Maize Cropland Research Articles

Evapotranspiration and its components over a rainfed spring maize cropland under plastic film on the Loess Plateau, China

Aim of study: To determine seasonal variations in evapotranspiration (ET) and its components; and ascertain the key factors controlling ET and its components in a rainfed spring maize field under plastic film.Area of study: Shouyang County in Shanxi Province on the eastern Loess Plateau, ChinaMaterial and methods: Eddy covariance system combined with micro-lysimeters and meteorological observing instruments were used in the field. The manual method was used to measure the green leaf area index (GLAI) during the growing season.Main results: In 2015 and 2016, the growing season ET accounted for 80% and 79% of annual ET, respectively. Soil evaporation (E) accounted for 36% and 33% of the growing season ET in 2015 and 2016, respectively. The daily crop coefficient increased with increasing GLAI until a threshold of ~3 m2 m−2 in the canopy-increasing stage, and decreased linearly with decreasing GLAI in the canopy-decreasing stage. At equivalent GLAI, daily basal crop coefficient and soil water evaporation coefficient were generally higher in the canopy-increasing and -decreasing stages, respectively. During the growing season, the most important factor controlling daily ET, T, and E was net radiation (Rn), followed by GLAI for daily ET and T, and soil water content at 10-cm depth for daily E; during the non-growing season, daily ET was mainly controlled by Rn.Research highlights: The daily crop coefficient and its components reacted differently to GLAI in the canopy-increasing and -decreasing stages.

生物炭对褐土旱地玉米季氮转化功能基因、丛枝菌根真菌及N2O释放的影响

以豫西旱地玉米农田为研究对象，设置不同生物炭施用量处理（T0：不施用生物炭；T1：施用生物炭20 t/hm²；T2：施用生物炭40 t/hm²），采用密闭式静态箱法测定N₂O排放通量和荧光定量PCR法分析丛枝菌根（arbuscular mycorrhizal，AM）真菌、氨单加氧酶（amoA）、亚硝酸盐还原酶（nirS、nirK）以及氧化亚氮还原酶（nosZ）的基因丰度，同时测定土壤理化性状的变化。研究结果表明，随着生物炭施用量的增加，土壤pH和含水量呈增加趋势，土壤有机碳、全氮和铵态氮含量显著提高，土壤容重和硝态氮含量显著降低。T1和T2处理土壤有机碳含量分别较T0显著提高38.44%和71.01%；T1和T2处理土壤铵态氮含量分别较T0显著增加15.89%和30.46%；T2处理土壤全氮含量较T0处理显著提高14.87%；T1和T2处理土壤硝态氮含量分别较T0减少10.57%和21.40%。随着生物炭施用量的增加，AM真菌侵染率显著增加，T1和T2处理分别较T0处理提高71.88%和115.88%；AOA、AOB、nirK和nirS基因丰度显著降低；nosZ基因丰度增加。施加生物炭处理的N₂O排放通量和累积排放量均低于不施生物炭处理，具体表现为：T0 > T1 > T2。相关分析表明，生物炭施用量与AM真菌基因丰度呈显著正相关；与nosZ基因丰度呈正相关；与AOA、AOB、nirK、nirS基因丰度呈极显著负相关。N₂O排放通量与AOA、nirK、nirS基因丰度呈极显著正相关；与土壤含水量和土壤硝态氮含量呈显著正相关；与AM真菌、nosZ基因丰度、易提取球囊霉素含量、铵态氮含量呈极显著负相关。集成推进树（ABT）分析表明，AOA对N₂O排放的影响最大，其次是AM真菌和nirS。总之，生物炭处理改善土壤理化性质、提高土壤AM真菌侵染率、调节硝化、反硝化相关功能基因的丰度，减少N₂O气体排放，为旱地农田合理施用生物炭减少N₂O气体排放提供理论依据。;Biochar soil amendments are attracting the increased attention as one strategy to improve soil microbially ecological environment and regulate soil nitrogen cycle. The rainfed maize cropland in the western Henan was established to study the effects of biochar application rates (T0:0 t/hm², T1:20 t/hm², and T2:40 t/hm²) on soil physicochemical properties and N₂O emission fluxes using the static chamber/gas chromatography method, and the function marker genes of arbuscular mycorrhizal (AM) fungi, ammonia monooxygenase gene (amoA), nirK, nirS and nosZ, which were responsible for nitrification and denitrification using real-time fluorescence quota PCR. The results showed that the soil pH and water content increased, soil organic carbon, total nitrogen and ammonium nitrogen content increased significantly, and soil bulk density and nitrate nitrogen content decreased significantly with increasing biochar applied. Compared with T0 treatment, soil organic carbon increased significantly by 38.44% and 71.01% under T1 and T2 treatments, respectively; soil ammonium nitrogen content increased significantly by 15.89% and 30.46% under T1 and T2 treatments, respectively; soil total nitrogen content increased significantly by 14.87% under T2 treatment; nitrate nitrogen content decreased by 10.57% and 21.40% under T1 and T2 treatments, respectively. Moreover, the AM fungi colonization rate and nosZ gene abundance increased significantly, and AOA, AOB, nirK and nirS gene abundance decreased significantly with increasing biochar applied. Compared with T0 treatment, AM fungi increased significantly by 71.88% and 115.88% under T1 and T2 treatments, respectively. The N₂O emission fluxes and emission accumulations under biochar addition were all lower than those under no biochar, ranked as T0 > T1 > T2. The correlation analysis showed that the abundance of AM fungi was significantly positively (P<0.05) correlated with the biochar rate, and the abundance of nosZ gene and biochar rate was significant. There was a significantly negative correlation between AOA, AOB, nirK, nirS gene abundance and biochar rate (P<0.01). The N₂O emission fluxes showed a significantly positive correlation (P<0.01) with AOA, nirK, nirS, soil water content and nitrate nitrogen, but significantly negatively (P<0.01) correlated with AM fungi, nosZ, ammonium nitrogen and extractable glomalin related soil protein content. Aggregated boosted trees (ABT) analysis showed that the relative influence of AOA on N₂O emission fluxes was the largest, followed by AM fungi and nirK. In summary, the application of biochar improved soil physicochemical properties, increased soil AM fungi colonization rates, regulated nitrification and denitrification functional genes, and reduced N₂O emission, which provided a theoretical basis for the rational application of biochar and reduction of N₂O emissions in rainfed maize cropland.

