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The infiltration of water into soil is an important component of the hydrologic cycle. Quantifying infiltration is useful for estimating overland flow, irrigation management, water distribution after rainfall, and soil erosion. A new approximate point source method for estimating the complete infiltration process is introduced in this paper. The experimental apparatus was designed to include a Mariotte bottle and a source outlet unit for water supply, as well as a scaled soil box. A mathematical model was derived to estimate the soil infiltration rate from the wetted soil surface. Soil infiltrations for three soil types, each with two or three different inflow rates, were investigated in laboratory experiments. To verify this new method, the results were compared with values measured using the linear source method. The balance between the supplied and recovered water showed that the relative errors of the experiments were all less than 2.5%, indicating the high accuracy of this method. The proposed point source method requires very little water and time, and is a useful tool for related lab studies and trickle irrigation designs.

Knowledge of root systems and soil water status across the root-zone is crucial in developing effective cropping technologies. Mulching improves soil water status and root water transport for increasing grain yield. Therefore, a field experiment with five treatments: (1) plastic film mulching ridge and non-mulching furrow (RF), (2) full plastic mulching with conventional flat cultivation (FPM), (3) straw mulching with conventional flat cultivation (SM), (4) partial plastic mulching with conventional flat cultivation (PPM) and (5) non-mulch with conventional flat cultivation (CK) was conducted during 2018 and 2019 in the eastern Loess Plateau of China. The total root biomass and the grain yield of all treatments were lower in 2019 than that of 2018 because of lower rainfall. However, all the mulching treatments improved root growth in both growing seasons mainly on the top 30 cm soil depth, which led to a distinct effect on grain yield as compared with CK. FPM produced the highest total root parameters in 2018 and at 45 DAS in 2019 due to the highest soil moisture content mainly in 0−30 cm soil depth. However, root biomass of FPM in 30−100 cm soil depth was lower than that of PPM, RF and SM because assimilate at reproductive stage was mostly for plant and seed growth than root growth, thus, there was negative correlation between grain yield and root biomass below 30 cm soil depth especially at grain filling stage. Over two growing seasons, soil moisture content (SMC) under FPM was 8.4 %, 0.6 %, 8.8 % and 11.1 % more than that of RF, SM, PPM and CK. FPM reduced soil evaporation, improved SMC, root distribution and transpiration rate, consequently, increased grain yield and net profit. Therefore FPM is an effective cropping system for improving the synchronization of soil water transport and root water uptake for maize production in rain-fed farming.

A good understanding of the response of photosynthesis rate (PN) and transpiration rate (Tr) to stomatal alteration during the diurnal variations is important to cumulative photosynthetic production and water loss of crops. Six wheat genotypes were studied for 2 years with pot cultivation in rain-shelter. Among different genotypes, stomatal conductance (gs) was significantly correlated with both PN and Tr. But for each genotype, though gs was significantly correlated with PN regardless of relative air humidity (RH) status and it was also significantly correlated with Tr under lower RH (LRH, 15.4%) and moderate RH (MRH, 28.3%), it was not correlated with Tr under higher RH (HRH, 36.7%) during the diurnal changes. The conditional correlation between gs and Tr of wheat evoked new thinking on the relationships among gs, PN and Tr. Path analysis was further carried out to clarify the correlations of gs with the four atmospheric factors, that of Tr with gs and the four factors and the direct and indirect effects of the factors, during their diurnal dynamic variation. The effects of these factors on gs or Tr were related to RH. All the four factors had a much higher correlation with gs under HRH than that under LRH and MRH. Air temperature (T) had a rather higher direct effect than RH and photosynthetically active radiation (PAR). Also, the other factors had a much higher indirect effect on gs through vapor pressure deficit (VPD) and T. Transpiration rate was highly correlated with gs under LRH and MRH, with gs having a higher direct effect on it. In comparison, Tr was not correlated with gs under HRH but highly correlated with the atmospheric factors, with T, RH, and PAR having a higher indirect effect through VPD.

