Soil organic matter (SOM) concentration and enzyme activity are important biochemical indicators of soil health for assessing the sustainability of agricultural management practices. However, little is known about the long-term effects of tillage and crop residue management on SOM and enzyme activities in soil particle-size fractions on the Loess Plateau of Northern China. The objective of this study was to investigate the effects of 11 years of combined tillage and crop residue management treatments on soil organic carbon (SOC), total nitrogen (TN) concentrations and enzyme activities in bulk soil and particle-size fractions from a rainfed wheat (Triticum aestivum. L.) monoculture system in this region. We hypothesized that reduced tillage and increased residue retention would increase SOC, TN and enzyme activities in both bulk soil and particle-size fractions, and that enzyme activity would serve as a more sensitive indicator of soil health in response to management. Compared with conventional tillage and residue removal (CTRR), reduced tillage and stubble mulch residue retention (RTSM) increased bulk soil activities of most enzymes (sulfatase +68%, invertase +62%, beta-glucosidase +58%, dehydrogenase +46%). These increases were greater than the relative increases in total SOC (34%) and TN (33%) concentrations, supporting our hypothesis of a stronger response in microbial activity to management than total element stocks. The RTSM treatment also increased SOC and TN concentrations, as well as beta-glucosidase, acid phosphatase and urease activities in all particle-size fractions (2000-250, 250-53, 53-2 and < 2 mu m) compared with the CTRR treatment. Both beta-glucosidase and acid phosphatase showed a general decrease from coarse-to fine-sized fractions, and resembled the distribution of SOC and TN concentrations in particle-size fractions. Conversely, urease activity was greater in sand and clay fractions, which was decoupled from SOC and TN distributions. Our results indicate that biological indicators of soil health were more sensitive than C and N stocks to cumulative long-term changes in tillage and residue management.

The semi-arid grasslands in northern China are subjected to accelerating land use change due to population growth and food demand. Considerable uncertainty exists on annual methane (CH4) fluxes of different land uses because most measurements have only been conducted during the growing season. Using static chamber - gas chromatographic technique, we quantified and characterized annual CH4 fluxes (from 2012 to 2015) from four land uses common in an agro-pastoral ecotone of northern China: summer-grazed grassland (SumGrazed), winter-grazed grassland (WinGrazed), ungrazed grassland since 1997 (Ungrazed) and oat cropland (OatCrop). The soil at all land uses functioned exclusively as a sink for atmospheric CH4 through the entire three years. Annual CH4 uptake rates averaged 1.42, 2.36,1.12 and 2.57 kg C ha(-1) yr(-1) for SumGrazed, WinGrazed, Ungrazed and OatCrop, respectively, during 2012-2015. Compared to Ungrazed, OatCrop and WinGrazed increased annual CH4 uptake by 129 and 111%, respectively. Non-growing season (October-April) contributed 28-43% of the annual CH4 uptake at all land uses. Across all four land uses, annual cumulative CH4 uptake decreased with increasing soil water-filled pore space (WFPS) explaining 81% of the variance in annual CH4 uptake. WFPS negatively correlated to CH4 uptake in the growing season (R-2 =0.16-0.35, P < 0.001). CH4 uptake increased with soil temperature through the entire observed period (R-2 = 0.38-0.63, P < 0.001) and the non-growing season (R-2 = 0.51-0.74, P < 0.001). We conclude that grazing has the potential to increase CH4 uptake from the atmosphere and consequently, contribute positively to CH4 related part of C budget. (C) 2017 Elsevier B.V. All rights reserved.