Određivanje pogodnosti poljoprivrednog zemljišta za uzgoj kukuruza (Zea mays L.) primjenom višerazinske GIS multikriterijske analize

Previous research in continental Croatia indicated that cropland suitability levels are highly variable and existing natural resources could be better utilized. To overcome this issue, a method of multilevel Geographic information system (GIS)-based multicriteria analysis based on Analytic hierarchy process (AHP) for maize cropland suitability determination was proposed and evaluated. Free spatial data and free open-source software were implemented in the research in 250 m spatial resolution. The effects of air temperature, precipitation, soil and topography were modelled with the multilevel approach to avoid inconsistency in pairwise comparison due to criteria count. The maize suitability index (MSI) was calculated using the weighted linear combination, with higher values indicating proportionally higher suitability. According to the results of the AHP method, the weight consistency ratio was lower than the borderline value (0.042 < 0.100). Soil type and mean air temperature in June had the most impact on the suitability result, with 14.3% and 13.6% influence, respectively. The highest MSI values were achieved along the Sava River, especially in the proximity of Sisak and Nova Gradiska, resulting up to 3.9 of the possible 5.0. The sensitivity analysis of criteria indicated precipitation data in May, July and August particularly impactful in continental Croatia, while mean air temperature in September had very low variability of the suitability and was the least impactful on calculated MSI values.

Carbon dioxide flux and soil carbon stock as affected by crop residue management and soil texture in semi‐arid maize croplands in Tanzania

AbstractCrop residue management strategies must be adapted for improving carbon (C) balance and soil C stock in agroecosystems in sub‐Saharan Africa with consideration of the crop residue availability and site‐specific soil characteristics. We conducted field experiments to determine the effects of crop residue application method (incorporation/mulching) and quality (maize/cowpea) and N fertilizer application on the soil respiration rate and soil C stock in the surface soil layer (0–15 cm) in maize croplands with contrasting soil textures (clay/sandy) over 2 years from 2012 to 2014 in Tanzania. At the clay site, the incorporation of maize residues showed a 38% increase in CO2 flux compared to mulching, whereas, at the sandy site, mulching showed a 16% increase compared to the incorporation. At the sandy site, mulching practice retained soil moisture content and apparently enhanced the decomposition of the original soil organic C in the surface layer. It is, therefore, suggested that mulching practice may accelerate a long‐term depletion of soil C stock at the sandy site. The cowpea residue incorporation led to rapid decomposition because of its high biodegradability at both sites. The N fertilizer application stimulated the decomposition of labile soil organic matter. The soil C stock in the surface layer did not significantly change after the 2‐year experiment, irrespective of crop residue treatment and soil type. In conclusion, adequate crop residue management in terms of suppressing CO2 flux during a cropping season depends on soil type, but the long‐term effect on soil C stock is unclear.