Crop consumptive water use is recognized as a key element to understand regional water management performance. This study documents an attempt to apply a regional evapotranspiration model (SEBAL) and crop information for assessment of regional crop (summer maize and winter wheat) actual evapotranspiration (ETa) in Huang-Huai-Hai (3H) Plain, China. The average seasonal ETa of summer maize and winter wheat were 354.8 and 521.5 mm respectively in 3H Plain. A high-ETa belt of summer maize occurs in piedmont plain, while a low ETa area was found in the hill-irrigable land and dry land area. For winter wheat, a high-ETa area was located in the middle part of 3H Plain, including low plain-hydropenia irrigable land and dry land, hill-irrigable land and dry land, and basin-irrigable land and dry land. Spatial analysis demonstrated a linear relationship between crop ETa, normalized difference vegetation index (NDVI), and the land surface temperature (LST). A stronger relationship between ETa and NDVI was found in the metaphase and last phase than other crop growing phase, as indicated by higher correlation coefficient values. Additionally, higher correlation coefficients were detected between ETa and LST than that between ETa and NDVI, and this significant relationship ran through the entire crop growing season. ETa in the summer maize growing season showed a significant relationship with longitude, while ETa in the winter wheat growing season showed a significant relationship with latitude. The results of this study will serve as baseline information for water resources management of 3H Plain.

Temperature, especially accumulated temperature, is an important environmental factor that plays a fundamental role in agricultural productivity. To examine temporal and spatial variation in accumulated temperature requirements of maize as indicated by ≥10 °C accumulated temperature and growing degree days (GDD), we conducted experiments during 2007–2012 at 35 locations in seven provinces in the north spring maize region between 35°11′ N and 48°08′ N and 6 locations in four provinces in the Huanghuaihai maize region between 32°52′ N and 41°05′ N in China. The most widely cultivated maize hybrids of ZD958 and XY335 were used in this study. We found that the coefficients of variation for ≥10 °C accumulated temperature and GDD requirements were different during different growth periods, with a descending rank order of sowing to emergence > silking to maturity > emergence to silking > sowing to maturity and greater in the north spring maize region than in the Huanghuaihai maize region. The coefficients of variation were lower for ≥10 °C accumulated temperature than GDD requirements for both cultivars in both planting regions. Significant differences existed between locations and years for the ≥10 °C accumulated temperature and GDD requirements. These have implications for appropriate maize cultivars recommendation, and high and stable yield achieving by reasonably using accumulated temperature across different regions of China.

Climate change will have important implications in water shore regions, such as Huang-Huai-Hai (3H) plain, where expected warmer and drier conditions might augment crop water demand. Sensitivity analysis is important in understanding the relative importance of climatic variables to the variation in reference evapotranspiration ( ET 0 ). In this study, the 51-yr ET 0 during winter wheat and summer maize growing season were calculated from a data set of daily climate variables in 40 meteorological stations. Sensitivity maps for key climate variables were estimated according to Kriging method and the spatial pattern of sensitivity coefficients for these key variables was plotted. In addition, the slopes of the linear regression lines for sensitivity coefficients were obtained. Results showed that ET 0 during winter wheat growing season accounted for the largest proportion of annual ET 0 , due to its long phenological days, while ET 0 was detected to decrease significantly with the magnitude of 0.5 mm yr −1 in summer maize growing season. Solar radiation is considered to be the most sensitive and primarily controlling variable for negative trend in ET 0 for summer maize season, and higher sensitive coefficient value of ET 0 to solar radiation and temperature were detected in east part and southwest part of 3H plain respectively. Relative humidity was demonstrated as the most sensitive factor for ET 0 in winter wheat growing season and declining relativity humidity also primarily controlled a negative trend in ET 0 , furthermore the sensitivity coefficient to relative humidity increased from west to southeast. The eight sensitivity centrals were all found located in Shandong Province. These ET 0 along with its sensitivity maps under winter wheat-summer maize rotation system can be applied to predict the agricultural water demand and will assist water resources planning and management for this region.

Vegetables are mainly cultivated through facility in early spring and late autumn in Northern of China. In the case of a serious shortage of water resources, water use efficiency of greenhouse vegetable is of an important scientific significance in both water and fertilizer management. On the basis of pan Evaporation (Ep) and real-time monitoring of soil moisture content, the amount of water irrigation adequate to big-arch shelter cucumber growth, water dissipation, yield and water use efficiency were determined through the combination of three nitrogen fertilizers including urea, urea containing nitrification inhibitors (5:1 with urea and nitrification inhibitor) and coated urea (slow fertilizer) and their various levels with 0 kg/ha, 350 kg/ha, 550 kg/ha, 750 kg/ha. The results showed that the most 10,9000 kg/ha production was gained by the treatment of 550 kg/ha urea containing inhibitors, which could increase 41.5% of a yield, 15.2% of a cumulative water consumption that was at 462.0mm and 44.7% of a water use efficiency that is at 14.11kg (dry matter)/(mmha), compared with that of control, respectively. In conclusion, the present study demonstrates that the application of moderate levels of urea containing nitrification inhibitor in greenhouse cucumber can gain higher yields and water use efficiency.

