Liwei Shao

Effects of defoliation on grain yield and water use of winter wheat

Field and pot experiments were conducted to investigate the effects of defoliation on crop performance and the possibility of using defoliation as a method for conserving soil moisture. The study was conducted during 2006-2008, over two growing seasons of winter wheat (Triticum aestivum L.) in the North China Plain. Three levels of defoliation (mild, moderate and severe) were imposed on winter wheat in the field during the following crop phases and conditions: at heading, at anthesis under water deficit conditions and at anthesis under two or three levels of irrigation. Additional pot experiments with three levels of defoliation under two water regimes were arranged. The results showed that both the intensity of defoliation and the timing of defoliation significantly reduced grain production. Under wet conditions the reduction was over 20 %, while under dry conditions the reduction was c. 12 %. Yield reduction was greater for defoliation at heading than at anthesis and it was mainly caused by a reduction in kernel weight. Mild defoliation (top three leaves retained) did not affect grain yield. Moderate defoliation (top two leaves retained) slightly reduced grain production. Root length density in the topsoil profile was significantly reduced by severe defoliation at anthesis under wet conditions, but it increased under dry conditions. Dry matter remobilization to grains under moderate and mild defoliation was increased and resulted in a relatively higher harvest index (HI). The photosynthetic rate of the leaves remaining after defoliation was enhanced under all soil moisture conditions. Although defoliation reduced the seasonal water use (ET), the yield reduction was much greater than the reduction in ET under severe defoliation, resulting in lower water use efficiency (WUE). The results show that conserving soil moisture by removing leaves might not be an economic choice. Under the conditions of the present study, the WUE of winter wheat was not improved by defoliation; however, in very dry conditions the reduction in ET by defoliation might help the crop survive.

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.