Modeling Gross Primary Production of Midwestern US Maize and Soybean Croplands with Satellite and Gridded Weather Data

Gross primary production (GPP) is a useful metric for determining trends in the terrestrial carbon cycle. To estimate daily GPP, the cloud-adjusted light use efficiency model (LUEc) was developed by adapting a light use efficiency (LUE, ε) model to include in situ meteorological data and biophysical parameters. The LUEc uses four scalars to quantify the impacts of temperature, water stress, and phenology on ε. This study continues the original investigation in using the LUEc, originally limited to three AmeriFlux sites (US-Ne1, US-Ne2, and US-Ne3) by applying gridded meteorological data sets and remotely sensed green leaf area index (gLAI) to estimate daily GPP over a larger spatial extent. This was achieved by including data from four additional AmeriFlux locations in the U.S. Corn Belt for a total of seven locations. Results show an increase in error (RMSE = 3.5 g C m−2 d−1) over the original study in which in situ data were used (RMSE = 2.6 g C m−2 d−1). This is attributed to poor representation of gridded weather inputs (vapor pressure and incoming solar radiation) and application of gLAI algorithms to sites in Iowa, Minnesota, and Illinois, calibrated using data from Nebraska sites only, as well as uncertainty due to climatic variation. Despite these constraints, the study showed good correlation between measured and LUEc-modeled GPP (R2 = 0.80 and RMSE of 3.5 g C m−2 d−1). The decrease in model accuracy is somewhat offset by the ability to function with gridded weather datasets and remotely sensed biophysical data. The level of acceptable error is dependent upon the scope and objectives of the research at hand; nevertheless, the approach holds promise in developing regional daily estimates of GPP.

Performance of the Remotely-Derived Products in Monitoring Gross Primary Production across Arid and Semi-Arid Ecosystems in Northwest China

As an important component to quantify the carbon budget, accurate evaluation of terrestrial gross primary production (GPP) is crucial for large-scale applications, especially in dryland ecosystems. Based on the in situ data from six flux sites in northwestern China from 2014 to 2016, this study compares seasonal and interannual dynamics of carbon fluxes between these arid and semi-arid ecosystems and the atmosphere. Meanwhile, the reliability of multiple remotely-derived GPP products in representative drylands was examined, including the Breathing Earth System Simulator (BESS), the Moderate Resolution Imaging Spectroradiometer (MODIS) and data derived from the OCO-2 solar-induced chlorophyll fluorescence (GOSIF). The results indicated that the carbon fluxes had clear seasonal patterns, with all ecosystems functioning as carbon sinks. The maize cropland had the highest GPP with 1183 g C m−2 y−1. Although the net ecosystem carbon exchange (NEE) in the Tamarix spp. ecosystem was the smallest among these flux sites, it reached 208 g C m−2 y−1. Furthermore, distinct advantages of GOSIF GPP (with R2 = 0.85–0.98, and RMSE = 0.87–2.66 g C m−2 d−1) were found with good performance. However, large underestimations in three GPP products existed during the growing seasons, except in grassland ecosystems. The main reasons can be ascribed to the uncertainties in the key model parameters, including the underestimated light use efficiency of the MODIS GPP, the same coarse land cover product for the BESS and MODIS GPP, the coarse gridded meteorological data, and distribution of C3 and C4 plants. Therefore, it still requires more work to accurately quantify the GPP across these dryland ecosystems.