Nitrate-nitrogen content of groundwater are ever-increasing in underneath vegetable growing areas, in this paper, based on field test of cucumber cultivated in Solar Greenhouse in North China, we study the effects of different nitrogen fertilizer application levels (250, 300, 350kg/hm2) and different nitrogen fertilizer types (urea, urea + nitrification inhibitor, slow-release fertilizer) on temporal and spatial variation of soil nitrate-nitrogen content in different soil depth, soil nitrogen fertilizer retention and nitrogen use efficiency during cucumber growth period. The results show that, in the cases of nitrogen fertilizer types (urea and urea + nitrification inhibitor), for surface soil (0 - 40 cm soil depth), the temporal trend of soil nitrate-nitrogen content variation is similar: during the early stage of cucumber growth, soil nitrate-nitrogen content is relatively high; during the middle stage of cucumber growth, as nitrogen is constantly being absorbed by the vegetable, soil nitrate-nitrogen content decrease; during the late stage of cucumber growth, soil nitrate-nitrogen content increase, and increase more significantly when nitrification inhibitor is added in the fertilizer. For deep soil layer (40 - 100 cm depth), when only using urea, the temporal trend of soil nitrate-nitrogen content variation is that of continuous increase, when adding nitrification inhibitor, the temporal trend of soil nitrate-nitrogen content variation is that of insignificant increase. In the case of slow-release fertilizer, for both surface soil and deep soil layer, the temporal trend of soil nitrate-nitrogen content variation is that of continuous decrease. For all three types of nitrogen fertilizer, as fertilization level increase, soil nitrate-nitrogen content in various soil layers increase with it. In the case of fertilization at 300 kg/hm2 and 350 kg/hm2, adding nitrification inhibitor can increase soil retention of nitrogen fertilizer. This study suggests that adding nitrification inhibitors can increase soil retention of nitrogen fertilizer, decrease nitrate-nitrogen leaching downward, thereby reducing the pollution to groundwater.

It is to review the sources and contributions of anthropogenic nitrogen into water bodies, to summary the relationships between nitrogen concentrations in water bodies and human factors, and to highlight the general trends of the nitrogen levels in different times.

The CO(2) flux was measured by the eddy covariance method on a temperate Leymus chinensis steppe over a period of 17 months spanning two consecutive growing seasons. The amount of precipitation was nearly normal, but it was low in the early and high in the late growing period in 2006. In the 2007 growing season, the amount of precipitation was about 45% less than the multi-year average and more evenly distributed. Comparisons were made between a moderately grazed site and a 28-year-old fenced site. The maximum instantaneous CO(2) release and uptake rates were 0.12 (May) and -0.11mg CO(2)m(-2)s(-1) (July) at the fenced site, and 0.11 and -0.16mg CO(2)m(-2)s(-1) (both in July) at the grazed site. In both growing seasons, the grazed site always had a higher daily uptake rate or lower release rate than the fenced site. The grazed site was a CO(2) sink during the growing season of 2007 and a CO(2) source in the growing season of 2006, whereas the fenced site was a CO(2) source in both seasons. Lower precipitation decreased CO(2) loss during the growing season more in the grazed site than in the fenced site, mainly because of depression of total ecosystem respiration (R(e)) in the former and stimulation in the latter. During the dormant season (from October to April), the fenced and grazed sites released 60.0 and 32.4g of C per m(2), respectively. Path analysis showed that temperature had the greatest effect on daily variation of ecosystem CO(2) exchange during the growing seasons at the two study sites. The results suggest that decrease of precipitation and/or increase of temperature will likely promote C loss from L. chinensis steppes, whether fenced or grazed, and that a grazed site is more sensitive.