Soil gas diffusion coefficient is an important parameter for describing soil gas diffusion process. Its value varies with soil texture, water content, bulk density, and thus is difficult to predict. In this study, we designed a testing apparatus of soil gas diffusion coefficient based Currie’s one chamber method and investigated its relationship with air filled porosity. The apparatus was composed of 2 components: a polyvinyl chloride soil chamber on the top with cutting ring and O ring, and gas chamber below. The soil chamber was connected with air and gas chamber on both sides. The gas chamber was made of transparent resin as an observation window. A stainless steel plate was located between soil chamber and gas chamber for gas diffusion control. In addition, KE-25 O2 sensor from Figaro Inc., Japan was used to transmit voltage to computer screen. From prepared calibration curve of gas concentration and voltage, the gas concentration and the gas diffusion coefficient could be calculated. A preliminary experiment showed that the measurement error caused by gas leakage was 0.000006, smaller than measurement results, indicating that the gas leakage could be ignored and the measurements were relatively accurate. In the laboratory experiment, quartz sand of 3 particle sizes were prepared to investigate the changes of relative gas diffusion coefficient with different total porosity and undisturbed and disturbed sandy loams were used to study the changes of relative gas diffusion coefficient with air-filled porosities. Meanwhile, the relative gas diffusion coefficient estimation based on measurements was compared with 3 models (Buckingham method, Millington and Quirk method, structure-dependent water-induced linear reduction model SWLR model). The results showed that relative diffusion coefficient of quartz sand increased with increasing total porosity regardless of particle sizes and also increased with particle sizes regardless of total porosity. The relationship between relative diffusion coefficient and air-filled porosity followed power function. For the sandy loam, disturbed and undisturbed soils yielded similar results with values smaller than 0.006. Among the three models, the relative diffusion coefficients estimated only from the Buckingham method was closer to that from measurement-based results with bias of -0.219×10-3 and root mean square error of 0.799×10-3, indicating caution should be paid when estimators from empirical models were used and the value couldn’t replace the measurements. The study would provide valuble information for relative gas diffusion coefficient measurements and calculation.

Overgrazing and intensive farming have led to severe land degradation in the past half century in the agro-pastoral ecotone of northern China. Currently, complete and periodical exclusions of grazing are commonly adopted for the restoration of these degraded grasslands. However, little is known about the effects of such land uses on nitrous oxide (N2O) emission in this region. Using static chamber technique, we quantified annual N2O emissions (from May 2012 to September 2013) from four land uses: summergrazed grassland (SG), winter-grazed grassland (WG), ungrazed grassland since 1997 (UG) and oat cropland (0C). N2O emissions occurred mainly after farmyard manure fertilization and during spring thaw periods. Annual N2O fluxes from the SG, WG, UG and OC were 0.19, 0.15, 0.43 and 0.98 kg N ha-1 yr(-1), respectively. The spring-thaw N2O emissions from UG and OC dominated the annual emission and accounted for 70% and 65% of the annual fluxes, respectively. In contrast, the contributions of spring thaw fluxes to total annual N2O emissions for SG and WG were only 32%. N2O fluxes during spring thaw season were positively related to soil NH4+ + NO3- content accounting for 80% of N2O flux variability across all land uses. Land use conversion from the native grassland to cropland increased N2O flux both during growing and spring thaw seasons due to farmyard manure application. Instead, grazing has the potential to decrease annual N2O losses mainly through reducing spring-thaw N2O emissions. (C) 2015 Elsevier B.V. All rights reserved.

Water-saving ground cover rice production systems (GCRPS) can increase grain yield in mountainous regions with seasonal water shortages and cold, stress-inducing temperatures. For GCRPS the soil surface is covered with a plastic film which can effectively alleviate low-temperature stress in the early growth stage due to thermal insulation. Since topdressing is not possible in GCRPS, farmers usually apply all fertilizer as basal dressing before transplanting; this can lead to excessive growth during the vegetative period and low crop growth during the reproductive stage. However, we hypothesized that the technique might be well suited for marginal rice growing regions in the Northeast of China. These areas are characterized by a short vegetation period and soils rich in organic matter, delivering the required amounts of nitrogen (N) over the course of the season due to N mineralization. Here we report on a two year experiment, conducted in the Northeast of China, that compared grain yields between GCRPS and conventional paddy rice production (paddy) at three N fertilizer rates (0, 90 and 135 kg N ha(-1)). Furthermore, crop growth rate, apparent nitrogen recovery rate and nitrogen physiological use efficiency were calculated. Compared to paddy, GCRPS significantly increased grain yield by 31%, 14% and 10% at N fertilizer rate of 0,90 and 135 kg N ha(-1), respectively. Grain yield at 135 kg N ha(-1) was significantly higher than 90 kg N ha(-1) in paddy, but no difference was found between N fertilizer rates in GCRPS. However, grain yield at 90 kg N ha(-1) in GCRPS was still higher than that at 135 kg N ha(-1) in paddy. The considerably higher number of filled grains in GCRPS indicates that crop growth rate during the reproductive stage was improved, likely due to the positive effect of higher mineralization of organic N on crops with a low rate of N fertilization. Our study demonstrates that GCRPS is a very promising and highly suitable technique for rice production in cold regions in the North of China that possess high content of soil organic matter. Moreover, it shows that N fertilization can be minimized due to the autochthonous N supply from soil rich in organic matter. In regards to the decomposition of SUM in GCRPS over time, mutual feedback mechanisms located both above and below ground revealed that the potential loss of SUM stocks can be compensated by a greater input of root biomass in GCRPS. (C) 2014 Elsevier B.V. All rights reserved.