Investigation of Maize Lethal Necrosis (MLN) severity and cropping systems mapping in agro-ecological maize systems in Bomet, Kenya utilizing RapidEye and Landsat-8 Imagery

ABSTRACT Spatiotemporal information on crops and cropping systems can provide useful insights into disease outbreak mechanisms in croplands. In September 2011, a severe outbreak of Maize Lethal Necrosis (MLN) disease was reported in Bomet County, Kenya. We aimed to detect severely MLN-infected fields and discriminate mono, inter, and continuous maize cropping systems. We collected in-situ MLN severity observations and acquired multi-date and multi-sensor data viz., RapidEye (RE), Sentinel-1 (S1), digital elevation model (DEM), and Landsat-8 (L8) imagery. A hierarchical classification approach was used to map the cropping systems and severely MLN-infected fields during the short rainy season (September 2014–February 2015) using the random forest (RF), one-class support vector machine (OCSVM) and biased SVM (BSVM) classifiers. RF showed better performance when a balanced multi-class dataset was available. Both OCSVM and BSVM did not lead to an accurate high severity MLN class separation. Moreover, the BSVM classifier was able to separate the mono and intercropping systems. During the long rainy season (March–August 2015), only maize crop data were available, hence the BSVM as one class classifiers (OCC) was used and maize fields were successfully mapped even with high confusion rate. Furthermore, the distribution of maize intercropping system increased in low rainfall sites, and the continuous cropping system limited to only 31% of total maize cropland.

Hybridization and introgression between Helicoverpa armigera and H. zea: an adaptational bridge

BackgroundInvasion of organisms into new ecosystems is increasingly common, due to the global trade in commodities. One of the most complex post-invasion scenarios occurs when an invasive species is related to a native pest, and even more so when they can hybridize and produce fertile progeny. The global pest Helicoverpa armigera was first detected in Brazil in 2013 and generated a wave of speculations about the possibility of hybridization with the native sister taxon Helicoverpa zea. In the present study, we used genome-wide single nucleotide polymorphisms from field-collected individuals to estimate hybridization between H. armigera and H. zea in different Brazilian agricultural landscapes.ResultsThe frequency of hybridization varied from 15 to 30% depending on the statistical analyses. These methods showed more congruence in estimating that hybrids contained approximately 10% mixed ancestry (i.e. introgression) from either species. Hybridization also varied considerably depending on the geographic locations where the sample was collected, forming a ‘mosaic’ hybrid zone where introgression may be facilitated by environmental and landscape variables. Both landscape composition and bioclimatic variables indicated that maize and soybean cropland are the main factors responsible for high levels of introgression in agricultural landscapes. The impact of multiple H. armigera incursions is reflected in the structured and inbred pattern of genetic diversity.ConclusionsOur data showed that the landscape composition and bioclimatic variables influence the introgression rate between H. armigera and H. zea in agricultural areas. Continuous monitoring of the hybridization process in the field is necessary, since agricultural expansion, climatic fluctuations, changing composition of crop species and varieties, and dynamic planting seasons are some factors in South America that could cause a sudden alteration in the introgression rate between Helicoverpa species. Introgression between invasive and native pests can dramatically impact the evolution of host ranges and resistance management.

Evapotranspiration partitioning and crop coefficient of maize in dry semi-humid climate regime

Guanzhong Plain is one of the most critical maize production areas in Northwest China. It is essential to study the maize irrigation requirement and improve water use efficiency in this area. There is a lack of knowledge about the evaporation portioning and irrigation requirements of crops grown in this region. Based on evapotranspiration observed in a maize cropland using the eddy covariance (EC) technique during four growing seasons (2013, 2014, 2015, and 2017), the seasonal variation of evapotranspiration components and the crop coefficients (Kc) for summer maize in a dry semi-arid area were determined. Energy partitioning has an obvious seasonal variation during growing seasons. The pattern of evapotranspiration partitioning has a clear seasonal variation with the development of the canopy. The pattern of the ratio of transpiration (T) to evapotranspiration (ET) is consistent with the canopy development. For four growing seasons, on a seasonal basis, the ratios of T to ET and E to ET were comparable. In addition, the locally developed crop coefficients were 0.57, 1.01, and 0.50 for the initial, mid, and late stages, respectively. The single crop coefficient derived from local datasets can provide a good prediction of ET. The Kc values reported in this paper were consistent with previous studies conducted in other regions using EC systems but were generally lower than the Kc values derived from ET data measured by lysimeters, the Bowen Ratio Energy Balance system, and the soil water balance method. This indicates that the variability of the locally developed crop coefficient caused by measurement methods is higher than the variability caused by climate.