The Angstrom–Prescott (A–P) model is one of the most accurate and widely used empirical methods to estimate global solar irradiance (Rs). In order to use this highly rated model, the first step is to choose its coefficients from literature or to calibrate them in a new locality. This seemingly simple matter can be confusing and difficult due to their large variability and many different calibration approaches. This paper addressed the role of time-dependent nature of these coefficients by comparing the Rs predictions of the simultaneously calibrated monthly, seasonal, bi-annual and annual (fixed) coefficients using data from 20 sites of temperate climate in China. When evaluated by performance indicators of RMSE, RRMSE, MBE, R2 and values of t-statistic, it is demonstrated that time-dependent A–P coefficients are not better than fixed ones in Rs prediction. This indicates that consideration of the time-dependent characteristics of these coefficients has little predictive value and thus unnecessary. The phenomenon can be interpreted by the concept of equifinality and the linearity inherent in the relationship of n/N vs. Rs/Ra. The implication of this study is that it gives more confidence in predictive accuracy of fixed coefficients and contributes to reducing unnecessary complexity of this model and thus easing their choice, calibration and application.

A field experiment was conducted to investigate the effect of long-term (30-year) fertilizer and organic manure treatments on grain yield, soil chemical properties and some microbiological properties of arable soils in Pingliang, Gansu, China. Six treatments were chosen for this work: unfertilized control (CK), nitrogen fertilizer annually (N), nitrogen and phosphorus (P) fertilizers annually (NP), straw plus N added annually and P fertilizer added every second year (NP + S), farmyard manure added annually (FYM), and farmyard manure plus N and P fertilizers added annually (NP + FYM). Mean winter wheat yields for the 20 years ranged from 1.60 Mg ha − 1 for the CK treatment to 4.62 Mg ha − 1 for the NP+FYM treatment. Maize yields for the 8 years averaged 3.40 and 7.66 Mg ha − 1 in the same treatments. The results showed that there was no interaction between farmyard manure and NP fertilizers. Compared with the CK treatment, the average soil organic carbon (SOC) and total nitrogen (TN) content were 2.0 and 3.1%, 1.9 and 13.3%, 32.7 and 24.5%, 23.0 and 19.4%, and 39.9 and 27.6% larger, respectively, for N, NP, FYM, NP + S and NP + FYM. The N only resulted in not only lowering of pH but also deficient of both P and K in the soil. Soil available K declined rapidly without straw or manure additions. The microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents increased with the application of nitrogen and phosphorus inorganic fertilizers. However, there was greater increase of these parameters when organic manure was applied along with inorganic fertilizers. Organic manure application also increased soil dehydrogenase, alkaline phosphatases, β-glucosidasen and urease activity significantly. The results indicated that long-term additions of organic manure have the most beneficial effects on grain yield and soil quality among the investigated types of fertilization.

Precipitation quantity and timing have been shown to fundamentally influence grassland ecosystem CO 2 exchange by both model simulation and field observation. Carbon dioxide exchange and patterns of variation (magnitude and timing) in precipitation were observed to determine their relationship in typical steppe in Inner Mongolia Plateau during four years (2003–2006) with different rainfall patterns. The response of ecosystem-level CO 2 fluxes to rainfall pulse events was also examined. The four years studied were classified into three levels of rainfall amount (100%, 2004; reduced by 70% in 2005 and by 45% in 2006 compared with 2004) and two temporal patterns of rain events (average temporal patterns in 2004 and altered precipitation timing in 2003, a year with precipitation fell during the first half of the growing season, compared with 2004). The grassland ecosystem switched from a carbon sink (2004) to carbon sources (2005 and 2006) under reduced rainfall amounts. Carbon sink reduced by 34% under variational rainfall timing conditions (2003). There was a significant positive correlation between annual rainfall and above-ground NPP across the study ( P = 0.05, r 2 = 0.9). Antecedent soil water before rainfall pulse and rainfall pulse size are important in controlling the response of CO 2 exchange to rainfall in this steppe. After rainfall pulse events, CO 2 fluxes had 4 to 5 days of system-level hysteresis and the increase degree of CO 2 exchange was different among the four years. Precipitation pulse size not only affected the duration of CO 2 fluxes, but also instant flux rate. Our results suggest that CO 2 exchange in temperate steppe will be more sensitive to altered rainfall timing and more affected by changes in rainfall quantity, with a longer dry season resulting in significant C losing from Eurasia grassland in Inner Mongolia Plateau.

