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Liu Z.,China Agricultural University | Yang X.,China Agricultural University | Lin X.,Kansas State University | Hubbard K.G.,University of Nebraska - Lincoln | And 3 more authors.
Science of the Total Environment | Year: 2016

Closing the gap between current and potential yields is one means of increasing agricultural production to feed the globally increasing population. Therefore, investigation of the geographic patterns, trends and causes of crop yield gaps is essential to identifying where yields might be increased and quantifying the contributions of yield-limiting factors that may provide us potentials to enhance crop productivity. In this study, the changes in potential yields, attainable yields, potential farmers' yields, and actual farmers' yields during the past five decades in Northeast China (NEC) were investigated. Additionally the yield gaps caused by non-controllable, agronomic, and socioeconomic factors were determined. Over the period 1961 to 2010 the estimated regional area-weighted mean maize potential yield, attainable yield, and potential farmers' yield were approximately 12.3tha-1, 11.5tha-1, and 6.4tha-1 which showed a decreasing tendency. The actual farmers' yield over NEC was 4.5tha-1, and showed a tendency to increase (p<0.01) by 1.27tha-1 per decade. The regional mean total yield gap (YGt), weighted by the area in each county dedicated to maize crop, was 64% of potential yield. Moreover, 8, 40, and 16% reductions in potential yields were due to non-controllable factors (YGI), agronomic factors (YGII), and socioeconomic factors (YGIII), respectively. Therefore, the exploitable yield gap, considered here as the difference between the potential yield and what one can expect considering non-controllable factors (i.e. YGt-YGI), of maize in NEC was about 56%. The regional area-weighted averages of YGt, and YGIII were found to have significant decreases of 11.0, and 10.7% per decade. At the time horizon 2010, the exploitable yield gaps were estimated to equal 36% of potential yield. This led to the conclusion that the yield gap could be deeply reduced by improving local agronomic management and controlling socioeconomic factors. © 2015 Elsevier B.V. Source

Hao L.,Nanjing University of Information Science and Technology | Zhang X.,Ningxia Institute of Meteorological Science | Liu S.,Nanjing University of Information Science and Technology
Natural Hazards | Year: 2012

China faces drought disaster risk under the changing climate. Risk analysis is a suitable approach in order to design ex-ante measure able to anticipate effects of drought on agricultural production. In this article, with the support of historic drought disaster data from 583 agro-meteorological observations (1991-2009), a risk analysis method based on information diffusion theory was applied to create a new drought risk analysis model, and the risk of China's agriculture drought disaster was evaluated on higher spatial resolution of county unit. The results show that in more than three hundred counties of China, risk probability was biyearly or annually when Drought Affected Index (DAI) was over 5%. When DAI was up to 40%, more than one hundred counties were prone to drought disaster annually or once every 5 years. This showed that the impact of drought disaster on China's agriculture, whether in frequency or intensity, was large. With the different level of DAI, China's agricultural drought risk pattern showed variable pattern characteristics. When DAI was low, the distribution of county agricultural drought risk in China presented the East-West pattern of differentiation, and high risk mainly lied in the eastern, low risk mainly in the western. On the other hand, when DAI was high, the distribution of county risk appeared a pattern of high in center, and the north areas higher than the south, increased gradually from southwest to northeast. Drought risk presents a clear zonal differentiation that may be result from stepped topography, different precipitation and hazard-affected bodies. Spread of high value area of drought risk in northern may be related to the southeast monsoon and ecological degradation in northern Ecotone. © 2011 Springer Science+Business Media B.V. Source

Niu S.,Nanjing University of Information Science and Technology | Jia X.,Nanjing University of Information Science and Technology | Sang J.,Ningxia Institute of Meteorological Science | Liu X.,Nanjing University of Information Science and Technology | And 2 more authors.
Journal of Applied Meteorology and Climatology | Year: 2010