Soil organic matter (SOM) and enzymes are essential for nutrient cycling, and are considered as important indicators of soil quality. The effects of organic and mineral fertilization on soil organic carbon (SOC), total nitrogen (TN) and enzyme activities in bulk soil and particle-size fractions were investigated under a winter wheat/maize cropping system in the North China Plain. The experiment established in 1993 includes three treatments: (1) unfertilized control (CK); (2) mineral fertilizers (MF); and (3) farmyard manure (FYM). Application of FYM significantly increased SOC and TN contents and activities of six enzymes: invertase, β-glucosidase, urease, acid and alkaline phosphatases and dehydrogenase in bulk soil and in all particle-size fractions as compared to those in MF and CK. Highest contents of SOC and TN were found in coarse sand and lowest in the silt fraction. The C/N ratios decreased with decreasing particle-size fractions. β-Glucosidase and acid phosphatase activities predominated in coarse sand fraction, reflecting high substrate availability. The urease activity was highest in clay-size fractions, depending on mineral sorption processes. The SOM and enzyme activities in the coarse sand were the most sensitive to fertilization. The smallest response of SOM in the clay fraction to fertilization confirmed that SOM on clay is the most stable C pool. The 15-year fertilization experiment clearly showed that FYM represented the best management practice for improving soil quality and microbial activity.

Soil porosity is usually taken as a constant over time for a given field, although in reality it decreases with time after tillage. For the gradient method, estimating soil CO2 production with a fixed porosity may lead to large errors when soil porosity varies over time. In this study, we compared soil air-filled porosity, gas diffusivity, and CO2 production based on a temporally variable soil porosity (ϕV) with those based on a constant porosity, either initial porosity just after soil tillage (ϕi) or final porosity at harvest after a tilled soil has settled (ϕf). Soil porosity was measured seven times during a maize (Zea mays L.) growing season, and an exponential relationship of soil porosity with time was developed to describe ϕV for the 0- to 5-cm soil layer. Soil CO2 production was estimated from the gradient method and the mass conservation law. Soil-surface CO2 efflux was measured with a dynamic chamber throughout the growing season. The ϕi value was 0.49 m3 m−3 and the ϕf value was 0.43 m3 m−3. Compared with results obtained from ϕV, soil air-filled porosity, gas diffusivity, and CO2 production values obtained from ϕf were 6, 11, and 22% lower, whereas values obtained from ϕi were 17, 36, and 70% larger. The soil-surface CO2 effluxes estimated with ϕV better matched the chamber values than did the estimates with ϕi or ϕf. We conclude that use of variable soil porosity improves estimations of soil-surface CO2 effluxes and soil CO2 production with the gradient method.