In water-limited grassland ecosystems, discrete and occasional precipitation events trigger brief but important episodes of biological activity. Differential responses of above- and below-ground biota to precipitation pulses may constrain biogeochemical transformations at the ecosystem scale. We examined the short-term dynamics of the whole ecosystem response to small precipitation events during 2003 and 2004 in a steppe on the Inner Mongolia Plateau. The results indicate that changes in soil moisture occur, with a 1–2 day time lag, only when the amount of precipitation exceeds 3 mm (from day of year [DOY] 120 to DOY 180) or 5 mm (after DOY 180). The interception of the developing plant canopy is a primary reason for the different temporal precipitation threshold. The lower threshold of effective rain is different between Net Ecosystem Exchange (NEE, 3 mm), Ecosystem Respiration (R e, 3 mm) and Gross Ecosystem Production (GEP, 5 mm). The NEE reached a maximum 4–5 days after the end of effective rain events and dropped to 60–70% of the original fluxes after 10 days. However, the drop in GEP was greater than that of NEE and reached 30–50% of the original fluxes after 10–15 days without “effective rainfall.” The characteristics of the response time can be attributed to the variation in soil water content and the time of readjusting for the ecological processes after the effective rainfall. In addition, the independent responses of photosynthesis, respiration and evapotranspiration to precipitation probably contributed to this time lag. The results support the hypothesis that the concept of an ecologically significant rainfall event can be developed for an ecosystem.

Estimation of global solar radiation (Rs) from the daily range of air temperature (ΔT) offers an important alternative in the absence of measured Rs or sunshine duration because of the wide availability of air temperature data. In this paper, we assessed 16 Rs models including modified versions of the Bristow and Campbell (B–C) and the Hargreaves (Harg) models across a wide range of agro-ecological conditions in China. Using long-term data from 15 sites in Northeast, North China Plain and Northwest China, we explored the main factors affecting model parameters and the predictive accuracy and proposed empirical equations to estimate these parameters. Two schemes in calculating ΔT were employed: ΔT1 (based on single day Tmin) used in the Harg and ΔT2 (based on 2-day average of Tmin) used in the B–C model. Results showed that the original B–C model performed similarly to the best performing modified Harg model, but significantly outperformed the original Harg model with a 4–7% higher accuracy. The common practice of fixing some parameters in the B–C model caused the most significant effect and resulted in a 3–9% lower accuracy than that of the original model. In contrast, modifications had the smallest effect and yielded little improvement and are thus unnecessary. The ΔT scheme had a moderate effect, with ΔT1 generally resulting in a higher accuracy especially in high altitude areas. This indicates that the effect of cold or warm air advection is negligible in the B–C model even in a temperate climate. The accuracy of the temperature-based models was affected mainly by the magnitude of ΔT, with larger ΔT resulting in higher accuracy. Parameters of the B–C model correlated significantly with many commonly used geographical and meteorological factors, meaning that they are more easily obtainable without the need for calibration and consequently Rs measurement. The parameter of the original Harg model correlated insignificantly with all the examined factors, meaning that it has to be calibrated. Main findings in this study are valuable in clarifying the relative impact of different approaches in applications on model accuracy, in demonstrating the advection effect, in identifying the dominant factors of model parameters and thus in increasing their availability.

Accurate estimation of the reference crop evapotranspiration ( ET 0 ) is investigated due to its critical role in affecting calculation of crop water use and efficiency in agricultural ecosystems. The main emphasis in this paper is to clarify the possible uncertainty in the estimation of ET 0 associated with using un-calibrated Angstrom–Prescott ( A – P ) coefficients. We first calibrated the coefficients using long-term data records from 34 sites in the Yellow River basin in China, and then applied these coefficients to estimate short wave irradiance ( R s ) and ET 0 at 16 sites to evaluate the difference in ET 0 between the FAO recommended and the locally calibrated. We found that the direct use of the FAO recommended coefficients significantly affected the estimation of ET 0 at most sites, which differed from −3% to 15% at daily scale and from −4% to 16% at monthly scale from the locally calibrated ones. These differences are comparable with or larger than those caused by some alternatives of the FAO recommended algorithms for net irradiance or vapor pressure, which further highlights the importance of using the locally calibrated coefficients. The degree of difference in ET 0 showed a significant threshold relation with altitude and longitude in such a way that relatively small impact lies around 2233 m and 98°E, and away from these, the effect begins to increase. Given the large overestimation in water use as a consequence of the significant overestimation in ET 0 associated with the direct use of the FAO coefficients, especially in those high yield production areas with altitude A – P coefficient a , b , ( a + b ) and other easily obtainable factors (altitude, longitude and air temperature). A three-step procedure was recommended in applying these relations, which was (1) determine if calibration is needed or not for a given location; (2) estimate one of the A – P coefficients, either a or b if calibration is needed; (3) estimate the remaining coefficient using relations of ( a + b ) due to its higher coefficient of determination. In summary, we have revealed the errors and areas that are most affected when using the un-calibrated coefficients, and discussed the consequence of such error on agricultural production, and proposed practical solutions to avoid large errors. These results are intended to make the research community aware of such errors so that more appropriate choice of these coefficients is made. We hope that similar assessment will be done in other climates, contributing to managing water resources efficiently in water basins.