Plastic-film mulch cropping increases mineral-associated organic carbon accumulation in maize cropped soils as revealed by natural 13C/12C ratio signature

Plastic-film mulch is used for increasing soil temperature and reducing water evaporation to enhance productivity in semiarid regions worldwide; however, its effects on soil organic carbon (SOC) level and stability are not clear. We tested hypotheses that increasing soil temperature and moisture by plastic-film mulch with an increase of carbon input would increase the accumulation of heavy-fraction SOC (HFOC) and decrease the mineralization potential of HFOC. Soils were sampled at 0–45 cm depth from four treatments: (i) no mulch and no straw incorporation, (ii) mulch only, (iii) straw incorporation only, and (iv) straw incorporation plus mulch. All treatments were cultivated with C4 maize (Zea mays L.) under ridge–furrow management continuously for nine years in a field previously planted with C3 crops in a cold environment. Proportionately to the increased aboveground biomass, root biomass in the 0–20 cm depth increased under mulch compared to no mulch. Nine years later, mulch reduced both maize-derived (new) and C3-crop-derived (old) light-fraction SOC (LFOC) stocks only at 0–15 cm soil depth compared to no mulch, regardless of whether straw was incorporated or not, reflecting the increased decomposition due to increased temperature and moisture in mulched soils. Mulch increased new HFOC stock at 0–30 cm soil depth relative to no mulch. These indicated that the faster decomposition of labile LFOC with increasing plant input under mulch relative to no mulch was paralleled by an enhancement in the accumulation of stable HFOC in mulched soils. Mulch enhanced the benefits of straw incorporation in terms of increasing the accumulation of new HFOC. Over nine years, the average sequestration rate of new HFOC at 0–45 cm soil depth was 204 (±18) and 266 (±10) kg ha−1 yr−1 without and with mulch, respectively, in non-straw-incorporated plots, and 514 (±14) and 752 (±18) kg ha−1 yr−1 without and with mulch, respectively, in straw-incorporated plots. Old HFOC was unaffected by mulch or straw incorporation. Overall, mulch did not change the total SOC storage in the top 45-cm soil. Mulch decreased the mineralization potential of new HFOC under laboratory incubation compared to no mulch, indicating that the new HFOC was more decomposed in mulched soils. We concluded that increasing soil temperature and moisture by using plastic-film mulch with high plant input increases the accumulation of stable HFOC in maize croplands.

Effects of long-term straw return on soil organic carbon storage and sequestration rate in North China upland crops: A meta-analysis.

Soil organic carbon (SOC) is essential for soil fertility and climate change mitigation, and carbon can be sequestered in soil through proper soil management, including straw return. However, results of studies of long-term straw return on SOC are contradictory and increasing SOC stocks in upland soils is challenging. This study of North China upland agricultural fields quantified the effects of several fertilizer and straw return treatments on SOC storage changes and crop yields, considering different cropping duration periods, soil types, and cropping systems to establish the relationships of SOC sequestration rates with initial SOC stocks and annual straw C inputs. Our meta-analysis using long-term field experiments showed that SOC stock responses to straw return were greater than that of mineral fertilizers alone. Black soils with higher initial SOC stocks also had lower SOC stock increases than did soils with lower initial SOC stocks (fluvo-aquic and loessial soils) following applications of nitrogen-phosphorous-potassium (NPK) fertilizer and NPK+S (straw). Soil C stocks under the NPK and NPK+S treatments increased in the more-than-20-year duration period, while significant SOC stock increases in the NP and NP+S treatment groups were limited to the 11- to 20-year period. Annual crop productivity was higher in double-cropped wheat and maize under all fertilization treatments, including control (no fertilization), than in the single-crop systems (wheat or maize). Also, the annual soil sequestration rates and annual straw C inputs of the treatments with straw return (NP+S and NPK+S) were significantly positively related. Moreover, initial SOC stocks and SOC sequestration rates of those treatments were highly negatively correlated. Thus, long-term straw return integrated with mineral fertilization in upland wheat and maize croplands leads to increased crop yields and SOC stocks. However, those effects of straw return are highly dependent on fertilizer management, cropping system, soil type, duration period, and the initial SOC content.