Soil organic carbon (SOC) and its labile fractions are strong determinants of chemical, physical, and biological properties, and soil quality. Thus, a 15-year experiment was established to assess how diverse soil fertility management treatments for winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) cropping system affect SOC and total N (TN) concentrations in the North China Plain. The field experiment included three treatments: (1) unfertilized control (CK); (2) inorganic fertilizers (INF); and (3) farmyard manure (FYM). Concentrations of SOC, TN, and different labile SOC fractions were evaluated to 1-m depth. In comparison with INF and CK, FYM significantly increased SOC and TN concentrations in the 0–30 cm depth, and also those of dissolved organic C (DOC), microbial biomass C (MBC), hot-water extractable C (HWC), permanganate oxidizable C (KMnO4–C), and particulate organic C (POC) in the 0–20 cm depth. Despite the higher crop yields over CK, application of INF neither increased the SOC nor the labile C fractions, suggesting that by itself INF is not a significant factor affecting SOC sequestration. Yet, POC (18.0–45.8% of SOC) and HWC (2.0–2.8%) were the most sensitive fractions affected by applications of FYM. Significantly positive correlations were observed between SOC and labile organic C fractions in the 0–20 cm depth. The data support the conclusion that, wherever feasible and practical, application of FYM is important to soil C sequestration and improving soil quality under a wheat/maize system in the North China Plain.

The objective of this study is to test the performance of time domain reflectometry(TDR) based on phase difference detecting with independent intellectual property rights measuring soil water content.A laboratory calibration experiment using soil column was conducted to obtain the calibration equations for TDR measuring soil water content,and field test was also conducted to validate these calibration equations.The results showed that,there was no significant effect of bulk density on the calibration relationship between time measured by TDR and soil water content,but the soil texture had a significant effect.It could be calibrated using three calibration formulas in sandy soil,loamy clay soil and clay soil,respectively.All of R2 were greater than 0.98,and the estimated standard errors were less than 0.020 cm3/cm3.The root mean square errors were less than 0.035 cm3/cm3 for TDR measuring soil water content in the field.Therefore,this new TDR instrument was reliable to measure soil water content in the field using calibration equations from the laboratory experiments.

The pot experiment was conducted to determine the water and nitrogen use efficiency of spinach at different salinity and nitrogen levels.Result indicate that at different salinity levels,the treatments N2 could increase the yield of spinach by 16.6% and water use efficiency（WUE） by 9.6%;the maximum of WUE was 25.8 kg m^-3 in treatment N2S0.The interaction of salinity and nitrogen had significant effect on WUE and increased WUE by 1.55 kg m^-3.In comparison with treatment of N1,those of N2 decreased nitrogen use efficiency（NUE） by 40%.Moreover,salinity increasing promoted NUE decreasing.At higher level of salinity and nitrogen,nitrogen fertilizer recovery efficiency（NRE） and agricultural nitrogen use efficiency（NAE） were the least and residual nitrogen was the most,so the potential danger to environment was most serious.

Soil salinity is a major challenge for soil moisture measurement using time domain reflectometry (TDR) and time domain transmission (TDT) technologies. Both technologies measure the travel time of an electromagnetic pulse propagating in soil, which is highly related to soil wetness. A TDT soil moisture sensor with coated helical transmission line has been developed and tested in nonsaline mineral soils and saline soils to evaluate its performance. For nonsaline mineral soils, a linear calibration equation between volumetric soil water content (θ v ) and output voltage ( V ) from the TDT soil moisture sensor was established, and soil texture showed minor influences on the linear relationship. The RMSE of the measured θ v was smaller than <0.022 m 3 m −3 Under saline conditions, the slope of the θ v – V linear relationship decreased exponentially as soil solution electrical conductivity (EC) increased. When the EC is <6.6 dS m −1 , however, the linear relationship for nonsaline mineral soils can be directly applied to saline soils if the required accuracy of moisture measurement is no less than 0.030 m 3 m −3 For soil solution EC in the range of 6.6 to 20.6 dS m −1 , the linearity of the relationship still holds, but the slope needs to be adjusted according to the EC values. The θ v – V linear relationship held for soil solution EC up to 198.2 dS m −1 The calibration equation for nonsaline mineral soils was also applicable to several natural saline mineral soils, and the RMSE was <0.026 m 3 m −3 Therefore it is possible to develop TDT sensors to measure soil moisture with similar accuracy to that of TDR on nonsaline soils but better performance under saline soil conditions.