The Angstrom–Prescott (A–P) equation relating in its current form the incident top-of-atmosphere solar radiation to the solar radiation received at the surface, is one of the most accurate and widely used sunshine-based methods estimating global solar radiation (Rs). The key in its application is the calibration of the locally specific coefficients. Although the coefficients have been extensively studied and calibrated in many places over the world, their relations with time scale are much less investigated. This paper addressed the variation in these coefficients caused by time scale and how this variation results on the accuracy of Rs predictions. This was done using long-term data at 31 sites from the Yellow River basin in China by parallel calibration at three time scales: daily, monthly mean daily and yearly mean daily. We found that the A–P coefficients obtained using monthly data generally had higher a and lower b and larger variations over those using daily data. At yearly time scale, the sunshine–radiation relationship can no longer be described by the linear A–P formula. The difference in coefficients between daily and monthly calibration was rather large accounting for 71% of the differences in a and 61% in b that in turn were greater than 0.03, corresponding to 81% for a and 49% for b being greater than 10%. Time scale had a larger effect on a than on b, and it caused a maximum variation of 82% in a and 43% in b in the basin, equaling half of the variation caused by geographical location. However, the large effect of time scales on a and b produced no significant impact on the estimation accuracy of Rs because of the conservative response of the sum a + b to time scale. In this sense, the coefficients calibrated at daily scale are interchangeable with those calibrated at monthly scale, indicating the high flexibility of the A–P formula. Nevertheless, calibration made at daily scale has two important advantages over monthly scale in that it requires fewer years’ data to obtain stabilized coefficients, and that it is easily predicted more accurately with common site information. Our findings have two implications. Firstly, they provide an additional guidance on the explanation of the large variability of the coefficients found in the literature for the same geographical location. Secondly, they facilitate the choice of the coefficients in practical applications by proving their interchangeability in the estimation of Rs.

We used an eddy covariance technique to measure evapotranspiration and carbon flux over two very different growing seasons for a typical steppe on the Inner Mongolia Plateau, China. The rainfall during the 2004 growing season (344.7 mm) was close to the annual average (350.43 mm). In contrast, precipitation during the 2005 growing season was significantly lower than average (only 126 mm). The wet 2004 growing season had a higher peak evapotranspiration (4 mm day(-1)) than did the dry 2005 growing season (3.3 mm day(-1)). In 2004, latent heat flux was mainly a consumption resource for net radiation, accounting for similar to 46% of net radiation. However, sensible heat flux dominated the energy budget over the whole growing season in 2005, accounting for 60% of net radiation. The evaporative rate (LE/R-n) dropped by a factor of four from the non-soil stress to soil water limiting conditions. Maximum half-hourly CO2 uptake was -0.68 mg m(-2) s(-1) and maximum ecosystem exchange was 4.3 g CO2 m(-2) day(-1) in 2004. The 2005 drought growing stage had a maximum CO2 exchange value of only -0.22 mg m(-2) s(-1) and a continuous positive integrated-daily CO2 flux over the entire growing season, i.e. the ecosystem became a net carbon source. Soil respiration was temperature dependent when the soil was under non-limiting soil moisture conditions, but this response declined with soil water stress. Water availability and a high vapor pressure deficit severely limited carbon fixing of this ecosystem; thus, during the growing season, the capacity to fix CO2 was closely related to both timing and frequency of rainfall events. (c) 2007 Published by Elsevier Masson SAS.