Diversity and composition of arbuscular mycorrhizal fungal communities in the cropland black soils of China

The black soil zone is a critical agricultural production region in China. Arbuscular mycorrhizal fungi (AMF) play key role in the functioning of agricultural ecosystems, but are little known in the black soil zone. We here estimated the diversity and composition of the AMF communities from ten maize cropland soils across the black soil zone of northeast China using MiSeq sequencing. Our results showed that all sequences from the 10 soil sites were classified into 4 orders, 9 families, and 12 genera, and Glomerales was the most abundance taxa. The composition and diversity of the AMF communities was affected by soil organic C, N, P and pH.

Sequential combustion separation of soil organic carbon fractions for AMS measurement of 14C and their application in fixation of carbon

A temperature stepped-combustion method for separating soil organic carbon (SOC) fractions and their 14C ages was developed to investigate SOC fixation and stability in soils. After acid-leaching, SOC was sequentially oxidized, and extracted from three temperature intervals: (1) 25–400 °C, (2) 400–600 °C, and (3) 600–900 °C. The acid-soluble carbon and SOC released below 600 °C are labile components, with relatively younger 14C ages, while the SOC released above 600 °C is stable with older 14C ages. We applied this method in a grassland, maize cropland and forest nursery cropland, to assist in understanding the stability of carbon in soils under different land use conditions.

Stemflow contributions to soil erosion around the stem base under simulated maize-planted and rainfall conditions

Stemflow is a primary pathway through which rainwater reaches the ground surface under crop cover. Substantial research suggests that stemflow amounts approach or exceed half the total precipitation on maize cropland; however, few studies have quantified the effect of stemflow on soil erosion during rainfall events. This study aimed to measure the effect of stemflow on soil erosion under controlled situations and determine the effects of stemflow on soil erosion. Maize stems were simulated using a 2-cm diameter PVC tube in 1.3 by 0.25 m steel boxes to introduce stemflows to the soil surface at a 10° slope. The rainfall intensities were 60, 90 and 120 mm/h; the stemflow amounts were 5, 10 and 15 g/s. The results showed that stemflow significantly increased soil erosion. As stemflow increased, the surface runoff and sediment rates sharply increased. Compared with a control slope (no stemflow), stemflow increased the surface runoff and sediment rates by more than three and twelve times, respectively. This result occurred because stemflow contributes to the formation of concentrated flows, which easily trigger rill erosion around the stem base. The sediment rate further increased with rill development. Soil erosion was small if stemflow did not occur during a rainfall event; otherwise, soil erosion was extensive due to stemflow-induced rill erosion. Our results provide new insights for the analysis of crop cover effects and soil erosion on cultivated lands. For maize-planted slopes, stemflow may also be indispensable when determining the soil erosion amount.

Direct and indirect effects of environmental factors on daily CO2 exchange in a rainfed maize cropland—A SEM analysis with 10 year observations

The carbon budget of agricultural ecosystems is of great importance to the global carbon balance. In this study, the structural equation modeling (SEM) method was employed to quantify the direct and indirect effects of environmental factors on daily net ecosystem CO2 exchange (NEE) in a rainfed maize cropland, northeast China. The results showed that net radiation (Rn) was the most important factor controlling daily NEE, followed by the leaf area index (LAI), air temperature (Ta), vapor pressure deficit (VPD), and clearness index (Kt). The strong effect of Rn was mainly attributed to its direct effect, while Ta and VPD showed comparable or even higher indirect effects than direct effects, indicating that Ta and VPD influenced NEE mainly through regulating canopy development on a daily scale. Moreover, the responses of NEE to individual environmental factors differed greatly among multiyear climatic conditions. Ta and VPD were shown to be more important in warm (WM) years and warm and dry (WD) years than in normal (NM) years and cold and wet (CW) years. LAI was the primary controlling factor of daily NEE in WD years, resulting in large indirect effects of Ta and VPD on NEE. Kt had a large effect on daily NEE only in CW years. SWC had significant effects on daily NEE in WM and WD years but in the opposite direction, i.e., daily NEE increased with SWC in WD years but decreased with SWC in CW years. The partitioning of direct and indirect effects of environmental factors with SEM can greatly enhance the understanding of the controlling mechanism of NEE and remind researchers to consider the distinct effects of environmental factors on NEE among multiyear climatic conditions in future models.