Soil water flux(Jw) is an important hydrological parameter which determines soil infiltration,runoff and solute transport,yet no corresponding practical techniques are available for its real-time measurement in situ.In this study,heat-pulse measurements were performed of deferent water fluxes in packed soil columns different in texture.Based on temperature changes between upstream and downstream locations from the heat-pulse probe,water flux was then calculated with the MDTD method(maximum dimensionless temperature increase difference),and the Td /Tu method(ratio of temperature changes between downstream and upstream positions),and a modified Td /Tu method along other known parameters.Results indicated that strong linear relationships(R2>0.99) existed between the estimated and the measured water fluxes(up to 6×10-5 m s-1).Though,the three methods all down-estimated,however,the Td /Tu method was highest precise and simplest in calculation,and needed the least number of additional parameters.In coarse sand,the Td /Tu method was relatively more accurate in estimation of Jw,yet in fine sandy clay loam,especially when Jw was greater,obvious discrepancies were observed between the estimated and the measured,reaching 20%.Besides,the reason of underestimation of Jw with the heat-pulse technique is explored and presented as a basis for further development of the heat-pulse technique.

A field experiment study was conducted in Bashang Plateau in North China in 2008 to determine the effect of three first cutting dates on the growth and water use efficiency (WUE) of Siberian wildrye (Elymus sibiricus L.) in the agropastoral ecotone of North China (APENC). The experiment was conducted in a split plot design with three replications with water supply regime as the main plot treatment and first cutting date as the subplot treatment. Two water supply regimes were used, which included rain-fed treatment as control (CK) and a single irrigation and straw mulch treatment (W). Three first cutting date treatments were conducted at early heading stage on July 1 (E), at late heading stage on July 12 (L), and at flowering stage on July 27 (F), respectively. The results showed that the forage yield and WUE were the lowest at early heading stage harvest, while the highest at flowering stage either in CK or W treatment. Under combined CK and W treatments, average forage yields of the F subplots were 2 900 and 6 703 kg ha(-1), and the values of WUE were 0.82 and 2.28 kg m(-3), respectively. Under the CK treatment, forage yields of the E and L subplots were 43.8 and 41.9% lower than the F subplots, and their values of WUE were 46.2 and 50.3% lower than F, respectively. Under the W treatment, the forage yields of the E and L subplots were 74.9 and 61.6% lower, and their values of WUE were 78.1 and 63.3% lower, respectively, as compared with F subplots. Therefore, earlier first cutting did not increase the regrowth of Siberian wildrye and improve the mismatch between rainy season and the period of high growth potential of the grass in the semiarid APENC.

为了评估时域反射仪测定水分非均匀分布土壤的含水率的性能,该研究在室内试验中将土柱纵向分为上下2层,设置土壤水分差为0.05、0.10和0.15 cm3/cm3 3种情况,进行不同含水率梯度下水分非均匀分布对该仪器测定土壤含水率的影响试验,并在田间试验中进行了实地测试.结果表明,在室内新型时域反射仪随着上下2层土壤含水率梯度差的增加,测定土壤含水率的均方根误差略有增大,在水分分布相对均匀的土壤中测定土壤含水率的均方根误差小于0.028 cm3/cm3.在田间竖直埋设探头,上湿下干和上干下湿的土壤含水率差异范围分别在0.011～0.026和0.026～0.064 cm3/cm3时,仪器测定含水率的均方根误差分别是0.037和0.027 cm3/cm3.时域反射仪测定水分不均匀分布情况下的土壤含水率是可行的.

Siberian wildrye grass ( Elymus sibiricus L.) is the primary forage species in alpine cold areas of North China. Scheduled irrigation is an important way to increase the forage mass because of water shortage and the inconsistency between rainy season and the most intense water use period. Irrigation experiments were conducted during 2006 to 2008 to study the feasibility of applying single irrigation before winter (WI) or at the elongating stage (EI), irrigating at these two stages (WEI, in 2006–2007), and irrigating before winter with mulching straw before next reviving (WMI, only in 2008) to increase forage mass (FM) and water use efficiency (WUE). The results showed that irrigation at the elongating stage played the most important role in mass and WUE increase. The FMs under EI achieved 6381, 6883, and 5763 kg ha −1 , increased by 66, 218, and 99%, respectively, and WUE was 1.9, 2.3, and 1.8 kg m −3 , increased by 56, 134, and 81%, respectively, compared with no irrigation treatment (NI) in 3 yr. The FMs under WI were increased by 40, 53, and 44%, and the WUE was increased by 30, 31, and 34%, respectively. No significant FM and WUE increment under WEI were found compared with EI during 2006 to 2007. The FM and WUE under WMI were higher than values under EI in 2008. Therefore, EI can achieve relatively high production and WUE of Siberian wildrye grass. If water resources at the elongating stage were deficient, the WMI treatment might be a good choice.