Effects of agricultural practices on ecosystem carbon storage have acquired widespread concern due to its alleviation of rising atmospheric CO2 concentrations. Recently, combining of furrow-ridge with plastic film mulching in spring maize ecosystem was widely applied to boost crop water productivity in the semiarid regions of China. However, there is still limited information about the potentials for increased ecosystem carbon storage of this tillage method. The objective of this study was to quantify and contrast net carbon dioxide exchange, biomass accumulation and carbon budgets of maize (Zea maize L.) fields under the traditional non-mulching with flat tillage (CK) and partial plastic film mulching with furrow-ridge tillage (MFR) on the China Loess Plateau. Half-hourly net ecosystem CO2 exchange (NEE) of both treatments were synchronously measured with two eddy covariance systems during the growing seasons of 2011 through 2013. At same time green leaf area index (GLAI) and biomass were also measured biweekly. Compared with CK, the warmer and wetter (+1.3°C and +4.3%) top soil at MFR accelerated the rates of biomass accumulation, promoted greater green leaf area and thus shortened the growing seasons by an average value of 10.4 days for three years. MFR stimulated assimilation more than respiration during whole growing season, resulting in a higher carbon sequestration in terms of NEE of -79 gC/m2 than CK. However, after considering carbon in harvested grain (or aboveground biomass), there is a slight higher carbon sink (or a stronger carbon source) in MFR due to its greater difference of aboveground biomass than that of grain between both treatments. These results demonstrate that partial plastic film mulched furrow-ridge tillage with aboveground biomass exclusive of grain returned to the soil is an effective way to enhance simultaneously carbon sequestration and grain yield of maize in the semiarid regions.

An understanding of the dynamics of soil organic carbon (SOC) as affected by farming practices is imperative for maintaining soil productivity and mitigating global warming. The objectives of this study were to investigate the effects of long-term fertilization on SOC and SOC fractions for the whole soil profile (0-100 cm) in northwest China. The study was initiated in 1979 in Gansu, China and included six treatments: unfertilized control (CK), nitrogen fertilizer (N), nitrogen and phosphorus (P) fertilizers (NP), straw plus N and P fertilizers (NP+S), farmyard manure (FYM), and farmyard manure plus N and P fertilizers (NP+FYM). Results showed that SOC concentration in the 0-20 cm soil layer increased with time except in the CK and N treatments. Long-term fertilization significantly influenced SOC concentrations and storage to 60 cm depth. Below 60 cm, SOC concentrations and storages were statistically not significant between all treatments. The concentration of SOC at different depths in 0-60 cm soil profile was higher under NP+FYM follow by under NP+S, compared to under CK. The SOC storage in 0-60 cm in NP+FYM, NP+S, FYM and NP treatments were increased by 41.3%, 32.9%, 28.1% and 17.9%, respectively, as compared to the CK treatment. Organic manure plus inorganic fertilizer application also increased labile soil organic carbon pools in 0-60 cm depth. The average concentration of particulate organic carbon (POC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC) in organic manure plus inorganic fertilizer treatments (NP+S and NP+FYM) in 0-60 cm depth were increased by 64.9-91.9%, 42.5-56.9%, and 74.7-99.4%, respectively, over the CK treatment. The POC, MBC and DOC concentrations increased linearly with increasing SOC content. These results indicate that long-term additions of organic manure have the most beneficial effects in building carbon pools among the investigated types of fertilization.

By using eddy covariance and remote sensing techniques, the relationships between winter wheat soil moisture content and farmland evapotranspiration or canopy temperature were analyzed at field scale under various environmental conditions in the North China Plain. The results showed that when the soil moisture content was below 65% of field capacity, the evaporative fraction under full canopy was low and stable during the middle part of clear days. Under clear sky condition, there was a good non-linear correlation between latent heat flux and crop canopy temperature with diurnal and seasonal patterns. The temperature difference between crop canopy and air as well as the relative evapotranspiration had a close link to the relative moisture content of 0 - 100 cm soil layer. Based on the in situ measurements of daily evapotranspiration amount (ET(d)), daily net radiation flux (Rn(d), mm), average canopy temperature (T(e), degrees C) from 13 : 30 to 14: 00, and daily maximum air temperature (T(a max), degrees C) during the field experiment, the parameters of simplified estimation model for daily evapotranspiration were established.