Joint size and fall velocity distributions of raindrops were measured with a Particle Size and Velocity (PARSIVEL) precipitation particle disdrometer in a field experiment conducted during July and August 2007 at a semiarid continental site located in Guyuan, Ningxia Province, China (36°N, 106°16́E). Data from both stratiform and convective clouds are analyzed. Comparison of the observed raindrop size distributions shows that the increase of convective rain rates arises from the increases of both drop concentration and drop diameter while the increase of the rain rate in the stratiform clouds is mainly due to the increase of median and large drop concentration. Another striking contrast between the stratiform and convective rains is that the size distributions from the stratiform (convective) rains tend to narrow (broaden) with increasing rain rates. Statistical analysis of the distribution pattern shows that the observed size distributions from both rain types can be well described by the gamma distribution. Examination of the raindrop fall velocity reveals that the difference in air density leads to a systematic change in the drop fall velocity while organized air motions (updrafts and downdrafts), turbulence, drop breakup, and coalescence likely cause the large spread of drop fall velocity, along with additional systematic deviation from terminal velocity at certain raindrop diameters. Small (large) drops tend to have superterminal (subterminal) velocities statistically, with the positive deviation from the terminal velocity of small drops being much larger than the negative deviation of large drops. © 2010 American Meteorological Society. Source

Liu Z.,China Agricultural University | Yang X.,China Agricultural University | Lin X.,Kansas State University | Hubbard K.G.,University of Nebraska - Lincoln | And 3 more authors.
Earth Interactions | Year: 2016

Northeast China (NEC) is one of the major agricultural production areas in China, producing about 30% of China’s total maize output. In the past five decades, maize yields in NEC increased rapidly. However, farmer yields still have potential to be increased. Therefore, it is important to quantify the impacts of agronomic factors, including soil physical properties, cultivar selections, and management practices on yield gaps of maize under the changing climate in NEC in order to provide reliable recommendations to narrow down the yield gaps. In this study, the Agricultural Production Systems Simulator (APSIM)-Maize model was used to separate the contributions of soil physical properties, cultivar selections, and management practices to maize yield gaps. The results indicate that approximately 5%, 12%, and 18% of potential yield loss of maize is attributable to soil physical properties, cultivar selection, and management practices. Simulation analyses showed that potential ascensions of yield of maize by improving soil physical properties PAYs, changing to cultivar with longer maturity PAYc, and improving management practices PAYm for the entire region were 0.6, 1.5, and 2.2 ton ha-1 or 9%, 23%, and 34% increases, respectively, in NEC. In addition, PAYc and PAYm varied considerably from location to location (0.4 to 2.2 and 0.9 to 4.5tonha-1 respectively), which may be associated with the spatial variation of growing season temperature and precipitation among climate zones in NEC. Therefore, changing to cultivars with longer growing season requirement and improving management practices are the top strategies for improving yield of maize in NEC, especially for the north and west areas. © 2016. Source

Zhao J.,China Agricultural University | Yang X.,China Agricultural University | Liu Z.,China Agricultural University | Lv S.,China Agricultural University | And 2 more authors.
Climatic Change | Year: 2016

As climate changes, suitability zones for the cultivation of some crops may shift. In Northeast China (NEC), it is critically important for the agricultural community (e.g. farmers, advisors) to understand the potential shift in suitable cropping zones for spring maize in order to adapt to climate change. The potential climatic suitability can be defined as how actual temperature and solar radiation conditions match the requirements of crop growth under non-limited situations. Here, we used yield potential to reflect the potential climatic suitability, which is determined by the characteristics of crop, solar radiation, temperature, and photoperiod, given the assumption that water, nutrients, pests, and diseases are not limiting the crop growth. We assessed the annual yield potential of spring maize during 1961–2010 in NEC with APSIM-Maize. And then we analyzed the variations in potential climatic suitability zones and the possible effects of these variations on maize production potential. The results show that growing degree-days (GDD) during the growing season for spring maize universally increased in all the locations of this study during the period of 1981–2010 (period II) as compared to the period of 1961–1980 (period I). A total of 66 % of the locations show a decrease in accumulated sunshine duration (ASD) during the growing season during period II as compared to period I. Both coefficient of variation (CV) of GDD and CV of ASD showed an increase during period II as compared to period I. Under the background of climate change, the potential climatic suitability for spring maize was worsened during the most recent five decades: the yield potential declined and the yield stability decreased. In particular, most of the very suitable zone in Jilin and Liaoning during period I turned into suitable or moderately suitable zone during period II. Meanwhile, the total area of marginally suitable zone and no suitable zone increased by 16 % during period II as compared to period I. We detected a close correlation between the decrease in ASD and the decrease in potential climatic suitability, R = 0.56, p < 0.01. We also found a close correlation between the increase in GDD and the decrease in potential climatic suitability, R = −0.25, p < 0.05. Given the same crop varieties and farming management, the total production potential for spring maize in the entire NEC reduced by 4.3 % during period II as compared to period I. © 2016 Springer Science+Business Media Dordrecht Source

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