. One moderately dry year (2010) and two extremely dry years (2009 and 2011) were observed; however, 2009 (an extremely dry year) had the same weather condition as that of 2010 (a moderately dry year), and 2011 set out as different from the other two years. The results indicated that the maximum daily ET in the 2009 (4.4 mm d−1) and 2010 (4.7 mm d−1) growth seasons was higher than that in 2011 (3.0 mm d−1). Cumulative annual ET values were 310.6, 318.0, and 210.2 mm in 2009 to 2011, which were 109%, 96%, and 72% of the precipitation (PPT) received, respectively. The contribution of PPT in summer to the annual ET was more than that in autumn, and the extremely dry climate during the pregrowth stage and early spring period restricted the annual ET in 2011. The lowest annual ET in 2011 was caused by low daytime ET rather than nighttime ET. The strong power relationship (R2 = 0.85) between the decoupling coefficient (Ω) and the canopy conductance (gc) indicated that ET was sensitive to gc, and gc control on ET increased as the day progressed. The physiological controls of ET were associated closely with soil moisture, and drought had a strong effect on the ET response to environmental factors, such as incoming shortwave radiation and vapor pressure deficit. These results have important potential implications for understanding and modeling water cycle feedback to the increasing drought climate in the Loess Plateau characterized by serious soil and water loss.

Delocalization of Salt Solution in a Semiarid Farmland Topsoil

Salt buildup is a global phenomenon in semiarid soils that leads to land degradation and water quality deterioration. These problems can be alleviated through the quantification of salt leaching from topsoil horizons. Delocalization of solid-phase salts and solution-phase leaching was evaluated within the topsoil layers of a semiarid farmland by utilizing a non-invasive electromagnetic sensing and stochastic modeling approach. The horizontal and vertical conductivity signals were strongly correlated (r = 0.988, P < 0.05) and characterized by high precision and low errors (0.12–0.18). Electrical conductivity across the field was highly variable within the 0.6-m profile with nearly all surveyed locations exhibiting values greater than 2 dS m−1. Around 86% of the salinity data in 0.3-m depth ranged from 2 to 8 dS m−1, and 56% data within 0.3–0.6 m surpassed 8 dS m−1. Spatial depletion in salinity within the 0.3-m depth plausibly resulted from salt delocalization. The salinity values generally exceeded plant tolerance threshold limits and indicated that most crops would be adversely affected unless management practices were aimed at removing salts past the topsoil horizons. The leaching fraction levels ranged from 5 to 40% across the topsoil layers, and indicated the need for salt removal practices for most crops. Overall, salt delocalization analysis can benefit agronomic decisions for irrigation and soil quality management. The approach can be applied worldwide in locating impaired soil zones that need salt reclamation for developing best management practices pertaining to site-specific crop selection and agricultural water budgeting.

Effects of Biochar Application on CO2 Emissions from a Cultivated Soil under Semiarid Climate Conditions in Northwest China

Biochar amendments to soil have potential as a climate change mitigation strategy. However, their effect on carbon exchange in different ecosystems has not been well evaluated. Understanding how biochar affects carbon exchange from agricultural soil is essential for clarifying the contribution of biochar management to the carbon budget. We performed a laboratory and a two-year field experiment to investigate the short- and medium-term effects of biochar application on CO2 emissions from semiarid farmland. There was no statistically significant alteration in the cumulative CO2 emissions from the mixture of soil with biochar alone, while the emissions increased significantly with additional nitrogen amendment over the 46-day experimental period. Over the two-year experimental period, the cumulative CO2 emissions from the field experiment decreased in the biochar-amended treatment, and the effects were significant at high application rates (20 and 30 t·ha−1) relative to the control in the MS. The seasonal CO2 dynamics were strongly dependent on soil temperature, with a higher correlation with the temperature at a depth of 10cm than with the temperature at a depth of 0cm. Soil temperature, rather than soil water content, was the major environmental factor controlling the soil carbon exchange in the semiarid farmland of the Loess Plateau. In general, biochar additions enhanced aboveground dry matter accumulation in both the early and late stages of maize growth. The results suggested that biochar amendment was a preferable management practice to help maintain or increase carbon sequestration for this region with lower CO2 emissions and higher dry matter production over a longer period.