Effects of conservation tillage measures on soil water and NO3--N leaching in dryland maize cropland

Based on a field experiment on conservation tillage over 15 years in Weibei Highland maize cropland, six conservation tillage patterns, i.e., conventional tillage (CT), no-tillage (NT), no-tillage plus biochar (NB), no-tillage and straw mulching (NS), no-tillage and plastic film mulching (NF), and no-tillage and straw-plastic film mulching (NSF), were investigated for their effects on soil water and nitrate nitrogen(NO3--N) leaching, to seek sustainable agricultural cultivation measures suitable for the region. Results showed that, compared with NT treatment in the first water recharge period, CT had no effect on water recharge in 0-100 cm soil layer, and NS, NB, NSF and NF significantly reduced soil water recharge. In 100-300 cm soil layer, NS, NB, NF and NSF significantly increased soil water recharge, but CT significantly reduced soil water recharge. During the second water recharge period, water recharge depth was mainly concentrated in 0-100 cm soil layer, and there was no significant difference between each treatment and NT. During the water depletion period, compared with NT treatment, other treatments had no significant effect on water depletion in 0-100 cm soil layer, but NF and NSF increased soil water depletion by 33.9% and 59.9% in 100-300 cm soil layer, respectively. In 0-200 cm soil layer, compared to NT, CT significantly increased the accumulation of NO3--N by 2.2 fold, NS, NB, NF and NSF reduced soil NO3--N accumulation by 44.6%, 61.5%, 69.2% and 69.8%, respectively. In 200-300 cm soil layer, NS significantly reduced the accumulation amount of NO3--N, but CT had no significant effect on the accumulation amount of NO3--N, and NS, NB, and NSF all had negative effects on NO3--N accumulation. Soil water movement had significant effect on the distribution of NO3--N in soil profile. Soil NO3--N was mainly distributed in 0-40 cm soil layer for NB, NF and NSF treatments, in 0-100 cm and 200-300 cm soil layers for NS treatment, and over the entire profile for NT and CT, and NS, NT and CT treatments had two NO3--N accumulation peaks in soil profile. Different agricultural cultivation measures could reduce soil NO3--N leaching by regulating soil water content, and subsequently improve nitrogen utilization efficiency. Among those measures, NSF could effectively control soil water movement to reduce the NO3--N leaching and accumulation, and thus is a feasible measure to improve soil water and fertility conditions and increase dryland maize yields.

Influencing factors and their simulation of summer maize land surface-air temperature difference under drought conditions

Crop water deficit status characterized by land surface-air temperature difference (Ts-Ta) has been widely investigated. However, empirical evidence for characteristics and impact factors of Ts-Ta considering the process of crop growth are less yet, which restricts the accurate simulation of Ts-Ta. Here, the data of Ts-Ta during the process of maize growth were obtained from five irrigation water control experiments after the period of summer maize 3-leaf stage in 2014 and jointing stage in 2015. The results showed that Ts-Ta of summer maize cropland was significantly affected by soil water content. Ts-Ta increased with the deficit of soil water. During summer maize water treatments, the normalized difference vegetation index (NDVI) was the main impact factor of Ts-Ta, with a significant linear relationship. However, during different growth stages, some additional factors including meteorological, biological and soil factors could also affect Ts-Ta, including canopy photosynthetic active radiation absorption ratio (fAPAR) after 3-leaf stage, relative soil water content (RSWC), and air relative humidity (RH) from 3-leaf stage to jointing stage. Then, the growth duration simulation model of Ts-Ta, vegetative growth simulation model of Ts-Ta and reproductive growth simulation model of Ts-Ta were established in terms of the data in 2014. Those simulation models were validated based on the experimental data of five irrigation water treatments after summer maize jointing stage in 2015. The results showed that the growth duration simulation mode of Ts-Ta could explain 63% variation of Ts-Ta in 2015. However, 79% variation of Ts-Ta could be explained by the simulation results of the vegetative growth simulation model of Ts-Ta and the reproductive growth simulation model of Ts-Ta. The results provided the basis for the quantitative evaluation of crop drought based on Ts-Ta.