The objective of the paper is to test the performance of self-developed time domain transmission(TDT)measuring soil water content.A laboratory experiment was conducted in sand soil,sandy loam soil,loamy clay soil and coastal saline soil.Results showed that there was a linear relationship between soil volumetric water content and TDT voltage output for non-saline agricultural soils and coastal saline soils.For sand and sandy loam soils,a universal relationship could be established to estimate soil water content when ignoring the effect of soil texture and bulk density,and the standard error of the estimate was 0.017 cm~3/cm~3.However,the influence of bulk density on calibration relationship was significant for loamy clay soil,the individual calibration was required and the standard error of the estimate was less than 0.016 cm~3/cm~3.In salt solution,there was a linear relationship between the TDT output voltage and the depth of immersed in salt solution,and the effect of electrical conductivity of solution was not significant.For coastal saline soils,the linear relationships between soil volumetric water content and TDT voltage output were established with different bulk densities,but che effect of bulk density was not obvious.Thus,a universal relationship could be established to estimate saline soil water content and the standard error of the estimate was 0.019cm~3/cm~3.It was indicated that TDT instrument could measure soil water content accurately for agricultural soils.It has good characteristic of high-salt tolerance in salt solution and can be used to measure saline soil water content.

Soil water repellency is a physical phenomenon in which water can not or be very difficult to wet the soil surface, and the soil is called water repellent soil. The study area was the Leymus chinensis steppe plot of Inner Mongolia grassland ecosystem research station of the Chinese Academy of Sciences, located in the Baiyinxile pasture in Xilinhaote of the Inner Mongolia. The objective of this study was to find out soil water repellency in grasslands of Inner Mongolia as influenced by different grassland utilization patterns (including ungrazed since 1979 and 1999, winter grazing and continuous grazing) using water drop penetration time (WDPT). The results showed that the slightly hydrophobic or hydrophilic soil samples were often observed, and soil water repellency showed stronger during rainy season or rainy year than during no rainy season or dry year. And its seasonal change was affected by grazing intensity, which is that many dydrophobic soil samples are found earlier in continuous grazing plot, later in winter grazing plot and ungrazing plot since 1999, then in ungrazing plot since 1979.

Soil degradation and the accompanying decline in crop yields are the main limiting factors for the further development of agriculture on the Chinese Loess Plateau. A 10-year experiment was conducted in Linfen on the Loess Plateau to assess the potential benefits of controlled traffic oil agricultural production. In this region, long-term traditional ploughing with straw removal has resulted in a decline of soil productivity and poor soil structure. Several treatments were compared: controlled traffic with no-tillage and straw cover (NTSC), controlled traffic with shallow tillage and straw cover, and traditional tillage (TT) in a winter wheat (Triticum aestivum L.) monoculture. Results show clear benefits of controlled traffic farming. Winter wheat growth in ploughed Plots Was Much slower than in controlled traffic plots. Mean yield from 1998 to 2007 was 11.2% lower for traditional tillage than for controlled traffic plots. The best results were achieved by a no-tillage straw cover and controlled traffic system (NTSC), which resulted in the greatest benefits to soil Structure after 10 years. The NTSC significantly improved soil organic matter content in the top 30 cut by 27.2%, total N by 10.8%, and available P (top 10 cm) by 92.3% compared with TT. Aeration (>60 mu m) and capillary porosity (2-60 mu m) were 155.0%, and 16.1% greater, respectively, in NTSC plots than in TT plots. Consequently, for NTSC, final water infiltration rates were 67.4% greater than for TT, whereas water content in the top 130 cm was 14.9% higher than in TT, respectively. We conclude therefore that controlled traffic combined with no-tillage and straw cover is a valuable system for restoring soil productivity and quality of seriously degraded soils on the Loess Plateau for the sustainable development of agriculture in dryland China.