Hongyong Sun

An integrated algorithm for estimating regional latent heat flux and daily evapotranspiration

Using remote‐sensing data and ground‐based data, we constructed an integrated algorithm for estimating regional surface latent heat flux (LE) and daily evapotranspiration (ET d). In the algorithm, we first used trapezoidal diagrams relating the surface temperature and fractional vegetation cover (f c) to calculate the surface temperature–vegetation cover index, a land surface moisture index with a range from 0.0 to 1.0. We then revised a sine function to assess ET d from LE estimated for the satellites overpass time. The algorithm was applied to farmland in the North China Plain using Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper Plus (ETM+) data and synchronous surface‐observed data as inputs. The estimated LE and ET d were tested against measured data from a Bowen Ratio Energy Balance (BREB) system and a large‐scale weighing lysimeter, respectively. The algorithm estimated LE with a root mean square error (RMSE) of 50.1 W m−2 as compared to measurements with the BREB System, and ET d with an RMSE of 0.93 mm d−1 as compared with the measurement by the lysimeter. Sensitivity analysis showed that changing meteorological variables have some influence on LE, while variation of f c has little effect on LE. The test of the model in the study indicated that the improved algorithm provides an accurate and easy‐to‐handle approach for assessing regional surface LE and ET d. Further improvement can be achieved in the assessments if we increase the accuracy of some key parameters on a large regional scale, such as the minimum stomatal conductance and the atmospheric vapour pressure deficit.

Effects of Different Cultivation Practices on Soil Temperature and Wheat Spike Differentiation

Field cultivation practices affected soil temperature that influenced the crop development of winter crops. This study was undertaken to determine the effects of different mulch materials, tillage depths and planting methods on spike differentiation of winter wheat (Triticum aestivum L.). The field experiment was consisted of three tests: (i) polythene mulch, straw mulch and no mulch; (ii) ridge planting and furrow planting; (iii) conventional tillage and shallow tillage. The results showed that soil temperature was affected by different practices. The higher soil temperature under polythene mulch resulted in the earlier initiation of spike differentiation, while straw mulch decreased soil temperature in spring that delayed the initiation compared with the non-mulch treatment. The spike initiation under ridge planting started earlier than that of furrow planting. Reduced tillage delayed the initiation compared with the conventional tillage. Duration of spike differentiation lasted longer under earlier starting of initiation that increased the grain numbers per spike. Other yield component characters were not affected by soil temperature. It was concluded that in the North China Plain where grain-filling duration of winter wheat was limited, agricultural practices that increased soil temperature in spring were favorable for grain production.

Effects of saline irrigation on soil salt accumulation and grain yield in the winter wheat-summer maize double cropping system in the low plain of North China

Abstract In the dominant winter wheat (WW)-summer maize (SM) double cropping system in the low plain located in the North China, limited access to fresh water, especially during dry season, constitutes a major obstacle to realize high crop productivity. Using the vast water resources of the saline upper aquifer for irrigation during WW jointing stage, may help to bridge the peak of dry season and relieve the tight water situation in the region. A field experiment was conducted during 2009–2012 to investigate the effects of saline irrigation during WW jointing stage on soil salt accumulation and productivity of WW and SM. The experiment treatments comprised no irrigation (T1), fresh water irrigation (T2), slightly saline water irrigation (T3: 2.8 dS m−1), and strongly saline water irrigation (T4: 8.2 dS m−1) at WW jointing stage. With regard to WW yields and aggregated annual WW-SM yields, clear benefits of saline water irrigation (T3 & T4) compared to no irrigation (T1), as well as insignificant yield losses compared to fresh water irrigation (T2) occurred in all three experiment years. However, the increased soil salinity in early SM season in consequence of saline irrigation exerted a negative effect on SM photosynthesis and final yield in two of three experiment years. To avoid the negative aftereffects of saline irrigation, sufficient fresh water irrigation during SM sowing phase (i.e., increase from 60 to 90 mm) is recommended to guarantee good growth conditions during the sensitive early growing period of SM. The risk of long-term accumulation of salts as a result of saline irrigation during the peak of dry season is considered low, due to deep leaching of salts during regularly occurring wet years, as demonstrated in the 2012 experiment year. Thus, applying saline water irrigation at jointing stage of WW and fresh water at sowing of SM is most promising to realize high yield and fresh irrigation water saving.