The use of pedo-transfer functions for estimating soil organic carbon contents in maize cropland ecosystem in the Coastal Plains of Tanzania

Soil organic carbon (OC) plays a vital role on physico-chemical and biological properties of soils and on climate change regulation. The use of pedo-transfer functions from easily available soil properties for estimating soil OC could be fast and cheap when considering field and laboratory work implications especially in Sub Saharan Africa including Tanzania. This paper attempts to develop a model for estimating soil OC contents under maize croplands ecosystem using pedo-transfer functions from soil texture. A total of 100 epipedon data entries were randomly collected from the previous soil sampling works that were conducted under maize croplands in coastal plains of Tanzania. Eighty percent of the collected data were used for training the model by using multiple regression analysis while the remained 20% were used to validate the model. The results indicated that, clay and silt had significant (p < 0.001) positive correlation with soil OC while sand contents in soils had negative (p < 0.001) correlation with soil OC. All together clay, sand and silt were revealed powerful predictors (p < 0.001, R2 = 0.82) of OC content in soils. On validation, the soil OC predicted agreed by 81.2% with the soil OC determined by laboratory test. These results imply that pedo-transfer functions for predicting soil OC based on soil texture is not only fast and cheap but also is an effective option for estimating OC content in soils.

The uncertainty analysis of the MODIS GPP product in global maize croplands

Gross primary productivity (GPP) is very important in the global carbon cycle. Currently, the newly released estimates of 8-day GPP at 500 m spatial resolution (Collection 6) are provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) Land Science Team for the global land surface via the improved light use efficiency (LUE) model. However, few studies have evaluated its performance. In this study, the MODIS GPP products (GPPMOD) were compared with the observed GPP (GPPEC) values from site-level eddy covariance measurements over seven maize flux sites in different areas around the world. The results indicate that the annual GPPMOD was underestimated by 6%‒58% across sites. Nevertheless, after incorporating the parameters of the calibrated LUE, the measurements of meteorological variables and the reconstructed Fractional Photosynthetic Active Radiation (FPAR) into the GPPMOD algorithm in steps, the accuracies of GPPMOD estimates were improved greatly, albeit to varying degrees. The differences between the GPPMOD and the GPPEC were primarily due to the magnitude of LUE and FPAR. The underestimate of maize cropland LUE was a widespread problem which exerted the largest impact on the GPPMOD algorithm. In American and European sites, the performance of the FPAR exhibited distinct differences in capturing vegetation GPP during the growing season due to the canopy heterogeneity. In addition, at the DE-Kli site, the GPPMOD abruptly produced extreme low values during the growing season because of the contaminated FPAR from a continuous rainy season. After correcting the noise of the FPAR, the accuracy of the GPPMOD was improved by approximately 14%. Therefore, it is crucial to further improve the accuracy of global GPPMOD, especially for the maize crop ecosystem, to maintain food security and better understand global carbon cycle.

Differences in ecosystem water-use efficiency among the typical croplands

Water use efficiency (WUE) is an important parameter to assess agricultural production and the reasonable utilization of water resources. Especially in the context of changing hydrological environment, more attention need to be paid on how to use limited water resource to improve crop yield for ensuring food security. Based on 33 site-years of flux measurements over 10 cropland sites using the eddy covariance (EC) technique, the study systematically evaluated the large differences in seasonal and interannual variations of gross primary productivity (GPP), evapotranspiration (ET) and ecosystem WUE across the four crops worldwide including soybean, maize, winter wheat and paddy rice. The lengths of the growing seasons across the main crops extracted from time-series MODIS NDVI data, implied that the longest growth period in winter wheat and the shortest growing season in paddy rice field. Further analyses suggest that maize cropland has the strongest ecosystem WUE with 2.48 ± 0.69 g C kg−1 H2O, followed by winter wheat (2.00 ± 0.39 g C kg−1 H2O), soybean (1.92 ± 0.52 g C kg−1 H2O), and paddy rice (1.88 ± 0.63 g C kg−1 H2O). Meanwhile, the variability in ecosystem WUE exhibited apparent seasonality, and peaked together with GPP in the most active summertime. A series of biotic and abiotic factors affected the GPP as well as WUE variability. Given the complicated interactions among these environmental factors, this study revealed the great potential to remotely retrieve the WUE variability using time-series MODIS NDVI data over large areas. Ecosystem WUE of the C4 crop –maize was obviously higher than the other three C3 crops. Engineering C4 feature into C3 crops may be a feasible way to increase photosynthesis and yield.