Assessing the Impact of Air Pollution on Grain Yield of Winter Wheat - A Case Study in the North China Plain

The major wheat production region of China the North China Plain (NCP) is seriously affected by air pollution. In this study, yield of winter wheat (Triticum aestivum L.) was analyzed with respect to the potential impact of air pollution index under conditions of optimal crop management in the NCP from 2001 to 2012. Results showed that air pollution was especially serious at the early phase of winter wheat growth significantly influencing various weather factors. However, no significant correlations were found between final grain yield and the weather factors during the early growth phase. In contrast, significant correlations were found between grain yield and total solar radiation gap, sunshine hour gap, diurnal temperature range and relative humidity during the late growing phase. To disentangle the confounding effects of various weather factors, and test the isolated effect of air pollution induced changes in incoming global solar radiation on yield under ceteris paribus conditions, crop model based scenario-analysis was conducted. The simulation results of the calibrated Agricultural Production Systems Simulator (APSIM) model indicated that a reduction in radiation by 10% might cause a yield reduction by more than 10%. Increasing incident radiation by 10% would lead to yield increases of (only) 7%, with the effects being much stronger during the late growing phase compared to the early growing phase. However, there is evidence that APSIM overestimates the effect of air pollution induced changes on radiation, as it does not consider the changes in radiative properties of solar insulation, i.e. the relative increase of diffuse over direct radiation, which may partly alleviate the negative effects of reduced total radiation by air pollution. Concluding, the present study could not detect a significantly negative effect of air pollution on wheat yields in the NCP.

The long-term impact of irrigation on selected soil properties and grain production

A sustainable agricultural system depends on good soil quality and crop performance. However, information is limited about the influence of long-term irrigation schedules on soil properties and crop performance on fields without crop residue incorporation or machine tillage. In this study, we investigated the changes of soil bulk density (BD), saturated hydraulic conductivity (Ksat), water-stable aggregate, soil organic matter (SOM), and total nitrogen (TN) at the depths of 0 to 5, 5 to 10, 10 to 20, and 20 to 40 cm relative to different irrigation amounts based on a 17-year-long experiment in a double-cropping system with crop residue removed and manual tillage in the North China Plain. Results showed that BD increased as the irrigation amount increased. Saturated hydraulic conductivity reached a maximum level at a moderate irrigation level. Irrigation timing also affected soil BD and Ksat. Water-stable aggregates did not show consistent trends. Soil organic matter and TN showed similar decreasing trends with increased irrigation amount. No significant relationships were found between soil physical properties and grain yield. However, SOM did affect crop production significantly. Overall, results indicated that continuous irrigation without crop residue return negatively affected soil properties and crop performance. Soil quality and crop production may benefit from a reasonable irrigation strategy and the return of crop residue to the field.

Impact of water transfer on interaction between surface water and groundwater in the lowland area of North China Plain

Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China Texas A&M AgriLife Research Center at El Paso 1380 A&M Circle, El Paso, TX 79927, USA Correspondence Shiqin Wang, Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China. Email: sqwang@sjziam.ac.cn Funding information Science and Technology Service Network Program of Chinese Academy of Sciences, Grant/Award Number: KFJ‐STS‐ZDTP‐001; The National Key Research and Development Program of China, Grant/Award Number: 2016YFD0800100; 100‐Talent Project of Chinese Academy of Sciences

Effects of water and nitrogen on root/shoot ratio and water use efficiency of winter wheat

Water and nitrogen(N) fertilizer have been identified as the two key factors that influence wheat root and shoot development.Root/shoot ratio and water use efficiency(WUE) of winter wheat were studied in the field and tub experiments at the Luancheng Agro-Ecosystem Experimental Station of Chinese Academy of Sciences in the North China Plain.The field experiment involved with 5 irrigation treatments(with zero to 4 irrigations) during winter wheat growth period.The tub experiment involved 15 treatments of five levels of N(0 g?tub?1,2 g?tub?1,4 g?tub?1,6 g?tub?1,8 g?tub?1) and three levels of irrigation(with 140 mm,210 mm,280 mm irrigation),with 6 replicas of each treatment.The PVC tub used in this experiment was 1 m in depth and 20 cm in diameter.The bottom of each tub was sealed with plastic film and buried in the field.Field data showed that soil water content significantly influenced root and shoot biomass accumulation.The root/shoot ratio was not affected by irrigation when water content of the top 60 cm soil layer was above 60% of field capacity.Below this soil water level,root/shoot ratio increased with decreasing soil water content.The tub experiment showed that the root/shoot ratio was significantly driven by N dose and not by the combined effect of water and N.Root dry weight decreased and grain yield increased with increasing N dose under deficit water supply.Concurrently,WUE increased with increasing N dose.Under sufficient water supply,winter wheat yield initially increased with increasing N dose to a certain level,after which it no longer changed with increasing N dose.A threshold value for N dose was noted under sufficient water supply.While under deficit water supply,more N meant higher WUE by reduced root/shoot ratio.This study suggested that N and water regulated biomass allocation to the parts of the above-ground and below-ground systems of the plant that influenced grain production and WUE.Both experiments showed a negative correlation between root/shoot ratio and WUE.That implied that higher root/shoot ratio increased biomass allocation to root but at the same time reduced above-ground biomass and WUE.